General Information on Track Circuits - RGS Online

Approved by 

Keith Turner 

Standards Project Manager 

Authorised by 

Richard Spoors 

Controller, Railway Group Standards 

Withdrawn Document 

Uncontrolled When Printed 

Railway Group Approved Code of Practice 

GK/RC0752 

Issue Two 

Date December 1998 

<strong>General</strong> 

<strong>Information</strong> on 

Track Circuits 

Synopsis 

<strong>General</strong> information to ensure that the 

Integrity of Track Circuits is 

maintained at all times. 

This document is the property of 

Railtrack PLC. It shall not be 

reproduced in whole or in part without 

the written permission of the Controller, 

Railway Group Standards, 

Railtrack PLC. 

Published by 

Safety & Standards Directorate, 

Railtrack PLC, 

Floor DP01, Railtrack House, 

Euston Square, 

London NW1 2EE 

© Copyright 1998 Railtrack PLC



This page has been left blank intentionally

<strong>General</strong> <strong>Information</strong> on Track Circuits 

Contents 


GK/RC0752 

Issue Two 


Page 1 of 2 

Section Description Page 

Part A 



Issue Record A1 

Distribtuion A1 

Health and Safety Responsibilities A1 

Supply A1 

Part B 

1 Purpose B1 

2 Scope B1 

3 Glossary of Terms B1 

4 Limitations B5 

5 Introduction B6 

6 Electrical Behaviour of Railway track B7 

7 Operation and Adjustment of the Simple Track Circuit B9 

8 Train Shunt Imperfection B10 

9 Detection of “Lightweight” Vehicles B12 

10 Track Circuit Insulations B13 

11 Bonding B16 

12 Mutual Interference Between Track Circuits B18 

13 Detection of Rail Breaks B19 

14 Jointless Track Circuits B20 

15 Track Circuits and Electric Traction B21 

16 The Impedance Bonds B24 

Part C Schematic Symbols 

1 Introduction C1 

2 Drawing Symbols on Bonding Plans C1 

3 Traction Return Bonding Symbols C8 

4 Civil Engineer’s Scale Diagrams C10 

Part D Planning and Design 

1 Introduction D1 

2 Responsibilities for Bonding Design D1 

3 Track Circuit Nomenclature D2 

4 Choice of Track Circuit Type D3 

5 Cut Sections D5 

6 Operating Times D6 

7 Track Circuit Interrupters D8 

8 Length of Track Circuits D8 

9 Track Circuit Gaps and Staggered IRJs D9 

10 Selective Operation of Track Circuits D9 

11 Bad Rail Surface D9 

12 Emergency Cross–overs D10 

13 Insulated Rail Joints and Bonding D10 

14 Track Circuit Equipment Positioning D19 

15 Layout and Wiring of Lineside Apparatus Housing D19 

16 Duplicate Rail Connections D20 

17 Communications D21 

RAILTRACK 1


GK/RC0752 

Issue Two 


Page 2 of 2 




Section Description Page 

Part E Components and Installation 

1 Introduction E1 

2 Responsibilities for Bonding Installation E1 

3 Track Circuit Interrupters E2 

4 Identification of Track Circuit Boundaries E3 

5 Protection of Cross Track Cables E3 

6 Mechanised track Maintenance E6 

7 Rail Drilling E6 

8 Rail Connections E7 

9 Track Circuit Disconnection Box E17 

10 Arrangement of Track Lead Rail Connections 

(Except Jointless) E19 

11 Fishplate Bonding E21 

12 Jumper Bonding E23 

13 High Voltages E24 

14 Lineside Apparatus Housing Wiring E24 

15 Impedance Bonds E25 

16 Impedance Bond Installation E30 

17 Aluminium Busbars E37 

18 Side Leads E46 

19 Traction Negative Return Jumpers E52 

Part F Instrumentation Description and Use 

1 Introduction F1 

2 Multi–meters F1 

3 The Universal Shunt Box F1 

4 Rail Clip Insulation Tester F2 

5 Track Circuit Fault Detector F4 

6 Mark 4 Direct Reading Phase Angle Meter F5 

Part G Testing and Commissioning 

1 Introduction G1 

2 High Voltages G1 

3 Lineside Apparatus Housing Inspection G1 

4 Bonding Inspection G1 

5 IRJ Inspection G2 

6 Performance Test G2 

Part H Maintenance 

1 Introduction H1 

2 Routine Examination H1 

3 Drop Shunt Test H1 

4 Full Test H2 

Part J Fault Finding 

1 Introduction J1 

2 Categories of Failure J1 

3 Intermittent Failures J1 

4 Right Side Failures J2 

5 Wrong Side Failures J4 

References Ref 1 

2 RAILTRACK


Issue Record 

Distribution 

Health and Safety 

Responsibilities 

Supply 



Part A 


GK/RC0752 

Issue Two 


Page A1 of 1 

This Approved Code of Practice will be updated when necessary by distribution 

of a replacement Part A and such other parts as are amended. 

Amended or additional parts of revised pages will be marked by a vertical black 

line in the adjacent margin. 

Part Issue Date Comments 

Part A One August 1994 Original document. 

Part B One August 1994 Original document. 

Part C One August 1994 Original document. 

Part D One August 1994 Original document. 

Part E One August 1994 Original document. 

Part F One August 1994 Original document. 

Part G One August 1994 Original document. 

Part H One August 1994 Original document. 

Part I not used. 

Part J One August 1994 Original document. 

References One August 1994 Original document. 

Part A Two December 1998 Revised document. 

Part B Two December 1998 Revised document. 

Part C Two December 1998 Revised document. 

Part D Two December 1998 Revised document. 

Part E Two December 1998 Revised document. 

Part F Two December 1998 Revised document. 

Part G Two December 1998 Revised document. 

Part H Two December 1998 Revised document. 

Part I not used. 

Part J Two December 1998 Revised document. 

References Two December 1998 Revised document. 

Controlled copies of this Approved Code of Practice should be made available 

to all personnel who are responsible for the design, installation, testing, 

maintenance and faulting of Track Circuits. 

In issuing this Approved Code of Practice, Railtrack PLC makes no warranties, 

express or implied, that compliance with all or any Railway Group Standards or 

Codes of Practice is sufficient on its own to ensure safe systems of work or 

operation. Each user is reminded of its own responsibilities to ensure health 

and safety at work and its individual duties under health and safety legislation. 

Controlled and uncontrolled copies of this Approved Code of Practice may be 

obtained from the Industry Safety Liaison Dept, Safety and Standards 

Directorate, Railtrack PLC, Railtrack House DP01, Euston Square, London, 

NW1 2EE. 

RAILTRACK A1



This page has been left blank intentionally


1 Purpose 

2 Scope 

3 Glossary of Terms 



Part B 


GK/RC0752 

Issue Two 


Page B1 of 25 

This Approved Code of Practice gives details of best practice in respect of track 

circuits in general, in order to achieve the requirements of GK/RT 0251. 

The contents of this Approved Code of Practice apply to all track circuits. 

The definitions of terms used by Signal Engineers vary depending on the 

location in which they were trained. The following terms will be used as standard 

throughout this handbook. 

Bearer 

An item of steel or concrete of non–standard dimensions used to support the 

track in S & C areas (see Sleeper and Timber). 

Bonding 

The electrical connection from one rail or part of a track circuit to any other rail or 

part of the track circuit. 

Cross Bond 

A traction bond cross connecting the traction rails of parallel tracks to form a 

mesh of alternate paths for traction return current. 

Fishplate Bond 

Provided to ensure electrical continuity between two rails mechanically 

connected by a steel fishplate. 

Impedance Bond 

Special device which presents a low impedance to traction current and a higher 

impedance to track circuit current. 

Parallel Bonding 

If any section of a track circuit is bonded in parallel to other sections of that track 

circuit, a disconnection will not cause the track circuit to indicate the presence of 

a train. The actual presence of a train within that section may not be indicated 

under certain failure conditions. This method of bonding is defined as Parallel 

Bonding and is the non–preferred method of bonding. Where it cannot be 

avoided, special precautions must be taken (see individual Sections). 

Red Bond 

A traction bond that has been designated by the Electrification Engineer as being 

dangerous to staff if disconnected. It is coloured red for identification. The 

Electric Control Room shall be advised whenever a disconnected red bond is 

observed. 

Series Bonding 

Series bonding is where the track is bonded together in series, so that if any 

short circuit or disconnection occurs, the track circuit will indicate the apparent 

presence of a train. It is the preferred method of bonding. 

Structure Bond 

A bond that connects adjacent lineside metal structures to the traction return rail 

system to ensure staff safety through equi–potential zoning. 

Traction Bond 

A cable specifically provided for continuity of traction current return, although it 

may additionally carry track circuit current. 

RAILTRACK B1


GK/RC0752 

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Page B2 of 25 




Traction Return Bonding 

The bonding required to carry the traction return current on both a.c. and d.c. 

electrified lines. Traction return bonding is generally parallel bonded. 

Transposition Bond 

A jumper cable where track circuit polarities and/or traction return rails are 

switched across a pair of IRJs. 

Yellow Bond 

A jumper cable that has been designated by the Signal Engineer to be an 

important part of the diverse bonding of common/single rail track circuit. It is 

coloured yellow or identified by yellow tape. Damage must be reported and 

repairs carried out as a matter of priority. 

Clearance Point 

The minimum distance from switches and crossings at which track circuits 

having the function of proving clearance may be terminated to ensure a passing 

clearance of at least 457mm between vehicles in all circumstances. 

Common Rail (CR) 

A track circuit arrangement where only one rail (the signal rail) is used with IRJs 

to separate the track circuits. The other rail (the common rail) is electrically 

continuous but is not used for traction return purposes. 

Cut Section 

A method of reducing the continuous length of a track circuit by the use of 

individual track circuits, each one controlling the same final TPR. These are 

indicated as one track circuit on the signalman’s panel. 

Double Rail (DR) 

A track circuit arrangement where both rails are fitted with IRJs, or tuned zones 

are used to completely isolate a track circuit. 

Drop–away Time 

The time between the application of a shunt to the rails and the front contacts of 

track relay (TR) fully opening (see also Pick–up Time). 

Drop Shunt 

The maximum value of non–inductive resistance which, when placed across the 

rails, will cause the track relay to fully open its front contacts. 

Fishplate 

Metal plates for joining rails together. 

Frequency Rotation 

The sequential application of specified frequencies. 

Insulated Rail Joint (IRJ) 

A method of joining rails together whilst maintaining electrical insulation between 

them. 

Jointed Track Circuits 

Track circuits whose extremities are defined by the use of Insulated Rail Joints 

(IRJs). 

Jointless Track Circuits 

Track circuits whose extremities are defined by the use of tuned circuit 

techniques. The extreme limits of a jointless track circuit area are either defined 

by the use of IRJs or by the use of a tuned circuit between the rails. 

B2 RAILTRACK





GK/RC0752 

Issue Two 


Page B3 of 25 

Joint Hopping 

Where fast moving short vehicles pass from one track circuit to the next, the 

difference between the pick–up and drop–away times can cause the vehicle to 

momentarily disappear. 

Jumper Cable 

Used to electrically connect, for track circuit or traction purposes, two pieces of 

rail that are not adjacent. 

Overlay Track Circuit 

A track circuit which can be superimposed over another, neither having any 

effect on the other and both operating independently. 

Pick–up Shunt 

The minimum value of resistance between the two running rails at which the 

track relay will just close its front contacts. 

Pick–up Time 

The time between the removal of a shunt from the rails and the front contacts of 

the track relay making (see also Drop–away Time). 

Plans 

For the definition of all types of Plans, see SDH E11. 

Selective Operation 

Operation of a portion of a track circuit by selection of the position of a set of 

points. Selective operation of track circuits is no longer permitted. 

Single Rail (SR) 

A track circuit arrangement where only one rail (the signal rail) is used with IRJs 

to separate the track circuits. The other rail (the common rail) is electrically 

continuous and is used for traction return purposes. 

Sleeper 

An item of wood, steel or concrete of standard dimensions, used to support and 

gauge the track (see Bearer and Timber). 

Spur 

A section of running rail required to be electrically common to a series bonded 

rail, but which is not itself in series. 

Stagger (Electrical) 

The phase or polarity difference between one track circuit and the next, or 

between the rails on either side of an IRJ within one track circuit. 

Stagger (Physical) 

Occurs where two IRJs in a pair of rails are not exactly opposite each other, 

thus creating a dead section between track circuits or within a track circuit. 

Switches & Crossings (S & C) 

Sections of track other than plain line. 

Tail Cable 

This is a cable which connects the lineside apparatus housing to the trackside 

equipment, but not direct to the running rails (see Track Cable). 

Timber 

An item of wood of non–standard dimensions, used to support the track in S & C 

areas (see Bearer and Sleeper). 

RAILTRACK B3


GK/RC0752 

Issue Two 


Page B4 of 25 

4 Limitations 




Track Cable 

This is a cable which connects the track disconnection links/fuses or trackside 

equipment to the rails. 

Track Jumping 

Occurs when a fast moving vehicle passes over a very short track circuit (or a 

short arm of a longer track circuit) and fails to de–energise the track relay. 

Track Circuit Interrupter 

A device that detects the passage of a vehicle by causing a permanent 

disconnection within the track circuit until the device has been replaced. 

Transposition Joint 

An IRJ where transposition bonds are used to transpose the traction and/or 

track circuit rails. 

Catch or Trap Point 

A switch (ie. blades and tiebar only), inserted in sidings etc., to divert runaway 

rolling stock away from the main line, or on gradients to de–rail runaway wagons 

etc. 

Crossing 

The inter section of two tracks on the level. Often known as a diamond crossing 

due to the shape produced by the intersecting tracks. Not to be confused with 

the crossover. 

Switch Toes 

Figure B1 

Switch Rails 

Heel Of Switch Rail 

Stock Rails 

Closure Rails 

Rail Joint 

Wing Rails 

Crossing Nose 

Closure Panels 

Crossing Angle 

Check Rail 

Crossing Back 

Switch and Crossing Terms 

Crossover 

A crossover consists of two points arranged to link parallel tracks. They are 

known as facing or trailing, depending on whether a train proceeding in its 

correct direction along the line can run directly over the facing crossover, or 

must reverse to cross the trailing crossover. 

Double Junction 

The point of junction of two double track routes. It comprises two turnouts and a 

crossing. 

Ladder Junction 

A form of junction eliminating the crossing. 

Where job titles are used within this Approved Code of Practice to reflect the 

anticipated functional splits of responsibility relevant to technical competence, 

they should not be interpreted as actual job titles. The specific split of 

B4 RAILTRACK


5 Introduction 




GK/RC0752 

Issue Two 


Page B5 of 25 

responsibility will be governed by a contractual framework, to which reference 

should be made. 

Catalogue Numbers shown within this document are not directly controlled by 

Railtrack and as such, will not be maintained and kept up to date. Although 

every effort has been made to ensure that these were correct at the time of 

publication, it is therefore recommended that your supplier is contacted and a 

check is made with regard to the accuracy of these catalogue numbers prior to 

use. 

Where references are made to other documents, a comprehensive list of these 

will be contained within the “Ref” section of this document. The information 

appertaining to these references was correct as of Issue 13 of the Railtrack 

Catalogue of Railway Group Standards. 

5.1 The Purpose of Track Circuits 

The track circuit is a device designed to continuously prove the absence of a 

train from a given section of track; it cannot absolutely prove the presence of a 

train, since its designed failure mode is to give the same indication as if a train is 

present. 

By proving the absence of a train, a clear track circuit can be used to confirm 

that it is safe to set a route and permit a train to proceed. 

5.2 Fundamental Design Principle 

A section of railway track is electrically defined by the provision of insulated rail 

joints (IRJs), or equivalent, in the rails at either end as shown in Figure B2. A 

source of electrical energy is connected, via a series impedance, across the rails 

at one end and a detector, which is receptive to the particular form of electrical 

energy, is connected across the rails at the other end. 

Figure B2 

Transmitter 

(Feed) 

Detector 

(Relay) 

Insulated 

Rail Joints 

With no train within its boundaries, the detector senses the transmitted electrical 

energy and energises the repeater circuit. This conveys the absence of a train to 

the signalling system (ie. track circuit clear). 

A train within the track circuit will cause the rails to be short circuited such that 

the detector no longer sees sufficient electrical energy; it therefore changes 

state and informs the signalling system (ie. track circuit occupied). 

It can be seen that an electrical short circuit between the rails, caused other than 

by a train, or any disconnection within the circuit, will fail the track circuit and 

inform the signalling system that the track circuit is occupied. Such a circuit 

configuration incorporates a high degree of “fail safe”; it does, however, depend 

upon good electrical contact between the wheel sets of the train and the rails 

RAILTRACK B5


GK/RC0752 

Issue Two 


Page B6 of 25 

6 Electrical Behaviour 

of Railway Track 




upon which they run. It also depends upon a continuous low impedance path 

between the steel tyres of each wheel via the connecting axle. 

Track circuits apply this basic principle in a variety of ways for various reasons. 

The source of electrical energy may be d.c., a.c. at power frequencies, a.c. at 

audio frequencies, or a series of impulses. The detector may be a simple relay, 

a more complex a.c. vane relay or a receiver tuned to a particular frequency or 

pattern of signals. Additional items may have to be added to overcome the 

problems arising from sharing the rails with heavy currents created by an electric 

traction system. 

6.1 Ballast Resistance 

Ballast resistance is the resistance between the two rails of a track circuit and 

comprises of leakage between the rail fixings, sleepers and earth. The value of 

this resistance is dependent upon the condition of any insulations, cleanliness of 

the ballast and the prevailing weather conditions. The ballast resistance is 

inversely proportional to track circuit length and is expressed as ohm kilometres, 

typical values being in the range 2 to 10Ωkm. Lower values may be obtained in 

wet conditions with bad drainage and/or contamination with conductive materials. 

Higher values may be obtained in dry/clean conditions or during frosty weather. 

A reliable track circuit must therefore be able to operate over a wide variation of 

ballast resistance. 

Most simple explanations of track circuit operation portray ballast resistance as a 

single resistance connected between the rails as shown in Figure B3. Whilst 

such a representation is useful in explaining the simple behaviour of d.c. track 

circuits, it is important to understand that the model’s limitations make it 

unsuitable to explain many of the more complex phenomena demonstrated by 

track circuits. For the types of track circuit used, the reactance of the ballast 

can be considered as negligible. 

Figure B3 

B6 RAILTRACK 

Rail 

Rail 

Ballast 

Resistance 

When considering other than the simple case, a more accurate model would 

represent the ballast resistance as a series of resistances between each rail and 

earth as shown in Figure B4. Although there is a further component of 

resistance between the rails independent of earth, it is high compared to the rail– 

earth resistance and can be discounted for most calculations.




Figure B4 


GK/RC0752 

Issue Two 


Page B7 of 25 

RAILTRACK B7 

Rail 

Rail 

Earth 

6.2 Rail Impedance 

The d.c. resistance of rail is very low, around 0.035Ω/km, although this is 

increased to approximately 0.25Ω/km by the relatively higher resistance of 

galvanised iron bonds in jointed track. The inductance of rail can raise the 

overall impedance per rail from approximately 0.3Ω/km (50Hz) to, in the case of 

reed track circuits, 2.5Ω/km (400Hz) and for TI21 track circuits, 10Ω/km (2kHz). 

These impedance values may be increased further by large traction currents, 

due to the rail being driven toward saturation. 

When considering a.c. track circuits, rail inductance must be taken into account 

by application of the further complex model including rail inductance as shown in 

Figure B5. Although of little consequence at power frequencies, audio frequency 

track circuits exhibit a steep decline in rail voltage as distance from the 

transmitter increases. Since the ballast resistance is now distributed throughout 

the length, detailed calculation requires the use of hyperbolic functions. 

These effects can usually be ignored when considering the operation of a.c. 

power frequency track circuits, where rail voltage can be expected to decline 

very little between the feed and relay ends. 

Figure B5 

Rail 

Earth 

6.3 Rail to Rail Capacitance 

Although an even more complete picture would include rail–to–rail capacitance, 

this is very small and of marginal significance relative to track circuit operation at 

audio frequencies. 

6.4 Workable Lengths of Track Circuits 

It can be seen that the workable length of a track circuit is limited by three 

factors: 

• the declining value of ballast resistance; 

• the increasing value of rail impedance; 

Rail


GK/RC0752 

Issue Two 


Page B8 of 25 

7 Operation and 

Adjustment of the 

Simple Track 

Circuit 




• Immunisation / Electrification requirements, including electromagnetic 

compatibility with trains. 

As the various types of track circuit feed/transmitter produce differing power 

outputs, and as rail impedance is frequency related, it follows that the maximum 

workable length will vary with design type and with the minimum ballast 

resistance at which the track circuit is expected to remain functional. 

Consider the simple d.c. track circuit depicted in Figure B6. 

Feed 

Resistance 

Figure B6 

Cable 

Resistance 

Cable 

Resistance 

Train 

Shunt 

Cable 

Resistance 

Cable 

Resistance 

B8 RAILTRACK 

Rail 

Ballast 

Resistance 

7.1 Track Circuit Clear 

The ballast resistance forms an additional load in parallel with the relay. As the 

ballast resistance falls due to wet weather, the current drawn from the feed 

increases. This will cause the voltage across the feed resistor to increase, so 

reducing the rail and relay voltages. If this reduction causes the relay voltage to 

fall below the relay pick–up value, the track circuit will not clear after an 

occupying train has departed. A further reduction of the relay voltage to below 

relay drop–away value will fail the track to the occupied state without the 

passage of a train. 

Reducing the value of feed resistance has the effect of increasing the current 

fed into the rails and raising the rail/relay voltage. 

Long feed end leads insert additional non–adjustable feed resistance and 

thereby reduce the effectiveness of the adjustable feed resistance. Long relay 

end leads reduce the ratio of relay voltage to rail voltage by potential divider 

action; the effect is to cause the track circuit to indicate occupied at a higher 

ballast resistance. It therefore imposes a shorter maximum workable length. 

7.2 Track Circuit Occupied 

When the track circuit is occupied by a train, a short circuit current will flow from 

the feed end equipment, which is limited by the value of the feed resistance and 

the characteristics of the feed end equipment itself. The feed end equipment is 

designed to cope with this worst case power dissipation. 

The train shunt resistance is in parallel with the ballast resistance. With any 

given value of feed resistance, the relay will operate at particular values of 

combined ballast/train shunt resistance. Thus, higher ballast resistance will 

require a lower value of train shunt resistance to operate the relay and vice 

versa. 

Rail 

TR


8 Train Shunt 

Imperfection 




GK/RC0752 

Issue Two 


Page B9 of 25 

The minimum permitted drop shunt resistance is 0.5Ω (0.3Ω on certain 

impedance bond track circuits). During very dry weather or severe frost 

conditions, the ballast resistance increases towards its natural maximum and will 

offer only a small contribution towards the overall shunt. Thus, when a 0.5Ω 

(0.3Ω) shunt is placed across the rails, it must still reduce the relay voltage to 

below drop–away value. 

It should also be noted that the track relay is dropped by short circuit rather than 

disconnection. Therefore, the drop–away time of the relay is increased due to 

the inductive circuit prolonging the decay of the coil current. 

7.3 Principles of Basic Adjustment 

The difficulty with adjusting track circuits (where such adjustment is provided) is 

knowing the prevailing value of ballast resistance. Details entered on the track 

circuit record card provide a useful history. These vary with track circuit type 

and the appropriate Code of Practice within the Track Circuit Handbook should 

be consulted. 

Assuming average conditions, the feed resistance is adjusted to obtain a relay 

voltage in the range 25% to 75% above the pick–up value whilst maintaining the 

drop shunt resistance at a value greater than the minimum required. If the track 

circuit fails due to wet weather, it may be possible to remedy the situation by 

reducing the feed resistance. It is important that the track circuit is re–tested 

after it has dried out. 

The energy seen by the relay with a train on the track circuit will depend upon 

the resistive value of the train shunt (see Figure B6). This energy will be zero 

only when the train shunt is zero. Whilst the ohmic resistance of an axle and 

wheels is virtually zero, there are a number of factors that can make the 

effective train shunt much higher. Since some factors are track based, whilst 

others are vehicle specific, the precise mixture of factors applying to a particular 

vehicle at a particular place can be very variable. 

8.1 Rust Films 

Light rust film on the rail head and/or tyre tends to act as a semi–conductor, in 

that it exhibits high resistance until the voltage exceeds a particular threshold 

value when it breaks down completely. The breakdown voltage rises in 

sympathy with the extent of the contamination; very heavy rust films, resulting 

from prolonged disuse, render many track circuit designs incapable of detecting 

vehicles. Figure B7 gives an approximate characteristic of such films. 

Current 

0.01V 

Figure B7 

RAILTRACK B9 

Very 

Good 

Damp 

Light Rust 

Dry 

Light Rust 

Heavy Rust 

Or 

Leaf Residue 

Good Poor Bad 

0.05V 0.1V 0.3V 0.6V - 200V 

Voltage


GK/RC0752 

Issue Two 


Page B10 of 25 




The mechanical strength of light rust films is much reduced by the presence of 

moisture when the contaminant tends to be squeezed out from the wheel–rail 

contact patch and doesn’t cause any shunting problems. Therefore, lightly 

rusted rails will only be a problem when dry. This problem is most severe when 

conditions are: 

• showery weather accompanied by drying wind; or 

• prolonged periods without trains. 

Special precautions need to be taken after relaying operations, when track 

circuits must not be restored to full operation until a reasonable surface has 

been created. 

8.2 Leaf Residue 

This problem is confined to particular areas where the extent of lineside 

afforestation is significant. It is also limited to autumn when trees are shedding 

their leaves. Leaves are drawn into the wheel–rail interface by the passage of a 

train, where they are squashed into a pulp which contaminates both rail and tyre. 

The severity of this problem in particular years is connected to the general 

weather situation. In simple terms, reasonably dry weather with little wind will 

cause the leaves to fall gradually over a long time period and to be reasonably 

sap free when they do fall. Conversely, gale conditions will lead to a sudden 

massive fall of sap laden leaves. It is the latter situation which gives rise to the 

worst conditions. 

In terms of track circuit operation, the electrical characteristics of severe leaf 

residue are similar to very heavy rust. Fortunately, the sites suffering such 

problems are generally known and special arrangements can be made. 

8.3 Coal Dust and Sand 

Problems with coal dust on the rail head tend to be confined to colliery areas, 

where coal deposited on the wagon chassis after loading/unloading is 

subsequently shaken off. Sand contamination is usually associated with slow 

moving locomotives using their sanders excessively. 

In each case, the effect is similar to heavy rust films. 

8.4 Composition Tread Brake Blocks 

Certain types of rolling stock are fitted with a composite type of tread brake block 

instead of the traditional cast iron variety, the intention being to improve brake 

performance. This is found to deposit a contaminant film on the steel tyre, which 

tends to insulate the train from the rails. 

8.5 Tread and Disc Brakes 

When considering the electrical contact between two pieces of metal separated 

by a thin film of insulation, it can be appreciated that surface roughness of the 

metal can permit high spots to penetrate the film. Where this occurs, the 

insulation will be ineffective. 

Tread brakes cause the tyres to be roughened at each brake application, 

whereas disc brakes allow the tyres to be rolled into a very smooth surface 

condition. This can be observed visually as tread braked tyres have a matt 

appearance, whilst disc braked tyres show a mirror–like quality. 

Therefore, tread braked vehicles provide a better train shunt than disc braked 

vehicles. 

8.6 Axle Weight and Suspension Design 

The pressure applied to any contaminant film is proportional to the downward 

force of the wheel on the rail and this is proportional to vehicle axle weight. 

B10 RAILTRACK


9 Detection of 

“Lightweight” 

Vehicles 




GK/RC0752 

Issue Two 



In practice, wheels do not roll smoothly and friction free. There is a guidance 

force continually pulling the wheelset into the correct trajectory and this guidance 

force is associated with microscopic slippage between wheel and rail. Advances 

in bogie design have tended to reduce this guidance force and slippage, giving a 

smoother ride for the passenger as well as reducing the wear rate of both rail 

and tyre. 

Unfortunately, these qualities reduce the ability of the tyres to penetrate any film, 

as well as reducing their ability to clean the rail by abrasion. 

8.7 Track Geometry 

Vehicle guidance force and wheel rail slippage are increased in curved track. 

Therefore, train shunt will be improved when the vehicles are travelling on 

curved track. 

If all rails and tyres were clean and wheel–rail contact was perfect, any type of 

vehicle would satisfactorily operate any type of track circuit. However, 

secondary lines in particular have suffered a fall in traffic leading to regular 

formation of light rust films. At the same time, the vehicles using such lines have 

been increasingly of the modern DMU variety, which magnify the train shunt 

difficulties because of their suspension design, brake type, weight (which, 

although still heavy, is relatively light) and small number of vehicles in a train. 

When a vehicle is static on a light rust film, the track circuit voltage will usually 

break it down and the track circuit will occupy. This is because the track clear 

rail voltage is higher than the film breakdown voltage. However, when that 

vehicle is moving, the wheels are continually rolling onto new film which requires 

to be repeatedly broken down. Consider the following sequence of events: 

When a wheel first enters the track circuit, the track clear rail voltage is 

presented across the film. The film breaks down resulting in the rail voltage 

collapsing towards zero. 

As the wheel moves on to new surface, there is insufficient voltage available to 

break through the new film. The train shunt is removed and the rail voltage rises 

towards the clear value. 

When the rail voltage attains the breakdown level, the film is punctured, the train 

shunt re–applies and the rail voltage once again plummets toward zero. 

The result is a high frequency noise voltage across the rails which can be 

observed with a suitably sensitive instrument. 

Where the threshold breakdown voltage is less than the rail voltage at which the 

relay drops away, the noise will not result in track circuit malfunction. This 

parameter is used to assess the performance of various track circuit types 

relative to their ability to detect lightweight vehicles. 

To assist vehicles to shunt track circuits, a device known as the “Track Circuit 

Assister” has been fitted to modern diesel multiple units. 

RAILTRACK B11


GK/RC0752 

Issue Two 



10 Track Circuit 

Insulations 




10.1 Insulated Rail Joints 

Insulated rail joints (IRJs) are required to join rails together mechanically but not 

electrically. The Permanent Way Engineer is responsible for the installation and 

maintenance of all IRJs. 

10.2 Point Equipment 

Apart from the IRJs, used to electrically separate sections of rail, the reliable 

operation of track circuits requires the provision of other insulations in particular 

circumstances. 

Any direct metallic connection between the two rails will be interpreted as a train 

and will cause the track circuit to fail occupied. At a set of points, there are 

many of these connections, which therefore need to be fitted with insulations, as 

shown in Figure B8, which is a typical example; there are, however, some 

regional variations. 

B12 RAILTRACK


Insulation 



C 


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Issue Two 



Insulation Insulation 

B 

A Soleplate 

The soleplate is formed from two metal plates secured together by a bolted connection at an intermediate 

position between the rails, which includes insulated ferrules, washers and plates to maintain electrical 

separation. 

Where the soleplate is extended to one side, as required for point machine operation, a second insulated 

connection is provided between the point machine and the nearest rail. 

B Permanent Way Stretcher Bars 

These connect the two point switches together and are formed from two separate pieces connected 

together with two bolts. The bolted connection includes insulation ferrules, washers and plates to 

maintain electrical separation. 

C FPL Stretcher Bar 

Insulation ferrules, washers and plates are fitted where the stretcher bar is connected to one of the point 

switch blades; usually that furthest from the drive mechanism. The design is such that the insulation can 

be fitted at either end of the stretcher bar, but should not be fitted at both ends. 

D Point Drive Rod 

Insulation is provided either separately, or is incorporated into the drive rod jaw connection onto the point 

machine. 

E Lock & Detector Rods 

Insulated bushes are fitted where the screwed end connections are attached to the switch extension 

pieces. 

Figure B8 

RAILTRACK B13 

D 

E 

A


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Issue Two 






10.3 Concrete Sleepers 

Early forms of concrete sleeper were fitted with chairs for bullhead rail in similar 

fashion to those fitted to timber sleepers. The chair was usually secured to the 

sleeper with a through bolt from the underside. These did not present any 

widespread problem since track circuits were not common in the rural areas, 

where concrete sleepers were seen to be advantageous. 

Although short track circuits can be made to work over such sleepers, the ballast 

resistance is usually quite low and subject to more severe weather related 

swings. It is also now known that damp concrete behaves as an electrochemical 

secondary cell which can give rise to residual voltage problems with d.c. track 

circuits. 

Modern concrete sleepers incorporate a rubber pad under the rail foot and 

moulded insulations where the fixings bear on the top of the foot, as shown in 

Figure B9. The effect is to increase ballast resistance to levels significantly 

higher than those obtained with timber sleepers. However, the insulations do 

erode due to the vibration of passing traffic and, consequently require periodical 

replacement. Lack of attention to insulation usually results in gradual 

degradation of the ballast resistance rather than sudden failure. 

Centre Leg 

Figure B9 

Front Arch 

Heelseat 

Rear Arch 

Insulation 

Rail Pad 

Rail Foot 

10.4 Steel Sleepers 

Steel sleepers are equipped with insulations similar to modern concrete sleepers 

and, provided they are subject to an effective preventative maintenance 

programme, track circuits will operate satisfactorily. 

However, as the sleeper is in more intimate electrical contact with general earth, 

much higher levels of track circuit unreliability will result from poor insulation than 

is the case with modern concrete sleepers. 

B14 RAILTRACK


11 Bonding 




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Issue Two 



Bonding describes the means by which the individual components of the railway 

track are connected together electrically for track circuit purposes. The term 

also includes the additional electrical connections necessary for the proper 

operation of electric traction. Symbols used on bonding plans are shown in Part 

C and various terms are explained in Section 3. Refer also to GK/RT0252. 

11.1 Series and Parallel Bonding 

In order for a track circuit to fail safe (to show occupied) in the event of a 

bonding disconnection, it is necessary to bond all elements of the track circuit in 

series. However, in S & C areas, it may not be physically possible to arrange 

total series bonding of both rails. Examples of series and parallel bonding are 

shown in Figure B10. 

Provided that a spur is very short, it is permissible to bond it in parallel without 

additional safeguard. However, where the spur is long, or in other cases where 

necessary, parallel bonding may be resorted to provided that steps are taken to 

ensure that vehicles are not lost due to disconnection of part of the parallel 

system. This is achieved by creating a mesh of alternative diverse bonding 

paths between parallel elements, and clearly identifying the associated bonds by 

their yellow colour. It is necessary to ensure that such yellow bonds are 

repaired quickly before other bonds in the mesh have time to fail in a manner 

likely to cause an unsafe failure. 

Because of the additional complication of significant rail impedance with parallel 

bonding, audio frequency track circuits are generally unsuitable in all but the 

simplest of pointwork. 

Figure B10 

Track Relay 

Preferred Series Bonding 

Track Feed 

Track Relay Track Feed 

Non-preffered Parallel Bonding 

RAILTRACK B15


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11.2 Double and Single Rail Track Circuit Bonding 

Double rail track circuit arrangements have both rails fitted with IRJs to 

completely isolate a track circuit. Impedance bonds are used when a traction 

current return path is required. IRJs and impedance bonds are not required with 

Jointless Track Circuits. 

Single rail track circuit arrangements have only one rail fitted with IRJs to 

separate the track circuits. The other rail is electrically continuous. If this 

continuous rail is used for traction return purposes, the bonding arrangement is 

called Single Rail Bonding. If this continuous rail is not used for traction return 

purposes, the bonding arrangement is called Common Rail Bonding. 

Whilst some designs of track circuit can be used in either single or double rail 

mode, others are limited to double rail application. 

In some S & C areas and certain electric traction areas, it is necessary for one 

or more adjacent track circuit to share one common rail. This arrangement can 

lead to unsafe failure modes unless special steps are taken to ensure that 

elements of the common rail cannot become isolated from the remainder. This is 

achieved by creating a mesh of alternative diverse bonding paths and marking 

the associated bonds yellow as for the previous parallel bonding case. 

11.3 Track Circuit Interrupters 

Track circuit interrupters are used at trap or run–back catch points on lines 

which are track circuited. The device is designed to interrupt the track circuit in 

the event of a rail vehicle leaving the track. This prevents automatic re– 

energisation of the track circuit after the removal of the train shunt. 

The interrupter is a metal device attached to the four foot side of the stock rail 

and usually insulated from it. It comprises a main body, a narrow neck and a 

head which is adjacent to the running edge and designed to break off when a rail 

vehicle passes over it. Connections are made to the head and the body such 

that electrical continuity is provided between them until the interrupter is broken. 

The arrangement is shown in Figure B11. 

The interrupter is fixed within the track circuit to the stock rail (as shown in 

Figure B12). It is not fixed to the switch rail. 


Connection 

Points 

Figure B11 

B16 RAILTRACK


12 Mutual Interference 

Between Track 

Circuits 




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Issue Two 



Note: In all cases, the interrupter is fixed to the stock rail (as shown in Figure 

B12). It must not be fixed to the switch rail. 

Figure B12 

Stock Rail 

Switch Rail 

Correct Position 

Incorrect Position 

It is important to realise that where track circuits are connected together by a 

common rail, and detectors are used that are unable to discriminate between 

their own and other track circuit feeds, a degree of mutual interference between 

such track circuits is inevitable. This condition may be introduced by design 

(single rail track circuits on electrified lines) or by failure (IRJ failure of double rail 

track circuits). 

The simplest way to describe mutual interference is to use the example of two 

d.c. single rail track circuits as shown in Figure B13 and Figure B14. It will be 

realised that this model also equates to a double rail insulated track circuit with a 

failed IRJ. Figure B13 shows the equivalent circuit in track circuit type format, 

whilst Figure B14 converts it to a standard electrical format for easier 

presentation of cause and effect. 

Consider the circuit in Figure B14 under conditions where VFB feed supply is 

disconnected. Clearly, a voltage will appear across RRB as a result of VFA, the 

value of which will depend on circuit parameters. The extent to which this 

voltage is of concern depends upon its value relative to the operating values of 

the relay. 

Provided that the bonding remains intact, an unsafe failure cannot arise from the 

mutual interference; either both track circuits will fail right side (occupied) or they 

will both show occupied when either one of them is legitimately occupied. 

However, there is the possibility of a wrong side failure where a bonding 

disconnection occurs. 

It is not appropriate to explain all possible scenarios here; the possibility is 

mentioned simply to convey the fact that some track circuit defects can be 

exceedingly difficult to understand and explain. Certain constraints are applied 

to various track circuit designs in order to limit the possibility of wrong side 

failure. Therefore, the design constraints described in the Track Circuit 

Handbook shall not be breached without expert advice. 

RAILTRACK B17


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13 Detection of 

Rail Breaks 




Common Rail TC A TC B 

Figure B13 

RCA 

RRA 

B18 RAILTRACK 

RSA 

Notes for Figure B13 and Figure B14: 

RFA 

VFA VFB 

Earth 

RFB 

RSB 

RRB 

RCB 

TC“A” TC“B” 

OPEN CIRCUIT FEED VOLTAGE VFA VFB 

FEED RESISTANCE RFA RFB 

RELAY RESISTANCE RRA RRB 

SIGNAL RAIL EARTH RESISTANCE RSA RSB 

COMMON RAIL EARTH RESISTANCE RCA RCB 

Common Rail 

Figure B14 

RFA 

VFA 

RRA 

Further Track Circuits 

R CA 

Earth 

Where rails are series bonded, a completely broken rail will be immediately 

detected as a right side track circuit failure (ie. occupied). 

Where the rails are not series bonded, a broken rail will not be detected by the 

track circuit. 

R SA 

R CB 

RSB 

RRB 

RFB 

V FB


14 Jointless Track 





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Issue Two 



Insulated rail joints can be expensive both to install and to maintain, especially on 

tracks subjected to high speed, high axle weight traffic or where there is an 

intensive service. 

The use of audio frequencies permits the physical limits of an individual track 

circuit to be defined by tuned short circuits between the rails rather than by 

insulation in the rails themselves. Consider two jointless track circuits abutting at 

a tuned zone as shown in Figure B15. Non–track mounted equipment has been 

omitted for clarity. 

RAILTRACK B19 

Tuned 

Zone 

Feed F1 Tuning Tuning 

Feed F2 

Unit F1 Unit F2 

Figure B15 

The tuned zone comprises a measured length of track with a tuning unit across 

the rails at each extremity. The track circuits operate at different audio 

frequencies and each tuning unit is designed to its own track frequency, such 

that the following criteria are obeyed: 

a) Consider frequency F1: 

The F2 tuning unit behaves as a short circuit between the rails, due to series 

resonance of its inductive and capacitive components. 

The F1 tuning unit tunes the two rails (inductive) and the F2 tuning unit short 

circuit to parallel resonance, thus presenting a significant impedance to 

frequency F1. 

b) Consider frequency F2: 

The F1 tuning unit behaves as a short circuit between the rails, due to series 

resonance of its inductive and capacitive components. 

The F2 tuning unit tunes the two rails (inductive) and the F1 tuning unit short 

circuit to parallel resonance, thus presenting a significant impedance to 

frequency F2. 

A wheelset proceeding along track circuit F1 will shunt the track circuit, but when 

it enters the tuned zone its effectiveness will reduce until, having passed tuning 

unit F2 (short circuit at frequency F1), it will no longer shunt track circuit F1. 

Similarly, the wheelset would not shunt track circuit F2 as long as it remained on 

track circuit F1, due to tuning unit F1 presenting a short circuit to frequency F2. 

As the wheelset passes F1 tuning unit, it commences to shunt frequency F2, 

becoming more effective as it progresses towards the F2 tuning unit and beyond 

into F2 track circuit proper.


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Issue Two 



15 Track Circuits and 

Electric Traction 




By careful design of components, it is possible to arrange a short overlap in the 

centre of the tuned zone where both track circuits are effectively shunted. 

Since the design of individual tuning units must take account of both frequencies, 

it is necessary to specify the exact frequencies involved. Such equipment is 

therefore produced for a fixed set of frequencies and those frequencies are 

used in pairs alternately along the track. 

Beyond the boundaries of electrified areas, track circuit type and configuration 

can be selected on the basis of train detection and economic criteria alone. 

However, track circuit arrangements in electrified areas are constrained by the 

need to ensure safe and reliable operation of both signalling and traction 

systems. This means that the track circuit must be immune to both false 

operation and damage by the flow of traction currents through the rails. 

Parallel tracks are cross-bonded at regular intervals, such that the traction return 

current from an individual train will have a number of different parallel paths back 

to the supply. This minimises the impedance to the traction supply and hence 

the volt drop, whilst it also limits the amount of current which can flow through an 

individual track circuit. 

Although permitted track circuits will be inherently immune to false operation 

(wrong side failure) from the presence of traction currents flowing in the rails, in 

some circumstances these can be of a magnitude sufficient to cause damage to 

equipment, or right side failure of the track circuit. The levels of traction current 

that the track circuit is subjected to can generally be sufficiently limited by well 

maintained bonding, track circuit length restrictions (single rail track circuits) and 

balance of traction currents between rails (double rail track circuits). 

Specific restrictions related to interference are contained within the individual 

track circuit type Codes of Practice. 

15.1 D.C. Electrified Areas 

In d.c. electrified areas, the relatively low supply voltage results in high currents 

returning to the sub-stations via the running rails. In order to minimise voltage 

drop in the d.c. traction supply, wherever possible, all running rails are used for 

the return of traction currents and therefore double rail track circuits are used. 

However, in S&C areas, it is not usually possible to bond the track in double rail 

form, therefore single rail track circuits have to be installed. 

Traditionally, all track circuits in d.c. electrified areas, were operated with 50Hz 

a.c. current, using phase sensitive vane relays. Double rail track circuits, with 

impedance bonds providing traction current continuity, were provided on plain 

line and single rail track circuits in S&C areas. More recently, jointless 

modulated audio frequency track circuits have been introduced, reducing the 

number of IRJs and impedance bonds required in plain line areas. 

B20 RAILTRACK





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Issue Two 



15.2 A.C. Electrified Areas 

In present 25kV a.c. electrified areas, traction currents are lower than in d.c. 

systems and in most cases, single rail traction return is sufficient for 

electrification purposes. Increased traffic levels and alternative feeding 

arrangements, may however, increase the need for both running rails to be used 

for traction return. 

Traditionally, all track circuits in a.c. electrified areas, were operated with d.c. 

current, although feed and relay components are specifically modified to provide 

protection from damage and immunity to interference. 

15.3 Dual Electrified Areas 

Where tracks may be subject to the flow of both a.c. and d.c. traction currents, 

the choice of track circuits is limited to those that are immune to both and do not 

use frequencies (including harmonics) contained in the traction supply. 

15.4 Single Rail Track Circuits 

Where traction return current flows through a single rail track circuit, the majority 

of the current will flow in the traction rail, resulting in a voltage drop along it’s 

length. This voltage drop is proportional to the current, the track circuit length 

and the impedance of the rail. With a train shunt applied toward the feed end of 

the track circuit, this voltage drop can be presented across the signal rail and 

track receiver in series. Dependent upon the relative impedance of the signal rail 

and the receiver at the frequencies of interest, a proportion of this voltage will be 

applied across the receiver. 

If the traction supply contains some voltage disturbance at a frequency to which 

the track circuit is sensitive, then this will be conducted through trains and flow 

as current through the running rails. If this is of sufficient magnitude, form and 

duration, then with a train shunt at the feed end, a wrong side failure could 

occur. 

In addition to conducting the voltage ripple present on the traction supply, 

modern traction units employing active control methods (such as three phase 

drives) can actively generate currents at other frequencies and superimpose 

them onto the supply. Whilst the traction control systems can be designed so as 

to avoid critical frequencies as far as possible, some interference content at 

frequencies used by track circuits may be produced. Depending upon the type 

of traction unit, the magnitude of this interference content may be limited by the 

use of an Interference Current Monitor Unit (ICMU) on the train, which will isolate 

the traction unit from the supply if sufficient interference flowing through the 

train, is detected. These ICMUs however, take a finite time to operate, and 

whilst the operate delay, due to the use of slow operating repeat relays, is 

generally sufficient to cope with transient interference, it may be necessary to 

modify the track circuits before the train can reliably operate. 

RAILTRACK B21


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Issue Two 






15.5 Double Rail Track Circuits 

Where both running rails are used for traction current return, the electrification 

arrangements, using impedance bonds, are designed to keep the currents 

flowing in each rail balanced. Under such conditions, any interference content 

within the traction current should similarly be balanced and little or no 

interference applied to the receiver. However, due to a number of reasons, 

interference currents flowing through the track circuit may be, or become, 

imbalanced: 

• presence of check rails; 

• track curves; 

• earthing of one rail; 

• bonding differences; 

• asymmetric position of conductor rail / catenary; 

• broken rails; 

• disconnected impedance bond sideleads 

When the track circuit becomes unbalanced any interference in the traction 

return current due either to disturbances in the supply, or generated by traction 

units, will result in interference being presented to the receiver. The magnitude 

of this interference is largely independent of the length of the track circuit, but is 

proportional to the imbalance of currents flowing through the receiver end of the 

track circuit (either an impedance bond or tuned zone). Therefore, with a train 

occupying the track circuit, interference can be applied to the track receiver, 

which if of sufficient magnitude, form and duration, will cause a wrong side failure 

of the track circuit. 

15.6 Rolling Stock Compatibility 

Means of providing compatibility between rolling stock and track circuits, without 

the use of ICMUs, is preferable and modern traction units may be acceptable for 

use with the existing track circuits, if it can be demonstrated that the predictable 

level of interference which may be generated, is insufficient to interfere with 

correct track circuit operation. Such an assessment will need to make 

reasonable assumptions as to the proportion of traction current that can flow 

through an individual track circuit, the resulting magnitude of interference which 

will be presented to the track receiver and the minimum response time of the 

receiver and interlocking. Therefore the validity of such assessments relies upon 

the following: 

• cross bonding between parallel tracks; 

• track circuit length limitations; 

• prevention and detection of imbalance; 

• integrity of rails and bonds; 

• operating times. 

CAUTION: Although general precautions and limits that provide 

compatibility between rolling stock and track circuits, have been included 

in the Train Detection Handbook Codes of Practice, these are not 

comprehensive and special conditions may apply to certain routes to 

permit the operation of rolling stock. 

Where new types of rolling stock are to be introduced, existing constraints 

will require reassessment, as to their adequacy. 

B22 RAILTRACK


16 Impedance Bonds 




GK/RC0752 

Issue Two 



16.1 Operation 

Impedance bonds are devices which allow traction current (d.c. or a.c.) to pass 

through, whilst limiting the track circuit current. They are necessary wherever 

double rail traction return and IRJ dependent track circuits coexist. 

An impedance bond is configured to provide a very low impedance path to 

double rail a.c. or d.c. traction return currents (typically less than 0.4mΩ per coil) 

whilst presenting a high enough a.c. impedance between the rails (typically 

greater than 15Ω) to allow the operation of track circuits. It also provides a 

centre connection for cross bonding, which minimises the passage of track 

circuit current between circuit currents. 

The winding connected between the rails is comprised of heavy gauge copper, 

fitted with a centre tap connection and wound on a heavy iron core. Provided 

that each running rail carries equal amounts of traction return current, the 

current from each rail passes in opposite directions through the coil from the rail 

to the centre tap connection. The net flux in the iron circuit will be zero and the 

impedance to traction current (d.c. or a.c.) will be very small, as shown in Figure 

B16. 

Figure B16 

IRJ IRJ 

1/2 Traction Current 

1/2 Traction 

Current 

Cross Bond Cross Bond 

Track 

Transmitter 


Receiver 

The a.c. track circuit current attempts to flow between the two rails and is 

therefore in the same direction through the two halves of the winding, resulting in 

the track circuit current seeing a larger, albeit still relatively small, impedance. 

Track–to–track cross bonding on double rail track circuits must be provided via 

the centre taps of impedance bonds on electrified lines, as shown in Figure B17. 

Figure B17 

Cross Bonds 

RAILTRACK B23


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16.2 Auxilary Winding 

The impedance available from the simple impedance bond remains a handicap. 

It is therefore usual to enhance the impedance by parallel resonance of the 

traction winding, use being made of a step–up (approximately 50:1) transformer 

to reduce the value of the necessary capacitance to realistic levels. Another 

solution is to connect the resonating winding to form an auto transformer, refer 

to 16.2.2. 

16.2.1 Resonated Impedance Bonds 

The induction of the traction winding is tuned to resonance at or near the track 

circuit operating frequency by use of a parallel capacitor, which raises the rail to 

rail impedance at the track circuit frequency, and thereby reduces the bond’s 

effect on the track circuit. 

For power frequency track circuits (eg. 50 Hz), the value of capacitance required 

to attain resonance is reduced to an achievable magnitude, by applying the 

capacitance via an auxiliary winding, as shown in Figure B18. 

To Next Bond 

Or Cross Bonding 

Figure B18 

Auxiliary Flux 

Winding 

B24 RAILTRACK 

IRJ 

IRJ 

The value of capacitance required to achieve resonance depends on the 

following: 

a) Traction winding inductance, which may differ between designs. The 

capacitance required will vary inversely to the inductance. 

b) Auxiliary turns ratio, which may differ between designs. The capacitance 

required will vary inversely as the square of the turns ratio. 

c) Track circuit frequency, where the capacitance required will vary inversely 

as the square of the frequency. 

Resonated impedance bonds are used at the feed and relay ends of jointed 

audio frequency track circuits and for all intermediate bonds associated with 

traction cross bonding.





GK/RC0752 

Issue Two 



16.2.2 Auto Coupled Impedance Bonds 

The method used to couple the feed and relay ends of certain designs of track 

circuit into the track as shown in Figure B19. At the feed end, the reduced 

voltage appearing across the the traction winding is applied to the rails whilst at 

the relay end, the current from the track circuit passing through the traction 

winding is usefully employed to drive the relay. 

IRJ 

To Next Bond 

Or Cross Bonding 

Figure B19 

IRJ 

To Track Relay Or 

Feed 

RAILTRACK B25 

OR 

To Rails 

To Track 

Relay Or Feed 

A double rail A.C. track circuit with auto–coupled impedance bonds is shown in 

Figure B20. 

Figure B20 

110V 

Resonant Bond 

Control 

Local 

110V 

If the traction current in each rail is not equal, the imbalance results in a net flux 

in the iron circuit, and if that flux is sufficient to saturate the iron core, the track 

circuit current will be presented with a short circuit. It is therefore important to 

make the bond as tolerant as possible of traction current imbalance and this is 

done by creating an air gap in the magnetic circuit. Such bonds will tolerate 20% 

imbalance before saturation.



This page is intentionally blank



2 Drawing Symbols on 

Bonding Plans 

Symbol 



Part C 

Schematic Symbols 


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Page C1 of 11 

The schematic symbols described here apply to bonding plans. Symbols 

depicting track circuits on signalling plans are to be in accordance with 

GK/RT0004. 

2.1 Bonding 

Bonding plans must show connections which require traction voltage warning 

labels, as shown in Part E. 

Description 

Electrified lines: Rails bonded, but not track circuited. 

Electrified lines: Only one rail continuity bonded. 

Non-electrified lines (In electrified areas): Rails not bonded. 

Single rail traction return: In non-electrified areas one rail 

shall be drawn bold, this shall be the series rail for CR 

Bonding and the positive or BX rail for DRDS Bonding. 

Signal rail insulated by IRJs 

Continuous traction return rail 

Stainless steel strip on rails. 

RAILTRACK C1


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Page C2 of 11 

Symbol 





Insulating rail joints: Separate track circuits on both sides. 

Insulating rail joints: Track circuit on left, none on right. 

Insulating rail joints: Track circuit on right, none on left. 

Insulating rail joints: Between different sections of the same 


Standard jumper bond. 

Traction bond. 

Yellow bond. 

C2 RAILTRACK


Symbol 



Structure bond. 


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Page C3 of 11 


Signal engineering equipment to rail bond. 

Structure to Earth Wire. 

Rail to rail bond (cross bonds) - (one example). 

Return conductor or earth wire to rail bond. 

Track circuit interrupter. 

Connections for dc track circuits. 

Connections for ac track circuits. 

RAILTRACK C3


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Page C4 of 11 

Symbol 





Connections for HVI track circuits. 

Guard boarding The provision of guard boarding will be 

indicated by a thin line on whichever side 

of the conductor rail it is required. 

A suitable note may be added if required. 

Insulated buffer stops. 

Non-insulated buffer stops. 

Insulated points. 

Non-insulated points. 

2.2 Track Circuit Actuator Interference Detector (TCAID) 

TCAID-N or TCAID (MC) 

TCAID-D, detection to the right 

TCAID-D, detection to the left 

C4 RAILTRACK


Symbol 




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Page C5 of 11 

2.3 Impedance Bonds 

If an impedance bond contains an internal resonating capacitor, the symbol must 

be shown filled in. 


Double rail to double rail track circuits. 

Double rail to single rail track circuits. 

Double rail track circuits to non-track circuited line. 

Intermediate impedance bond. 

Cross Bonds (Track to track bonds): Using impedance bonds 

in double rail areas. 

Tuned impedance bond. 

RAILTRACK C5


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Page C6 of 11 

Symbol 




2.4 Symbols For TI21 Jointless Track Circuits 


Tuned zone with a transmitter and a receiver. 

Transmitter of centre fed track circuit at an end tuning unit (ETU). 

Receiver at an IRJ with an end tuning unit (ETU). 

Low power: Show at transmitter only. 

Example of a TI21 track circuit bonding plan. 

C6 RAILTRACK


Symbol 



2.5 Symbols For Reed Track Circuits 

Transmitter. 

Receiver. 


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Page C7 of 11 


Intermediate simple loop (loop symbol points towards TX). 

Compound loop (loop symbol points towards TX). 

Example of a jointed reed track circuit bonding plan electrified. 

Example of a jointless reed track circuit bonding plan. 

Note: Track circuit frequency is indicated in ( ) brackets following the track circuit name. 

RAILTRACK C7


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Page C8 of 11 

3 Traction Return 

Bonding Symbols 

Symbol 




Separate Traction Return Bonding Plans are only used on the former Southern 

Region. 


Running rail bonded at each rail joint for dc electric traction. 

Insulated rail joint. 

Resonating bond. 

Impedance bond. 

Track circuit cut section. 

To specify that more than one bond 

is required, indicate as shown. 

C8 RAILTRACK


Symbol 

Cable Identification Codes 



Single protective boarding. 

Double protective boarding. 


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Page C9 of 11 


Insulated rail joint and continuity cable 

to eliminate magnetisation of points. 

Aluminium advance plate: Only installed for attachment 

of traction return bonds in areas 

of single rail traction return. 

a Single 500mm sheathed copper cable (soldered lugs) or single 800mm 

sheathed aluminium cable (crimped aluminium or Cadweld aluminium lug). 

c Single 161mm sheathed copper cable (gas weld heads). 

d Single 161mm sheathed copper cable (soldered lugs) or single 240mm sheathed 

aluminium cable (Cadweld aluminium or copper lug or crimped aluminium lug). 

f Single 161mm bare copper cable (gas weld heads) or single 150mm aluminium 

cable (crimped 20 bi-metal bond heads). 

g Single 161mm copper cable (soldered 20 copper bond heads). 

h Single 161mm sheathed cable (one gas weld head and one soldered lug). 

j Single 161mm sheathed cable (one soldered lug and one soldered 20 copper bond 

head) or single 150mm sheathed aluminium cable (one crimped 20 bi-metal bond 

head and one crimped aluminium lug). 

m Single 1,000mm sheathed aluminium cable. 

Nn Single 630mm sheathed copper cable. 

RAILTRACK C9


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Page C10 of 11 

Symbol 

4 Engineer’s 

Scale Diagrams 




4.1 <strong>General</strong> Symbols 

These symbols are to be used on the 1:100 and 1:200 scale diagrams when 

requesting IRJs and point insulations to be installed by the Permanent Way 

Engineer. The symbols are to be coloured red on plans returned to the 

Permanent Way Engineer. 

Note: On Permanent Way Engineer’s Plans, dimensions are to the inside 

edges of rails. 

Insulated rail joint required. 


Insulated soleplate and stretcher bars required (position of insulation 

to be shown). 

Drilling of insulated soleplate for facing point lock required, to 

MD 82017 (position of insulation to be shown). 

Extended sleepers and soleplate required for the installation of 

combined type machines with left hand drive (show in reverse for right 

hand drive). Standard facing points (not clamp locks), drilled to 

BRS-SM 318. 


combined type machine. Right hand drive for single or double slips (not 

clamp locks), drilled to BRS-SM 319. 

C10 RAILTRACK


Symbol 




GK/RC0752 

Issue Two 


Page C11 of 11 



combined type machine. Left hand drive for single or double slips (not 

clamp locks), drilled to BRS-SM 320. 

Indicates switch rail, stock rail and soleplate to be pre-drilled for 

hydraulic clamp locks with multiple drives and soleplate, in accordance 

with BRS-SM 2200, 2228, 2240, 2244 or 2260, as appropriate. If 

concrete sleepers are to be used, they are required to be drilled in 

accordance with BRS-SM 622. 

Stainless steel strip welded to rails required. 

RAILTRACK C11



This page is intentionally blank.



2 Responsibilities for 

Bonding Design 



Part D 

Planning and Design 


GK/RC0752 

Issue Two 


Page D1 of 20 

The principles laid down here apply to the planning, layout and design of all 

types of track circuits and track circuit bonding. Special requirements for 

individual types of track circuit are given in subsequent Codes of Practice within 

the Track Circuit Handbook. Signalling design requirements are contained in 

GK/RT0201. 

Many of the parameters affecting track circuit design are related to the physical 

and electrical characteristics of the trains operating over the track circuits. 

Dimensions of track sections which are critical for achieving safe and reliable 

detection are contained in GK/RT0011 Appendix A. If the accuracy quoted 

cannot be attained, dimensions should be rounded up unless otherwise stated 

(ie. if a maximum is given). 

For a description of terms and definitions used in track circuit design and 

operation, see Part B. 

For details of symbols used on scheme plans and bonding plans, see Part C. 

2.1 <strong>General</strong> 

Bonding requirements are contained in GK/RT0252. 

2.2 Non–electrified Lines 

The design of all track circuit bonding on non–electrified lines is the responsibility 

of the Signal Engineer. 

This requires the production of detailed scale bonding plans for all track circuiting 

in switch & crossing work, usually based on the Permanent Way Engineer’s 

track layout plan. On plain line a detailed bonding plan need not be produced, 

as long as sufficient detail of feed and relay leads is provided in lineside 

apparatus housing diagrams. 

2.3 Electrified Lines 

Both Signal and Electric Traction Engineers require connections to the running 

rails, so compatibility between them is essential. In addition, there are a number 

of connections upon which there is common reliance. It is therefore necessary 

to have common plans/records that show in detail the track bonding 

arrangements. There must be agreement between both parties before any new 

work or alterations are carried out. Design Standards are contained in 

GM/TT0126 and GM/TT0129. 

The Signal Engineer is responsible for the design of: 

a) All fishplate bonds in non–traction rails. 

b) All fishplate bonds in traction rails of a.c. only electrified areas. 

c) The position of all insulated rail joints. 

d) All jumper bonds between separate sections of non–traction rails. 

RAILTRACK D1


GK/RC0752 

Issue Two 


Page D2 of 20 


Nomenclature 




e) In a.c. electrified areas (excluding the former Southern Region), all rail to 

impedance bond connections and connections between impedance bonds on 

the same track. 

f) In dual a.c./d.c. and d.c. electrified areas (excluding the former Southern 

Region), the responsibility for impedance bond connections is subject to 

special arrangements between the Signal and Electric Traction Engineers. 

g) On the former Southern Region, impedance bond connections for track 

circuit only purposes. 

h) All track circuit rail connections. 

i) Identifying the need for Yellow Bonding and specifying which bonds are to 

be yellow. 

The Electric Traction Engineer is responsible for the design of: 

a) All fishplate bonds in d.c. or dual a.c./d.c. traction rails. 

b) All jumpers bonds between separate sections of traction rails and between 

the centre connection of impedance bonds in different tracks. 

c) On the former Southern Region, rail to impedance bond connections for 

traction purposes. 

d) All other permanent traction related bonding. 

2.4 Adjacent Lines 

In all cases where lines run adjacent to or cross each other, but are not 

physically connected, all these lines must be represented on the bonding plans 

and the bonding plans cross referenced to each other. 

Identification of individual track circuits is to be in accordance with Standard 

Signalling Principle No. 54 and must be shown on plans at convenient intervals 

within the respective track circuit. 

To avoid confusion with other plan annotation, the following Track Circuit 

designations are to be avoided: 

B, F, I, N, O, R, Q, T, CL, OL, HVI, RB, RN, RR, RT, RX, TB, TC, TF, TFR, TI, 

TJ, TN, TO, TR, TX, VT, IBJ, IRJ, OCC. 

D2 RAILTRACK


4 Choice of Track 

Circuit Type 




GK/RC0752 

Issue Two 


Page D3 of 20 

There are a number of design features of track circuits which constrain choice 

for a given application: 

a) The need to detect vehicles on poor rail surfaces. 

b) The need or otherwise to avoid insulated rail joints. 

c) The need for immunity to a.c. and/or d.c. traction interference. 

d) The need to achieve maximum reliability at economic cost. 

e) The need to track circuit through complex S & C. 

The Figure D1 summarises the key attributes and limitations of each type of 


CAUTION: Although general precautions and limits that provide 

compatibility between rolling stock and track circuits, have been included 

in the Train Detection Handbook Codes of Practice, these are not 

comprehensive and special conditions may apply to certain routes to 

permit the operation of rolling stock. 

Where new types of rolling stock are to be introduced, existing constraints 

will require reassessment, as to their adequacy. 

RAILTRACK D3


GK/RC0752 

Issue Two 


Page D4 of 20 

Type Suitable For 

Lightly Used 

Lines 

D.C. Medium Voltage 

A.C. Immune #1 


IRJs 

Required 

Immunity From Suitable 

For S & C 

a.c. 

50Hz d.c. 

Yes Yes Yes No Yes 

D.C. Diode #1 Yes Yes No No No 

TI21 #1 No No Yes#4 Yes No 

HVI #1 Yes Yes Yes Yes Yes 

D.C. Low Voltage Plain No Yes No No Yes 

D.C. Low Voltage 

A.C. Immune 


Plain 


A.C. Immune/D.C. 

Tolerant 

A.C. WR Quick 

Release 



No Yes Yes No Yes 

Yes Yes No No Yes 

Yes Yes Yes Yes#2 Yes 

No Yes No No Yes 

A.C. 50Hz Vane No Yes No Yes Yes#3 

A.C. 83.3Hz Vane No Yes Yes Yes Yes#3 

Reed No Yes Yes Yes Yes 

Aster/SF15 No No No No No 

Notes: 

# 1 Preferred track circuits for new works. 

# 2 Limited dc immunity. Used in an area of ac lines close to ac/dc dual 

lines not fitted with any means of isolating the traction rail systems. Use 

must be subject to a proper immunisation evaluation exercise. 

# 3 Single rail type has restricted length but adequate for S & C 

application. Double rail type is difficult in complex S & C but permits long 

length in plain line. 

# 4 The use of TI21 on ac electrified lines requires the earthing of 

lineside structures to be to a separate conductor rather than to the rail. 

This precludes the use of TI21 on ac lines unless part of a major new 

electrification scheme. 

Figure D1 

D4 RAILTRACK


5 Cut Sections 




GK/RC0752 

Issue Two 


Page D5 of 20 

Designing cut sections into a track circuit is a method of reducing the continuous 

length. The track circuit is split into individual track circuits, each one controlling 

the same final TPR. They are indicated as one track circuit on the signalman’s 

panel. Special care must be taken where an individual section of such a track 

circuit is used separately for control purposes (eg. level crossing timing). 

The cascading of cut sections (ie. controlling the feed to a track circuit by the 

relay of the next track circuit) is not permitted. The individual cut sections should 

be either returned individually to the interlocking or summated in the TPR lineside 

circuit or, in the case of SSI, summated in the data. 

Cut sections must be identified in accordance with GK/RT0009 (ie. AA1, AA2, 

AA3, etc) in the direction of normal running. The two portions of a centre fed 

jointless track circuit are treated separately for this purpose (eg. AA2 and AA3 in 

Figure D2). 

Figure D2 

(50HZ) 

Track Circuit 

AA1 AA2 AA3 AB 

Relay Feed 

(Centre Fed) 

Jointless 


AA2 AA3 AB 

RX 

AA2/3 

TX 

RX RX 

Where a monitoring device is provided, it must indicate to the technician the 

location at which the failed relay/receiver is housed, irrespective of the line 

affected. With reference to Figure D3, an example of the labelling for an 

individual display would be “Loc 10 (AA2, AA3, BC2, BC3)”. 

AA2 

BC3 

Figure D3 

AA2 AA3 

RX RX 

AA3/4 

AA4 

TX RX 

AA3 AA4 

BC2 BC1 

BC3 BC2 

BC1/2 

BC1 BB6 

RX RX TX 

RX RX 

LOC. 10 LOC. 11 LOC. 12 

Track circuits must not consist of more than two non–monitored cut sections 

(where track circuits are centre fed, four receivers (Rxs) may be non– 

monitored). 

RAILTRACK D5 

AB1 

TR 

AB1 

BB6


GK/RC0752 

Issue Two 


Page D6 of 20 

6 Operating Times 




The monitoring device will usually be housed at the nearest interlocking, but this 

will largely be governed by the routine and out–of–hours fault finding cover 

arrangements which exist in the vicinity. 

The transmission of information to the monitoring device may be achieved by 

additional FDM channels, a low–cost FDM system approved for use in signalling 

or telecommunications cables or direct wire circuits. 

6.1 Time Delays 

There can be significant differences between the drop–away and pick–up times 

of different types of track circuit, such that the rear track may register clear 

before the forward one registers occupied. The detection of the vehicle is 

therefore momentarily lost, resulting in a wrong side failure, which could permit 

the irregular release of vital interlocking. To overcome this, additional time 

delays must be built into the pick–up time of track repeaters, the precise 

requirement being dependent upon the combination of track circuit types 

involved. 

The indication circuits to the signalman may be transmitted via a TDM or FDM 

link. Therefore the transmission system reaction times must also be considered 

to ensure that the signalman does not observe an apparent loss of train 

detection. 

6.2 Operating Categories And Conditions 

In order to simplify the number of possible permutations, track circuits are 

assigned to operating categories as follows: 

Track Relay Operating Characteristics Operating Category 

Slow to Pick Up - Quick to Drop Away A 

Medium to Pick Up - Medium to Drop Away B 

Quick to Pick Up - Slow to Drop Away C 

Track Circuit Type Operating Category 

TI21 A 

UM71 (French A 

D.C. (all types) B 

Phase sensitive a.c. (50Hz, 75Hz & 83.3Hz) B 

Aster B 

Reed with adjustable track filter B 

Western Region “Quick Release” (a.c./d.c.) B 

Diode B 

Coded B 

GEC Alsthom High Voltage Impulse (HVI) C 

Reed without adjustable track filter C 

D6 RAILTRACK



GK/RC0752 

Issue Two 


Page D7 of 20 

With Geographical systems, the differing combinations of abutting categories of 

track circuits need to be examined and dealt with specially, according to the 

original design principles. With free wired relay interlocking and SSI, they must 

be dealt with as follows: 

Category A 

When used with a free wired relay interlocking, these track circuits do not require 

a slow to pick up TPR. Therefore, the TR may be used directly in controls. 

When used with an SSI, standard track circuit data must be used. 

Category B 

When used with a free wired relay interlocking, these track circuits require one 

slow to pick up TPR, in accordance with Figure D4 

When used with an SSI, standard track circuit data must be used. 

Category C and Category B abutting Category C 

When used with a free wired relay interlocking, these track circuits must be 

provided with two slow to pick up TPRs, in accordance with Figure D5. The TR 

and TPR must be in the same location case or equipment room. The T2PR 

must be controlled directly by contacts of both TR and TPR to prevent the drop– 

away of T2PR from being unnecessarily delayed whilst still achieving the delayed 

pick–up required. 

When used with an SSI, track circuit data with “extra delay” must be used. 

Where the time delay is achieved by relay cascade, it is important that other 

contacts of the TR and any intermediate repeater relays are not used for control 

indication purposes. To prevent inadvertent subsequent use, a suitable note 

must be made on the Contact Analysis Sheet. 

A schedule must be provided listing all TPRs, the individual sections repeated by 

each TPR and the type of track circuit (including the frequency in the case of a 

jointless track circuit). 

B50 

N50 

Figure D4 

B50 

N50 



Figure D5 

EG TR 

EG TR 

BR 933 

EG TPR 

RAILTRACK D7 

EG TR 

EG TR 

EG TPR 

EG TPR 

BR 933 

BR 933 

EG TPR 

EG T2PR


GK/RC0752 

Issue Two 


Page D8 of 20 


Interrupters 

8 Length of Track 





The interrupter (BRS-SM 374) is designed to be mounted on the stock rail, not 

the switch rail, and is electrically insulated from it. It is to be mounted as near as 

possible to the switch toe, at a position where the flangeway gap is not less than 

70mm when the switch is closed. 

An interrupter may be either directly controlled in series with the track circuit or 

part of a separate circuit utilising an interrupter relay according to circumstances. 

The interrupter must be part of a separate circuit unless all of the following 

conditions apply: 

• The line is non–electrified. 

• The track circuit on which the interrupter is wired is a d.c. track circuit. 

• The operation of a track circuit by by the interrupter will place to danger any 

necessary signal on adjoining lines. 

Note: The bonding of the interrupter must be of opposite polarity to the rail on 

which it is mounted. 

In all other circumstances, the interrupter must be part of a separate circuit 

incorporating a track circuit interrupter relay. The interrupter relay is controlled 

directly by the interrupter itself and its front contacts are used to control all 

repeat relays of the required track circuit. Where necessary, an interrupter relay 

may control more than one track circuit or may be controlled by more than one 

interrupter. 

Minimum 

To cater for the longest wheel base vehicles, a standard minimum effective track 

circuit length of 18.3m must be provided for new and altered works. If this 

minimum length cannot be achieved, alternative safeguards must be provided, 

(eg. sequential clearance of the track circuits in the interlockings). 

Maximum 

The maximum lengths quoted in individual Codes of Practice within the Track 

Circuit Handbook are based on a ballast resistance of 3Ωkm for timber 

sleepered track and 5Ωkm for concrete sleepered track. If it appears likely that 

a track circuit will be required to operate at or near its maximum permitted 

length, tests should be made to ascertain whether ballast conditions etc, are 

satisfactory, particularly in wet weather, before the scheme design is finalised. 

The unpredictable effect of level crossings should also be borne in mind. 

On electrified lines, track circuits may have to be further restricted in length in 

order to limit the effects of interference from the traction system. 

Certain track circuit types require a greater minimum length due to their 

operating characteristics. See the relevant Code of Practice within the Track 

Circuit Handbook 

D8 RAILTRACK


9 Track Circuit Gaps 

and Staggered 

IRJs 

10 Selective Operation 

of Track Circuits 

11 Bad Rail Surface 




GK/RC0752 

Issue Two 


Page D9 of 20 

It is essential that all classes of vehicle, irrespective of wheelbase arrangement, 

are detected by the track circuiting, otherwise false track circuit clearance may 

lead to premature movements of points or irregular release of signals. Based on 

the dimensions of existing rolling stock and allowing for future developments, the 

following shall apply: 

a) The maximum dead section between two track circuits in areas of 

continuous track circuiting is 2.6m. This is the minimum wheelbase of 

vehicles working unattached. 

b) Opposite IRJs must be regarded as the ideal arrangement. If unavoidable, 

physically staggered overlaps between nominally opposite IRJs must not 

exceed the following limits: 

Non–electrified areas 2.6m 

Electrified areas if the traction rails overlap 2.6m 

Electrified areas if the insulated rails overlap 2.1m * 

Isle of Wight lines 1.7m * 

Note*: These distances are stipulated by the Electric Traction Engineer to 

prevent a motor bogie losing its negative return path (see Figure D12 for 

clarification). 

a) There must be at least 18.3m between the nearest joint of any physically 

staggered pair and an IRJ defining a clearance point at the end of the track 

circuit. Where this cannot be obtained, special sequential controls must be 

provided. 

b) If the physical stagger exceeds 1.6m, there must be at least 18.3m between 

the nearest joint of the staggered pair and the next IRJ. If the stagger is less 

than 1.6m, this distance may be reduced to 11m. Where the requirement 

cannot be met, special sequential controls must be provided. 

c) Full details of critical dimensions for train detection are contained in 

GK/RT0011. 

Operation of a portion of a track circuit by the selection of the positions of a set 

of points is not permitted. Such portions must be separately track circuited. 

At locations where oil film or rust is excessive, (eg. traction depots, terminal 

platform lines, etc), a stainless steel strip can be applied to the surface of the 

running rail by the Permanent Way Engineer. This must be shown on bonding 

plans, using the symbol specified in Part C. The vibration caused by the 

resulting uneven rail surface restricts its application to very low speed 

applications (5 mph maximum). 

Alternatively, the GEC Alsthom High Voltage Impulse (HVI) track circuit may be 

used (see GK/RC0756). 

12 Emergency 

Crossovers Where a crossover is clipped and padlocked or worked from an adjacent ground 

frame and subject only to an emergency release, track circuiting is not required 

for movements over the crossover. 

RAILTRACK D9


GK/RC0752 

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Page D10 of 20 

13 Insulated Rail Joints 

and Bonding 




13.1 Definition of Bonding Types 

When bonding sections of rail together to form track circuits, equipment of 

differing performance has to be used depending upon the type of track circuit 

and the type or absence of electrification; eg. a jumper bond or fishplate bonding 

may vary in design depending upon: 

• whether or not it is part of a traction rail system; 

• whether or not it is proved intact via series bonding.; 

• whether or not it is part of a non–series “safety–through–diversity” system. 

In order to avoid repetition of bonding equipment detail in each section of this 

handbook, a method of classifying bonding types has been developed in which 

fishplate bonding is identified separately from jumper bonding, the ‘family tree’ 

being shown in Figure D6. 

Standard 

Jumper 

Bond(ing) 

Figure D6 

Jumper 


Traction 

Jumper 


Yellow 

Standard 



Yellow 



Standard 

Fishplate 


Fishplate 



Fishplate 


13.1.1 Fishplate Bonding 

This type of bonding is used to improve the reliability of the electrical connection 

between pieces of rail which are already in casual electrical contact by virtue of 

their construction. Whilst the most obvious item in this category is the un– 

insulated fishplate, this method of bonding extends to elements of S & C, such 

as crossings, wing rails etc, where the components are also bolted together 

without intervening insulation. Fishplate bonding is not shown on bonding plans. 

There are two types of this bonding: 

Standard Fishplate Bonding 

Used to bond all fishplate rail joints on non–electrified lines and a.c. only 

electrified lines. 

On d.c. or dual a.c./d.c. electrified lines, this bonding is only used on the 

insulated (signal) rail of single rail track circuits. The most common method is 

two galvanised iron bonds attached to the rail at each end with driven taper pins. 

It is installed by the Signal Engineer in all cases. 

Traction Fishplate Bonding 

Used to bond all fishplate rail joints on d.c. or dual a.c./d.c. electrified lines which 

form part of the traction current system. It is the responsibility of the Electric 

Traction Engineer. 

13.1.2 Jumper Bonding 

This covers jumper cables which bond together sections of rail for track circuit 

and/or traction purposes; those sections may themselves be formed from many 

D10 RAILTRACK





GK/RC0752 

Issue Two 



individual pieces of rail which are bonded together with fishplate bonding. There 

are four types of jumper bonding: 

Standard Jumper Bonding 

A jumper bond between sections of rail which is proved intact as part of fail–safe 

series bonding and does not form any part of a traction current system. 

It is a light current cable installed by the Signal Engineer. 

Yellow Standard Bonding 

Used on non–electrified lines or long spurs of insulated (signal) rail on electrified 

lines. 

A jumper bond between sections of rail which is not proved intact by fail–safe 

series bonding. Safety is assured by installing at least three alternative jumpers, 

such that two jumper disconnections are not, by themselves, unsafe. It is a 

mechanically robust light current cable installed by the Signal Engineer and 

identified either by a yellow sheath or a yellow sleeve at its termination. Its 

mechanical strength allows its electrical integrity to be inferred from regular visual 

inspection. 

Traction Jumper Bonding 

Traction rated bonding attached to the traction rail of electrified lines but which is 

not relied upon for the integrity of track circuit operation. 

Yellow Traction Bonding 

Provided in accordance with the same design principles as Yellow Standard 

Bonding, except that it is traction current rated. 

It is installed by the Electric Traction Engineer (except impedance bond end 

connections which are connected by the Signal Engineer). 

13.2 Design Principles for Yellow Bonding 

The design principles whereby the need for yellow bonding is identified are the 

same for both non–electrified and electrified lines. Electrification only affects the 

rating of bond to be installed and the organisation responsible for its installation 

and subsequent maintenance. 

Yellow bonding shall ensure that a single or double disconnection will not result 

in an unsafe condition. See GK/RT 0252. 

13.2.1 Yellow Bonding 

Where separate sections of rail are required to be electrically interconnected in 

parallel, each section is to be bonded to the adjacent section at each point of 

abutment using a yellow bond. 

Each spur extremity is to be bonded to another part of the same electrically 

common network, which is not itself a part of the same spur, using a yellow 

bond. 

In addition to any switch reinforcement yellow bond, each section must have at 

least three yellow bonds attached to it in different physical locations, which 

should be a minimum of 20m apart. Additional yellow bonds are to be installed 

to achieve this and, wherever possible, the additional bonds must connect to a 

different section from those already fitted. 

In the case of non–electrified multiple track plain line, the common rails of parallel 

tracks must be cross bonded together using yellow bonds at the site of 

feed/relay ends and at least 1km intervals. 

Yellow bonds are to be clearly identified on bonding plans as shown in Part C. 

RAILTRACK D11


GK/RC0752 

Issue Two 






Examples of the application of this principle are shown in Figure D7. 

Figure D7 

Other Yellow Bonds 

Y Y Y 

Switch Reinforcement Yellow Bond 

D12 RAILTRACK 

Y 

13.2.2 Switch Reinforcement Yellow Bonding 

Wherever the rail designated to require yellow bonding passes through a set of 

point switches, its continuity is to be strengthened by a “Yellow Bond” as shown 

in Figure D8. Installation for traction rails is the responsibility of the Electric 

Traction Engineer, and for non–traction rails is that of the the Signal Engineer. 

Figure D8 

Common Rail Through Points 

13.3 Bonding Configurations 

In order to avoid repetition whilst clearly identifying requirements, it is useful to 

define the four bonding configurations and associated bonding standards which 

can be used for particular cases: 

13.3.1 DRDS (Double Rail/Double Series) 

This is where each track circuit is fully isolated from its neighbours by IRJs in 

both rails or tuned zones and each rail of the track circuit is series bonded 

OR 

Y 

Y





GK/RC0752 

Issue Two 



throughout except for permissible spurs (see 13.4). In electrified areas, there 

are no other electrification related bonds from either rail other than via the centre 

connection of impedance bonds. 

Non–electrified Lines - Standard jumper bonds to both running rails. 

Electrified Lines - Traction jumper bonds to both running rails. 

13.3.2 DRSS (Double Rail/Single Series) 

This is where each track circuit is fully isolated from its neighbours by IRJs in 

both rails, and one rail of the track circuit is series bonded throughout except for 

permissible spurs (see 13.4). The other rail of the track circuit contains elements 

of parallel bonding. 

Non–electrified Lines - Standard jumper bonds to the series bonded 

rail and to the true series bonded elements of 

the other rail. 

Electrified Lines - Not applicable 

Yellow standard bonds to interconnect the 

parallel elements. 

13.3.3 CR Class (Common Rail) 

This is where each track circuit is isolated from its neighbours by IRJs in one rail 

only (the signal rail), and that rail is series bonded except for permissible spurs 

(see 13.4). The other rail is electrically common with adjacent track circuits and 

may have parallel bonded elements, but does not carry traction current. 

Non-electrified Lines 

bonded 

- Standard jumper bonds to the series 

Signal Rail. 

Yellow standard bonds to the common rail. 

Electrified Lines 

13.3.4 SR (Single Rail) 

- Not Applicable 

This is where each track circuit is isolated from its neighbours by IRJs in one rail 

only (the signal rail), and that rail is series bonded except for permissible spurs 

(see 13.4). The other rail is electrically common with adjacent track circuits and 

forms part of a mesh carrying traction current. 

Non–electrified Lines - Not applicable 

Electrified Lines 

13.4 Permissible Spurs 

- Standard jumper bonds to the signal rail. 

Yellow traction bonds to the traction rail. 

This clause covers the permissible arrangements for parallel bonded spur 

sections of an otherwise series bonded track circuit section. Parallel bonded 

spurs on common/traction rail sections are not separately identified, since they 

are covered by the general requirements for bonding of such rails. 

Spurs up to 13m, measured from the first joint or weld of a crossing, shall be 

permitted as shown in Figure D9. provided that there is a maximum of one 

fishplated joint between the series bonded rail and the end of the spur, and that 

this joint is properly bonded. 

Spurs up to a maximum of 60m, measured from the first joint or weld of a 

crossing, shall be permitted, provided they are yellow bonded to the parent 

series rail. 

RAILTRACK D13


GK/RC0752 

Issue Two 




Only One Bonded Fishplate Joint Permitted 

13 METRES MAX. 

If X Or Y >13m Then Additional Cross Bonds To The Stock Rails Will Be Required 

Figure D9 

D14 RAILTRACK 

Y 

X 

13.5 Series Bonding Simplification 

If series bonding becomes complex, it imposes penalties on both reliability and 

maintenance. The option of cut sections should then be considered. A 

maximum of four point ends or fifteen IRJs (including boundary joints) per track 

circuit is strongly recommended. 

13.6 Applications of Bonding Configurations 

Type of 


Non–electrified 

Lines 

A.C. Electrified 

Lines 

D.C. Electrified 

Lines 

Plain Line DRDS or CR DRDS or SR DRDS or SR♣ 

S & C DRSS * SR SR 

Complex 

S & C 

Figure D10 

Notes: 



CR # SR SR 

* Where DRDS is impracticable. 

# Where DRDS and DRSS are impracticable. 

♣ Maximum permitted length is 200m. 

13.7 IRJs Between Differing Track Circuit Types 

IRJs must be provided in both running rails at the point where differing track 

circuit types abut. Special cases will be discussed in the relevant sections. 

13.8 IRJs at Signals 

Where a signal is replaced to danger by occupation of the first track circuit 

ahead, the IRJs will generally be positioned between 5m - 20m beyond the 

signal. For further information see SSP 62. 

13.9 Jointed Track Circuits Abutting Non–track Circuited Line 

In order to detect defective IRJs where a jointed track circuit adjoins a non–track 

circuited section, a short circuit bond must be provided immediately beyond the 

IRJs, as shown in Figure D11. This bond shall be a standard bond on non– 

electrified lines, or a traction standard bond on electrified lines.




Figure D11 

AA 

13.10 IRJs at Electrified/Non–electrified Boundary 


GK/RC0752 

Issue Two 



13.10.1 Running Lines 

At the boundary between electrified and non–electrified lines, initial isolation IRJs 

must be provided in both running rails at a sufficient distance beyond the end of 

the catenary/conductor rail to prevent an overrunning train from injecting traction 

current into the rails on the non–electrified side of the joints. The collector 

shoes on d.c. multiple units are interconnected within each multiple unit set. 

Therefore, it is the length of the longest multiple unit which will dictate the 

position of the initial isolation IRJs in d.c. traction areas. 

All track circuits within 800m of the initial isolation IRJs on the non–electrified side 

must be immune to the traction system and provided with double rail IRJs. 

Where there are no track circuits on the non–electrified side of the initial isolation 

IRJs, a second set of isolation IRJs must be provided in each rail 800m beyond 

the initial isolation IRJs. 

If any siding occurs within the above 800m areas, a second set of isolation IRJs 

must be provided in each rail of the siding immediately clear of the running line. 

13.10.2 Sidings Off Electrified Lines 

In electrified traction areas, two sets of IRJs are to be provided in both rails at 

least 27m apart. These are to be provided beyond the last track circuit in private 

sidings leading to stores or depots containing flammable or explosive 

substances, and in other sidings where isolation from electric traction is required. 

In d.c. electrified areas, the traction return bonding must be extended by the 

Electric Traction Engineer onto track circuited non–electrified lines and sidings 

for at least 120m beyond the conductor rail or the tips of the points. Track 

circuits beyond this distance must be fully isolated with double rail IRJ’s or the 

traction return bonding must be continued for at least another 335m. This 

ensures that an electric traction unit inadvertently entering a non–electrified area 

will not lose its negative return whilst any shoe is still in contact with a conductor 

rail. 

On lines where Eurostar operations are authorised, the above distances will 

need to be extended accordingly. 

If the line concerned connects with a d.c. electrified line at more than one point, 

it must have continuous traction bonding throughout in order to prevent traction 

return current passing through the couplings of a train which is bridging two 

traction portions of a siding. 

13.11 A.C. and D.C. Electric Traction Areas Abutting 

Where there is a requirement for inter–running with trains operating on differing 

electrification systems, IRJ separation between the differing traction systems 

cannot generally be achieved. In these areas, a suitable “buffer” zone of dual 

immunisation must be provided. 

As a general guide, for track circuit applications, immunisation against 50Hz 

electrification should be maintained for a distance of 3km beyond the extremity 

RAILTRACK D15


GK/RC0752 

Issue Two 






of the 50Hz system. Immunisation of track circuits on the a.c. electrified system 

and non-electrified lines against d.c. interference, will usually involve significantly 

greater distances (up to 20 km). 

The extent of such a zone is dependent upon track layout, position of feeder 

stations and traction load etc, and requires specialist assessment and 

subsequent verification. 

13.12 Buffer Stops 

Rail mounted buffer stops in double rail track circuited areas must be fully 

insulated. In the case of single rail track circuits in a.c. electrified territory, they 

should be insulated from the signal rail. 

The type of IRJ provided close to buffer stops must be of a design which offers 

similar tensile strength to conventional steel fishplates (see GK/RT0031). 

13.13 Electrical Stagger 

Where the electrical energy of one track circuit is capable of operating the 

adjacent track circuit due to IRJ failure, the polarity (d.c.) or phase (a.c.) of each 

must be arranged so that they oppose rather than reinforce each other. The 

intent being that IRJ failure will not result in false operation. 

The following methods are available to counteract lack of proper electrical 

stagger: 

• Provide an additional transposition to restore correct electrical stagger. 

• Abut feed ends. 

• Provide a feed end relay (d.c. track circuits only). 

• Convert one track circuit to a non–interfering form of energy. 

13.14 Fouling and Clearance Points 

Where tracks cross or diverge etc, it is necessary to define track circuit limit 

dimensions which ensure that traffic passing along one route is not obstructed 

by vehicles standing on the other. The two critical dimensions are referred to as 

the fouling point and the clearance point, as shown in Figure D12. 

Figure D12 

1970mm (Between Running Edges) 

4880 MM 

Crossing Nose Fouling Point Clearance Point 

D16 RAILTRACK





GK/RC0752 

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13.14.1 Fouling Point 

This is a position a short distance away from the point of running line divergence 

(crossing nose). Should any part of a vehicle on one track be between the 

crossing nose and the fouling point, it will make physical contact with any 

vehicles passing on the other route. 

Where the angle of divergence is less than 45°, the fouling point occurs where 

the distance between the running edges of the two rails is 1970mm, measured 

at right angles from the track for which the fouling point is being determined. 

Where the angle of divergence is greater than 45°, the fouling point occurs at 

1970mm from the crossing nose, measured along the track for which the 

clearance point is being determined. 

In the case where tracks become parallel with a running edge separation of less 

than 1970mm, the fouling point occurs where the tracks first become parallel. 

13.14.2 Clearance Point 

As track circuits detect the wheelsets of vehicles which are inboard of bodyshell 

limits, the boundary of any track circuit designed to give assurance of clear 

passage along the other route must be some distance beyond the actual fouling 

point. This is defined as the clearance point. 

In the absence of protecting trap points, the clearance point is 4880mm further 

from the crossing nose than the fouling point. Where trap points are provided, 

the clearance point is defined as the switch tips of the trap points. In both 

cases, the IRJ defining the track circuit limit is positioned at the first suitable rail 

joint beyond the clearance point. All clearance points shall be shown on the 

bonding plans. 

13.14.3 Minimum Length of Track Circuits 

To prevent a vehicle bridging a short track circuit and consequently providing a 

false clear condition, the minimum length of a track circuit is 18.3m. 

13.14.4 Staggered IRJs 

Where practical, IRJs should be positioned in each rail so that they are opposite 

to each other. Where a physical stagger between opposite IRJs is unavoidable, 

the maximum physical stagger must not exceed 2.6m. This is the minimum 

wheelbase of vehicles which can work unattached. 

To ensure that motor bogies do not become insulated from the traction return 

path, the physical stagger for a signal rail overlap in electric traction areas must 

not exceed 2.1m. On the Isle of Wight, vehicles used have smaller bogies and 

as such, the maximum physical stagger is reduced to 1.7m. 

In order to avoid loss of detection of a single car, four wheel vehicle, the 

permitted distance between inner joints of staggered pairs of IRJs must not be 

less than 11m, where the IRJs are staggered at a distance of less than 1.6m 

(the minimum bogie wheelbase). If however, either pair of IRJs are staggered at 

a distance greater than 1.6m, or provide a clearance point (see Clause 13.14.2), 

then the distance between inner joints of staggered pairs must be not less than 

the 18.3m minimum track circuit length. 

Note: When consulting other documents, care should be taken to ascertain 

whether “running edges” or “outside edges” of rails are being referred to. 

RAILTRACK D17


GK/RC0752 

Issue Two 



Notes on Figure D13: 


Figure D13 gives examples of the application criteria for IRJs, the references 

being as follows: 

13.15 RJ Summary 

C Clearance for vehicle overhang. Not less than 4880mm from the fouling point to the IRJ. 

D Distance between inner joints of 

staggered pairs. 

E Distance between staggered 

pair and end of track circuit. 



Not less than 11m if both of pairs staggered < 1.6m. 

Otherwise, not less than 18.3m. 

18.3m minimum. 

F Fouling point. 1970mm between running edges 

L Minimum effective length 

of track circuit. 

18.3m minimum 

S Physical Stagger 1.7m max: Isle of Wight lines only. 

2.1m max: Signal rail overlap on electrified lines. 

2.6 max: Other cases. 

Figure D13 

D18 RAILTRACK



Equipment 

Positioning 

15 Layout and Wiring 

of Lineside Apparatus 

Housing Equipment 




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Issue Two 



13.16 Permanent Way Engineering Considerations 

The following should be considered relative to IRJ provision in S & C as 

constrained by permanent way engineering considerations: 

• IRJs adjacent to cast crossings should be avoided wherever possible. 

• IRJs run over in the high speed route should be avoided as far as possible. 

• There should be a minimum distance of 200mm between chair or rail 

fastenings of opposite polarity/phase to reduce the probability of failures due 

to metallic litter, etc. 

With a view to obtaining the best possible performance, track circuit equipment 

should be positioned as close as practicably possible to the associated rail 

connections, and any maximum limits laid down in the individual track circuit 

sections must not be exceeded. This also permits better communication 

between technicians when working apart, undertaking drop shunt tests, etc. 

In tunnels and on viaducts, the feed and relay ends of a track circuit should be 

mounted in the same lineside apparatus housing, provided that no electrical 

parameters are infringed. 

If the design of track circuit is such that staff are not required to make 

adjustments (eg. HVI track circuits), the relay or receiver equipment may be 

grouped in equipment buildings provided that no electrical parameters are 

thereby infringed. 

Disconnection boxes may be provided if site conditions warrant. These must be 

shown on wiring diagrams, but are not required on bonding plans unless they 

contain fuses or arresters. 

All relays should be mounted as near to the top of the lineside apparatus 

housing as possible. 

Tail cables are to be terminated at the bottom of the lineside apparatus housing 

in one of the following manners, as appropriate: 

• Directly onto the track fuse and link. 

• Directly onto the track fuses. 

• Directly onto two links. 

• Directly onto a surge arrestor. 

In d.c. traction areas where the lineside apparatus housing is remote from the 

track connections, the surge arrester (where provided) and track fuse must be 

located at the tail cable terminations nearest to the rail connections. 

Where special restrictions apply to wiring and/or positioning of equipment, this 

must be clearly shown on all wiring/layout drawings, so that if any alterations are 

made at a later date, the restrictions are readily apparent 

RAILTRACK D19


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16 Duplicate Rail 

Connections 

17 Communications 




Duplicate connections to the rails are the preferred arrangement for all track 

circuits, except those which operate at audio frequencies (see the relevant 

sections for further information). 

Where duplicate connections are used the method of wiring is as shown in Part 

E. 

It is desirable that communication circuits are available between the 

feed/transmitter and relay/receiver sites to facilitate setting up and fault 

finding.The communication circuits may be run in the same multicore cables as 

the feed, transmitter, relay or receiver circuits. 

At certain SSI installations, the data cables carry communication cores which 

may be used for this purpose. 

D20 RAILTRACK



2 Responsibilities for 

Bonding Installation 



Part E 

Components and Installation 


GK/RC0752 

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Page E1 of 52 

This part explains the general components applicable to all track circuits. 

Components specific to a particular type of track circuit are listed in the relevant 

Approved Code of Practice within this handbook. 

Installation procedures for individual track circuit types are detailed in the 

relevant Approved Code of Practice within this handbook. 

Note: The Catalogue Numbers shown within this document are not directly 

controlled by Railtrack and as such, will not be maintained and kept up to date. 

Although every effort has been made to ensure that these were correct at the 

time of publication, it is therefore recommended that your supplier is contacted 

and a check is made with regard to the accuracy of these catalogue numbers 

prior to use. 

The Signal Engineer is responsible for: 

a) All fishplate bonds in non–traction return rails. 

b) All fishplate bonds in traction return rails of a.c. only electrified areas. 

c) The position of all IRJs. 

d) All jumper bonds between separate sections of non–traction rails. 

e) In a.c. electrified areas (excluding the former Southern Region), all rail to 

impedance bond connections and connections between impedance bonds on 

the same track. 

f) In dual and d.c. electrified areas (excluding the former Southern Region), the 

responsibility for impedance bond connections is subject to special 

arrangements between the Signal and Electric Traction Engineers. 

g) All track circuit rail connections. 

h) The insulation of all rods connected to the rails and switches (eg. detection, 

facing point lock, point main drive and supplementary drives). 

The Electric Traction Engineer is responsible for: 

a) All rail joint bonds in d.c. or dual a.c./d.c. traction return rails. 

b) All jumper bonds between separate sections of traction return rails and 

between the centre connection of impedance bonds in different tracks. 

c) On the former Southern Region, rail to impedance bond connections for 

traction purposes. 

d) All other permanent traction related bonding. 

The Permanent Way Engineer is responsible for: 

a) The insulation of all point soleplates, tiebars and stretcher bars. 

b) The installation of all IRJs. 

The requirements and responsibilities for the installation of bonding on electrified 

lines are laid down in GM/TT0126 and GM/TT0129. 

R A I L T R A C K E 1


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Page E2 of 52 


Interrupters 




The standard insulated track circuit interrupter assembly is shown on drawing 

BRS-SM 374, an extract of which is shown in Figure B11. 

Catalogue numbers are as follows: 

Description Catalogue No. 

Assembly complete to BRS-SM 374 : 86/44001 

Taper pin, BRS-SM 411, 60mm : 86/44011 

Body unit to BRS-SM 375 : 86/44003 

Insulations to BRS-SM 376 : 55/27570 

Item 1 Insulating bush : 55/25976 

Item 2 Insulating washer : 55/28981 

Item 3 Channel insulation : 55/27201 

The interrupter is mounted on the stock rail, not the switch rail, by means of an 

M20 insulated bolt passing through a 28mm hole in the rail web. A second 

28mm hole, 130mm from the first, may be provided to enable the wiring to be 

brought out towards the sleeper ends. The interrupter is positioned as near as 

possible to the switch toe, commensurate with maintaining a flangeway gap of 

not less than 70mm with the switch closed. Figure E1 gives the nominal 

positioning. 

The temporary repair of track circuit interrupters by means of wrapping the cable 

around the stock rail is forbidden. Refer also to Part D. 

POSITION OF INTERRUPTER 

E 2 R A I L T R A C K 

A 

Rail Type Switch Type Dimension 'A'(mm) 

95 lb.Bullhead A 4180 

B 4780 

C 5900 

D 7620 

113 lb. Inclined A 4180 

B 4955 

C 6675 

D 7635 

E 10185 

113 lb. Vertical A 4705 

B 6125 

C 6835 

D 8255 

E 11095 

Figure E1



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Page E3 of 52 

4 Identification of 


Boundaries Where required, a plate may be fixed to the sleepers or to the lineside track 

circuit equipment to assist identification of track circuit limits. 

5 Protection of 

Cross Track 

Cables 



Wherever a track circuit boundary occurs in a tunnel, a plate bearing the track 

circuit name or number must be fixed to the tunnel wall on each side of the IRJ 

(or equivalent in the case of a jointless track circuit). 

5.1 <strong>General</strong> 

Cross track tail cables and jumpers should be protected from damage, eg. by 

means of orange plastic pipe. This protection need not be continuous across the 

cess or six–foot, but should be used where tail cables pass under walkways. 

5.2 Orange Pipe Installation 

Cut the pipes to length so that the ends are clear of the ballast shoulder. This 

helps to prevent ballast from entering. Restrict each pipe length to 3 metres 

maximum as long lengths of pipe will not move out of the way if struck by a 

tamper tine. However, in S & C areas it may be necessary to use longer lengths 

to give full protection across the sleeper bay. It is particularly important that the 

pipe is laid straight and centrally in the sleeper bay, and that holes for rail leads 

are as close to the rail as possible, in order to give maximum protection from 

tamping machines. 

Do not use the ballast to restrain sideways movement. Dig the pipe into a 

shallow depression in the ballast keep it visible but allow sideways movement if 

struck. 

Do not fill a pipe more than half full with cables. This reduces the chance of cable 

damage if the pipe is crushed by a tamper. If more cables have to be run, 

provide another pipe. 

Wherever possible, do not install a pipe in a sleeper bay adjacent to conductor 

rail ramped end to prevent the pipe being ignited by sparks from the collector 

shoe. 

To allow the Permanent Way Engineer maximum opportunity for tamping, do not 

position a pipe: 

• in a bay where there is a rail joint or weld, or in a bay adjacent to them; 

• in a bay which is less than 0.37 metres (1 foot 3 inches) wide, unless there 

is no other choice; 

• in a bay which already has an orange pipe or other obstruction, or in one 

adjacent to it. Always leave at least one clear bay between obstructed bays. 

If a pipe needs side holes for the exit of track connection cables: 

a) Cut the holes with a good quality 40 to 50 mm fixed diameter hole saw. Do 

not use other methods of making holes. Round off the sharp edges of the 

hole with a file or deburring tool. 



GK/RC0752 

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Page E4 of 52 




b) Clip the pipe to the foot of the outside of flat bottom rail. On bull-head rail a 

cab-lock round the pipe may be secured to the rail web with a taper pin. 

These fixings prevent the pipe rotating or moving along its length and cutting 

into the cable. The clip will still permit some sideways movement if the pipe is 

struck. 

c) Leave sufficient slack in the cable so that if the pipe does become detached 

from the rail, the connection will not be pulled away. However, excessive 

amounts of slack cable should be avoided in order to minimise the likelihood 

of vandalism. 

Orange pipe must not be cut along its length unless special dispensation has 

been given. 

Orange pipe must not be used in tunnels or other areas of restricted Ventilation. 

If the pipe does ignite, it is difficult to extinguish and gives off heavy fumes. 

Orange pipe is generally suitable as protection for crossing walkways if it is let 

into the surface. When tail cables need to be protected for other reasons, such 

as chemical spillage in sidings or for staff safety, a concrete route or under track 

buried crossing should be used. 

Catalogue numbers are given in clause E11. 

E 4 R A I L T R A C K





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Page E5 of 52 

Figure E2 shows the general arrangement for orange pipe installation. 

Leave some slack here 

to allow for minor slews. 

Dis 

Box 

Rail web 

pipe clip 

Orange pipe 

Cable strap 

(use as few as possible) 

No rail web 

pipe clip 

Orange pipe 

No rail web 

pipe clip 

Cable route 

Note Dis Boxes should be mounted in a permanent Green Zone as defined in 

GO/RT3073. 

Figure E2 



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Page E6 of 52 

6 Mechanised Track 

Maintenance 

7 Rail Drilling 


All equipment on the track must be installed clear of the tamping zones indicated 

in Figure E3, except cross track orange pipe. 

All sleepers may be tamped, except those on either side of Silec treadles and 

point rodding. 

Figure E3 


290 

405 

Tamping Zone 

For conventional grades of rail steel, Signal Engineers use rail drilling machines. 

They are preset to drill the two holes required accurately with no adjustment 

necessary. Available drilling machines and attachments, together with the 

Catalogue Numbers, are listed below: 


Rail bond drilling machine, hand operated (single spindle) : 39/41822 * 

Rail bond drilling machine, 110V/500W (twin spindle) : 86/43690 # 

Rail bond drilling machine, petrol engine (twin spindle) : 39/41823 * 

S & C drilling attachment, for use with 39/41823 : 39/200000 

Flexible drive, 8 feet long, for use with 39/41823 : 39/54510 

Notes: 



* The drilling machine fits over the rail and cannot be left in position whilst 

trains pass. 

# The drilling machine clamps to the underside of the rail and can be left in 

position whilst trains pass. 

At sites of heavy wear, particularly in S & C, The Permanent Way Engineer may 

fit specially hardened steel rails which can only be drilled with special drill bits. 

Whilst the Permanent Way Engineer permits drilling of 7.2mm holes for taper 

pins by Signal Engineers, drilling of larger holes in hardened steel is a specialist 

job to be undertaken by Permanent Way Engineering staff. 

405 

290


8 Rail Connections 




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Page E7 of 52 

The following table of Permanent Way Engineer’s rail markings is included to 

assist staff in the identification of rail types. The brand marks appear as raised 

characters on the rail web; confirmation is also provided by paint marks on new 

rail and (in some cases) by its magnetic properties. 

Remarks: 

Figure E4 

Type Brand Mark Paint Marks Magnetic Remarks 

Normal None None Yes 1 

Wear resisting A A 2 blue Yes 1 

Wear resisting B B 3 blue Yes 1 

BSC 90 AA 1 blue/1 white Yes 1 

90kg chrome 1CR 1 red Yes 1 

100kg chrome 1CR 2 red Yes 1 

AMS HC Manganese 1 green No 2 

AMS LC Manganese W 1 green No 2 

MHT - - Yes 1&3 

1: Can be drilled using conventional methods. 

2: Can be drilled only with special tools/techniques. 

3: Identification not yet agreed. 

8.1 Introduction 

The various methods of making electrical connections to the rail are explained 

below: 

8.2 Taper Pins 

The taper pin requires a 7.2mm hole, 57±2mm above the base of the rail, to be 

drilled through the rail. The taper pin consists of a threaded section to which the 

various connectors are attached, and a non–threaded end which is tapered to 

ensure that the pin is firmly fixed to the rail. 

Fit the taper pins into the holes and hit the non–threaded ends with a hammer to 

ensure that the pins and the rail are in electrical contact. 



Track circuit maintenance kit 

Comprising: 

: 88/10037 

Pin, taper, BRS-SM 411, 55mm long (10) : 86/44013 

Nut, self locking, stainless steel,M6 (10) : 3/179995 

Washer, stainless steel, M6 (20) : 3/190825 

Nut, stainless steel, M6 (10) : 3/175013 



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Page E8 of 52 




8.3 Pin Brazing 

Pin brazing is a method of connecting threaded pins to the rail using electric–arc 

brazing. This method will usually be used at new sites or where re–railing takes 

place and may be used on standard and hardened steel rails. Pin–brazed studs 

will be installed by Signal or Permanent Way Engineering staff; any person 

engaged in these operations must hold a Certificate of Competency for the task 

to be undertaken. 

An M12 pin brazed stud may be brazed to the rail web, as shown in Figure E5. 

The minimum spacing between connectors is 85mm. The correct torque for 

attachment of the rail lug to the M12 studs is 60Nm. 

NOTE 

Self Locking Nut (Supplied) to be 

tightened to a torque of 60Nm 

200 240 


115 

Pin Brazed TEE Connector 

Figure E5 

The threaded pins are brazed to the rail, at a position 57±2mm above the base 

of the rail, with a silver based filler metal, using a hand held brazing gun operated 

by either of the following pieces of equipment: 


Portable machine, battery driven on single 

rail trolley, suitable for track maintenance, 

which will braze approx. 50 pins to the rail. : 20/3003 

Large machine, battery driven on double rail 

trolley. The batteries are recharged by an 

integral petrol driven generator. This unit has 

a capacity for 50 brazes per hour and is 

suitable for new works. : 20/3001 

57





GK/RC0752 

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Page E9 of 52 

Both of the above machines require the batteries and the brazing gun to be 

ordered separately. These are listed along with other spares and attachments 

as follows: 


VF 2300 Brazing gun : 40/515 

VF 2300 Angled gun : 20/3021 

VF 2300 Extended gun : 20/3011 

VF 2300KA Brazing gun : 20/3010 

VFRG Batteries : 20/3002 

VFLC Batteries : 20/3004 

VFKA Batteries : 20/3007 

VFKA 250 Battery unit : 20/3005 

VFKA 250 Attache case : 20/3006 

Battery charger for vehicle : 20/3008 

Battery charger for depot : 20/3009 

8mm Ceramic ferrule : 55/27287 

9.5mm Ceramic ferrule : 55/16001 

8mm Brazing pin : 55/27706 

9.5mm Brazing pin : 55/41011 

Spark shield : 40/543 

Contact arm : 40/507 

12mm/M8 Pin holder : 40/561 

Contact set complete : 40/521 

Contact nipple and disc : 40/555 

Ejector rod complete : 40/536 

Key set : 40/520 

Screw set : 40/556 

Rail bond 25mm x 500mm long : 88/23906 

Rail bond 25mm x 145mm long : 88/23907 

Rail Bond 25mm x 1500mm long : 86/43511 

T connector M12 : 55/9366 

Track end connector : 20/3013 

V Connector 2 x 25mm x 90mm long : 46/2183 



GK/RC0752 

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Page E10 of 52 




8.4 Cembre 

Cembre is a method by which a copper bush is expanded inside a 22mm hole 

drilled into the rail web. A bolt is then passed through the copper bush and is 

used to fix a cable lug to the rail. The copper bush should be inserted and 

expanded a soon as the hole has been drilled. If this is not possible, the hole 

should be given a protective coating of jointing paste at the time of drilling and 

thoroughly cleaned, in the same manner a described for pin drive fittings when 

the bush is fitted. Refer to clause 8.6 

Cembre Parts Catalogue No. 

Rail lead installation kit (M12 steel screw with hollow : 86/017025 

hex. head, flat steel washer & self locking nut) 

Copper bush for 22mm dia. hole : 86/017026 

Expansion plunger. Calibrated high tensile steel : 86/017027 

Hydraulic tool with hand pump c/w carrying case : 86/017028 

Go/No Go gauge for checking 22mm rail hole : 86/017029 

To ensure that the drilled hole is the correct size a gauge is used as detailed 

below and shown in Figure E6 : 

a) Insert the Go/No Go gauge into the hole. 

b) The hole may be used only if the green part passes through and the red part 

does not. 

c) If the red part passes through, redrill a hole in a different position. 

d) The inside of existing holes should be thoroughly cleaned and bright. 

Red (No GO Column) 

GO / No GO Column 

Figure E6 

Green (No GO Column) 


22 Dia 

57





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Once the drilled hole has passed the gauging test the following procedure is 

used to expand the copper bush : 

Refer to Figure E7. 

a) Insert the copper bush (Item A) into the rail web. 

b) Insert the calibrated plunger (Item B) on bush flange side, ensuring threaded 

end projects through to the other side. 

c) Depress the tool pressure discharge lever (Item C) to ensure the piston is 

fully retracted. 

d) Insert the calibrated plunger (Item B) into threaded housing of either tool 

seating (Item D) by using gauge (Item E) located on hexagon end of item B. 

e) Pump until the calibrated plunger is completely through. 

Figure E7 

Running Edge 

R A I L T R A C K E 11 

C 

D 

A 

D 

B 

E


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Issue Two 






With reference to Figure E8, the general assembly procedure of the connector 

is as follows: 

a) Insert the hollow hexagonal headed stud into the copper bush so that the 

thread projects from the bush flange side (this will usually be into the four 

foot). 

b) The stud head will surround the projecting part of the bush without touching 

it. Locate lug onto the stud, add washer and lock nut, then tighten to 60Nm 

torque. 

Type AR 60-3 Steel Stud With 

Hollow Hex Head (M12) 

Figure E8 

Figure E9 shows a typical bonding arrangement. 

These dimensions are only 

typical. Refer to Layout Drawing 

for individual situations. 

Figure E9 

Running Edge 

M12 Washer 

Cable Lug 

Self Locking Nut 


240 

76 

NOTE; 

Self locking Nut (supplied)to be 

Tightened to a torque of 60 Nm. 

57





GK/RC0752 

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8.5 Aluminio–thermic Welding 

Thermic welding is a method of fixing threaded pins to the rail by means of a 

thermo–chemical reaction. It can be used for traction bonding in both a.c. and 

d.c. traction areas. 

Two types of studs are available: 


1 

/2 ” x 7 / ” fully threaded stud, complete with 

8 

nut and washers. 

5 

/8 ” stud with nut, spring washer and 

: Available from ERICO. 

flat washer. : 46/19800. 

Note (1): Aluminio–thermic welding is also referred to as Cadweld and 

Thermoweld. 

Note (2): Any person engaged in these operations must hold a Certificate of 

Competency for the task to be undertaken. 

8.6 Pin Drive 

This method should be used only where pin braze or Cembre fittings cannot be 

used. 

A bimetal rail lug (Railway Catalogue No. 55/27614) provides an aluminium barrel 

for crimping to aluminium cable and a copper lug for insertion into the rail. 

Where pin–drive lugs are used to make connections to the running rails, the 

22mm holes are drilled by Permanent Way Engineering staff. If the rail 

connection is not made at the time of drilling, the hole is immediately given a 

coating of jointing paste (Railway Catalogue No. 7/026200) to minimise the risk 

of a high resistance connection due to corrosion. 

The connection is made as follows: 

Before the lug is inserted in the rail, it is cleaned of all existing jointing paste and 

all contact surfaces should be clean, bright, brushed with a circular wire brush 

(Railway Catalogue No. 5/4266) and re–coated with a uniform layer of jointing 

paste (Railway Catalogue No. 7/026200). 

The lug is secured to the rail by means of the rail lug bond pin, refer to Figure 

E10. Pin size No.1 (Railway Catalogue No. 55/27860) , is driven in with a 

hammer and is used for the first installation. Pin size No. 2 (Railway Catalogue 

No. 55/27862) is used for subsequent installations of a lug. Pin size No.3 

(Railway Catalogue No. 55/27863) should be used only when the rail hole is 

oversize, eg. 7 / 8 ” rather than 22mm. After installation, surplus jointing paste 

should be wiped off. 

All rail lug connections should be inspected after installation to ensure that the 

lug is tight and free from cracks. Any cracked or loose connections are to be 

remade. 



GK/RC0752 

Issue Two 






6R 


41 

28 

2 x 45 O 

Bond Pin Number Stamped Here Height 6 

Figure E10 shows the rail lug bond pin. 

Material : Steel to BS 970 Part 1. 070 M20 

 

 

 

 

 

‘X’ 

0.13 

Figure E10 

8.7 The Preformed Moulded Rubber Connector 

The rail should have previously been fitted with two threaded studs by one of the 

methods described in 8.2 to 8.4. 

Secure the moulded connector onto the threaded studs using the self locking 

nuts and washers, tightened to a torque of 13 Nm, as shown in Figure E11. 

Ensure that the stud protrudes at least one full turn through the nut. Do not fit a 

nut or washer between the rail and moulded connector. 

Fit the flange clip over the cable and push the clip onto the foot of the rail. 



Flange Clip, 6.5mm BRS–SM 849 (1) 86/43489 

Moulded Flexible TC Lead 2.5mm² 

3.0 metres : 86/44022 

4.5 metres : 86/44023 

6.5 metres : 86/44024 

8.0 metres : 86/44025 

30.0 metres : 86/44026




Cable Termination Label 

TCABRB (1) 

Flange Clip 


GK/RC0752 

Issue Two 



Taper Pin 

Stainless Steel 

Washer 


Locking Nut 


76mm 

57 + 2mm 

Figure E11 

8.8 The “L” Plate Connector 

“L” Plate connectors are used only where preformed cables are inappropriate. 

The rail is drilled in accordance with Figure E12. 


Track circuit rail connection kit : 86/44019 

Comprising: 

Pin, taper, BRS-SM 411, 55mm long (2) : 86/44013 

Nut, self locking, stainless steel, M6 (2) : 03/179995 

Washer, stainless steel, M6 (4) : 03/190825 

Nut, stainless steel, M6 (2) : 03/175013 

Plate, BRS-SM 848 (1) : 86/43488 

Terminal, crimped, black sleeve, M6 (1) : 54/119568 

Flange clip, 6.5mm, BRS–SM 849 (1) : 86/43489 

Tube, heat shrinkable, 55mm long (1) : 55/120989


GK/RC0752 

Issue Two 






Flange clips may also be obtained for larger cable sizes: 


Flange clip, 15mm, BRS–SM 849 (2) : 86/43498 

Aster and TI21 Track Circuits 

Flange clip, 23mm, BRS–SM 849 (3) : 86/43499 

Inductive Loop Reed Track Circuits 

Cable Termination Label 

TCABRB (1) 

Flange 

Clip 

`L' Plate 


Washer & Locking Nut 

Heat Shrink Sleeve 


Washer & Nut 


76mm 

Two Holes 

7.2 Dia. 

57 + 2mm 

Figure E12 

The rail should have previously been fitted with two threaded studs by one of the 

methods described in 8.2 to 8.4. 

Fit a washer and nut to each threaded stud and tighten to a torque of 13 Nm. 

Strip back 20mm of the outer sheath of the 2.5mm²(f) cable, followed by 

8 - 9mm of the inner sheath to expose the conductor. 

Slide the crimp terminal onto the cable and crimp it. Ensure that the crimping 

tool is the correct size, and matches the crimp terminal being used. The kit 

currently contains an AMP PIDG 6mm terminal, for which a yellow/black handled 

AMP tool (59239-4) must be used. 

Slide the heat–shrink sleeve onto the “L” plate and thread the cable through the 

sleeve until the eye of the crimp is over the end hole of the ‘‘L’’ plate.



Disconnection 

Box 




GK/RC0752 

Issue Two 



Move the heat–shrink sleeve until the entire stripped length of the cable is 

covered by the sleeve without restricting the securing hole. 

Apply heat to the heat–shrink sleeve. Before heating, the sleeve is 55mm long, 

and reduces to about 50mm when it is fully heat–shrunk onto the cable and the 

plate. 

Place the “L” plate assembly onto the threaded studs and secure using the 

remaining washers and the self locking nuts, tightened to a torque of 13 Nm. 

Fit the flange clip over the cable and push the clip onto the rail. 

The typical arrangement of the track circuit disconnection box is shown in Figure 

E13. It is mounted on a stake using two M8 studs (supplied with the box) and 

comprises a moulded rubber back with a slide–on metal cover which can be 

padlocked using the standard RKB221 padlock. Provision is made to securely 

clamp both the lineside apparatus housing tail cables and track lead cables in the 

base of the box. A longer stake is available for use where ground conditions are 

poor. 


Stake (Angle), 760mm long, to BRS-SM 104/13 : 

Catalogue No. 

86/10751 

Stake (Angle), 1070mm long to BRS-SM 104/11 : 86/88250 

Track Circuit Disconnection Box : 86/43877 

The termination for each track circuit comprises a four way 2BA link block. The 

various cables should be terminated as shown in Figure E14 (this enables the 

individual track leads of duplicated arrangements to be disconnected/tested 

separately). 

Note 1: Only one track circuit is allowed in a Disconnection Box and hence 

double track circuit boxes are not to be used. 

Note 2: Separate tail cables must be provided for each track circuit end. 

Note 3: Disconnection Boxes should be mounted in a permanent Green Zone 

as defined in GO/RT3073. 



GK/RC0752 

Issue Two 





Figure E13 

Figure E14 


Rail 2 

Duplicate 


Cable 

Tail 

Cable 


Rail 2 

Lead 

To 

Lineside 

Apparatus 

Housing 

Rail 1 

Lead 

Rail 1 

Duplicate 


Cable


10 Arrangement of 

Track Lead Rail 

Connections 

(Except Jointless) 

A 

B 

Dis 

Box 

C 

D 




GK/RC0752 

Issue Two 



Figure E15 and Figure E16 show typical arrangements of rail connections 

either side of an insulated joint. Figure E15 uses 90mm diameter orange pipe 

and is the preferred arrangement, except where the pipe is unable to be 

threaded under the rail, (eg. tunnels and other areas of restricted use). Figure 

E16 shows the alternative method where the cables are clipped to the top of the 

sleepers. 

In both cases, duplicated single core 2.5mm²(f) flexible cable, fitted with moulded 

rubber connectors, is the preferred arrangement to be used between the 

disconnection box and the rail. It is terminated on the four foot side of the rail. 

Under no circumstances should the track leads of different track circuits share a 

common rail connection. 

Note Combining two track circuits into one 4 core cable is not permitted. 

If required, in order to avoid vandalism, the disconnection box can be replaced 

by a heat–shrink jointing kit. 

Track lead arrangements for jointless track circuits are described in the relevant 

section dealing with the particular design. 

IRJ 

Traction Return Bond 

w Y 


IRJ 

On non-electrified lines the first bay 

to be left clear 

Cable Route 

X 

Dis 

Box 


GO/RT3073. 

Figure E15 

Z


GK/RC0752 

Issue Two 



A C 

B 

D 

Dis 

Box 




IRJ 

Traction Return Bond 

IRJ 

On non-electrified lines the first bay 

to be left clear 

Cable Route 


W 

X 

Dis 

Box 


GO/RT3073. 

Figure E16 


Pipe, Medium Density, Orange, 

6 metres x 90mm : 86/44141 

Clip, Pipe for 90mm o/d pipe : 86/44140 

Fastaway Clip, 6.5mm for 2.5mm²(f) cable : 86/43489 

Moulded Flexible TC Lead 2.5mm²(f): 

3.0 metre : 86/44022 

4.5 metre : 86/44023 

6.5 metre : 86/44024 

8.0 metre : 86/44025 

30.0 metre : 86/44026 

Disconnection Box for Track Circuit : 86/43877 

Stake for Disconnection Box 760mm Long : 86/10751 

Stake for Disconnection Box 1070mm Long : 86/10751 

Cable Joint Kit, 1 x 2.5mm²(f) single to 

1 x 2.5mm² single : 54/15875 


1 x 2.5mm² two core : 54/15873 


1 x 2.5mm² single : 54/36101 


1 x 2.5mm² two core : 54/36102 

Y 

Z


11 Fishplate Bonding 




GK/RC0752 

Issue Two 



The method and components described in this section are to be used to improve 

the reliability of the electrical connection between pieces of rail which are already 

in casual electrical contact by virtue of their construction. 

Whilst the most obvious item in this category is the non–insulated fishplate type 

rail joint on all non–electrified and a.c. electrified lines, this method of bonding 

extends to elements of S & C, such as crossings, wing rails etc, where the 

components are also bolted together without intervening insulation. 

On d.c. or dual a.c./d.c. electrified lines, it is to be used on the signal rail only of 

single rail track circuits. Bonding of fishplates in the traction return rail of d.c. 

electrified railways is the responsibility of the Electric Traction Engineer. 

11.1 Standard Fishplate Arrangement 

Two 7.2mm holes, 76mm apart, are drilled through the rail web in the first 

sleeper bay each side of the joint. The holes should be 57 ±2mm above the 

base of the rail. The bonds should generally be fitted on the four foot side of the 

rail using channel pins and run close to the base of the rail, as shown in Figure 

E17. The short exposed end of the bond should be folded flat and hammered 

against the rail. Bonds should not be threaded through the fishplates or rail 

fastenings. In areas prone to vandalism the bonds may be passed under the rail 

so that they are less vulnerable; when this is done one end of each bond is 

attached to the inside of the rail and the other end to the outside. However, 

bonds should not be passed to the outside of the rail if there is a conductor rail 

on that side. 



Bond, solid steel, galvanised, 4.29mm x 1670mm : 86/44149 

Channel Pin to BRS-SE33 : 86/44012 

A 

Figure E17 

76 

B 

535 

57 ± 2mm 


535 

A 

76 

B 

Running Edge 

Channel Pin 7.2mm DIA. Hole 

Bond


GK/RC0752 

Issue Two 






11.2 Standard S&C Arrangements 

11.2.1 Switch/Stock Rail 

Figure E18 

Switch Rail 

Stock Rail 

11.2.2 Acute Fabricated Crossing 


* 

* 

Parallel Wing Extension 

Figure E19 

If a parallel wing is fitted, holes marked * should have bond leads fitted prior to 

assembly of vee and before the parallel wing is attached. The leads should be 

tied along the rail to prevent damage in transit. 

11.2.3 Obtuse Fabricated Crossing 

Figure E20


12 Jumper Bonding 




GK/RC0752 

Issue Two 



11.3 Fishplates in Concrete Bearer Pointwork 

Rail to rail fishplate bonding in concrete bearer S & C should be achieved using 

the same techniques as specified for Standard Jumper Bonding. 

11.4 Redundant Insulated Rail Joints 

Where redundant insulated rail joints cannot be avoided: 

a) In d.c. traction areas, the Electric Traction Engineer should be requested to 

install all temporary bonds across IRJs which will carry Traction Return 

Current. If the bond is to carry track circuit currents only, Galvanised Iron 

(GI) bonds may be used and be fitted by the Signal Engineer. 

b) In a.c. traction areas, if either side of an IRJ is a traction return rail, the 

Electric Traction Engineer should install the temporary bond, but if both sides 

of the IRJ are signal rails then standard fishplate bonds may be used as a 

temporary measure. 

c) In non–electric traction areas, ordinary bonds should be used. 

This section describes the components and installation of jumper bonds 

designed to carry track circuit currents only. Apart from special cases of 

impedance bonds, traction jumpers are the responsibility of the Electric Traction 

Engineer. Refer to Section 2. 

12.1 Standard Jumper Bonding 

This arrangement should be used on non–electrified lines and on the signal rail 

only of d.c. or dual a.c./d.c. electrified lines. It should not be used for yellow 

bonding purposes. 

Standard jumper bonding uses the same single core cable as used for track 

terminations (GS/ES 0872 Type C1 2.5mm²(f)) terminated in the rail web, using 

either the “L” Plate connector or preformed moulded rubber connector. 

For cable lengths and catalogue numbers see 10. 

12.2 Yellow Standard Bonding 

Yellow standard bonding uses GS/ES 0872, 35mm² cable, identified with a 

yellow sheath or a yellow sleeve at the termination. The bonds are supplied in 

various lengths with a moulded rubber connector for connection to the rail at one 

end and unterminated at the other. Yellow bonds should not be installed more 

than 20m apart. 



Moulded Flexible TC Lead 35mm² : 

3.0 metre : 86/44155 

4.5 metre : 86/44154 

6.5 metre : 86/44153 

8.0 metre : 86/44152 

30.0 metre : 86/44151 

Jointing Kit For Moulded Flexible TC 

Lead 35mm² : 54/037092 



GK/RC0752 

Issue Two 



13 High Voltages 

14 Lineside Apparatus 

Housing Wiring 




Fix warning signs (Figure E21) to all exposed track circuit capacitors and to the 

outside of lineside apparatus housings containing high voltage track circuit 

equipment. 



Safety sign, yellow triangle 

“caution risk of electric shock”, 

50mm wide : 56/144135 



100mm wide : 56/144111 



150mm wide : 56/144130 


“caution risk of electric shock” 

plastic laminate 300mm x 300mm : 56/144611 

Figure E21 

For general wiring procedures the appropriate Code of Practice should be 

consulted. Refer to Codes of Practice within the Track Circuit Handbook for 

special cases. 

14.1 Protection of Terminals 

Terminals in lineside apparatus housings, dis. boxes, etc and impedance bond 

terminal boxes should be corrosion proofed using Valvoline Tectyl 506 

(Catalogue No. 7/58553) as soon as wiring and testing are complete. Valvoline 

should not be applied to capacitor adjusting slides, fuse clips or end caps, or the 

windings of wire–wound resistors. 



15 Impedance Bonds 

Manufacturer Style Freq. 

(Hz) 

Howells or 

WBS 

Howells or 

WBS 


GK/RC0752 

Issue Two 



15.1 Handling Precautions 

When transporting impedance bonds, they should be lifted only by the lifting lugs 

or at the defined lifting points. Under no circumstances should any weight be 

taken on the traction lead terminals or cable lugs as this can result in damage to 

the insulation, allowing water to enter. 

Type 3 impedance bonds have positions for lifting lugs to be fitted, which should 

be removed as soon as the impedance bond has been placed in the track and 

replaced with the supplied means of protecting the threads. 

15.2 Impedance Bond Types and Restrictions 

Refer to the table in Figure E22 

Function Type Cat No Oil 

Filled 

Aux. Coil 

Ratio 

Weight 

(Kg) 

Supply 

WH3 50 Universal 3 86/17024 No 56: 1 160 N 

MR or 

S 

50 Universal 2 86/17023 No 56:1 160 O 

WBS P3 50 Universal 1 88/1237 Yes 45:1 S 

SGE DE 50 Universal I 88/83945 Yes 40:1 120 S 

WBS M 50/75 Specific 0 Yes 42:1 230 O 

WBS M2/5 50/75 Specific* 0 88/83948 Yes 42:1 190 S 

WBS M650/ 

75 



Specific 0 88/83952 Yes 45:1 230 O 

SGE DD 50 Universal 0 Yes 42:1 230 O 

GRS B 50 Specific 0 Yes 45:1 O 

Figure E22 

The table in Figure E22 is interpreted as follows: 

Function 

Universal 

Impedance bonds shown as ”Universal” may be used for all functions in all 

styles of track circuit approved for use in d.c. electric traction areas, 

subject only to their ability to cope with the designed traction current load. 

Note: Saturation levels and avoidance of particular combinations of bond 

and track relay, should be considered when replacing bonds of one style 

with another (see Clause 15.4). 

The impedance bonds are tuned to 50Hz. For other frequencies, internal 

resonating capacitors are fitted. 

Specific 

Impedance bonds shown as ”Specific” are specially set or tuned to perform 

feed, relay or intermediate functions at a particular frequency. If, in an 

emergency, an impedance bond is required to perform a different function 

or operate at the other frequency, it should be re–tuned. 



GK/RC0752 

Issue Two 






* WBS style M2/5 impedance bonds have been serviced as ”Universal” 

since 1984. 

Notes 

N. (New) - In production and serviced. 

S. (Serviced) - Out of production, but still serviced. 

O. (Obsolete) - Out of production and not serviced. 

Type 

All new impedance bonds are manufactured to specification BR863, the current 

rating of which is shown in Figure E23: 

Bond Type 

Type 3 3000A continuous, 4500A for 2 hours 

Type 2 2400A continuous, 3600A for I hour 

Type I 950A continuous, 1100A for I hour (Not to BR863) 

Type 0 (Not to BR863) 

Figure E23 

On high current dc. traction lines, ie. where classes 92, 373, 465 and 471 

locomotives and multiple units run in revenue–earning service, only Type 3 

impedance bonds fitted with six side leads (three on each side) are to be used. 

On other lines, any type of impedance bond may be used and need only be 

fitted with two side leads. 

15.3 Sleeper Spacing 

The sleeper spacing required for impedance bonds is shown in Figure E24. 

Bond Style Type Sleeper Centres (mm) 

WH3 3 650* 

MR or S 2 750** 

P3 1 635 

DE 1 585 

M 0 700 

M2/5 0 700 

M6 0 700 

DD 0 725 

B 0 710 

Figure E24 

* The fixing centres for Type 3 impedance bonds is 650mm. However, any 

spacing between 570mm and 730mm will be satisfactory as the 

impedance bond is not fixed down at the terminal box end (see Figure 

E26). 

* * S and MR impedance bonds are also only fixed at one end, therefore the 

spacing of the sleepers is not critical 






GK/RC0752 

Issue Two 



15.4 Impedance Bond Interchangeability 

When an impedance bond is changed for another type, it is usually necessary to 

change some or all of the associated connections. Figure E25 is included as a 

guide to the items affected. The preferred replacement is shown shaded. 

As well as physical interchangeability, the replacement bond will need to be 

sufficiently rated for the peak and continuous traction currents that occur on that 

line. 

Imbalance in traction return currents will tend to apply a proportion of any 

interference content to track circuit receivers, which under particular conditions 

could lead to a wrong side failure. One mechanism whereby imbalance is 

detected, is due to saturation of the impedance bonds. As the difference 

between the traction currents flowing through the impedance bond’s half 

windings increase, the transformer action of the impedance bond becomes less 

efficient as it is driven into saturation, thereby suppressing the track circuit 

voltage. The operation of the track circuit will become unreliable, but some 

protection against wrong side failure of the track circuit is provided. 

The level of imbalance current required to saturate impedance bonds is roughly 

proportional to their rating, with higher rated type 3 bonds able to withstand 

greater imbalance current levels than type 2 bonds for example. This saturation 

of impedance bonds leading to right side failure of the track circuit, can provide 

useful protection against wrong side failure due to traction interference. 

Therefore, care should be applied when replacing one type of bond for another, 

as the tolerance to imbalance may be increased, but at the expense of detection 

of situations where track circuits become exposed to traction interference which 

could lead to wrong side failure. 

Additionally, certain bond/relay combinations should be avoided as they may 

create problems in correctly setting up 50Hz a.c. double rail track circuits. In 

particular, G4 relays should not be used with type 2 or type 3 bonds. If the track 

relay is a style CE391, the recommended replacement impedance bond is style 

DE, but if this is not available, it will usually be necessary to change the relay and 

base to a VT1. It is also recommended that the impedance bond at the other 

end of the track circuit is changed in order to get a satisfactory adjustment, 

particularly if a style B impedance bond is being displaced. 



GK/RC0752 

Issue Two 






TABLE OF IMPEDANCE BOND INTERCHANGEABILITY 

Old 

Impedance Bond Component New Impedance Bonds 

WH3 P3 DE M2/5 

Side leads C E T C 

MR Plate C C C C 

Tail cable E J J J 

Side leads E C C T 

S Plate C C C C 

Tail cable E J J J 

Side leads C E C T 

P3 Plate D E D C 

Tail cable R E R J 

Side leads E C E T 

DE Plate D D E D 

Tail cable R R E J 

Side leads C T C T 

M Plate D C C E 

Tail cable R E R E 

Side leads C C C E 

M2/5 Plate D D D E 

Tail cable R R R E 

Side leads C C C E 

M6 Plate D D D E 

Tail cable R R R E 

Side leads C C C T 

DD Plate D C C D 

Tail cable R E E E 

Side leads C C C T 

B Plate D C C T 

Tail cable R R J J 

Legend 

E Existing component can be re–used. 

C Existing component to be changed. 

T Existing component can be used temporarily. 

D Existing re–drilled and/or cut 

J Joint required. 

R Re–use (may be jointed using kit, Railway Catalogue No S411S289. 

Figure E25 






GK/RC0752 

Issue Two 



15.5 Impedance Bond Spares and Repairs 

Maintenance and local stock holding will generally be made easier if different 

styles of impedance bond are not intermixed within a track circuit. 

Surplus and defective impedance bonds should be returned intact to the local 

Infrastructure Store for servicing. New or re–serviced impedance bonds are 

available to order from the stores organisation. 

In an emergency, ie. if a possession or a replacement impedance bond cannot 

be obtained, replacement of faulty parts may be carried out in–situ in some 

cases. The following spare parts are available. Railway catalogue numbers are 

given where applicable: 

15.5.1 Style WH3 

Not repairable. 

15.5.2 Style MR 

Obsolete, parts out of production. 

15.5.3 Style S 

Description Catalogue No 

Terminal box (CD1073) : 86/43866 

Terminal block (WBS Drg B41464/1) : N/A 

Terminal label (WBS Drg J14676/– : N/A 

Cable gland 25mm (Hawke type 300 P25) : N/A 

Cable gland 20mm : 54/109127 

Blanking grommet 25mm (RS605–677) : N/A 

Blanking grommet 20mm (RS 605–661) : N/A 

Resilient mounting : 86/117018 

15.5.4 Style P3 


Coil, universal : 88/49566 

Covers, main : 88/84009 

Covers, terminal box : 88/84010 

Gasket, main cover : 88/84011 

Gasket, terminal box cover : 88/84012 

Plate lug centre connection : 88/27761 

Seal rubber, side lead A/57117/1 : 88/26415 

Terminal assy. CD.1055/S : 88/84013 

15.5.5 Style DE 


Coil, auxiliary (2BA lugs) : 88/2308 

Coil, auxiliary (OBA lugs) D4/21048A : 88/84038 

Cover, main : 88/84039 

Cover, terminal box : 88/84040 

Gasket main cover : 88/84041 

Gasket terminal box cover : 88/84042 

15.5.6 Style M 


Coil, auxiliary, feed or relay : 88/83976 

Coil, auxiliary, resonated : 88/2321 



GK/RC0752 

Issue Two 



16 Impedance Bond 

Installation 




15.5.7 Style M2/5 


Coil, condenser : 88/26065 

Plate, lug, steel (pairs with screws) 

for fitting side connections : 88/83987 

15.5.8 Style M6 

Obsolete, parts out of production. 

15.5.9 Style DD 


Coil, auxiliary : 88/83553 

Gasket, main cover : 88/27047 

15.5.10 Style B 


Coil auxiliary : 88/83958 

Terminal box : 88/25802 

Cover, terminal box : 88/83959 

15.5.11 <strong>General</strong> Spares 


Sealing Compound Red Hermabte no. 5400 : 7/60180 

Oil, insulating (impedance bonds) 2.5 litre : 27/13802 

CAUTION: Care should be taken to avoid trapping fingers when handling 

impedance bonds. 

16.1 Type 3 Impedance Bond 

Type 3 impedance bonds supplied to BR863 have blanking plates, grommets or 

plastic plugs in the terminal box holes, together with one M25 gland, for 2c Type 

C2 2.5mm²(f) and four M20 glands, for single core Type C1 2. 5mm²(f). 

The impedance bond is also supplied with resilient mountings, either fitted or 

supplied separately. The resilient mounting feet comprise two portions and, if 

not already fitted, should be glued together using Araldite Rapide or Araldite 

(Railway Catalogue No. 7/103330). 

The cable glands should be fitted as required and the internal lock nuts glued 

with Araldite. If unused holes are fitted with plastic plugs, these should be 

replaced with threaded blanking plates. Surplus blanking plates, grommets and 

glands should be retained as spares. 

In instances where the auxiliary coil box is prone to water accumulation, a 3mm 

hole may be carefully drilled in the bottom of the terminal box and all swarf 

cleared away. 

The bond is now ready for installation. 

The standard installation arrangements for Type 3 bonds on concrete or wooden 

sleepers (Howells or WBS Style WH3) are shown in Figure E26, Figure E27 

and Figure E28. 



CL 

200 

200 




GK/RC0752 

Issue Two 



After installation, it is particularly important to ensure that all glands are securely 

tightened onto the cables and that all unused entry holes are properly sealed. 

This will reduce the incidence of failures resulting from an accumulation of brake 

dust on the terminal block and tuning capacitor. 

Debris exclusion covers should be fitted to Type 3 bonds: 

For WBS WH3 Railway Catalogue No 86/17030 

For Howells WH3 Railway Catalogue No 86/17031 

Note Under no circumstances may a bond be commissioned unless all glands 

are correctly fitted and any unused holes are fitted with a threaded 

blanking plate. 

For drilling of holes in concrete sleepers/bearers, see GK/RC0754 Part D. 

Figure E26 shows the Typical Pin Brazed Arrangement for the Type 3 

Impedance Bond. 

Arrangement This Side of IRJ To Be Used For Double/Single & 

Double/Double Layout For Type 3 Bond 

Bond Not Secured To 

sleeper At This End 

For Cable Lengths 

See Section E18 

85 240 

85 

85 240 

200 

85 

200 

Cable Lugs Secured on Top 

of Bond Lug 

Holes for Temporary 

Jumpers When Required 

Cable Lugs Secured 

Underside of Bond Lug 

For Rail Connections 

see Section E8 


I.R.J. 

For Arrangement 

This Side of IRJ 

See Figure E27 & Figure E28 

For Busbar Packing 


For Busbar Details 


All Cables To Be Clear of 

Tamping Zones 


I.R.J. 

For securing bond on concrete sleepers drill on centre line at 400 ctrs 12 dia and secure with Hilti heavy duty 

anchors HSA 12x 110 Hilti code 66337 (2 OFF). For wooden sleepers use coach screws 5/8" x 6". 

Catalogue No 35/13950. Screws not to be driven fully home but left approximately 25 above bond lugs. 

Figure E26


GK/RC0752 

Issue Two 



Arrangement This 

Side of IRJ To Be Used 

For Double/Single & 

Double/Double 

Layout For Type 3 Bond 

Arrangement This 

Side of IRJ To Be Used 

For Double/Single & 

Double/Double 

Layout For Type 3 Bond 

I.R.J. 

I.R.J. 


Figure E27 shows the Busbar Pin Brazed Connections for Plain Line/Long 

Switch Fronts. 







Arrangements This Side of IRJ To Be Used For 

Double/Single Layouts 

Figure E27 

200 

200 

Hole Positions In Busbar 

To Be Drilled On Site 

For Rail Connections see 

Section E8 

Notes 


Tamping Zones 



155 

240 

155 

240 

For Busbar Restrictor 

Arrangement 

See Figure E43 

200 

200 

For Rail Connections see Section E8 

Figure E27 shows the Busbar Pin Brazed Connections for Short Switch Fronts. 

I.R.J. 







I.R.J. 



Arrangements This Side of IRJ To Be Used For 

Double/Single Layouts 

Notes 


Tamping Zones Section E6 

Figure E28 

S S 

For Rail Connections see Section E8 

155 

240 

155 

240 


Arrangement 

See Figure E43 




see Section E8


Bond Not Secured To 

sleeper At This End 



S S 

Plastic Pipe 

Type 2 Bond 




GK/RC0752 

Issue Two 




The standard installation arrangements for Type 2 (Style MR or S) impedance 

bonds on concrete or wooden sleepers are shown in Figure E28 and Figure 

E29. 

Arrangement This Side of IRJ To Be Used 

For Double/Single & Double/Double Layout For 

Type 2 Bond 





This Drawing Should Only Be Used For 

Renewal of Individual Components in 

Existing Installations 

I.R.J. 



Notes 

All Cables To Be Clear 

of Tamping 

Zones see Section E6 


I.R.J. 

Arrangements This Side of IRJ To Be Used 

For Double/Single Layouts 

S S 


Arrangement 

see Figure E43 



For securing bond on concrete sleepers drill on centre line at 400 ctrs 12 dia and secure with Hilti heavy duty 

anchors HSA 12x 110 Hilti code 66337 (2 OFF). For wooden sleepers use coach screws 5/8" x 6". 

Catalogue No 35/13950. Screws not to be driven fully home but left approximately 25 above bond lugs. 

Figure E29


GK/RC0752 

Issue Two 







The standard installation arrangements for Type 1 (Style P3 or DE) bonds are 

shown in Figure E30 and Figure E31. On timber sleepers, the bond should be 

fixed using 6” x 5/8” coach screws (railway cat no: 35/13950). Approximately 

25mm clearance between the bond fixing lug and the underside of the coach 

screw is required to allow settlement of the sleepers without causing the bond 

fixing lugs to come under strain. For installation on concrete sleepers, see 

Figure E36. 

Track Leads 

Figure E30 

Figure E31 

76 

Timber Timber 

200 

P3 

585 CRS 


76 

Timber Timber 

76 

D.E. 

585 CRS 

200 

Track Leads





GK/RC0752 

Issue Two 




The standard installation arrangements for a Type 0 (Style B, DD, M, M2, M5 or 

M6) bond is shown in Figure E32, Figure E33, Figure E34 & Figure E35 . On 

timber sleepers, the bond should be fixed using 6” x 5/8” coach screws (Railway 

Catalogue No: 35/13950). Approximately 25mm clearance between the bond 

fixing lug and the underside of the coach screw is required to allow settlement of 

the sleepers without causing the bond fixing lugs to come under strain. For 

installation on concrete sleepers, see Figure E36. 


Figure E32 


 

Timber Timber 

710 CRS 


76 

B 

200 

Timber Timber 

DD 

710 CRS 

200 

76


GK/RC0752 

Issue Two 






Figure E34 


Figure E35 


Timber Timber 

200 

585 CRS 


`M' 

76 

Timber Timber 

M2. M5. 

700 CRS 

200 

16.5 Concrete Sleeper Fixing Arrangements 

The fixing of impedance bonds to concrete sleepers/bearers requires the 

sleeper/bearer to be drilled off centre. This problem is overcome by using 

adjustable fixing straps (see Figure E36). Signal Engineering staff are permitted 

to drill holes in concrete sleepers, however, these may only be drilled on the 

centre line of the sleeper. If concrete bearers are required to be drilled, prior 

agreement should be obtained from the Permanent Way Engineer. 

76


17 Aluminium Busbars 



400 

Figure E36 

Sleeper Drilled 18 on Centre Line X 95 Deep (Min) Metal 

Anchor HSL M12/25 Hilti Code 6692 2 Off 

M20 X 50 Long Hex. Hd. Screw 

Sleeper Not To Be Drilled 

Typical Arrangement if Impedance Bond 

Fixing to Concrete Sleepers 


GK/RC0752 

Issue Two 



3 X 45 degree Chamfer 

40 65 

140 

3 Fillet Weld 

7.5 Radius 

All Dimensions in mm 

16.6 Safety Labelling 

Warning labels as described in Section 14 should be fitted to the outside of the 

auxiliary coil terminal box cover. 

17.1 Introduction 

The various layouts and installation arrangements of aluminium busbars are 

shown on the drawings as described below: 

Inter–track circuit connections are shown in Figure E37 and Figure E38. Details 

of busbar lengths and Railway Catalogue Nos. are given in Figure E39, Figure 

E40, Figure E41 and Figure E42. 

Busbar drillings for connection to the bond and rail side leads are shown in 

Figure E28, Figure E29 and Figure E39. 

Style S impedance bonds are fitted with down–set busbars. Details can be found 

in Figure E37, Figure E38, Figure E39 and Figure E40. 

Installation details of the aluminium busbars are shown in Figure E26, Figure 

E27, Figure E28, Figure E29 and Figure E43. 

Installation of the busbar to earlier types of impedance bond is shown in Figure 

E32, Figure E33, Figure E34 and Figure E35. 


Ø 16 

18 

30 

12 

" 

40 

"


GK/RC0752 

Issue Two 






17.2 Impedance Bond Lug Plates 

In the case of the Style P3 impedance bond, the busbar is not secured directly to 

the impedance bond lug plate as with all other impedance bond types. A 

separate lug plate (Railway Catalogue No. 88/27761) is required, as shown in 

Figure E44. This is secured to the impedance bond lugs with four 1¼” x 3 /8” 

hexagon headed BSW bolts, plain spring washers and nuts, which are provided 

with the impedance bond. 

17.3 Packing Pieces 

The arrangement of packing pieces required between busbar and sleeper is 

shown in Figure E29. The packing pieces are illustrated in Figure E45. They are 

not attached to the sleepers but secured to the busbar using No.10 x 1¼” wood 

screws. 

17.4 Busbar Restrictor 

The busbar is maintained in position by a busbar restrictor arrangement. This 

comprises a pair of side stops (Railway Catalogue No 88/27760) as shown in 

Figure E46. The side stops incorporate a steel rod assembly to prevent 

excessive vertical movement. Installation of the busbar restrictor is shown in 

Figure E43. 

17.5 Impedance Bond Connection Arrangements 

Figure E37 shows the various connection arrangements to be applied to Type 3 impedance bonds installed in new 

works. Connections for maintenance replacement of other types of impedance bond are shown in Figure 38. 



Notes 

* 

Intertrack Cables A 

* IRJ 

Intertrack CablesB 

2 For details of all busbars see Figure E39. 

Item 1 

DOUBLE RAIL TRACK CIRCUIT TO NO TRACK CIRCUITED LINES 

T.P. Huts Neg Return B 

Item 3 

IRJ 

Double Rail Track Circuit to Double Rail Track Circuit Substations 

4 Traction Return cable sizes : A = 240mm2 Aluminium B = 800mm2 Aluminium 

5 Where TI.21 Track Circuits rail bonds require to share the first sleeper bay with the traction return cable, 

they must be taped to the traction return cable. Orange pipe must not be used 

IRJ 

IRJ 

T.P Hut Neg Return A Neg Reinforcing CableB 

* IRJ 


Item 5 

IRJ 

Double Rail Track Circuit to Single Rail Track Circuits 

T.P. Huts Or Cross Bonding Sites. 

1 All lugs complete with bolts, nuts and washers for negative cross bonding substations and T.P. hut 

cable attached to busbar to be supplied and fitted by Electric Traction Engineer. 

3 For full details of layouts see Figure E26, Figure E27, Figure E28. 

6 The Electric Traction Engineers lugs to be attached to the top of the busbar (Figure E55 for marking jig). 

7 Impedance bonds at substations and T.P. Huts to be sited in co-operation with the Electric Traction Engineer. 

8 In all layouts a longer busbar may be provided where necessary to accommodate reinforcing cables. 

* Cross track orange plastic pipe for protection of signalling cables. 

* 



* 

* 


GK/RC0752 

Issue Two 



* * 


Substation Neg ReturnB 

* IRJ 

Intertrack Cables B 


Item 4 

IRJ 

Double Rail Track Circuit to Single Rail Track Circuits Substations 

N.B. This Arrangement is Also Used at Sites Other Than Substations 

IRJ 

IRJ 

Item 2 

Double Rail Track Circuit to Double Rail Track Circuit 

Substation Neg Returns 


Item 6 

Double Rail Track Circuit Intermediate Bond 

At Substation 

T.P. Huts or Cross Bonding Sites 

B 

* 

* 

Neg Reinforcing Cable 

See Note 9 

B 

T.P. Hut 

B 

Neg Return 

Intertrack CablesA 

Item 7 

Double Rail Track Circuit Intermediate 

Bond T.P. Huts Or Cross Bonding Sites


GK/RC0752 

Issue Two 



Notes 

* IRJ 


* IRJ 


Item 1 


IRJ 

IRJ 

Double Rail Track Circuit to Non Track Circuited Lines 

Double Rail Track Circuit to Double Rail Track Circuit Substations 

T.P Hut Neg Return A 

* IRJ 



Item 3 

Substations Neg Return B 


IRJ 

Double Rail Track Circuit to Single Rail Track Circuits 

T.P. Huts or Cross Bonding Sites. 

1 All lugs complete with bolts, nuts and washers for negative cross bonding substations and T.P. hut 

cable attached to busbar to be supplied and fitted by Electric Traction Engineer. 

2 For details of all busbars see Figure E39. 

3 For full details of layouts see Figure E27, Figure E28. 

* 

* 


Intertrack 

Cables 

4 Traction Return cable sizes : A = 240mm2 Aluminium B = 800mm2 Aluminium 

5 Where TI.21 Track Circuits rail bonds require to share the first sleeper bay with the traction return cable, 

they must be taped to the traction return cable. Orange pipe must not be used. 

* 

T.P. Huts Neg Return A 

* * 

Intertrack Cable A 

* IRJ 


Double Rail Track Circuit Intermediate Bond 

at Substation 


B 


6 The Electric Traction Engineers lugs to be attached to the top of the busbar (See Figure E55 for marking jig). 

7 Impedance bonds at substations and T.P. Huts to be sited in co-operation with the Electric Traction Engineer. 

8 In all layouts a longer busbar may be provided where necessary to accommodate reinforcing cables. 

* Cross track orange plastic pipe for protection of signalling cables. 



IRJ 

IRJ 

Double Rail Track Circuit to Double Rail Track Circuit 

T.P. Huts Or Cross Bonding Sites 

Intertrack Cables B Substations Neg Return B 

IRJ 

Double Rail Track Circuit to Single Rail Track Circuits Substations 

Substation 

Neg Returns B 

Substation 

Neg Returns 

B 

* 

* 


T.P. Hut 

Neg Returns 


Item 5 Item 6 Item 7 

Figure E38 Impedance Bond Connection Arrangements (Other than 

Type 3) 

Item 2 

Item 4 

Double Rail Track Circuit Intermediate 

Bond T.p. Huts or Cross Bonding Sites 

B




17.6 Busbar Details and Layouts 

Figure E39 shows busbar drilling layouts. 

2 Holes 12 Dia 

B 

Figure E39 

P3 

M6 

WH3 or MR 

15 

15 

11 

11 


15 

15 


100 




GK/RC0752 

Issue Two 




55 

55 

50 

55 

44.5 

51 

45 

25 

41 

41 

41 

19 

76 

25 

44.5 

75 

20 

M,M2,M5 

15 

15 


DE 

DD 



55 44.5 

100 

100 

50 

19 

44.5 

50 19 

57 

41 

25 

35 

38 

35 

22


GK/RC0752 

Issue Two 




Figure E40 gives details of Style S impedance bond busbar and drilling layouts. 

20 

75 



45 

Material 


# 

# 

4000 

Before Bending 

100 

800 

Before Bending 

100 

Aluminum Plate 150mm X 6mm to BS 2898(E1) In 4 Metre Lengths to 

Railway Catalogue No 88/24804 

5 Metre Lengths are Available to Railway Catalogue No 88/24805 

Holes Marked # are for Temporary Side Lead Connections 

Figure E40 

# 

# 

220 45 20 


150 100 

220 

45 o 


75 R 

75 R 

45 

150 100 

45 o 

20 

75 

90 

75 

90



GK/RC0752 

Issue Two 



Figure E41 shows the layout of Style S impedance bond busbars. 

Busbar Joint 

IRJ 

IRJ 

Busbars: One Long ( Drill and cut as required) and one short 

IRJ 

IRJ 

Busbar: One Long (Cut flush with sleeper edge if required) 

Busbar: One Short 



Figure E41 



GK/RC0752 

Issue Two 






The layout of Style S impedance bond busbar connections is shown in Figure 

E42 

Note 

4 x M16 x 50 LG Hex. HD Bolts 

4 x M16 Self Locking Nuts. EZP. 

Recommended Torque 90Nm 

8 X M16 Washers 


20 Min 

50 Max 

1 Ensure all Mating Surfaces are Wire Brushed Thoroughly and Coated With 

Electrolytic Paste (Catalogue No 7/262001) Before Assembly 

2 This Drawing to be Read in Conjunction With Figure E40 & Figure E41 

Figure E42 

The busbar restrictor assembly is shown in Figure E43. 

2 X 6mm Starlock Push On Fasteners Uncapped Finish EZP. 

6 Dia Rod X 180 Long Steel BS970.070 M20 

Busbar See Fig 14 

Busbar Packing Planed Deal 

Size 150 X 75 X 35 

Busbar Side Stops 

to be Fitted to all 

Busbars Which Extend 

Beyond the Second + 

Sleeper Bed from Bond 

Except Where a 

Double/Double Installation 

Occurs Side Stops Secured: 

To Timber Sleepers by No 12 X 2" Woodscrews 

To Concrete Sleepers 

Drill Sleeper on Centre Line 

5/16" Dia X 2" Deep Insert Nylon Rawlplug M8.96.008. 

Locate Side Stop. Hammer in Steel Round Head Zinc 

Plated Drive Screw 14 Gauge X 40mm Through 1/4" 

Phosphorus Bronze Serrated Lock Washer. 

Figure E43





GK/RC0752 

Issue Two 



Figure E44 shows the lug plate for style P3 impedance bonds. 

Figure E44 

= = 

41 41 

41 

Impedance Bond Busbar Packing (Railway Catalogue No. 88/27772) is shown in 

Figure E45. 

150 


270 

248 

75 32 

Material Planed Deal, End Grain To T 

Figure E45 

Impedance bond busbar side stop details are shown in Figure E46. 

42 

50 

Figure E46 

50 


T 

30 50 

11


GK/RC0752 

Issue Two 



18 Side Leads 




18.1 Side Lead Manufacture 

Impedance bond and busbar side leads are manufactured in accordance with 

Figure E47 & Figure E48 and the tables in Figure E49, Figure E50 & Figure 

E51. 

Figure E47 shows the general procedure in diagrammatically form: 

45 

1. Strip Back Insulation 

2. Crimp Lugs 

3. Fit heat shrink tube 

(where required) and label 

37/2.25 Aluminium Cable 

Catalogue No 6/116601 

Heat Shrink Tube with Sealant 

Catalogue No 55/118332 


45 

OR 

Clear heat shrink tube to completely cover adhesive 

paper label. For colour of label, legend and Railway 

Catalogue No see Figure E48, Figure E49, 

Figure E50 and Figure E51. 

Label size 50 x 20 nom fitted this end only 

Figure E47 

Figure E48 gives cable lengths (dimension A) for crimped lug and busbar 

connections. It should be used in conjunction with the cables in Figure E49, 

Figure E50 and Figure E51 which give details for each group of cables (green, 

white or orange group) according to the rail connection.


A 


GK/RC0752 

Issue Two 



B H or E B H or E C A 

Item 1 

Item 2 

Item 3 / 4 

A 

A A 

A 



A 

D A or E D 

Item 6 

A or E D A or E 

Item 7 

Item 5 

A 

D A or E F A or E D A or E 

Item 8 Item 9 Item 10 

C A or E G H or E G 

Item 11/12 

Item 13/14 

E 

Item 15 

A A A 

Note The relative position of the lugs is different on items 1 & 2, 5 & 6, 7 & 8 

and 9 & 10. 

Cable End Connectors are listed below with the (former) Southern Region Drawing No. 

and Railway Catalogue No. 

Connector Type SR Drawing No Catalogue No. 

A Rail Lug 50° (Pin Drive) ME72-86 55/27630 

B Bond Lug (P3) ME72-88 55/27629 

C Bond Lug (DD & DE) ME72-92 55/27626 

D Bond Lug (M, M2, 5 & 6) ME72-89 55/27627 

E Rail Lug (Stud Fixing) 20° M39-34/1 54/39307 

F Bond Lug (B) ME72-91 55/27625 

G BusBar and Bond Lug (S, MR & Type 3) ME72-107 55/27631 

H Rail Lug 20° (Pin Drive) M39-34/2 55/27614 

Figure E48 


A 

A 

A


GK/RC0752 

Issue Two 






Figure E49 gives details of Green Group Cables (For Connection to Cembre 

Studs). 

Item Cable Connection Green Label Legend Catalogue 

No. 

Length 

(mm) 

Lug 

Types 

1 P3 Bond to Rail Top P3 to M12 Stud Top 88/29464 715 B & E 

2 P3 Bond to Rail Bottom P3 to M12 Stud Bottom 88/29463 715 B & E 

3 Busbar to Rail Long Busbar to M12 Stud Long 88/29462 # C & E 

4 Busbar to Rail Short Busbar to M12 Stud Short 88/29461 # C & E 

5 M Bond to Rail Top M to M12 Stud Top 88/29460 # D & E 

6 M Bond to Rail Bottom M to M12 Stud Bottom 88/29459 # D & E 

7 M2, 5 & 6 Bond to Rail Top M2, 5, 6 to M12 Stud Top 88/29458 685 D & E 

8 M2, 5 & 6 Bond to Rail Bottom M2, 5, 6 to M12 Stud Bottom 88/29457 660 D & E 

9 B Bond to Rail Top B to M12 Stud Top 88/29456 # F & E 

10 B Bond to Rail Bottom B to M12 Stud Bottom 88/29455 # F & E 

11 DE Bond to Rail DE to M12 Stud 88/29454 # C & E 

12 DD Bond to Rail DD to M12 Stud 88/29453 # C & E 

13 S or MR Bond to Rail S or MR to M12 Stud 88/29452 740 G & E 

14 Busbar to Rail Busbar to M12 Stud 88/29451 800 G & E 

15 Type 3 Bond to Rail Type 3 Bond to M12 Stud 88/29450 740 G & E 

Figure E49 

Figure E50 gives details of White Group Cables (For Connection to Pin Brazed 

Studs). 

Item Cable Connection White Label Legend Catalogue No Length 

(mm) ( 

Lug 

Types 

1 P3 Bond to Rail Top P3 to M12 Stud Top 88/29477 665 B & E 

2 P3 Bond to Rail Bottom P3 to M12 Stud Bottom 88/29476 665 B & E 

3 Busbar to Rail Long Not Required Install as Item 14 N/A N/A N/A 

4 Busbar to Rail Short Not Required Install as Item 14 N/A N/A N/A 

5 M Bond to Rail Top M to M12 Stud Top 88/29475 # D & E 

6 M Bond to Rail Bottom M to M12 Stud Bottom 88/29474 # D & E 

7 M2, 5 & 6 Bond to Rail Top M2, 5, 6 to M12 Stud Top 88/29473 # D & E 

8 M2, 5 & 6 Bond to Rail Bottom M2, 5, 6 to M12 Stud Bottom 88/29472 # D & E 

9 B Bond to Rail Top B to M12 Stud Top 88/29471 # F & E 

10 B Bond to Rail Bottom B to M12 Stud Bottom 88/29470 # F & E 

11 DE Bond to Rail DE to M12 Stud 88/29469 # C & E 

12 DD Bond to Rail DD to M12 Stud 88/29468 # C & E 

13 S or MR Bond to Rail S or MR to M12 Stud 88/29467 # G & E 

14 Busbar to Rail Busbar to M12 Stud 88/29466 725 G & E 

15 Type 3 Bond to Rail Type 3 Bond to M12 Stud 88/29465 665 G & E 

# Size not determined 

Figure E50 






GK/RC0752 

Issue Two 



Figure E51 gives details of Orange Group Cables (For Pin Drive Connections). 

Note Orange Group cables are shown for reference only – preferred rail 

connection is by 12mm dia. stud (pin brazed or Cembre). 

Item Cable Connection Orange Label Legend Catalogue 

No 

Length 

(mm) 

Lug 

Types 

1 P3 Bond to Rail Top P3 to Pin Drive Top 88/29477 765 B & H 

2 P3 Bond to Rail Bottom P3 to Pin Drive Bottom 88/29476 715 B & H 

3 Busbar to Rail Long Busbar to Pin Drive Long N/A 1070 C & A 

4 Busbar to Rail Short Busbar to Pin Drive Short N/A 690 C & A 

5 M Bond to Rail Top M to Pin Drive Top 88/29475 765 D & D 

6 M Bond to Rail Bottom M to Pin Drive Bottom 88/29474 715 D & D 

7 M2, 5 & 6 Bond to Rail Top M2, 5, 6 to Pin Drive Top 88/29473 685 D & A 

8 M2, 5 & 6 Bond to Rail Bottom M2, 5, 6 to Pin Drive Bottom 88/29472 660 D & A 

9 B Bond to Rail Top B to Pin Drive Top 88/29471 690 F & A 

10 B Bond to Rail Bottom B to Pin Drive Bottom 88/29470 690 F & A 

11 DE Bond to Rail DE to Pin Drive 88/29469 765 C & A 

12 DD Bond to Rail DD to Pin Drive 88/29468 485 C & A 

13 S or MR Bond to Rail S or MR to Pin Drive 88/29467 740 G & A 

14 Busbar to Pin Drive Busbar to Pin Drive 88/27723 800 G & H 

Figure E51 

18.2 Side Lead Connection 

In order to minimise imbalance of traction return current in the impedance bond 

traction coil, every attempt should be made to ensure electrical balance of the 

two sets of rail to impedance bond connections. Only aluminium conductors 

should be used. Copper and aluminium side leads should not be mixed on the 

same impedance bond as they have different characteristics and the bond will 

become unbalanced. 

When a Type 3 impedance bond is used at a site requiring only two side leads 

these should be connected to the impedance bond lugs using the two holes 

nearest to the impedance bond casing. At all sites where the impedance bond 

lugs are at different heights, the side lead connections to the higher lug must be 

fixed to the underside of the lug. 

If only the side leads on one side of the impedance bond are renewed, the 

balance should be checked afterwards, as the new ones may have been 

installed with a high resistance or the existing leads on the other side may not be 

as good as the new ones. 

Before any connections are made to the aluminium plate, any burrs or 

protrusions should be removed from the mating surfaces of the plate, lug, 

washers and nuts. A wire brush or steel wool should then be used to make 

these surfaces clean and bright. 



GK/RC0752 

Issue Two 






All contact surfaces should be coated with a uniform layer of jointing paste 

(Catalogue No. 7/26200) immediately after cleaning and any surplus cleaned 

away after tightening. The paste prevents moisture filling the resultant air 

spaces between the dissimilar metal surfaces, preventing corrosion which occurs 

very rapidly, particularly when aluminium is exposed to air or moisture. 

Where screw and nut connections are made to aluminium plate, eg. the 

aluminium busbar or P3 impedance bond lug plate, it is essential that 

mechanical connections are not over-tightened. This is because aluminium 

displays the property known as ‘‘cold flow” under pressure and if a certain 

pressure is exceeded, a flow away from the pressure area occurs and the 

connection becomes loose, resulting in a high resistance connection. 

Details of side lead/busbar connections and torque values are shown in the 

tables in Figure E52 and Figure E53. 

Where possible, the side lead connections should be tested, using a millivolt 

meter in accordance with GK/RC0754 Part G. 

Figure E52 

Type 

of Impedance Bond 

Type Of Connection 

Busbar(Item) Side lead (Item) 

Type 3 D E 

MR D E 

B A C 

M A A 

P3 A C 

DE A B 

DD A A 

S D E 

Item Description Torque Setting Catalogue No. 

A M12 x 50 Long Hex Hd Screw, Steel EZP 30Nm 35/101102 

B M12 x 70 Long Hex Hd Screw, Steel EZP 

35/101142 

M12 Nut, Lock (Bent Beam) Steel EZP 

30Nm 

03/180167 

M12 Washer, Steel EZP 

03/190932 

C M10 x 50 Long Hex Hd Screw, Steel EZP 

35/100842 


16Nm 

03/180166 


03/190930 

D M16 x 50 Long Hex Hd Screw, Steel EZP 60Nm 35/101272 

E M16 x 70 Long Hex Hd Screw, Steel EZP 

35/101312 


60Nm 

03/180168 


03/190936 

Figure E53 






GK/RC0752 

Issue Two 



A label with the legend ”TRACTION VOLTAGE DO NOT REMOVE THIS LEAD” 

(see Figure E54) should be attached to or alongside all impedance bond leads 

at substations, TP huts and TIR sites. These cables are identified on the 

Bonding Plan as described in GK/RC0754 Part C. 

TRACTION VOLTAGE 

DO NOT REMOVE 

Red Lettering on White Background 

Figure E54 

THIS LEAD 

18.3 Side Lead Removal 

An insulated bond punch (Railway Catalogue No. 39/48850) is available and 

should be used for the removal of side leads from the rail where they are pinned 

in 22mm or 7 /8” holes. This punch may be used adjacent to the conductor rail 

provided the Railway Group Standard Code of Practice is adhered to. 

To prevent arcing whilst side leads are being removed or reconnected, 

particularly where bolted stud connections exist, a temporary jumper of a size 

equivalent to the side lead being removed, should be connected between the 

aluminium plate and the rail concerned before the last lead is disconnected. 

If the impedance bond side lead is identified by a label as shown in Figure E54, 

it can only be disconnected under an absolute electric traction isolation and in 

accordance with GK/RC0754 Part D. 



GK/RC0752 

Issue Two 



19 Traction Negative 

Return Jumpers 

50 mm 

50 mm 


These are supplied by the Electric Traction Engineer and are connected to the 

aluminium busbar by Signal Engineering staff in accordance with GK/RC0754 

Part D. A marking jig (see Figure E55) should be utilised for marking out the 

busbar for drilling. 

16.5 mm 



NOTES 

63.5mm 

191.0mm 

To Be Suitably 

Drilled and Riveted 


63.5mm 

20mm 

5 0 

150 mm 

4 Holes at 17.5 mm Dia. 

150 mm 

1. Material is aluminium plate 150 x 6 (Off cut from impedance 

bond busbar.) 

2. Remove all burrs and sharp edges. 

3. Jig must be located in the centre of the bed. 

4. This jig is for marking out only. 

Figure E55 

A label with the legend ”TRACTION VOLTAGE DO NOT REMOVE THIS LEAD” 

(see Figure E54) should be attached to negative return jumpers at substations, 

TP Huts and TIR sites. Such leads may be disconnected only under an absolute 

traction isolation and in accordance with GK/RC0754 Part G.



2 Multi–meters 

3 The Universal 

Shunt Box 




GK/RC0752 

Issue Two 


Page F1 of 5 

Part F 

Instrumentation Description and Use 

This section gives details of the tools and instrumentation available for general 

use on track circuits. 

Instruments designed to be used with particular designs of track circuit can be 

found in the relevant Code of Practice within the track Circuit Handbook. 

2.1 Types 

In general, both analogue and digital multi–meters can be used when testing 

track circuits. 

Analogue Meters: 


Lineman’s AVO HD6 : 86/11001 

(No longer available) 

Digital Meters: 


Megger Instruments M2006 : 40/56003 

Carrying Case : 40/56016 

Test Lead Kit : 40/17758 

Digital meters will usually require a loading resistor of 150kΩ (Catalogue No. 

86/11041) fitted to the meter to ensure that a load current is drawn when used 

on voltage tests. 

3.1 Description 

Various designs of track circuit shunt box have been produced over the years, 

some early designs being incapable of coping with the power dissipation 

requirements when shunting higher powered track circuits. The only design 

described in this handbook is the current standard design, which is suitable for 

use on all track circuit designs (Figure F1). 


Universal Track Circuit Shunt Box : 40/5450) 

Figure F1 

R A I L T R A C K F1


GK/RC0752 

Issue Two 


Page F2 of 5 

4 Rail Clip Insulation 

Tester 




The shunt box has two resistance selection dials: 0 - 9Ω and 0 - 0.9Ω which are 

additive to give a combined range of 0 - 9.9Ω in 0.1Ω steps. In order to avoid 

overheating when left connected, the selected resistance is only placed between 

the test leads when the button is pressed. 

The unit comes complete with connecting leads fitted with 4mm plugs, and with 

two rail clamps for making attachment to the rail foot. These clamps have upper 

and lower contact points and should be attached to a section of cleaned rail foot 

without over tightening. The contact points should be replaced if they become 

blunt. 

3.2 Drop Shunt Test 

Test: 

1 Connect the shunt box across the rails at the relay end of the track circuit. 

2 To ensure that the clamps make a good electrical contact with the rails, 

connect a voltmeter between the rail heads. With zero ohms set on the 

shunt box and the button or switch operated, ensure the rail to rail voltage 

falls to zero. 

3 Set the shunt box to maximum resistance. 

4 Whilst keeping the button depressed, steadily reduce the resistance value 

until the track relay front contacts are fully open and remain open. The value 

of drop shunt can then be read directly from the shunt box. The following 

points should be borne in mind: 

a) Track circuits do not react instantly to changes in shunt value and time 

should be allowed for the relay to respond (2-3 seconds is adequate). 

b) It is obviously impractical to start at 9.9Ω and reduce in 0.1Ω steps at 3 

second intervals. Do a preliminary test by setting the 0 - 0.9Ω selector to 

0Ω and stepping down the 0 - 9Ω selector to identify the approximate 

value. Set the 0 - 0.9Ω selector to 0.9Ω and step down to obtain the 

exact value. 

For example, if the relay drops at 1.0Ω on the preliminary test, the actual 

value lies between 1.0Ω - 1.9Ω. 

3.3 Pick–up Shunt Test 

Test: 

1 Connect the shunt box as for the drop shunt test and set both resistance 

selector switches to 0Ω.. 

2 Whilst keeping the button depressed, steadily increase the resistance value 

until the track relay front contacts just close. The value of pick–up shunt can 

then be read directly from the shunt box (as for the Drop Shunt Test, similar 

techniques of delayed stepping and preliminary approximation should be 

used). 

The vast majority of concrete sleepered track comprises a resilient insulating pad 

between the underside of the rail and the sleeper, with the rail secured on each 

side by a clip bearing on the rail foot. Insulation is maintained by plastic pads 

between the clip and the rail foot. 

F2 R A I L T R A C K





GK/RC0752 

Issue Two 


Page F3 of 5 

Vibration causes the clip to wear through the pad, putting the rail in electrical 

contact with the concrete, which degrades the ballast resistance, and, if the 

track circuit is d.c. operated, may increase the levels of residual voltage. The 

degradation occurs gradually and identification of the failed insulations can be 

difficult. 

The Rail Clip Insulation Tester, sometimes known as “PRIT” or “K9”, consists of 

a unit with an extending handle, which can be rolled along the rail head (see 

Figure F2). Metal brushes mounted on each side “sweep” the rail clips, 

measuring the rail to clip insulation. Low values are indicated by an audible 

alarm. 


Rail Clip Insulation Tester : 40/17741 

4.1 Operation 

In d.c. traction areas, the machine must not be used on the rail adjacent to the 

conductor rail unless an isolation has been obtained. The brushes must be fully 

retracted and the insulated brush guards fitted before lifting over conductor rails. 

Figure F2 

4.1.1 Preparation 

Set the brushes to the correct height. 

The unit is equipped with “on/off” and “polarity change” switches on the chassis 

and “test” and “silence alarm” buttons on the handle. 

Switch “on” and set the “polarity change” switch to +ve. 

Press the “test” button, note the continuous alarm tone and then silence it by 

pressing the “silence alarm” button. 

If no alarm is given, or if the alarm sounds only when the “test” button is 

depressed, the battery should be replaced with type PP9 or equivalent and the 

unit re–checked. 

4.1.2 Use 

Push the unit along the rail. 

When an alarm is received, press the “silence alarm” button and check by re– 

sweeping the suspect fastening. Turn the “change polarity” switch to -ve and 

re–sweep: If an alarm is received, the clip is faulty; if there is no alarm, the clip 

on the other rail is suspect. 



GK/RC0752 

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Page F4 of 5 

5 Track Circuit Fault 

Detector 




The clip assembly should then be plainly marked for attention by the Permanent 

Way Engineer. 

The brush carriers can be raised/lowered to cater for flat or Pandrol type rail 

clips by moving the brush carrier handle to its vertical position to release the 

locking mechanism. 

Care must be taken to ensure that the rollers of the unit do not straddle any 

IRJs, causing “flicking” of adjacent track circuits. 

Short circuits between the rails can be difficult to locate, since, except for audio 

frequency types, the short circuit results in an identical drop in rail voltage along 

the length of the track circuit and gives no clue as to its physical location. 

Without the Track Circuit Fault Detector, it would often be necessary to sub– 

divide the trackwork to locate the faulty section. 

The detector is designed to be used on the trackwork of a track circuit where the 

feed and relay have been disconnected. It consists of two portable battery 

powered units: a transmitter and a receiver. 

Transmitter This is housed in a box incorporating an “on/off” switch and an LED 

indication. Yellow leads with clips are provided to connect the unit 

across the rails or lineside apparatus housing links. It is battery 

powered and outputs an intermittent high frequency voltage. 

Receiver This is housed in a box incorporating an “on/off” switch and an LED 

indication. It is battery powered and incorporates an internal aerial, 

amplifier and loudspeaker. When the receiver detects a signal 

from the transmitter it outputs an audible tone. 

Before commencing to test the bonding of a track circuit, the track circuit fault 

detector should be checked as follows: 

a) The transmitter leads should be connected together and the transmitter 

switched on. 

b) The receiver should then be switched on and held near the transmitter leads; 

an audible tone should be heard emitting from the receiver (this simple test 

will prove that the fault detector is working correctly). 

c) The feed and relay ends of the track circuit under test should be 

disconnected. With jointless track circuits, the track circuits either side of the 

track circuit under test should also be shorted out. 

d) The transmitter should then be connected across the rails at the feed end 

and switched on. The receiver is switched on and held near the rail; an 

audible tone should be heard emitting from the receiver. No tone may 

indicate a bad connection to the rails. If the rail connections are good, the 

fault is an open circuit, which may be found in the conventional manner. If an 

audible tone is heard, the receiver should then be carried along the track 

near to the rail and when the receiver passes the short circuit, a distinct drop 

in the volume of the tone will be noted. 

F4 R A I L T R A C K


6 Mark 4 Direct Reading 

Phase Angle Meter 




GK/RC0752 

Issue Two 


Page F5 of 5 

e) With audio frequency track circuits it may not be necessary to disconnect the 

feed, as the receiver will detect the steady tone of the feed frequency until 

the short circuit is passed. If this method does not prove successful, the 

transmitter should be used in the conventional manner. 

f) The rail impedance limits the useful range of the device (as measured from 

the transmitter). Where this occurs, the transmitter is simply moved to 

another position within the track circuit and the test repeated. 

Details are contained in GK/RC0757 Part E. 







2 High Voltages 

3 Lineside Apparatus 

Housing Inspection 

4 Bonding Inspection 



Part G 

Testing and Commissioning 


GK/RC0752 

Issue Two 


Page G1 of 3 

The requirements for testing and commissioning of track circuits are detailed in 

the following: 

New Works : GK/RH 0730 

Maintenance/Fault Finding : GK/RH 0740 

Details of available instrumentation and its uses are given in Part F. 

This Part details the general requirements for testing and commissioning. 

Reference should also be made to the Testing & Commissioning Part of the 

Code of Practice for the particular track circuit design involved. 

Ensure that warning signs (Figure E21) are fixed to all exposed track circuit 

capacitors and to the outside of lineside apparatus housings containing high 

voltage track circuit equipment. 

Details of the warning signs can be found in Part E. 

Check that: 

a) All track equipment is of the correct type, as specified in the wiring diagrams, 

and that applicable pin code configurations are correct. 

b) All equipment is correctly labelled. 

c) There are no prohibited combinations of adjoining or parallel types of track 

circuits. 

d) There are no prohibited track circuit equipment combinations. 

e) A wire count is carried out on all terminations, and the wiring proved correct. 

Check that: 

a) The physical positions of all IRJs or track ends are correct, especially those 

defining overlaps or clearance points. 

b) The physical stagger between nominally opposite IRJs does not exceed the 

permissible dimensions, and that no sub–section of the track circuit is shorter 

than the permitted minimum. 

c) All rail bonds, rail jumpers, traction bonds, track circuit interrupters and track 

feed/relay cables are in accordance with the bonding plan and scheme plan, 

and are secure. 

R A I L T R A C K G1


GK/RC0752 

Issue Two 


Page G2 of 3 

5 IRJ Inspection 

6 Performance Test 


5.1 Testing of IRJs 

IRJs should be visually checked for indications of insulation deterioration, general 

condition and rail burring over the insulation. 

If an IRJ is suspect, a possession of the track circuits concerned should be 

obtained and the IRJ tested for insulation break–down with the track circuits 

taken out of service. The metallic components of the IRJ being tested should be 

cleaned to allow a good electrical contact with the test leads. If the insulation 

resistance between either plate and rail is less than 2kΩ at 50V, thew joint is 

likely to fail or has partially failed and requires attention. The Engineering 

Supervisor should be notified so that arrangements can be made with the 

Permanent Way Engineer to replace the faulty IRJ. 

In the case of d.c. track circuits, IRJ’s may be tested with the track circuits in 

service under certain conditions. This procedure is described in GK/RC0755 

Part F. 

5.2 Prefabricated IRJs 

Edilon and similar prefabricated IRJs must be tested with a 50V insulation tester 

prior to installation in the track, taking care that the IRJ assembly is not in 

contact with any conducting surface. 

Test: 



a) Between the two rails. 

b) Between both fishplates and the two rails. 

c) Between each bolt and the two rails. 

The minimum acceptable reading is 500kΩ.. 

a) The track circuit should be energised and adjusted in accordance with the 

relevant section in this handbook. If difficulties are experienced, refer to the 

Fault Finding Procedures. 

b) Ensure that the polarity/phase is correct and that the correct electrical 

stagger is achieved. 

c) Track circuit interrupters must be tested by disconnection. 

d) Ensure that all adjoining track circuits are energised. Remove the feed links 

of the track circuit under test to check that only the correct track relay or 

relays respond. Check that any remaining extraneous voltage on the track 

relay does not exceed that permitted for the particular track circuit design 

(see the Testing & Commissioning Part in the Code of Practice for the 

relevant track circuit). 

e) Set the shunt box to the minimum permitted drop shunt value, and apply 

sequentially at all extremities and at selected places within any S & C, to 

prove the functionality of the track circuit bonding; the correct track relay 

must be seen to drop each time. For jointless track circuits, prove that the 

theoretical extremities are the actual extremities. 

G2 R A I L T R A C K





GK/RC0752 

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Page G3 of 3 

f) Carry out a correspondence test between the rails of each track circuit and 

any indications or to the final TPR, where no indications are provided. 

A track circuit must not be commissioned until the person in charge of S&T work 

is satisfied that the rail surface is sufficiently free of rust and other contamination 

to ensure correct shunting. 

R A I L T R A C K G3



This page is intentionally blank.



2 Routine Examination 

3 Drop Shunt Test 



Part H 

Maintenance 


GK/RC0752 

Issue Two 


Page H1 of 2 

This Part is a general guide to the principles of track circuit maintenance. 

Procedures specific to a particular design of track circuit are given in the relevant 

Code of Practice within the Track Circuit Handbook. 

Instructions regarding maintenance of track circuits are given in GK/RH0740 and 

GK/RC0241. 

Track circuit maintenance can be classified into the following activities: 

a) Routine Examination. 

b) Drop Shunt Test. 

c) Full Test. 

The objective of the examination is to find/remove potential failures and to 

ensure that, as far as possible, the track circuit will function satisfactorily until the 

next examination. The examination is mainly visual and can be undertaken 

without any need for possession of the track circuit. 

Any obstructions or conditions likely to prove detrimental to the reliability of the 

track circuit must be dealt with as soon as possible. 

The requirements and responsibilities for maintenance and inspection of bonding 

are laid down in GM/TT0127 and GM/TT0128. Refer also to GK/RT0252 

Specific attention must be given to the examination of the following: 

a) Track cables and jumper cables, their connection to the rail and clearance 

when passing under other rails. 

b) Fishplate type bonding, including traction return bonding where provided. 

c) Impedance bonds and connections where provided. 

d) Metallic and other conductive debris around insulations and rails. 

e) Point rodding, signal wires etc, touching or liable to touch either rail. 

f) Insulation deterioration and rail burring over insulations. 

g) Rust or other rail contaminants on the surface of the rails. 

The relay voltage should be checked and compared with the entries on the 

Track Circuit Record Card. If the value is significantly different from previously 

recorded values under similar weather conditions, a full test should be 

conducted. 

The commissioning drop shunt test is always carried out with the shunt box 

connected between the rails at the relay end of the track circuit. 

However, for routine drop shunt tests on d.c. or a.c. power frequency (50Hz - 

831 / 3Hz) track circuits (other than auto–coupled impedance bond types), the 

R A I L T R A C K H1


GK/RC0752 

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Page H2 of 2 

4 Full Test 




shunt box may be connected across the track circuit relay links in the lineside 

apparatus housing. The value of drop shunt obtained at the lineside apparatus 

housing will usually be higher than that obtained at the rails, the resistance of the 

relay end track leads being the most significant factor. 

It is only permissible to undertake drop shunt tests at the track circuit relay links 

in the lineside apparatus housing. where comparative shunts have previously 

been carried out both at the rails and at the lineside apparatus housing, and the 

two values are endorsed on the record card. It is then possible to judge any 

value obtained at the lineside apparatus housing relative to its theoretical 

railequivalent. Where such a theoretical value can be seen to approach the 

minimum acceptable, the test should be verified at the rails. 

The procedure for carrying out a drop shunt test is detailed in Part F 3.2. 

A variation in the drop shunt value may be caused by variations in equipment 

performance, or by expected variations in environmental conditions, with the 

drop shunt reaching the upper end of its range in wet weather and the lower end 

in dry weather. 

If the drop shunt exceeds the maximum value for the track circuit (see the 

relevant Code of Practice ), it is likely that the track circuit is being shunted by 

poor ballast or debris. The track circuit should be examined for these faults. If it 

appears to be in good physical condition, the track circuit equipment should be 

regarded as failed and the cause of the failure investigated through the fault 

finding procedure (see the relevant Code of Practice). 

If the drop shunt is lower than the minimum value for the track circuit (see the 

relevant Code of Practice), there has been an unexpected equipment failure. 

The Engineering Supervisor is to be informed, and immediate investigations 

undertaken to ascertain the cause of the low drop shunt value. 

The full test must be applied whenever alterations are made (eg. relaying, 

lead/jumper renewal, equipment replacement, adjustment, etc). The full test 

comprises the following: 

a) Carry out a Routine Examination. 

b) At the feed end, measure and record the voltages, currents and other 

parameters as required on the front of the record card. Any adjustments 

required must be in accordance with the relevant section of this handbook for 

the type of track circuit under test. 

c) At the relay end, with the track circuit clear, measure and record the 

voltages, currents and other parameters required and enter on the front of 

the record card. 

d) Perform a drop shunt test with the shunt box across the rails at the relay end 

and enter details on the record card. Where the track circuit is of a type able 

to be routine shunted at the relay links in the lineside apparatus housing, 

perform a second drop shunt test at this position and endorse the record 

card with that value. 

e) Set the shunt box to the minimum for that track circuit and connect across 

the rails at all extremities of the track circuit, confirming that the track circuit 

occupies on each occasion. This test must obtain simultaneous track circuit 

occupation where an overlapping section exists. 

H2 R A I L T R A C K



2 Categories of Failure 

3 Intermittent Failures 



Part J 

Fault Finding 


GK/RC0752 

Issue Two 


Page J1 of 5 

This Part gives a general outline to faults common to all types of track circuits; 

faults caused by electric traction systems or peculiar to a particular track circuit 

design are given in the appropriate Code of Practice of the Track Circuit 

Handbook. 

When clearing a fault, details of all readings and results should be noted, to 

establish a logical pattern of testing and adjustment. The track circuit record 

card(s) should always be investigated, as deteriorating readings during 

maintenance can show the impending failure of a component. 

When a fault has been located, the relevant tests carried out up to that point 

should be repeated, as, in the case of multiple simultaneous faults, one fault can 

mask another. 

Once a fault has been cleared, the track circuit must be fully tested prior to 

restoration. 

Track circuit failures fall into the following categories: 

Right Side: Indication shows occupied with no train in the 

section. 

Protected Wrong Side: Indication shows clear when a train is in the section, 

but is caused by a failure of the indication system 

only; the train is still protected by the interlocking. 

Unprotected Wrong Side: Track circuit or repeat relay fails to de–energise 

when a train is in the section; the train is no longer 

protected by the interlocking. 

The nature of the failure can be further categorised: 

Permanent: Failure remains static. 

Intermittent: Failure is only apparent for short periods. 

Intermittent faults are often the most difficult to solve, as the failure does not 

usually remain static long enough to take all necessary readings and 

observations. The following are possible causes dependent on circumstances: 

Vibration Vibration caused by the passage of trains can create 

intermittent high resistance in bonding or intermittent 

short circuits between the rails (ie. the failure may 

remain after one train but be cleared by a 

subsequent one). Trains, or operation of other 

equipment such as point machines, should be 

observed on site or on the signalman’s diagram; If 

the failure always occurs with a train at a particular 

point or coincides with operation of other equipment, 

that geographic site should be fully investigated. 

R A I L T R A C K J1


GK/RC0752 

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Page J2 of 5 




Traction Interference This is usually associated with d.c. traction railways 

and arises because of the high currents necessary 

with the low supply voltage. If a failure occurs with 

trains in certain positions or during times of heavy 

traffic, the traction return system should be 

investigated. 

Earth Faults Due to track circuits being very “earthy”, especially 

during wet weather, trains at certain positions on 

other lines may affect the rail to rail voltage of a track 

circuit, causing intermittent failures. An earth fault is 

usually noticed with a second fault caused by a 

defective continuity bond. 

Broken Rails/Bonds These can cause intermittent continuity problems. 

4 Right Side Failures When called to a fault, it is first necessary to determine whether the cause lies in 

the track circuit itself or its associated repeater circuits. This can be resolved by 

proceeding directly to the relay end and examining the track relay (having 

confirmed that the track is supposed to be clear !). This section is concerned 

with fault location in the track circuit itself. 

4.1 Types of Fault 

Since the various track circuits used have differing types of feed units, ranging 

from a single d.c. cell to complex transmitters, the methods for checking these 

different feed units are described in the relevant Code of Practice within the 

Track Circuit Handbook. 

If the transmitter or feed is found to be functioning correctly, it can then be used 

to determine the general nature of the fault (ie. short circuit or disconnection). 

This can be done by taking voltage and current measurements at the feed end 

as shown in Figure J1 . 

Figure J1 

Remove Link For Current Measurement 

J2 R A I L T R A C K 

A 

V 

Feed




A disconnection in the series bonding will: 

a) Reduce the current being fed into the track circuit. 


GK/RC0752 

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Page J3 of 5 

b) Reduce the voltage normally dropped across the feed impedance. 

c) Increase the rail voltage at the feed end. 

A short circuit will: 

a) Increase the current fed into the track circuit. 

b) Increase the voltage dropped across the feed impedance. 

c) Reduce the rail voltage at the feed end. 

4.2 Locating a Disconnection 

The higher rail voltage can be measured at all positions along the track circuit 

from the feed end up to the point of disconnection. On the relay side of the 

disconnection the rail voltage will be very low. Fault location therefore entails 

walking through and checking the rail voltage to identify the position of the step 

change in value. The faulty bond etc, can be confirmed by measuring a voltage 

across it. 

4.3 Locating a Short Circuit 

4.3.1 <strong>General</strong> 

The extent of the change in feed end voltages and currents will depend upon the 

type of track circuit and the physical position of the fault along the length of the 

track circuit. Consult the relevant section concerned with the specific type of 

track circuit, as appropriate. The general position is as follows: 

a) At d.c. and power frequency a.c., the rail impedance is negligible, and the 

resulting electrical circuit is constant, wherever the short circuit is located 

within the track circuit. Thus, any voltage across the rails, permitted by an 

imperfect short circuit, will be constant throughout the length, giving no clue 

as to its physical position. 

b) With audio frequencies and impulses, the rails have significant impedance, 

and the effect of a short circuit will vary depending upon its physical position. 

The closer it is to the feed end, the more it will increase the feed current and 

decrease the rail voltage. 

In either case, it is not possible to precisely locate the short circuit by simple 

observation of rail voltage along the track circuit. Other methods available are 

as follows: 

4.3.2 Visual Inspection and Provocation 

This is particularly useful where track circuit equipment is not responsible. 

Examples of such a fault include signal wire or point rods touching the rails, and 

faulty insulation in point connections etc. 

Connect a meter across the rails and observe its reaction when the item of 

equipment is provoked (eg. waggle the signal wire or stand on the rods, having 

first ensured that they will not be operated). In the case of faulty insulations, a 

hammer blow to the metalwork adjacent to the insulation will often produce sharp 

changes of rail voltage. Alternatively, the insulation should be carefully 

dismantled and reassembled. 



GK/RC0752 

Issue Two 


Page J4 of 5 

5 Wrong Side Failures 




4.3.3 Use of Track Circuit Fault Detector 

The track circuit fault detector comprises a test signal transmitter and a receiver, 

both units being self contained with their own battery power supply. The 

detector is designed to be used on a track circuit whose feed has been 

disconnected and replaced by the test transmitter. However, with audio 

frequency track circuits, the transmitter may not be required, as the receiver will 

detect the steady tone of the feed frequency. 

A full description and details of operation are given in Part F. 

4.3.4 Subdivision of Track Circuit 

This technique is particularly useful for track circuits in S & C where the sections 

of the track circuit are pieced together with jumper cables. It can be applied in 

other situations by removal of fishplates and associated bonds in conjunction 

with the Permanent Way Engineer. 

Note: This technique must not be applied to a traction return rail or jumper 

unless the work is under the direct control of the Electric Traction 

Engineer. 

Where the feed end test indicates a short circuit and a jumper part of the way 

through the track circuit is subsequently disconnected, the effect on the feed end 

will provide clues as to the location of the short circuit. If the short circuit lies 

between the feed and the disconnected jumper, the feed current and rail voltage 

will be largely unaffected. However, if the short circuit is between the 

disconnected jumper and the relay end, the feed end test will now indicate the 

symptoms of a disconnection. 

4.3.5 Faulty Concrete Sleeper Insulations 

Rails on concrete sleepers are usually insulated from the chair fastenings; the 

rail sits on a pad whilst clips (eg. Pandrol clips) bear on a plastic insulation piece 

against the foot of the rail. It is unusual for individual faulty rail insulations to fail 

a track circuit. Rather, a number of such failures may contribute to a general 

deterioration of ballast resistance. 

For the specific investigation of faulty rail insulations, a special test unit; the Rail 

Clip Insulation Tester, is available. For the applicable description and operating 

instructions see Part G. 

4.3.6 Failure of Insulated Rail Joints 

Care must be taken when attempting to check the insulation resistance of IRJs 

in situ due to the parallel path provided by the ballast on either side of the joint. 

Methods of testing IRJs are given in Part G. 

5.1 Rail Surface 

Permanent or intermittent wrong side failures involving loss of train shunt can 

occur because of a poor rail surface due to rust, leaf debris, oil film, or crushed 

coal/sand/ballast. The surface condition should be visually checked throughout 

the track circuit and suitably cleared if possible. 

At locations where oil film or rust is excessive and speeds are less than 5 mph 

(eg. locomotive depots, terminal stations), a stainless steel “zig–zag” strip can be 

applied to the surface of the running rail by the Permanent Way Engineer. 

J4 R A I L T R A C K





GK/RC0752 

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Page J5 of 5 

5.2 Faulty Track Relay 

It is possible that a track relay may be mechanically damaged in some way which 

prevents it properly de–energising. A check should be made to see that the 

relay operates correctly when a shunt is applied. 

5.3 Extraneous Interference 

It is possible that the track circuit is receiving energy from other than its own feed 

unit. Disconnect the feed and confirm that the relay voltage is less than 30% of 

its drop–away value. 

5.4 Gaps In Track Circuits 

This is a problem arising particularly on electric traction railways due to the need 

to provide parallel alternative paths for traction return current in the rails, but can 

arise in any situation where the bonding is not in series. It can be seen from 

Figure J2 that defective bonding in the traction return rail can lead to a wrong 

side failure; a train between the two disconnected bonds would not shunt the 

track circuit current. Yellow Bonding is now provided to prevent such 

occurrences. Where parallel bonding exists, it must be inspected and short 

circuits applied to confirm correct detection. 

Figure J2 

Two Disconnections 






References 


GK/RC0752 

Issue Two 


Page Ref1 of 2 

(Railway Group Standards references correct as at Catalogue 13) 

Railway Standards 

GK/RC0741 Signalling Maintenance Specifications 

GK/RH0751 Train Detection Handbook 

GK/RC0755 D.C. Track Circuits 

GK/RC0756 HVI Track Circuits 

GK/RC0757 50Hz. Track Circuits 

GK/RH0730 Signalling Testing Handbook 

GK/RH0740 Signalling Maintenance Testing Handbook 

GK/RT0004 Symbols for use on Signalling Plans and Sketches 

GK/RT0009 Identification of Signalling Related Equipment 

GK/RT0011 Train Detection 

GK/RT0031 Lineside Signals and Indicators 

GK/RT0201 Signalling Design Production 

GK/RT0251 Track Circuits 



GK/RT0252 Reinforcement of Track Circuit Bonding (Yellow Bonding 

GM/TT0126 Production and Modifications of Bonding Plans and the 

Installation of Bonding on all Electrified Lines except the 

SE, SC & SW Divisions of NSE. 

GM/TT0127 Inspection of Bonds on all Electrified Lines except the SC, SE 

& SW Divisions of NSE. 

GM/TT0128 Maintenance and Inspection of Negative Bonding on the SC, 

SE & SW Divisions of NSE. 

GM/TT0129 Production of Drawings for and the Installation of Negative 

Bonding on the SC, SE & SW Divisions of NSE. 

RT3170 Track Safety Handbook 

G0/RT3091 D.C. Electrified Line Instructions. 

GS/ES0872 Railway Signaling Cable 

BR863 Impedance Bonds for use with Track Circuits 

SSP 62 Replacement of Colour Light Signals to Danger 

BRS-SE 33 Channel Pin for Track Circuit Rail Bonds 

BRS-SM 104/11 Stake (Angle) for Track Side Equipment (1070) 

BRS-SM 104/13 Stake (Angle) for Track Side Equipment (760) 

RAILTRACK Ref1


GK/RC0752 

Issue Two 


Page Ref2 of 2 




Railway Standards (continued) 

BRS-SM 318 Facing Point Layouts Left and Right Hand Drives 

BRS-SM 319 Single and Double Slip Layout Right Hand Drive 

BRS-SM 320 Single and Double Slip Layout Left Hand Drive 

BRS-SM 374 Track Circuit Interrupter Assembly 

BRS-SM 375 Track Circuit Interrupter Body Unit 

BRS-SM 376 Track Circuit Interrupter Insulations 

BRS-SM 411 Taper Pin for Track Circuit Connections 

BRS-SM 622 Concrete Bearer Layout, S&T Equipment 

BRS-SM 848 Track Circuit Cables Plate for Rail Connection 

BRS-SM 849 Track Circuit Cables Flange Clip/Cable Clip for Cable 

Terminations 

BRS-SM 2200 Rail Clamp Point Lock MK2 Facing Point Layout Single Acting 

Cylinders & Cast Body 

BRS-SM 2228 Rail Clamp Point Lock MK2 Double Slip Points Layout Single 

Acting Cyl - Cast Body - A6 Mods 

BRS-SM 2240 Rail Clamp Point Lock MK2 Switch Diamond Layouts 

BRS-SM 2244 Rail Clamp Point Lock MK2 Point Layout with Hydraulic 

Actuators Tandem Turnout in 113FBV Rail for Cast Body 

Single Acting Cylinder 

BRS-SM 2260 Rail Clamp Point Lock Facing Point Layout for UIC-541113A 

Plain Lead Switches 

MD82017 Flat Bottom Rail Soleplate for Use with F.P.L. 

Ref2 RAILTRACK

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