ElectricalToolbox

3-Phase Voltage Drop Calculator

Circuit inputs
Phase
Three-phase · line-to-line (√3)

Assumes PVC conduit, unity power factor (resistive load), and NEC Chapter 9 Table 9 conductor values at 75°C. Three-phase drop uses the √3 line-to-line factor.

Calculate line-to-line voltage drop on three-phase feeders and motor branch circuits — the long 480V runs and large 208V commercial feeders where drop actually drives conductor sizing. Results use NEC 2020 Chapter 9, Table 9 AC resistance for #2 AWG and larger, and the Table 8 K-factor for smaller conductors, at a 75°C basis and unity power factor.

How to use this calculator

  1. Select the line-to-line system voltage (480V, 208V, 240V, or 600V).
  2. Enter the load current in amps and the conductor material.
  3. Select the conductor size (AWG or kcmil).
  4. Enter the one-way distance from source to load in feet.
  5. Read total voltage drop, percentage, and the 3% / 5% status. If it exceeds 3%, the tool recommends the next conductor size that brings it back under 3%.

NEC reference

Three-phase voltage drop is calculated as VD = √3 × R × I × L ÷ 1000, where R is the AC resistance in ohms per 1000 ft from NEC Chapter 9, Table 9 (NEC 2020). The 3% branch-circuit and 5% combined feeder-plus-branch figures come from the informational notes to NEC 210.19 and 215.2 — they are recommendations, not requirements, unless adopted locally.

Results are for reference only. Verify against the applicable adopted edition of the NEC and consult a licensed electrician for code compliance.