All, I was reviewing the rationale document IEC TR 62368-2 and found a comment in 5.4.3: "*However, there is no rationale why the creepage distances are different for printed wiring boards and other isolation material under the same condition (same PD and same CTI). *"
Apparently some important concepts have been lost over the years. So I am writing this email to provide a historical perspective that is a detailed basis of my understanding for this concern. I have personally studied the IEC 60664-x standards since the days it was simply known as IEC 664A. This, along with the old VDE 0160 which was eventually the basis for EN 50178. This European Norm was strongly influenced by the 664 family of standards. EN 50178 has a reference to reduced creepage distances for printed circuit boards. Back in the day, the rationale, as explained to me through DIN VDE 0160, EN 50178, and by representatives at LGA Landesgewerbeanstalt Bayern, was that printed circuit material has very well controlled tolerances and is dimensionally stable. Therefore, if it passes the engineering type tests, then there is very good confidence that subsequent manufacture will remain so. When I asked if the fact that most PCB laminate material is CTI III, and if this makes any difference, the answer was consistently No. EN 50178 (1997 & 1998) Table 6 Minimum Creepage Distances, has a note referring to PCBs for Pollution Degree 1 and 2: "*These columns apply also to components and parts on PCBs and to other insulation arrangements with a comparable control of tolerances*" This was thinking in those days and yes a rationale does exist. Also, as I understand it, this rationale came out of a many months long German-American research project: *Schau, P.v., Middendorf, W.H.: An International Research Project to Determine New Dimensioning Rules for Creepage Distances.IEEE Trans. on Electrical Insulations, Vol.EI-18, No.2, April 1983; *https://ieeexplore.ieee.org/document/4081070/ I really would like to review the original IEEE paper but unfortunately it is locked in my subscription. -Doug Douglas E Powell Laporte, Colorado USA doug...@gmail.com LinkedIn <https://www.linkedin.com/in/coloradocomplianceguy/> (UTC -06:00) Mountain Time (US-MDT) - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com> _________________________________________________ To unsubscribe from the EMC-PSTC list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1
