Locked-Rotor kVA Calculator

How the result is calculated

For this worksheet, the governing relationship is kVA = √3 × V × I ÷ 1000. The participating entries are Line voltage and Locked-rotor current.

With the current entries, the primary answer is 124.71 kVA. Preserve the raw inputs when replacing this example.

Calculate locked-rotor kVA from line voltage and locked-rotor current. For the companion motor power factor calculation, open Motor Power Factor Calculator.

Values this page needs

Record supply arrangement, speed, duty cycle, enclosure, and winding temperature. If operating conditions changed between readings, calculate separate cases.

A prefix error can move the result by several orders of magnitude. Continue with Appliance Energy Use Calculator to evaluate appliance energy.

Line voltage

Default example: 400 V. Enter line voltage in V.

Locked-rotor current

Default example: 180 A. Enter locked-rotor current in A.

How to use the result

The primary answer, Locked-rotor kVA, describes only the entered scenario. Compare it with motor, drive, cable, and protective-device limits.

Store the measurement state and conversion notes with the answer. If you also need starting demand, continue with Motor Starting kVA Calculator.

What the formula leaves out

Use line quantities for a three-phase motor.

A complete model can also include starting method, service factor, enclosure, and thermal duty. Document which effects were checked elsewhere in the analysis.

Record supply arrangement, speed, duty cycle, enclosure, and winding temperature.

A second scenario

Change Line voltage from 400 V to 480 V while preserving the other measurements. The output changes from 124.71 kVA to 149.65 kVA.

Do not average the two cases if either could define an operating limit.

Documenting the calculation

Document line voltage and locked-rotor current with locked-rotor kVA. Keep enough context to reproduce the result later.

Transfer locked-rotor kVA as the raw numerical value until the final step. Apply standard sizes only after all checks are complete.

Review the case step by step

Check the source of line voltage before calculating. A credible result requires every field to describe the same physical condition and unit basis.

After calculating locked-rotor kVA, compare its magnitude with starting demand, running current, torque, efficiency, slip, and thermal loading. An independent order-of-magnitude check can reveal a misplaced decimal or unit prefix.

Document any effect handled outside this page, especially load inertia, acceleration profile, harmonics, reduced-speed cooling, and mechanical loss. That note prevents a later reader from assuming the simple equation covered it.