4 AWG voltage drop at 100 feet
Computed voltage drop for 4 AWG copper conductors on a 100 ft one-way run.
4.19 V
drop on 4 AWG copper, 100 ft one-way, 68 A load · 3.5% of 120 V · 1.7% of 240 V
4 AWG at 100 ft by load
| Load | Drop | % at 120 V | % at 240 V | 3% rule (240 V) |
|---|---|---|---|---|
| 17 A | 1.05 V | 0.9% | 0.4% | OK |
| 34 A | 2.09 V | 1.7% | 0.9% | OK |
| 51 A | 3.14 V | 2.6% | 1.3% | OK |
| 68 A | 4.19 V | 3.5% | 1.7% | OK |
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 · 125 ft · 150 ft · 200 ft · 250 ft · 300 ft
FAQ
What is the voltage drop on 4 AWG wire at 100 feet?
At 68 A (80% of its 85 A 75°C rating) 4 AWG copper drops 4.19 V over 100 ft one-way: 3.5% at 120 V or 1.7% 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.