Boxford G200 grinder wiring

Hi all, does anyone have a wiring diagram for the above Boxford G200 tool & cutter grinder ?

Any information gratefully received !

Regards John

Hi I need some advice ! Electricity apart from simple wiring etc is not my forte - I know my limits ! Had look at the switch gear on my Boxford grinder, its been playing up for a while, ran in reverse but not forwards and eventually reverse stopped working.

I discovered there is a cut out on the reverse switch, presumably thermal? pressed it in and reverse works again. The forward unit will not "lock in" it runs if I push in the switch bar but doesn't hold. Now I need to know what to search for on the internet to find a replacement unit so please advise what these units are called, its the LHS one in the photo.  Thanks John

Edited By JohnF on 10/10/2022 09:02:55

Edited By JohnF on 10/10/2022 09:07:45

The units in your picture are contactors It sounds as if the holding coil circuit is at fault. Is the machine 3 or single phase ? Without seeing the wiring or a circuit diagram it may be hard to sort out. If a thermal cutout has popped then may be there is a fault on the motor. Much more info needed. Noel.

The first thing that comes to mind is to check you have forward and reverse correctly wired up (if it is three phase and you reverse a phase going into the machine, it will reverse the direction).

To me, the thermal cutout should be on the forward direction. After all, that is the direction in which it spends 90% of its working life.

Think of a plausible mode of operation in which it could overheat in reverse but not in forward.

The latching property also makes more sense in the forward direction as you want to press the button and it work until you press stop.

I can also see an argument for not having a latching mechanism on reverse operation. If you want the motor to run in reverse, you have to keep the button pressed. As soon as you release the button, it stops running. An analogy to this is the jog mode on a VFD.

There is nothing special needed to make the contactor latching. You just wire its output to the input of its coil, with a normally closed momentary switch in series as the stop switch.

If it is supposed to latch and does not, either a wire is loose/disconnected or the NC switch is stuck open.

A manual for the machine is available here: https://www.machinemanuals.co.uk/manual.php?p=104

The thermal overload will be applicable to both running directions - it is usually mounted on the output side of the contactor pair.

As the motor starts when the button is pressed but won't stay latched I suspect the "holding contact" on the contactor isn't making. This isn't unusual, as the contacts carry very little current & don't "self clean" as a result. Over time they can tarnish and, while closed, don't make electrical contact. Carefull dismantling of the contactor and contact block and cleaning the contact faces with a wipe of fine wet & dry paper often gets them working again.

There may be a mechanical interlock module between the two contactors (photo unclear due to wires passing over the area) that prevents both being actuated at the same time. If this is the case, then an identical replacement contactor would be required. Benedikt & Jaeger still exist, but the holding company and internet presence is now called Benedict - catalogues can be found online & Farnell are the UK agents.

Chances of a mechanically identical contactor still being in the range 20/30/40 years after the grinder was built are pretty slim, though, and lack of an identical replacement individual contactor would probably mean replacement of the entire 2x contactors + interlock module + overload arrangement, as all component parts are designed to work with each other for each manufacturer (no interchangeabilty between brands). Plenty of choice of manufactures in that case, but a quick look at RS suggests around £30 each for the contactors + £10 for an interlock & £30 for an overload + Vat for the lowest cost Lovato brand (which I usually choose for replacements at work & they work fine).

Nigel B.

It is a 3 pole contactor or starter. If the operation was intermittent and then stopped it is unlikely to be the contactor coil that is at fault, and until you know the contactor is faulty it is pointless replacing it. You need to get familiar with electrics on the hurry up, or find someone in your area that can go through it with a multimeter. Is it three phase or single? find the stop and start buttons and check all the connections, are there any safety switches on doors or belt guards that inhibit starting, could they be faulty? systematic approach with a multimeter and logical thought is required, your'e never to old to learn, and every day is a school day! what type of grinder is it? Model number? there are wiring diagrams on the net, have you tried groups.io to see if there is a Boxford group with access to wiring diagrams? Pictures always help! first port of call is to test at the coil connections on the contactor to see if it becomes live when the start button is pressed

Good luck, and keep posting!

Phil

Edited By Phil Whitley on 10/10/2022 10:13:20

Thank you all, lots to chew over ! The machine is single phase although I have been reliably informed the switch gear will suit 3-phase as well.

Machine has run fine for around 15 years but been playing up for about 12 months, forward and reverse is normal on T & C grinders and used in equal amounts depending on the job in hand. This machine doubles as a small surface grinders where forward [clockwise] running is the order of the day.

Nigel B thanks I will look into Farnell and see what they can suggest, as you say it may well be a case of replace the whole set, I do have a good local electrician who will assist -- its way above my pay grade !

DC31K I do have the original manual from Boxford but there is no wiring diagram, I contacted Boxford and unfortunately they no longer have a copy available.

Thanks all for the comments

John

Edit P S The thermal overload reset is the small blue button bottom right in photo 1

Edited By JohnF on 10/10/2022 12:17:42

The switch gear will suit, but the coil in the contactors has to suit the mains voltage.

That would be a a good first check, that the contactor coils are indeed 230v ones and that they both have continuity.

Have you any feeling in your water that the machine is wired as it came from the factory or has a previous owner been fingerpoken?

Check, as suggested above that the thermal overload is on the output, and is used in both directions.

Someone else will hopefully chip in here, but on the MEM Memota-type DOL starters, you had to wire the thermal overload in a different manner depending on whether it was single or three phase.

If it is single phase, temporarily wire a cable direct to the motor and make sure the motor runs properly both forward and reverse. Then you know the problem is elsewhere.

Then you know the problem is elsewhere.

The OP did state " The forward unit will not "lock in" it runs if I push in the switch bar but doesn't hold. "

So the motor & contactor coil appear good and function, just that the contactor won't stay latched.

240V coil contactors could be used on either 240 single phase or 415V 3 phase machines - just need a neutral on the 3 phase installation for the control voltage side of things.

I would rather use a low voltage control circuit (24 or 110V), but simple machines often use mains voltage to save the cost of a transformer, fuses etc.

Nigel B.

DC31k, Hi thanks for your thoughts, the machine was supplied with single phase electrics and I am 99% confident the wiring is also as supplied. This was confirmed by Boxford shortly after purchase, I contacted them for some spares shortly after acquiring the machine, some were available others not.

It has run without problem for around 15 years since I bought it so fairly sure it’s just the switch gear that’s the problem. I have run the motor alone and it runs perfectly in either direction but the forward switch will not lock in so it certainly appears to be the coil that’s duff.

Thanks for your thoughts John

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