Class 2 insulation tests

[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.