Testing your three phase motor06/08/2017 As a precaution, you should test your three phase motor periodically or any time you send a drive or soft start out for repair. It’s not very common for a three phase motor to have problems. They can run for years and years with no problems at all. A couple of quick tests will put your mind at ease and potentially save you lots of money. First things first. Always keep safety in mind. If your motor is not a spare but one that is currently in use, be sure to shut power to the motor off completely. Once this is done, it is also mandatory to remove any connections at the motor itself so there will less chance of erroneous readings or damage to any drives, soft starters, or other electronics. Ensure any wire nuts or insulation tape is removed from the connection so that you have direct access to the motor leads. Using a volt ohmmeter, switch the ohms setting. Connect the meter leads to two of the motor leads. The reading you get should be low ohms. Repeat this step connecting to and testing all three phases of the motor. Next, conduct the same test between the motor leads and the motor frame. If the reading you get is anything other than OL or infinite ohms, then the motor is bad and will need to be replaced. If your motor passes the ohms test, it’s a good first step, but a test with a megohmmeter or megger will verify the integrity if the motor insulation and let you know the insulation resistance is as it should be. A megger provides a much higher voltage than the ohmmeter. It bears mentioning again that any device used to control the motor should be disconnected prior to performing this test. A 480 volt motor should be tested at 1000 volts. Consequently, a 230V motor should be tested at 500 volts. Connect the megger leads to two of the motor leads. Crank the handle of the megger for about a minute and notice the reading. A low reading is generally good. Repeat this step connecting to and testing between all three phases of the motor. Next, conduct the same test between the motor leads and the motor frame. Again, crank the handle of the megger for about a minute. For this test, a high reading or infinite ohms is good. If you get a reading different than these, you will need to replace the motor. There are also meggers that instead of a hand crank to generate the high voltage, will have internal controls to generate the voltage automatically and for a duration that can be varied by the user. The third and final test to perform is a surge test. This is done with a surge tester. Connect the tester leads to each phase of the motor and check them individually. The standard is to inject a varying voltage up to twice the working voltage plus 1000. Observe the pattern of the wave on the tester as you vary the voltage that may indicate a short. Repeat this procedure for all three phases. Completing and having your motor pass these three tests will let you know that it is good and will operate as it should before reconnecting your drive or soft start. However this testing does not account for any mechanical issues that may exist, such as bad bearings. Back To Blog
Testing your three phase motor06/08/2017 As a precaution, you should test your three phase motor periodically or any time you send a drive or soft start out for repair. It’s not very common for a three phase motor to have problems. They can run for years and years with no problems at all. A couple of quick tests will put your mind at ease and potentially save you lots of money. First things first. Always keep safety in mind. If your motor is not a spare but one that is currently in use, be sure to shut power to the motor off completely. Once this is done, it is also mandatory to remove any connections at the motor itself so there will less chance of erroneous readings or damage to any drives, soft starters, or other electronics. Ensure any wire nuts or insulation tape is removed from the connection so that you have direct access to the motor leads. Using a volt ohmmeter, switch the ohms setting. Connect the meter leads to two of the motor leads. The reading you get should be low ohms. Repeat this step connecting to and testing all three phases of the motor. Next, conduct the same test between the motor leads and the motor frame. If the reading you get is anything other than OL or infinite ohms, then the motor is bad and will need to be replaced. If your motor passes the ohms test, it’s a good first step, but a test with a megohmmeter or megger will verify the integrity if the motor insulation and let you know the insulation resistance is as it should be. A megger provides a much higher voltage than the ohmmeter. It bears mentioning again that any device used to control the motor should be disconnected prior to performing this test. A 480 volt motor should be tested at 1000 volts. Consequently, a 230V motor should be tested at 500 volts. Connect the megger leads to two of the motor leads. Crank the handle of the megger for about a minute and notice the reading. A low reading is generally good. Repeat this step connecting to and testing between all three phases of the motor. Next, conduct the same test between the motor leads and the motor frame. Again, crank the handle of the megger for about a minute. For this test, a high reading or infinite ohms is good. If you get a reading different than these, you will need to replace the motor. There are also meggers that instead of a hand crank to generate the high voltage, will have internal controls to generate the voltage automatically and for a duration that can be varied by the user. The third and final test to perform is a surge test. This is done with a surge tester. Connect the tester leads to each phase of the motor and check them individually. The standard is to inject a varying voltage up to twice the working voltage plus 1000. Observe the pattern of the wave on the tester as you vary the voltage that may indicate a short. Repeat this procedure for all three phases. Completing and having your motor pass these three tests will let you know that it is good and will operate as it should before reconnecting your drive or soft start. However this testing does not account for any mechanical issues that may exist, such as bad bearings.