Page 146 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Rule no.61: Connection with earth
1 The following provisions shall apply to the connection with earth of systems at low voltage in cases where the
voltage between phases or outers normally exceeds 125 volts and of systems at medium voltage.

a The neutral conductor of a three-phase four-wire system, and the middle conductor of a two-phase three-
wire system shall be earthed by not less than two separate and distinct connections with earth both at the
generating station and at the substation. It may also be earthed at one or more points along the distribution
system or service line in addition to any connection with earth which may be at the consumer’s premises.
b In the case of a system comprising electric sypply lines having concentric cables, the external
conductor of such cables shall be earthed by two separate and distinct connections with earth.
c The connection with earth may include a link by means of which the connection may be temporarily
interrupted for the purpose of testing or for locating a fault.
d In the case of an alternating current system, there shall not be inserted in the connection with earth
any impedance (other than that required solely for the operation of switchgear or instrumets), cut-out or
circuit-breaker, and the result of a test made to ascertain whether the current (if any) passing through the
connection with earth is normal, shall be duly recorded by the supplier.
e No person shall make connection with earth by the aid of, nor shall keep it in contact with, any water main
not belonging to him except with the consent of the owner thereof and of the inspector.
f Alternating current systems which are connected with earth as aforesaid may be electrically interconnected.
Provided that each connection with earth is bonded to the metal sheathing and metallic armouring (if any)
of the electric supply lines concerned.
2 The frame of every generator, stationary motor, and so far as is practicable, portable motor, and the metallic
parts (not intended as conductors) of all transformers and any other apparatus used for regulation or controlling
energy and all medium voltage energy consuming apparatus shall be earthed by the owner by two separate
and distinct connections with earth.
3 All metal casings or metallic coverings contained or protecting any electric supply-line or apparatus shall be
connected with earth and shall be so joined and connected across all junction-boxes and other openings as to
make good mechanical and electrical connection throughout their whole length:
Provided that where the supply is at low voltage, this sub-rule shall not apply to isolated wall tubes or to brackets,
electroliers, switches, ceiling fans or other fittings (other than portable hand lamps and portable and transportable
apparatus) unless provided with earth terminal.
Provided further that where the supply is at low voltage and where the installations are either new or renovated,
all plug sockets shall be of the three-pin type and the third pin shall be permanently and efficiently earthed.
4 All earthing systems shall, before electric supply lines or apparatus are energised, be tested for electrical
resistance to ensure efficient earthing.
5 All earthing systems belonging to the supplier shall, in addition, be tested for resistance on a dry day during
the dry season not less than once every two years.

6 A record of every earth test made and the result thereof shall be kept by the supplier for a period of not less
than two years after the day of testing and shall be available to the Inspector when required.
Rule no.62: Systems at medium voltage
Where a medium voltage supply system is employed, the voltage between earth and any conductor forming part
of the same system shall not, under normal conditions, exceed low voltage.
Rule no.67: Connection with earth
1 The following provisions shall apply to the connection with earth of three-phase systems for use at high or
extra-high voltages:-

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