| Rule | Copper | Aluminum |
|---|---|---|
| 60°C column — NM-B cable, or any termination not marked 75°C | 4 AWG | 3 AWG |
| 75°C column — THHN/THWN-2 with 75°C-rated breaker and lugs | 6 AWG | 4 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.
Sub-panels, large EV chargers, heavy equipment
| 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 | 1.47 V | 0.6% | Within the 3% branch-circuit target |
| 50 ft | 2.95 V | 1.2% | Within the 3% branch-circuit target |
| 75 ft | 4.42 V | 1.8% | Within the 3% branch-circuit target |
| 100 ft | 5.89 V | 2.5% | Within the 3% branch-circuit target |
| 150 ft | 8.84 V | 3.7% | Over 3% — upsize one gauge |
| 200 ft | 11.78 V | 4.9% | 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 60-amp circuit needs 4 AWG copper or 3 AWG aluminum. With THHN/THWN-2 conductors and breakers and lugs rated 75°C, 6 AWG copper or 4 AWG aluminum is permitted.
A 60-amp circuit uses a 60A 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 60-amp garage sub-panel feeder uses 6 AWG copper or 4 AWG aluminum THHN/XHHW with 75°C terminations, or 4 AWG copper or 3 AWG aluminum if the 60°C column applies (NM-B cable or 60°C lugs). It supports a small workshop with lighting, outlets and one 240V tool circuit.
Wire size can differ. At 50A, 6 AWG copper works in either column (55A at 60°C). At 60A, 6 AWG copper is only enough with 75°C-rated terminations and THHN (65A); with NM-B or 60°C terminations you need 4 AWG copper (70A). 50A circuits typically feed ranges, hot tubs and EV chargers; 60A circuits feed sub-panels, larger welders and high-draw HVAC equipment.