Calculator
This calculator computes the voltage drop across a conductor run for single-phase and three-phase AC circuits. It uses the exact phasor method, which is more accurate than the simplified approximation formula commonly used in basic tools. The key result — the scalar voltage drop — is computed as the difference in magnitudes between the source voltage and the load voltage, accounting for both the resistive and reactive components of the conductor impedance at the actual power factor angle.
Voltage Drop Calculator
Exact phasor method · Single-phase & Three-phase · NEC Table 9
Inputs
The user provides load current, power factor (lagging), source voltage, one-way circuit length, and the number of parallel conductors per phase. For conductor impedance, the user can either enter R and X values manually or select from a built-in lookup table sourced from NEC Table 9, which covers conductor sizes from 14 AWG through 1000 kcmil, in copper or aluminum, across three conduit types: PVC, aluminum, and steel.
Outputs
The calculator returns the voltage drop in volts, the percentage voltage drop relative to the source, and the resulting load voltage. It also displays a color-coded NEC compliance indicator — green if the drop is at or below 3% (branch circuit recommendation), yellow if it falls between 3% and 5% (total system limit), and red if it exceeds 5%. An expandable detail panel shows every intermediate step of the phasor calculation for verification purposes.
