Machine main power isolator switch - useable ?

Chaps, when I purchased my J&S grinder it was being fed by a supply line coming out of a random hole in the right-hand sidewall of the machine. This line terminated externally in a standard five-pin 3phase 415V red capped plug. The socket that it went into on the wall presumably had a built-in isolator.

The original MEM 10A isolator box (see pic below) on the left side of the machine had been totally bypassed, from the supply point of view. I've just stripped it, cleaned it and don't see anything wrong with it from a functional point of view. I am therefore wondering if there is any good reason why I shouldn't rewire my 'new' supply via this original box?

I'm thinking perhaps standards or regulation updates might have changed making the MEM box unsuitable. The only thing that occurs to me is that the original box only has terminals for 3 lives and an earth. Perhaps a neutral connection needs to be included these days? (....though quite where it would go to in the machine, Im not sure as both motors are just 3xL+E.) All comments appreciated.

You appear to be missing a square Tufnol rod with the blades that engage in the slots on the ceramic connection block and the mechanical parts that engage with the door switch handle. They were not my favourite isolator as the mechanical parts were not difficult to damage if the door was not properly closed. Personally I would not use it and buy a more modern unit. The neutral was not usually switched and if required a neutral block was fitted, I don’t think it was optional so it also appears to be missing.

Mike

Edited By Mike Poole on 07/11/2022 19:56:47

Edited By Mike Poole on 07/11/2022 19:59:48

Hi Mike, dont worry, I have all the internal parts including tufnol rod etc, just didnt show them in this picture. I agree on the door, the handle has to be just in the right position or it all goes to pot ! But I'm used to that quirk now

Oh and re the neutral, thats an interesting point you make. I'm not sure there is much room for anything else in this box but I will rebuild it shortly and see if there is evidence of a missing part.

Ok Gerry if it is complete and switches on and off reliably then I suppose it would be usable. I just have a personal dislike of that version as I have encountered so many that were in poor working order. A friend had a very nasty accident with one as a common method of testing with these switches was to open the door and then switch back on using a screwdriver to operate the mechanics, unfortunately the screwdriver slipped and a short to earth resulted in an explosion resulting flash injuries to his face and hand but fortunately he was wearing safety glasses. He escaped any permanent scarring and that style of isolator was phased out of use in our factory. The later models in the squared off casing were much better with a proper hinge.

Mike

ps. Just had a bit of a Google and thre are some pictures without a neutral block but the newer square case versions seem to have a neutral block. They are usually mounted in the top left corner of the enclosure and there does seem to be a hole in that area. Many machines were just 3 phase input and a transformer was fitted if control voltages were required or a lighting supply.

Edited By Mike Poole on 07/11/2022 20:44:29

If you are the owner of an industrial unit and you need it wiring up, you would install five pin sockets, complete with neutral. That way, you can plug any machine into them. If you install both four and five pin sockets, you guarantee that you will park a machine that needs all five pins next to a socket that has only four.

If you bring a machine into a workshop that is only equipped with five pin sockets, you would put a five pin plug on the machine whether it needed it or not as that will be the only way to make it run.

I have several MEM 10 amp isolators of the old style and I find them to be perfectly acceptable. I have used them for years without any problem.

Andrew.

As said by others that type of switch does have a tendency to malfunction, but if you have overcome this with years of use carry on.

The isolator wouldn't be installed now in an industrial situation as there is no provision to Lock Off for machine maintenance.

A new enclosed 16A TP IP65 rotary isolator costs around £15 so perhaps replacing would be good advice.

Emgee

Question, why do you not want to stick with the current arrangement if it's all in working order?

The beauty of connecting machines by switch-socket is that you can get perfect isolation every time, and the switch mechanism prevents disconnection under load.

His current arrangement is one that was not part of the manufacturer-provided system. He says the isolator box 'had been totally bypassed' so he is seeking to revert it to the factory-spec.

While what you say is true, it does contain two assumptions that are necessary to make it function.

First, that the switch-socket is easily accessible when you want to isolate the machine - i.e. you do not have to move a tool cart or climb up on top of the machine to access it. A switched isolator located on the machine itself, within arm's length of the place you stand when operating it is more likely to be used.

Second, three phase switched isolators are expensive and will duplicate the function of the one he already has. One of these correctly wired up is all that is needed screwed to the wall:

https://www.screwfix.com/p/abb-16a-3p-e-surface-socket-415v/5699f

A prudent person wanting to work on the machine would first isolate it at the box he shows and then physically unplug it from the socket.

Thanks all for your useful comments and guidance.

It seems then that I can go ahead and take put my power-in via this box once its fully refurbished. I will of course have a 5pin 415V on the end of the lead for a wall socket. I would of course always pull this out to ensure guaranteed isolation before doing any work on the machine.

Gerry

Hi, note to OP , it is most important to make sure that behind the porcelain block with the terminals and contacts there should be a yellow/brown insulation card, this must not be ommited on reassembly as I have personal experience of flashover occuring if it is missing!!

Phil

Thanks, Phil, for the reminder. I have this part. Its intact and will be re-installed.

G.

Normal manufacturer installed isolation switches relate to factory conditions and are usually intended to simply lock out a machine to prevent use pending repair, servicing or other operations. Commonly they are somewhat out of the way being low down on the side or even rear of the machine. Its not generally considered necessary to be especially easy to see if the machine is turned on or off. In most places a damn great "Don't Use" label gets plonked on top when its turned off.

Risks in the home shop are a bit different. In my view the primary "Ooops, shouldn't have done that!" to avoid when it comes to power is inadvertently starting a machine because you'd forgotten it still had power to it.

I like these Lewden ISO series lever type isolators feeding a 5 pin round plug and socket for my 3 phase machine supply.

The isolators are screwed to the wall close to chin / eye level so a quick sweep of the eye when coming in or moving around the workshop makes it clear if a machine has power or not. Even from a significant distance. Like all proper isolators there are holes for a lock off padlock. If its just me pulling the plug is fine but if I have a guest worker something a little more positive is desirable.

I loathe the round operator isolators because you cannot clearly see if they are on or off from a distance.

Objectively the Lewdens are a bit on the plasticy side but they work well enough with a satisfying clunk when operated and the terminal blocks have plenty of wire room. The front screws are prone to shear if you get heavy handed with a screwdriver tho'. Cost is around £25 I think.

Clive

Edited By Clive Foster on 08/11/2022 15:50:44