70 amp wire size
For 70 amps, use 4 AWG copper or 3 AWG aluminum wire when the breaker and terminals are rated 75 °C.
70 amp wire size by termination rating
| Termination rating | Copper | Aluminum |
|---|---|---|
| 60 °C, NM-B | 4 AWG | 2 AWG |
| 75 °C, THHN | 4 AWG | 3 AWG |
| Ground wire | 8 AWG | 6 AWG |
70 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 70 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 | 4 AWG | 0.5% | 8 AWG | 3 AWG | 0.6% |
| 50 ft | 4 AWG | 0.9% | 8 AWG | 3 AWG | 1.2% |
| 100 ft | 4 AWG | 1.8% | 8 AWG | 3 AWG | 2.4% |
| 150 ft | 4 AWG | 2.7% | 8 AWG | 2 AWG | 2.8% |
| 200 ft | 3 AWG | 2.9% | 6 AWG | 1 AWG | 3.0% |
| 300 ft | 1 AWG | 2.7% | 4 AWG | 2/0 AWG | 2.8% |
- Copper
- Aluminum
Check your own 70 amp run
What are you sizing for?
A
ft
From the panel to the load, not there and back
Voltage
Conductor
Termination rating
Result
4 AWG copper
Ampacity sets the size; the voltage drop is within 3%.
- Breaker
- 70 A
- Voltage drop
- 2.2 V (0.9%)
- Volts at the load
- 237.8 V
- Ground wire
- 8 AWG copper
How it is calculated
- Breaker: 70 A rounded up to a standard size = 70 A.
- Smallest copper conductor rated for 70 A at 75 °C: 4 AWG.
- Drop = 2 × K × 70 A × 50 ft ÷ 41,740 cmil = 2.16 V, target 3% of 240 V.
What a 70 amp circuit is used for
- Sub panel feeder
- Large heat pump with backup heat