Page 462 - IRSEM_Main Book

(e) Sheath & Armour of Main cables to be earthed. Armour of OFC shall be
earthed at both ends. It is not necessary to earth the armouring of
unscreened cables when they are used as a tail cables except in special
cases where the length of the tail cable exceeds normal prescribed limits.

(f) In case of signals falling within 2 meters from the electrified track, the
protection screen shall be connected to an earth.

(g) There shall not be any possibility of simultaneous human contact with
metallic bodies connected to different earths, where it is not possible to
provide suitable spacing or partition between various metallic objects
referred to above, they shall be connected to a common earth.

(h) Common/Equi-potential earth for modern electronic equipment such as EI,
DAC, Datalogger etc. to be used in Relay room. Earth value shall not be
more than one ohm and shall be measured annually during dry season.

(i) Earthing wires from subsystems to 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.

(j) All earth wires shall be as straight as possible and shall never be coiled.
Earth wires should be of adequate current carrying capacity and should
not be less than 4 Square mm copper cross-section or its equivalent.

(k) Earth resistance up to 10 ohm is normally permissible for protective earth
except when specified otherwise. For electronic equipment, Earth resistance
shall not be more than one ohm.

(l) Earthing of approved type shall be provided for each block instruments and
other signalling equipment at a station. Dedicated earthing arrangement to
be provided for earth return circuits individually if any.

(m) The resistance of earth for signalling circuits shall not exceed 10 ohm or
as prescribed by OEM/RDSO. If the resistance is more than the required
value, steps to reduce the earth resistance shall be taken. If it is still not
possible to reduce the value below the required value, even with the
adoption of these methods, additional earths may be provided in parallel.

(n) Where more than one earth electrode is used, the distance between two
earthing electrodes shall be as per approved design.

19.11.4 Earthing Leads

(a) Earth wires shall be protected against mechanical damage and possibility
of corrosion particularly at the point of connection of earth electrode.

(b) The earthing lead shall be mild steel flat of size 40 mm x 6 mm or as per
the approved earthing practice/drawing.

(c) The earthing lead shall be soldered or crimped on a lug, which shall be
bolted to the earth electrode or preferably exothermically welded. The nut
& bolt to be painted with anti corrosive paint.

Chapter 19: Installation, Testing & Maintenance of Signalling Equipment Page 410 of 535