What Size Wire for 100 Amps at 300 Feet?
Voltage-drop-aware wire sizing for a 100-amp circuit running 300 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 2.4%. For ≤5% drop: 2 (4.9%).
Actual drop 2.5%. For ≤5% drop: 2/0 (4.0%).
At 300 ft, voltage drop governs: ampacity alone would allow 3 AWG copper, but staying ≤3% requires upsizing to 2/0.
Voltage Drop at 300 Feet
Voltage drop is calculated for a 240V single-phase circuit over a 300 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 | 6.1% | 10.1% | — |
| 2 | 4.9% | 8.0% | — |
| 1 | 3.9% | 6.3% | — |
| 1/0 | 3.1% | 5.0% | — |
| 2/0 | 2.4% | 4.0% | |
| 3/0 | 1.9% | 3.1% |
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, 300 ft to adjust material, temperature and drop target.