Voltage drop on a lighting circuit depends on the wire gauge, the run length, and the current. This table gives the DC resistance of common copper and aluminum conductors, the basis for any voltage-drop calculation.
| Wire (AWG) | Copper (ohm/1000 ft) | Aluminum (ohm/1000 ft) |
|---|---|---|
| 14 | 3.07 | — |
| 12 | 1.93 | 3.18 |
| 10 | 1.21 | 2.00 |
| 8 | 0.764 | 1.26 |
| 6 | 0.491 | 0.808 |
| 4 | 0.308 | 0.508 |
| 2 | 0.194 | 0.319 |
The drop formula. For a single-phase run: voltage drop = 2 × (resistance per 1000 ft ÷ 1000) × length × current. Keep branch-circuit drop under about 3%.
See the Voltage Drop Calculator and the Voltage Drop Formula.