Basic Motor Starter Troubleshooting

When you’re having trouble getting a motor started there can be many reasons, but we’ll take you through some simple techniques to determine the motor starter problem and simple fixes.

When the motor won’t start, there are a few things to check to determine the cause. If this is a new installation that has never worked, it is important to check the wiring diagram and ensure the wires are all connected correctly. If this is an older installation and has worked in the past, it should still be wired correctly unless there have been some recent changes that may have caused the wiring to be altered. Here is a quick guide to magnetic motor starter troubleshooting

    1. Visually inspect the cables and terminals to look for any signs of burning, corrosion, cable insulation cracking or damage of any kind. If there is any visual evidence of damage, TURN OFF THE POWER and have an experienced electrician review the components, wiring, and installation. If you don’t see any visual indication of a problem, proceed with step 2.


    1. Relay IEC The easiest fix (and most common occurrence) is that the motor overload tripped. The overload is designed to protect the motor if the current exceeds the full load amperage. This is a bit like checking/resetting the circuit breaker in your home breaker box. To reset the overload, just press the red button on the overload, or if you have an external reset button, press that. This is also a good time to make sure the reset is set to “Manual” mode. Check the position of the red button to verify it’s set to “manual.”


    1. If resetting the overload does not work, we can do a quick check to see if the overload has failed. Verify the power is disconnected, lock out/tag out the circuit if appropriate, and using an ohm meter, check the continuity between the two Normally Closed (NC) terminals on the overload. The actual resistance measurement is not important, we are just checking to see if there is continuity. If the ohm meter shows “OPEN” then the overload is bad and should be replaced.


    1. If the overload shows continuity between the two NC terminals, we’ll have to dig in a bit further. Take a photo of or record the information from the motor nameplate. It’s important to know the Voltage, phases, and Full Load Amperage (FLA) of the motor. Having that information handy can make things go a bit more smoothly.


    1. Verify the overload setting (yellow dial) is set to the Full Load Amperage from the motor nameplate based on the supplied Line power to the motor.


    1. Once you know the required input voltage, use a digital multimeter to verify that all 3 phases of electrical potential are present. (or if it is single phase, verify the single-phase voltage is present). It is best to check this on the cable going into the contactor at terminals L1, L2 and L3, or if there is a disconnect switch, check the incoming wires to the disconnect. Measure between the legs L1, L2, and L3 to verify you have full voltage according to your input line power to the motor.


    1. If you are missing one or more phases and the circuit includes fuses, disconnect the line power and use your multimeter to check for continuity across the fuses.


    1. If one is blown, replace it. Sometimes fuse holders can become corroded and prevent continuity, so look at the fuse holders for any corrosion and if some is present, clean it with electrical contact cleaner and an old toothbrush.


If all the above have been completed and the motor still won’t start, it’s time to call an electrician.

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