Three Phase Motor Test with Multi-Meter

[Tim McCarthy]

Hi All,

Can anyone tell me if/how a three phase motor can be tested with a multi-meter? I am going to look at a planer that has such a motor and no way to run it.

Thanks very much,

Tim

[Rod Sheridan]

Hi, measure the motor resistance phase to phase, probably a few ohms.

Measure phase to ground, should be infinite (open)...............Regards, Rod.

[John McClanahan]

You should get the same reading across all wire pairs. 3 phase motors are rather tough. My guess is it is ok, but it doesn't hurt to check.


John

[George Makra]

You will get a reading going from leg to leg and that's pretty much a worthless test.
Go from leg to ground if you see any hint of anything other than an open circuit the motor is probably shot.
The proper way to test them is with a Megger but few people have them and they are expensive.

[Michael Dye]

Three phase motors are, for the most part, bulletproof. If you have an industrial stethoscope, check the bearings. In all the motors I've rebuilt, three phase motors typically just need bearings. Good luck.

[John K Jordan]

Can anyone tell me if/how a three phase motor can be tested with a multi-meter? I am going to look at a planer that has such a motor and no way to run it.


Checking across the three pairs of coils is a good test for a broken wire or internal winding short. Testing between the terminals and ground is a good test for a short from coil to ground.

This page is one of the best I've seen - it has a good section on testing unconnected motors, step by step HOW along with the WHY:
http://www.pcbheaven.com/userpages/check_the_windings_of_a_3phase_ac_motor/

JKJ

[Dennis Ford]

All good advise above. A couple of additional items: Use a good quality multi-meter if you can not borrow a megger. Make sure there is a nameplate with a wiring diagram and that the markings on all wires are readable. Check the diagram and verify that the motor can be wired for the voltage that you will be using.

[Mike Henderson]

While not a multimeter function, smell the motor. Burned insulation has a very distinctive smell and would be an indication that the motor overheated earlier. While testing coil resistance with an Ohm meter is good, if you have a couple of turns shorted in the field, it will cause excessive heating.

But I agree with others, most electric motors last a long time.

Mike

[Tim McCarthy]

Thanks to all who posted! Great advice.

Merry Christmas

Tim