Page 492 - IRSEM_Main Book

(c) Design of signal circuits and equipment shall be suitable for 25 KV AC
electrified areas as per provisions of Chapter 22 of SEM on
"Requirements of signalling in 25 KV AC electrified areas".

(d) Common return shall not be provided in vital circuits.

(e) Where relays other than 24 V, 1000 ohm relay with metal to carbon
contacts are used, the circuits shall be so designed that not more than 45
such contacts are used in series in a circuit.

(f) The proving of back contacts of metal to metal relays should be done in
the circuitry.

(g) All new installations shall be of route setting type interlocking.

21.1.6 Route Setting Type

(a) The route setting and clearance of signal shall be with the following
conditions:

(i) SM's key is In

(ii) The interlocking is free

(b) The points are correctly set and locked in the route including overlap
and isolation (if any) to desired position.

(c) The crank handle keys for all the motor operated points in the route,
overlap and isolation are locked and their control is not released, shall
be proved in Signal Clearance only. The keys for all the key-locked
points in the route, overlap and isolation are locked and their control is
not released.

(d) All interlocked level crossing gates are closed and locked against the
road traffic in the route and overlap, if any, shall be proved in Signal
Clearance only to allow gate closing in the last.

(e) Slot if any, from other agency has been received.

(f) The track circuits in the route up to the next signal/dead end, overlap
and isolation and Fouling, if any, are clear.

(g) Stop signal ahead is not blank

(h) The interlocking between conflicting routes shall be achieved through
route interlocking electric circuits at route initiation stage.

(i) Approach locking or dead approach locking shall be provided for all
manual stop signals. Approach locking shall be continuously effective
from the predetermined point on approach of the signal.

(j) Controls on level crossings, ground frames, cabins, sidings etc., shall be
suitably interlocked.

Chapter 21: Relay & Electronic Interlocking Page 438 of 535