Motor Overload Test

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kencoel

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I suspect an old 3PH 240v 40A motor is going bad. The contactor keeps kicking out. What is the best way or proper procedure to test to see if the motor is going bad! Thanks!

I did not mention: If the contactor is by-passed to run the motor manually the motor heats up. This test was not verified by me. It sounds like an amperage reading is a place to start as suggested. Thanks for the imput!
 
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kencoel said:
I suspect an old 3PH 240v 40A motor is going bad. The contactor keeps kicking out. What is the best way or proper procedure to test to see if the motor is going bad! Thanks!
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Clamp-on ammeter.
 
Something to look into. I had a motor trip the starter, on hot days and the panel is in the sun, for about 2 months. I checked everything over and over again. I think I finally found it when the control transformer smoked. My guess is it was weak, even though it was testing good. After replacing it I haven't had a trip on it in weeks.
 
motor test

motor test

that and a megger...


Forgive me if I digress for a moment,but, when one gets old they seem to be more full of s......, I mean stories.
I worked with an electricain one time in a plant where we had a motor with speed controlled by an old electronic clutch. The assembly would fill with dust and the output would be higher than the clutch called for. Following a long standing practice, the fellow put a 36" pipe wrecch on the clutch output shaft and stood on it. Then called for the motor to be started with the clutch on minimum. This would usally cause the clutch to break free from the dust clog.
One day the problem wasn;t dust but a bad circuit board allwoing the clutch to stay engaged. His "motor test" threw him across the building. luckily unhurt except pride :)

sorry, Larrry for the thread jack, but ole memories.
 
1. Did you perform a FOP test across the contactor to is if this is a impedance/resistance issue?
2. Did you take amperage readings? (as noted above).
3. Do you have tracking records of the motor megger reports?
4. What about the equipment being driven by the motor? Bad bearings, pump restriction, improper belt tension...
5. Did you check voltage at the pump.
 
Check all of the above mentioned. Sometimes the problem is in the overload block. Depending on the starter, sometimes it's cheaper to replace the starter than replacing just the overload block. Intermittent overload trips are a PITA.
 
If the contactor is by-passed to run the motor manually the motor heats up.
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Before you do anything else, please remember this very important fact:

THE OVERLOAD RELAY IS THERE TO PREVENT A FIRE!

Bypassing the motor starter is eliminating the overload relay! Don't do that!

If you are thinking that by bypassing only the contactor with pieces of wire and leaving the overload relay in place, the motor is still protected, you are DEAD WRONG! The overload relay only acts to DROP OUT THE CONTACTOR. If you have used wires to bypass the contactor, the overload relay has nothing to act upon!

Other than that, the only true way to know for sure if your motor is OK is to take it out and have it tested by a qualified motor shop. Start there, because to ASS-U-ME the starter or overload is bad first is to put yourself and other equipment at risk of fire.
 
There are several test one can perform and should perform without contacting a motor shop. In fact other than for a re-wind I have never contacted a motor shop for testing help. Not that I am pig headed, just don't need them for this portion of the job. An electrician should be able to figure this out.

Motor got hot, what's the temperature? What the temperature of similar motors at this facility.

DO NOT BYPASS THE OL's, test and isolate the problem.

Thermal OL's have ISSUES in my opinion I prefer solid state OL's.
 
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