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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