Formula (copper, 1 second fault):
[ A_mm^2 = I \times \sqrt\fract\Delta T \times k ] 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): [ A_mm^2 =
| 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