Engineering Reference

Voltage drop

The reduction in voltage along a conductor caused by its resistance.

Definition

Voltage drop is a function of current, conductor resistance and length — and the length is the round trip for a single-phase circuit, because the current returns on the neutral.

Common limits are 3% on a branch circuit and 5% overall. The usual temptations are to notice it only on long runs, when in fact a short run at high current drops just as much.

Common misuse

Using the one-way length in a voltage-drop calculation. For single-phase the return path doubles the resistance, so the drop is twice what a one-way calculation gives.

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