What Size Wire for a 25 Amp Breaker?
A 25 A breaker needs 10 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 25 amps
| Application | Copper (75°C) | Aluminum (75°C) |
|---|---|---|
| Branch circuit / feeder (Table 310.16) | 10 AWG | not typical |
Worth knowing: 12 AWG would carry 25 A in the 75°C column, but NEC 240.4(D) caps it at 20 A — so a 25 A breaker needs 10 AWG copper.
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 20 A load (80% of the breaker), 10 AWG copper is good for roughly:
| System voltage | Max one-way run (10 AWG Cu) |
|---|---|
| 120 V | ≈ 72 ft |
| 240 V | ≈ 144 ft |
Past these distances, step up one gauge. Run your exact length and load through the voltage drop calculator.
What runs on 25 amps
- Small mini-split condensers
- Hot tub sub-circuits
Frequently asked questions
10 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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