Electric motor testing

Electrical motor is the common used in industry all over the world.It very important device to made production smoothly.To ensure the electrical motor condition is good or not,we must know how to testing it.

The electrician or maintenance person must have this skill to determine the electrical motor condition,defected or cannot use anymore.It can save the repair cost and maintenance expenditure.

How to testing electric motor?

  • Check the appearance of motor.find any defect at body,cooling fan or shaft.
  • Try to swing manually the rotor shaft check the bearing condition.Check either it smooth rotating or not.
  • Collect the motor data from motor NAME PLATE.It very important to know about specs of motor before we testing.
  • Ensure the terminal for power supply in good condition.Check the connection bar for terminal ( U,V,W ).What kind of connection for terminal.( STAR OR DELTA ).
  • Please confirm first the power supply VOLTAGE for electric motor.It single phase or three phase type.
  • Using the multimeter,check the continuity of winding from phase to phase ( U to V,V to W ,W to U ).Each phase to phase must have a continuity if winding is OK.
  • Check the motor winding ohms reading using multimeter or ohmmeter for phase to phase terminal ( U to V,V to W ,W to U ).Reading for each phase must same within one or two ohms deference.If no reading,maybe winding was defect.
  • Check the insulation resistance of motor winding using Insulation tester meter on 500 Volt scale.First check from phase to phase  ( U to V,V to W ,W to U ) and second check from phase to earthing ( U to E,V to E ,W to E ).According to standard IEEE 43: IR test minimum value of the electric motor is a 1 Mega Ohm ( 1 MΩ ) . It mean winding is in good condition.Refer my last post how to test motor using insulation tester meter.
  • After all step we perform and the testing result is OK,now we test in actual condition.Why we test it with power supply?It is to ensure no mechanical defect like bearing problem or unbalance rotor movement.
  • When motor is running,we must check the AMPERE of motor using Clamp on meter.Refer to FLA at name plate of  motor.
  • If every step is completed,now we can decide the condition of electrical motor either OK or NEED TO REPAIR.

Now i hope you`ll can get some step how to check or testing  the electrical motor from my post this time.This is a guide for all technician or maintenance person for improve their skills for troubleshooting….TROUBLESHOOTING IS ART :D


  1. Should we check the no load current and noise level too?.

  2. deepak jha says

    sir, i want to know how we can find out six terminal name (u1, u2 etc) if their name is not given on motor name plate.

  3. Danilo says

    Thank you for your post; From above it was recommended that insulation test be done on phase to phase. I want to ask why need to test for phase to phase. we already tested phase to phase using multimeter for continuity or being opened; hence phase to phase insulation testing for me would not be needed.

    • For me it for checked insulation between phase to phase of winding to ensure it not leakage to each other due to insulation varnish failed.In my last experience,i already faced with winding leakage phase to phase.I cannot detected when using multimeter but found it when perform insulation tester :D some time the insulation varnish not working in proper condition…

      • Danilo says

        So before this Phase to phase insulation test is conducted; the phases are isolated first are isolated sir. Thank you very much.

  4. Safiq Khan says

    I wonder how could I test the range hood single phase electric motors and the sliding switches?

  5. Hello Joe.

    High respect you for share your experience.

    I would like to fulfill more at least with one important point about testing of motors insulation:
    Motors in factory (producer) have to be checked phase to ground 2*Un+1000V according EN 60 034-1 (acc. Europe standard at least).
    You can do it by multimeter with small (manual) power generator. Because it is very important, when you control motor by frequency inverter(FI). All FI has parasitic voltage effect 2,5*Un supply each sinusoidal peak for few piko-seconds (I don’t know any FI producer, who doesn’t have it and all motors lifespan (winding) is calculated twice shorter if it’s controlled by FI). For example BEVI brand all motors for 400V are tested winding insulation with 2500V.
    If you connect FI to old didn’t tested motor, it can cause fault frequency inverter, because obsolete and impaired insulation, which is enough for direct connection.

  6. shankar says

    There is a problem with my star delta motor. It runs in star but when changes to delta the mains power is tripping what could be the possible reason. Pls let me know

  7. Hello.How do I know I know that my values are within 5% of one another when testing for continuity? is there a formula I can use?

  8. Electric motors are used in many different machines and I am sure it is really important to be sure that they are working properly. One of the electric motors that I have hasn’t been used for a while, so it would be really nice to get it tested. You have some really great suggestions here on how to get an electric motor tested. I will get it tested and then see if I need to get it repaired. Thanks for the great post!

  9. Velmani says

    Sir very nice morning
    I am totally zero knowledge about motors induction but i can able to understand
    Ok please explain in detail how to check before and after erection and while run of motor from the defectecs of coil burnt and or any other problem imcluding contactor relay setting time how much ampere per hp etc please

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