General Information on Track Circuits - RGS Online

Railway Group Approved Code of Practice
GK/RC0752
Issue Two
Date December 1998
Page J4 of 5
5 Wrong Side Failures
Withdrawn Document
Uncontrolled When Printed
<strong>General</strong> <strong>Information</strong> on Track Circuits
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