Section 122(2)(g) in The Indian Electricity Rules, 1956
(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.