Wire size for a 15 amp breaker
| Wire | Condition | Minimum size for 15 A |
|---|---|---|
| Copper | NM-B (Romex) cable or 60°C terminals | 14 AWG |
| Copper | THHN/THWN in conduit, 75°C terminals | 14 AWG |
| Aluminum | 75°C terminals | 12 AWG |
| Aluminum | 60°C terminals | 12 AWG |
14 AWG copper is rated 15 A in the 60°C column, 20 A at 75°C and 25 A at 90°C. The 75°C column lists 20 A, but NEC 240.4(D) limits 14 AWG copper to 15 A. The size above is the smallest whose ampacity is at least 15 A. Most modern breakers and panels have 75°C terminals, but a 15 A circuit is presumed 60°C unless the equipment is marked otherwise (NEC 110.14(C)).
Voltage drop: how far can 14 AWG run at 15 A?
The 14 AWG above carries 15 A safely but loses voltage over distance. At the full 15 A and 120 V, 14 AWG copper stays within the NEC's 3% recommendation for about 38 ft one way. 12 AWG stretches that to 61 ft.
| One-way distance | 14 AWG copper | 12 AWG copper | 10 AWG copper |
|---|---|---|---|
| 25 ft | 2.0% | 1.2% | 0.8% |
| 50 ft | 3.9% | 2.5% | 1.6% |
| 100 ft | 7.8% | 4.9% | 3.1% |
| 150 ft | 11.8% | 7.4% | 4.7% |
| 200 ft | 15.7% | 9.9% | 6.2% |
Percent drop at 15 A and 120 V.
Check your own 15 A run with the voltage drop calculator, or let the wire size calculator choose the size for you.
What a 15 amp circuit is used for
- Lighting circuits and smoke alarms
- General receptacles in bedrooms, hallways and living areas
- Small dedicated loads such as a bathroom fan or a garage door opener
Cable type matters
14/2 NM-B (Romex) is the standard cable here. It has two insulated conductors and a bare ground. The moment a circuit has a 20 A breaker, every wire on it has to be 12 AWG, so don't mix sizes on one circuit.
Continuous loads and common mistakes
On a 15 A breaker, a continuous load running three hours or more should not exceed 80% of the rating. That is 12 A, or about 1,440 W at 120 V. Aluminum needs 12 AWG for 15 A, so a 14 AWG aluminum circuit does not exist in the table. If you find old aluminum wiring in a house, have an electrician look at it.
For a 15 A breaker the ground wire comes from NEC Table 250.122. Use the ground wire size calculator. For other breaker sizes, see the breaker to wire size chart, or jump to 20 amps, 30 amps, 40 amps, 50 amps, 60 amps, 100 amps.
Frequently asked questions
What size wire for a 15 amp breaker?
14 AWG copper at 75°C terminals. In aluminum use 12 AWG.
How far can 14 AWG wire run on 15 amps?
About 38 feet one way at 120 V before the voltage drop passes the NEC's 3% recommendation. Past that distance, step up to 12 AWG.
What size wire for a 15 amp breaker?
14 AWG copper. In aluminum use 12 AWG.
Can I use 12 gauge wire on a 15 amp breaker?
Yes. 12 AWG copper is rated for 20 A, so it is fine on a 15 A breaker, and it is a good idea on long runs where voltage drop matters.