What Size Wire for 40 Amps at 200 Feet?
Voltage-drop-aware wire sizing for a 40-amp circuit running 200 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 2.1%. For ≤5% drop: 6 (3.3%).
Actual drop 2.7%. For ≤5% drop: 4 (3.4%).
At 200 ft, voltage drop governs: ampacity alone would allow 8 AWG copper, but staying ≤3% requires upsizing to 4.
Voltage Drop at 200 Feet
Voltage drop is calculated for a 240V single-phase circuit over a 200 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%? |
|---|---|---|---|
| 8 | 5.1% | 8.4% | — |
| 6 | 3.3% | 5.4% | — |
| 4 | 2.1% | 3.4% | |
| 3 | 1.6% | 2.7% | |
| 2 | 1.3% | 2.1% | |
| 1 | 1.0% | 1.7% |
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 40A, 240V, 200 ft to adjust material, temperature and drop target.