On long feeder runs — typically 200 feet or more — voltage drop often controls conductor sizing rather than ampacity. A feeder that is perfectly adequate at 50 feet can produce unacceptable voltage drop at 250 feet with the same wire. Common long-run scenarios include service feeds to detached garages, barn feeds on agricultural properties, sub-panel feeders in large commercial buildings, and outdoor lighting circuits. For these runs, it is standard practice to upsize the conductor two or three AWG sizes beyond the minimum ampacity requirement to maintain voltage drop within NEC guidelines. This calculator shows both the voltage drop percentage and the minimum wire size needed to achieve 3% or 5% targets at your specific distance.
For a 240V 60A feeder at 300 ft using 6 AWG copper: VD = 2 × 12.9 × 60 × 300 / 26,240 ≈ 17.7V (7.4%). Exceeds 5% combined limit — upgrade to 2/0 AWG copper to achieve VD ≈ 2.2%.
This is a variant of the full Voltage Drop Calculator — which supports all phases, wire materials, and distances in a single tool.
Try all options in the full Voltage Drop Calculator →