What Size Wire for a 20 Amp Breaker?
A 20 A breaker needs 12 AWG copper with 75°C terminations (NEC Table 310.16). Longer runs may need a size up for voltage drop — distances below.
Minimum wire size for 20 amps
| Application | Copper (75°C) | Aluminum (75°C) |
|---|---|---|
| Branch circuit / feeder (Table 310.16) | 12 AWG | not typical |
Worth knowing: 12 AWG copper is capped at a 20 A breaker by NEC 240.4(D).
Assumes 75°C-rated terminations (NEC 110.14(C)) and no more than three current-carrying conductors in a raceway at 30°C ambient. Derating, continuous loads, and local amendments can change the answer — confirm with a licensed electrician.
How far can you run it? (voltage drop)
Keeping voltage drop under the recommended 3% at a 16 A load (80% of the breaker), 12 AWG copper is good for roughly:
| System voltage | Max one-way run (12 AWG Cu) |
|---|---|
| 120 V | ≈ 56 ft |
| 240 V | ≈ 113 ft |
Past these distances, step up one gauge. Run your exact length and load through the voltage drop calculator.
What runs on 20 amps
- Kitchen small-appliance circuits
- Bathroom & garage outlets
- Laundry receptacle
Common receptacle at this rating: NEMA 5-20.
Frequently asked questions
12 AWG copper with 75°C terminations (NEC Table 310.16, with the NEC 240.4(D) small-conductor cap applied). Aluminum is rarely used at this rating. Longer runs, high ambient temperatures, or bundling can require upsizing.
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