122. Cables .-All cables, other than flexible cables for portable or transportable apparatus, shall comply with the following requirements:-
(a)All such cables (other than the outer conductor of a concentric cable) shall be covered with insulating material and shall be efficiently protected from mechanical damage and supported at sufficiently frequent intervals, and in such a manner as to prevent damage to such cables;(b)(i)Except as provided in clause (c), no cables other than concentric cables or two-core or multicore cables protected by a metallic covering or single core cables protected by a metallic covering and which contain all the conductors of a circuit shall be used-(1)where the voltage exceeds 125 volts, or(2)when an Inspector considers that there is risk of igniting gas or coal-dust or other inflammable material, and so directs;(ii)The sheath of metal-sheated cables and the metallic armouring of armoured cables shall be of a thickness not less than that recommended from time to time [in the appropriate standard of the [Bureau of Indian Standards];](c)where a medium voltage direct current system is used, two single core cables may be used for any circuit provided that their metallic coverings are bounded together by earth conductors so placed that the distance between any two consecutive bonds is not greater than 30 metres measured along either cable;(d)the metallic covering of every cable shall be-(i)electrically and mechanically continuous throughout;(ii)earthed, if it is required by sub-rule (1) of rule 117 to be earthed by a connection to the earthing system of conductivity not less than of the same length of the said metallic covering;(iii)efficiently protected against corrosion where necessary;(iv)of a conductivity at all parts and at all joints at least equal to 50 per cent of the conductivity of the largest conductor enclosed by the said metallic covering; and(v)where there may be risk of igniting gas, coal-dust, or other inflammable material, so constructed as to prevent, as far as practicable, the occurrence of open sparking so as the result of any fault or leakage from live conductors;(e)cables and conductors where connected to motors, transformers, switch-gear and other apparatus, shall be installed so that:-(i)they are mechanically protected by securely attaching the metallic covering to the apparatus; and(ii)the insulating material at each cable end is efficiently sealed so as to prevent the diminution of its insulating properties;(f)where necessary to prevent abrasion or to secure gas-tightness properly constructed glands or bushes shall be provided;(g)unarmoured cables or conductors shall be conveyed either in metallic pipes or metal casings or suspended from efficient insulators by means of non-conducting materials which will not cut the covering and which will prevent contact with any timbering or metal work. If separate insulated conductors are used, they shall be installed at least 3.75 cm. (one and one half inches) apart and shall not be brought together except at lamps, switches and fittings.
