I think the clue is in the fact that it started OK the first time, and only made the straining noise when you moved the switch. That's a faulty switch. No I would definitely not be happy to let that go out of my shop behaving like that, but I think the fault is in the rotary switch.

Looks like it's a pretty standard sort of switch – the internals and the spring return will be specially designed for this application but you should be able to obtain a direct replacement.

If you would like to put up a photo of the labels on the switch which hopefully will show a manufacturer (Kraus and Naimer?) and a type number we can probably locate a supplier.

You may even be able to get a replacement from Marcrist as it seems to be their name on the drawing.

Worth spending the money for the right thing – should be £20 – 30 or thereabouts. While you're at it replace the contactor as well at the same time and have done with it. That looks to me like a Siemens contactor (edit – sorry the clue's on the picture it's Eaton if you blow it up big enough – but any similar contactor will do) – should be possible again to buy a direct replacement for about the same again. If you can get a picture of the label on the side of the contactor it will show manufacturer and part number.

HTH Simon

Edited By Simon Williams 3 on 04/03/2020 23:03:26

Is this a single phase motor or a 3 Phase one that has been altered..

Brian

I'm confused by the description as an induction motor with a permanent magnet rotor. Can anyone clarify?

The motor name plate and details will teel us all a lot , This looks like a 5hp or more size motor. Are you running this through a 3ph Inverter .The motor sound chages when running I wonder if this is running on 2 phases because the inverter has brocken down and lost a phase .

Brian M

Sounds like a dud bearing, damaged ball or balls skidding rather than rotating.This may only be happening when the motor has run at full speed for a few seconds and a lack of lubrication and or roundness starts the music.

Paul