Motor Starting Current Calculator
Enter motor rated current and starting method to get the expected inrush (starting) current and reduction factor.
Motor Parameters
Found on the motor nameplate as FLC or In.
Starting current at motor = tap² × DOL current.
Typical range: 1.5–3× FLC. Set on the soft starter itself.
Standard is 6×. Check motor datasheet for exact value (range 5–8×).
Results
Enter motor rated current and click Calculate.
Starting Current (Istart)
Full-Load Current (FLC)
Effective Multiplier (× FLC)
Reduction vs. DOL
Starting Method
Method Notes
Starting Method Comparison
| Method | Multiplier | Istart (A) |
|---|
Summary
Enter motor rated current and starting method to get the expected inrush (starting) current and reduction factor.
How it works
- Enter the motor's full-load rated current (FLC) from the nameplate.
- Select the starting method: DOL, star-delta, auto-transformer, or soft starter.
- For auto-transformer, specify the tap ratio (50%, 65%, or 80%).
- For soft starter, specify the current limit multiplier (typically 1.5–3× FLC).
- The calculator applies the standard multiplier for the chosen method and returns the starting current.
- Review the reduction factor to understand how much inrush is reduced versus DOL.
Use cases
- Size circuit breakers and fuses for motor branch circuits.
- Determine contactor and cable ratings for reduced-voltage starters.
- Estimate voltage dip on the supply bus during motor start.
- Compare starting methods to choose the best fit for a given load.
- Verify that a generator set can handle the starting surge.
- Document expected inrush values in electrical design reports.
Frequently Asked Questions
Last updated: 2026-07-01 ·
Reviewed by Nham Vu