Section 117(3) in The Indian Electricity Rules, 1956
(3)All conductors of an earthing system shall have conductivity, at all parts and all joints, at least equal to 50 per cent of that of the largest conductor used solely to supply the apparatus, a part of which it is desired to earth:Provided that no conductor of an earthing system shall have a cross-sectional area less than 0.15 sq. cm. except in the case of the earth conductor of a flexible cable used with portable apparatus where the voltage does not exceed 125 volts, and the cross-sectional area and conductance of the earthcore is not less than that of the largest of the live conductors in the cable.
