The short answer
10 AWG copper (10,380 circular mils) carrying 30 A on a 240 V single-phase circuit reaches 3% voltage drop at about 97 feet. At lighter loads it can go farther, as the tables below show.
Percent voltage drop at 240 V single-phase
Values over 3% are marked.
| Load | 25 ft | 50 ft | 75 ft | 100 ft | 150 ft | 200 ft | 250 ft | 300 ft |
|---|---|---|---|---|---|---|---|---|
| 5 A | 0.1% | 0.3% | 0.4% | 0.5% | 0.8% | 1% | 1.3% | 1.6% |
| 10 A | 0.3% | 0.5% | 0.8% | 1% | 1.6% | 2.1% | 2.6% | 3.1% |
| 15 A | 0.4% | 0.8% | 1.2% | 1.6% | 2.3% | 3.1% | 3.9% | 4.7% |
| 20 A | 0.5% | 1% | 1.6% | 2.1% | 3.1% | 4.1% | 5.2% | 6.2% |
| 25 A | 0.6% | 1.3% | 1.9% | 2.6% | 3.9% | 5.2% | 6.5% | 7.8% |
| 30 A | 0.8% | 1.6% | 2.3% | 3.1% | 4.7% | 6.2% | 7.8% | 9.3% |
Longest run that stays under 3%
| Load | 120 V 1φ | 240 V 1φ | 208 V 3φ | 480 V 3φ |
|---|---|---|---|---|
| 5 A | 290 ft | 579 ft | 580 ft | 1,338 ft |
| 10 A | 145 ft | 290 ft | 290 ft | 669 ft |
| 15 A | 97 ft | 193 ft | 193 ft | 446 ft |
| 20 A | 72 ft | 145 ft | 145 ft | 334 ft |
| 25 A | 58 ft | 116 ft | 116 ft | 268 ft |
| 30 A | 48 ft | 97 ft | 97 ft | 223 ft |
How it's calculated
Table 310.16 lists 10 AWG copper at 30 A (60 °C) and 35 A (75 °C), before any 240.4(D) limit on the breaker size. Voltage drop is a separate check. On long runs it usually decides the wire size.
Other copper sizes
12 AWG · 14 AWG · 8 AWG · 6 AWG · 4 AWG · 2 AWG · 3 AWG · 1 AWG · 1/0 AWG · 2/0 AWG · 3/0 AWG · 4/0 AWG
Open the full voltage drop calculator with these numbers
Results are estimates for planning and education. Verify against the current code edition your jurisdiction has adopted, manufacturer data and a licensed professional before you build or install.