Calculate voltage drop across a wire run to ensure safe and efficient electrical installations
This voltage drop calculator helps electricians and engineers determine voltage loss in electrical circuits due to wire resistance. The National Electrical Code (NEC) recommends keeping voltage drop under 3% for branch circuits. Factors include wire material, gauge, length, current, and phase configuration.
The NEC recommends branch circuit voltage drop not exceed 3%, and combined feeder plus branch circuit drop not exceed 5%. Exceeding these limits can cause equipment malfunction, reduced efficiency, and overheating. This calculator flags drops above 3% as a concern.
Thicker wires (lower AWG number) have less resistance per foot, resulting in lower voltage drop. For long runs, you may need to increase wire size to keep voltage drop within acceptable limits. Copper also offers about 40% lower resistance than aluminum for the same gauge.