125 amp wire size
125 amp wire size: 1 AWG copper or 2/0 AWG aluminum, with 75 °C terminations. As the main service wire of a house, a 125 amp service may use 2 AWG copper or 1/0 AWG aluminum under the 83% rule: see 125 amp service wire size.
125 amp wire size by termination rating
| Termination rating | Copper | Aluminum |
|---|---|---|
| 60 °C | 1/0 AWG | 3/0 AWG |
| 75 °C, THHN | 1 AWG | 2/0 AWG |
| Ground wire | 6 AWG | 4 AWG |
125 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 125 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 | 1 AWG | 0.4% | 6 AWG | 2/0 AWG | 0.4% |
| 50 ft | 1 AWG | 0.8% | 6 AWG | 2/0 AWG | 0.8% |
| 100 ft | 1 AWG | 1.6% | 6 AWG | 2/0 AWG | 1.7% |
| 150 ft | 1 AWG | 2.4% | 6 AWG | 2/0 AWG | 2.5% |
| 200 ft | 1/0 AWG | 2.5% | 4 AWG | 3/0 AWG | 2.6% |
| 300 ft | 3/0 AWG | 2.4% | 3 AWG | 250 kcmil | 2.7% |
- Copper
- Aluminum
Check your own 125 amp run
What are you sizing for?
A
ft
From the panel to the load, not there and back
Voltage
Conductor
Termination rating
Result
1 AWG copper
Ampacity sets the size; the voltage drop is within 3%.
- Breaker
- 125 A
- Voltage drop
- 1.9 V (0.8%)
- Volts at the load
- 238.1 V
- Ground wire
- 6 AWG copper
How it is calculated
- Breaker: 125 A rounded up to a standard size = 125 A.
- Smallest copper conductor rated for 125 A at 75 °C: 1 AWG.
- Drop = 2 × K × 125 A × 50 ft ÷ 83,690 cmil = 1.93 V, target 3% of 240 V.
What a 125 amp circuit is used for
- Sub panel feeder
- Small house service