Earthing Conductor Sizes

The following table lists the recommended minimum sizes of earthing conductors.
Note: This serves only as a guide, calculations are still required for verification.

Minimum Copper Earthing Conductor Size
Nominal size of active conductor mm²	Nominal size of copper earthing conductor
	mm²
	With copper active conductors	With aluminium active conductors
1	1*	-
1.5	1.5*	-
2.5	2.5	-
4	2.5	-
6	2.5	-
10	4	-
16	6	4
25	6	6
35	10	6
50	16	10
70	25	10
95	25	16
120	35	25
150	50	25
185	70	35
240	95	50
300	120	70
400	≥120⁺	≥95⁺
500	≥120⁺	≥95⁺
630	≥120⁺	≥120⁺
>630	≥25% of active size⁺	≥25% of active size⁺

* - May be used only when incorporated in a multicore cable
+ - A larger conductor may be required.

Source: AS/NZ 3000-2007, Table 5.1

Update (29-Jan-2011):
Calculating the fault loop impedance of a circuit will provide a more precise selection of the size of the earth conductor. See the article on fault loop impedance for more details.

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