Earth Conductor Sizing Calculator
AS/NZS 3000:2018 (Table 5.1 & Adiabatic methods)
Inputs
Results
Minimum Earth Conductor Size
4
mm² copper
Table 5.1 Lookup
Earth Conductor Size
4 mm² (>= 4 mm²)
Minimum 2.5mm² for active > 1mm²
4 mm² (>= 2.5 mm²)
Earth Conductor Sizing Guide — AS/NZS 3000:2018
Earth conductor sizing in Australia is governed by AS/NZS 3000:2018 (Wiring Rules). The earth conductor must be capable of carrying the maximum prospective earth fault current and safely clearing this fault within the protective device disconnection time. This calculator provides two methods: a simplified Table 5.1 lookup or a precise adiabatic equation calculation.
Two Calculation Methods
- Table 5.1 Lookup: Simplified method based on active conductor size. Suitable for general installations where fault current is not precisely known.
- Adiabatic Equation: Precise method based on prospective earth fault current and protective device disconnection time. Required for critical circuits and precise design validation.
Key Principles
- Protective earthing: The earth conductor forms the protective earthing system and must be sized to safely handle earth faults.
- Temperature rise: The adiabatic equation limits conductor temperature rise from initial (typically 75°C) to final state (typically 160°C for PVC insulation).
- Standard sizes: Both methods round to standard conductor sizes: 1, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240, 300 mm².
- Conductor material: Copper requires smaller conductors than aluminium for the same fault scenario.
When to Use Each Method
- Use Table 5.1 when:
- You know the active conductor size but have not calculated the precise prospective earth fault current.
- Use Adiabatic when:
- You have performed a fault level study and know the prospective earth fault current and protective device disconnection time.
Disclaimer: This calculator is provided as a guide only and must be verified by a qualified electrical engineer before use in design or installation. The placeholder values in Table 5.1 and k constants require CPEng validation against AS/NZS 3000:2018. Always refer to the current edition of AS/NZS 3000:2018.