Ampacity is the maximum continuous current (in amps) a wire can carry safely without overheating its insulation. NEC Table 310.16 lists ampacity for conductors in conduit at ambient temperature of 30°C (86°F).

What is the ampacity of 12 AWG copper wire?

12 AWG copper wire has an ampacity of 20A at 60°C, 25A at 75°C, and 30A at 90°C insulation rating per NEC Table 310.16. Most residential wiring uses the 75°C column (THWN-2 insulation).

Why does insulation temperature affect ampacity?

Higher-rated insulation can withstand more heat, allowing more current through the same conductor. NEC publishes ampacity values at 60°C, 75°C, and 90°C. Most modern THWN-2 wire is rated to 75°C in wet locations, so the 75°C column applies.

What is the ampacity of 10 AWG wire?

10 AWG copper wire has an ampacity of 30A at 60°C, 35A at 75°C, and 40A at 90°C per NEC Table 310.16. 10 AWG aluminum wire rates at 25A (60°C), 30A (75°C), 35A (90°C).

Wire Ampacity Tables

Allowable ampacities of insulated conductors based on NEC Table 310.16. Not more than 3 current-carrying conductors in raceway or cable, 30°C ambient temperature.

AWG	Cu 60°C (TW, UF)	Cu 75°C (THWN)	Cu 90°C (THHN)	Al 75°C
4/0	195	230	260	180
3/0	165	200	225	155
2/0	145	175	195	135
1/0	125	150	170	120
1	110	130	145	100
2	95	115	130	90
3	85	100	115	75
4	70	85	95	65
6	55	65	75	50
8	40	50	55	40
10	30	35	40	30
12	20	25	30	20
14	15	20	25	None
16	None	13	18	None
18	None	10	14	None

Note: These ampacity values assume no more than 3 current-carrying conductors in a raceway, cable, or direct burial at 30°C ambient temperature. Derate for higher temperatures, more conductors, or conduit fill per NEC 310.15.

Circuit breaker size chart → Wire types and insulation ratings → NEC Table 310.16 — conductor ampacity → NEC Table 310.15 — derating factors →

Wire Ampacity Tables

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