Code reference · NEC Table 310.16; 240.4(D); 110.14(C); 310.15
NEC Table 310.16 ampacity, explained
Table 310.16 gives allowable ampacities for insulated copper and aluminum conductors, up to three current-carrying conductors in raceway or cable, at 30°C ambient. The three columns are insulation temperature ratings: 60°C (TW), 75°C (THWN), 90°C (THHN/XHHW-2).
Common copper values (60/75/90°C): 14 AWG 15/20/25 A · 12 AWG 20/25/30 A · 10 AWG 30/35/40 A · 8 AWG 40/50/55 A · 6 AWG 55/65/75 A · 4 AWG 70/85/95 A · 2 AWG 95/115/130 A · 1/0 125/150/170 A · 4/0 195/230/260 A.
Three traps: (1) 240.4(D) caps small-conductor overcurrent devices at 15/20/30 A for 14/12/10 AWG copper regardless of the 90°C column; (2) terminations are usually rated 60/75°C — the 90°C column is a derating basis, not a free lunch (110.14(C)); (3) above 30°C ambient or more than 3 conductors, apply the 310.15 correction factors.
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