A breaker protects the wire. Put a breaker that is too big on a small wire and the wire can overheat before the breaker trips.
What size wire goes with a 20, 30, 40 or 50 amp breaker?
Common copper sizes in homes (with typical 60°C-rated NM "Romex" cable or terminations):
| Breaker | Copper wire (typical) |
|---|---|
| 15 A | 14 AWG |
| 20 A | 12 AWG |
| 30 A | 10 AWG |
| 40 A | 8 AWG |
| 50 A | 6 AWG* |
*Depends on the cable type and the terminal temperature rating; for example 6 AWG NM cable is rated 55 A at 60°C, which the code allows on a 60-amp breaker only under specific conditions, while individual conductors in conduit with 75°C terminations are rated higher. Your electrician applies the full code rules, ambient temperature and bundling adjustments.
Is aluminum wire OK?
Modern stranded aluminum is common for large feeders and services and needs a size or two larger than copper for the same amps. Small solid aluminum branch wiring from the 1960s and 70s is a different story: see aluminum wiring.
What about long runs?
Long runs to a detached garage, shop, well pump or EV charger may need bigger wire to limit voltage drop. Try the wire size calculator and the voltage drop calculator for a rough idea.
Common questions
What size wire for a 30 amp breaker?
Typically 10 AWG copper. Larger wire may be needed for long runs or certain conditions.
Can I put a 20 amp breaker on 14 gauge wire?
No. 14 AWG copper is limited to 15-amp overcurrent protection. A larger breaker can let the wire overheat.
General information for California homes under the California Electrical Code (based on the NEC). Local rules and inspectors can vary. Not a substitute for an on-site inspection. Never work inside a panel, at the meter or on live circuits.