Three columns, three answers
NM-B cable is held to the 60 °C column, THHN in conduit on 60/75 °C breakers uses 75 °C. That is why 3 AWG NM-B and 4 AWG THHN can both serve 80 A.
What size wire for 80 amps?
A 80 A circuit takes 3 AWG NM-B in the wall or 4 AWG copper THHN in conduit (75 °C), with a 8 AWG ground; aluminum needs 2 AWG. At an 64 A load the copper reaches 182 ft at 240 V (3 % drop). Used for subpanels and 64 A EV chargers.
02 · Ampacity · NEC 2023 Table 310.16
4 AWG copper · 90 °C insulation, 75 °C terminals, 30 °C, 3 conductors
USE:
4 AWG COPPER · 85 A ALLOWABLE · 80 A MAX BREAKER
Allowable
85 A
4 AWG Cu
Max breaker
80 A
ampacity ≥ breaker
For your load
4 AWG
80 A
4 AWG copper carries 95 A after derating from the 90 °C column and 85 A at its 75 °C terminals, so it is good for 85 A on a breaker up to 80 A.
- Meets NEC 2023 Table 310.16 at 75°C — verify with your local AHJ/inspector110.14(C)
- Load 80 A ≤ 85 A310.14
Derating math
- Table 310.16 at 90 °C
- 95 Aderating starts at the insulation rating
- Ambient factor
- × 1.0030 °C, Table 310.15(B)(1)
- Bundling factor
- × 1.003 current-carrying conductors, 310.15(C)(1)
- Derated
- 95 A
- Terminal limit (75 °C)
- 85 A110.14(C)
- Allowable
- 85 Athe terminals decide
4 AWG
- Copper 60 / 75 / 90 °C
- 70 / 85 / 95 ANM-B uses the 60 °C column (334.80)
- Aluminum 60 / 75 / 90 °C
- 55 / 65 / 75 A
- Largest breaker (Cu, 75 °C)
- 80 Aampacity ≥ breaker
- Solid diameter
- 0.204"5.19 mm · ASTM B258 formula
- Stranded (7 strands)
- 0.232"5.89 mm · Table 8
- THHN outside
- 0.324"8.23 mm · 0.0824 in² · Table 5
- Area
- 41,740 cmil21.15 mm² · nearest IEC 25 mm²
- DC resistance, 75 °C
- 0.308 Ω/1000 ftaluminum 0.508 Ω/1000 ft · Table 8
- Copper weight
- 126.3 lb/1000 ft
80 A circuit at a glance
Wire
- Copper NM-B (60 °C)
- 3 AWG
- Copper THHN (75 °C)
- 4 AWG
- Aluminum (75 °C)
- 2 AWG
- Aluminum, next size up
- 3 AWG
Ground & breaker
- Copper ground
- 8 AWG
- Aluminum ground
- 6 AWG
- Continuous load max
- 64 A
- Breaker
- 80 A
Distance (3 %)
- Cu at 120 V, 64 A
- 91 ft
- Cu at 240 V, 64 A
- 182 ft
- Al at 240 V, 64 A
- 176 ft
80 A circuit tables 12 rows
Sort any column, print a shop sheet, download CSV. Click a row to load it in the calculator.
| Actions | |||||
|---|---|---|---|---|---|
| 3 AWG | 3 AWG | 8 AWG | 229 ft | ||
| 4 AWG | 4 AWG | 8 AWG | 182 ft | ||
| 2 AWG | 3 AWG | 6 AWG | 176 ft |
Feet one way (the current goes out and back). Ampacity is a separate check: a long run may need a heavier wire for drop, never a lighter one for heat.
05 / Field guide
80 amps:
which wire, which method.
An 80 A circuit takes 3 AWG NM-B in the wall or 4 AWG copper THHN in conduit (75 °C), with an 8 AWG ground; aluminum needs 2 AWG. At an 64 A load the copper reaches 182 ft at 240 V (3 % drop). Used for subpanels and 64 A EV chargers.
Breaker rules
240.4(B) lets a conductor whose ampacity is not a standard size take the next breaker up (not on multi-outlet receptacle circuits). The headline here uses ampacity at least 80 A.
Distance
The answer above is the minimum for heat. On a long run upsize for voltage drop, and grow the ground with it: the table below gives the longest 240 V run at 3 % for each candidate size.
Questions
Answered plainly.
01What size wire for an 80 amp breaker?
+−
3 AWG copper NM-B in the wall, 4 AWG copper THHN in conduit or 2 AWG aluminum, all with ampacity at least 80 A (NEC 2023 Table 310.16).
02Can I use 4 AWG wire on an 80 amp breaker in NM-B cable?
+−
Not at the ampacity rule: NM-B is limited to the 60 °C column (334.80), where 4 AWG carries 70 A; use 3 AWG.
03What size ground wire for 80 amps?
+−
8 AWG copper or 6 AWG aluminum (Table 250.122), larger in proportion if the circuit wire is upsized for distance (250.122(B)).
04How far can I run an 80 amp circuit?
+−
At 64 A (80 %) on 4 AWG copper, 182 ft one way at 240 V or 91 ft at 120 V before the drop passes 3 %. Beyond that, go up a size.
05What is the largest continuous load on an 80 amp circuit?
+−
64 A: a continuous load (3 hours or more) may use only 80 % of the breaker rating (the 125 % rule).