What Size Wire for a 15 Amp Circuit?
Short answer: a 15 amp circuit uses 14 AWG copper, typically 14/2 NM-B with ground (white jacket). With aluminum, the minimum is 12 AWG aluminum. For runs over about 40 feet at full load, 12 AWG copper keeps voltage drop in check.
15 amp wire size by wiring method
| Wiring method | Copper | Aluminum |
|---|---|---|
| NM-B or UF cable | 14 AWG | 12 AWG |
| THHN/THWN-2 in conduit | 14 AWG | 12 AWG |
| MC cable | 14 AWG | — |
Ground wire: 14 AWG copper or 12 AWG aluminum (Table 250.122).
14 AWG copper is the smallest conductor permitted for general branch circuits. Table 310.16 rates it 15 A in the 60°C column, and NEC 240.4(D) caps its breaker at 15 A regardless of the higher 75°C and 90°C values, so NM-B and THHN come out the same. Aluminum 12 AWG branch wiring is rare in new work; where it exists, devices must be marked CO/ALR.
15 amp wire size by distance (120 V)
| Conductor | 25 ft | 50 ft | 75 ft | 100 ft |
|---|---|---|---|---|
| Copper | 14 AWG (2.0%) | 12 AWG (2.5%) | 10 AWG (2.3%) | 8 AWG (2.0%) |
| Aluminum | 12 AWG (2.0%) | 10 AWG (2.6%) | 8 AWG (2.4%) | 6 AWG (2.0%) |
Smallest conductor that meets both the 75°C ampacity for a 15 A circuit and a 3% voltage drop at 15 A (100% of the rating), 120 V single-phase, one-way distance. Percent drop in brackets. If the circuit uses NM-B cable or 60°C terminations, start from the 60°C column instead.
At a steady 15 A on 120 V, 14 AWG copper reaches 3% drop at about 38 feet. Lighting circuits with LED fixtures usually carry far less current, so longer runs on 14 AWG are common and fine. Calculate with the real load, not the breaker rating.
How far can you run 14 gauge? Maximum one-way distance at 3% drop, 120 V
| Actual load | 14 AWG copper | 12 AWG copper |
|---|---|---|
| 5 A | 115 ft | 182 ft |
| 8 A | 72 ft | 114 ft |
| 10 A | 57 ft | 91 ft |
| 12 A | 48 ft | 76 ft |
| 15 A | 38 ft | 61 ft |
One-way distance, single-phase, K = 12.9 for copper. The 3% figure is a design recommendation from the informational notes to 210.19(A), not a mandatory limit.
Worked example: 15 A circuit to a backyard pergola
A 15 A, 120 V circuit feeds LED string lights and fixtures on a pergola 70 feet from the panel. The lights draw 12 A and run for more than 3 hours, so they count as a continuous load.
- Continuous load check: a 15 A breaker may carry 15 × 0.8 = 12 A continuous. Put the other way, 12 A × 1.25 = 15 A, so the 15 A circuit is exactly at the limit. No other loads should go on it.
- Voltage drop with 14 AWG: 2 × 12.9 × 12 × 70 ÷ 4,110 = 5.27 V, or 4.4%. Too much.
- Voltage drop with 12 AWG: 2 × 12.9 × 12 × 70 ÷ 6,530 = 3.32 V, or 2.8%. Acceptable.
Result: 12 AWG copper on a 15 A breaker. Run your own load in the voltage drop calculator.
Typical 15 amp circuits
- General lighting circuits.
- Bedroom, living room and hallway receptacles (AFCI protection required in most dwelling areas, 210.12).
- Bathroom exhaust fans and lighting (the bathroom receptacle circuit must be 20 A).
- Garage door openers, smoke alarm circuits, and other small dedicated loads per the manufacturer.
- 240 V baseboard heat on 14/2. A 15 A, 240 V circuit carries up to 12 A continuous, which is 12 × 240 = 2,880 W of heaters. The same circuit at 120 V carries 12 × 120 = 1,440 W continuous.
14 AWG in conduit and boxes
- Conduit fill: ½" EMT holds up to 12 14 AWG THHN conductors and ½" PVC Schedule 40 holds 11, per Chapter 9. See the conduit fill chart for other sizes.
- Derating: more than three current-carrying conductors in a raceway need an adjustment from Table 310.15(C)(1), and hot locations a correction from Table 310.15(B)(1). THHN may start from its 90°C value.
- Box fill: each 14 AWG conductor counts as 2.00 in³ under Table 314.16(B).
Common mistakes inspectors flag
- A 20 A breaker on 14 AWG. The most common one, often after a homeowner swaps a "tripping" breaker for a bigger one.
- A 14 AWG pigtail or extension on a 20 A circuit. Every conductor on the circuit must be rated for the breaker, including short jumpers in boxes.
- Bathroom, kitchen countertop or laundry receptacles on a 15 A circuit. Those circuits must be 20 A (210.11(C)).
14 AWG vs. 12 AWG cost
12 AWG has about 1.59 times the copper of 14 AWG (6,530 vs. 4,110 circular mils), so it costs more and is stiffer to terminate. Some contractors run 12 AWG everywhere anyway to avoid mixed-gauge circuits; price both from a current supplier quote.
Frequently asked questions
How many amps can 14 gauge wire handle?
Its breaker is limited to 15 A (NEC 240.4(D)). Table 310.16 lists 15 A at 60°C, 20 A at 75°C and 25 A at 90°C for 14 AWG copper; the higher values are used only as the starting point for derating calculations. See the ampacity chart.
Can I put a 20 amp breaker on 14 gauge wire?
No. That violates 240.4(D) and can overheat the wire. If the circuit trips, reduce the load or add a circuit; don't upsize the breaker. A 20 A circuit needs 12 AWG copper.
How many lights can be on a 15 amp circuit?
A 15 A, 120 V circuit supplies 1,800 W, or 1,440 W for continuous use. With 10 W LED fixtures, that's well over 100 fixtures in theory; in practice, circuits are split by area for convenience and code requirements.
Can I use 14 gauge wire for a 240 volt, 15 amp circuit?
Yes. 14/2 NM-B with a 15 A two-pole breaker is common for baseboard heaters and some small 240 V equipment. Re-mark the white conductor as a hot with tape at both ends.
Related
Last updated: October 6, 2026. Based on NEC 2023. Check results against the code edition and local amendments your jurisdiction enforces and with the AHJ; electrical work should be done by qualified people.