Minimum size by temperature column
| Conductor | 60°C | 75°C | 90°C |
|---|---|---|---|
| Copper | 3 AWG85 A | 4 AWG85 A | 4 AWG95 A |
| Aluminum | 1 AWG85 A | 2 AWG90 A | 3 AWG85 A |
Equipment grounding conductor
A circuit protected at 80 A takes a 8 AWG copper or 6 AWG aluminum equipment grounding conductor, from the 100 A row of NEC Table 250.122. Raise the ground with the ungrounded conductors when you increase them for voltage drop or any reason other than 310.15(B) or (C) derating, because 250.122(B) requires the same proportion. The ground is never required to be larger than the circuit conductors.
Longest run at 3% voltage drop
| Conductor | 120 V | 240 V |
|---|---|---|
| 3 AWG copper | 90 ft | 180 ft |
| 1 AWG aluminum | 85 ft | 175 ft |
NEC 210.19(A)(1) Informational Note 4 recommends keeping branch-circuit drop at or below 3%. These lengths come from the Table 8 resistance at 75°C for a stranded conductor at unity power factor, rounded to the nearest 5 ft. Reactance is not included, so a large conductor in a steel raceway falls short of the figure. A three-phase run reaches about 15% farther than these single-phase figures.
What a 80 A circuit feeds
- Subpanel feeders
- Large resistance heating loads
Eighty amps sits between the panel sizes that suppliers keep in stock. 3 AWG copper reaches it at 60°C and 4 AWG copper reaches it at 75°C, so the same circuit lands on different conductors depending on the cable type and the termination markings.
Fixed electric space heating is a continuous load under 424.3(B), and both the conductors and the overcurrent device must be at least 125% of the heating load. An 80 A circuit therefore carries 64 A of heating and no more, which is why heating circuits are sized from the load calculation rather than from the nameplate of one heater.
Eighty amps is a standard rating under 240.6(A) even though 80 A panels are uncommon, so it appears on equipment that draws just above 70 A and on feeders where 100 A would be oversized. Check whether the load is continuous before choosing the conductor: heating is, so 64 A is the ceiling, while a noncontinuous load uses the full 80 A.
80 A wire size questions
- What size wire do I need for an 80 amp circuit?
- Use 3 AWG copper or 1 AWG aluminum at the 60°C column, which sets the default under 110.14(C)(1)(a) for equipment rated 100 A or less, and 334.80 and 340.80 hold NM-B and UF-B cable to that column regardless of the terminals. With 75°C terminations, 4 AWG copper or 2 AWG aluminum carries the circuit.
- What size ground wire for a 80 amp circuit?
- 8 AWG copper or 6 AWG aluminum, taken from the 100 A row of NEC Table 250.122.
- What size aluminum wire for 80 amps?
- 1 AWG aluminum at the 60°C column carries 85 A. Terminations on aluminum conductors must be identified for the material.
- Can I use 4 AWG copper for 80 A?
- Table 310.16 lists 4 AWG copper at 70 A at 60°C, 85 A at 75°C, and 95 A at 90°C. It falls short at 60°C, the column this circuit uses. The 75°C and 90°C columns do reach 80 A, and a higher column applies only where every termination is listed for it.