Earthing Cable Sizing < Secure ⇒ >

Formula (copper, 1 second fault):

| Phase conductor size (mm²) | Minimum protective conductor (mm²) | |----------------------------|-------------------------------------| | ≤ 16 | Same as phase | | 25 – 35 | 16 | | 50 – 95 | 25 | | ≥ 120 | 50 | earthing cable sizing

Where ( k ) = 226 for Cu (annealed, 40°C to 250°C). Simplified: [ A_mm^2 = I \times \sqrtt \times 0.143 \quad (\textfor Cu, 1–3s) ] Most accurate for fault current withstand. From IEC 60364-5-54 : Formula (copper, 1 second fault): | Phase conductor

[ S = \frac\sqrtI^2 \times tk ]

| Largest service conductor (AWG/kcmil Cu) | GEC size (AWG Cu) | |------------------------------------------|-------------------| | 2 AWG or smaller | 8 AWG | | 1/0 – 4/0 | 4 AWG | | 250 – 500 kcmil | 2 AWG | | Over 1100 kcmil | 3/0 AWG | Used for large installations (generators, substations, industrial plants). earthing cable sizing