Locked Rotor Current Calculator
Use full-load current and a locked-rotor multiplier to screen locked-rotor amps before checking the motor nameplate, NEMA code letter, starter data, and utility requirements.
- Estimated locked-rotor current
- A
- Full-load current reference
- A
- Locked-rotor multiplier used
- x
- Starting-current reference
- A
- Comparison margin
- A
Calculation details
- Comparison ratio
- x
- Calculation basis
- Selection boundary
Recent results
Formulas
- Estimated locked-rotor current = full-load current x locked-rotor multiplier
- Comparison margin = estimated locked-rotor current - starting-current reference
- Comparison ratio = estimated locked-rotor current / starting-current reference
Use this calculator
Estimate locked-rotor current and compare it with an entered starting-current reference.
Read the result
Review the calculated values with their displayed units and assumptions. The result is a planning aid for the stated inputs, not a final equipment or installation decision.
Check before final work
This locked-rotor current estimate is a screening calculation. It does not replace motor nameplate locked-rotor amps, NEMA code-letter data, controller ratings, protection settings, utility review, or code compliance.
FAQs
Is locked-rotor current the same as starting current?
Not always. Locked-rotor current is a motor condition reference. Actual starting current depends on starter type, voltage, motor design, and load conditions.
Where should the multiplier come from?
Use motor nameplate, manufacturer, NEMA code-letter, or project data. A guessed multiplier should only be used for rough screening.
Can this set protection or starter ratings?
No. Protection, controller, conductor, and utility decisions need manufacturer data and applicable code review.