What Gauge Wire for a 30-Amp Circuit?
Use 10 AWG copper for 30-amp circuits per NEC 240.4(D). 10 AWG THHN is rated 35A at 75°C, providing 5A margin for the 30A breaker.
10 AWG copper is the standard wire gauge for 30-amp circuits, per NEC 240.4(D)(7). 10 AWG THHN has a 90°C ampacity of 40A and a 75°C ampacity of 35A — both above the 30A breaker rating.
NEC reference
| Rule | Effect |
|---|---|
| NEC 240.4(D)(7) | 10 AWG copper limited to 30A overcurrent protection (small-conductor rule) |
| NEC Table 310.16 | 10 AWG @ 90°C = 40A; @ 75°C = 35A; @ 60°C terminals = 30A |
| NEC 210.21(B) | 30A receptacle types: NEMA 6-30, 14-30, L6-30, L14-30 |
Common 30-amp circuits
- Electric water heater (4500W typical, 240V) — 30A 2-pole breaker
- Electric clothes dryer (5500W typical) — 30A 2-pole breaker, neutral required for 120V controls
- Window/mini-split A/C (large units) — 30A 240V
- Travel trailer / RV pedestal — 30A TT-30 receptacle
- Baseboard heat circuit — 30A 240V for ~5500W
- Level 2 EV charger at 24A continuous — 30A 240V
Conductors per circuit
| Circuit type | Conductors | Wire fill in 3/4" EMT |
|---|---|---|
| 30A 240V (no neutral): water heater, AC | 2 hots + 1 EGC = 3 | 11.9% fill |
| 30A 240V with neutral (dryer): | 2 hots + 1 neutral + 1 EGC = 4 | 15.8% fill |
3/4" EMT fits 10 of 10 AWG THHN. Three full dryer circuits (12 conductors) requires 1" EMT (16 of 10 AWG, 39.0% fill).
Ampacity derating
With 4–6 CCCs in conduit: 40A × 0.80 = 32A — sufficient for 30A breaker.
With 7–9 CCCs: 40A × 0.70 = 28A — drops below 30A breaker rating. Either reduce conductor count or upsize to 8 AWG (55A × 0.70 = 38.5A).
Voltage drop at 30A
10 AWG copper: 0.999 Ω/1000 ft. At 30A on 100 ft one-way (240V circuit, 200 ft round trip):
V drop = 200 × 30 × (0.999 / 1000) = 6.0V (2.5% of 240V)
Within 3% — 10 AWG is fine up to ~120 ft for 30A circuits.
Quick reference
- Wire: 10 AWG copper THHN/THWN-2
- Breaker: 30A 1-pole or 2-pole (240V)
- Receptacle: NEMA 6-30 (no neutral), 14-30 (with neutral), L-style for locking applications
- Conduit minimum: 1/2" EMT for one circuit; 3/4" for two; 1" for three
For specific configurations, run the conduit fill calculator.
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This page's figures are transcribed from NEC 2023 (NFPA 70) Chapter 9, Tables 1, 4 and 5, and checked by a version-controlled automated test suite — they are not signed off by a licensed professional. WireFillChart is an independent reference, not affiliated with or endorsed by NFPA. Always verify against the code edition adopted by your local authority having jurisdiction (AHJ).