Sorry all, I knew the listserv would not support images, but since it regularly sends me HTML email, I had thought it would allow tables in the body of the email <table> </table>. Hopefully you'll still get the gist of the email.
~Doug On Tue, Jan 25, 2022 at 11:26 AM Douglas E Powell <doug...@gmail.com> wrote: > 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>
