Wire size
10 AWG
Copper
What size wire for a 30 amp 120 volt circuit?
Short answer
10 AWG copper
A 30 A circuit at 120 V takes 10 AWG copper wire on a 30 A breaker, as long as the run stays under 60 ft.
Breaker
30 A
Longest run
60 ft
Longest run at 3% drop
Why 10 AWG
- Ampacity: 10 AWG copper is rated 30 A in the 60 degC column of NEC Table 310.16, which covers the 30 A this circuit needs.
How far you can run it
Past a certain length the wire still carries the current safely, but too much voltage is lost on the way. These are the lengths where you should move up a size.
| Wire size | Longest run at 3% drop |
|---|---|
| 10 AWG | 60 ft |
| 8 AWG | 95 ft |
| 6 AWG | 151 ft |
| 4 AWG | 241 ft |
| 3 AWG | 304 ft |
One-way distance, copper, 120 V.
Before you buy
- Check what your breaker terminals are rated for. Most residential breakers are 60 degC or 75 degC, and that is the column you must use, not the 90 degC column on the wire jacket.
- If the load runs three hours or more at a stretch, size for 125% of it. That is most heating, EV charging and shop lighting.
- Local amendments beat the national Code. Your inspector has the last word.