Quick answer: wire size for a 50 amp breaker
Minimum conductor whose table ampacity is at least 50 A, with not more than three current-carrying conductors at 30 °C (86 °F) ambient.
| Wire and terminal rating | Minimum size | Table ampacity |
|---|---|---|
| Copper, 60 °C column (NM cable, unmarked terminals) | 6 AWG | 55 A |
| Copper, 75 °C column (THHN/THWN-2, 75 °C terminals) | 8 AWG | 50 A |
| Aluminum, 60 °C column | 4 AWG | 55 A |
| Aluminum, 75 °C column (XHHW-2, SER, 75 °C terminals) | 6 AWG | 50 A |
NEC 110.14(C)(1)(a) limits circuits of 100 A or less to the 60 °C column unless the equipment is listed and marked for 75 °C, which most current breakers and panels are. Both ends of the circuit count: if a receptacle, range terminal block or appliance is marked 60 °C, use the 60 °C sizes. The 90 °C column (55 A for 8 AWG copper) is only a starting point for derating.
NM cable (Romex) on a 50 amp breaker
NM-B must use the 60 °C column (NEC 334.80), so the sizes that look right in the 75 °C column do not work in NM cable:
| NM-B copper size | 60 °C ampacity | On a 50 A breaker? |
|---|---|---|
| 8 AWG (8/2, 8/3) | 40 A | No: 40 A is a standard breaker size, so 240.4(B) does not apply |
| 6 AWG (6/2, 6/3) | 55 A | Yes |
NEC 240.4(B) lets a conductor go on the next standard breaker size only when its ampacity is not itself a standard rating. 40 A is in the 240.6(A) list, so 8 AWG NM-B is a 40 A cable, full stop. This is the most common mistake at 50 A.
Wire size for a 50 amp EV charger or NEMA 14-50 outlet
| Charger output | Breaker (125%) | Copper THHN, 75 °C | Copper NM-B, 60 °C |
|---|---|---|---|
| 24 A | 30 A | 10 AWG (35 A) | 10 AWG (30 A) |
| 32 A | 40 A | 8 AWG (50 A) | 8 AWG (40 A) |
| 40 A | 50 A | 8 AWG (50 A) | 6 AWG (55 A) |
EV supply equipment is a continuous load, so NEC 625.41 sizes the breaker at 125% of the charger's rating and 210.19(A)(1) sizes the conductors the same way. A charger set to 40 A therefore needs a 50 A breaker and conductors rated at least 50 A. A plug-in charger on a NEMA 14-50 receptacle uses four wires (two hots, neutral, ground), and NEC Table 210.21(B)(3) allows a 50 A receptacle on a 40 A or 50 A circuit. Check the charger manual for its maximum setting on a 14-50 plug.
Wire size for a 50 amp range, cooktop or oven
NEC 210.19(A)(3) sets the minimum branch-circuit rating for a household range of 8¾ kW or more at 40 A, and Table 220.55 gives the demand load used to size it. Many ranges list a 40 A or 50 A circuit on the nameplate; follow the nameplate. For a 50 A range circuit:
- 6/3 NM-B with ground (6 AWG, 55 A at 60 °C), or
- 8 AWG copper THHN in conduit (50 A) when the range terminal block and breaker are rated 75 °C, or
- 6 AWG aluminum SER (50 A at 75 °C) where the terminals are rated for aluminum.
New range circuits need a separate insulated neutral and equipment ground (four-wire). The older three-wire connection using the neutral as the ground is only allowed to stay on existing branch circuits (NEC 250.140 exception).
Wire size for 50 amps by distance (240 V)
Smallest size that keeps a 120/240 V single-phase run at or under a 3% voltage drop. The 40 A columns are for a continuous load on a 50 A breaker, such as an EV charger. Ampacity sets the floor, so the table never goes below 8 AWG copper or 6 AWG aluminum (75 °C).
| Run | Cu, 50 A | Cu, 40 A | Al, 50 A | Al, 40 A |
|---|---|---|---|---|
| 50 ft | 8 AWG | 8 AWG | 6 AWG | 6 AWG |
| 75 ft | 8 AWG | 8 AWG | 6 AWG | 6 AWG |
| 100 ft | 6 AWG | 8 AWG | 4 AWG | 6 AWG |
| 125 ft | 6 AWG | 6 AWG | 4 AWG | 4 AWG |
| 150 ft | 4 AWG | 6 AWG | 3 AWG | 4 AWG |
| 200 ft | 4 AWG | 4 AWG | 2 AWG | 3 AWG |
| 250 ft | 3 AWG | 4 AWG | 1 AWG | 2 AWG |
| 300 ft | 2 AWG | 3 AWG | 1/0 AWG | 1 AWG |
Example: a 40 A EV charger in a detached garage 150 ft from the panel. 8 AWG copper reaches 117 ft at 40 A, so the run needs 6 AWG copper, which reaches 183 ft. The ground must then be upsized too (see ground).
Maximum length at 50 amps by wire size
The longest one-way run, in feet, before each size reaches the drop shown. Three-phase columns use the √3 formula. These are DC resistance figures.
Copper
| Size | 240 V, 3% | 240 V at 40 A, 3% | 240 V, 5% | 208 V 3-ph, 3% | 480 V 3-ph, 3% |
|---|---|---|---|---|---|
| 8 AWG | 94 | 117 | 157 | 94 | 217 |
| 6 AWG | 146 | 183 | 244 | 146 | 338 |
| 4 AWG | 233 | 292 | 389 | 233 | 539 |
| 3 AWG | 293 | 367 | 489 | 294 | 678 |
| 2 AWG | 371 | 463 | 618 | 371 | 857 |
| 1 AWG | 467 | 584 | 779 | 467 | 1079 |
| 1/0 AWG | 590 | 737 | 983 | 590 | 1362 |
Aluminum
| Size | 240 V, 3% | 240 V at 40 A, 3% | 240 V, 5% | 208 V 3-ph, 3% | 480 V 3-ph, 3% |
|---|---|---|---|---|---|
| 6 AWG | 89 | 111 | 148 | 89 | 205 |
| 4 AWG | 141 | 177 | 236 | 141 | 327 |
| 3 AWG | 178 | 223 | 297 | 178 | 412 |
| 2 AWG | 225 | 282 | 376 | 225 | 521 |
| 1 AWG | 284 | 355 | 474 | 284 | 657 |
| 1/0 AWG | 358 | 447 | 597 | 358 | 827 |
| 2/0 AWG | 452 | 566 | 754 | 453 | 1045 |
| 3/0 AWG | 571 | 714 | 952 | 571 | 1319 |
Formulas: single phase L = %·V·1000 / (2·I·R), three phase L = %·V·1000 / (√3·I·R), with R in ohms per 1000 ft. The NEC informational notes in 210.19 and 215.2 recommend 3% on a branch circuit or feeder and 5% total. Use the voltage drop calculator for your exact load.
Ground wire for 50 amps
- Equipment grounding conductor: 10 AWG copper or 8 AWG aluminum, from the 60 A row of NEC Table 250.122 (a 50 A breaker falls in that row).
- Upsized hots: going from 8 AWG (16,510 cmil) to 6 AWG (26,240 cmil) is a ratio of 1.59, so under 250.122(B) the 10 AWG ground (10,380 cmil) must be at least 16,498 cmil, which is 8 AWG copper (16,510 cmil).
Conduit size for 50 amp wire
Smallest conduit at 40% fill (NEC Chapter 9 Table 1) using THHN/THWN-2 areas from Chapter 9 Table 5.
| Run | Conductors | Area, in² | EMT | PVC 40 |
|---|---|---|---|---|
| Range or subpanel feeder, copper 75 °C (2 hots + neutral) | 3 × 8 AWG + 10 AWG | 0.131 | 3/4 | 3/4 |
| Subpanel feeder, aluminum 75 °C (2 hots + neutral) | 3 × 6 AWG + 8 AWG | 0.189 | 3/4 | 3/4 |
| 240 V EV charger, welder or other 2-wire load, copper | 2 × 8 AWG + 10 AWG | 0.094 | 1/2 | 1/2 |
| Feeder upsized for 150 ft, copper | 3 × 6 AWG + 8 AWG | 0.189 | 3/4 | 3/4 |
XHHW-2 aluminum areas differ slightly from THHN, so check the conduit fill calculator for your insulation.
How much load can a 50 amp circuit carry?
| System | At 50 A | Continuous (40 A) |
|---|---|---|
| 120 V single phase | 6.0 kW | 4.8 kW |
| 240 V single phase | 12.0 kW | 9.6 kW |
| 208 V three phase | 18.0 kW | 14.4 kW |
| 480 V three phase | 41.6 kW | 33.3 kW |
| 600 V three phase | 52.0 kW | 41.6 kW |
Balanced load, unity power factor. The amps to watts calculator handles power factor.
When more than three wires share a conduit
With four to six current-carrying conductors in one raceway, NEC 310.15(C)(1) cuts ampacity to 80%. From the 90 °C column, 8 AWG copper drops to 44 A, which is under 50 A, so upsize to 6 AWG (60 A). At seven to nine conductors (70%) 6 AWG gives 52 A, still enough. See wire derating.
In Canada
CEC Table 2 (copper) and Table 4 (aluminum) give the same ampacities for these sizes, so 8 AWG copper or 6 AWG aluminum carries 50 A at 75 °C. Rule 8-102 makes the 3% and 5% voltage drop limits mandatory, and distances are in metres. Use the Canadian wire size calculator or see CEC Table 2.
For larger circuits, see wire size for 60 amps, 100 amps and 200 amps.
This page is a quick reference. Confirm against the code edition your jurisdiction has adopted, the equipment markings and your inspector.