Wiring an MEM starter for 240v Lathe

Hi Chaps.

As a complete newbie to lathe work and model engineering I am having a few difficulties as expected. I hope to pick up some hints and tips on good practice from the more established engineers here abouts.

My current problem is wiring up a start/stop switch. I managed to pick up an old MEM Auto-Memota switch. It says on the label 240v 50~ and 2-4 Amps. So I assume it will be ok to use with the 240v 1.5 amp motor on my lathe(Myford Drummond).

Currently it is wired directly to a 13amp plug that I've never been happy about.

Can someone give me some advice on connecting up the switch. The terminals are marked L1 L2 L3 on one side and A B C on the other.

I can wire up a plug and lights but this has me stumped.

John

MEM, that brings back memories, one of my aunts worked there (Birmingham) in the 50/60's.

Sorry that's not much help to you I know, hopefully you will get a reply that is.

Bill D.

That's fine Bill, glad I could conjure up some memories.

John

Hi John,
The fact that the starter is rated a little higher than the current rating of your motor means it will not provide full overload protection. I worked with these in the early 60's but the only thing I can remember in detail is that the overload trips worked with a heating coil around bi metal strips.If any of the 3 strips deflected they moved a bar that tripped the starter. (They were also used for three phase hence the three overload trips.) If I had the starter in front of me I'm sure I could sort it out. This is how I think it is probably wired. I think one side of the coil connects directly to either L1, L2, or L3 (incoming power.). It should be possible to see where the wires from the coil connect to. The other side of the coil will connect via the stop button to one of the output connections A, B, or C If you have a multimeter you should be able to identify which 2 of the 3 inputs are used to energise the coil. If you hold the contactor in manually you should see the coil resistance (I would guess it will be a few hundred ohms.) between 2 of the 3 input connections. The input connection that connects directly to the coil I would use to switch neutral. The other input connection that showed the coil resistance when held in should be connected to live. Live should also be connected to the third input terminal. One wire from the motor should be connected to the other side of the contact set whose input is connected to the coil. The other wire from the motor should be connected to the other side of the contact set that I said also connect live to. I think that you should be able to see the wires from the coil and stop/start buttons connecting to the 6 contactor terminals.

Les.

Hello John,

I wouldn't recommend it, those old units were very simple and didn't come with the no-volt release protection that is common pracrice on machine tools today. If your power fails, it automatically trips out, the old MEM's and others in that age group didn't and machines could start up again unexpectedly when power was restored if you hadn't taken steps to push the off button while the power was down..

There were many nasty accidents as a result.

If you have a friendly electrician he would provide and wire up a modern starter for you, I think you would be better trusting his experience this time.

Best wishes

Brian

I'm getting very irritated as I can't find it again, but recently i saw in a catalogue or a website, a very short 13A extension lead, but it had an NVR switch built into the socket. What a brilliant idea and a great way to add NVR function to almost anything.

Neil

THIS is what you are looking for I think.

These are a wee bit cheaper.

**LINK**

IanT

I just had a look at my MEM contactor that is fitted to my Myford and it certainly seems to function as a no volt release. If I press the start button, the lathe starts. If I then unplug the mains the contactor releases and the lathe doesn't restart when I replace the plug.

The wiring seems to be incoming live and neutral connected to the left side of contacts A and C, and the outgoing live and neutral connected to the right side of A and C, with the casing connected to earth.

In my case, the output is routed to a Dewhurst reversing switch, thence to the 3/4hp lathe motor. One thing I need to watch is if I turn the Dewhurst switch off, the motor stops but the contactor is still powering the switch, so I must still hit the contactor stop button.

If you run a search with the term "MEM circuit protection and control" or follow this link you should wind up with a publication by MEM (2003 version) that will tell you all you need about wiring up a MEM contactor for 3 or single phase and how to select the overload unit according to your motor power. There may be a more up-to-date version, but that comes up as the first item in the search on Google so I suspect that it's still the current version.

All the contactors that I've come across in industry since 1970 are designed to drop out if the supply fails and need resetting to start the motor. If yours doesn't do that - throw it away and replace it - it's DANGEROUS.

Keith

John

Your MEM starter is ok to use and as Otley suggests it does function as a NVR device ! The overlaod at 2.-4 is just about ok I always set an overload at 50% of the FCL so at on the lower setting of 2 amp you have some protection. Many years ago when I was a apprentice electrician I was taught that when useing the MEM starter on a single phase supply the 'live' should go through all 3 of the contacts in order to balance the load through the overload heaters so you would connect the 'live' to A1 then put a link between A & B then a link between L2 & L3 the live would then go from terminal C to the reversing switch or motor whichever the case maybe, your earth wire should go to the 'earth' terminal on the starter case along with the earth to your reversing switch or motor and the neutral should run to your reversing switch or motor but you will need to join it with a connector block. Alternatively you could wire it the following way live to L1 and live out from A neutral to L3 and nuetral out from C never run the earth though a set of contacts always use the earth terminal on the starter, reversing switch etc..Strangely when I acquired my S7 the MEM starter was wired in the way I first suggested hope this is of help

H

Gentlemen,

At the risk of sounding like a schoolmaster, what John Bromley described sounded very much like the early push button starters that relied solely on the load current drawn to trip out. There was NO protection for power failure and the 'overload' tripping could be varied with a rather crude slider gripped by a cheese headed screw.

These were roughly 4 inch square box shaped devices maybe 3 inches thick, the general pattern in the 1950's; times have thankfully moved forward.

My advice to John in his admittedly uncertain understanding of such things was to get a professional in to do it for him; I still stand by that. I am not even sure if John would know how to recognise the differences, so I join in with Keith Long and advise him not to use what he has acquired.

Brian

Morning all, I have a copy of MEN Motor Control Gear 1964 with all the details and price list, your starter cost 62 shilling and 4 pence in 1964. Actually there is no need to cross link the overload, they will operate OK as they are.Some how electrician have got in their heads that it is necessary to cross link. We carried out tests at work and exploded the mith, but it does no harm. As others have said Auto-Memota series 5 starters have No-Volt release, so you are OK. Also, most of my model engineering friends run their machines via 13 amp socket outlets without any problems. Actually the 13 amp fuse is there to protect the flex and cable, not as many suppose the motor.As Harry said, ensure you maintain the earth (CPC) wire through out and finally enjoy making swarf. Ted

Edited By WALLACE on 06/02/2014 11:19:23

Thanks for the replies. There seems to be a lot of conflicting advice and I'm still not that confident. The unit I have is a Series 6 Model 426 ADS, it is identical to this one. It seems It will do the job if installed correctly. Although the makers plate says 2-4 amps the units adjuster appears to start at 0. So It may offer the overload protection my motor requires.

If I cut the lead going to the motor and put the (plug end)Brown to L1 and Blue to L3 then (motor end)Brown from A to motor and Blue from C to motor, that will work and be safe?

There is no earth wire from the plug it's just a Brown and Blue cable.

john fletcher 1-

Hi Ted, we all think we have to cross link the old 3-coil MEMs because Tubal Cain said so in his Model Engineers Handbook! At least that's where I got it.

John Bromley - if your 3-pin plug has no earth wire then ditch it and get one that has. Then follow Ted's advice above.

Hi John,
Your first step should be to replace the twin cable with three core and earth the motor and the metal box that houses the starter. It is not safe to play round with it when it is not earthed. The starter in the picture looks like it uses the two contact sets L1 to A and L3 to C If the coil and start/stop buttons of your starter are connected in the same way as the one in the picture then it should work. In this configuration it is using one set of contacts to maintain the coil and feed one leg of the motor. The way I describe it in my last post I used one set of contacts just as maintainer contacts for the coil. The only disadvantage I can see in not having a separate set of contacts for the coil is that the moment the start button is pressed it will be carrying the full motor current until the contactor closes. This should not be a problem as this must occur when used on three phase.
On the subject of linking the thermal overloads I do not know if it is being suggested to connecting them in series or parallel. If the suggestion is to connect them in parallel then I am sure this is wrong as it would increase the current required to trip them.In the normal configuration the would be one in each leg so as well as protecting the motor from normal overload it would provide some protection for leakage from the windings to earth. As it will probably be fed via an RCD that would trip first with any leakage to earth from the windings. Connecting the third normally unused thermal trip in series with one of the others would do no harm but equally it would serve no purpose. The way the thermal trips press on the bar is in effect a mechanical three input "OR" gate.

Les.

Edited By Les Jones 1 on 06/02/2014 20:58:54

Thanks for all the the input guys, I will pick up some 3 core cable at the weekend. My brother in law is coming over Saturday, He's a lift engineer, so I might ask him to watch me wire this thing up so I don't burn the place down.

I have still to get to grips with my new to me Boxford lathe yet, but I really would like the Myford a little safer to use.

Switching the Myford on and off at the socket was dodgy enough. Since getting the Boxford it has now been moved away from the wall socket so definitely not a safe proposition. Proper start stop buttons will be much nicer.

I'll report back in a few days.

Thanks again. JB

A really good reason to ditch those old MEM DOL starters is that they are full of asbestos.

Obviously when you wire them up the first place you end up putting your nose is straight in the asbestos cloth, so you can see what wire you're following.

I won't say you shouldn't.

Just be mindful. If it's not you it'll be someone younger than you in future.

They were great bits of kit. Much better than the modern plastic stuff, but they're still a health hazard today.

Broadly all motors should have both over temperature, and NVR.

NVR for power failure.

Thermal trip is important, because a simple fuse will not detect a winding burnout until after the event.

If you've never seen the smoke from a burning motor or a transformer, you wont understand that you'll leave the area before ever turning the power off.

If you have a choice between asbestos and no electrical protection, then asbestos it must be.

All IMO of course.

The cheap far eastern one is £30 on ebay, and it's "no worries".

Edited By Andy Ash on 07/02/2014 00:39:21