The short answer
12 AWG aluminum (6,530 circular mils) carrying 20 A on a 240 V single-phase circuit reaches 3% voltage drop at about 55 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 | 0.3% | 0.7% | 1% | 1.4% | 2% | 2.7% | 3.4% | 4.1% |
| 10 A | 0.7% | 1.4% | 2% | 2.7% | 4.1% | 5.4% | 6.8% | 8.1% |
| 15 A | 1% | 2% | 3% | 4.1% | 6.1% | 8.1% | 10.1% | 12.2% |
| 20 A | 1.4% | 2.7% | 4.1% | 5.4% | 8.1% | 10.8% | 13.5% | 16.2% |
Longest run that stays under 3%
| Load | 120 V 1φ | 240 V 1φ | 208 V 3φ | 480 V 3φ |
|---|---|---|---|---|
| 5 A | 111 ft | 222 ft | 222 ft | 512 ft |
| 10 A | 55 ft | 111 ft | 111 ft | 256 ft |
| 15 A | 37 ft | 74 ft | 74 ft | 171 ft |
| 20 A | 28 ft | 55 ft | 55 ft | 128 ft |
How it's calculated
Table 310.16 lists 12 AWG aluminum at 15 A (60 °C) and 20 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 aluminum sizes
10 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.