Voltage Drop Calculator

Calculate voltage drop for single-phase and three-phase circuits.

Load Current (Amps)

System Voltage

Phase

One-Way Distance (feet) Distance from panel to load (not round trip)

Wire Size

Conductor Material

Voltage Drop Formulas

Single Phase:


                            VD = (2 × L × I × R) / 1000

Three Phase:


                            VD = (1.732 × L × I × R) / 1000

L = length (ft), I = current (A), R = resistance (Ω/1000ft)

NEC Voltage Drop Guidelines

Branch Circuits

NEC recommends maximum 3% voltage drop for branch circuits to ensure proper equipment operation.

Feeders

NEC recommends maximum 3% for feeders, with combined feeder + branch not exceeding 5%.

Total System

Total voltage drop from service entrance to final outlet should not exceed 5%.

Note: While NEC 210.19(A) and 215.2(A) provide these as recommendations (FPN), some jurisdictions and specifications may require them as mandatory limits.