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ElecToolsHQ

Motor Examples

These worked examples apply the motor full load current formula and the locked rotor current relationship to find a motor's running and starting current.

  1. Step 1

    A 5 HP, 230 V motor has 90% efficiency and a power factor of 0.85. Find the full load current.

    FLC = (HP × 746) ÷ (V × Eff × PF) = (5 × 746) ÷ (230 × 0.9 × 0.85) ≈ 21.2 A

  2. Step 2

    A 5 HP, 230 V motor has a power factor of 0.85. Find the current (without efficiency).

    A = (HP × 746) ÷ (V × PF) = (5 × 746) ÷ (230 × 0.85) ≈ 19.1 A

  3. Step 3

    A motor has a full load current of 21.2 A and a locked rotor multiplier of 6.5. Find the locked rotor current.

    LRC = FLC × Multiplier = 21.2 × 6.5 ≈ 137.8 A

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