Voltage drop by wire size (30 A, 200 ft, 240 V)
| Copper wire | Drop (V) | Drop (%) | Within 3% |
|---|---|---|---|
| 10 AWG | 14.52 V | 6.05% | ✗ |
| 8 AWG | 9.17 V | 3.82% | ✗ |
| 6 AWG | 5.89 V | 2.46% | ✓ |
| 4 AWG | 3.70 V | 1.54% | ✓ |
| 3 AWG | 2.94 V | 1.23% | ✓ |
Voltage drop = 2 × 200 ft × 30 A × resistance ÷ 1000. Keeping it under 3% on branch circuits (5% total) is the NEC recommendation in the informational notes to 210.19 and 215.2.
Frequently asked questions
Is 10 AWG enough for 30 amps at 200 feet?
It carries 30 A, but at 200 ft the voltage drop is 6.0%. That is over 3%, so the next size up is recommended.
Does the distance include the return wire?
No. Enter the one-way distance; the formula already counts both conductors.