What Size Wire for 125 Amps at 75 Feet?
Voltage-drop-aware wire sizing for a 125-amp circuit running 75 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 1.2%. For ≤5% drop: 1 (1.2%).
Actual drop 1.2%. For ≤5% drop: 2/0 (1.2%).
At 75 ft, ampacity still governs: 1 AWG copper carries 125A and its drop (1.2%) is already within 3% — no upsizing needed.
Voltage Drop at 75 Feet
Voltage drop is calculated for a 240V single-phase circuit over a 75 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%? |
|---|---|---|---|
| 1 | 1.2% | 2.0% | |
| 1/0 | 1.0% | 1.6% | |
| 2/0 | 0.8% | 1.2% | |
| 3/0 | 0.6% | 1.0% | |
| 4/0 | 0.5% | 0.8% | |
| 250 kcmil | 0.4% | 0.7% |
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 125A, 240V, 75 ft to adjust material, temperature and drop target.