What Size Wire for a 15 Amp Circuit?
Use 14 AWG copper for a 15 amp breaker. With aluminum wire the smallest size is 12 AWG. For long runs you may need thicker wire to limit voltage drop.
The answer
14 AWG copper
12 AWG aluminum (75 °C terminals)
| Case | Wire size | Table ampacity | Area |
|---|---|---|---|
| Copper · 75 °C THHN in conduit, most modern equipment | 14 AWG | 20 A | 2.1 mm² |
| Copper · 60 °C NM / Romex cable, older terminals | 14 AWG | 15 A | 2.1 mm² |
| Aluminum · 75 °C Needs connectors and terminals listed for aluminum | 12 AWG | 20 A | 3.3 mm² |
On this page
How the answer is worked out
The breaker is 15 A. The smallest copper wire with a 75 °C table ampacity at or above 15 A is 14 AWG, rated 20 A, with a cross-section of 2.1 mm².
For 60 °C terminals or NM cable the smallest copper size is 14 AWG, rated 15 A in the 60 °C column.
Aluminum uses its own column. The smallest aluminum size at 75 °C for this rating is 12 AWG, rated 20 A. Aluminum conductors need connectors and terminals listed for aluminum.
NEC 240.4(D) also limits the breaker for small conductors: 14 AWG copper is capped at 15 A, 12 AWG copper at 20 A, 10 AWG copper at 30 A, 12 AWG aluminum at 15 A and 10 AWG aluminum at 25 A. The sizes in the table respect those caps, so a wire is never paired with a breaker larger than its limit.
Why 14 AWG and not smaller
14 AWG copper is the smallest size in this calculator, and NEC 240.4(D) caps it at a 15 amp breaker even though the ampacity table lists 20 A at 75 °C for the wire. That is why a 14 AWG wire on a 20 amp breaker is not allowed. A 15 amp breaker is the largest protection you can pair with 14 AWG copper.
When to use 12 AWG instead
Some installers run 12 AWG on a 15 amp circuit. It costs a little more but lowers voltage drop on long runs and leaves room to upgrade the breaker to 20 A later if the receptacles and loads allow it. The tables below show how far each size can go before the drop passes 3%.
Aluminum wire
Aluminum 14 AWG is not covered by the ampacity table used here. The smallest aluminum size for a 15 amp breaker is 12 AWG, and aluminum conductors must be connected with terminals and connectors rated for aluminum.
How far can you run it? (3% voltage drop)
The distance table uses the same resistance-only model as the calculator, with a 3% limit and the wire at 75 °C. Aluminum has about 1.6 times the resistance of copper for the same size, so an aluminum run of the same length drops more voltage.
Assumes the full 15 A load on a single-phase 120 V circuit, a 75 °C conductor, copper or aluminum, a 3% voltage drop limit and the one-way length in the table. Aluminum shows a dash where that size cannot carry the full current.
| Wire size | Copper | Aluminum |
|---|---|---|
| 14 AWG | 38.3 ft [11.7 m] | — |
| 12 AWG | 60.9 ft [18.6 m] | 37.0 ft [11.3 m] |
| 10 AWG | 96.8 ft [29.5 m] | 58.8 ft [17.9 m] |
| 8 AWG | 154.0 ft [46.9 m] | 93.5 ft [28.5 m] |
Before you buy wire
The table is a starting point. Work through this list before you order conductors, and keep the answer that matches your real installation.
- Read the equipment nameplate and the breaker. A manufacturer's required circuit size overrides any general table.
- Check the terminal rating on the breaker, the panel lugs and the equipment. Use the 60 °C or 75 °C column that matches the lowest rated part.
- Identify the cable type. NM (Romex) cable is limited to the 60 °C column by NEC 334.80, while conductors in conduit are usually rated 75 °C or higher.
- Measure the one-way distance from the panel to the load, then check voltage drop with the table or the calculator. If the run is long, go up one size.
- Confirm the design with your local code, the authority having jurisdiction and a licensed electrician before you cut wire or install a breaker.
This is general information based on NEC tables, not a permit or an installation plan. Local amendments, the equipment nameplate and an inspector decide what is acceptable. Read the disclaimer.