Motor Windings have Shorted

[Sahib]

It gives context to the readings.

It also gives direction to where to look for:high resistance connections, as the motor could run without smoke till the OL trips and also the motor might be small one.

 

[ptonsparky]

OP...has anyone given it the smell test? Usually infallible.

 

[iwire]

OP...has anyone given it the smell test? Usually infallible.

:thumbsup:

 

[Besoeker]

OP...has anyone given it the smell test? Usually infallible.

He seems to have done a runner......

 

[Sahib]

In that case we may have it among ourselves. The unequal resistances would cause severe voltage unbalance in motor winding. However if O/L relay is operational, it would save motor except for a certain motor hp range for which negative sequence relay protection is required.

 

[ATSman]

That was my thought.

Ok lets take this one step further. If we go by the odds, the changes of 2 windings failing (opening) as opposed to just one (shorting) I would think are much higher so I stand with my diagnosis.

 

[Besoeker]

Ok lets take this one step further. If we go by the odds, the changes of 2 windings failing (opening) as opposed to just one (shorting) I would think are much higher so I stand with my diagnosis.

OK.

 

[moelect]

Wye, Delta

Wye, Delta

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.

I'm sorry I forgot to mention that the motor is a two speed motor, with Wye, Delta connection, does this make a difference?

 

[topgone]

I'm sorry I forgot to mention that the motor is a two speed motor, with Wye, Delta connection, does this make a difference?

There goes the devil! It's in the details!

You must make sure you have properly identified the windings!

 

[iwire]

There goes the devil! It's in the details!

You must make sure you have properly identified the windings!

:thumbsup:

 

[ptonsparky]

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

I'm sorry I forgot to mention that the motor is a two speed motor, with Wye, Delta connection, does this make a difference?

This doesn't help your solution at all. Then again maybe it does. I am assuming this is not a new install.


1. Open the pecker head at the motor. Are the connections good?
2. Inhale through the nose. Does it pass the smell test? Get new motor or send out for repair if it does not.

These steps are for education and confirmation of the above.

3. Make note of all connections. Open all of them.
4. Meg each winding to ground. Reading should be high and similar to all of the others
5. Meg each winding to another. Reading should be high and similar to all of the others.
6. Ohm each winding. Reading should be low and similar to all of the others.