Minimum size by temperature column
| Conductor | 60°C | 75°C | 90°C |
|---|---|---|---|
| Copper | 6 AWG55 A | 8 AWG50 A | 8 AWG55 A |
| Aluminum | 4 AWG55 A | 6 AWG50 A | 6 AWG55 A |
Equipment grounding conductor
A circuit protected at 50 A takes a 10 AWG copper or 8 AWG aluminum equipment grounding conductor, from the 60 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 |
|---|---|---|
| 6 AWG copper | 70 ft | 145 ft |
| 4 AWG aluminum | 70 ft | 140 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 50 A circuit feeds
- Electric ranges on a NEMA 14-50 receptacle
- EV charging and RV pedestals
- Welders and small subpanel feeders
Fifty amps is the range and RV rating and the usual home charging circuit. It takes 6 AWG copper or 4 AWG aluminum at 60°C, which is what 6/3 NM-B and 6/3 UF provide. Where the equipment is marked for 75°C, 8 AWG copper or 6 AWG aluminum reaches exactly 50 A with nothing left over for derating or voltage drop.
The 14-50 receptacle is the standard for ranges and RV pedestals, and it is what most home chargers plug into. Welders are the case where the rating is not used directly: Article 630 sizes a welder circuit from the duty cycle in Table 630.11(A) instead of the nameplate primary current, so a welder with a 50 A nameplate can sit on a smaller circuit.
Many 14-50 outlets in homes were added for a charger rather than a range. The circuit needs a four-wire cable and a box sized for the conductors, and a 14-50 in a garage, outdoors, or a crawl space falls under 210.8(A), which requires ground-fault protection for the receptacle. The same outlet inside a living space does not.
50 A wire size questions
- What size wire do I need for a 50 amp circuit?
- Use 6 AWG copper or 4 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, 8 AWG copper or 6 AWG aluminum carries the circuit.
- What size ground wire for a 50 amp circuit?
- 10 AWG copper or 8 AWG aluminum, taken from the 60 A row of NEC Table 250.122.
- What size aluminum wire for 50 amps?
- 4 AWG aluminum at the 60°C column carries 55 A. Terminations on aluminum conductors must be identified for the material.
- Can I use 8 AWG copper for 50 A?
- Table 310.16 lists 8 AWG copper at 40 A at 60°C, 50 A at 75°C, and 55 A at 90°C. It falls short at 60°C, the column this circuit uses. The 75°C and 90°C columns do reach 50 A, and a higher column applies only where every termination is listed for it.
- Is 50 A enough for EV charging?
- A 40 A EV charger is the largest continuous load a 50 A circuit can supply, because 625.41 requires a branch circuit rated at 125% of the charger's maximum load. That is why a 14-50 outlet is the usual home charging circuit.