Over 200 feet one-way, 10 AWG copper drops 6.2% at 15A on 120V and 6.2% at 30A on 240V: no load in this table stays under 3% at 120V, and no load in this table stays under 3% at 240V.
Single phase, copper conductor, one-way distance. ✅ = under 3%, ⚠️ = 3-5%, ❌ = over 5%
| Load | V-Drop | @ 120V | @ 240V |
|---|---|---|---|
| 15A | 7.4V | ❌ 6.2% | ⚠️ 3.1% |
| 20A | 9.9V | ❌ 8.3% | ⚠️ 4.1% |
| 25A | 12.4V | ❌ 10.3% | ❌ 5.2% |
| 30A | 14.9V | ❌ 12.4% | ❌ 6.2% |
Longest one-way distance that keeps single-phase copper within 3%.
| Load | @ 120V | @ 240V |
|---|---|---|
| 15A | 95 ft | 195 ft |
| 20A | 75 ft | 145 ft |
| 25A | 60 ft | 115 ft |
| 30A | 50 ft | 95 ft |
Voltage drop for single-phase circuits: Vdrop = 2 × I × R × L
Where I = current in amps, R = resistance per foot (0.00124 Ω/ft for 10 AWG copper, from NEC Chapter 9 Table 8 at 75°C), and L = one-way distance (200 ft).
The factor of 2 accounts for both the supply and return conductors. NEC recommends a maximum 3% voltage drop for branch circuits and 5% for the total circuit (feeder + branch).
If voltage drop is too high: Use the next larger wire size. Each single AWG step up in size cuts voltage drop by about 21% — it takes three steps to roughly halve it, since each step increases the conductor area by a factor of 1.26. Alternatively, for 120V loads, consider rewiring for 240V — same absolute drop but half the percentage.
It depends on the load and voltage. With NEC Table 8 resistance (1.24 Ω per 1000 ft at 75°C), a 200-foot run of 10 AWG copper drops 6.2% at 15A, 8.3% at 20A, 10.3% at 25A, 12.4% at 30A on 120V, and half those percentages on 240V. None meet the 3% guideline, so a larger wire is needed.
To stay within 3% voltage drop, 10 AWG copper can run about 95 ft at 15A on 120V, or 95 ft at 30A on 240V (one-way). Its maximum load is 30A (the NEC 240.4(D) limit); lighter loads can run proportionally farther.
Upsize when your load pushes drop above 3%. At 30A on 240V over 200 feet, 10 AWG drops 6.2%; stepping up to 8 AWG cuts that to 3.9%. For motors, well pumps or sensitive electronics, aim for 2% or less.