ELECTRIC SUPPLY LINES, SYSTEMS AND APPARATUS FOR LOW AND MEDIUM
VOLTAGES
Rule-60: Test for resistance of insulation:
(1) Where any electric supply
line for use at low or medium voltage has been disconnected from a system for
the purpose of addition, alteration or repair, such electric supply line shall
not be reconnected to the system until the supplier or the owner has applied
the test prescribed under rule 48.
(2) The provision of sub-rule (1)
shall not apply to overhead lines except, overhead insulated cables unless the
Inspector otherwise directs in any particular case.
Rule-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 normally exceeds 125 volts and of systems at medium voltage:
(a) 1[Neutral
conductor of a phase, 4 wire system and the middle conductor of a 2 phase,
3-wire system shall be earthed by not less than two separate and distinct
connections with a minimum of two different earth electrodes of such large
number as may be necessary to bring the earth resistance to a satisfactory
value both at the generating station and at the sub-station. The earth
electrodes so provided, may be interconnected to reduce earth resistance. 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 supply 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)
(i) In a
direct current three wire system the middle conductor shall be earthed at the
generating station only, and the current from the middle conductor to earth
shall be continuously recorded by means of a recording ammeter, and if any time
the current exceeds one-thousandth part of the maximum supply-current immediate
steps shall be taken to improve the insulation of the system.
(ii) Where the
middle conductor is earthed by means of a circuit breaker with a resistance
connected in parallel, the resistance shall not exceed 10 ohms and on the
opening of the circuit breaker, immediate steps shall be taken to improve the
insulation of the system, and the circuit-breaker shall be reclosed as soon as
possible.
(iii) The
resistance shall be used only as a protection for the ammeter in case of earths
on the system and until such earths are removed. Immediate steps shall be taken
to locate and remove the earth.
(e) In the
case of an alternating current system, there shall not be inserted in the
connected with earth any impedance (other than that required solely for the
operation of switch-gear of instruments), cut-out or circuit-breaker, and the
result of any test made to ascertain whether the current (if any) passing
through the connection with earth is normal shall be duly recorded by the
supplier.
(f) No person
shall make connection with earth by the aid of, nor shall be keep it in contact
with, any water main not belonging to him except with the consent of the owner
thereof and of the Inspector.
(g) 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, portable motor, and the metallic parts
(not intended as conductors) of all transformers and any other apparatus used
for regulating 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) 2[All metal castings or
metallic coverings containing 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 and to class-II apparatus/ appliances.
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.
Explanation- The words “Class-II
apparatus/appliance” will have the same meaning as assigned to these words in
the relevant ISS.]
(4) 3[All earthing systems
shall
(a) Consist of
equipotential bonding conductors capable of carrying the prospective earth
fault current and a group of pipe/rod/plate electrodes for dissipating the
current to the general mass of earth without exceeding the allowable
temperature limits as per relevant Indian Standards in order to maintain all
non-current carrying metal works reasonably at earth potential and to avoid
dangerous contact potentials being developed on such metal works;
(b) Limit
earth resistance sufficiently low to permit adequate fault current for the
operation of protective devices in time and to reduce neutral shifting;
(c) Be
mechanically strong, withstand corrosion and retain electrical continuity during
the life of the installation. All earthing systems shall be tested to ensure
efficient earthing, before the electric supply lines or apparatus are
energised.]
(5) All earthing systems
belonging to the supplier shall in addition, be tested for resistance on 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 or any officer appointed to assist the Inspector and authorised under
sub-rule (2) of rule 4A when required.
Rule-61A: 4[Earth leakage protective device:
The supply of Energy to every
electrical installation other than low voltage installation below 5 KW and
those low voltage installations which do not attract provisions of section 30
of the Indian Electricity Act, 1910, shall be controlled by an earth leakage
protective device so as to disconnect the supply instantly on the occurrence of
earth fault or leakage of current.
Provided that the above shall not
apply to overhead supply lines having protective devices which are effectively
bonded to the neutral of supply transformers and conforming to rule 91 of 1,E.
Rules, 1956.]
Rule-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.
1. Subs. by GSR 1051, Date. 25.10.1985, with effect
from: 9.11.1985.
2. Subs. by GSR 256, Date. 28.2.1983, with effect
from: 26.3.1983.
3. Subs. by GSR 358, Date. 30.4.1987, with effect
from: 9.7.1987.
4. Ins. by GSR 844, Date. 31.7.1985, with effect
from: 7.9.1985.
