What Gauge Wire for a 15-Amp Circuit?
Use 14 AWG copper for 15-amp branch circuits per NEC 240.4(D). With ampacity adjustment for 4+ CCCs in conduit, the rating still covers 15A at 60°C terminals.
14 AWG copper is the standard wire gauge for 15-amp branch circuits, per NEC 240.4(D). Copper 14 AWG THHN has a 90°C ampacity of 25A but is limited to 15A by the NEC small-conductor protection rule.
NEC reference
| Rule | Effect |
|---|---|
| NEC 240.4(D)(3) | 14 AWG copper limited to 15A overcurrent protection |
| NEC Table 310.16 | 14 AWG @ 90°C = 25A; @ 75°C = 20A; @ 60°C terminals = 15A |
| NEC 110.14(C)(1) | Most residential terminals rated 60°C — 15A holds |
Why not 16 AWG or smaller?
NEC 240.4(D) treats 14, 12, and 10 AWG as "small conductors" with mandatory overcurrent limits regardless of insulation temperature rating. Below 14 AWG (16, 18, 20 AWG) is only permitted for taps, fixture wires, and a few special applications — never general branch circuits.
Common 15-amp circuits
- General lighting: 1500W at 120V = 12.5A — 15A breaker on 14 AWG is standard
- Bedroom/living room receptacles: general use, 15A
- Smoke alarms: dedicated 15A circuit (NEC 210.12 — AFCI required)
- Bathroom lighting (separate from receptacles which need 20A GFCI)
Conduit fill for multi-circuit 15A homeruns
15A branches typically share homeruns in conduit. With 14 AWG THHN:
- 3 circuits homerun (9 conductors): 9 × 0.0097 = 0.0873 in² → 28.7% fill in 1/2" EMT ✓
- 4 circuits (12 conductors): 12 × 0.0097 = 0.1164 in² → 38.3% fill in 1/2" EMT ✓ (at the limit)
- 5 circuits (15 conductors): 15 × 0.0097 = 0.1455 in² → 47.9% in 1/2" EMT ✗ → 3/4" EMT instead
Voltage drop consideration
NEC 210.19(A) Informational Note recommends voltage drop ≤3% for branch circuits. At 15A on 14 AWG copper, the resistance is 2.525 Ω/1000 ft. One-way 100 ft round-trip drop:
V drop = 2 × 100 × 15 × (2.525 / 1000) = 7.58V (6.3% of 120V)
Over 3% — for runs longer than 50 ft at 15A on 14 AWG, upsize to 12 AWG.
Quick reference
- Wire: 14 AWG copper THHN/THWN-2
- Breaker: 15A
- Receptacle: 15A or 20A (15A circuit can use either)
- Conduit minimum: 1/2" EMT for up to 4 branches (12 conductors)
For mixed-circuit installations, plug your conductor list into the conduit fill calculator.