A gauge 3 aluminum or a gauge 4 copper makes a perfect choice for a 70 Amp breaker assuming there aren’t other factors impacting the performance, such as material and temperature.
What Size Wire for 70 Amp Breaker
Before you decide to upgrade the breaker you need to consider whether your wires can take the load or not. Considering there aren’t other factors impacting the performance, the right wire is either a gauge 3 aluminum or a gauge 4 copper for 70 amp. At an ambient temperature of 140°F, you can use 4-gauge copper for a circuit breaker with this rating.
Rule of Thumb
General rule of thumb is an uncomplicated way to measure and choose wirings. Have a look at the chart below to find the right wirings, based on conductor temperatures taken from the NEC 310.16.
Ground wire, service entrance, circuit, breaker size chart rating:
| Service or Feeder Rating (amp) | Aluminum conductor | Copper conductor |
| 70 | #2 AWG | #4 AWG |
| 80 | #1 AWG | #3 AWG |
| 100 | #1/0 AWG | #1 AWG |
| 125 | #3/0 AWG | #1/0 AWG |
| 150 | #4/0 AWG | #3/0 AWG |
| 200 | 350 kcmil | 250 kcmil |
| 300 | 700 kcmil | 500 kcmil |
| 400 | 1,250 kcmil | 750 kcmil |
| 600 | 2,000 kcmil (194°F) | 1,500 kcmil (167°F) |
Check out the list below to check which wires are best for you regarding different voltage, distance, and materials.
| Volt with 70 Amps | Max Distance | AWG(Copper) | Aluminum |
| 120V | 95 ft | 4AWG | 2AWG |
| 240V | 191ft | 4AWG | 2AWG |
| 480V | 383 ft | 4AWG | 2AWG |
| Volt with 70 Amps | Max Distance | AWG(Copper) | Aluminum |
| 120V | 120 ft | 3AWG | 1AWG |
| 240V | 241ft | 3AWG | 1AWG |
| 480V | 483 ft | 3AWG | 1AWG |
| Volt with 70 Amps | Max Distance | AWG(Copper) | Aluminum |
| 120V | 152 ft | 2AWG | 1/0AWG |
| 240V | 302ft | 2AWG | 1/0AWG |
| 480V | 609 ft | 3AWG | 1/0AWG |
Voltage Drop is 3%, Line=Single phase
Wire size for 70 Amp 3 Phase
| Volt with 70 Amps | Max Distance | AWG(Copper) | Aluminum |
| 120V | 150 ft | 2AWG | 1/0WG |
| 240V | 150ft | 4AWG | 2AWG |
| 480V | 150ft | 4AWG | 2AWG |
Voltage Drop is 3%, Line=3 phase
To Conclude
After you select the right size of your wire you can select either the flexible aluminum option or high-conducting and robust copper. Make sure to consider price and safety measures before buying the wires and other components for your project.
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