MasterElecWire size · NEC 2023
Can I use 14 gauge wire on a 20-amp breaker?
No, not in general240.4(D) limits 14 AWG copper to a 15-amp breaker, unless 240.4(E) or 240.4(G) specifically permits otherwise.
Why it isn't allowed
Table 310.16 shows 14 AWG copper at 20 A in the 75°C column, which makes it look fine. But 240.4(D) sets a separate limit on the breaker size for small conductors.
| Size | 60°C | 75°C | Note |
|---|---|---|---|
| 14 AWG copper | 15 A | 20 A | 240.4(D) limit: 15 A |
| 12 AWG copper | 20 A | 25 A | 240.4(D) limit: 20 A |
What to do instead
- Keep the 20-amp circuit: the wire needs to be 12 AWG copper.
- Keep the 14 AWG wire: protect it with a breaker of 15 A or less, if the circuit's load allows it.
The exceptions
240.4(D) opens with "unless specifically permitted in 240.4(E) or 240.4(G)". Those sections cover specific cases, so confirm yours is listed before relying on them.
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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.