Full-Load Current

Converting power to current, and why the result is not the motor table value.

1. What this check does

Converts a load given in kW, HP or kVA into line current for a single- or three-phase system.

2. Inputs used

Load value and unit, system voltage (line-to-line for three-phase), number of phases.
Power factor (kW, HP) and efficiency (HP required; kW optional).

3. Formulas and assumptions

Three-phase I = S / (√3 · V) S in VA I = P / (√3 · V · PF · η) Single-phase I = S / V I = P / (V · PF · η) HP P = HP × 745.7 W (shaft output) kW without η treated as electrical input power (η = 1)

Voltage is the nominal system voltage you enter. Operating at reduced voltage increases current for the same power.
Balanced three-phase load; no harmonic content.

4. What is NOT checked

This is not the NEC motor full-load current. Conductors and most protection for motors are sized from the NEC table values, not from nameplate or calculated current.
Motor service factor, starting current and unbalanced loads.

5. Reference standards

NEC 2023 430.6(A)(1), Tables 430.248 and 430.250 — motor full-load current for conductor sizing

6. Validation cases

Hand-calculated cases run on every change. See Validation.

7. Known issues and changes

See the Changelog. Try the tool: Full-Load Current.