Ranges, cooktops, RV hookups, welders and many car chargers sit on a circuit of this size, so this is one of the most common questions at the electrical aisle. The table below shows how the answer changes as the run gets longer.
How to use this calculator
- Keep the current at the breaker size, 50 amps, unless your load's label says it draws less and you size for that.
- Enter the one-way distance from the panel to the outlet or the appliance, not the length of cable you buy for the loop.
- Choose copper or aluminum, and for copper whether you pull NM-B cable through the walls or single wires in conduit.
- If the load runs at full current for 3 hours or more, mark it as continuous. A car charger does, so its circuit is usually sized for 125 percent of the charger's current.
Worked examples
An electric range across the kitchen
Load current: 50 A · Circuit voltage: 240 V · One-way distance: 30 ft
- Wire size
- 6 AWG copper
- Current the wire must carry
- 50.0 A
- Rated for
- 55 A
- Voltage drop
- 0.61%
- Longest run within 3%
- 147 ft
An RV pedestal at the end of the driveway
Load current: 50 A · Circuit voltage: 240 V · One-way distance: 120 ft · Wire type: THHN/THWN wires in conduit (75 °C)
- Wire size
- 6 AWG copper
- Current the wire must carry
- 50.0 A
- Rated for
- 65 A
- Voltage drop
- 2.46%
- Longest run within 3%
- 147 ft
A car charger set to its full output
Load current: 40 A · Circuit voltage: 240 V · One-way distance: 45 ft · Wire type: THHN/THWN wires in conduit (75 °C) · Runs for 3 hours or more at a time: Yes, a continuous load
- Wire size
- 8 AWG copper
- Current the wire must carry
- 50.0 A
- Rated for
- 50 A
- Voltage drop
- 1.17%
- Longest run within 3%
- 116 ft
An aluminum feeder to a welder in the barn
Load current: 50 A · Circuit voltage: 240 V · One-way distance: 160 ft · Conductor: Aluminum
- Wire size
- 3 AWG aluminum
- Current the wire must carry
- 50.0 A
- Rated for
- 75 A
- Voltage drop
- 2.69%
- Longest run within 3%
- 179 ft
Wire size for a 50 amp, 240 volt circuit by one-way distance
| One-way distance | Copper, NM-B or UF-B cable (60 °C) | Copper, THHN/THWN wires in conduit (75 °C) | Aluminum |
|---|---|---|---|
| 25 ft | 6 AWG | 8 AWG | 6 AWG |
| 50 ft | 6 AWG | 8 AWG | 6 AWG |
| 75 ft | 6 AWG | 8 AWG | 6 AWG |
| 100 ft | 6 AWG | 6 AWG | 4 AWG |
| 150 ft | 4 AWG | 4 AWG | 3 AWG |
| 200 ft | 4 AWG | 4 AWG | 2 AWG |
Each cell: the smallest size that carries the current and keeps the drop within the branch-circuit limit. Base table only: a hot attic or a bundle of cables can call for a size up.
Why NM-B cable needs 6 AWG and THHN only 8 AWG
The code's ampacity table has a column for each insulation temperature. NM-B cable has to use the lowest one, where 8 AWG copper is good for 40 amps and 6 AWG for 55 amps, so a 50 amp breaker on NM-B needs 6 AWG. Single THHN or THWN wires in conduit may use the next column, where 8 AWG carries 50 amps, but only when the breaker and the receptacle or appliance terminals are marked for that temperature. Most residential breakers are; a cheap receptacle may not be.
Aluminum is rated lower than copper of the same size: 6 AWG aluminum carries 50 amps, just enough for this circuit. It is common for feeders and long outdoor runs because it costs less, but the terminals must be rated for aluminum.
When the distance changes the answer
Current alone settles the size on a short run. On a long one the wire also has to keep voltage drop within about 3 percent, or a range element heats slowly and a welder's arc gets weak. At this current that starts to matter beyond roughly the length of a big house, and the table shows each size where it takes over. For an RV pedestal or a detached shop, enter the real distance rather than reading the short-run answer.
A car charger on a 50 amp circuit
A charger that runs for hours is a continuous load, so the wire and breaker must carry 125 percent of what it draws. That is why a charger set to forty amps goes on a 50 amp circuit, and why the calculator asks whether the load is continuous. Check the charger's manual for its setting and the breaker it calls for, and the voltage drop calculator for a long run to a driveway post.
Common questions
Is 8 gauge wire enough for 50 amps?
Only as single copper THHN or THWN wires rated for the higher temperature column, with terminals rated for it, where 8 AWG carries 50 amps. In NM-B cable 8 AWG is good for 40 amps, so a 50 amp breaker needs 6 AWG.
What size aluminum wire for 50 amps?
6 AWG aluminum carries 50 amps in the higher temperature column, enough for a short run. Over a long distance voltage drop pushes it to 4 AWG or larger; the table shows where.
Can I use 6/3 NM-B for a 50 amp range?
Yes. 6 AWG copper NM-B is rated 55 amps, above the 50 amp breaker, and the third wire carries the neutral a range needs for its clock and controls.
What wire do I need for a 50 amp RV hookup?
A 50 amp RV pedestal is a 120/240 volt circuit with two hots, a neutral and a ground. The size follows the same rule as any 50 amp circuit, but pedestals are often far from the panel, so enter the distance: past a long driveway voltage drop usually calls for the next size up.