Page 506 - IRSEM_Main Book

Section 2: Installation & Testing of Relays

21.2.1 Relays – General Requirements:

(a) Approved type of Plug-in Line relays of Neutral/Polar Biased/Magnetic
latch/Interlocked type rated at 24/48/60 V DC shall normally be used. Approved
type of LED Lamp proving relays shall be used for LED signal lamps.

(b) Approved type of Relays shall be used in RE & Non-RE areas. Various
types of relays used in signaling are given in Annexure: 21-A1.

(c) Time element relays of approved type shall be used. Where approved
electronic time element relays are used, these shall be two in number and
their contacts shall be in series in the concerned time release circuits.

(d) The relays, including track relays, located in the track side location boxes,
shall be plug-in type.

(e) All plug-in relays and relay groups shall be provided with coding pin
arrangement to prevent the wrong relays/relay group being accidentally
plugged-in during replacement. All relays, relay groups shall be sealed.

(f) As far as possible, all relays shall be housed in the relay room of the
controlling cabin to achieve maximum centralization.

(g) Sequential proving of front and back contact shall be ensured where metal
to metal contact relays are provided.
(h) Removal or replacement of plug-in relays/relay groups from the relay racks
during operation shall not cause any unsafe conditions in the circuits.

(i) Where feasible all relays except track relays, shall have 10% of working
contacts as spare subject to a minimum of one front and one back to
facilitate addition and alteration to the circuits at a later date. Extra space
(minimum 10%) to accommodate repeater relays shall be provided in the
relay rack to cater for future expansion.

(j) Where magnetic latch relays are used, the circuit shall be so designed so
as to prevent undue dropping of the relay due to back EMF generated by
other relays.

(k) Wiring of 'Q' type relays shall be done through flexible multi strand wire
preferably and contacts to be paralleled as feasible.

(l) Mercury wet contact type relay shall be used for flasher circuits,
alternatively, a solid state flasher may be used. If solid state flasher is
used, flashing indication on operating panel should be provided for
indicating healthy condition of flasher.

(m) Relays shall not be stored in the vicinity of damp or chemically polluted
environment.

(n) Sealing screws of the relays shall be intact.

(o) Care shall be exercised in transporting the relays from the place of storage
to the work site so that the relays do not get damaged.

Chapter 21: Relay & Electronic Interlocking Page 449 of 535