I read in !emc-pstc that Nick Williams <nick.willi...@conformance.co.uk> wrote (in <p05200f03ba60957364e4@[192.168.1.28]>) about 'EN60950 protective conductor test (was Re: Circuit Breaker Tripping Dring Fault Tests)' on Fri, 31 Jan 2003: > >At 12:22 +0000 31/1/03, John Woodgate wrote: >> >>There is a proposed amendment to IEC/EN 60950-1 requiring a test of the >>protective conductor network at *prospective short-circuit current* for >>the time it takes for the mains circuit protective device to operate. >>The details are controversial at present, because the test currents >>appear not to have taken into account the differences between >>prospective short-circuit currents in different wiring systems and >>supply voltages. Given that reservation, the lowest test current is 200 >>A. >> >>The amendment is aimed at protective conductors which are surface or >>internal traces of multi-layer printed boards. It is said that such >>traces have failed in the field under high-current fault conditions. >>-- > >Is the proposal to replace the existing test in the standard or to >add an additional test only for certain special circumstances?
It's additional. > >Is there any evidence that this test would actually result in a >significant number of poorly designed products which currently pass >the requirements of the standard being rejected? This is the claimed justification for the introduction. Field problems have occurred where printed board conductors have failed in high-current short-circuit conditions. The printed-board mounting versions of the IEC 60320 appliance connector encourage the use of board traces to carry the PEC; something that I would not be happy about, in principle. > >The existing test has its faults but it is easy to do with some very >cheap apparatus. It strikes me that the cost of doing a test at 200+A >is potentially very substantial. I don't think 200 A is too much of a problem, but testing at higher currents is proposed for some equipment. I don't want to be too explicit, because the figures in the draft are highly suspect (of applying to 120 V supplies!). >If the result of an amendment to the >standard is that significant numbers of self-certified products which >have not been properly tested in this aspect of their design reach >the market, then the net result will actually be a significant >reduction in the safety of end users. I don't understand that. You mean that if people cheat, safety will be compromised? That's always the case. But in fact, the presence of the test may well concentrate attention on the need to make such traces substantial, whether they are tested or not. > >A cynic's view might also be that an amendment of this nature would >suit the test labs and larger manufacturers fine, since they will be >able to justify the cost of the apparatus required, whereas smaller >manufacturers (and yes, small consultancy companies like mine) will >not. Remember you don't necessarily need 200 A at 230 V. I can get 200 A at a bit over 1 V from a single turn on a big toroidal transformer. > >OK, I admit I'm putting two and two together and getting about seven >but I believe one should get one's retaliation in first in these >circumstances! Any amendment along the lines suggested should be >prepared to sacrifice a fair degree of technical accuracy against the >need for the test to be cheap, quick and easy to perform. It doesn't call for technical accuracy. You zap the equipment with the 200 A current for the operating time of the protective device and the PEC either remains intact or doesn't. > >Nowadays, standards writing should not just about getting accuracy >and repeatability in testing but should also take into account the >need to ensure that the requirements (and hence the tests) are >actually possible to apply in the real world, and not just by people >at specialist test houses. > I quite agree, but as you indicate above, there isn't too much *active* support for that view. When I talk in the committees about low-cost testing, people tend to remain silent. In any case, at present it's difficult enough coping with the problems of the costly test equipment not measuring correctly or not being feasible (low-distortion, high- current mains supplies for IEC 61000-3-12, as a case in point). If you want a copy of the draft, to make comments to the BSI committee, please e-mail. Note that this offer can only be made to people in UK. Others should approach their national standards body. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
