Class 2 insulation tests

[deedar]

Hi, I did C&G 2377 a couple of years ago and have only recently been asked by company to do some portable appliance testing for them.
Now, I'm trying to remember how to test class 2 equipment. I've looked around the internet the best I can and haven't really found an answer.

How I understand it class 1 items testing consists of 1, visual inspection, 2, earth continuity, 3, insulation test 4, polarity (on IEC leads)

However, when testing class 2 appliances and 2 core leads testing consists of 1, visual inspection, 2, insulation test

Am I right in saying that on class 2 appliances, 2 core leads and SELV equipment that you can only do an insulation test if there is exposed metal work? And if there isn't any exposed metal work then the only test that can be done is a visual inspection? So, for example I'd only be able to do a visual check on mobile phone chargers and on laptop transformers?
Are they any other tests that can be carried out on class 2 equipment?

I've heard mixed advised given on this subject, but I would really like to find out the correct procedure if anyone can help.

Thanks

 

[telectrix]

on the "PSU in a plug" equipment, all you can do is a visual.

 

[Graeme Moo]

You do insulation test between L-N for Class2. Exposed metalwork is for earth continuity on Class 1

 

[telectrix]

and most of the time you can;t do IR test L-N. 1. you will read the resistance of the appliance. 2. you might destroy trhe appliance.

 

[deedar]

You do insulation test between L-N for Class2. Exposed metalwork is for earth continuity on Class 1

I read somewhere that when you do an insulation test on a class 2 appliance you need to connect your probe to any exposed metalwork so that if a fault occurred then a reading would be sent back to the PAT Test machine, is this not correct?

Please see this video on youtube from seawards explaining the insulation tests on a class 2 appliance: An Introduction to PAT Testing - YouTube hopefully you'll see where my confusion comes in.

Thanks for replying

 

[telectrix]

you are correct . but a lot of class II appliances do not have any exposed metalwork, so you can't test it.

 

[deedar]

you are correct . but a lot of class II appliances do not have any exposed metalwork, so you can't test it.

Does that mean that only a visual check can be done?

 

[RISElectrical]

Plug in machine, machine asks if its class 1 or 2, you tell machine, machine does test, computer says YES or NO and you give GREEN sticker or RED...

Sorry, i just came back from doing 50 PATS and that was enough for this year!

 

[telectrix]

yep. visual + check correct fuse is fitted.

 

[deedar]

yep. visual + check correct fuse is fitted.

Just doing and insulation test on a class 2 appliance without a probe would basically do nothing then?

Thanks for your answers you've helped a lot

 

[Graeme Moo]

Class 2 equipment has double or reinforced insulation around the live parts. exposed metalwork should never be able to become live unless there was a major fault that would be visually obvious. That is what i was taught anyway. Dont know where they are coming from with that utube clip.

 

[deedar]

Class 2 equipment has double or reinforced insulation around the live parts. exposed metalwork should never be able to become live unless there was a major fault that would be visually obvious. That is what i was taught anyway. Dont know where they are coming from with that utube clip.

So, you can do in insulation test on a class 2 appliance/lead without using a probe? just run the 500v insulation test on my tester?

 

[deedar]

A sample from Leeds University PAT Testing requirements:

1- IT equipment – summary
Class 1 IT appliance:
Earth bond test:
· If the equipment has a metal case, carry out normal earth bond test.
· If the equipment has a plastic case and the only exposed metal parts are connectors, carry out a low current earth bond test
· If the equipment has no exposed metal parts, there is no need to carry out the earth bond test.
Insulation test:
· This test should only be carried out if the appliance conforms to BS EN 60 950.

Class 2 IT appliance:
Earth bond test:
· This test should not be used on class 2 appliances.
Insulation test:
· All insulated appliance (no exposed metal parts) - no test necessary
· Double insulated appliance (some exposed metal parts) – carry out the insulation test only if the appliance conforms to BS EN 60 950


Hmmm I don't what to think . . . anybody able to give me a definite answer please?

 

[Adam W]

The way I was taught is with a class 2 appliance you do the IR test (which joins line and neutral) and touch the wander lead over any metallic parts and parts the user will touch, which should pick up any electric which is leaking out.

 

[deedar]

So would u say that a class 2 appliance with no exposed metal parts can't have an insulation test conducted on it?

 

[Adam W]

Chances are there will be metal screws exposed. Otherwise you can touch the wander lead on any parts the user will touch, eg buttons, casing etc where the insulation may have become thin or worn. That is the point of an insulation resistance test - to measure the resistance of the insulation.

 

[deedar]

Chances are there will be metal screws exposed. Otherwise you can touch the wander lead on any parts the user will touch, eg buttons, casing etc where the insulation may have become thin or worn. That is the point of an insulation resistance test - to measure the resistance of the insulation.

so doing it without a probe would be pointless?

 

[rich.250]

Yes, you need to do a ins test to prove the outer casing isn't breaking down or been contaminated with a conducting substance. Eg oil and the like.
Get a copy of the pat testing guidelines from the iet.
Can't think of The name

 

[rich.250]

http://electrical.------.org/books/inspection-test/in-service-inspection.cfm

 

[deedar]

Code of Practice - IET Electrical

Thanks. I did have this book when I did the 2377 course. But l can't find it atm. All I'm really trying to find out is how to carry out insulation test on class 2 items both with exposed metal parts eg. Drills, hairdryers etc without exposed metal parts eg. Phone chargers, class 2 detachable leads, radios etc.

 

[190ebob]

We are having very similar problems testing our Class 2 items, can anbody tell me the difference between a standard class 2 test that covers insulation, leakage and load and a touch leakage test that only covers insulation and touch leakage.

 

[Astris]

Class 2 equipment has double or reinforced insulation around the live parts. exposed metalwork should never be able to become live unless there was a major fault that would be visually obvious. That is what i was taught anyway. Dont know where they are coming from with that utube clip.

Yes; but insulation can deteriorate with age and use or could be damaged (hairline crack and moist environment) leading to a leakage path to exposed metalwork? Building sites are notorious ...

 

[Astris]

Thanks. I did have this book when I did the 2377 course. But l can't find it atm. All I'm really trying to find out is how to carry out insulation test on class 2 items both with exposed metal parts eg. Drills, hairdryers etc without exposed metal parts eg. Phone chargers, class 2 detachable leads, radios etc.

The book you need is the Code of Practice for In-service Inspection and Testing of Electrical Equipment, 3rd Edition.

For Class 2 insulation test, connect live and neutral together so you can then test the insulation resistance between live conductors and any exposed metalwork or suspect point on the insulation (there can be a conducting material deposited on the surface of the insulation). Probe between the live conductor common point and any exposed metalwork or suspect joints on the outside of the equipment under test.

 

[Glen Powell]

I deal in class II products and thought this was 101 ??

 

[ohreally]

What do you think of this chaps class II testing Testing class 2 equipment with easytestDUO - YouTube (watch the drilling machine).

 

[Megahertz]

Hi - just seen this post. Testing Class 2 appliances does cause a lot of confusion, and there has been a lot of debate on other forums about this issue.

When the insulation test is carried out on an appliance, we're checking for a breakdown of insulation between live/neutral and the metalwork on the appliance. So, for example, on a drill we'd be checking to see if the chuck/drill bit would be live when we operate it.

The important point here is that live and neutral are joined together inside the tester (so that there's no potential difference between them) and we measure any breakdown of resistance by putting the probe (clip) onto a metal part of the appliance. This is different from installation testing on a building (PIR) where an insulation is carried out BETWEEN live and neutral.

If you think about it, this is why electricians have to go around unplugging all the appliances and removing all the light bulbs before an insulation test between live and neutral, and why a drill doesn't start up when we insulation test it during a PAT Test.

The clip HAS to be attached to a metal part in order for the test to have any value. If there is a breakdown of insulation, current will flow back down the test lead and so the PAT machine will indicate a fault.

On the same token, if we don't connect the clip to anything at all, no current will flow down the test lead, and a PASS will be indicated, even though we're not testing anything! I have witnessed some so called 'professional' PAT Testers testing things like wall wart power supplies by plugging them in, pressing the insulation test button, and then 'passing' them when the insulation test comes back as a pass!

If there is no metalwork on the appliance (such as a plastic hairdryer or a laptop power supply) then there is no need to do an insulation test. And, because it's Class 2, you don't need to do an earth test either, which is why we say that an inspection is ALL that is required on a Class 2, plastic appliance.

If you have a Class 2 appliance with some metal parts the you will need to carry out a full inspection, followed by an insulation test.

It is normal practice to refer to Class 2 appliances with metal parts as 'DOUBLE INSULATED' and those with all plastic parts as 'ALL INSULATED'

Hope this helps!

 

[Megahertz]

Yes; but insulation can deteriorate with age and use or could be damaged (hairline crack and moist environment) leading to a leakage path to exposed metalwork? Building sites are notorious ...

This is a good point, but a 500V insulation test won't normally detect this sort of fault. In the early days of PAT Testing we used to carry out FLASH TESTS to detect this sort of fault, but this isn't recommended now unless a repair has been carried out. I have seen people wrapping appliances in tin foil and then doing the insulation test - again completely pointless.

Modern manufacturing standards take account of things like hairline cracks - so that if there was a tiny crack which wasn't visible then it wouldn't be dangerous. Any more obvious physical damage or moisture in the appliance would be picked up by the Visual Inspection - providing of course this is done properly by the tester and he/she doesn't dive straight in and test it without looking VERY carefully at the appliance first!

 

[deedar]

Thanks very much this has verified what I was thinking ..

 

[tooreq]

Hello,
So if I have a household appliance which has a plastic enclosure and there are only 4 metal screws fixed in this enclosure (metal screws don't touch any live or neutral conductors) I have to check the insulation resistance by touching all of these 4 screws one by one? Am I right? Or this insulation test is not needed then?

Thanks in advance for answer.

 

[Adam W]

You need to use the probe to test the insulation where users are likely to touch the appliance. So you put 500v down the line and neutral and see how much comes back through the insulation. Screws are conductive so it is worth running the probe across the screws.
The insulation on a class 2 appliance is a method of fault protection as well as basic protection, so this should be tested.

 

[oldtimer]

Delongie have a convector heater that has a metal cover but 2 plastic side panels with a class II badge on it so I put the probe on the metal frame to confirm there is no leakage but even then I flicked the tester to class I to make sure there was no continuity but in the case of a plastic hoover then there is no point doing a insulation test yet speak to PAT tester and its yep plug it in and push the button now that worries me because they dont understand without the earth lead there can be no return path. The only other problem as i have is because the industry is full of Urban Myths so you now get a caretaker saying either well the last guy tested it or I have been told you dont have to test class II equipment mind I was lucky as an older Delongie class I heater was sitting beside ther class II model so I could explain to the customer

 

[Mistertee]

Hi, Class II (and Class I) insulation test is carried out with Live and Neutral shorted together. With Class I the return path is the Earth connection - IF THERE IS A FAULT. With Class II the return path is any user touchable metal part. When testing a phone charger, the test lead crocodile clip needs to be clipped to the metal jack. Otherwise if there was a fault, this could be missed.

 

[Darkwood]

Hi, Class II (and Class I) insulation test is carried out with Live and Neutral shorted together. With Class I the return path is the Earth connection - IF THERE IS A FAULT. With Class II the return path is any user touchable metal part. When testing a phone charger, the test lead crocodile clip needs to be clipped to the metal jack. Otherwise if there was a fault, this could be missed.

Welcome to the Forum Mistertee... when wanting to reply to a thread just check the dates of the previous postings, this is a 3yr old thread so unlikely any responses to your post from the OP.

Closing thread on that note , feel free to open a new thread if your are interested in discussing this subject :smiley2: