How to determine the size of earthing conductor?

What is earthing conductor?

BS 7671 defined earthing conductor as...

A conductor which provides a conductive path, or part of the conductive path, between a given point in a system or in an installation or in equipment and an earth electrode.

It is very important to determine the proper size of earthing conductor to ensure safety of every in every electrical system design.

The following table provide us the formula on how to compute the right size of earthing conductor:

Cross Sectional Area of the line conductor, S mm2	Minimum cross-sectional area of the corresponding protective conductor, mm2
	If the protective conductor is of the same material as the line conductor	If the protective conductor is not of the same material as the line conductor
S is lesser than or equal to 16	S	(k1/k2) x S
S is more than 16 but lesser than or equal to 35	16	(k1/k2) x 16
S is more than 35	S/2	(k1/k2) x (S/2)

where:

k1 = the k value of line conductor define by IEC

k2 = the k value of  earth conductor define by IEC

Source: IEC60364-5-54 Annex A