DOC · ARTICLE
What Gauge Wire for a 50-Amp Circuit?
Use 6 AWG copper for 50-amp circuits at 75°C terminals. 6 AWG THHN: 75A at 90°C, 65A at 75°C, 55A at 60°C terminals.
·2 MIN READ·EDITORIAL
6 AWG copper is the standard wire gauge for 50-amp circuits, providing comfortable margin at the 75°C terminal rating common in residential equipment.
NEC reference
| Rule | Effect |
|---|---|
| NEC Table 310.16 | 6 AWG copper @ 90°C = 75A; @ 75°C = 65A; @ 60°C = 55A |
| NEC 110.14(C)(1)(a) | ≤ 100A circuits use 60°C column at receptacles unless equipment marked otherwise |
| NEC 210.21(B)(3) | 50A receptacles: NEMA 14-50, 6-50, 50-amp locking variants |
Common 50-amp circuits
- Electric range (full-size, 50A 240V with neutral)
- NEMA 14-50 RV/EV outlet (most common 50A application today)
- Welder receptacle (NEMA 6-50, no neutral)
- Pool heater (some models)
- Spa / hot tub (large units)
Conductor count + conduit
| Circuit | Conductors | Min EMT |
|---|---|---|
| 50A range (with neutral): 2 hots + N + EGC | 4 | 3/4" (27% fill) |
| 50A EV / welder (no neutral): 2 hots + EGC | 3 | 3/4" (20% fill) |
| Two 50A circuits sharing EGC | 5 | 1" (29% fill) |
Ampacity derating
With 4–6 CCCs: 75A × 0.80 = 60A — comfortably above 50A.
With 7–9 CCCs: 75A × 0.70 = 52.5A — still above 50A but tight.
With 10+ CCCs: 75A × 0.50 = 37.5A — insufficient. Upsize to 4 AWG.
Voltage drop at 50A
6 AWG copper: 0.398 Ω/1000 ft. At 50A on 100 ft (240V circuit, 200 ft round-trip):
V drop = 200 × 50 × (0.398 / 1000) = 3.98V (1.7% of 240V)
Within 3% — 6 AWG is fine to ~175 ft for 50A circuits.
Quick reference
- Wire: 6 AWG copper THHN/THWN-2 (or 4 AWG aluminum)
- Breaker: 50A 2-pole
- Receptacle: NEMA 14-50 (4-wire) or 6-50 (3-wire)
- Conduit: 3/4" EMT fits one circuit; 1" for two
For RV / EV applications running long distances, consider 4 AWG to reduce drop at high continuous current.
FIG. 99
FAQ
6 AWG copper THHN is the standard. Rated 75A at 90°C and 65A at 75°C terminations — well above the 50A breaker rating. Some installs use 8 AWG copper at 90°C (55A), but only if all terminations are rated 90°C — uncommon in residential.
FIG. 98