What Size Wire for 100 Amps at 250 Feet?
Voltage-drop-aware wire sizing for a 100-amp circuit running 250 ft (one-way) at 240V — because over distance, voltage drop, not ampacity, often sets the wire size.
Calculations are built on the 2023 National Electrical Code (NEC) and cross-checked against the published code tables. How we verify. Last reviewed June 2026.
Actual drop 2.5%. For ≤5% drop: 2 (4.0%).
Actual drop 2.6%. For ≤5% drop: 1/0 (4.2%).
At 250 ft, voltage drop governs: ampacity alone would allow 3 AWG copper, but staying ≤3% requires upsizing to 1/0.
Voltage Drop at 250 Feet
Voltage drop is calculated for a 240V single-phase circuit over a 250 ft one-way run (conductor length doubled for the return). Sizes meeting the ≤3% target are highlighted.
| Wire size | Copper drop | Aluminum drop | Within 3%? |
|---|---|---|---|
| 3 | 5.1% | 8.4% | — |
| 2 | 4.0% | 6.6% | — |
| 1 | 3.2% | 5.3% | — |
| 1/0 | 2.5% | 4.2% | |
| 2/0 | 2.0% | 3.3% | |
| 3/0 | 1.6% | 2.6% |
Drop % uses NEC Chapter 9, Table 8 DC resistance — an accepted approximation for typical power-factor AC branch circuits. The wire must also meet ampacity; both checks are applied above.
Different distance or voltage?
Open the calculator pre-filled with 100A, 240V, 250 ft to adjust material, temperature and drop target.