Recommissioning an old motor

[Robin GrahamParticipant @robingraham42208]

[Robin GrahamParticipant @robingraham42208]

I've bought an old machine (a Multico mortiser) which had been sitting unused in various sheds for an unknown length of time. I think it probably dates from the 60's or 70's. This is the motor:

I'm a bit reluctant to power it up without checking it's safe – especially as the grommet where the power cord enters is badly perished. Are there any basic electrical checks I can make (given I have only a multimeter) as it is, or would it be advisable to strip it down and have a shufty inside before firing it up?

It's 240V single phase 2850 rmp cap start according to plate.

Ta, Robin

[not done it yetParticipant @notdoneityet]

Does it turn? Is it lubed? Does the earth show continuity? Anything obviously loose? Is it a fully enclosed motor?

Bolt or nail it down, stand well clear and flip the switch. It will likely run OK. Then stand it on something insulated and check for volts from frame to earth, while running, before grabbing hold of it!

Replacing the grommet is pence. A new lead might be a good idea.

Alternatively, get an electrician to check it over.

[Mike PooleParticipant @mikepoole82104]

I would carefully have a look at the wires from the windings to the terminal block, the insulation is often perished and very fragile on a motor of this vintage. Sleeving the tails is probably the easiest way to make the motor safe without disturbing the windings. A meggar is the tool you really need to check you have no earth faults or shorts between windings. A bridge meggar would tell you the accurate value of the winding resistance but unless you have the spec for the windings resistance there is not much point in testing it. If the tails can be checked and if necessary repaired and it meggars clear of earth you may as well switch it on and see if it runs. If it has a centrifugal switch for starting then check it works properly when the motor is up to speed.

Mike

[Robin GrahamParticipant @robingraham42208]

Thanks. Motor spins freely by hand, no slop or bad noises. Earth to live/neutral > 40Mohm, earth to case 0.9 ohm, live to neutral about 3 ohms all measured from plug pins with a (1.5V!) multimeter. I don't have access to a megga – I guess I have to get inside and check visually.

Ta, Robin

[duncan webster 1Participant @duncanwebster1]

If there is any possibility it's been wet it might be worth blowing warm air through it for a few hours to dry it out before you connect it to the mains. If you're dismantling it leave the stator in the airing cupboard for a few days.

[EmgeeParticipant @emgee]

Robin, are those measurements taken from the plug, ?

Emgee

[Robin GrahamParticipant @robingraham42208]

Yes Emgee, from the plug. The last person who used the machine had disconnected the NVR box from from the motor and wired the plug direct to the motor. With red/black wire, so a while ago!

Robin

[john fletcher 1Participant @johnfletcher1]

If you know an electrician get him to test the windings with his 500 volt INSULATION tester, it might be a Megger.There are other makes of insulation testers around. Insulation testing with a multimeter isn't good enough, they usually only have 9 volts and the motor needs 500 volts DC. Insulation testing is the electrical equivalent to boiler pressure testing looking for possible leaks. If after Insulation testing and all is OK I suggest you leave well alone, its all to easy to break one of those fine wires and not being knowledgeable enough on motor repair to fix it. John

[Perko7Participant @perko7]

IMHO don't waste your time opening it up and testing, give it to an electrician to do that for you. In Queensland Australia all appliances or equipment which plugs into a power outlet is required to be tested and tagged as safe to use by a qualified electrician. It costs little and provides great peace of mind. Too many horror stories of houses being burnt down while the owner was absent as a result of some dodgy home electrical appliance repair.

[Chris Evans 6Participant @chrisevans6]

Interesting subject. I have a "Wolf" branded drill a huge lowish revs high torque job. Bought second hand in around 1965 it is on a stand and I have a 1/2" chisel morticer attachment for it. I have not used it for 40 years and would not dare to try it, reading this post I think I will find someone to check it over and replace the cord. It will then sit in the shed until I fall off my perch knowing it is safe for its next owner. Or go in a skip….

[Robin GrahamParticipant @robingraham42208]

Right , you've convinced me – I don't know anyone in the trade, but I'll look around. Would a PAT be good enough do you think, or something more thorough?

Robin

[Martin NewboldParticipant @martinnewbold]

if you have modern workshop or house consumer unit with an RCD then plug it in hands free. It will either trip the RCD or run up .

Warming it up may induce condensation in it it which might short out windings be careful if you are running warm air through it as this can do same .

Basically with a modern fuse box with an inbuilt RCD an earth leak with throw the RCD trip and stop you getting electrocuted. . Obviously if you are at all worried or dont have an RCD consumer unit or a separtate one get someone who is an electriction to do it or get one that you are more sure of.

You havent said what its going onto and what power it is as it might be unsuitable and more worthy of the dumpster .

M

Edited By Martin Newbold on 13/05/2018 21:45:40

[EmgeeParticipant @emgee]

Robin, in it's stated condition it would no doubt fail a Class 1 PAT, you will need to reduce the Earth resistance between plug and motor frame. It could however test the insulation resistance of the windings to the frame.

Emgee

[Mike PooleParticipant @mikepoole82104]

PAT testing is a basic go no go test, it is a process that can be done by a person who requires little electrical knowledge and it either passes or fails. To repair a failed item will require a person skilled in diagnosis and repair of the failed equipment.

Mike

[duncan webster 1Participant @duncanwebster1]

Posted by Martin Newbold on 13/05/2018 21:44:47:

if you have modern workshop or house consumer unit with an RCD then plug it in hands free. It will either trip the RCD or run up .

Warming it up may induce condensation in it it which might short out windings be careful if you are running warm air through it as this can do same .

Basically with a modern fuse box with an inbuilt RCD an earth leak with throw the RCD trip and stop you getting electrocuted. . Obviously if you are at all worried or dont have an RCD consumer unit or a separtate one get someone who is an electriction to do it or get one that you are more sure of.

You havent said what its going onto and what power it is as it might be unsuitable and more worthy of the dumpster .

M

Edited By Martin Newbold on 13/05/2018 21:45:40

if the motor is at ambient temperature then blowing air which started at that temperature and was then warmed up cannot cause condensation. If you take warm air from elsewhere and blow it through a cold motor then you can get condensation. Similarly warming the motor by other means cannot cause condensation. Best of all is a dehumidifier

[Robin GrahamParticipant @robingraham42208]

Martin – the motor is 3/4 HP single phase 2-pole induction capacitor start. It is the original motor on a Multico K1 mortising machine which I am trying to restore to life, so I assume it is suitable for its purpose. I do have a modern consumer unit ,one half of which is dedicated to the workshop, but having read other replies I think I'd like to get the motor tested independently – I don't like the idea of using the consumer unit as a test device, maybe irrationally.

Emgee – the earth to frame connection is visible on the outside of the motor, it's corroded, so fixable before PA testing. Thanks for that input.

Apart from superficial rust and flaking paint the machine is in good nick (milling marks on slides still crisp!) and I'd like to restore it to as near original as I can. It's a brute of a machine, If I can get it going it'll last me out for sure!

Cheers, Robin

[EmgeeParticipant @emgee]

Posted by Mike Poole on 13/05/2018 23:01:12:

PAT testing is a basic go no go test, it is a process that can be done by a person who requires little electrical knowledge and it either passes or fails. To repair a failed item will require a person skilled in diagnosis and repair of the failed equipment.

Mike, many PAT instruments do measure the important aspects such as earth continuity, insulation resistance and if those tests passed will test run the item and record the current and earth leakage current, so more test results than you can get by using just a Megger (Insulation Tester) to test insulation resistance to frame and earth continuity..

The type of device you mention is not a test, it is a check..

Emgee

[Mike PooleParticipant @mikepoole82104]

I think most of the Meggers I have used and certainly the one I own have a continuity range as well as an insulation test so would give me the information needed about the motor. I have fallen into the brand name trap to describe the equipment I had in mind. In our factory PAT was done by an electrician and he would make repairs to any failed equipment if appropriate or confiscate it if it could not be repaired. Many of the testers are designed to be used with a basic training course by unskilled people whose main part in the process is to stick the label on the tested item, a fail is not their problem.

Mike

[GeorgineerParticipant @georgineer]

Robin, as a qualified electrical engineer and certified PAT tester I would make the following comments, based on the IEE Code of Practice 3rd edition (there is a 4th edition but it won't be different in substance).

It is acceptable to do your earth continuity test with a current as low as 20 to 200 mA. This is described as a 'soft test'. The acceptable resistance is 0.1 ohms PLUS "the resistance of the protective conductor of the supply cord". (The pass/fail threshold in most PAT testing kit is a generic number set for average conditions.) Obviously you will want to clean and check any connections, including inside the plug (a check which many technicians omit) and remove any oxidation on the plug pins which can cause a high reading. You should also wiggle the cord about while testing to check for broken conductors. I would be perfectly happy to accept the reading of an ordinary multimeter on this. Incidentally, a smear of petroleum jelly can work wonders on poor contacts. Ordinary grease is not recommended because it can be acidic, though it has never caused me any problems.

As for the insulation resistance, in PAT terms yours is a Class 1 equipment. Yes, the test should be carried out at 500 volts, but again for my own purposes I would be happy to accept the reading from a multimeter. The minimum acceptable insulation resistance for this class of equipment is 1.0 megohm, and your reading shows well above this.

From your description I would have no hesitation in plugging it in and letting it run. I would run it unloaded for a couple of hours and measure insulation resistance again. If there was any moisture in the windings, the resistance will increase as the motor warms through from the inside. I recently treated a 1920s repulsion motor this way and the insulation resistance increased from 0.7 to 37 megohms after several hours' running, converting a fail to a solid pass.

Electricity is only dangerous if it gets in the wrong places. Don't touch exposed metalwork while testing, make sure your hands are dry and you're standing on a dry floor, keep one hand in your pocket while things are live (so there's no possibility of a return path through your heart).

What I have said is what I would accept for my own purposes, not what I would do for equipment to be used in public places. Remember that my advice is worth exactly as much as you paid for it. Be sensible.

George

[Martin NewboldParticipant @martinnewbold]

In regard to the run cap these fail regularly I have a pump for my airsystem which these start run caps fail regularly. The last one blew a hole in the side and started smoking. I cant see any prob with hands free test on your consumer unit if it has RCD equiped .

I doubt it will start as most of these motors with run capacitors are thrown to one side when the start run caps fail. My air pump is in shed at moment waiting a new cap which time wont let me arrange.

You have not said what its being fitted too. This is why i implied it might be best to bin it

Most charity shops have a certified PAT tester if you really feel out of your depth. They might give you thier contact details. George gave you sensible advice as have others the cable and gromet sound like they need replacing. This will require soldering skills and purchase of connectors for the motor posts.

Best Regards

M

[Robin GrahamParticipant @robingraham42208]

George, many thanks for your comments – on the basis of what you said (while completely accepting responsibility for my own actions!) I just checked the connections in the mains plug then fired it up (from a safe distance!). Ran sweet as nut. I was probably worrying about nothing, but the ratty appearance of the external wiring alarmed me. I'll redo the wiring as far as the terminal block within the motor housing though.

Martin, – sorry if I wasn't clear about what I'm doing in my previous posts – the motor came as an original part of a old mortising machine which I'm trying to restore for my own use. It wouldn't be straightforward to replace it with a modern motor I think, Anyhow, seems like it's going to be OK. I paid 75 quid for the machine, bit of a gamble, but it looks like it's going to to pay off.

Robin

[not done it yetParticipant @notdoneityet]

Ahh, so sorted at first reply, then? Drying out was a good suggestion, but I would do that if it was likely to be damp. It did not look corroded with rust, did it?

Re capacitors – old ones are often the better ones, Those that have to replace them very regularly need to buy a better quality of capacitor?

You were very clear that the motor was part of the mortiser. Again, reading the posts properly does help. I misread sometimes, but not as often as some!

Edited By not done it yet on 15/05/2018 06:29:36

[GeorgineerParticipant @georgineer]

Robin, I'm glad my comments were useful and doubly glad that you had a successful outcome. Thanks for letting us know.

George

[Author]

Posts