You cannot determine cable size by cross-sectional area alone. Several environmental and installation factors "derate" (reduce) the capacity of the cable: A. Ambient Temperature
Actual capacity varies by standard (e.g., IEC, BS 7671, or NEC), but typical ratings for common copper cables include: 4mm twin and earth current carrying capacity - Quickbit UK
If the current exceeds the cable’s capacity, the heat generated will be greater than the heat the cable can dissipate. This causes the conductor's temperature to rise. If the temperature rises beyond the thermal limit of the cable’s insulation (sheathing), the insulation will degrade, melt, or catch fire. cable size current carrying capacity
In general, the larger the cross-sectional area of the conductor (measured in mm2m m squared
He handed her a worn copy of the electrical code, dog-eared at the ampacity tables. You cannot determine cable size by cross-sectional area
or AWG), the lower its electrical resistance. Lower resistance means less heat is generated, allowing the cable to carry more current. Small Cables (e.g., 1.5mm21.5 m m squared
): Used for lighting circuits with low current requirements. Medium Cables (e.g., 6mm26 m m squared 10mm210 m m squared This causes the conductor's temperature to rise
“Rule one,” he said. “Respect the derating factors. Rule two—there is no rule two. Just don’t trust a cable in a vacuum.”