Allowable Voltage Drop [repack] Jun 2026

Note: While the NEC often mentions these figures in "Fine Print Notes" (informational annexes), they are often enforced by local inspectors as mandatory requirements to ensure safety and efficiency.

As electrons move through a wire:

If you find your voltage drop is exceeding the 3% or 5% threshold, there are three primary ways to fix it: allowable voltage drop

), professionals often use this basic formula for single-phase circuits:

To minimize voltage drop and ensure electrical safety and efficiency: Note: While the NEC often mentions these figures

Where:

where: L = length of the conductor (in feet or meters) I = current flowing through the conductor (in amperes) R = resistance of the conductor (in ohms per 1000 feet or meters) Voltage Drop (VD) = (2 x L x I x R) / 1000

This is the most common fix. Moving from 14 AWG to 12 AWG wire, for example, significantly reduces resistance.

Voltage Drop (VD) = (2 x L x I x R) / 1000