Fix or throw away

Only you can test it to find out what bit's shorting out. We can't.

If its a partial short on the motor it'll be simple to make it work without even needing to repair. For now, I'd suggest turning the blade round a bit before restarting it, if it then runs its fairly likely to be a partial motor short.

NT

Yup, I had that on an old washing machine motor. I squeezed another few months out of it by blowing the carbon out with an airline.

Cheers, T i m

so as soon as I try to start it.

anymore money on.

What has tripped on the CU? an MCB or the RCD Can you remove and inspect the carbon brushes? Inspect the commutator while they are out.

No clues were provided as to what types of device actually tripped - overload, MCB, RCD?

I wonder if the "inbuilt circuit breaker" was also an RCD?

What sort of saw are we talking about (make, model)?

and what sort of motor (i.e. universal with brushes, or an induction motor?)

Thanks for the replies so far.

The make/model is Performance FMTC10TSW.

When it trips the CU, it trips the whole board and not just the circuit it is plugged in to.

A web search shows lots of places supplying replacement brushes for these - so we can assume its a universal motor and not an induction one.

Sounds like a RCD trip then.

It also sounds like you have a "whole house" RCD that covers all the circuits. This in itself may be part of the problem. If the combined imbalance sensed at the RCD due to the number of circuits mean that it is close to its tripping threshold anyway, even a switch on surge of a reasonably large motor may push it over the edge.

Check to see if it has a two wire or three wire mains lead. If its a two wire, then the above trip scenario sounds likely.

If three wire, then investigate further.

Make sure there is no damp in there. A visual check inside the unit for damaged wires etc. Check the brushes are not heavily worn[1]. Badly worn brushes ccould also have shed excess conductive carbon around the motor

- so a blow out with an airline may help.

If you have a multimeter, stick it on its highest resistance range and measure between the live and earth and neutral and earth connections on the plug with the switch at the saw in the on position (if possible - if the saw has a double pole NVR switch, then you may need to do this test on the wiring inside after the switch). You should get an open circuit indication in both cases - but a measurable resistance would indicate a problem.

Almost certanly an RCD trip then, not MCB. Really you need to properly fault find on it, but if you really cant then a couple things can be tried:

1. clean away carbon deposits on and aroud the motor very thoroughly
2. swap L & N wires in the plug. Either might work.

NT

As I mentioned previously, that was what 'cured' my first RCD trip although it may not have been 100% the cause (see below).

My second (some months later) was a partial short from the motor windings to earth and it would trip the RCD by just plugging it in and not even turning it on at the wall (and yes my sockets are wired correctly). ;-)

Cheers, T i m

That sounds like an RCD, is there a test button on the item which trips?

In which case there is some leakage from L or N to the earth, which most probably is due to carbon (or moist sawdust) accumulating in the motor from the motor brushes. Try removing the motor, leaving it for a while on a warm radiator to dry out, then blowing it out via the vents with an air line.

Many thanks to you all for the suggestions and advice, it is very much appreciated.

Probably going to be a week or so until I can follow up on your suggestions but I will do so and let you all know the outcome.

Thanks again.

C.

Ideal job for WD40

hi try checking the carbon brushes i think you will find that is the cause of your trouble easy to check turn over and remove the bottom cover and you will see the motor there is 2 brushes 1 at each side of the motor use a pl ane screwdriver to turn the access cover the brush should pop out if they a re well worn replace it and same the other side.good luck joe

Ooooh, sooo close. Just another month and it would have been 5 whole years since that post. Sorry, no prizes this time. Do try playing Thread Ressurection Bingo again soon!