4 AWG voltage drop at 300 feet
Computed voltage drop for 4 AWG copper conductors on a 300 ft one-way run.
12.57 V
drop on 4 AWG copper, 300 ft one-way, 68 A load · 10.5% of 120 V · 5.2% of 240 V
4 AWG at 300 ft by load
| Load | Drop | % at 120 V | % at 240 V | 3% rule (240 V) |
|---|---|---|---|---|
| 17 A | 3.14 V | 2.6% | 1.3% | OK |
| 34 A | 6.28 V | 5.2% | 2.6% | OK |
| 51 A | 9.42 V | 7.9% | 3.9% | OK at 240 V up to 5% |
| 68 A | 12.57 V | 10.5% | 5.2% | Upsize |
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 · 250 ft
FAQ
What is the voltage drop on 4 AWG wire at 300 feet?
At 68 A (80% of its 85 A 75°C rating) 4 AWG copper drops 12.57 V over 300 ft one-way: 10.5% at 120 V or 5.2% 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.