What size wire for 50 amps?
6 AWG copper is the minimum for a 50 A circuit under standard conditions, or 8 AWG where every termination is rated 75 °C. Aluminum: 4 AWG (6 AWG at 75 °C). Long runs, hot spaces and crowded conduit need bigger wire.
Standard conditions only: 30 °C ambient, no more than three current-carrying conductors together, short run. Check your conditions with the wire size calculator. Local codes vary; a licensed electrician should size and install the conductors.
Why 6 AWG?
NEC 110.14(C) limits circuits of 100 A or less to the 60 °C ampacity column unless every termination is marked for 75 °C, and NM-B cable (Romex) is always limited to 60 °C (334.80). In the 60 °C column of Table 310.16, the smallest copper conductor rated for at least 50 A is 6 AWG (55 A).
With individual THHN/THWN conductors in conduit and a breaker and equipment marked 75 °C, the 75 °C column applies and 8 AWG (50 A) is enough. When in doubt, use 6 AWG.
Maximum distance for 3% voltage drop
One-way length in feet, copper, at 80% of 50 A (40 A), from NEC Chapter 9 Table 8 resistance.
| Copper size | 120 V | 240 V |
|---|---|---|
| 6 AWG | 92 ft | 183 ft |
| 4 AWG | 146 ft | 292 ft |
| 3 AWG | 184 ft | 367 ft |
| 2 AWG | 232 ft | 464 ft |
| 1 AWG | 292 ft | 584 ft |
For your exact load and length, use the voltage drop calculator.
Questions
What gauge wire for a 50 amp breaker?
6 AWG copper is the minimum under standard conditions (30 °C, no more than three current-carrying conductors, 60 °C terminals or NM-B cable). With THHN/THWN in conduit and equipment marked 75 °C, 8 AWG copper is permitted. Aluminum: 4 AWG.
How far can I run 6 AWG on 50 amps?
At 80% load (40 A), 6 AWG copper stays within 3% voltage drop for about 183 ft one-way at 240 V and 92 ft at 120 V. Longer runs need a larger size.
Can I use 8 AWG for 50 amps?
Not on a 50 A breaker under standard conditions. The breaker protects the wire, so the wire's allowable ampacity (and the 240.4(D) limits for 14–10 AWG) must be at least the breaker rating, except where the NEC specifically permits otherwise, such as motor and HVAC circuits.