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What size wire for 300 amps?
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350 kcmil copper
minimum for 300 A (75 °C column, NEC 310.16) · 500 kcmil aluminum
300 amp wire size by distance (3% voltage drop, copper)
| One-way distance | 120 V | 240 V |
|---|---|---|
| 25 ft | 350 kcmil | 350 kcmil |
| 50 ft | 350 kcmil | 350 kcmil |
| 75 ft | 350 kcmil | 350 kcmil |
| 100 ft | 350 kcmil | 350 kcmil |
| 125 ft | 350 kcmil | 350 kcmil |
| 150 ft | 350 kcmil | 350 kcmil |
| 200 ft | 500 kcmil | 350 kcmil |
| 250 ft | 600 kcmil | 350 kcmil |
| 300 ft | >600 kcmil | 350 kcmil |
Load assumed at the full 300 A. For continuous loads the circuit must be sized at 125% of the load (e.g. a 240 A continuous load on a 300 A breaker).
Check your exact run
FAQ
What size wire for a 300 amp circuit?
350 kcmil copper or 500 kcmil aluminum at 75 °C for short runs; longer runs need larger wire to limit voltage drop.
Can I use 350 kcmil on a 300 amp breaker for 150 feet?
Check voltage drop: see the distance table on this page.
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