Page 507 - IRSEM_Main Book

21.2.2 Fixing in Relay Room

As far as practicable, the relay room is not located in the vicinity of chemical
factory, loco shed or engine ash pits etc. In case it becomes unavoidable,
necessary precautions shall be taken so that relays are least affected by the
chemical fumes, dust etc. and are provided with dust free environment. Relay
room shall be provided with double locks and door opening shall be monitored
through Datalogger.

(a) Where Relays cannot be located in the Cabin, they shall be housed in
location box of approved type which are properly secured.

(b) In 'Q' style relay the code pins configurations for plug in relay shall not be
changed by drilling additional holes on plug board to avoid fixing of a
wrong relay which may lead to unsafe condition. In Siemen's K-50 relays,
the Code pins position on base plate should not be changed and to be
retained as fixed by the manufacturer.

(c) All relay clips shall be checked for proper locking in the base when
plugged in. Extreme care shall be exercised while removing the clips from
the jacks of the plug-in type relay.

(d) In all installations, a relay index board shall be provided for locating relays
easily.

(e) Relays involving external circuits shall have cross protection and double
cutting. Signal control relays shall preferably be provided with double cutting.

(f) A contact analysis chart shall be prepared duly showing the contacts used
circuit-wise with reference and spare contacts available, wire count for
each contact and relay position in the rack.

(g) Number of contacts in a circuit shall not exceed 45 Nos. due to voltage
drop consideration. The voltage across R1&R2 of a relay shall not be less
than 22 V.

(h) Where available, spare contacts shall be paralled with working contacts.

21.2.3 Sealing of Plug-in Relays

(a) In case of metal to carbon contact type relays, sealing shall be done at
Manufacturer's premises before dispatch and if the seals have to be broken
due to any defect noticed, resealing must be done at the workshops.

(b) In case of metal to metal contact type relays, sealing of the cover shall be
done by not below the rank of JE (Signal) at site. Whenever seals have to
be broken at site for maintenance purposes, the same shall be done by an
official not below the rank of JE(Signal).

(c) Line Relays shall be energized at the rated voltage specified in the
specification.

Chapter 21: Relay & Electronic Interlocking Page 450 of 535