Never assume a 4mm² cable can carry 40A simply because the table says so. The installation method and circuit length are the true determinants of its safe working current.
*Only if the full run is verified to be free of insulation packing and ambient temp ≤40°C. In Australia, a 4mm² copper cable has a nominal capacity of 36-42 amps under ideal laboratory conditions. However, real-world installations—particularly those involving insulation, high ambient temperatures, or cable grouping—can reduce this capacity by 30-50%. Always consult AS/NZS 3008.1.1 and AS/NZS 3000 (Wiring Rules), and when in doubt, upsize to 6mm² for sustained loads above 25A in enclosed or insulated spaces. current carrying capacity of 4mm cable australia
