Page 536 - IRSEM_Main Book

Section 4: Signaling Circuits in RE Area

22.4.1 As a rule, no aerial circuits shall be retained in the electrified zone. In every
case, the length of parallelism and the distance of Block Wires from the
nearest electrified track shall be checked to ensure that the maximum induced
voltage does not the exceed 60 volts limits prescribed by CCITT.

22.4.2 Barring block-instrument circuits, no other earth-return circuit shall be permitted in
A.C electrified territory. Block instruments, however, shall be suitably protected by
a filter of approved design as explained in Chapter 18 of SEM.

22.4.3 The following electrical signalling equipment are not safe to withstand AC
induced voltage. The coils of this equipment can only be used inside a cabin or
a location box or internal circuits only. The coils of these equipment shall be
worked from a separate battery/DC-DC Converter and this battery/DC-DC
Converter shall not be connected to any external circuits going outside the
cabin/location box.

(a) Luminous Indicators.

(b) Telephone type relays.

(c) Electrical Lever Locks.

(d) Door Coil of IRS Block Instrument.

(e) 250 Ohm D.C. neutral Line Relay.

(f) Rotary Key Transmitter.

(g) D.C. Neutral Polar Relays.

22.4.4 All Batteries and the wiring in the equipment, location box or cabin shall be well
insulated from the ground. PVC insulated wires to an approved specification (IRS-
S-76) shall be used for wiring in location boxes and cabins.

22.4.5 Separate Batteries/DC-DC Converters shall be provided for external and internal
circuits.

22.4.6 When more than one cable is laid between two locations or cabins, it shall be
ensured that as far as possible, all wires pertaining to any individual circuit are
within the same cable.

22.4.7 Polarized Relays using permanent magnet shall not be used in any external circuit
in 25 KV AC electrified areas as the permanent magnet in the relay tends to lose its
magnetic properties due to continuous application of induced voltages. Competent
authority shall authorise any exception in specific cases.

22.4.8 The relays, which release an interlocking, shall be slow acting so that the
interlocking is not released inadvertently by voltage variations of short
duration. Time delay may be of the order of 0.6 to 0.8 seconds.

22.4.9 All external circuits in AC. electrified area shall work with double cutting.

Chapter 22: Requirements Of Signalling in 25 KV AC Electrified Area Page 479 of 535