How to Test a 3-Phase Motor With a Multi-Meter

A multimeter measures electrical voltage and current flows.
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A three-phase motor converts electricity into mechanical energy via an alternating current provided by three leading power wires. The electricity is fed into the interior of the motor, where it creates a magnetic field that pushes the strator and makes it rotate, turning the motor shaft. Three-phase motors require testing with a multimeter during installation and inspections. The multimeter detects the flow of electricity and determines whether it is correct, as the wrong alternating current pattern can cause the motor strator to move the wrong way and malfunction.

    Select the Phase Rotation setting on your mutlimeter.

    Inspect the three-phase motor and look for terminals — where three wires connect to the motor — labeled L1, L2 and L3. Connect the meter jacks that are similarly labeled (L1, L2, L3) to the power wires.

    Observe the display on your multimeter. The display will read "OK" if the power feed is flowing in the correct direction. If it reads "ER", this means that the power feed has been reversed, which causes the motor to turn in the wrong direction.

    Fix the reversed power feed by first turning off the motor and unplugging it. Switch the position of two of the wires — the order doesn't matter — then reattach the mulitmeter leads to the wires. Turn on the motor. The mulitmeter should read "OK." This means that the 3-phase motor is turning in the correct direction and running correctly.


About the Author

Alexis Rohlin is a professional writer for various websites. She has produced works for Red Anvil Publishing and was one of the top 10 finalists in the 2007 Midnight Hour Short Story Contest for Rohlin holds a Bachelor of Fine Arts in English from Madonna University.

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