In Australia, earth cable size can be determined using Table 5.1 in AS/NZS 3000:2018 or by calculation.
Table 5.1 works by specifying a minimum earth cable size based on the active conductor size and the material. The method below is conservative and often over-sizes the earth cable.
Read our article Protective Earth Cable Sizing for equations and example calculations.
Cable Pro Web Software calculates earth cable size based on fault loop impedance and short-circuit performance, which results in smaller earth cable sizes.
Try our other 12 Free Electrical Calculators.
The following are important notes about earth conductor sizing from AS/NZS 3000:2018.
The earthing conductor cross-sectional area must meet the following criteria (Section 5.3.3.1.1):
- Adequate short-circuit rating for the prospective earth fault current and fault clearing time of the associated protective device. Refer to this article about short circuit rating calculations.
- Appropriate earth fault loop impedance. Refer to this article about understanding fault loop impedance.
- Adequate mechanical strength and resistance to the external environment.
- To allow for deterioration in conductivity of elements (other than earth cables) part of the earth loop impedance.
Section 5.3.3.1.2 states any copper protective earthing conductor can be determined either:
- from Table 5.1 in relation to the cross-sectional area of the largest active conductor; or
- by calculation based on short-circuit rating (and fault loop impedance)
