A 80 amp circuit needs 4 AWG copper or 2 AWG aluminum wire with 75 °C terminations. In NM-B cable (Romex), which is limited to the 60 °C column, a 80 amp circuit needs 3 AWG copper.
80 amp wire size by termination rating
Wire size for a 80 amp circuit by termination temperature rating (60 °C: NM-B cable; 75 °C: THHN and most breakers), with the ground wire
Termination rating
Copper
Aluminum
60 °C, NM-B
3 AWG
1 AWG
75 °C, THHN
4 AWG
2 AWG
Ground wire
8 AWG
6 AWG
80 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 80 A, 75 °C terminations. The copper ground wire grows with the hot wires on long runs.
Wire size for a 80 amp, 240 V circuit by one-way distance, keeping the voltage drop within 3%
One-way distance
Copper
Drop
Copper ground
Aluminum
Drop
25 ft
4 AWG
0.5%
8 AWG
2 AWG
0.5%
50 ft
4 AWG
1.0%
8 AWG
2 AWG
1.1%
100 ft
4 AWG
2.1%
8 AWG
2 AWG
2.1%
150 ft
3 AWG
2.5%
6 AWG
1 AWG
2.5%
200 ft
2 AWG
2.6%
4 AWG
1/0 AWG
2.7%
300 ft
1/0 AWG
2.4%
3 AWG
3/0 AWG
2.5%
Copper
Aluminum
Wire size for 80 A at 240 V by distance, within 3% voltage drop.
Check your own 80 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
80 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: 80 A rounded up to a standard size = 80 A.
Smallest copper conductor rated for 80 A at 75 °C: 4 AWG.
Drop = 2 × K × 80 A × 50 ft ÷ 41,740 cmil = 2.47 V, target 3% of 240 V.