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What size wire for 40 amps?
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8 AWG copper
minimum for 40 A (75 °C column, NEC 310.16) · 6 AWG aluminum · typical for electric ranges and cooktops
40 amp wire size by distance (3% voltage drop, copper)
| One-way distance | 120 V | 240 V |
|---|---|---|
| 25 ft | 8 AWG | 8 AWG |
| 50 ft | 8 AWG | 8 AWG |
| 75 ft | 6 AWG | 8 AWG |
| 100 ft | 4 AWG | 8 AWG |
| 125 ft | 4 AWG | 6 AWG |
| 150 ft | 3 AWG | 6 AWG |
| 200 ft | 2 AWG | 4 AWG |
| 250 ft | 1 AWG | 4 AWG |
| 300 ft | 1/0 AWG | 3 AWG |
Load assumed at the full 40 A. For continuous loads the circuit must be sized at 125% of the load (e.g. a 32 A continuous load on a 40 A breaker).
Check your exact run
FAQ
What size wire for a 40 amp circuit?
8 AWG copper or 6 AWG aluminum at 75 °C for short runs; longer runs need larger wire to limit voltage drop.
Can I use 8 AWG on a 40 amp breaker for 150 feet?
Check voltage drop: see the distance table on this page.
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