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Squirrel Cage Motor


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I wish to share this with you something whic defeats the very basic understanding of electrical engineering, I just got a call from a customer claiming that he could not reverse the rotation of a three phase electric motor. He did change the phase on the terminals of the motor itself but the motor keep rotating in a clockwise direction. There is nothing connected at the output shaft of the motor, its a 1.5 k W 400 V motor.

I will drive there( 8 hours drive ) and keep the forum informed.



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Hi Bob


I recently had a similar experience with an installation using a VFD.

The client insisted on reversing the phases at the input to the VFD rather than the output. Once the output phases were reversed, the problem went away.


I have also seen people reversing/swapping three phases rather than just two.


Interested to see what you find.


Best regards,

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It could also be that he has an IMD unit (Integrated Motor-Drive) which has the VFD built right on to the motor.




So he may not be aware of the VFD. If he is swapping leads at a remote motor starter or circuit breaker, it will have no effect on the motor rotation as Marke pointed out.



"He's not dead, he's just pinin' for the fjords!"
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Perhaps he has lost a phase? A three phase motor running on two phases with no load connected will often rotate randomly.

One thing that I am sure about, you will not get the full story over the phone unfortunatly.

Good luck and I hope its a pleasant drive.


An expert is one who knows more and more about less and less until he knows absolutely everything about nothing
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Very true kens. A 6 SCR soft starter in which 1 SCR has an open gate can also exhibit similar behaviour. There again Bob, if the weather is good and the customer is paying, the drive might present as a well earnt break!




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