Doug -- Joe Musso, staff engineer at UL, might be worth contacting.
About 10 years ago I was is a similar position with what I considered an outdated spacings table in UL 1450. Joe was the staff engineer supporting 1450 at the time. What Joe suggested, and what ended up working out well, was adding UL 840 (which is aligned with IEC 60664) as an alternate acceptable spacings requirement. This ballot item was easily approved and we never looked back. So we sidestepped any discussion of the old spacings table, but Joe might know more about why he wanted to keep it and what its origins are. Let me know if you need any language examples from the new section in UL 1450. BTW, anyone can write a proposed change to any UL standard at any time---you don't have to be on the committee. Copying language from another approved UL standard (e.g., 1450) gets you off to a strong start. And please share what you find out about these table values! thanks, Mike > On 01/25/2022 12:26 PM 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 mailto:doug...@gmail.com > LinkedIn https://www.linkedin.com/in/coloradocomplianceguy/ > - > ---------------------------------------------------------------- > > 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 mailto: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) http://www.ieee-pses.org/list.html > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <sdoug...@ieee.org mailto:sdoug...@ieee.org > > Mike Cantwell <mcantw...@ieee.org mailto:mcantw...@ieee.org > > > For policy questions, send mail to: > Jim Bacher <j.bac...@ieee.org mailto:j.bac...@ieee.org > > David Heald <dhe...@gmail.com mailto:dhe...@gmail.com > > - ---------------------------------------------------------------- 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>
