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Topic Title: PAT testing 3 phase motors?
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Created On: 30 June 2008 11:12 PM
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 30 June 2008 11:12 PM
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kt66se

Posts: 53
Joined: 22 May 2008

Hi,
I've just been asked to PAT test a bank of 3phase industrial sewing machines. They are connected via a bank of outlet sockets that connect via a push and twist male plug and under the cover are located what looks like 3 in line fuses. These are cabled back to a 3phase dist board.

I use a fluke 6500 which comes with a 3phase yellow plug adaptor but I am not sure if I should make a lead up to interface with the sewing machine plugs.

I am 2377 qualified but not an electrician and 3 phase was not covered on the course. The owner of the site has tried to get sparkies to PAT test but no one is interested....is it because 3 phase cannot be tested? Even if this type of testing is beyond the scope of the PAT tester, what advice could I offer the owner.

Any advice greatly recieved


Kind regards

Adam

Ps, is it possible that they may be single phase motors and are using one side of the 3 phase? I did not get chance to look at the motor specs?
 30 June 2008 11:22 PM
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Testit

Posts: 2962
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Well I'm not sure what u r saying is different... a machine with cables and wires and voltage..... I'm also not sure if you are saying the machine motors are 3 phase or whether they are single phase machines simply being fed by a three phase supply...

Well are they earthed... earth leakage
Metal? - earth continuity..
Condition of leads...
IR tests...

bla bla..

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Experience can sometimes show that cost prevails over quality and safety, such little self-value that people hold.
 30 June 2008 11:35 PM
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Pauldf1

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3 phase yellow plug adaptor? You sure it isn't for testing 110v appliances?
 30 June 2008 11:36 PM
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intrinsic4225B

Posts: 1623
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The testing of three-phase equipment is covered in the IEE Code of Practice for In-service Inspection and Testing of Electrical Equipment (3rd Edition).
 01 July 2008 12:03 AM
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ericmark

Posts: 318
Joined: 12 February 2008

I have just down loaded the manual for your fluke 6500 and it is not even able to handle 110 volt split phase it is 230 volt only and not suitable to test three phase machines and as yet I have not seen one. To test three phase machines normally requires some knowledge of the machine. Where contactors are used an insulation tester needs to be used after the contactor and care is needed to ensure voltages used to test do not damage the electronics so items of this type are normally inspected by who ever maintains them. The same applies to any items with timers for example washing machines to test a washing machine you would need to have your PAT tester attached while it completed whole cycle so they are normally done by the maintainance guy. What the owner means is he can't get anyone who will test his machines on the cheap I am sure the manufactures offer some maintainance contract which the owner finds too expensive.
The idea of a semi-skilled person doing repeat PAT testing for standard items does make a lot of sense and is cost effective but I maintain the first one should always be tested by an experienced spark who would then lay out the procedure for those who follow.
It is so easy to make a mistake for example I saw a mag mount drill where the drill was class II but magnet base was class I and the guy had tested whole item as class II. Easy mistake for a qualified spark to make never mind a semi-skilled tester.
First thing you need to learn is your own limitations. But full marks for posting in that you have done the right thing.
All the best Eric
 01 July 2008 10:55 AM
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kt66se

Posts: 53
Joined: 22 May 2008

ericmark,

Thank you for your reply and positive comments. I wonder if I could in theory test this motor, as another post suggests, I could perform a visual/earth bond but I'm not sure about an insulation test at 500v, would this damage windings etc. (although the low current should not blow the coils perhaps)?
The only test I would be unsure about would be a load test.

As a qualified PAT tester would recording the above tests in this manner be the professional thing to do? The business is small, 5 staff, 6 sewing machines. The owner has trouble getting anyone to carry out test on 6 machines. Location is remote Wales. No excuse I know but there must be times when a PAT tester has come across such items and had to make a descion?

Many thanks again

Adam
 01 July 2008 11:47 AM
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deleted_1_Grizzly01

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Originally posted by: ericmark
...items with timers for example washing machines to test a washing machine you would need to have your PAT tester attached while it completed whole cycle so they are normally done by the maintainance guy.


Only if you wanted/needed to perform a test that required the washing machine to be powered up to 230V (protective conductor/touch current test, load test etc). These tests are additional/complementary to the 'core' tests of visual inspection, earth bond continuity and insulation resistance, all of which can easily be performed on such an appliance.

Originally posted by: kt66se
...I could perform a visual/earth bond but I'm not sure about an insulation test at 500v, would this damage windings etc. (although the low current should not blow the coils perhaps)?
The only test I would be unsure about would be a load test.


As the insulation test links live (phases) and neutral together, and puts 500V (or 250V if your PAT instrument can do that) between this and earth, there should be no current flowing in the windings.

Are these sewing machines actually 3-phase appliances (the push & twist male plug you mention has 4 or 5 pins) or are they single phase (plug has 3 pins), each one operating on a different phase of the supply?
If it's the former, then a load test (using a single phase PAT tester) would be totally out of the question anyway. If it's the latter, you would need to make sure that the rated power/current that the sewing machine operates at can be safely supplied by your PAT tester. If not, then don't load test.

It might be useful to get in touch with the manufacturers technical/service department, who may be able to give you some advice (then again, they might not, but you never know).
 01 July 2008 12:36 PM
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kt66se

Posts: 53
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Hi,

Thanks again. The male plugs are 3-pin with x3 in line fuses. I am guessing that they could be single phase as you suggest working of different phases. Not being an electrician I am guessing this kind of kit set-up is done to spread the load? I will have to go back to site to look at the motor specs to see if single phase. I could have saved myself the "posts on this site time" if I had looked but I am glad I posted as I now know about 3 phase supplies - at least a little bit!

I have to be honest having taken my 2377 last year I do find that there is still a lot to be learnt. Is there a C&G course that covers the basics of electrics, its all very good having the qualifications to PAT test but this sort of work puts you in to an environment where a little more knowledge would be very useful.

Thanks again

Adam
 01 July 2008 01:40 PM
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Testit

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The book you need is The IEE Code of PRactice 3rd Edition as already stated. ISBN978-0-86341-833-4 available from ther IET site.

From what you say I would just recommend not getting phased by 3 phase.. firstly you are not concerned with the supply charqcteristics for PAT testing, other than knowing its plugged in properly to the correct voltage of course... tes tthe machines as you would any other.. class1 I expect. you just have 3 phases instead of one..

If you use a PAT tester you can make a 3phase to single phase conversion plug or use separate insulation and continuity test instruments... 10.2.1 of Code of practice 3rd edition. The testing is the same... probably single phase though, but you never know....

-------------------------
Online Services - http://propertydevelopment.org.uk

Experience can sometimes show that cost prevails over quality and safety, such little self-value that people hold.

Edited: 01 July 2008 at 01:41 PM by Testit
 01 July 2008 01:58 PM
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kt66se

Posts: 53
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Oh! I got the IEE code of practice for Portable Appliances for the C&G course last year but this looks different?
I think another purchase is required! Thanks for pointing this out to me. I try not to get "phased" by all this stuff but am really just trying to get round my head 'how do I test this bit of equipment' without damaging it or my own testers - and keep customers happy.

I've just looked at the Code of Practice for In-Service Inspection and Testing of Electrical Equipment (3rd edition) menu and it seems to cover a lot more ground.

Thanks again for all comments

Ps, As the IEE is updated and revised, is there a requirement to re-take C&G 2377 after a certain time frame?

Adam
 01 July 2008 02:18 PM
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deleted_1_Grizzly01

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Originally posted by: kt66se
Ps, As the IEE is updated and revised, is there a requirement to re-take C&G 2377 after a certain time frame?


There's no actual requirement to take 2377 in the first place (other than any imposed on people by employers, customers, etc). It's just a useful qualification to have, to help towards showing your competence (although doesn't prove competence on it's own).
 01 July 2008 02:47 PM
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ericmark

Posts: 318
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First remember this is a bit of guess work so could be wrong. I have used the plug and socket arrangement you refer to red button realises the plug and the socket incorporates a switch turned on by turning the plug. And so I think it could well be three phase. With a sewing machine you will require some speed control so electronics in the form of an inverter very likely and the latter could be damaged by using 500 volt insulation tester. I know we had considered many ways of testing items like this in the past. After some debate we decided a good visual inspection and earth continuity test plus feeding through an RCD would suffice. We had to write out our test in the form of a check list and filled it as part of our routine maintenance.
But should anything ever go wrong the HSE will be checking on what you have done and you have to ask yourself could I satisfy the HSE that you possesses sufficient technical knowledge, relevant practical skills and experience for the nature of the electrical work undertaken and you are able at all times to prevent danger and, where
appropriate, injury to yourself and others? From what you say I would not think so. On the other hand you could act as an instructed person and if someone made out the check list for you then you could at the prescribed times complete the checks. Many items of plant have such a service schedule made out by the manufactures. At the end of the day you need to recognise what your ability is. And consider any insurance required before offering your services. One problem I have seen is where we stick a little green sticker on an item to say it is checked for electrical safety and the user sees the sticker and assumes it is safe unaware the mechanical safety may be still compromised. And this could still be an electrical fault for example a faulty guard switch. As to Cymru Am Byth location I am in the North of the country myself and I do see your problems.
Yours Eric
 01 July 2008 03:06 PM
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deleted_1_Grizzly01

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Originally posted by: ericmark
With a sewing machine you will require some speed control so electronics in the form of an inverter very likely and the latter could be damaged by using 500 volt insulation tester.


One way round this would be to perform a 250V insulation test (available on a number of testers such as Seaward Supernova and PrimeTest 350). Unfortunatly, the Fluke 6500 (which Adam is using) only seems able to do the 500V test.
 01 July 2008 04:03 PM
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kt66se

Posts: 53
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Many thanks ericmark and grizzly - excellent advice.
I'll have another look at the motors, I could be fretting over nothing. The push and twist connectors do not have any red buttons and are switched on/off via an isolation switch mounted on the wall. I did in fact ask my C&G instructor about a PAT tester and the Fluke 6500 was recommended. I need to read the book again but I think an auto class II test on SELV and PELV devices does run at 250v. I could be wrong, it's been 6 weeks since I last PAT tested.

Thanks again

Adam
 01 July 2008 04:45 PM
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deleted_1_Grizzly01

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Originally posted by: kt66se
I need to read the book again but I think an auto class II test on SELV and PELV devices does run at 250v. I could be wrong, it's been 6 weeks since I last PAT tested.


You'd need to check the appliance class of the sewing machines, though. If they are Class I, then a test meant for Class II appliances would not be appropriate.

Looking at the Fluke 6500 manual, it doesn't look like the PELV Test would do what you want, certainly not anything akin to a 250V insulation test.
 01 July 2008 04:59 PM
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kt66se

Posts: 53
Joined: 22 May 2008

Grizzly,
Ok - I'll have another look tonight at the manual. I seem to be having a memory surge and need to re-visit my course notes. Everything I have questioned in my head seems to be creating more questions!

Just ordered the Code of Practice for In-Service Inspection and Testing of Electrical Equipment (3rd edition)...£40 incl P&P!!! Better be a good read!

I seem to recall 500v providing a better insulation test over 250v for class I due to capacitance / resistance measurements between insulation - like I said, need to brush up; but if this is the case and the "appliance" is class I, and I carry out a 250v insulation test would the HSE pick me up on that should it come to an investigation?

Cheers

Adam

Thanks again
 01 July 2008 05:31 PM
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deleted_1_Grizzly01

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Yes, a 500V insulation test may be better in some cases, but in other instances it may cause potential damage to equipment (ie IT equipment not built to BS EN 60950, in which case a protective conductor/touch current test should be carried out) or may give misleading results: for instance, an extension lead with built-in surge protection would invariably fail a class I insulation test @ 500V. This is because the Metal Oxide Varistors (MOVs) that are connected L-N, L-E & N-E, and provide the surge protection, would start conducting at 500V. A 250V version of the insulation test would not start the MOVs conducting, and so would give a truer indication of the insulation resistance.

It all comes down to applying the tests that are most appropriate for the appliance you are testing. If a test can cause damage to the appliance, or will give a misleading result, then it should not be carried out, and a more suitable test done in it's place.

When your 3rd edition IEE CoP turns up, have a read of the section starting at the top of page 75, which mentions all the various insulation tests and equivalents.
I wouldn't count on a thrilling read, but it is certainly useful!
 01 July 2008 09:13 PM
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dlane

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Hi Adam,

I would say the test regime needs to be based on a risk assessment on how the machines are operated and maintained.
e.g. Lets say,
There is a yearly service contract in place for the machines from the manufacturer or agent.
Only the manufacturer or his agent repairs the machines
Only trained employees use the machines.
The machines remain in place and are never moved around.
The users carryout daily checks on the machines.
The machines are cleaned down at the end of every shift.
and so on.
Machines are reliable and rarely break down.
If this is the case then you can probably restrict your tests to a visual inspection of the appliance and electrical testing of the lead and plug.
On the other hand;
If the machines are constantly moved around, used by any tom, dick or harry, no servicing carried out, machines are dirty and in a poor condition, constantly breaking down and other such nasties, then the machines will need a more rigorous inspection.

I am not personally convinced by the argument that because it has a plug on it, its portable and has to be plugged in to a PAT tester and tested.

Kind regards

Donald Lane
 01 July 2008 09:47 PM
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Pacific

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I used to work for Clarks shoes, each factory had hundreds of 3ph sewing machines which had to be tested, we used a 3ph socket with all 3 phses connected together into a 13amp plug as an adapter

Hold starter contactor in for test duration, the control unit was a separate unit powerd by a tap off the motor windings, never had a problem testing at full voltage

Sadly Clarks have now closed all their UK factories but I reckon thousands of their machines are in use in small units
 02 July 2008 09:29 AM
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kt66se

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Joined: 22 May 2008

Donald - very valid point. The customer has agreed a date of the 25th July for me to test which gives me time to confirm your points. They are fixed in place, easily over 18kg and are in good, clean condition so it will be worth asking...but they have been previously PAT tested and I did not get chance to look at the motor spec or PAT report as it was a tight survey with machines in use and people walking about. PAT test will be done out of hours and my first visit was basically a risk assessment having gained CHAS this was my initial priority!

Thanks for your input

Adam
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