How to Adjust Old Breaker

Hi,

The attached photos show the contactor fitted to my Centec 2A. Although the contacts close and the motor runs well almost any load will cause it to trip. I've checked the motor windings and they have good insulation and the whole machine runs smoothly.

The label on the contact suggests they're adjustable, but I can see where or what I would adjust - any ideas gratefully received.

One thought I had was that the trip is activated by overcurrent affecting a bimetallic strip and I wonder whether its due to the insulation material around the thermal strip having perished and dropped away over the years. If so can anyone suggest what to replace it with?

Grateful for any ideas.

Regards

Peter

I would remove that & fit a 2 pole MCB type D. They are motor rated. Looks like plenty of room in there for one.

Steve.

Hi Steve,

I'll investigate that idea. Do you know of any that could have remote make and break contacts. I ask because I'm keen to retain the front panel which has the Start button in the centre of the panel and the stop at top right. I doubt anything current will be laid out exactly the same and so a couple of small microswitchs could be used to trigger the MCB.

Regards

Peter

I see conductors for a single phase motor. The original was probably 3 phase and therefore drawing far less current..

You might find that the switch doesn't have the adjustment capacity for the extra current draw. To get around this you could remove the neutral line from the contactor and split the live phase between two of them to share the load and if it still tripped you could share between all three. If you have the room to fit one, you could even fit a modern overload and remove the heating coils altogether to turn the overload switch into just a switch.

Peter

as Pete Rimmer says above the conactor is a three phase unit. The live should be connected so that the current passes through all three poles (ie wire all three poles in series) otherwise there will be an imbalance and the overload will trip. The neutral should not be switched but should be permanently connected. These thermal overloads are designed to trip on true three phase overload and also on loss of one phase hence the need to have equal current in all three poles.

HTH

Dave

Thanks Dave, I'll do that, that said it's been single phase as long as I remember and I've merely replaced the old wiring.

Ill have a go over the weekend.

A motor rated MCB will not provide much in the way of motor overload protection.

I understand Dave and Pete's thoughts, but looking at the overload, I don't think phase current inbalance was on the agenda when it was manufactured!

I can't see how it is adjusted from the images, I would be asking myself what has changed.

Michael

Edited By Michael Briggs on 19/11/2020 23:18:43

Yes indeed that is correct a MCB would not be appropriate or a MMS (Manual motor starter) as that is a contactor. We did use to use a device made by i think MEM called a startet. This was manual push button with an overload built in. As said above is also correct that you should loop the live through each contact to get an even pull on the overload.  Best of luck.

Steve.

Edited By Steviegtr on 19/11/2020 23:31:26

I didn't know about them being able to detect a lost phase but they will certainly trip the bar if any one of the heaters cooks the strip too much. It might have inadvertently been 'adjusted' during the re-wire. If it worked before it should work again, I would inspect it to see if any of the components got bent slightly from working in the cramped enclosure.

Hi, being that the same current flows through the neutral wire as it does through the live wire and the trip coils are current sensitive, you can still retain the neutral in the circuit, but the live side needs to pass through both the other two trip coils. Therefore in Avon's case, all that needs to be done, is to move the two wires on the top left to the empty one on the top right and then connect a wire from the top left to the empty one on the bottom right.

Regards Nick.

I think it’s probably time to retire that starter and replace with a motor starter that includes the NVR function for a step up in safety. NVR is no volt release which means the mill will not unexpectedly restart after a power failure. It looks as though it would be too tight a squeeze to get the replacement in that space so I would mount the starter remotely in a convenient place and fit some new buttons in the cover that will just be a remote operator station for the starter. Beware that the insulation on the heater coils is likely to be asbestos based so resist blowing any dust around. Tool station have reasonably priced Motor starters with the option of fitting an overload unit and remote buttons. The other benefit of starter is that you can easily add remote stop buttons to give a kick or knee operated stop or a stop button anywhere you find convenient. Of course this upgrade is not cheap but £50 should cover most of the components.

Mike

If you pull the whole thing out you will almost certainly find a screw on the side to adjust the throw of the bimetallic strip before the contactor releases.

Various designs have been used. Fancy ones have a spiffy label for current settings with a pointer fixed to the screw.

Less fancy have a mark on the screw and a pair of marks on the contactor body for highest and lowest settings.

Bottom end unfancy just have a screw with nowt to indicate setting. By the time I see them they have always been adjusted by one of Bodgitt & Bend (Sevice Division) failed apprentices.

Its rare for the adjusters to be accessible in situ when mounted in the machine.

I second Mikes suggestion of getting a new modern unit that will just work. If nothing else tripping of a known good unit on reasonable settings is a reliable indication of a failing motor. If yours has worked as is in for some time its possible that the motor is coming to the end of its life.

Clive

Thanks Clive,

I'll take it out this weekend and see what I can find.

I don't actually know when it last ran properly as I stripped and rebuilt it without having tried to run it (probably should have done). I have stripped and cleaned the motor and both windings have insulation readings in excess of 10M.

Regardless of what I discover I will pursue Mike's suggestion of fitting a new unit - it had crossed my mind to do so anyway.

I'll update the thread with findings!!

Peter

That just looks like an isolator, all Be it might have a current trip not the actual starter. Are you sure there is not a separate contactor that is operated by the start/ stop and already has NVR function?

If it the isolated the neutral should in my opinion be switched and the live feed in series via the other poles.

Peter

I think you will find this is the interior of a MEM Startet motor starter, there is no coil it is just a latch and trip switch with an over current trip, the buttons are just a pusher to latch the mechanism in and a stop button that has a ramp to trip the bail rod across the overload heaters.

Mike

Hi, well it looks as if it can be a contactor with a coil, the top connections both have two wires each, where one pair would go to the motor and the other pair would go to the coil. The bar will operate an inbuilt switch in series with one of the wires going to the coil if it is the case. One way to prove it would be to get the motor running and then stop it only by switching it off at the wall socket or pulling the plug, if there is no switch on the wall socket, once stopped plugging back in or switching the wall socket back on the motor should not start until you press the start button again. you can do this procedure a few times to give you peace of mind that it has a no volt release contactor, of course, if it does start when power is restored without pressing the start button, then it won't have a no volt release contactor.

Regards Nick.

Edited By Nicholas Farr on 20/11/2020 11:37:46

I think Mike P is probably spot on - a good description of the device.

Nick, there's no other switchgear and certainly no coils - I've had it all out to replace degraded cabling. The two pairs of wires at the top: one pair to the main winding and the second (via a changeover switch for forward/reverse) go to the switched starter winding (physically out of phase with the main winding to create a starting effect as I understand it, it is switched by a centrifugal switch in the motor). There's no NVR mechanism.

Hi Avon, thanks for clearing that up and yes your best bet is to replace it, I probably would have anyway if it was mine.

Regards Nick.

It is as Mr poole says, a mechnical latch MEM startet, it has no NVR function. It is not neccasary to wire anything through the third pair of contacts or the third overload, wiring live through one pair and neutral through another is all that is required. I retained the startet on my Grafton drill press for the same reason, it is original, and it looks the part! An MCB would be totally useless at protectong a motor, current to trip on MCB's is far too coarse, and nowhere near as accurate as this 1930's technology. If it is tripping, I would first check the motor centrufugal switch is operating correctly, as leaving the start winding in circuit will cause overcurrent as soon as the motor is up to speed. Although I can't remember the details, I am pretty sure, as is said above that when you remove the starter, the adjustment becomes obvious, I think you slacken a screw and operate some sort of cam which moves the tripping bar further away from the bimetals. I will chack my Grafton rebuild video to see if it is in there, but I am sure whenm you take it out you will see the adjustment.

Phil

HI All,

Well some success with the existing setup. It appears that the adjustment on this contactor is simply to pull the clips tabs out on each contactor (2A pushed in, 2.75A pulled out according to the notice which I found hiding in the bottom). See photo below. The clips are looped bits of brass at the end of each arm - they appear to be holding the bale arm in the photo.

Definitely no NVR, but it seems to be working ok now and I'm the only one who uses the workshop.

Will probably investigate a starter, but for now I just need to find some sharp tools!

Many thanks.

Peter