Contactors and overloads

[KenL]

Hi, bit of history of my problem. I have a dust extractor in my shed, recently it started to blow the 13amp fuse. I took the motor to get it checked out, i was told the motor was fine and pulling 7amps when running. The motor has a start capacitor this is disengaged by bob weight at the end of the motor. The guy that checked out the motor said that it should be wired direct into my sheds wiring, this i have done.

After i had done all this when switching it takes the main house rcd out.

In to box where the start/stop switch located there is a contactor with overload which i think is the problem as the motor and wiring are all ok.

The starter and overload  are SDE MA15 and MA09, these appear to be american according to my searches. What i would like to know is what UK available parts would i need to replace the contactor and overload or as i am now wired direct can i use just use a stop/start switch without the contactor and overload.

I was an A/C engineer so used to wiring up the main supply to these machines.

 

[ProDave]

If it did not trip the RCD when it was plugged into a plug top, but does trip the RCD now it is hard wired I would STRONGLY suspect it is now not wired properly.

 

[Geoff1946]

Have you checked the insulation of the motor and the whole modified circuit. RCD trip strongly suggests an earth fault.

 

[Evans Electric]

Also point out that motors should have a no-volt release  , (contactor )  to prevent restarting . 

Is it definitely an RCD  that is tripping  or an MCB  ?       Motor start currents can often be high and need a type C  MCB .

 

[KenL]

Thanks for the replies.

I was thinking the same about the rcd but cannot see why.

I marked the live and neutral when i took the motor out to be tested ( by AES  rewinds in Ash near Farnborough, they have had it running which is where i got the 7 amps run figure ) 

There is 230v at the incoming to the contactor and the neutral is ok.

I have run the feed through a commando plug and socket and checked the wiring, twice.

Can i replace the start stop switch with the contactor with a start stop NVR switch rated at 10 amp, i see that new contactors are quite expensive. Never rally gave it a thought when i was replacing them when working, just ordered them and fitted them.

 

[Tony S]

Testing a single phase motor isn’t the easiest of things. There are four separate elements, each can be a swine to fault find.

Look in https://talk.electricianforum.co.uk/knowledgebase/electric-motors-and-generators/single-phase-motors/

 

[KenL]

Testing a single phase motor isn’t the easiest of things. There are four separate elements, each can be a swine to fault find.

Look in https://talk.electricianforum.co.uk/knowledgebase/electric-motors-and-generators/single-phase-motors/

Well yes that did go over my head lol, three phase motor are easier to test plus no capacitors. 

 

[binky]

If it did not trip the RCD when it was plugged into a plug top, but does trip the RCD now it is hard wired I would STRONGLY suspect it is now not wired properly.

I have to concurr with Pd on this one, hard wiring is no reason for something to fail

 

[phil d]

assuming you can get access to the outgoing or load cables from the control setup, try disconnecting the fan from here and see if the starter goes in without tripping the RCD in the house, if this works then connect a normal 60W lamp across the load terminals and try again, if this stays in you have a fault on the motor, if it trips out then I'd be checking to see if you have somehow got the neutral and earth crossed somewhere. You can measure between L and E and it won't trip the RCD, but put a load on it and it will, it may seem obvious but it's worth checking.

 

[Evans Electric]

Thanks for the replies.

 I was thinking the same about the rcd but cannot see why.

So is it an RCD or an MCB  that is tripping ?  

And as Phil says  ,  try disconnecting the motor and just start /stop the starter  (Contactor)   without a load  then with a load such as a lamp as Phil says  .. if it works  but trips as soon as you try the motor ...and you have decided that the device that trips is in fact an RCD  then , again as Phil says , could be a N - E fault , capacitor could be earthing .

If however its an MCB that trips  then that could just be the start up load  .   If the rewinders have tested it  then we assume the motor is OK .  

Is it possible to start the motor spinning by hand  then press the start button  , which should  reduce the start current . ?  

 

[binky]

NB some contactor / isolator  wring isn't straight through on the terminals, some go diaganol - worth double checking

 

[KenL]

Thanks for the replies again.

Earlier on this morning (before reading you replies)  i disconnected the motor at the box on the motor. Checked the live and neutral to earth and the live is to earth, so much for professional services. I have taken it back and i am now wait to hear.

What get me is that the engineer said that he had run it the first time i took it in. Surely to do that he just connected the live and neutral and not the earth, but if he did that that would make the case live.

Now got to wait and see what a rewind will cost.

 

[Evans Electric]

Perhaps they don't have an RCD on their test bench , wouldn't surprise me .   It that motor in a damp environment  at all?   

 

[KenL]

Not really, its in my shed that's not insulated. I have many other electrical bits in the shed, a lathe, a big bench disc sander that has the same sized motor. 

The extractor has run this year no problem, in fact the day it went i was using it, switch it off then 10mins later switched it on again and the fuse blew.

 

[Evans Electric]

That does sound as if the winding has gone down .    

 

[phil d]

Get a price on a new motor, machine mart do several, as well as a price on a rewind, quite often on smaller motors it's often cheaper to get a replacement rather than a rewind, unless of course there's something special about it.

 

[Sidewinder]

TBH I doubt that I would even bother with asking my rewinder to look at a small 1ph motor unless it was a special.

A replacement would be cheaper.

 

[KenL]

The only thing that maybe different it the spindle size has to be the same and the distance from the base to the spindle to match up with the mounting on the extractor.

 

[KenL]

Have checked Machine Mart and they certainly have a lot of motors, I have asked for details of the hole centres and the height from the base to the centre of the spindle. I think these maybe a standard sizing but want to make sure.

 

[Apache]

What kind of dust extractor is it? Might be easier to replace with a new one. The modern throwaway age does make me sad, but it is often the easiest option