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Tricky PAT question

TrigPoint
Hello everybody! I could use a bit of sage advice regarding PAT testing unusual items.


To give you a bit of background, I'm in a bit of a tricky spot because I just took over a role as a PAT tester and it came with two very smart testing devices which save the identification number, create a bar code and save the tests required for whatever item it is. Subsequently everyone in my company seems to think that all I have to do is type in a number and the test is automatic.


Unfortunately, the more items I test, the more I notice that the tests that have been inputted, are not anything I want to put my name/initials to. I mean, a few days ago I was prompted to complete a touch current test on a bog standard class I toaster. I've found; tests on leads that do not test for polarity, a test that checks IR at 500V and also checks leakage but nothing else, and it seems to have been standard to cobble together 4 and 5 pin plug and socket adapters for testing 35/63/125A cables using 3 pin plugs and sockets which connect to the PAT tester... d'oh! So it's taking me a lot longer to test things than my company expects. It's a bit of a nightmare if I'm honest as almost every test needs checking and most need reprogramming. 


To make the problem worse, it seems my bosses really trusted the person who was doing this before me and so every time I run into a problem or a test that doesn't work properly, sometimes in front of them, it's sort of taken as me being incompetent rather than the test being substandard in the first place. So, I can't really ask my colleagues for advice because it kind of works against me. So that's why I joined here and I'm asking you. Thank you for reading this far by the way. I'll get down to the real question now...

I test everything from museum exhibits and set for TV shows to your average kettles, toasters, microwaves and so on. But occasionally something comes up with a lot of exposed painted metal which is earthed using an earth nut. In this case it's a booth for a TV game show. How would one decide what a suitable resistance might be for such items during an earth bond test? Also what are the implications for Insulation resistance? You'd think it would fail because of the large amount of metal with no real insulation on it connected to the circuit. This has me beat! I have no idea what to do to test it properly.

If anybody out there has any advice I would really appreciate it.


Thanks


Trig  


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  • 0
    Some thoughts in defence of the 'brutal' Seaward Machine.

    If the cpc and any internal bond to the case  cannot handle 25 amps for a few seconds, it should not be relied upon blow a 13A fuse, rather the CPC may blow clear, and the 13A fuse remain intact, and the case energised. The tester's intention is to emulate this, and although it is a 25 A test, it is derived from an ELV transformer, so the touch potential is limited.


    Yes, you may well feel it buzzing in your hand if the contact is a croc clip, but unless the test lead is coiled it is unlikely to be magneto striction, but thermal oscillation at the points of contact being heated and cooled - similar to the operation ball-bearing "motor".  a digression, into how heat can move things.


    I'd suggest that it is only truly live working, if the case is open and the parts that come live to mains voltage when it is powered  up are exposed. The preceeding visual inspection should reveal this.

    Insulation testing even at the 500V, (and in some models also a flash test at 3500V) is carefully current limited, designed to simply deliver an agonsing but non-lethal shock to anyone fool enough to insulation test themselves as well as the device under investigation.

    I would agree there is a case for not performing an on-load test for certain pieces of equipment that can be damaged if run up without other things in place - rotating machines with cutters and certain types of pump that do not like to be dry run come to mind.

    To be any use the PAT machines have to emulate realistic fault conditions- which are by definition single fault to danger.
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  • 0
    Some thoughts in defence of the 'brutal' Seaward Machine.

    If the cpc and any internal bond to the case  cannot handle 25 amps for a few seconds, it should not be relied upon blow a 13A fuse, rather the CPC may blow clear, and the 13A fuse remain intact, and the case energised. The tester's intention is to emulate this, and although it is a 25 A test, it is derived from an ELV transformer, so the touch potential is limited.


    Yes, you may well feel it buzzing in your hand if the contact is a croc clip, but unless the test lead is coiled it is unlikely to be magneto striction, but thermal oscillation at the points of contact being heated and cooled - similar to the operation ball-bearing "motor".  a digression, into how heat can move things.


    I'd suggest that it is only truly live working, if the case is open and the parts that come live to mains voltage when it is powered  up are exposed. The preceeding visual inspection should reveal this.

    Insulation testing even at the 500V, (and in some models also a flash test at 3500V) is carefully current limited, designed to simply deliver an agonsing but non-lethal shock to anyone fool enough to insulation test themselves as well as the device under investigation.

    I would agree there is a case for not performing an on-load test for certain pieces of equipment that can be damaged if run up without other things in place - rotating machines with cutters and certain types of pump that do not like to be dry run come to mind.

    To be any use the PAT machines have to emulate realistic fault conditions- which are by definition single fault to danger.
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