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 | — |
| 16 | — | — | 18† | — |
| 18 | — | — | 14† | — |
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.
* NEC 240.4(D) caps overcurrent protection at 15A (14 AWG), 20A (12 AWG) and 30A (10 AWG) copper; 15A and 25A for 12 and 10 AWG aluminum. † 18 and 16 AWG appear only in the 90°C column and are not permitted for general branch circuits.
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).
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. NEC 240.4(D) still limits it to a 20A breaker, and NM-B cable must use the 60°C column (NEC 334.80).
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. THHN/THWN-2 is rated 90°C wet or dry, but the usable ampacity is limited by the lowest-rated termination (NEC 110.14(C)): usually 75°C for THHN in conduit, and 60°C for NM-B cable or equipment 100A and below not marked 75°C.
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).