Aluminum conductors are widely used for service entrances, sub-panel feeders, and large branch circuits because of their lower cost compared to copper. However, aluminum has a higher resistivity constant — K = 21.2 at 75°C compared to 12.9 for copper — which means aluminum wiring produces about 64% more voltage drop than the equivalent copper wire at the same ampacity. When sizing aluminum feeders, the NEC's 3% branch-circuit and 5% combined voltage drop recommendations become harder to meet on longer runs. This calculator uses the correct K value for aluminum conductors. Common aluminum feeder sizes include 2/0 AWG (90A), 350 kcmil (175A), and 500 kcmil (205A) at 75°C.
For a 240V single-phase 100A feeder at 100 ft using 2/0 AWG aluminum: VD = 2 × 21.2 × 100 × 100 / 133,100 ≈ 3.18V (1.33%). Within NEC guidelines.
This is a variant of the full Voltage Drop Calculator — which supports all phases, wire materials, and distances in a single tool.
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