Motor Starting Current Calculator

Calculate the inrush (starting) current of an electric motor from its nameplate data and starting method.

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DOL=6-8x, Soft start=2-3x, VFD=1-1.5x

Full Load Current (FLA)

11.7 A

Starting (Inrush) Current70.4 A
Starting kVA Demand58.5 kVA
Input Power8.29 kW

Full Load Current (FLA) vs Motor Horsepower

View formula & how it works →

Motor Starting Current

Electric motors draw significantly more current during startup than at full speed. This inrush can be 6-8 times the full-load current.

Formulas

FLA (3-phase) = HP x 746 / (sqrt(3) x V x Eff x PF)

Starting Current = FLA x Multiplier

Starting Methods and Multipliers

  • Direct-On-Line (DOL): 6-8x FLA
  • Star-Delta: 2-3x (reduced torque)
  • Soft Starter: 2-4x (adjustable)
  • VFD: 1-1.5x (best control)

    • Example Calculation

    10 HP motor, 480 V 3-phase, 90% efficient, PF 0.85, DOL start (6x).

    1. 01Motor watts: 10 x 746 = 7,460 W
    2. 02FLA: 7460 / (1.732 x 480 x 0.90 x 0.85) = 7460 / 635.6 = 11.7 A
    3. 03Starting current: 11.7 x 6 = 70.4 A
    4. 04Starting kVA: 70.4 x 1.732 x 480 / 1000 = 58.5 kVA

    Frequently Asked Questions

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