General Information on Track Circuits - RGS Online

<strong>General</strong> <strong>Information</strong> on Track Circuits
1 Purpose
2 Scope
3 Glossary of Terms
Withdrawn Document
Uncontrolled When Printed
Part B
Railway Group Approved Code of Practice
GK/RC0752
Issue Two
Date December 1998
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.
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