PAT

[Matthew Robinson]

I have been working with a sparky friend of mine to do some PAT testing. I understand the tests and what constitutes a pass or fail, but am wondering if I can start testing equipment on my own (without supervision)? I would use a multimeter rather than a testing machine.

 

To help you with your answer, I am 17 and studying for my A-levels (Physics, Maths, etc) and have applied to universities to study Electrical/Electronic Engineering.

 

Thanks

Matthew

[Andrew C]

Sorry, but if you think that you can use a multimeter to PAT, then you DO NOT understand the tests and CANNOT start on your own. Do some training; try your local technical college for the City & Guilds course, and buy the IEE code of practice.

[Matthew Robinson]

Surely its possible to use the multimeter to do the insulation checks and also (if relevant) the earth continuity checks? Furthermore, I'll only be testing a few appliances/cables, not setting myself up to PAT calbles on an industrial scale!

[Russ83]

Insulation and earth continuity are not the only checks you may be required to carry out though. You also have to have your testing device calibrated/certified before you can use it, I'm not 100% sure but I doubt they will accept a standard multimeter as a PAT device.

[Andrew C]

Earth Bond. The purpose of this test is to establish that the earth connection is good enough to allow a sufficiently high current to flow for long enough to operate a protective device (fuse or circuit breaker). Your multimeter will tell you if the resistance is low, but you could be testing the final strand of the earth core. A PAT machine tests at 2.5 times the cable rating, up to 25A. This is designed to rupture a nearly dead cable.

 

As I said above, you need training to be competent.

[boatman]

Surely its possible to use the multimeter to do the insulation checks and also (if relevant) the earth continuity checks? Furthermore, I'll only be testing a few appliances/cables, not setting myself up to PAT calbles on an industrial scale!

 

As Andrew said above, you clearly do not understand the principles of PAT. Start off with the fact that a multimeter will generally use a PP3 9V battery for resistance measurements and then think about it a little.

[paulears]

There's quite a bit you haven't thought about. The idea of using a multimeter to check if if a cable is ok to pass audio through, and check some ejit hasn't swapped live and neutral works = but= doesn't tell you if a cable is safe to use. Before the era of PAT people tested electrical installations with a gadget called a Megger. To measure really big resistances, in the MegOhm area (good choice of company name?) you need high voltage (think about Ohm's Law). Your multimeter can't do that very well running off a 9V battery. So your measuring tool is flawed before you start. On top of that, if you're testing mains cables you also have to think about insulation a bit differently. A Whisker from the Live that is near to the Neutral or Earth might well be close enough for a spark, but will your meter detect this? Nope. The purpose of the PAT is to give an indication if an appliance is safe. Your meter would suggest it is. The proper PAT machine would probably say no, in some circumstances.

 

One of the snags of using a proper tester is that you need knowledge to be able to interpret the results. Some things will fail just because of what they are. They may not be dangerous, but without the knowledge, a testing person could conclude an item is duff, and condemn it when it isn't.

 

Plenty of things need electrical knowledge, which you've already realised is knowledge you're not currently in possession of.

 

Common sense in this area often produces obvious, but very wrong foundations for testing.

[pritch]

Try this:

 

Take your multimeter, set it to the 20Mohm range. Hold both probes in your hands. Feel anything?

Now take a PAT tester, and set it to do a class I insulation test. Hold the earth clip in your hand.

 

Actually... don't. It's not the same thing, and will really hurt; I've seen a spark come off an earth clip that wasn't well affixed to the appliance.

[Matthew Robinson]

Ok, Thats a no then! For the (few) devices I have to test, its not economical to buy a tester.

 

From what you're saying, it doesn't appear that my friend is testing correctly, he uses his multi-meter for 32A cables!

 

I'll have to go back to stealing using his tester when I need to do PAT testing (It has a Pass/Fail read out and he has briefed me on its use)

[Dmills]

The simple minded testers that only display pass/fail are probably better then nothing for testing office stuff for example, but there are some subtle points that most such machines do not consider:

 

Take for example your humble generic lantern, the appropriate electrical standard for these (anyone remember the number) specifies an earth bond test at 10A, and with a different fail threshold to the normal default, if you test at 25A, you risk damaging the earth braid and spuriously failing the lantern (IIRC The early Source 4s had a known issue with this). Even things like extension leads can be a can of worms as the earth resistance threshold changes with cable length.

 

This is not simple, and production technology is one of the more complex edge cases, you need to do the course AND understand the physics.

 

IMHO, you can get MOST of the benefit of regular testing from just doing the visual inspection regularly, 90+ percent of the fails when I test are fails at visual inspection time (Loose screws, damaged cables, cord grips, that kind of thing), it is rare for something to pass the visual then fail when put on the tester.

 

Nothing wrong with a multimeter for SOME tests, but earth continuity and insulation tests need something more.

 

Regards, Dan.

[sparkyweb]

From what you're saying, it doesn't appear that my friend is testing correctly, he uses his multi-meter for 32A cables!

 

Are you sure its a multi-meter he uses, although as some posters have pointed out these devices have a PP3 battery in them, there are proper Insulation Resistance meters (Meggers) that look like a multimeter but will stick the relevant voltage down cables for measuring IR

[Matthew Robinson]

I'm pretty sure it is, I've seen him use the same one for voltage tests...

 

It does seem quite old: it has an analogue meter and it seems generally worse for wear...

[Brian]

Mathew,

 

if you're serious about PAT then I'd highly recommend getting a copy of the Code of Practice. Ok, it's not a cheap publication but it does tell you the proper way to do things and what is expected of each test.

 

http://images-eu.amazon.com/images/P/0863418333.01.MZZZZZZZ.jpg

[Matthew Robinson]

Well, I'm not particularly serious about PAT testing. I do very few events (and what I do do is on a amateur level), its just that a lot of venues have discovered the buzz word 'PAT testing'*. I have very little equipment, I generally use what is there/ beg/ borrow/ steal/ hire (if on a budget of >£0 - which is rare!). However, as mentioned above, venues seem to want things 'PAT tested', so I was wondering if I could PAT my small collection of equipment/ PAT other people's in return for them lending me theirs (with the common or garden tools I already own). From what has already been said, it seems unlikely, unless I can borrow a PAT tester...

 

Currently, I am doing very little- even less than before- as I'm quite bogged down in college work (see first post). I don't think that there is any point in me forking out £30-£40 for guidelines which are likely to be out of date when I come to using them in anger!

 

*it always makes me smile a little when people talk about PAT testing- Portable Appliance Testing Testing!

 

Thanks anyway

Matthew

[Russ83]

I have been working with a sparky friend of mine to do some PAT testing.

I'll have to go back to stealing using his tester when I need to do PAT testing

*it always makes me smile a little when people talk about PAT testing- Portable Appliance Testing Testing!

*cough* Ditto ;) , sorry to say Matthew but you are the only one making the mistake in this thread.