AQ: Earthing conductors size calculation
1. As per IEE/BS7671, The Minimum cross-sectional area of protective conductor in relation to the cross-sectional area of associated line conductor (Say =S mm2) by taking into consideration that are of same material, as follows:
If S ≤ 16 then the Minimum cross-sectional area of the corresponding earth conductor = S mm2
If 16 < S ≤ 35 then the Minimum cross-sectional area of the corresponding earth conductor = 16 mm2
if S > 16 , then the Minimum cross-sectional area of the corresponding earth conductor = S/2 mm2
2. It may be necessary to verify the same by using the following equation
I²t ≤ S²K
I earth fault current and t tripping time.
while the following equation is applicable for bonding conductor
Zs < 50/Ia where Zs = Earth loop impedance and Ia is protective device operating current
