# Electrickery



## twentysix by twentyfive (22 Sep 2021)

Not sure this is on the correct forum page. Apols @Mods if I've put it in the wrong place.

Problem with single phase relay switch gear for motor start/stop. Help please.

The wood turning lathe won't turn on now. Previous problem was down to the surge capacitor failing but I've tried new ones with no joy. So I guess it might be the switch gear. So pulled it out of the housing with the following photographs taken to assist in remote diagnosis.

So I've only got as far as checking the green and red buttons. Both seem to be open circuit whether pressed in or not. From Googling I expected (rightly or wrongly) that the on switch would normally be open and the off switch would normally be on. Since neither are behaving as I thought I'm in a quandary. Am I doing something silly as I wouldn't expect both switches to fail simultaneously (or would I?). 

As far as I can see the (two only) relay contacts inside are open and the two tube like things on the outside on one side (I think may be thermal fuses operated by bitmetal strip?) are closed. 

So what next please - I'm at a loss.


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## presta (22 Sep 2021)

Not something I have any direct experience of, but it's simple, so I'd be inclined to draw the circuit diagram so you can see the wood for the trees. The buttons don't sound right, but they might be momentary contact ones - worth another check. From the poor quality soldering, dry joints are a possibility. Have you checked the continuity of the relay coil? Does the motor run if you connect the mains to it directly?


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## twentysix by twentyfive (22 Sep 2021)

presta said:


> Does the motor run if you connect the mains to it directly?




I did wonder if that was safe. I assume the few on/offs for testing won't knacker the switch on the wall?

Thanks for your thoughts. The coil I haven't investigated. Need to work out which contacts they are on the circuit board so I guess a circuit diagram is a good idea.


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## slowmotion (22 Sep 2021)

Looking at the fourth photo, the second and third soldered joints (from the left) at the top of the relay PCB look like they might be shorted together. It may just be the camera angle, of course.


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## Low Gear Guy (22 Sep 2021)

I Don't think those devices next to the relay are cut-outs. They look like magnetic reed switches which are activated by the relay coil.

It is not clear why these are present.


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## Tenkaykev (22 Sep 2021)

Hello. How many capacitors are fitted to the motor. If two, then one will be the “ Start “ capacitor about 100-200 Mfd depending on motor power, and the other will be the “ Run” capacitor typically 8 - 25 ish Mfd. 
Most single phase motors have a centrifugal switch on the shaft at the non drive end which disconnects the start capacitor and start windings once the motor is at about 75% of full speed. This is to protect the motor “ start “ windings and capacitor which will burn out if left connected for more than a few seconds. If it is a cheapie machine then they may be using the relay as a bimetallic strip to take the start windings out of circuit.


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## twentysix by twentyfive (22 Sep 2021)

slowmotion said:


> Looking at the fourth photo, the second and third soldered joints (from the left) at the top of the relay PCB look like they might be shorted together. It may just be the camera angle, of course.



They are and I assume intended to be as that's what I found when I took it out


Low Gear Guy said:


> I Don't think those devices next to the relay are cut-outs. They look like magnetic reed switches which are activated by the relay coil.
> 
> It is not clear why these are present.



Hmmmph - I don't know either but they don't lie along the axis of the coil which suggests that they aren't magnetically coupled


SydZ said:


> I’d expect, in this type of setup, for the “ON” switch to close when pressed applying power to the relay. The relay would then close, both powering the device and providing feedback to itself to hold it on. The “OFF” switch would break the feedback loop thus shutting on the system.


That was my expectation having Googled


Tenkaykev said:


> Hello. How many capacitors are fitted to the motor. If two, then one will be the “ Start “ capacitor about 100-200 Mfd depending on motor power, and the other will be the “ Run” capacitor typically 8 - 25 ish Mfd.
> 
> Most single phase motors have a centrifugal switch on the shaft at the non drive end which disconnects the start capacitor and start windings once the motor is at about 75% of full speed. This is to protect the motor “ start “ windings and capacitor which will burn out if left connected for more than a few seconds. If it is a cheapie machine then they may be using the relay as a bimetallic strip to take the start windings out of circuit.


I've only found one capacitor (100uF) which is disconnected by a centrifugal shaft switch as you mention. That 100uF failed a while ago and I replaced it with 80uF and all was well again until now when replacing the 80uF with others of same value didn't achieve the required result.


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## Tenkaykev (22 Sep 2021)

SydZ said:


> As it’s an AC motor the capacitor‘s sole purpose is to ensure the motor turns in the correct direction when power is applied


The capacitor puts the start windings out of phase with the main windings. The start windings are also physically displaced with regard to the main windings. If you swap either the run winding leads or the start winding leads then the motor will run in the opposite direction. There are several types of switch / starters that allow you to do this. With a " Shaded Pole" motor the start windings are replaced by a solid loop of copper offset to one side of the windings. These typically have low starting torque but don't require a capacitor. They are a fixed rotation but often physically reversible by dismantling and reassembling with the main body reversed.


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## MrGrumpy (22 Sep 2021)

twentysix by twentyfive said:


> Not sure this is on the correct forum page. Apols @Mods if I've put it in the wrong place.
> 
> Problem with single phase relay switch gear for motor start/stop. Help please.
> 
> ...


The switches will be momentary , can you push the coil in on the contactor ? Be careful as need the mains on. It should start if motor is ok , after which check you have 24v or 12v on the relay coil of contactor ? If coil working you should have 0v across the coil .


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## twentysix by twentyfive (23 Sep 2021)

MrGrumpy said:


> The switches will be momentary , can you push the coil in on the contactor ? Be careful as need the mains on. It should start if motor is ok , after which check you have 24v or 12v on the relay coil of contactor ? If coil working you should have 0v across the coil .


Are the switches momentary when no power applied?? I've used my multimeter on ohms setting and only see open circuit whether pushed in or not. No access (physically) to the coil. I'm yet to identify which contacts (on the outside) are at the ends of the coil. I'm guessing an "on the bench apply mains power" test is next best. Got to sort out the safety aspects before I try that. Thanks.


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## twentysix by twentyfive (23 Sep 2021)

One of the booooogers with all this is that there are no part numbers on anything


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## MrGrumpy (23 Sep 2021)

twentysix by twentyfive said:


> Are the switches momentary when no power applied?? I've used my multimeter on ohms setting and only see open circuit whether pushed in or not. No access (physically) to the coil. I'm yet to identify which contacts (on the outside) are at the ends of the coil. I'm guessing an "on the bench apply mains power" test is next best. Got to sort out the safety aspects before I try that. Thanks.


When pressed in they should make a contact across the switch, even if just when pressed ? I need to look at the pictures you posted. A set of contacts on the contactor maybe acting as the holding circuit to keep the coil in. You stop switch will drop that out. Need to get a look at them ?

Where do the wires come from/go to that have white tape wrapped round them ?


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## Tenkaykev (23 Sep 2021)

You should be able to see the fine wires that go from the contactor coil to the pins. Put a multimeter on them and check continuity.
Is there a manufacturers name on the Lathe?


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## twentysix by twentyfive (23 Sep 2021)

MrGrumpy said:


> Where do the wires come from/go to that have white tape wrapped round them ?


Those wires are the input cable to the mains plug and the output to the motor


Tenkaykev said:


> Is there a manufacturers name on the Lathe?


There is and I've checked. Very old model it is and no spares. 

I put mains directly on the input wires and pressed Green. Nothing. I was expecting to maybe hear the relay clunk over and maybe see some volts at the output. But nothing.

My next move is to bypass the Green button to see if that's any better. And maybe try to test the coil continuity.


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## Tenkaykev (23 Sep 2021)

twentysix by twentyfive said:


> Those wires are the input cable to the mains plug and the output to the motor
> 
> There is and I've checked. Very old model it is and no spares.
> 
> ...


What make is it and how old is “ very old “ ? ( I’ve worked on Electric motors that are getting on for 100 years old )


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## twentysix by twentyfive (23 Sep 2021)

@Tenkaykev It seems it's not as old as 100 yrs . The Lathe is from Axminster Power Tool Company. There's a label on the motor which says it's an Induction Motor, 0.5 kW, 4 A, 240 V, Single Phase, 4 pole, 1420 rpm and the date has been changed from 1991 to 1992 (I assume the up date reflects the sales date while the earlier is the manufacture date?) There's a Serial Number _Y0700 where the " _ " is unreadable.

Feeling a bit shattered at the moment so reluctant to play with live mains "out in the open" . Tomorrow is another day.


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## MrGrumpy (23 Sep 2021)

twentysix by twentyfive said:


> Those wires are the input cable to the mains plug and the output to the motor
> 
> There is and I've checked. Very old model it is and no spares.
> 
> ...


When your less tired , maybe get the meter on those connections and check your getting voltage. Need to trace this out. Thought you had some modern contactor but it’s ancient ! Same principle with the relay though.


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## twentysix by twentyfive (24 Sep 2021)

MrGrumpy said:


> When your less tired , maybe get the meter on those connections and check your getting voltage. Need to trace this out. Thought you had some modern contactor but it’s ancient ! Same principle with the relay though.


Yep - attempting to work my way through. Was hoping to do it with battery volts from the meter but playing with live mains seems to be necessary. Need my A game when playing with live mains.......


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## twentysix by twentyfive (24 Sep 2021)

Update

Checked the continuity of the coil. Seems it's open circuit. Which would explain quite a bit. Still confused about the on/off buttons tho'. Not that that matters now as I need a new shebang. Think I'll ask Axminster Power Tools first. Unless any of the experts on here know what's available that would suit.

Cheers all.


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## Tenkaykev (24 Sep 2021)

twentysix by twentyfive said:


> Update
> 
> Checked the continuity of the coil. Seems it's open circuit. Which would explain quite a bit. Still confused about the on/off buttons tho'. Not that that matters now as I need a new shebang. Think I'll ask Axminster Power Tools first. Unless any of the experts on here know what's available that would suit.
> 
> Cheers all.


There’s several ways of wiring starting switches, depending on the connections on the terminal board which will be under a small cover plate on the non drive end of the motor. I’d see if Axminster can be of any assistance.


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## twentysix by twentyfive (24 Sep 2021)

Tenkaykev said:


> There’s several ways of wiring starting switches, depending on the connections on the terminal board which will be under a small cover plate on the non drive end of the motor. I’d see if Axminster can be of any assistance.


I've got a roughly drawn circuit diagram now which, if I can tidy it up I may post. As far as I can understand these switches aren't wired beyond the circuit board. Also the thing that puzzles me is that the tiny tiny wires of the coil (inside the relay) are energised by the full mains. Or is there some mitigation applied in the depths of the switches? It can't be this difficult can it?


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## Tenkaykev (24 Sep 2021)

A


twentysix by twentyfive said:


> I've got a roughly drawn circuit diagram now which, if I can tidy it up I may post. As far as I can understand these switches aren't wired beyond the circuit board. Also the thing that puzzles me is that the tiny tiny wires of the coil (inside the relay) are energised by the full mains. Or is there some mitigation applied in the depths of the switches? It can't be this difficult can it?


Inside the motor there should be a terminal board . The Main or “ Run “ windings are usually labelled “ A” and “ AA” ( or “ A1and A2” ) 
Start windings are Z and ZZ .
For a fixed rotation motor they usually “ Common “ for example A1 and Z1 on one terminal post which is where one of the mains is connected. The other mains is connected to the other “ A2 “. From there the power will travel through the start windings, capacitor and centrifugal switch before returning through a link to a separate post on the terminal board and linked back to A2.
When you apply the power it travels through the Run windings, and temporarily through the start windings, capacitor and centrifugal switch. When the motor is at approximately 75% of full load speed the weights on the centrifugal switch throw it open to protect the capacitor and start windings. When you switch the motor off, the springs on the centrifugal switch cause it to re engage ready for next time.


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## twentysix by twentyfive (24 Sep 2021)

Tenkaykev said:


> A
> 
> Inside the motor there should be a terminal board . The Main or “ Run “ windings are usually labelled “ A” and “ AA” ( or “ A1and A2” )
> Start windings are Z and ZZ .
> ...


Thanks. I haven't penetrated quite as far as that. I have replaced the start capacitor (which has it's wires poking through a hole in the motor housing) in the past and I've seen the centrifugal switch operating at the non drive end as that cover comes off easily so your description makes much sense. 

I've tidied up my attempt at the circuit diagram a bit and I've missed something. The power to the motor from the circuit board appears to have no feed at all . This is clearly rubbish so I had a closer peer at it all and couldn't see how it is connected. I did notice that it might be possible to pull the plastic cover away from the relay which might provide a better look at the connections in there and at the coil/switches. I feel more tinkering coming on.

Meantime I've contacted Axminster with all the details so I await a response.


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## Tenkaykev (24 Sep 2021)

twentysix by twentyfive said:


> Thanks. I haven't penetrated quite as far as that. I have replaced the start capacitor (which has it's wires poking through a hole in the motor housing) in the past and I've seen the centrifugal switch operating at the non drive end as that cover comes off easily so your description makes much sense.
> 
> I've tidied up my attempt at the circuit diagram a bit and I've missed something. The power to the motor from the circuit board appears to have no feed at all . This is clearly rubbish so I had a closer peer at it all and couldn't see how it is connected. I did notice that it might be possible to pull the plastic cover away from the relay which might provide a better look at the connections in there and at the coil/switches. I feel more tinkering coming on.
> 
> Meantime I've contacted Axminster with all the details so I await a response.


If you are poking about make sure the plug is out of the wall. If you look at the relay it looks like there are a couple of black tabs in the transparent casing. Pushing them in should allow you to remove the cover of the relay and see where the very fine wires from the solenoid coil are attached. You can then check for continuity. If the coil is open circuit then you will need a new relay.
EDIT: If you send me your circuit diagram I can see if I can make sense of it.


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## twentysix by twentyfive (25 Sep 2021)

Tenkaykev said:


> If you are poking about make sure the plug is out of the wall. If you look at the relay it looks like there are a couple of black tabs in the transparent casing. Pushing them in should allow you to remove the cover of the relay and see where the very fine wires from the solenoid coil are attached. You can then check for continuity. If the coil is open circuit then you will need a new relay.
> EDIT: If you send me your circuit diagram I can see if I can make sense of it.


Thanks @Tenkaykev . I got the plastic cover off and tried to find continuity through the coil. The little wires may be coated with insulation stuff maybe so I ended up on where they had been soldered on for a good contact. No continuity. The relay switches themselves move freely when pushed and I get continuity through those when held closed. So it seems it's the coil 

For completeness I checked my original circuit diagram and realised I had drawn the relay switches between the wrong pins. With the cover off this was obvious so here's what it looks like now. All very understandable I think.






So thanks @Tenkaykev and @MrGrumpy for your assistance and patience with this old fart who's brain is turning to mush. Perhaps one last question if I may be so bold. Any thoughts on where I could source a suitable replacement (should Axminster PTC fail me)? What am I asking for?


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## Tenkaykev (25 Sep 2021)

twentysix by twentyfive said:


> Thanks @Tenkaykev . I got the plastic cover off and tried to find continuity through the coil. The little wires may be coated with insulation stuff maybe so I ended up on where they had been soldered on for a good contact. No continuity. The relay switches themselves move freely when pushed and I get continuity through those when held closed. So it seems it's the coil
> 
> For completeness I checked my original circuit diagram and realised I had drawn the relay switches between the wrong pins. With the cover off this was obvious so here's what it looks like now. All very understandable I think.
> View attachment 610816
> ...


Ah, so just Live and Neutral out to the motor? Fixed rotation then. 
This should do the trick. It wont fit in the existing start location but it is self contained. You would need to set the overload current to the nameplate current on the motor ( usually a slider or dial inside the contactor )

I would *STRESS *that you should get a suitably qualified electrician to carry out the work ( over the years we " lost " a couple of competent guys who were fully qualified but got distracted and electrocuted themselves 😢)

https://www.electrotechdrives.co.uk...red-with-2-5-to-4-amp-overload-0-55kw-0-75hp/


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## twentysix by twentyfive (25 Sep 2021)

Tenkaykev said:


> Ah, so just Live and Neutral out to the motor? Fixed rotation then.
> This should do the trick. It wont fit in the existing start location but it is self contained. You would need to set the overload current to the nameplate current on the motor ( usually a slider or dial inside the contactor )
> 
> I would *STRESS *that you should get a suitably qualified electrician to carry out the work ( over the years we " lost " a couple of competent guys who were fully qualified but got distracted and electrocuted themselves 😢)
> ...


Thanks again @Tenkaykev . Looks like the cable routing will need to be totally changed as the current housing is probably too small/wrong shape if using the above. So I'll get a "man who can" in. I had to make a new "blister" to accommodate the replacement starter capacitor in a safe fashion. Drainpipe is a good insulator. You'd think over the years the capacitors would have gotten smaller.


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## Tenkaykev (25 Sep 2021)

twentysix by twentyfive said:


> Thanks again @Tenkaykev . Looks like the cable routing will need to be totally changed as the current housing is probably too small/wrong shape if using the above. So I'll get a "man who can" in. I had to make a new "blister" to accommodate the replacement starter capacitor in a safe fashion. Drainpipe is a good insulator. You'd think over the years the capacitors would have gotten smaller.


Electrolytic or "Starter " capacitors don't like it up em! they go pop, often quite spectacularly if left connected to mains power for more than a few seconds. The actual capacitance isn't critical ( they often have a value range printed on them, " 80 -100 Mfd " for example.
Run Capacitors are designed to be permanently connected while the motor is running. Sometimes the run capacitor will be switched internally in the " Run " position to be in series with the start windings. ( this is more efficient as the start windings are usually disconnected once the motor is up to speed ) It is ok to substitute a " Run " capacitor of the same value as the Start Capacitor but not vice versa, though run capacitors tend to be a lot bigger physically. Run capacitors also need to be rated at 450V or thereabouts as that electrickery is alternating, + / - 220 volts above and below 0 volts.


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## Tenkaykev (25 Sep 2021)

twentysix by twentyfive said:


> Thanks again @Tenkaykev . Looks like the cable routing will need to be totally changed as the current housing is probably too small/wrong shape if using the above. So I'll get a "man who can" in. I had to make a new "blister" to accommodate the replacement starter capacitor in a safe fashion. Drainpipe is a good insulator. You'd think over the years the capacitors would have gotten smaller.


Some motor manufacturers save money ( and physical size ) by fitting start capacitors that are rated for 120 Volts. They get away with this by tapping into the internal mid point connection of the starting winding . In your 4 Pole motor there are four groups of Run winding coils arranged around the core. If you imagine a clock face the main run winding coil groups will be at 12 - 3, 3-6, 6-9 and 9-12, with the start winding coil groups spanning them ( 1:30 - 4:30 etc )


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## twentysix by twentyfive (25 Sep 2021)

Tenkaykev said:


> Some motor manufacturers save money ( and physical size ) by fitting start capacitors that are rated for 120 Volts. They get away with this by tapping into the internal mid point connection of the starting winding . In your 4 Pole motor there are four groups of start winding coils arranged around the core. If you imagine a clock face the main run winding coil groups will be at 12 - 3, 3-6, 6-9 and 9-12, with the start winding coil groups spanning them ( 1:30 - 4:30 etc )


The grey one was fitted by the manufacturer in 1991/2 I believe. It died so I've been running the black one since. You'll see that it's a smaller capacitance value but is longer and slightly bigger diameter. The "worry" I had when I bought it (as a start capacitor) was that the quoted life was (I thought) quite short. So I bought two. So far so good tho' on that side of things.


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## Tenkaykev (25 Sep 2021)

twentysix by twentyfive said:


> The grey one was fitted by the manufacturer in 1991/2 I believe. It died so I've been running the black one since. You'll see that it's a smaller capacitance value but is longer and slightly bigger diameter. The "worry" I had when I bought it (as a start capacitor) was that the quoted life was (I thought) quite short. So I bought two. So far so good tho' on that side of things.
> View attachment 610845


They're pretty standard. We used to buy from a specialist trade supplier and always kept a stock of several of the main values. The black one is 3 Minute rated ( is should be able to withstand mains voltage for that length of time 🤞) They do gradually lose capacitance over time but we've had motors that were 30 - 40 years old and the capacitors were still functioning ok.


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## MrGrumpy (26 Sep 2021)

twentysix by twentyfive said:


> Thanks @Tenkaykev . I got the plastic cover off and tried to find continuity through the coil. The little wires may be coated with insulation stuff maybe so I ended up on where they had been soldered on for a good contact. No continuity. The relay switches themselves move freely when pushed and I get continuity through those when held closed. So it seems it's the coil
> 
> For completeness I checked my original circuit diagram and realised I had drawn the relay switches between the wrong pins. With the cover off this was obvious so here's what it looks like now. All very understandable I think.
> View attachment 610816
> ...


Looking at they drawing, relay coil is powered by the normally open ON switch . Your normally closed off switch completes the circuit once you press ON. Completes the path and your contacts switch over and power the motor. If your getting power out of the relay to the motor then , it’s maybe the capacitor start that’s not working . Unusual to be a motor shorting ? However any motors we replace at work are sealed units and only fault to the connections after which it’s replaced and sent away.


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## twentysix by twentyfive (26 Sep 2021)

I'm just waiting for Axminster PTC to get back to me first as, if they have the same old kit on the shelf it'll fit directly. I'm away next week so it'll be very quiet in here. If no response from Axminster when I get back I'll go down your route @Tenkaykev


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## Tenkaykev (26 Sep 2021)

MrGrumpy said:


> Looking at they drawing, relay coil is powered by the normally open ON switch . Your normally closed off switch completes the circuit once you press ON. Completes the path and your contacts switch over and power the motor. If your getting power out of the relay to the motor then , it’s maybe the capacitor start that’s not working . Unusual to be a motor shorting ? However any motors we replace at work are sealed units and only fault to the connections after which it’s replaced and sent away.


If the power is going to the motor then you would hear it trying to start, as the main run windings would be energised ( unless they are “ open circuit “ ) . The capacitor / start windings / centrifugal switch are taken out of circuit once the motor is up to speed, but the main “ run “ windings are always in circuit. 
You do raise an excellent point though. On more than one occasion we’ve had a customer bring in a single phase motor thats not working. Our first step is to sniff the motor, there’s an unmistakable smell you get if the windings have burnt out. The second step is to look for the little red reset button that is sometimes fitted. It is a “ Klixon “ type of bimetallic button mechanism that snaps to open circuit on overload. A simple press and it resets. I’m assuming that @twentysix by twentyfive has checked that there’s no such mechanism on his motor.


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## twentysix by twentyfive (26 Sep 2021)

Tenkaykev said:


> I’m assuming that @twentysix by twentyfive has checked that there’s no such mechanism on his motor.


I'm blissfully unaware of that. Also I have no sense of smell anymore. So I'll need A.N. Other for the sniff test and a I'll maybe have a hunt about for that mechanism.


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