Page 147 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

In the case of star-connected with earthed neutrals or delta-connected systems with earthed artificial neutral point
a The neutral point shall be earthed by not less than two separate and distinct connections with earth, each
having its own electrode at the generating station and at the sub-station and may be earthed at any other
point, provided that no interference of any description is caused by such earthing;
b In the event of an appreciable harmonic current flowing in the neutral connections so as to cause
interference with communication circuits, the generator or transformer neutral shall be earthed through a
suitable impedance.
2 In the case of a system comprising electric supply lines having concentric cables, the external conductor
shall be the one to be connected with earth.
3 Where the earthing lead and earth connection are used only in connection with earthing guards erected under
high or extra-high voltage overhead lines where they cross a telecommunication line or a railway line, and
where such lines are equipped with earth leakage relays of a type and setting approved by the Inspector, the
resistance shall not exceed 25 ohms.

Rule no.69: Pole type substations
1 Where platform type construction is used for a pole type substation and sufficient space for a person to stand
on the platform is provided, a substantial hand rail shall be built around the said platform, and if the hand rail
is of metal, it shall be connected with earth:
Provided that in the case of pole type substation on wooden support and wooden platform the metal hand-rail
shall not be connected with earth.
Rule no.88: Guarding
1 Every guard-wire shall be connected with earth at each point at which its electrical continuity is broken.
Rule no.90: Earthing
1 All metal support of overhead line and metallic fittings attached thereto, shall be permanently and efficiently
earthed. For this purpose a continuous earth wire shall be provided and securely fastened to each pole and
connected ordinarily at four points in every mile or 1.601 km, the spacing between the points being as nearly
equidistant as possible. Alternatively, each support and metallic fitting attached thereto shall be efficiently
earthed.

2 Each stay-wire shall be similarly earthed unless an insulator has been placed in at a height not less than 10 ft.
from the ground.

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CITS : Power - Electrician & Wireman - Lesson 20-25