For a split phase motor, without capacitors, the Red and Black wires are the run winding. The yellow and blue wires are the starting winding and the centrifugal switch is connected in series with it. You can connect these windings in parallel either way, but you may need to reverse the connections to one winding if the motor runs in the wrong direction.

The additional red wire and the striped wire probably go to the centrifugal switch in which case your wiring is correct.

If it's the main Residual Current Device (RCD) serving all circuits which trips, then some kind of insulation breakdown from winding or switch to the frame is indicated. If on the other hand it's a Miniature Circuit Breaker (MCB) serving say a ring main which trips then an overload in indicated.

When the contacts of the switch break the back emf will result in a high voltage between them. This could be jumping across to the frame tripping the RCD.

You could try disconnecting the start winding and hand starting the motor by spinning the shaft. If the motor runs OK this confirms a problem with the start winding or switch.

Edited By MAX THE MILLER on 15/08/2014 14:20:19

[QUOTE=Brian Wood]What I think you have done is wire live and neutral across the cenrifugal switch, and providing a dead short when the switch is activated at speed[/quote]

That can't be the case. The centrifugal switch is a BREAK switch designed to disconnect the start winding when the motor get up to speed leaving just the run winding connected. It's not a MAKE switch.

Sorry. Can't work how  to do a partial quote. This forum is different to every other one I use.

Edited By MAX THE MILLER on 15/08/2014 17:12:32

Edited By MAX THE MILLER on 15/08/2014 17:13:31

Hello Mark and Max,

Yes Max, you are of course right. I was swayed by Mark's description which suggested the short takes place when the motor is up to speed.

Mark.

I would remove the two link wires you put in and leave the supply coupled to AZ and A. It doesn't really matter which is to live being AC. As in my last response, motor reversal is done by swapping the yellow and blue leads.

Better luck this time Brian

Edited By MAX THE MILLER on 15/08/2014 22:31:16

I’ve got a Makita cut off saw that trips the circuit breaker the moment it starts. Any solutions to this problem are welcome.

According to my copy of 'Model Engineers Handbook' the red wire and the yellow wire go to live, the blue wire and the black wire go to neutral. To reverse direction then reverse the yellow and blue only. Of course earth the motor frame. The yellow and blue are the start winding in series with the centrifugal start switch.

I have had trouble like this. The problem started as an occasional trip and got worse and worse. If the flashover (to frame) has persisted for some time the mica insulation will track and it may be impossible to clean it up to remove embedded metal particles. Worth a try though. The alternative is the skip.

Hi Mark and others,
First Mark. From Roger's comments I think I guessed wrongly which connections were the centrifugal switch and which was the start winding. So in the tests I suggested I think you should get a reading of a few ohms between T and S and almost zero between S and Z (The opposite way round to my last post.)

Next Chris. If the cut off saw is a slow speed one with an HSS or carbide tipped blade then it will probably be an induction motor. If so a spark suppressor consisting of about a 100 ohm resistor in series with about a 100 nf capacitor (Of suitable rating for 250 volts AC) connected across the centrifugal switch contacts might help. You can get this type of suppressor with the resistor and capacitor encapsulated as a package. Another possibility is a transient suppressor (Sometimes called a metrosil I think.) connected across the start winding. (These are the devices use in surge suppressor sockets.) If the cutoff saw is the abrasive wheel type it will probably be a series (Also known as a universal) motor. If this is the case then the resistor/capacitor spark suppressor connected across the start switch might help. Also look for a build up of carbon dust around the brushes which might cause leakage to earth.

Finally Roger. Your tracking to earth theory is also my favourite one. As a test I would be tempted to see if the fault still occurred with the earth removed and the motor insulated from earth. !!!! I WOULD NOT SUGGEST THAT YOU SHOULD TRY THIS MARK !!!!!!

Les.

So, my apologies, its a capacitor start/induction run motor so my earlier comment was wrong. But the windings do not seem to be on the usual terminals, so going by winding colours (harder to confuse) we have red+black as the running winding so to live and neutral. The starting winding plus switch is blue+yellow and go in series with the capacitor to live and neutral. To reverse direction then change over either red+black or the blue+yellow.

You may be tempted by Les' suggestion which I would also follow – but be careful.