Pat testing help

[goodconnection]

I'm taking C&G 2377 22 next year probably around May ish My hunch is that asking some qualified electricians a few somewhat daft questions may give me a better idea of what my strengths and weaknesses are with regard to my current understanding of the In-service Inspection and Testing of Electrical Equipment. I'm qualified in IT HNC level so maybe there is some hope eh !

I'd like to do a good job and have enough background knowledge to be in a position to fully understand the results obtained from all the tests carried out and if necessary advice duty holders if a qualified electrical engineer is required to investigate further. I hope you get the general gist of this ....


I currently have a Metrel gamma pat battery powered device and as such lack the ability to carry out certain tests.
my purpose in buying one has been to observe the functions of the device it's features how it presents it's results and the opportunity to practice carrying out basic tests in the proscribed manner on pieces of my own equipment.

Note to moderators: please move the posting to wherever you feel this belongs in the forums ....

Ok this is the end of my preamble and up next is question 1.



Laptop Power Supplies .... how to keep end users safe !

I do IT and have seen hundreds of the blessed things and to be honest many get bashed about and lots seem to malfunction.

In the UK we appear to have two versions

type a class1 device enabled with a protective earth conductor and a class 1 3 core cord set onto a BS fused 3 pin Fused Plug
type b class 2 device enabled with double insulation live/neutral input and a class 2 core cord onto a 3 pin BS Fused Plug

similar sort of arrangements for some peripherals including printers ....


does class 1 AC 2 DC power supply = Sensitive Device = 100 mA / 200mA Earth Bond /Continuity test parameter ?
but how to check it when there in NO obvious means to attach the probe . only metal surface point available is the negative line of the dc output terminal that supplies the laptop.

A good visual check will obviously pick up signs of damage to the moulded case of the Power supply and any chemical invasion or otherwise signs of trouble eg melted / smelly polymer/ overheating the cord set is treated as a class 3 device and tested as such.

I suppose the first thing to be done at the start of test would be to deduce if the equipment and the environment that it was being used in and the purpose of use was suitable from the view of safety ....

are there any circumstances where the PS can output high voltages through the dc line ? and if so what would be the cause ?


Please feel free to comment and throw in your views and experiences of dealing with such matters in your course of business I'm grateful to the forum for providing this facility and hope that actually making a connection with those with far greater knowledge and abilities will help me in my learning process.

 

[Marvo]

.........Note to moderators: please move the posting to wherever you feel this belongs in the forums ....

I've moved this thread to the PAT testing forum for you.

 

[Lucien Nunes]

If the PSU DC output is grounded (and some smaller ones are not), I often do a low current test just to prove the CPC continuity without necessarily testing its robustness. In many cases the earth is functional only and not needed for fault protection. It usually serves to collect leakage (e.g. from RF filtering) that would otherwise raise the DC output to sit on half mains voltage if the load is well insulated from earth. The source impedance of this voltage is too high to be dangerous but it can be annoying, you get tingles off laptops etc due to the (typically 0.1- 0.5 mA) of leakage.

In the event of an internal failure of the input/output isolation, the CPC connection might save the output swinging up to hard mains, although in normal usage that is ultra-rare. I've been handling small SMPSUs under really adverse conditions for years and doing post-mortems on them and never seen it happen once yet. But I still test ground-through where I can (because of the environment some of my equipment works in) and of course with a class II supply the insulation test between input and output is essential.

Out in the real world, you would be amazed how many would test a class II PSU by plugging it into the tester, leaving the wander probe on the table, and pressing 'Test'. Yet more would just put the sticker on without unpacking the tester, which is actually better as it doesn't show electrical incompetence. OTOH this morning I found pass stickers on a USB-powered device, a Scart cable and part of the fixed installation...

 

[goodconnection]

Thank you Lucien for your valuable insight. I started with laptop / appliance AC/DC PSU's for a reason and it's an interesting story and one of the factors why I am trying to improve my electrical knowledge and practical abilities regarding equipment failure and safety issues. I on occasions provide assistance/support to those who are visually impaired and or severely disabled. Anything in the way of PAT items for this client group could be a real danger if said item was damaged. One person recently had a Power supply failure where the casing split open exposing the wiring and live parts and I guess it was only luck that saved them from contact with the 230 v ....

I also have in my procession a laptop supply that has gone the same way it's casing has split again exposing the inner workings. All made in the same location and you do not need to have a knowledge of Ohms law to work out where.

It was interesting reading your comments on the real world and to be honest I have mixed feelings about my own observations regarding how some PAT operators conduct themselves out in the field. I have an image in my minds eye where such a person might try putting a PAT item into the freezer for a few hours in the hope of inducing super conductivity in order to achieve an acceptable earth continuity reading and thus be able to attach a pass sticker !

Moving on from question 1 I would now ask how would you test a laptop or similar piece of IT ? eg something that is DC supplied IET guidelines and other legal related stuff all point towards employers and users having to take responsibility for their own safety. I have encountered many Laptops with a pass sticker on them and wondered what would be the "Lucien Standard" for you to afford a device the same honour ? I guess those that passed the equipment on previous occasions had just visually inspected it ..

 

[goodconnection]

Many Thanks

 

[Lucien Nunes]

I haven't dealt with general PAT for a long time, so your best practice might differ. I only meet it nowadays in my specific field where equipment is used by instructed and skilled persons but subjected to heavy wear and tear.

If I found a laptop with a pass sticker, I'd peel it off. Class III devices are outside the scope of our testing and there could be confusion if a device with a pass sticker was used with a PSU that hadn't been tested or had failed. We consider PSUs as stand-alone items as they are often stocked in large numbers and the first available one picked out of the box and used with the first available device. In our industry they don't live together as pairs.

 

[goodconnection]

I'm glad of your answer ... My reasoning was that a laptop was essentially a battery powered device that could be charged up when and if needed and therefore not really subject to PAT.

Of course the 230V supply is the potentially dangerous item and is !

 

[goodconnection]

A question about Pat Testing involving Washing machines / Tumble dryers / Irons etc etc

Need to understand a principle about the logistics of the earth leakage test and how the result is presented by a PAT test instrument.

Observation: I brought myself a plugin type energy meter from Maplins a while back that essentially plugs in before a device and provides usage telemetry in real time regarding Amps, Watts , Volts and VA readings.

I now have a fair idea of how many AMPS my washing machine and other household items need to draw from the fixed installation for the various programmes / setings depending on what is being asked of the equipment.

OK my question is thus if I carry out a class 1 earth leakage at Mains voltage (powered up) on a Washer and energise all the device circuitry how does a PAT test device work out if it exceeds the pass level. Say I just turn the washing machine on and it's not heating water it's on at a basic quick wash thats drawing less Amps would that give a false result ? do you have to test the machine at the point where it draws the most current and therefore at the time when it could be dangerous to the end user ?

Insulation resistance and it's ability to protect against leakage to my knowledge can be dependent on various factors Moisture , Humidity, Temperature, Atmospheric pressure and or a combination of all ........

I don't have a PAT Tester capable of a 230 v Earth Leakage test at this moment My Metrell has only a Sub leakage option due to the fact that it is battery powered.

How do the more complex test instruments work out the correct Earth leakage current reading is it just whatever it finds when the machine/appliance is switched on eg cold wash /1 bar on a 2 bar electric fire / low heat setting on a tumble dryer. or am I missing something ?

Thanks for any help you may be able to offer !

GC

 

[telectrix]

this is one area where PAT falls flat on it's face. you can only plug the machine into your tester and do the tests as it is. in other words, machine may well give an IR reading that is perfect, yet a faulty heater may trip RCD when machine goes into heat cycle.

 

[goodconnection]

Thanks telectrix I thought as much ..

No advice in the IET COP to use brain in any particular way just a list of fail pass limits ...

So turn dial press button on washing machine press test on PAT instrument and get protective conductor current leakage result that is probably not the correct reading unless you know which part of the washing programme and or cycle hits the max Watts rating and Amps on the plating.

Hmmm Yes earth leakage testing at nominal 230 v in respect of washing machines would appear then to be inherently inaccurate.

Washine machine manufactures need to put an electrical max watts test cycle shortcut on their equipment or rather BS standards should demand one eh !

 

[Lucien Nunes]

The situation is not as bad as you make out. Inside equipment, most functional switching is single-pole even though the main power switch is often double-pole. So once the main switch is on, most of the 230V 'guts' will be connected to the plug via the neutral, regardless of whether or not they are in operation. Because the tester links L & N for insulation testing, it will detect most faults via the neutral even if the line is switched off by the internal controls.

Take the case of the washing machine - there are a dozen or so 230V loads - motor, heating element, drain pump, various solenoid valves etc, all of which are usually permanently connected at least to the neutral. If the insulation of the heating element is low, this will show up as a failure on the PAT without the relay or contact in the programmer being closed. Of course with manually controlled devices like the 2-bar fire, it makes sense to turn on all the switches, although the test results will usually be correct anyway.

Earth leakage is different, as this is does vary according to what is energised. It makes sense to attempt to energise whatever one can, in particular any troublesome components, not necessarily those that use the most power. However, importantly, most genuine faults that cause excessive earth leakage, also cause low insulation readings. With parts like motors and elements, the IR will be very low before the leakage even starts to be readable, so the insulation test will find these problems. Much of the leakage of modern equipment comes from interference filters - it's designed in - and if they go bad they will immediately show up with low IR.

There just a few situations where you can have excess leakage that does not manifest with low IR, and in this case the PAT tester will miss them if the fault is switched off by the control system at the moment of testing. I leave as an exercise for the reader, to identify what kinds of component can cause these...

 

[Dcf]

I have a metrel gammapat also and find it fine for my all be it limited use.
you will find most pat testers use a battery powered tester these days anyway.
i used to use a seaward mains tester which was about the size of a small suitcase which apart from a load test I see no difference in the tests.
i had it out at a job last week to find the appliance which was causing the rcd to trip and it highlighted the washing machine was faulty.
i would stick with it for the moment as it will do all you require testing wise.
if you need 110v adapters don't buy metrels overpriced plug and socket adapters
get a spare eic lead and cut it in half fit a 110v trailing plug and socket combo to the two ends for about a tenner all in.

 

[goodconnection]

I am learning guys and your comments will serve me well ... nothing like hands on experience and that comes with field work ... I guess doing this very thing asking questions and getting feedback from knowledgeable people is part of the process ...

I read this quote and this was set me thinking about Washers etc ..


"What would be the result of simply applying the PAT routine to the scenario on page 2 i.e. an appliance with double pole latching relays?
As stated the applied PAT ‘insulation’ test would essentially only test wiring and components up to the two ‘open circuit’ relays and if there were no problems up to that point then the appliance would be labelled ‘Passed’.

However, as can be seen the items beyond the two latching relays would not have been subjected to the ‘insulation’ test which an EEESafe DAT or DAR is required to undertake."

These are folk dealing with refurbs so thought they may have some experience ....


Dcf thanks for the advise re the Metrel it's not a bad piece of kit picked mine up for £330 inc Vat new unit and had some freebies too Socket tester mains LED type labels pat logbook and two adapters for laptops .... PASS were the supplier Stockton on Tees .... I'm on the look out for a full function second hand tester something like an older Seaward, Fluke, Megger for using as a bench tester or as a 25 AMP earth continuity test /protective conductor bond test for anything that I find that is running Windows 8 ..... will of course only use 200 mA on Linux enabled IT !

 

[goodconnection]

Anything in the way of extra data and observation will be put to good use and hopefully your knowledge will become part of my skill set.

Safe working out in the real world ...

Rubber boots ? double insulation gloves ? Faraday cage ?

tips please !

 

[Lucien Nunes]

an appliance with double pole latching relays

I think (and I'm not involved with domestic appliances much these days although I've seen inside a few thousand in my time) this is the exception rather than the rule. They probably used it as an example to re-inforce understanding of the limitations, not to suggest it was a common situation.

I raise you the case of a line-interactive UPS.

 

[goodconnection]

Lucien here is the article without the diagrams ..... I understand what you are saying and take on board your expertise and hands on experience and maybe you could have a look at the copy and pasted info. I am a newbie so am in the hands of those in the know and a little bit of knowledge can be dangerous which is why I am grateful to people like you yourself for taking the time and trouble to assist me !

The type of test applied when PAT testing an
appliance essentially depends of the electrical
classification the appliance falls into. However, it
is not always as simple as some believe it to be.
Here we look at two Class 1 products a kettle and
a modern electronically controlled washing
machine. Kettles have changed little over the
years but automatic washing machines along
with other major white goods have internally
changed quite a lot. Therefore depth of
knowledge and practical experience of the
product being tested becomes extremely
important as this rather simple explanation hopes
to illustrate.
L
E
N
The schematic diagram on the left is of the
electrical circuit of a standard kettle and it shows
the operating circuit the appliance mains lead
connects to. The following is only considering the
‘Insulation Resistance’ test of the PAT test
procedure in order to illustrate the need for
knowledge and practical experience of product
when testing appliances.
When a Class 1 appliance is correctly connected
to a PAT tester for the insulation test i.e. plugged
into the three pin supply on the PAT test unit and the earth test lead connected to a suitable earth point on the
appliance the test can begin (in this instance it would also require enough water added to the kettle to cover the
element (as a dry element could give a false reading).
When the PAT tester applies the required insulation DC test voltage (for a 230 AC volt appliance this will be 500
volts DC) they will (should) ensure that the On/Off switch of the appliance is in the On position so as to ensure
that the test voltage reaches the internal components that are after the On/Off switch. In this instance the
heating element.
Interestingly it can be seen in this instance that the appliance only has a single switch on the ‘live’ supply to the
circuit the therefore a test reading could still be obtained even if the On/Off switch was not closed . Although this
would not constitute a professional approach to testing such products.
A basic view of PAT testing Class 1 appliances - Part 2
The schematic diagram below is another Class 1 appliance in this instance a modern ‘computer controlled’ washing
machine. Unlike the kettle this appliance has far more internal components and more importantly has a more
complex wiring system. As before the three core mains lead connects to the appliance and in this instance passes
through a suppression unit before continuing on to the main control circuitry (PCB). If you look closely as the top of
the board the L & N terminals connect to two ‘Normally Open’ relay switches i.e. they do not ‘latch’ mechanically
as with simple push On and push again for Off type mains switches. These PCB mounted ‘relay switches’ can only
close when instructed to do so i.e. when a programme has been selected and the ‘start’ ‘short stoke’ low voltage
selection button is pressed. NOTE: This action ’Cannot’ be carried out when using the PAT tester for insulation
testing. Therefore an insulation test on this type of circuitry is unable to go beyond the two ‘Normally Open’ relay
switches which means that critical components such as the heating element, wash motor etc. are not tested. In
such cases the applied test essentially only tests the plug, the mains lead, the suppression unit and the two wire up
to the main control board. Although there are methods of compensating for this type of situation it takes
knowledge of the product and additional equipment as a PAT test unit is unsuitable for the additional testing
required.
 A point to note is that there are many other appliances that utilise ‘double pole’ switching.
 Are you or your supplier of product aware of these features?
 More importantly is the person charged with PAT testing the appliances?
Normally ‘Open’ relay switches are found on many products - washing machines, washer dryers, dishwashers ,
microwave ovens etc. in-depth appliance technical and practical knowledge is therefore required when testing such
products.
A basic view of PAT testing Class 1 appliances - Part 3
Why are there concerns with using a PAT test to verify that reconditioned/refurbished major appliance and
what are they?
 Firstly PAT testing procedures were not primarily designed for the specific purpose of verifying electrical safety
of reconditioned/refurbished appliances. The PAT testing procedures, guidance and resulting ‘none
mandatory’ ‘qualification’ target was for electrical appliances used in the work place.
 Instead of developing a testing procedure specifically for the reconditioned/refurbished sector it was deemed
by the powers that be that the PAT test procedure should implemented so as to indicate a reconditioned/
refurbished appliance was electrically fit for resale.
 PAT testing requires an operative only to be ‘competent’ in the PAT testing procedures. This can be self taught
by studying the IET guidance procedures or attending a training seminar where upon a ‘recognised’ certificate
of qualification (2377) is issued. Unfortunately such courses are often of one days duration regardless of any
pre-existing knowledge or not and an open book written assessment is often carried out to verify ability. This is
an area of concern in itself as the simple ability to follow guidance procedures is not a demonstration of the
individuals depth of technical knowledge and practical understanding of the various types of equipment
needed to safely and effectively carry out such testing and just as importantly know when testing should not
be carried out.
 Many in the Recycling sector choose to employ/use ‘qualified electricians’ that have gained the above
certification/qualification. However, although electricians will have had to demonstrate extensive technical
knowledge, understanding and practical experience of electrical installations such knowledge rarely if ever
covers the internal workings of electrical appliances themselves. As can be seen from the two simple scenario's
on pages 1 & 2 appliance construction and function are a key factor in ensuring that safety testing is not just
skin deep.
What would be the result of simply applying the PAT routine to the scenario on page 2 i.e. an appliance with
double pole latching relays?
As stated the applied PAT ‘insulation’ test would essentially only test wiring and components up to the two ‘open
circuit’ relays and if there were no problems up to that point then the appliance would be labelled ‘Passed’.
However, as can be seen the items beyond the two latching relays would not have been subjected to the
‘insulation’ test which an EEESafe DAT or DAR is required to undertake.
What could result if the above occurred?
Firstly lets assume that the components beyond the latching relays were unknowingly OK i.e. above the required
minimum insulation level then essentially there would be no problem with labelling the item as passing the
applied safety test. However, this scenario is reliant on luck and not fact. In reality there are many reasons that
wiring and/or component within appliances may have degradation (a breaking down) of their insulation. In
relation to the washing machine scenario on page 2 the two most likely items for lower than acceptable insulation
are the heating element and main motor and these are also common items across a range of such major
appliances.
What could be the result of having low insulation of items not tested?
Like all accidents and incidents things are rarely all that simple and the result if any bad or good are more often
than not dependant on a series of apparent diverse factors coming together. In this scenario if the appliance was
passed as ‘Safe’ and was correctly installed into a premises which had the correct electrical supply criteria
depending on the severity of the insulation breakdown the appliance may work for sometime before failing by
blowing a fuse or tripping and RCD (Residual Current Device ) or similar protective device. Annoying for the
customers and not instilling confidence in the suppliers of the supplied product either.
However, the installation of appliances is in itself often not carried out to a suitable standard (as essentially none
exists). In the case of washing machines (and similar appliances) it is often a case of - connect fill and drain hoses -
plug it in - fill and empty the appliance and leave. In many instance it does not even go that far. All Qualifed
EEESafe DARq’s who undertake delivery, will be required to record the required safety readings.
A basic view of PAT testing Class 1 appliances - Part 3 continued
What’s the problem with that it works doesn’t it?
The problem is that just because something works it does not mean it is doing so correctly or more
importantly ‘Safely’. For instance if the installation of the premises had a poor or none existent earth in
the electrical supply then components with ‘low insulation’ could essentially make the external metal
shell of the appliance ‘live’ to the touch exposing those in the vicinity to electric shock hazard or worse
electrocution. However, there is another potentially fatal event of greater magnitude that could occur
in such instances and that is fire.
If an installation has a poor or none existent earth in the supply the appliance would be unable to
rupture (blow) its protective fuse which could result in a faulty component over heating and in a worse
case scenario setting fire to the appliance and its surroundings.
*There are numerous variables that can adversely or otherwise affect the outcome of the safety issues
raised which have not been included in an attempt to keep the article understandable by those not so
technically knowledgeable.

 

[Lucien Nunes]

I've only read this for gist but it would help to see the dwgs. Does it actually show the schematic of a genuine real-world washing machine or appliance with double-pole control relays, or is this only a theoretical example?

I'm wary of the number of slips and simplifications in this text, that suggest it is less than authoritative. Odd terminology, a couple of unwarranted assumptions...

 

[goodconnection]

Hi here is the link to the material .pdf format it's file in the google cache so you need to copy and paste the search data too ----> <---- copy and paste everything between the arrows and then hit return sorry if this sounds like me teaching you to suck eggs . you should then be offered the opportunity to download the original pdf document. If you use linux like me it just downloads and opens without any fuss or bother if you have android mac ios or windows then you might need to download something to open said doc. to be honest given your electrical knowledge and abilities it's likely that you are already well aware of this procedure. it may even open direcly in your browser by simply clicking the link.

---->http://www.google.co.uk/url?sa=t&rc...n5TP1oIvBfJh293vItWXTQA&bvm=bv.79142246,d.d2s <-----------

 

[Lucien Nunes]

So the guy writing the article has probably misread the drawing. I read 'Mains contacts within 16-way programme selector switch'. I.e. not a relay, a user-operated switch, that presumably DP isolates the machine when no programme is selected. You will see that all the internal programmer controls, whether triac or relay, are single-pole only. In this case many of them are in the neutral but the test voltage will reach the loads so long as a programme is selected.

What he could have picked up on, that illustrates the point perfectly, is that the heating element is controlled in both line (programmer relay) and neutral (pressure switch). Therefore the element is not under test until the machine is filled to normal level with water.

 

[goodconnection]

I'm beginning to get the idea Lucien

"What he could have picked up on, that illustrates the point perfectly, is that the heating element is controlled in both line (programmer relay) and neutral (pressure switch). Therefore the element is not under test until the machine is filled to normal level with water. "

That bit of data has been written to memory.