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Cable Voltage Drop

Current down a cable and back loses voltage in the conductor: V = 2·I·ρ·L / A (the 2 is the return path). Keep the drop under about 3% on a branch and 5% overall, or loads misbehave at the far end.

Current (A)

One-way run (m)

Conductor area (mm²)

Supply voltage (V)

Conductor

Voltage drop

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Drop as % of supply

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Voltage at load

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Power lost in cable

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DC / resistive AC at 20 °C. Hot conductors have higher resistance (about +0.4%/°C for copper), and long AC runs add inductive reactance.

A helper, not a substitute for engineering judgment. Verify against the governing standard.