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 |
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