couple of PAT testing questions

arashabb · Apr 14, 2020

Hi Everyone,
I have recently bought a UNI-T PAT tester ( UT528) and have few questions:

It is mentioned in the handbook, to limit the earth continuity test for some appliances such as TV between 20 and 200 mA. When I check the UNI-T operation manual, it is mentioned the test current for earth continuity is 200mA ‘Minimum ‘. Can this create problem? Or can we change that somewhere?
For which type of tests the PAT tester needs to be plugged in to wall socket while the appliance is connected to PAT tester? when I connect my tester to the mains, it does not perform any test. just verifies if the wall socket is correctly wired.
To conduct IR test, it is mentioned to switch the appliance ON. What if there is not a mechanical switch? ( for example on a printer or a microwave, you can not switch it ON if it is not plugged into a 230V power)
When shall I change the test voltage to 250 V for testing IR in the equipment? Which devices shall not be tested with 500 V?

Thanks alot guys in advance for sharing your experience

pc1966 · Apr 21, 2020

No experience with that tester but a couple of thoughts:

Generally continuity testing to 200mA is not usually a problem, but some testers can do up to 20A which can exceed the safe rating of many item's cable, connectors, etc.
Usually the PAT tester measures leakage current using an internal source, often much below 230V and scales it by the test voltage used, etc, to get "equivalent leakage". However to get the real-world leakage (e.g. when operating, as not always practical - your next point) some can measure the protective conductor current in operation, for which you need it plugged in.
Yes, you should test with switches closed, if not you can (on some models of PAT tester) do protective conductor current instead while operating.
Most obvious case are surge protection devices in things like power distribution blocks - they will show failure as tens of k Ohm at 500V, by several M Ohm at 250V. Also some low power electronics can ba damaged by 500V L-N testing as it can push the internal voltage above the normal ~340V operation point for 230V AC peak charging of capacitors. You would have to check that point, as probably most PAT testers only do L+N to E so should be safe.

pirate · Apr 22, 2020

Interesting questions, and an interesting response pc1966, thank you for that.
I use a simple Pass/Fail tester, so no actual readings or fancy downloadable results, but it is primarily for assisting landlords with testing of domestic appliances.
I queried direct with the supplier and manufacturer about, for example, testing IT equipment and was assured the tester would not damage PCs etc, however i normally don't include these in a testing regime because the value of the info stored on a PC is vastly greater than the cost of a new PC and the site owner should have his/her own backup for such info. I have never come across a PC that would kill you...yet!

There is no circumstance where my tester would be plugged into the mains supply. It's not designed to check such things as supply voltage or supply polarity. It will, of course, check polarity through IEC leads, extension cables and surge protection cables, but the last-mentioned are tricky and have been the subject of another thread on this forum.

It has a "switched on?" query function, and this is useful for items with mechanical switching, but i do take your point regarding printers etc. The manual instructs that if you cannot switch on, the test button is pressed again and the test proceeds. As pc1966 mentioned above, the test for protective conductor current instead.

Similarly, if you cannot find any exposed metal parts on a class 1 appliance, you test it as Class 2. Clearly, this is restrictive in scope, but in practice it is usually fine.

Again, with class 2, on my tester, if you can't switch on, you just hit the test button again and look for a Pass or Fail.

Surge protected leads are a nightmare, in my experience, and it seems that the better the quality the more fails you will get. This is due to the method of manufacture, and is just a fact of life for the humble PA tester. However, somewhere in a previous thread I posted this comment from the manufacturer:
"One consequence is that some surge protected leads can cause a ‘false fail’ indication on polarity as the surge suppression components allow a small current to flow between live and neutral, which the machine incorrectly interprets as a fault current. Providing the only failure indicated is polarity, PROVIDING that neither earth continuity or insulation resistance indicate a fail, the lead is safe to use."

Printers and other plastic bodied appliances with no touchable metal parts are inherently quite safe anyway, and as you will know the testing is only about 10% of the regime, with a Full Visual Inspection being the most important aspect.
Testing of fixed appliances requires proper isolation and proper gear to carry out the normal tests, but is an important aspect of ISITEE. That is a different subject, but if you are properly to carry out "PAT" you have to be competent to do this too.
I hope this helps.

pc1966 · Apr 22, 2020

I think most general purpose PAT testers are safe for electronics, certainly our Seaward never troubled our stuff.

However, in most cases the faults you will find are related to cables and connectors as they get the most abuse, etc, so for PCs and similar where you can unplug the mains lead and test it you are achieving most of what you might hope to achieve safety-wise and with less risk to PCs, etc.

If you do test electronics though you really need a "tester" that reads out the numbers as many have input filters with a couple of mA leakage that will fail many fixed checkers' threshold. Our technician looked at the numbers and if sane for the type of equipment (e.g. less than 4mA or so) just recorded the value and marked as a pass.

arashabb · May 2, 2020

pc1966 said:
No experience with that tester but a couple of thoughts:

Generally continuity testing to 200mA is not usually a problem, but some testers can do up to 20A which can exceed the safe rating of many item's cable, connectors, etc.

Usually the PAT tester measures leakage current using an internal source, often much below 230V and scales it by the test voltage used, etc, to get "equivalent leakage". However to get the real-world leakage (e.g. when operating, as not always practical - your next point) some can measure the protective conductor current in operation, for which you need it plugged in.

Yes, you should test with switches closed, if not you can (on some models of PAT tester) do protective conductor current instead while operating.

Most obvious case are surge protection devices in things like power distribution blocks - they will show failure as tens of k Ohm at 500V, by several M Ohm at 250V. Also some low power electronics can ba damaged by 500V L-N testing as it can push the internal voltage above the normal ~340V operation point for 230V AC peak charging of capacitors. You would have to check that point, as probably most PAT testers only do L+N to E so should be safe.

Thank you guys for very informative replies. really appreciate it.
I have seen that some testers do ‘ Protective Conductor Current Test’ and ‘ Touch Current Test’ as well in which the tester shall be plugged to 230 V supply.
Are these tests part of general PAT routine or this is something extra? when we say we do PAT, does it mean we have to do these 2 tests as well?!

pc1966 · May 2, 2020

arashabb said:
Thank you guys for very informative replies. really appreciate it.
I have seen that some testers do ‘ Protective Conductor Current Test’ and ‘ Touch Current Test’ as well in which the tester shall be plugged to 230 V supply.
Are these tests part of general PAT routine or this is something extra? when we say we do PAT, does it mean we have to do these 2 tests as well?!

The law (in the UK at least, you might be different as your details say UAE) does not specify exactly what has to be tested, how it is tested, or how often it should be tested. The legal requirement is simply to maintain a safe environment for work.

However, the Health and safety Executive does publish guidance on PAT testing to allow employers to sensibly balance the risks against the cost/inconvenience of testing. As such what is done and how often depends very much on the environment, so equipment on a building site that is frequently moved and abused by unskilled (electrically speaking) workers should be tested far more frequently than more or less stationary IT equipment in an office, for example.

Here are some of the HSE guidance on PAT testing for the UK:

PAT (Portable appliance testing) - HSE's answers to popular questions

Health and Safety Executive (HSE) answers; frequency of tests, legal requirements, record keeping, new equipment, who can test, hire tools

www.hse.gov.uk

General guide for equipment:

https://www.hse.gov.uk/pubns/priced/hsg107.pdf

Guide for low-risk environments:

https://www.hse.gov.uk/pubns/indg236.pdf

But ultimately if you are doing this as a service then it is up to you and your client to decide the extent of testing and how responsibility is divided.

For example, if you are looking at a low-risk office where the only people using equipment are employees with reasonably intelligence then you might rely on them to report problems of concerns for additional testing, but if you have rented accommodation or public spaces you should not assume any sense or cooperation and you as the electrician would be the one to be trusted to inspect and test everything more regularly.

So aspects such as touch current and protective conductor current are just better ways to establish leakages values and to decide if the equipment looks to be operating normally when powered up, and in some cases to use the values for system planning (for example, to work out how many can be put on one circuit and not reach the In/2 lower trip threshold of an RCD, etc).

pc1966 · May 2, 2020

As already mentioned, the environment can make a big difference. One site I visited had a policy of PAT testing everything brought on-site, even if brand new, before you were allowed to plug it in as the buildings were highly vulnerable to fire. Testing was repeated every year at the longest even if HSE guidance did not require it.

arashabb · May 2, 2020

pc1966 said:
As already mentioned, the environment can make a big difference. One site I visited had a policy of PAT testing everything brought on-site, even if brand new, before you were allowed to plug it in as the buildings were highly vulnerable to fire. Testing was repeated every year at the longest even if HSE guidance did not require it.

Thank you so much . very helpful