Page 538 - IRSEM_Main Book

22.6.3 Maximum permitted length of direct feed of signal shall be as per Table given
below.

Type of Cable 110 Volts feed system

Single Track Double Track

Unscreened 180 m 220 m

22.6.4 When a signal is located at a distance greater than that specified in para
22.6.3 the signal shall be fed locally by controlling relays located at the
location. Such signals may also be remotely fed from the cabin by using a
controlling relay at the location. Typical circuit is given in Drg. No. 22-D9.

22.6.5 It shall be ensured that the power transformer for feeding circuits as per para
22.6.2 shall be different from the transformer feeding longer circuits.

Section 7: Point Operation & Detection in RE Area

22.7.1 Point can be operated electrically or mechanically by rodding. Mechanical
operation of point will require special measures for the protection of operating
staff. Electric operation shall have restriction on maximum length between
point control relays and point machine depending upon their immunity level.

22.7.2 Electric Operation of Point

(a) Point detection and point detection repeat circuits shall use ac-immunized
relay.

(b) The maximum permissible length for various types of commonly used Point
Machines is as under:

Maximum permissible parallelism in meters
Type of AC immunity between Point Contactor and Point Motor
Machine level in volts
Single line Double line

As per 160 910 1100
IRS S-24
400 2200 2800

Factor of safety is 1.5

(c) 3 phase point machine is inherently immune to induced voltage and
therefore can be used for operating point to any length subject to its own
operating limitation.

Chapter 22: Requirements Of Signalling in 25 KV AC Electrified Area Page 481 of 535