Ralf I think I pretty muchagree with you !
Most of the standards are developed in partial isolation from many others -> different standards say same/different things in different ways. Occasionally some group sits down and shakes the bones out a standard - but mainly they just patch the old version and finish up with something they understand, and many other people (particularly those who have to apply it for self-certification purposes) can't and never will. It is only when you take a document apart sentence by sentence and then reassemble it so that you have a series of questions to which there are only THREE possible answers (compliant, non-compliant and not-applicable) that you can get a document that will (probably!) make sense to most people, or at least they can see where it does not. The resulting document is long and detailed - but at least it is pretty clear and most engineers can read and understand it logically. (I did that to 60950:1992 and someone else on this forum did that to an earlier version of 61010 - but we nevcr had the time and effort update our documents). I say this as an ex-BSI standards project manager who has seen too many cut and paste jobs - and whilst I have the greatest of respect for those who do the committee work (it can be mind-numbingly tedious at times!), I think that far more effort should (in general) be put into making standards into clear, precise and non-ambiguous documents (and with FAR fewer ambiguous and confusing cross-references in particular) than is currently the case. Then questions like the one that started this thread would be far fewer, and we would all have much less trouble overall. John Allen (from home) ----- Original Message ----- From: "Ralph McDiarmid" <[email protected]> To: <[email protected]> Sent: Monday, December 08, 2003 5:54 PM Subject: RE: UL60950-1 update There appears to be something desperately wrong with the way standards like this one are written and developed. The 60950 in particular appears to suffer from the bloatware phenomenon and the definition of SELV appears to be inconsistent between standards. ("too many chefs" perhaps?) As I read more of these standards, I become more discouraged and they really need not be so complex. Ralph McDiarmid, AScT Compliance Engineering Group Xantrex Technology Inc. From: Peter L. Tarver [mailto:[email protected]] Sent: December 5, 2003 3:26 PM To: EMC-PSTC - forum Cc: Sylvia Toma; Jim Eichner Subject: RE: UL60950-1 update Sylvia is right, at first glance. But all is not necessarily revealed by reading Table 5B and assuming ยง5.3.4 applies. The referenced column in Table 5B, Part 1, is for secondaries within ELV/SELV voltage limits to chassis and between independent secondary circuits of 'similar' circuit types. BUT ... one must be careful and read all of the applicable kibbles and bits. For instance, in reviewing Table 2G, Figure 2F with Table 5B: 1) an ELV Circuit and an unearthed SELV Circuit are within the same voltage limits where the referenced column of Table 5B seems to apply 2) assume the ELV Circuit has Basic Insulation to a Primary Circuit 3) also assume the SELV Circuit is unearthed 4) Figure 2F indicates ELV to unearthed SELV requires Supplementary Insulation (S1), but there's no Supplementary EST value in Table 5B 5) Table 2G, for S1, refers to Condition 2 of that table 6) Table 2G, Condition 2 states that the worst-case voltage involved for the Basic Insulation is used to determine the insulation requirements, in this example, between the ELV Circuit and the Primary Circuit 7) the ELV Circuit to unearthed to the SELV Circuit requires an EST based on Supplementary Insulation in one of the five columns (two through six) of table 5B If this example is faulty, someone let me know. Regards, Peter L. Tarver, PE [email protected] > From: Sylvia Toma > Sent: Friday, December 05, 2003 11:00 AM > > There is no test for Basic, Supplemental, or > Reinforced insulation since > for those three categories; you need to meet the > spacing requirements. > > For Functional insulation, you can conduct hipot > test in lieu of spacing per sub-clause 5.3.4. > > > From: Jim Eichner > Sent: Friday, December 05, 2003 10:15 AM > > I have a question about 60950-1 based on what I > suspect might be an error. > > In Table 5B listing voltages for hipot tests, the > second last column from > the right shows a 500V test for Functional > insulation but no test for Basic, > Supplemental, or Reinforced insulation. Is this > an error or am I missing > something? It seems to me that this should be reversed. > > Thanks, > > Jim This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
