Motor Windings have Shorted

[moelect]

Can someone please let me know if my motor winding have shorted, I have a three phase 440v motor, I took a merrer reading to ground, and all three phases was okay, then I took a megger reading from phase to phase and the reading where 332 oms, 333 oms, and 4 oms, does this mean that the motor windings are shorted. it keeps tipping on overload current. Thanks

 

[iwire]

Sure sounds like the motor is shot.

 

[ATSman]

If you measured the winding resistances as:

332 ohms
333 ohms
4 ohms
then yes, the one phase winding has shorted turns and would trip the OL on that phase. A reading difference of around 1% between phases would be suspect.

 

[Besoeker]

Can someone please let me know if my motor winding have shorted, I have a three phase 440v motor, I took a merrer reading to ground, and all three phases was okay, then I took a megger reading from phase to phase and the reading where 332 oms, 333 oms, and 4 oms, does this mean that the motor windings are shorted. it keeps tipping on overload current. Thanks

What rating is the motor?

 

[iwire]

What rating is the motor?

I am most curious why this would make a difference.

 

[Besoeker]

I am most curious why this would make a difference.

Curiosity killed the cat...........
Ever so slightly more seriously, the rating will give an indication of what the winding resistance should be.
The 333 ohms seems rather high and maybe the 4 ohms may be more realistic. That would point to open circuit rather than short circuit windings.

 

[ptonsparky]

I am looking at it differently.
4 ohm is good, the other two are high.

Still a bad motor.

 

[Besoeker]

I am looking at it differently.
4 ohm is good, the other two are high.

Still a bad motor.

That was my thought.

 

[Strathead]

Curiosity killed the cat...........
Ever so slightly more seriously, the rating will give an indication of what the winding resistance should be.
The 333 ohms seems rather high and maybe the 4 ohms may be more realistic. That would point to open circuit rather than short circuit windings.

My thought too, but I also nitpicked the fact that the OP said he "meggered:?" the windings.

 

[Besoeker]

My thought too, but I also nitpicked the fact that the OP said he "meggered:?" the windings.

Perhaps moelect can fill in some details.

 

[ptonsparky]

My thought too, but I also nitpicked the fact that the OP said he "meggered:?" the windings.

My megaohm meter has a pretty good ohm meter scale, I allowed that option.

 

[Jraef]

My thought too, but I also nitpicked the fact that the OP said he "meggered:?" the windings.

No, he said he "took a merrer reading to ground".
I don't know what that means, but I assumed he "meant" megger...
But a megger is not the proper tool for doing a phase-to-phase (coil) test of a motor, it's function is to test the insulation resistance to ground.

On the analog meggers I've seen that can be switched into being a basic ohmmeter, the scales are reversed and a different color.

 

[Strathead]

No, he said he "took a merrer reading to ground".
I don't know what that means, but I assumed he "meant" megger...
But a megger is not the proper tool for doing a phase-to-phase (coil) test of a motor, it's function is to test the insulation resistance to ground.

On the analog meggers I've seen that can be switched into being a basic ohmmeter, the scales are reversed and a different color.

read it again, he said he took a megger reading phase to phase, I paraphrased it as windings... (they don't have a nah, nah, na, nah, nah emoticon)

 

[Jraef]

read it again, he said he took a megger reading phase to phase, I paraphrased it as windings... (they don't have a nah, nah, na, nah, nah emoticon)

You are right... at least they have that "D'oh" emoticon... :slaphead:

 

[Saturn_Europa]

I'd call those readings "open windings" or very nearly so. Bad ohm readings plus the fact that its going out on overload is definitely an indication that the motor is shot.

The next question is what caused the failure. Early in my career, I replaced a $500 pump, 3 times before I figured out that it was pumping off the pump curve and that was causing the failure. (I didnt actually figure it out. It was someone else. But I'll take credit for it here!)

It'll be worth opening up the motor and taking a look inside of it. I've taken apart motors and seen the stator windings covered in grease. A lot of newer motors dont have grease relief ports and its easy for plant mechanics to PM them to death.

 

[iwire]

Man oh man, you guys must be trying to run up the bill.

Three readings, one wildly different from the others. The motor overload keeps opening.


I pronounce this motor junk, time for new or rebuild it.

Can we do seventeen posts on a burned out incandescent lamp next?

 

[Besoeker]

Man oh man, you guys must be trying to run up the bill.

Three readings, one wildly different from the others. The motor overload keeps opening.


I pronounce this motor junk, time for new or rebuild it.

Can we do seventeen posts on a burned out incandescent lamp next?

But can you at least see why the rating is a significant factor?
Yes, it does sound like the motor is shot but it could also be loose connections giving high resistance readings.
And it will probably remain one of life's great mysteries.

 

[iwire]

But can you at least see why the rating is a significant factor?

No, it is not relevant given those readings and the the fact it keeps tripping the OLs.

If it was a loose connection smoke would be escaping by now.

 

[topgone]

No, it is not relevant given those readings and the the fact it keeps tripping the OLs.

If it was a loose connection smoke would be escaping by now.

It depends on where the loose connection occurred.

IMO, if it's on the peckerhead, motor will be a garbage item. If it occurred at the starter, I guess replacement of the OL or contactor is in order!

 

[Besoeker]

No, it is not relevant given those readings

It gives context to the readings.