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.
Intry Verified. The maximum-breaker values in the chart below and the YES/NO verdict matrix are not typed in by hand. Each one is computed from the cited NEC sections (240.4(B), 240.4(D), and Table 310.16) by the same locked engine on every build. Those figures are computed by a locked engine straight from the source it cites, not hand-typed, and that computation re-runs inside a deterministic test on every deploy. Source-checked. Locked. This is our own deterministic gate, not a third-party audit. What Intry Verified means
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.
Can I Put a Bigger Breaker On This Wire?
For 14, 12, and 10 AWG copper the answer does not depend on the temperature column: NEC 240.4(D) fixes the maximum breaker at 15A, 20A, and 30A. Below, a Yes means the NEC permits that breaker on that wire; a No means it exceeds the 240.4(D) cap and is not permitted.
| Wire (Cu) | 15A breaker | 20A breaker | 30A breaker | 40A breaker |
|---|---|---|---|---|
| #14 AWG (max 15A) | Yes | No | No | No |
| #12 AWG (max 20A) | Yes | Yes | No | No |
| #10 AWG (max 30A) | Yes | Yes | Yes | No |
A No is never fixed by swapping the breaker: to run a bigger load you size the wire up first, then the breaker follows. This matrix is the general-purpose branch-circuit rule; motor, air-conditioning, and welder circuits follow their own exceptions (NEC 240.4(E) through (G)) and are sized from Article 430/440 or the nameplate, not this cap.
Frequently Asked Questions
Can I put a 20 amp breaker on 14 gauge wire?
No. NEC 240.4(D) caps 14 AWG copper at 15 amps, so a 20A breaker is not permitted on 14 AWG regardless of the load. A 20A circuit requires 12 AWG copper. Putting a 20A breaker on 14 AWG means the wire can carry more current than it is rated for before the breaker trips, which is why the small-conductor rule forbids it.
Can I put in a bigger breaker to run a bigger load?
No, not on the same wire. The breaker protects the conductor, not the appliance, so its size is fixed by the wire it protects: 14 AWG = 15A, 12 AWG = 20A, 10 AWG = 30A copper (NEC 240.4(D)). To power a bigger load you size the wire up first, then the breaker follows. Swapping in a larger breaker on existing wire is the single most dangerous wiring mistake, because the wire becomes the fuse.
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.
Is the Intry Breaker Size Chart accurate and NEC compliant?
Every figure an Intry calculator computes comes from a locked source module, not hand-typed. 21026 automated checks re-derive and source-check the numbers against the cited NEC section before each deploy. This is our own deterministic gate, not a third-party audit. The per-tool receipt is public at https://www.intrysys.com/verified.
Related Calculators
What Size Breaker Do I Need?
The breaker for a specific load (stove, dryer, water heater, EV charger) and how to size any breaker from watts.
Wire Size Calculator
The reverse: the conductor for a given breaker and load per NEC 310.16, with derating.
Wire Ampacity Chart
What the conductor carries in your actual conditions, and the largest device it takes, copper and aluminum.
Wire & Breaker for Appliances
The breaker and wire for a dryer, range, water heater, EV charger, and more.
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