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WireWorks
Longer wire runs and thinner gauges lose more voltage — this quantifies exactly how much.
Current flows out to the load and back through the circuit, so the actual resistance encountered is based on double the one-way distance — this calculator already accounts for that in its formula.
A voltage drop under about 3% of the circuit's nominal voltage is generally considered acceptable for branch circuits — bigger drops waste energy as heat in the wire and can cause dim lights or underperforming motors at the far end of a long run.
Voltage drop
9.21 V
12 AWG copper is about 1.98 Ω/1000ft, 14 AWG is about 3.07 Ω/1000ft — look up your specific gauge's resistance.
What you entered
Apply the voltage drop formula (round-trip distance)
(2 × 15 × 100 × 3.07) ÷ 1000= 9.21 VResult
Voltage drop: 9.21 V
15 A over a 100 ft one-way run drops about 9.21 volts — keep this under 3% of the circuit voltage for good practice.