Wire size for a 20 amp breaker
| Wire | Condition | Minimum size for 20 A |
|---|---|---|
| Copper | NM-B (Romex) cable or 60°C terminals | 12 AWG |
| Copper | THHN/THWN in conduit, 75°C terminals | 12 AWG |
| Aluminum | 75°C terminals | 10 AWG |
| Aluminum | 60°C terminals | 10 AWG |
12 AWG copper is rated 20 A in the 60°C column, 25 A at 75°C and 30 A at 90°C. The 75°C column lists 25 A, but NEC 240.4(D) limits 12 AWG copper to 20 A. The size above is the smallest whose ampacity is at least 20 A. Most modern breakers and panels have 75°C terminals, but a 20 A circuit is presumed 60°C unless the equipment is marked otherwise (NEC 110.14(C)).
Voltage drop: how far can 12 AWG run at 20 A?
The 12 AWG above carries 20 A safely but loses voltage over distance. At the full 20 A and 120 V, 12 AWG copper stays within the NEC's 3% recommendation for about 46 ft one way. 10 AWG stretches that to 72 ft.
| One-way distance | 12 AWG copper | 10 AWG copper | 8 AWG copper |
|---|---|---|---|
| 25 ft | 1.6% | 1.0% | 0.7% |
| 50 ft | 3.3% | 2.1% | 1.3% |
| 100 ft | 6.6% | 4.1% | 2.6% |
| 150 ft | 9.9% | 6.2% | 3.9% |
| 200 ft | 13.2% | 8.3% | 5.2% |
Percent drop at 20 A and 120 V.
Check your own 20 A run with the voltage drop calculator, or let the wire size calculator choose the size for you.
What a 20 amp circuit is used for
- General receptacle circuits and kitchen small-appliance circuits (two or more 20 A circuits are required in a kitchen)
- Bathroom, garage and laundry receptacles
- Window air conditioners and dedicated circuits for a refrigerator, microwave or dishwasher
- 20 A 240 V loads such as small baseboard heaters
Cable type matters
12/2 and 12/3 NM-B (Romex) have 12 AWG conductors and are rated 20 A. 14/2 cable must never be paired with a 20 A breaker. A 20 A circuit with several receptacles may use 15 A or 20 A receptacles, but a single receptacle on its own circuit must be rated 20 A.
Continuous loads and common mistakes
On a 20 A breaker, a continuous load running three hours or more should not exceed 80% of the rating. That is 16 A, or about 1,920 W at 120 V. A frequent mistake is putting 12 AWG aluminum on a 20 A breaker. It is limited to 15 A, so aluminum needs 10 AWG for 20 A.
For a 20 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 30 amps, 40 amps, 50 amps, 60 amps, 100 amps.
Frequently asked questions
What size wire for a 20 amp breaker?
12 AWG copper at 75°C terminals. In aluminum use 10 AWG.
How far can 12 AWG wire run on 20 amps?
About 46 feet one way at 120 V before the voltage drop passes the NEC's 3% recommendation. Past that distance, step up to 10 AWG.
Can I use 14 gauge wire on a 20 amp breaker?
No. 14 AWG copper is limited to a 15 amp breaker by NEC 240.4(D). Use 12 AWG for 20 amps.
What size wire for a 20 amp 240 volt circuit?
12 AWG copper, the same as a 120 V circuit. The higher voltage lets the wire run twice as far for the same percentage drop.