NEC 240.4
What Size Breaker for Each Wire Gauge?
The maximum breaker that protects each copper wire size, with the NEC 240.4(D) small-conductor rule and the ampacity-based sizing for larger wire.
Max Breaker by Copper Wire Gauge
| Wire (Cu) | Ampacity 60°C | Ampacity 75°C | Max Breaker 60°C | Max Breaker 75°C |
|---|---|---|---|---|
| #14 AWG * | 15A | 20A | 15A | 15A |
| #12 AWG * | 20A | 25A | 20A | 20A |
| #10 AWG * | 30A | 35A | 30A | 30A |
| #8 AWG | 40A | 50A | 40A | 50A |
| #6 AWG | 55A | 65A | 60A | 70A |
| #4 AWG | 70A | 85A | 70A | 90A |
| #3 AWG | 85A | 100A | 90A | 100A |
| #2 AWG | 95A | 115A | 100A | 125A |
| #1 AWG | 110A | 130A | 110A | 150A |
* 14, 12, and 10 AWG are capped by the NEC 240.4(D) small-conductor rule (15A, 20A, 30A) and cannot be protected higher, whatever the ampacity shows. For 8 AWG and larger, a wire whose ampacity is between standard sizes may use the next standard breaker up (NEC 240.4(B)). Use the 60°C column for NM-B (Romex) and the 75°C column for conductors in conduit on 75°C terminals.
The Small-Conductor Rule (NEC 240.4(D))
For 14, 12, and 10 AWG the breaker size is fixed no matter what the ampacity table says. Copper 14 AWG is protected at 15A, 12 AWG at 20A, and 10 AWG at 30A. This overrides the higher 75°C and 90°C ampacities, because small conductors heat quickly and the overcurrent device must trip before the insulation is damaged. It is the rule behind nearly every residential circuit.
The reverse of this page is the wire size for a given breaker, and the two must always agree: the wire and the breaker go up together. Never install a larger breaker to power a bigger load on existing wire, because the breaker protects the conductor, not the appliance.
Frequently Asked Questions
What size breaker for 10 gauge wire?
A 30 amp breaker. NEC 240.4(D), the small-conductor rule, caps 10 AWG copper at 30 amps no matter what the ampacity table shows, so a 10 AWG conductor is protected at 30A maximum. This is the firm answer for 10 AWG copper on a 30A / 240V dryer or water-heater circuit; 10 AWG aluminum is limited to 25A.
What size breaker for 12 gauge wire?
A 20 amp breaker. NEC 240.4(D) caps 12 AWG copper at 20 amps, so it is used on standard 20A general-purpose and small-appliance circuits. Never put 12 AWG on a 30A breaker: the small-conductor rule forbids it, and the wire could overheat before the breaker trips. 12 AWG aluminum is limited to 15A.
What size breaker for 8 gauge wire?
8 AWG copper is protected at 40 amps using the 60C column (NM-B cable) and up to 50 amps on 75C terminations in conduit. Its ampacity is 40A at 60C and 50A at 75C (NEC 310.16). 8 AWG is common on 40A and 50A circuits such as ranges, ovens, and hardwired EV chargers.
What size breaker for 6 gauge wire?
6 AWG copper carries 55A at 60C and 65A at 75C (NEC 310.16). Because neither is a standard breaker size, NEC 240.4(B) permits the next standard size up: 60A at 60C or 70A at 75C. In practice 6 AWG copper is used on 50A and 60A circuits (ranges, hot tubs, 48A EV chargers).
Why can't I put a bigger breaker on small wire?
Because the breaker protects the wire, not the load. NEC 240.4(D) sets a hard cap on 14, 12, and 10 AWG (15A, 20A, 30A) regardless of the ampacity table, because small conductors heat up fast and a properly matched breaker must trip before the insulation is damaged. Oversizing the breaker to run a bigger load is the single most dangerous wiring mistake: the wire becomes the fuse. Size the wire up first, then the breaker.
Does the breaker size change for aluminum wire?
Yes. Aluminum has lower ampacity, so it needs a larger gauge for the same breaker. The 240.4(D) small-conductor caps for aluminum are 15A for 12 AWG and 25A for 10 AWG. For larger circuits, use the 75C aluminum column: for example, 6 AWG aluminum carries 50A versus 6 AWG copper at 65A.
Related Calculators
Wire Size Calculator
The reverse: the conductor for a given breaker and load per NEC 310.16, with derating.
Wire Ampacity Chart
The full NEC 310.16 ampacity table at 60, 75, and 90 degrees C, copper and aluminum.
Wire & Breaker for Appliances
The breaker and wire for a dryer, range, water heater, EV charger, and more.