Wire Derating Chart May 2026

At 55°C ambient, the factor is .

Multiply the wire’s original 90°C ampacity (30A for 12 AWG) by 0.71: wire derating chart

Without derating, that 16-amp load would push conductor temperature over the limit. Insulation hardens, cracks, and eventually shorts. Alex opens the NEC (National Electrical Code) Table 310.16 — the standard wire derating chart. It tells him: At 55°C ambient, the factor is