Single Phase Switch Wiring for lathe

My switch (800T H2) Simple Rotary for ON (and back for off )on/off switch has 4 connections marked AB (1 of), B (1 of) and 2 marked A. I can't find these letter combinations on line. Any suggestions?

Pic here :- switch

I'm guessing AB and B are live and neutral in and A are the two connections out to the motor which can be reversed for direction of rotation?

Lathe is a Myford 3 1/2" lathe for one way use only.

Mike

Edited By Mike Teaman on 23/11/2013 20:38:13

I suspect that one pair of contacts is closed in one position and the other contacts closed in the second position.

Simplest thing is to check with meter or continuity tester (or just lash up a battery and bulb). The part number you quote is incomplete, and only really defines the series.

The manufacturers have created their own language to describe the switch. 'Maintained' means it stays where you put it!

Ian P

Edit,

You don't actually say what you are switching, whether it mains or signal? but that type of switch is not normally used as the main 240VAC power on/off

Edited By Ian Phillips on 23/11/2013 20:37:53

It's for 230v mains to power a 1/2 hp motor.

Mike

Hi Mike,
Just test the switch with a multimeter (Or a battery and a bulb if you don't have a meter.) With the switch in the off position confirm that there is no continuity between any pair of connections. With the switch in the on position test again for continuity between the connections. You should find that there is continuity between two pairs of contacts but no continuity between the pairs. I suspect there will be continuity between the two right hand contacts and continuity between the two left hand contacts. but no continuity between the right and left hand sets. If you come back with the results of these tests myself or many others on the forum will be be able to tell you how to connect it up. (Or if the results of the tests are not as I describe it may be a changeover switch. If this is the case then it could only be used in single pole mode which is not a good idea.) You should also have an NVR switch on your lathe so it can not start by itself after a loss of power.

Les.

I doubt its rated for motor switching.

If if has 1xNO and 1xNC contacts then you can only use one pair in series with a supply to make and break the circuit.

I would definitely not recommend that switch for a lathe motor (well its OK for suds)

Not important but I am just curious about the site you linked to with all the prices and URL in the UK, but the company is in the USA, just a bit odd.

Ian P

Ian P

It's just a pic I found on the net that matched my switch. The switch is marked 600V AC max.  Feels like it's heavy duty too. Perhaps it looks like I'm going to have to find another switch though? Thanks for the advice,

Mike

Edited By Mike Teaman on 23/11/2013 21:37:58

Mike,

I strongly advise you to fit a proper motor starter with voltage and overloads to suit your lathe motor. This will give reliable starting and stopping, protection to the motor against burn-out from overloading, (fuses only protect the wiring not the motor) and most importantly "no volt release" .protection in the event of a power outage. It is also easy to include interlocks and an emergency stop in the contactor latching circuit of the starter.

Simple on / off switches of sufficient capacity, along with the ubiquitous Dewhurst switch will work but are very elementary in their action and have little to commend them.

A Dewhurst switch is OK if it is used in conjunction with a proper started just to provide forward and reverse facility (with the power off whilst selecting direction.).

Eric

Edited By Lambton on 24/11/2013 10:27:46

Mike

The switch that you have is made by Allen-Bradley, part of Rockwell Automation. The 800 HT only refers to the actuating mechanism, doesn't tell you anything about the contact rating. there are at least 3 different rated contact blocks that could be fitted, and really non of them would be considered suitable for long term motor starting and stopping duties. These switches usually were used in industrial panels switching loads via contactors or for light / medium duties, often they could be used as mains switches in industrial instrumentation units when the physical size of the switch was often of greatest importance as operators could be wearing gloves. As others have said you really need to get the proper starter with the overload protection and the no-volt release function, for your own safety and well being as well as that of your motor.

Keith

Thank you folks. Overload protection starter it is then. Any suggestions for the best type etc? I'm not bothered about new, so long as it will be up to the job.

Cheers to all for comments and advice,

Mike

You could use that switch for reversing a single phase motor, but not the way you are thinking, I fear.

The switch is of a type intended to go inside a cabinet with other control gear. It's not rated for motor switching (inductive load) even if it looks like it might be by the numbers.

It would be desirable to have sequenced contactors/switchgear mounted up on a DIN rail. Your rotary switch would sequence the switchgear. The switchgear would switch the start and run windings, provide no volt release and thermal overload for the motor windings.

A no volt release unit is nothing more than a limited version of what could be done with your reversing switch.

In the end, unless you get someone to do it for you, you're going to have to be confident about what you are doing. If you insist on doing it yourself but are not confident, just buy a cheap Chinese motor starter on e-bay. The instruction sheet is clear about how to connect it.

Single phase motor reversing isn't complicated but there is no hard and fast rule about how to implement it.

All you have to do is arrange for the start winding to be electrically reversed. The run winding will power the motor equally well in either direction no matter which way around it is connected. If you can reverse connection of the start winding relative to it, then you will "poke" the motor one way or another from a standstill. Which ever way you poke it, it will continue to run.

Normally you will have five fully rated conductors passing between a single phase motor and the reversing switch. 1 earth, 1 fixed run winding pair, 1 reversible start winding pair.

Hi there, Mike,

On my ML7, I have a Dewhurst switch backed-up with a gizmo called a 'MEMDOL', the 'MEM'stands for 'Midland Electrical Manufacturing' while the 'DOL' stands for 'Direct-on-Line'.

When I was setting up my workshop in the early 1970s, the MEMDOL was the only single phase motor starter I could find. They were available in several flavours and mine combines the thermal overload protection with a zero-volt release. The common use of the three-phase starter on single phase with two channels of the overload connected in series struck me as inelegant and still does! The MEMDOL has served me well and definitely justified my small effort to seek it out.

I'm writing this without having done a Google search to see if the MEMDOL is still available, it does deserve to be!

Best regards,

Swarf, Mostly!

Hi

THIS is the type of starter switch to fit - a Direct- on-Line Starter . Fit an overload if you think it appropriate. If you have a Dewhurst reversing switch fit this between the D-O-L starter and the motor.

Note - the big red STOP button is a good idea - you want to find this easily if ever a panic situation arises!

Norman

Edited By NJH on 24/11/2013 15:25:38

Swarf, Mostly!

What you should really do with your 3 phase starter to use it on single phase supply is to put a link wire to connect two of the thermal overload coils in series. This way all coils three sense the current passing through them. This stops the starter from "seeing" an unbalanced load. I appreciate it has worked satisfactorily for many years as presently wired but as you quite rightly say it is a bit inelegant.

Eric

Hi there, Norman and Eric,

Norman, the devices shown in the TLC page to which you link are three-phase devices, not the single phase device to which I referred in my post. 'MEM' + 'DOL' isn't the same as 'MEMDOL' (maybe I should have spelt it 'Memdol'? ).

Eric, I think you've misunderstood my post. The starter I have IS a dedicated single phase device - strapping overload coils in series doesn't come into it.

I'll try to take a couple of photos of the device I have and add them to my albums sometime this coming week.

Best regards,

Swarf, Mostly!

Edited By Swarf, Mostly! on 24/11/2013 19:19:32

Not so Swarf

The page link shows both 3 phase and single phase versions. MM28ADS1X is the single phase version - I have one fitted to my milling machine.

Regards

Norman

Swarf,

I did slightly misunderstand your post -sorry.

However I was really responding to your comment about using 3 phase starters on single phase applications and offered the generally accepted way of getting around the problem. I hope this may be useful to others.

Eric

If you are a member of a model eng.club chances are that another member will have proper motor starter for sale and will help with the wiring.As stated the reversing switch if NEEDED,should be fitted after the starter.If buying second hand via the net, ensure that the operating coil is wound for 240 volt opperation. A trip to an electrical wholesaler could be useful as you may bump into a friendly electrician who might fix you up on the cheap and also give advice.Be care when running a Myford in reverse as the chuck might wind itself off. Oh, and that switch is not a reversing switch, the lower part is inter changable for a part which is, but I think it will be expensive.Ted