Can 12 gauge wire handle 30 amps?
No. 12 AWG copper wire is limited to a 20 amp breaker by the small-conductor rule (NEC 2023, Section 240.4(D)). A 30 amp circuit needs 10 AWG copper wire.
12 AWG copper ampacity and breaker limit
| Rating | 12 AWG copper | Can carry 30 A? |
|---|---|---|
| 60 °C ampacity | 20 A | no |
| 75 °C ampacity | 25 A | no |
| 90 °C ampacity | 30 A | ampacity only; breaker limit still applies |
| Largest breaker allowed | 20 A | no |
Why 12 AWG copper cannot be used on a 30 amp breaker
12 AWG copper has a 60 °C ampacity of 20 A and a small-conductor breaker limit of 20 A. The lower of the two, 20 A, is the largest breaker allowed, which is below 30 A.
Why the 90 °C column does not make 12 AWG a 30 amp wire
The 90 °C column is the source of the confusion. It lists a higher figure for 12 AWG copper, but that column is the starting point for derating, not the final rating of a circuit. Breakers, outlets and cable are rated 60 °C or 75 °C, and the small-conductor rule caps 12 AWG copper at a 20 amp breaker whatever the column says.
A 30 amp circuit for a dryer, water heater or RV outlet needs 10 AWG copper. On a 30 amp breaker, 12 AWG wire can overheat before the breaker trips.