Thread: Bench grinder fail

I had a similar experience with a 3 Hp 3Ph motor on my thicknesser. It kept dropping the earth leakage breaker. My electrician mate said it would more likely be a mechanical problem rather than an electrical fault. (The motor would be a 50s vintage). I pulled the motor to bits and changed the bearings, turned it on and ......dropped the earth leakage again. The mate came down and we had more of a look and discovered that the wires coming out of the field coil were shorting out to the frame because the insulation had gotten brittle. I stripped any old insulation off the offending wires and slid "spaghetti" over the wires, put the whole lot back together and......went like a dream.
In your case the high temperature from buffing may have softened the wires similar to what my motor had done. It would be worth a look. For the sake of a little time, it may be a lot less than replacing the grinder

Could be a number of things but the first thing to fix is the earth since that provides major protection.
Until that works I would not do anything else.

Those types of switches can sometimes get grit and dust inside them which will cause all sorts of problems.

It sounds like the cord also needs a close inspection.
Grinder cords are prone to get metallic grit embedded in them which will reduces their insulation capability.

BTW Most of those small grinders don't have a motor cooling mechanism and are not really designed to run for long periods of time (e.g. Buffing) so it could have overheated and that has damaged something inside it.

Thanks for the responses, they gave me courage to open things up and search for specifics. I found the earthwire disconnected after its nut had vibrated loose and crackled and slightly brittle insulation on two wires. Both a quick, easy fix thanks to advice on here. I further learnt the difference between grinders & buffers, condensers & capacitors and starting systems. BobL was right about the lack of cooling vents on grinders, an obvious hint not taken until now by me. Tested, tested, and retested prior to connecting it now runs a treat but now with a close eye on its temperature. A dedicated buffer may be in my sights soon.

Hasn't learning and the sharing of information & skill come a long way in the last 20 years. There is no need for skill & knowledge to decay, there is plenty of help right at our fingertips.

Thank you.