50 amp wire size
The wire size for a 50 amp circuit depends on the wiring method more than at any other rating. In NM-B cable, held to the 60 °C column, 8 AWG copper reaches only 40 A, so the minimum is 6 AWG copper (55 A). As THHN in conduit with 75 °C terminations, 8 AWG copper is rated exactly 50 A and is the minimum.
Minimum wire size for 50 A
| Conductor | 60 °C column | 75 °C column |
|---|---|---|
| Copper | 6 AWG | 8 AWG |
| Aluminum | Not listed | 6 AWG |
Usually chosen: 6 AWG copper (6/3 NM-B) for a cable run, or 8 AWG copper THHN in conduit with 75 °C terminations. In aluminum the minimum is 6 AWG.
Breaker rating taken as the required ampacity; 240.4(D) limits applied. The charts list no 60 °C aluminum, and 60 °C copper only to 2 AWG (95 A), the largest NM-B. Manufacturer chart values (2017 NEC basis). Verify against the NEC edition adopted locally.
That split explains why 50 A range and EV charger circuits are found in both sizes. The answer box gives both columns; the sections below cover ranges, RV hookups, EV chargers and subpanels, which are the four main 50 A loads.
Where 50 amp circuits are used
Large freestanding ranges, double wall ovens and combination range-and-oven setups are often listed for a 50 A circuit, and the NEMA 14-50 receptacle is the standard range connection. Under 210.21(B)(3) a 50 A branch circuit must use a 50 A receptacle.
RV parks and home RV pads use a 50 A, 120/240 V NEMA 14-50 outlet for larger motorhomes. Unlike a range, an RV can draw close to 50 A on each leg for hours with air conditioners running, so the full-load drop figures are a fair guide on long runs to a pad.
A 40 A EV charger output needs a 50 A circuit, because charging is continuous and Article 625 applies 125%. Many plug-in chargers use a 14-50 receptacle on such a circuit. A 50 A feeder is also a common size for a small subpanel in a garage or workshop, where it feeds a few 20 A circuits and a tool circuit or two.
Voltage drop at 50 A
With 8 AWG copper at the full 50 A, the drop reaches 3% at about 92 ft at 240 V; 6 AWG copper stretches that to about 146 ft. RV pads and detached garages are the usual long runs at this rating.
Because an RV hookup feeds 120 V loads on each leg, its practical voltage drop is closer to the 240 V column when the two legs are balanced and to the 120 V column when one leg carries most of the load.
| One-way length (ft) | Drop at 120 V (%) | Drop at 240 V (%) | Copper for 3% at 120 V | Copper for 3% at 240 V |
|---|---|---|---|---|
| 25 | 1.62 | 0.81 | 8 AWG | 8 AWG |
| 50 | 3.25 | 1.62 | 6 AWG | 8 AWG |
| 75 | 4.87 | 2.44 | 4 AWG | 8 AWG |
| 100 | 6.49 | 3.25 | 4 AWG | 6 AWG |
| 150 | 9.74 | 4.87 | 2 AWG | 4 AWG |
| 200 | 12.99 | 6.49 | 1 AWG | 4 AWG |
| 250 | 16.23 | 8.12 | 1/0 AWG | 3 AWG |
| 300 | 19.48 | 9.74 | 2/0 AWG | 2 AWG |
Full rating on a single-phase circuit, copper at 75 °C, stranded.
Breaker pairing
A 50 A circuit uses a two-pole 50 A breaker. With 6 AWG NM-B, the cable's 55 A rating is above the breaker; with 8 AWG THHN in conduit, the 50 A rating matches it, but only if the breaker and the receptacle or equipment are both marked for 75 °C.
The next-size-up allowance of 240.4(B) does not help 8 AWG NM-B onto a 50 A breaker: its 60 °C ampacity, 40 A, is itself a standard rating, and 240.4(B) applies only when a conductor's ampacity falls between standard ratings.
NM-B cable or THHN in conduit
6/3 NM-B with ground is the common cable for a 50 A range or RV outlet, providing two hot conductors, a neutral and a ground. 6/2 with ground serves a 240 V-only charger. 6 AWG cable is stiff, and it often has to be landed in a deep box with a receptacle that has back-wired clamps.
8 AWG THHN in conduit is lighter and cheaper but depends on the 75 °C rating of both ends. Many 14-50 receptacles are rated 60/75 °C; a receptacle marked 60 °C only would send the conductor back to 6 AWG.
Copper or aluminum
6 AWG aluminum reads 50 A in the 75 °C column of the manufacturer charts and is the aluminum minimum. Aluminum SER cable or aluminum conductors in conduit are used for 50 A subpanel feeders, where the lugs are routinely rated for aluminum.
Range and RV receptacles often accept copper only, so a branch circuit to one of them is normally copper even where the feeder is aluminum.
Common mistakes
8 AWG NM-B on a 50 A breaker
8 AWG NM-B is a 40 A cable. Using it for a 50 A range or RV outlet is the most frequent error at this rating; the cable must be 6 AWG copper.
A 14-50 receptacle on a smaller circuit for an EV
Fitting a 14-50 to a 30 A or 40 A circuit and leaving the charger at its 40 A default overloads the circuit. The charger's current setting must match 80% of the breaker.
Three-wire feeders to a subpanel
A subpanel feeder needs a separate neutral and equipment grounding conductor, and the neutral bar in the subpanel is kept isolated from the enclosure.
Undersized RV pad runs
A 50 A RV outlet 150 ft from the panel on 6 AWG copper drops more than 3% at full load. Air conditioners on low voltage run hot; 4 AWG or aluminum of equivalent size is the usual answer.
Frequently asked questions
Is 8 gauge wire good for 50 amps?
Only as THHN or THWN-2 in conduit with 75 °C terminations, where 8 AWG copper is rated 50 A. In NM-B cable, 8 AWG is limited to 40 A, so 6 AWG copper is required.
What size wire is needed for a 50 amp RV outlet?
A 50 A, 120/240 V RV outlet is normally wired with 6 AWG copper (6/3 with ground). Long runs to the pad may need 4 AWG copper to keep the voltage drop within 3%.
Can 6 gauge wire be used on a 60 amp breaker?
In conduit with 75 °C terminations, 6 AWG copper is rated 65 A and suits a 60 A breaker. 6 AWG NM-B, rated 55 A, may sit on a 60 A breaker only under the next-size-up rule of 240.4(B), with a calculated load of 55 A or less.
What wire size is used for a 50 amp subpanel?
6 AWG copper or 4 AWG aluminum is a common choice for a 50 A feeder; the 75 °C minimums are 8 AWG copper and 6 AWG aluminum. The feeder needs four conductors: two hots, a neutral and a ground.
What size wire is used for a 40 amp EV charger on a 50 amp circuit?
A charger delivering 40 A needs a 50 A circuit, wired with 6 AWG copper in NM-B or 8 AWG copper THHN in conduit with 75 °C terminations.