On my last post,I’d discussed about motor overload relay that are common used for motor starter application.As we known,the main purpose of motor overload relay is to protect our electric motor winding from mechanical overload that can result the serious damage.
This time I want share basic guideline or troubleshooting method how to troubleshooting when motor overload relay trip.I hope this post can give some ideas or clear view when you face this similar problem during your routine jobs.
What you need to do when overloads in the motor starter trip?
1) Obtain works permit from authorize person and lockout the motor main power supply.check to see if it and the load turn freely or not.
2) Determine if the overload rated are properly sized, or if the overload is set properly, Normally the overload setting is 110 % based on the motor’s nameplate full load amps (FLA).Please refer my last post about How to setting overload relay for electrical motor.
3) An electrical possibility is that the motor has an open phase. This is known as single phasing. Verify the motor phases have continuity from phase to phase for all combinations using a multimeter from the motor starter. Check Red to Blue, Blue to Yellow, and Red to Yellow phases. Check the motor starter contactor, the fuses, and the overload relay.
4) Rectify the root cause of overload and reset the overloads by push the reset button.Start the motor and check the running motor amps and compare to rated FLA and overload heater size using a clamp-on ammeter.
5) If the amps are greater than needed to trip the motor the reason is generally mechanical overloading. This could be bearing failure, too much load, motor/load misalignment, etc.
6) If the amps are less that FLA and the Overloads are properly sized/set properly the motor overloads should not trip. In this case the Overload block is likely to be defective.
What you need to do when fuses or breaker open circuit?
The following should be done from the motor starter first. If a problem is found the motor and feeder must be separated and checked individually:
1) Lockout the motor and check the motor winding from phase to phase using a multimeter. The motor should have continuity from phase to phase.
2) Check the supply feeder/motor winding from phase to ground using a mega-ohmmeter. It should be open from phase to ground.
3) Verify the fuses are properly sized based on the nameplate data and National Electrical Code Article 430. If fuse one is blown you must replace all three fuses.