Dryers, water heaters, small AC units
| Diameter | 2.5882 mm (0.101897") |
| Area | 5.2612 mm² |
| Resistance at 20°C | 3.2768 Ω/km |
| Weight | 47.14 kg/km |
| Ampacity (75°C) | 35 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.
NEC Table 310.16 rates 10 AWG copper at 35 A at 75°C, which looks like more headroom than a 30A circuit needs. It is not usable headroom. NEC 240.4(D), the small-conductor rule, caps the overcurrent device on 10 AWG copper at 30 A regardless of what the ampacity table says.
This is why 10 AWG is the answer for a 30A circuit and why the next size down is not: the smaller conductor’s own 240.4(D) cap falls below 30 A. Any calculator that reads Table 310.16 without applying 240.4(D) will hand you an undersized, code-violating conductor.
The rule covers 18 through 10 AWG copper and 12 through 10 AWG aluminum. NEC 240.4(E) and 240.4(G) carve out narrow exceptions — tap conductors, motor circuits, air-conditioning equipment, and welders are sized under their own articles instead. See the full table on the wire size calculator.
| One-way run | Drop | % of 240V | Verdict |
|---|---|---|---|
| 25 ft | 1.50 V | 0.6% | Within the 3% branch-circuit target |
| 50 ft | 3.00 V | 1.2% | Within the 3% branch-circuit target |
| 75 ft | 4.49 V | 1.9% | Within the 3% branch-circuit target |
| 100 ft | 5.99 V | 2.5% | Within the 3% branch-circuit target |
| 150 ft | 8.99 V | 3.7% | Over 3% — upsize one gauge |
| 200 ft | 11.99 V | 5.0% | Over 3% — upsize one gauge |