Page 520 - IRSEM_Main Book

(i) External Lightning Protection on Top of Buildings housing S&T
equipment.

(ii) Class B/Type-I devices at the Input of Power Supply Equipment.

(iii) Class C/Type-II devices at Output of Power Supply Equipment.

(iv) Class D/Type-III devices at Indoor and Field Equipment.

21.7.2 Earthing for Electronic Interlocking

(a) Earthing shall be provided as per approved specifications, drawings and
code of practice.

(b) To the extent possible, perimeter earth shall be provided around the
Electronic Interlocking room.

(c) Earth value shall be less than one ohm and shall be measured annually
during dry season.

(d) Copper tape (Bonding ring conductor) as per drawing mounted on
insulated stand-off is provided to cover the maximum area in the Relay
room and the connection to equipment shall be made at the nearest point.

(e) Earth wire from Surge protection device to main earth terminal inside the
room should be as straight and short as possible to provide a low
impedance path for discharge of surge energies.

(f) Earthing wires from electronic interlocking subsystems to main earth
terminal shall be of distinctive color. Green or Green Yellow (GNYE) color
is recommended for quick identification of a loose or disconnected earth
wire.

(g) All earth wires shall be as straight as possible and shall never be coiled.
All Earth wires should be made of copper of adequate current carrying
capacity and should never be less than 4 Sq.mm cross section.

Chapter 21: Relay & Electronic Interlocking Page 463 of 535