Wire size
12 AWG
Copper
What size wire for a 15 amp 120 volt circuit?
Short answer
12 AWG copper
A 15 A circuit at 120 V takes 12 AWG copper wire on a 15 A breaker, as long as the run stays under 75 ft.
Breaker
15 A
Longest run
75 ft
Longest run at 3% drop
Why 12 AWG
- Ampacity: 14 AWG copper is rated 15 A in the 60 degC column of NEC Table 310.16, which covers the 15 A this circuit needs.
- Voltage drop: 14 AWG would carry the current, but it would drop 3.2% over 50 ft. 12 AWG brings it to 2%.
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 |
|---|---|
| 14 AWG | 47 ft |
| 12 AWG | 75 ft |
| 10 AWG | 120 ft |
| 8 AWG | 191 ft |
| 6 AWG | 303 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.