Motor Starting Current Calculator

Startup is when a motor is cruelest to the supply: for a brief moment it can demand six times its running current, dipping voltage, heating cables and slamming the generator. That surge — not the FLA — decides whether the protection and supply can cope.

Motor Starting Current Calculator estimates inrush from your FLA or motor power and chosen starting method, then checks the surge against breaker, generator and transformer capacity so the design absorbs the start instead of tripping on it.

Everything runs in the browser; nothing is uploaded.

• FLA or kW input: Enter the full-load current or the motor rating.
• Starting method: DOL, star-delta, soft starter, reactor or VFD.
• Motor types: Induction, slip-ring, synchronous and DC profiles.
• Locked-rotor kVA: The surge demand on the supply.
• Supply checks: Breaker, generator and transformer headroom.
• Export: Copy or download the assessment as text, CSV or JSON.
• Learning guide: Which start method fits which system.

1. Enter the motor current in FLA or as kW with the nameplate details.
2. Choose the starting method — this sets the multiplier.
3. Select the motor type for the profile.
4. Enter the supply ratings you want to check against.
5. Read the starting current and whether the supply survives it.
6. Export the assessment if needed.

Example 1 — DOL pump. 11 kW motor, 400 V, FLA 20.8 A, DOL at 6x: starts at about 125 A.

Example 2 — Star-delta. The same motor star-delta starts near 42 A — about a third of DOL line current.

Example 3 — Generator check. The 125 A start at 400 V is about 87 kVA of momentary demand on the generator.

Example 4 — Soft start. 7.5 kW fan, FLA 14 A, soft starter at 3x: starts around 42 A, below the running breaker.

• See the surge: Inrush quantified instead of guessed at.
• Method compared: DOL vs star-delta vs soft start side by side.
• Supply-proof: Breaker, generator and transformer checks in one view.
• Explained maths: The LRA formula shown live.
• Free and private: No uploads, no accounts, no logging.