Wire size for 100 amps by distance (240 V, 3% drop)
| One-way distance | Copper | Drop | Aluminum |
|---|---|---|---|
| 25 ft | 3 AWG | 0.51% | 1 AWG |
| 50 ft | 3 AWG | 1.02% | 1 AWG |
| 75 ft | 3 AWG | 1.53% | 1 AWG |
| 100 ft | 3 AWG | 2.04% | 1 AWG |
| 150 ft | 2 AWG | 2.43% | 1/0 AWG |
| 200 ft | 1 AWG | 2.57% | 2/0 AWG |
| 250 ft | 1/0 AWG | 2.54% | 3/0 AWG |
| 300 ft | 2/0 AWG | 2.42% | 4/0 AWG |
Single-phase 240 V, 75°C terminals, non-continuous load. For continuous loads (3+ hours) size for 125 A.
Common 100 A circuits
100 amp circuits typically feed subpanels and small services. The breaker protects the wire, so never pair a 100 A breaker with wire rated below 100 A.
Service entrance conductors
For a 100 A dwelling service (not a subpanel feeder), NEC 310.12 lets the conductors be sized at 83% of the rating, so 4 AWG copper or 2 AWG aluminum is typical. Feeders to a subpanel use the full 100 A table above.
Frequently asked questions
Can I use 1 AWG wire on a 100 amp breaker?
Yes. 1 AWG copper is rated at least 100 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 3 AWG wire at 100 amps?
At 240 V with a 3% voltage-drop limit, about 100 ft one way. Beyond that, go up one size.