Hi Rich, Yes, I obtained a copy of Mr. Stimper's book in 1995 and after learning it is no longer published in English, I obtained permission from him to use it in my own work; with proper attribution. This book is an excellent the resource. I first learned my compliance with IEC, DIN-VDE and EN standards. When I was finally exposed to UL standards it was somewhat discouraging and felt like taking many steps backward. As a result of that experience, I occasionally like to challenge the status quo.
I can't help but wonder if the old school UL spacings were somehow based in industrial equipment for rather dirty locations. All the best, Doug On Tue, Jan 25, 2022 at 12:38 PM Richard Nute <ri...@ieee.org> wrote: > > > > > Hi Doug: > > > > I don’t have any history. But I do have data for how air behaves as an > insulator and protection methods for creepage distances. > > > > The data for air insulation as a function of distance (2000 meters > altitude) and field shape was given in IEC 664, first edition, 1980. The > data was not carried over to later editions. The upper line is for a > homogeneous field, the lower line for an inhomogeneous field. I believe > the changes in slope are due to anomalies in the measurement method (they > should be straight lines). The lines converge at about 327 volts, the > Paschen lower limit for air. (It makes no sense to require clearances for > voltages below the Paschen limit!) > > > > > > Creepage distances were researched by Klaus Stimper, “The physical > fundamentals of low-voltage insulation co-ordination,” VDE 57, 104 pages. > I have this but it is too large a file to send by e-mail. If you are > interested in studying this text, I can make this available in Dropbox. > > > > Best regards, > > Rich > > > > > > > > *From:* Douglas E Powell <doug...@gmail.com> > *Sent:* Tuesday, January 25, 2022 10:27 AM > *To:* EMC-PSTC@LISTSERV.IEEE.ORG > *Subject:* [PSES] UL Standards - Old School Spacings > > > > All, > > > > I'm interested in learning the history behind what I call old school > spacings found in UL standards. In recent years there has been > considerable progress toward harmonizing UL spacings to international > standards, derived from IEC 60664-x. However, still today I encounter > many UL standards with the old spacings table (interpolation is not > allowed). > > > > Circuit Ratings > V > > *Minimum Spacings* > > > *Through air*Between parts of opposite polarity, > live and non-current carrying parts > and live and ground connections > mm (in) > > *Over surface* > Between parts of opposite polarity, > live and non-current carrying parts > and live and ground connections > mm (in) > > 30 - 50 > > 1.6 (1/16) > > 1.6 (1/16) > > 51 - 150 > > 3.2 (1/8) > > 6.4 (1/4) > > 151 - 300 > > 6.4 (1/4) > > 9.5 (3/8) > > 301 - 660 > > 9.5 (3/8) > > 12.7 (1/2) > > 661 - 1000 > > 19.1 (3/4) > > 19.1 (3/4) > > > > I've had more than a few "discussions" with design engineers about tables > like this since the numbers seem very arbitrary, and I have to agree. The > most frequent trouble I have is trying to explain why an increase of just 1 > volt over 300V results in such a large jump in the over surface > requirements. Usually I am forced to end with, "it is what it is, and we > have to follow the rules". > > > > Any thoughts? > > > > -Doug > > > > Douglas E Powell > > Laporte, Colorado USA > > doug...@gmail.com > > LinkedIn <https://www.linkedin.com/in/coloradocomplianceguy/> > > > -- -Doug Douglas E Powell Laporte, Colorado USA doug...@gmail.com http://www.linkedin.com/in/dougp01 - ---------------------------------------------------------------- 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 Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. 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: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>