Testing with no exposed metal parts...

[D J Sheridan]

In an office environment...
So please tell me I'm a dunce on this one (I'll gladly wear a hat with a 'D' on it) but one thing I've never really got with PA Testing is when testing Class 2 equipment part of the test is one where you need to use the fly lead to clamp to some exposed metal part of the unit.
Now correct me if I'm wrong but if a Class 2 equipment unit does not have any exposed metal then where does one put it for the test?
I have been using a heavy-duty paper clip clamped to the lead clamp and held it against a deep-routed screw in the casing as it's the only way to reach some metal part - although that in itself is not right as the screw is usually screwed into plastic.
Similar goes for any power adapter for any piece of equipment that does not have any exposed metal part...

Also - as it's that time of year again - if a string of Christmas lights are of the old style type (in series where if one bulb out then the whole lot are out) and it's wired to a plug using only the Live and Neutral as no Earth wire - there is a label on with CE mark and Double Insulation mark. Bulbs indicate 12v 1.1w.
...so I'm of the opinion that a visual check is the only requirement. Also I'll be ensuring they plug them into an RCD socket.
Am I right this?

 

[telectrix]

if it's class II, you don't do an earth bond test. there's no earth on the appliance. if a class I appliance has no way of clamping to exposed metal, put it down as a LIM or N/A.

 

[D J Sheridan]

Hi,
Thanks for the reply - but on the test machine the procedure starts on Class 2 wand asks to connect the fly-lead. Yes you can skip the test but it seems to automatically shut down and finish the test without doing the operation test.

 

[davesparks]

I think you'd be best getting some training and a copy of the code of practice.

Class 2 appliances can have exposed metal parts, if they do then a test needs to be carried out to ensure that these are suitably insulated and no touch potential appears on them. This is why a class 2 insulation test can require the use of a test probe (not clip) also the class 2 leakage test uses the probe. The test should be repeated for each separate exposed metal part the same as the bond test of a class 1 appliance

 

[D J Sheridan]

Thanks for your response...
I have been on the PA Testing course and passed both the testing and management parts, but there were some things they did not tell you and they seem vague.
The Metrel Omega PAT machine asks you to connect the wander lead (which is a clamp and not probe) to the equipment - but if there is no exposed parts at all on Class 2 units then where do you put it to maintain the process of the Class 2 test on the machine? Do you just clamp it to any part of the unit if no possible metal exposed?
Sorry if I am being vague on this...
Just to clarify I am a Health and Safety Officer and not an electrician - we were just asked to do the course and check all office equipment.

 

[D J Sheridan]

Just saw Eodneil's post...
Yes this is what I do but as close to a part that gets touched or used (IE a button) by the user...

 

[davesparks]

For an insulation resistance test on a Class 2 equipment you have to use a Fly lead, you try and get it touch a screw or a conductive part, but as you mentioned some equipment doesn't have any exposed conductive parts so the best you can do is just place the fly lead on the outer casing.

What on earth is the point in carrying out a test designed to prove that exposed conductive parts are reliably insulated where you connect a probe to a non-conductive part?

If there are no metal parts to test then the test is unnecessary.

 

[davesparks]

Thanks for your response...
I have been on the PA Testing course and passed both the testing and management parts, but there were some things they did not tell you and they seem vague.
The Metrel Omega PAT machine asks you to connect the wander lead (which is a clamp and not probe) to the equipment - but if there is no exposed parts at all on Class 2 units then where do you put it to maintain the process of the Class 2 test on the machine? Do you just clamp it to any part of the unit if no possible metal exposed?
Sorry if I am being vague on this...
Just to clarify I am a Health and Safety Officer and not an electrician - we were just asked to do the course and check all office equipment.

Forget what the machine is telling you to do, it is non-sentient and is following a pre programmed sequence.
You are supposed to be the skilled person with good knowledge of electrical theories capable of selecting and carrying out the tests necessary to prove that appliances are safe to use.
If there are no exposed metal parts then you don't need to test them and if your test sequence requires you to test them then are are carrying out the wrong tests for that appliance.

If you don't know enough electrical theory to understand what a test does, why it does it and what the results actually mean then you should not be doing the testing unsupervised, otherwise it becomes a pointless box ticking exercise and has no benefit to anyone's safety.

 

[D J Sheridan]

Forget what the machine is telling you to do, it is non-sentient and is following a pre programmed sequence.

I do understand this - but as with all things then i would question why these manufacturers and designers of equipment like this are allowed to do so if they are not up to scratch to allow for user ease of use - that said all PA Testing should be done by qualified electricians...in my honest opinion..

If there are no exposed metal parts then you don't need to test them and if your test sequence requires you to test them then are are carrying out the wrong tests for that appliance.

No i'm not as the Class 2 setting on the Metrel Omega PAT always requests the wander lead is attached on the first test - then it asks for you to remove it upon the second test in the process...
That said on Class 2 I am common sense approach to realise if all plastic casing with no way of metal touching I would not do the test - but the machine if you skip it will automatically stop the test. However if metal showing i'd touch the wander lead accordingly and carry on.
Even on numerous websites it states "although you really only need the test on Class 1..." they indicate to use a probe to touch deep-seated screws (which in my opinion is waste of time if the screw only hold two pieces of casing plastic and not screwed into any internal metal chassis. Even Class 2 fans they state to touch the probe to the outer metal casing of the motor through the vents!

As quoted on one site:-
"Insulation resistance
Realistically, this test can only be carried out on Class I equipment. It is made to ensure that there is no breakdown of insulation between the protective earth and live (line and neutral) parts of the appliance and its lead.
For Class II items, there are no earthed parts and one test probe would need to be placed at various points on the body of the appliance in order to check the integrity of the casing."

And this was written by an electrician!

If you don't know enough electrical theory to understand what a test does, why it does it and what the results actually mean then you should not be doing the testing unsupervised, otherwise it becomes a pointless box ticking exercise and has no benefit to anyone's safety.

I do however agree with this - it was just another thing we were expected to do!
...but again if these machines are designed for ease of use with the shortcut settings pre-programmed into them then anyone with a slight sense of knowledge and common sense should be able to use them... BUT it is so vague and not all variables and tangents are catered for and explained in their user manuals.

 

[Richard Burns]

As quoted on one site:-
"Insulation resistance
Realistically, this test can only be carried out on Class I equipment. It is made to ensure that there is no breakdown of insulation between the protective earth and live (line and neutral) parts of the appliance and its lead.
For Class II items, there are no earthed parts and one test probe would need to be placed at various points on the body of the appliance in order to check the integrity of the casing."

And this was written by an electrician!


BUT it is so vague and not all variables and tangents are catered for and explained in their user manuals.

The quote above is pretty much repeating the advice in the code of practice.
When testing the probe should be connected to any metal parts or suspects joints in the enclosure where conductive material may accumulate, this may require multiple tests.

The instruction manual cannot provide for all circumstances and all construction types for all equipment, but the code of practice does attempt to cover the majority of them.
It would probably help to read the code of practice and get the full information and guidance on testing.