# PAT testing



## sains_uk (Jul 24, 2011)

We recently had our PAT testing completed, whilst the engineer was testing my area I noticed that when testing ac adapters the adapter is plugged into the tester and class 2 button pressed. Having some electronics knowledge I was under the impression that testing insulation required a path back to earth in order to test resistance. I questioned the guy regarding this and he told me this is the correct testing procedure and continued to confirm this with his office. So out of curiosity what are these meters testing in the case of an ac adaptor, it seems to make no sense to me?


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## frank (Feb 6, 2007)

The adapter is really a junction box. The test that your PAT guy undertook would have been an insulation test and probably a flash test. He will also have undertaken an earth pole to earth pole continuity test. Testing for insulation does not require an earth path return but should the appliance have an earth integral this would be tested against a current carrying conductor for insulation value.This requirement would be neccessary for earth loop tests. Your guy chose the Class 2 option for the adapter test. Although the adapter is a class 2 appliance I would have chosen the class 2 option and tested the earth path return for continuity utilising the machines test probe. But an adapter test is a tricky one.

The PAT test instruments are a none technical apparatus that undertakes multi checks automatically. This can be done by a trained electrician utilising a variety of instruments but the PAT tester can be used by a non tecchnical person. It's a matter of plug in and play. Pass or fail.

Frank


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## sains_uk (Jul 24, 2011)

when u say earth pole to earth pole continuity however the adapter in question has a plastic earth pin and all plastic low voltage end hence my query as to what the tester is testing when no earth flylead is used, is it testing how conductive the plastic casing is?


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## frank (Feb 6, 2007)

Some confusion here. When you say 'adapter'. Are you talking about a' transformer' as used for mobile phones etc?When I say adapter I mean to speak of a plug connector. ie 2 way or 3 way etc. I think you are talikng about a Class 2 all insulated transformer with plug head connection faciity.

If the latter the test can be only as follows. Insulation test between poles of plug head ie live and neutral. This test will also include primary windings and or secondary windings depending upon transformer type or indeed the open circuit diodes that are sometimes used in these appliances. In any case. The test is a simple insulation test
between live and neutral.

Frank


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## sains_uk (Jul 24, 2011)

Hi Frank, yes I am talking about the transformer type. Thanks for the info regarding the insulation test. It seems that most dedicated PAT testers do not conduct the test in the way you mention, i.e. the insulation test only shorts L & N and uses the earth probe as the 2nd leg, but does not conduct any test between L&N other than establishing that a resistance exists to indicate if the device is turned off. 

Having played with the Primtest 250 we have here it will infact pass a plug where I have directly shorted L & N together. The only way I could produce a fail was to short the earth directly to L or N. This leads me back to the transformer test, unless the plastic earth pin can short to L or N which seems impossible this machine would never fail one and the test seems pointless.


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## frank (Feb 6, 2007)

Electrical tests to 'adapters' are pointless. The only appropriate test would be visual Any electrical test proves nothing.

Frank


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