MasterElecWire size · NEC 2023
What size wire for 30 amps?
10 AWG copperThat's the minimum for a typical 30-amp circuit. 12 AWG copper is not permitted on a 30-amp breaker.
Why 10 AWG
10 AWG copper is rated 30 A in the 60°C column of Table 310.16, and 240.4(D) allows it on a breaker up to 30 A.
| Size | 60°C | 75°C | Note |
|---|---|---|---|
| 12 AWG copper | 20 A | 25 A | 240.4(D) limit: 20 A |
| 10 AWG copper | 30 A | 35 A | 240.4(D) limit: 30 A |
12 AWG shows 25 A at 75°C, but its breaker is limited to 20 A, so it can never go on a 30-amp circuit.
What about aluminum?
Use 8 AWG aluminum or copper-clad aluminum, rated 35 A at 60°C. 10 AWG aluminum falls short at 25 A in that column.
Ground wire
Table 250.122 gives a minimum 10 AWG copper equipment grounding conductor for a 30-amp breaker.
Long runs: check voltage drop
A 30 A load, 100 ft one way, on 240 V single-phase, with 10 AWG copper drops about 7.5 V, or 3.1%. Longer runs may need a larger wire.
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Get MasterElec on iPhoneGeneral guidance for a typical circuit under NEC 2023. Ambient temperature, bundling, terminations and local amendments can change the result. Check the code adopted in your area and your local inspector. Spot an error? Email contact@twoscripts.com.