| Rule | Copper | Aluminum |
|---|---|---|
| 60°C column — NM-B cable, or any termination not marked 75°C | 6 AWG | 4 AWG |
| 75°C column — THHN/THWN-2 with 75°C-rated breaker and lugs | 8 AWG | 6 AWG |
Most breakers and panelboards rated 100A or less are listed 60/75°C, but NM-B cable is always limited to the 60°C column (NEC 334.80). When in doubt, use the 60°C answer.
Ranges, hot tubs, EV chargers, sub-panels
| Diameter | 4.1154 mm (0.162023") |
| Area | 13.3018 mm² |
| Resistance at 20°C | 1.2961 Ω/km |
| Weight | 119.184 kg/km |
| Ampacity (75°C) | 65 A |
Important: For long wire runs, you may need to upsize the wire to compensate for voltage drop. NEC recommends keeping voltage drop under 3% for branch circuits. Use our voltage drop calculator to check.
| One-way run | Drop | % of 240V | Verdict |
|---|---|---|---|
| 25 ft | 1.23 V | 0.5% | Within the 3% branch-circuit target |
| 50 ft | 2.46 V | 1.0% | Within the 3% branch-circuit target |
| 75 ft | 3.68 V | 1.5% | Within the 3% branch-circuit target |
| 100 ft | 4.91 V | 2.0% | Within the 3% branch-circuit target |
| 150 ft | 7.37 V | 3.1% | Over 3% — upsize one gauge |
| 200 ft | 9.82 V | 4.1% | Over 3% — upsize one gauge |
Using the 60°C column of NEC Table 310.16, which NEC 110.14(C) requires by default for circuits of 100A or less and always for NM-B cable, a 50-amp circuit needs 6 AWG copper or 4 AWG aluminum. With THHN/THWN-2 conductors and breakers and lugs rated 75°C, 8 AWG copper or 6 AWG aluminum is permitted.
A 50-amp circuit uses a 50A double-pole circuit breaker. The breaker protects the 6 AWG copper (or 4 AWG aluminum) wire from overload. Double-pole breakers are used for 240V circuits and occupy two slots in the panel.
A 50-amp hot tub circuit requires 6 AWG copper or 4 AWG aluminum wire on a 50A GFCI double-pole breaker. NEC 680.44 requires GFCI protection for hot tub feeders. The disconnect must be within sight of the spa, 5–50 feet away.
EV chargers are continuous loads, so the circuit must be rated at 125% of the charger current (NEC 625.41). A 40A charger needs a 50A circuit: 6 AWG copper in NM-B, or 8 AWG THHN with 75°C terminations. A 48A charger needs a 60A circuit: 6 AWG THHN with 75°C terminations, or 4 AWG copper if the 60°C column applies (including NM-B).