4 AWG voltage drop at 250 feet
Computed voltage drop for 4 AWG copper conductors on a 250 ft one-way run.
10.47 V
drop on 4 AWG copper, 250 ft one-way, 68 A load · 8.7% of 120 V · 4.4% of 240 V
4 AWG at 250 ft by load
| Load | Drop | % at 120 V | % at 240 V | 3% rule (240 V) |
|---|---|---|---|---|
| 17 A | 2.62 V | 2.2% | 1.1% | OK |
| 34 A | 5.24 V | 4.4% | 2.2% | OK |
| 51 A | 7.85 V | 6.5% | 3.3% | OK at 240 V up to 5% |
| 68 A | 10.47 V | 8.7% | 4.4% | OK at 240 V up to 5% |
Vd = 2 × length × R × I ÷ 1000, R = 0.308 Ω/1000 ft (copper, NEC Ch. 9 Table 8). Aluminum is about 1.6× higher.
Same wire, other distances
25 ft · 50 ft · 75 ft · 100 ft · 125 ft · 150 ft · 200 ft · 300 ft
FAQ
What is the voltage drop on 4 AWG wire at 250 feet?
At 68 A (80% of its 85 A 75°C rating) 4 AWG copper drops 10.47 V over 250 ft one-way: 8.7% at 120 V or 4.4% at 240 V.
How far can I run 4 AWG at 68 amps?
To stay within 3% at 120 V, about 86 ft one-way; at 240 V about 172 ft.