PAT testing. Anyone else think that sometimes, it causes damage?
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From: Adrian C on 17 Jun 2010 05:25 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
From: N_Cook on 17 Jun 2010 07:03 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 What about 5KV or 10KV flash testers being used in the wrong situations?
From: Adrian C on 17 Jun 2010 07:35 On 17/06/2010 11:15, Dave Plowman (News) wrote: > In article<87tl0lFm1qU1(a)mid.individual.net>, > Phil Allison<phil_a(a)tpg.com.au> wrote: >> ** Why on earth would a unit like that have to be PAT tested ???? > > Every mains powered electrical item has to be if used in the work place, > etc. However, the procedure isn't the same for everything. > >> 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. For example, within Victoria the Occupation Health & Safety Act 2004 states: �An employer must, so far as reasonably practicable, provide and maintain for employees of the employer a working environment that is safe and without risk to health.� Exact same statement is in the UK H&S Act (probably no surprise there - we probably wrote it on paper first... ;-) The standard AS/NZS 3760 is referred as a way of implementing this. Here is the testing interval from that standard. http://policies.swinburne.edu.au/ppdonline/showdoc.aspx?recnum=TEM/2009/7 In the UK however, we have a document published by the IET called "Code of Practice for In-Service Inspection and testing of electrical equipment" that recommends the following PAT testing schedule. It is a bit different ... http://www.linpat.co.uk/Suggested%20Frequency%20of%20Testing.htm > Australia ain't the world... > He doesn't live in the world ... -- Adrian C
From: Adrian C on 17 Jun 2010 07:52 On 17/06/2010 12:03, N_Cook wrote: > > > What about 5KV or 10KV flash testers being used in the wrong situations? > Flash testing (AKA Dielectric Strength testing / Hi-POT testing) is done by manufacturers as part of their 'out the door' production checks. The IET code recommends NOT doing this as part of a user testing programme, for guidence will be required from the manufacturer for precautions applying the test AND the flash testing itself may encorage after failure of the insulation. -- Adrian C
From: Mark Allread on 17 Jun 2010 17:33
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. |