Hello esteemed colleagues, In IEC 60950:1999 table 2J; EN 60950:1992 table 4; UL 1950:1998 table 4 and several previous versions of each of these, I am having trouble interpreting the Additional Clearances Table, sometimes referred to as repetitive peak clearances. All these standards derive from the IEC so I will restrict the my comments to IEC 60950:1999 alone. My concern is with the Maximum Peak Working Voltage in each of the first three columns of table 2J. There are two voltages listed, the foot note indicates that the values in parenthesis are used in accordance with table 2H item 2). This in turn says that if a manufacturing process is subjected to quality control program with same level of assurance as Annex R2, then the values in parenthesis may be used. Annex R2 indicates that if I want to use reduced clearances, I may test and inspect for closely controlled dimensions of the insulating materials. The bottom line is that under certain controlled conditions, a product may use reduced spacings. Sounds good for me when space is always at a premium. Here's the gotcha... When I look at Table 2H, the clearance values in parenthesis are indeed smaller, as might be expected for better quality material. For example: 150Vrms, Mains <150V, PD 2, the reinforced clearance is 2.0mm. For closely controlled dimensions (Annex R2) it is 1.0mm. So far so good. When I look at Table 2J, the values in parenthesis are the voltages not the clearances. And in fact the voltage value was reduced not the clearance value, effectively increasing the physical clearance requirement for closely controlled dimensions at the same voltage applied, not decreasing. Stated another way, if I invoke Annex R2, I must reduce the applied voltage for the same clearance value! I am missing something here??? For how many revisions has this actually been in the standard? It's really hard for me to believe that I am the first to notice the problem. Comments from any and all are welcome, but I would be especially interested to know if an members of TC77 are in this group and if they have an explanation. BTW - I don't think I will be taking advantage of the increased clearance requirements any time soon, especially when I have better quality control over my materials. Respectfully, -doug
================================= Douglas E. Powell Regulatory Compliance Engineer Advanced Energy Industries, Inc. 1625 Sharp Point Dr. Ft. Collins, Co 80525 mailto:[email protected] <mailto:[email protected]> http:\\www.advanced-energy.com\ <http://www.advanced-energy.com/> ================================= ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
