The locked-rotor amperage is normally ________ times as great as the run-load amperage.

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Multiple Choice

The locked-rotor amperage is normally ________ times as great as the run-load amperage.

When a motor starts, the current drawn while the rotor is not yet turning (locked rotor) is much higher than the current once it reaches running speed. This happens because there’s no back-EMF yet, so the winding behaves mainly as a simple resistance. With back-EMF absent, the impedance is low and current surges. As the rotor accelerates, back-EMF builds up, opposing the applied voltage and increasing the effective impedance, which pulls the current down to the normal run-load value. For many motors, this starting current is about five times the running current, though it can vary with design. That’s why the typical answer is five times. The other multipliers are less representative of standard inrush behavior for common motors.

When a motor starts, the current drawn while the rotor is not yet turning (locked rotor) is much higher than the current once it reaches running speed. This happens because there’s no back-EMF yet, so the winding behaves mainly as a simple resistance. With back-EMF absent, the impedance is low and current surges. As the rotor accelerates, back-EMF builds up, opposing the applied voltage and increasing the effective impedance, which pulls the current down to the normal run-load value. For many motors, this starting current is about five times the running current, though it can vary with design. That’s why the typical answer is five times. The other multipliers are less representative of standard inrush behavior for common motors.

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