12 AWG voltage drop at 300 feet
Computed voltage drop for 12 AWG copper conductors on a 300 ft one-way run.
18.53 V
drop on 12 AWG copper, 300 ft one-way, 16 A load · 15.4% of 120 V · 7.7% of 240 V
12 AWG at 300 ft by load
| Load | Drop | % at 120 V | % at 240 V | 3% rule (240 V) |
|---|---|---|---|---|
| 4 A | 4.63 V | 3.9% | 1.9% | OK |
| 8 A | 9.26 V | 7.7% | 3.9% | OK at 240 V up to 5% |
| 12 A | 13.90 V | 11.6% | 5.8% | Upsize |
| 16 A | 18.53 V | 15.4% | 7.7% | Upsize |
Vd = 2 × length × R × I ÷ 1000, R = 1.93 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 12 AWG wire at 300 feet?
At 16 A (80% of its 20 A 75°C rating) 12 AWG copper drops 18.53 V over 300 ft one-way: 15.4% at 120 V or 7.7% at 240 V.
How far can I run 12 AWG at 16 amps?
To stay within 3% at 120 V, about 58 ft one-way; at 240 V about 117 ft.