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Chapter-VI- Indian Electricity Rules

Indian electricity rules, 1956

Electric supply lines, systems and apparatus for low and medium voltages

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 or 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.

The provisions of sub-ru1e (1) shall not apply to overhead lines except overhead insulated cables unless the Inspector otherwise directs in any particular case.

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:-

1(a) Neutral conductor of a 3-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 or 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 inter connected 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 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 at 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 to 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 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 connection with earth any impedance (other than that required solely for the operation of switch-gear or 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 he 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 armoring (if any) of the electric supply lines connected.

(2) The frame of every generator, stationary motor, 2* * * portable motor, and the metallic parts (not in tended 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(3) All metal casings 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 connections throughout their whole length :

PROVIDED that where the supply of energy is at low voltage, this sub-rule shall not apply to the 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 an earth teImina1 and to Class II apparatuses / appliances:

PROVIDED FURTHER that where the supply of energy is at low voltage and where the installations are either new or renovated all plug sockets shall be of the three-pin types, 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(4) All earthing systems sha1l-

(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 5or any officer appointed to assist the Inspector and holding gazetted rank and 6authorised under sub-rule (2) of rule 4A when required.

761A. 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 Indian Electricity Rules, 1956.

62. Systems at medium voltage

When 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 Substituted by GSR 1051, dt. 25-10-1985, w.e.f. 9-11-1985. 
2 Certain words omited by GSR 1723, dt 21-11-1977, w.e.f. 31-12-1977. 
3 Substituted by GSR 256, dt. 28-2-1983, w.e.f. 26-3-1983. 
4 Substituted by GSR 358 dt. 30-4-1987, w.e.f. 9-5-1987.
5 Inserted by GSR 522, dt.17-3-1970, w.e.f. 4-4-1970.
6 Substituted by GSR 1723, dt. 21-11-1977, w.e.f. 31-12-1977.
7 Inserted by GSR 844, dt. 31-7-1985, w.e.f.7-9-1985.

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