Contactor Problem

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Little Bill

Little Bill

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Tennessee NEC:2017
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Semi-Retired Electrician
I had a call to check a machine and found the contactor was burnt up. I have a couple of questions...........
There was no fuse blown or breaker tripped, can you tell from the pics what might have caused this?

The mfg rep wanted me to check the motor before replacing the contactor. My question is when checking with a Megohmeter, can I just check the leads in the control cabinet, or would I have to go in the "pecker head" and take the power leads off the motor windings?
I've never used my Meg to check a motor, so I need a little guidance on that.


 
Apparent Heating at the Ground to box connection, and apparent neutral bonded at same location. Parallel fault path reducing fault current available to trip the breaker. Significant heating at terminations of contactor, Loose connections?

I would think you would desire meg the motor separately in addition to test the wiring at this time also.
 
Fred B said:
Apparent Heating at the Ground to box connection, and apparent neutral bonded at same location. Parallel fault path reducing fault current available to trip the breaker. Significant heating at terminations of contactor, Loose connections?

I would think you would desire meg the motor separately in addition to test the wiring at this time also.
Click to expand...
I would do it all together at first, and then, if that shows an issue, look at the motor and the wiring separately.
 
Fred B said:
Apparent Heating at the Ground to box connection, and apparent neutral bonded at same location. Parallel fault path reducing fault current available to trip the breaker. Significant heating at terminations of contactor, Loose connections?

I would think you would desire meg the motor separately in addition to test the wiring at this time also.
Click to expand...
Probably not. Likely the white wire on the ground lug is the grounded conductor for the control power transformer. It seems evident that control power is NOT what burned up.

The OCPD for the power going to this contactor probably should have tripped preventing this mess. It may have failed.
 
Looks pretty clear to me loose connections between the overload and starter, heat rises. When you get a good meg reading, it will prove that it was faulty connections. Now you need an overload and a contactor.
 
Fred B said:
Apparent Heating at the Ground to box connection, and apparent neutral bonded at same location. Parallel fault path reducing fault current available to trip the breaker. Significant heating at terminations of contactor, Loose connections?

I would think you would desire meg the motor separately in addition to test the wiring at this time also.
Click to expand...
Yeah I would want to know why this white wire is bonded to the Equipment ground:
2.jpg
Could be a poor equipment ground acting as a hi resistance neutral.
 
ptonsparky said:
Bill, is this 480?

Anyway you look at it, that's a big parts washer.
Click to expand...
It's fed with 240V but there is a transformer that may be a 240V to 480V. I haven't been able to check anything much yet. I was sent the pics and only dropped by to check the fuses for now. I will check everything when I go back to Meg the motor.
 
The motor could read bad but would be a symptom, not a problem. If the motor had a open or short, the controller would open the circuit, but not burn up. However if the controller caused a prolonged single phasing situation, it could fry the motor. Like if two sets of contacts welded together in the controller, it tried to open the circuit on overload, but only the third set of contacts actually opened, it would cause the motor to single phase.
 
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