# MTE motor overload weird tripping



## oldtimer (Jun 10, 2010)

kevmanTA said:


> 208 3/p table saw, I didn't write down the motor size, but I tested it lead to lead, and to ground, and the motor tests out fine with my Fluke 87.
> This is the problem.
> Overload seems to only kick out one phase, so you can press start, and the motor just goes... BUUUUUUUUUUHHHHHHHHH... Instead of the normal nice 60 hertz hum..
> What could cause only one leg of the overload to trip?


 Are they adjustable overloads? Are all three overloads set the same?

It does not sound like a motor problem, it sounds like a contactor problem.

When motor is running, check amperage on each, T 1 T 2 T 3.


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## Zog (Apr 15, 2009)

1 phase grounded. Your fluke 87 won't find that.


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## Jlarson (Jun 28, 2009)

Yeah you need to megger it and current checks on each leg wouldn't be a bad idea either.


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## JRaef (Mar 23, 2009)

An overload relay should not disconnect the power to a specific phase, it should open the control circuit so that the contactor drops out, and it should drop out all 3 phases.

If you have what's called a "Manual Motor Starter" then the OLs will trigger a common mechanical trip mechanism that is in turn connected to the main power contact system, but again all 3 main contacts would open.

If when you re-close the switching device, either the contactor or the MMS, the motor is not getting power through all 3 phases, you have smoked one phase of the switching device. 

If power is getting through all 3 phases of the switching device and your motor is not spinning, you have smoked the motor. 

A DMM is virtually useless in determining the health of an AC motor, it's barely more than an "idiot light" because the only thing useful it can determine is if your windings have totally melted and fused, which is usually fairly obvious anyway, or a conductor has totally opened. there are thousands of other modalities of failure in between those two extremes.


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## mrmike (Dec 10, 2010)

JRaef said:


> An overload relay should not disconnect the power to a specific phase, it should open the control circuit so that the contactor drops out, and it should drop out all 3 phases.
> 
> If you have what's called a "Manual Motor Starter" then the OLs will trigger a common mechanical trip mechanism that is in turn connected to the main power contact system, but again all 3 main contacts would open.
> 
> Very good info here, and I would like to add that before you burn that motor out to check continuity from the top to the bottom of each phase of that overload before resetting it. If only one is open-replace that O/L. Even if one phase of the motor/line was grounded it would trip out as designed as stated above.........................


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## JRaef (Mar 23, 2009)

Looks like MTE was bought out by ABB some time ago, but from what I could tell it was just a standard OL relay, so it would be wired into the contactor control circuit as I mentioned.


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