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From: Arfa Daily on 17 Jun 2010 05:49


"Adrian C" <email(a)here.invalid> wrote in message
news:87u819FskfU1(a)mid.individual.net...
> On 17/06/2010 01:14, Arfa Daily wrote:
>>
>> Last week, we had a couple of claps of thunder locally, so I began to
>> think that this might be a 'storm damage' job. Either way, in view of
>> its age, it was not going to be a practical repair, so I informed the
>> store that it came to me from, and put it back together. It was at this
>> point that I noticed the PAT test label wrapped around its power lead,
>> and this indicated that the test had been carried out only a week or so
>> before it became faulty. At this point, I began wondering if the fact
>> that it had had the tests performed on it, probably by someone with an
>> automatic tester and little understanding of what it is doing, and where
>> it is appropriate to run which tests, had resulted in damage to the
>> microcontroller. I have seen other equipment on a number of occasions
>> over the years, with similar 'odd' failures, and sometimes power supply
>> failures, shortly after being PAT tested.
>
> Yup, PAT testing killed it, or correctly the incorrect procedure
>
> This would have been Class II double insulated, so a tester would have a
> choice of either a 'hard test' or 'soft test' to check the insulation
> resistance, as part of the test.
>
> The 'hard test' is a measurement of resistance (over 2Mohm ClassII) found
> using a test voltage of 500V DC applied between 1) L&N connected AND 2)
> any exposed possibly conductive surfaces (wandering probe)
>
> The 'soft test' is powering the thing up normally on supply, and using a
> wandering probe to measure any leakage current fron exposed possibly
> conductive surfaces.
>
> A 'hard test' is the thing for non-electronic equipment, 'soft' for
> everything else. However, the wizzy do-everything electronic testers make
> selecting soft and hard tests as easy as clicking a button, and mistakes
> can and do happen.
>
> I trained (C&G 2377) in doing this as a possible part/full time job, but
> the risks of blowing up perfectly OK equipment, plus the meagre earnings
> doing hundreds of items in an office, made me abandon the idea quite
> quickly.
>
> --
> Adrian C

OK Adrian. That's just the sort of detailed and informed input that I was
looking for, and backs my feelings on the matter. I think I might mention
this to the shop who took this item in, when I return it tomorrow.

Arfa

From: Arfa Daily on 17 Jun 2010 19:37


"Mark Allread" <markA(a)once.org> wrote in message
news:D_6dnWzbDpWdCIfRnZ2dnUVZ_gydnZ2d(a)sysmatrix.net...
> Arfa Daily wrote:
>
> (some content snipped)
>> I've never been a great believer in the appropriateness of applying
>> these tests to double insulated and transformer based equipment,
>> particularly given that large DC spikes are applied, which with some
>> testers are actually twice the nominal line voltage. Given that in much
>> microcontroller based electronic equipment, digital grounds are not
>> directly bonded to other system grounds, it seems to me that having big
>> voltage spikes flashing around between the primary side of the power
>> supply, and cabinet metalwork, which is not grounded to any line power
>> earth, but may well be AC common to internal DC grounds via low puff (
>> and sometimes not-so-low ) caps and high value resistors, is asking for
>> trouble of the same nature as you might expect from static damage, or
>> pulse damage from nearby lightning strikes.
>>
>> I would be interested in knowing if I'm on my own on this one, or if
>> anybody else involved professionally in service work - or indeed anyone
>> who carries out PAT testing - has any similar experience, or opinions on
>> this.
>>
>> Arfa
>
> I had to look up "PAT Testing" online. It sounds like yet one more
> unnecessary time-and-money-wasting government annoyance, like lead-free
> solder and banned cleaning solvents. I'm sure we in the USA will be doing
> that too, soon enough. At first glance, an incorrectly applied PAT sounds
> like a fine way to destroy MOV protection devices.

Yep, I'm sure that where we've been, you boys in the U.S. won't be far
behind, although in the case of such things as health and safety, the green
mist, the supposed hazards of lead, and belief in the dogma of global
warming (with the possible exception of Al Gore), you seem to maintain a
proud and dogged resistance to being dragged in. I wish that the people and
powers of Europe in general, and the UK in particular, had a similar point
of view ... :-(

Arfa

From: Michael A. Terrell on 17 Jun 2010 22:00

Arfa Daily wrote:
>
> Yep, I'm sure that where we've been, you boys in the U.S. won't be far
> behind, although in the case of such things as health and safety, the green
> mist, the supposed hazards of lead, and belief in the dogma of global
> warming (with the possible exception of Al Gore), you seem to maintain a
> proud and dogged resistance to being dragged in. I wish that the people and
> powers of Europe in general, and the UK in particular, had a similar point
> of view ... :-(


It's time for the European pheasants to gather pitchforks and burning
torches, for an all out assult on Brussels. Don't bother to pack a
lunch, since there will be plenty of fattened pigs to roast! ;-)


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
From: Phil Allison on 17 Jun 2010 22:08

"Adrian C"
> Phil Allison
>>
>>> ** Why on earth would a unit like that have to be PAT tested ????
>>
>>> No requirement exists here in Australia for low risk items used in non
>>> hazardous work environments to be regularly tested.
>>
>
> Nope. It's 5 Years in an "Environment where the equipment or supply cord
> is NOT subject to flexing in normal use and is NOT open to abuse and is
> NOT in a hostile environment"
>
> Australia PAT testing (they call it 'test and tag') does looks fairly
> similar, if not the same to the UK.


** This guide from WorkCover NSW makes it CLEAR that there is NO testing
needed in this example.

http://www.workcover.nsw.gov.au/formspublications/publications/Documents/competent_person_testing_tagging_electrical_equipment_1336.pdf

See item 7: " How often should I 'test and tag' my electrical equipment. "

" For all other workplaces, the inspection and testing intervals are
described in the standard, AS/NZS 3760 but ONLY need be applied to
electrical equipment that has been assessed as operating in a hostile
operating environment as described in clause 64 of the OHS Regulation."

BTW:

The issue here is PAT testing, I have no argument that regular visual
inspections for damage or deterioration etc are needed under the OHS laws
here.


..... Phil


From: Phil Allison on 17 Jun 2010 22:19

"Mark Allread"

> I had to look up "PAT Testing" online. It sounds like yet one more
> unnecessary time-and-money-wasting government annoyance, like lead-free
> solder and banned cleaning solvents. I'm sure we in the USA will be doing
> that too, soon enough. At first glance, an incorrectly applied PAT sounds
> like a fine way to destroy MOV protection devices.


** MOVs are NOT connected from line to ground inside equipment sold in
Europe or Australia - cos it is a very dangerous practice.

In any case, the appliance tester only outputs a very small current to the
device under test in order to measure leakage to frame or chassis and is not
normally applied across the AC line terminals.


..... Phil








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