Wire size for 70 amps by distance (240 V, 3% drop)
| One-way distance | Copper | Drop | Aluminum |
|---|---|---|---|
| 25 ft | 4 AWG | 0.45% | 3 AWG |
| 50 ft | 4 AWG | 0.90% | 3 AWG |
| 75 ft | 4 AWG | 1.35% | 3 AWG |
| 100 ft | 4 AWG | 1.80% | 3 AWG |
| 150 ft | 4 AWG | 2.69% | 2 AWG |
| 200 ft | 3 AWG | 2.86% | 1 AWG |
| 250 ft | 2 AWG | 2.83% | 1/0 AWG |
| 300 ft | 1 AWG | 2.69% | 2/0 AWG |
Single-phase 240 V, 75°C terminals, non-continuous load. For continuous loads (3+ hours) size for 88 A.
Common 70 A circuits
70 amp circuits typically feed large heat pumps and subpanels. The breaker protects the wire, so never pair a 70 A breaker with wire rated below 70 A.
Frequently asked questions
Can I use 4 AWG wire on a 70 amp breaker?
Yes. 4 AWG copper is rated at least 70 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 4 AWG wire at 70 amps?
At 240 V with a 3% voltage-drop limit, about 150 ft one way. Beyond that, go up one size.