100 amp wire size
For 100 amps, use 3 AWG copper or 1 AWG aluminum wire when the breaker and terminals are rated 75 °C. As the main service wire of a house, a 100 amp service may use 4 AWG copper or 2 AWG aluminum under the 83% rule: see 100 amp service wire size.
100 amp wire size by termination rating
| Termination rating | Copper | Aluminum |
|---|---|---|
| 60 °C | 1 AWG | 1/0 AWG |
| 75 °C, THHN | 3 AWG | 1 AWG |
| Ground wire | 8 AWG | 6 AWG |
100 amp wire size by distance at 240 V
Sizes that keep the voltage drop within 3% on a 240 V circuit loaded to the full 100 A, 75 °C terminations. The copper ground wire grows with the hot wires on long runs.
| One-way distance | Copper | Drop | Copper ground | Aluminum | Drop |
|---|---|---|---|---|---|
| 25 ft | 3 AWG | 0.5% | 8 AWG | 1 AWG | 0.5% |
| 50 ft | 3 AWG | 1.0% | 8 AWG | 1 AWG | 1.1% |
| 100 ft | 3 AWG | 2.0% | 8 AWG | 1 AWG | 2.1% |
| 150 ft | 2 AWG | 2.4% | 6 AWG | 1/0 AWG | 2.5% |
| 200 ft | 1 AWG | 2.6% | 4 AWG | 2/0 AWG | 2.7% |
| 300 ft | 2/0 AWG | 2.4% | 3 AWG | 4/0 AWG | 2.5% |
- Copper
- Aluminum
Check your own 100 amp run
What are you sizing for?
A
ft
From the panel to the load, not there and back
Voltage
Conductor
Termination rating
Result
3 AWG copper
Ampacity sets the size; the voltage drop is within 3%.
- Breaker
- 100 A
- Voltage drop
- 2.5 V (1.0%)
- Volts at the load
- 237.5 V
- Ground wire
- 8 AWG copper
How it is calculated
- Breaker: 100 A rounded up to a standard size = 100 A.
- Smallest copper conductor rated for 100 A at 75 °C: 3 AWG.
- Drop = 2 × K × 100 A × 50 ft ÷ 52,620 cmil = 2.45 V, target 3% of 240 V.
What a 100 amp circuit is used for
- Sub panel for a detached building
- Service for a small house