Wire size for an 80 amp breaker
| Wire | Condition | Minimum size for 80 A |
|---|---|---|
| Copper | NM-B (Romex) cable or 60°C terminals | 3 AWG |
| Copper | THHN/THWN in conduit, 75°C terminals | 4 AWG |
| Aluminum | 75°C terminals | 2 AWG |
| Aluminum | 60°C terminals | 1 AWG |
4 AWG copper is rated 70 A in the 60°C column, 85 A at 75°C and 95 A at 90°C. The size above is the smallest whose ampacity is at least 80 A. Most modern breakers and panels have 75°C terminals, but an 80 A circuit is presumed 60°C unless the equipment is marked otherwise (NEC 110.14(C)).
Voltage drop: how far can 4 AWG run at 80 A?
The 4 AWG above carries 80 A safely but loses voltage over distance. At the full 80 A and 240 V, 4 AWG copper stays within the NEC's 3% recommendation for about 146 ft one way. 3 AWG stretches that to 184 ft.
| One-way distance | 4 AWG copper | 3 AWG copper | 2 AWG copper |
|---|---|---|---|
| 25 ft | 0.5% | 0.4% | 0.3% |
| 50 ft | 1.0% | 0.8% | 0.6% |
| 100 ft | 2.1% | 1.6% | 1.3% |
| 150 ft | 3.1% | 2.5% | 1.9% |
| 200 ft | 4.1% | 3.3% | 2.6% |
Percent drop at 80 A and 240 V.
On 120 V circuits, the 80 A percentages are twice these values.
Check your own 80 A run with the voltage drop calculator, or let the wire size calculator choose the size for you.
What an 80 amp circuit is used for
- Sub panels for a garage, barn or addition
- Large electric furnaces and heat pumps
- A charger drawing 64 A continuous (64 × 1.25 = 80 A)
Cable type matters
NM-B for an 80 A circuit has to be 3 AWG, because 4 AWG NM-B tops out at 70 A. In conduit, 4 AWG THHN is rated 85 A at 75°C and covers an 80 A breaker.
Continuous loads and common mistakes
On an 80 A breaker, a continuous load running three hours or more should not exceed 80% of the rating. That is 64 A, or about 15,360 W at 240 V. The difference between 3 AWG and 4 AWG is the cable type. Pick the wire for how it is installed, and check that the terminals are rated 75°C if you want the smaller size.
For an 80 A breaker the ground wire comes from NEC Table 250.122. Use the ground wire size calculator. For other breaker sizes, see the breaker to wire size chart, or jump to 20 amps, 30 amps, 40 amps, 50 amps, 60 amps, 100 amps.
Frequently asked questions
What size wire for an 80 amp breaker?
4 AWG copper at 75°C terminals, or 3 AWG for NM-B cable. In aluminum use 2 AWG.
How far can 4 AWG wire run on 80 amps?
About 146 feet one way at 240 V before the voltage drop passes the NEC's 3% recommendation. Past that distance, step up to 3 AWG.
What size wire for an 80 amp breaker?
4 AWG copper in conduit with 75°C terminals, or 3 AWG for NM-B cable. In aluminum use 3 AWG at 75°C.
What size wire for an 80 amp sub panel?
4 AWG copper in conduit, or 3 AWG cable. For long runs, step up for voltage drop.