Wire size for 125 amps by distance (240 V, 3% drop)
| One-way distance | Copper | Drop | Aluminum |
|---|---|---|---|
| 25 ft | 1 AWG | 0.40% | 2/0 AWG |
| 50 ft | 1 AWG | 0.80% | 2/0 AWG |
| 75 ft | 1 AWG | 1.20% | 2/0 AWG |
| 100 ft | 1 AWG | 1.60% | 2/0 AWG |
| 150 ft | 1 AWG | 2.41% | 2/0 AWG |
| 200 ft | 1/0 AWG | 2.54% | 3/0 AWG |
| 250 ft | 2/0 AWG | 2.52% | 4/0 AWG |
| 300 ft | 3/0 AWG | 2.39% | 250 kcmil |
Single-phase 240 V, 75°C terminals, non-continuous load. For continuous loads (3+ hours) size for 156 A.
Common 125 A circuits
125 amp circuits typically feed subpanels and 125 A services. The breaker protects the wire, so never pair a 125 A breaker with wire rated below 125 A.
Service entrance conductors
For a 125 A dwelling service (not a subpanel feeder), NEC 310.12 lets the conductors be sized at 83% of the rating, so 2 AWG copper or 1/0 AWG aluminum is typical. Feeders to a subpanel use the full 125 A table above.
Frequently asked questions
Can I use 1/0 AWG wire on a 125 amp breaker?
Yes. 1/0 AWG copper is rated at least 125 A even in the 60°C column, so it works for NM-B cable and THHN alike, as long as voltage drop is acceptable.
How far can I run 1 AWG wire at 125 amps?
At 240 V with a 3% voltage-drop limit, about 150 ft one way. Beyond that, go up one size.