The short answer
8 AWG copper (16,510 circular mils) carrying 50 A on a 240 V single-phase circuit reaches 3% voltage drop at about 92 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 |
|---|---|---|---|---|---|---|---|---|
| 15 A | 0.2% | 0.5% | 0.7% | 1% | 1.5% | 2% | 2.4% | 2.9% |
| 20 A | 0.3% | 0.7% | 1% | 1.3% | 2% | 2.6% | 3.3% | 3.9% |
| 25 A | 0.4% | 0.8% | 1.2% | 1.6% | 2.4% | 3.3% | 4.1% | 4.9% |
| 30 A | 0.5% | 1% | 1.5% | 2% | 2.9% | 3.9% | 4.9% | 5.9% |
| 40 A | 0.7% | 1.3% | 2% | 2.6% | 3.9% | 5.2% | 6.5% | 7.8% |
| 50 A | 0.8% | 1.6% | 2.4% | 3.3% | 4.9% | 6.5% | 8.1% | 9.8% |
Longest run that stays under 3%
| Load | 120 V 1φ | 240 V 1φ | 208 V 3φ | 480 V 3φ |
|---|---|---|---|---|
| 15 A | 154 ft | 307 ft | 307 ft | 709 ft |
| 20 A | 115 ft | 230 ft | 231 ft | 532 ft |
| 25 A | 92 ft | 184 ft | 184 ft | 426 ft |
| 30 A | 77 ft | 154 ft | 154 ft | 355 ft |
| 40 A | 58 ft | 115 ft | 115 ft | 266 ft |
| 50 A | 46 ft | 92 ft | 92 ft | 213 ft |
How it's calculated
Table 310.16 lists 8 AWG copper at 40 A (60 °C) and 50 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 · 10 AWG · 14 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.