The power supply PCB’s I see have holes or slots cut in them between the pointy conductors. The arc occurs across the air gap. This avoids the carbon tracking on the PCB condition raised below.
Gary T. From: Doug Powell [mailto:doug...@gmail.com] Sent: Friday, September 6, 2013 9:33 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Spark Gap PCB Layout on AC Mains Brian, I am personally opposed to such an idea. The first time I saw this was circa 1982 on an electronic security system; designed to tie into the public telephone network. The manufacturer wanted additional protection above the outdoor surge protector. The design involved two parallel zig-zag traces, one ground and the other telephone line with alternating points in close proximity. The problem with this is if the gaps you created ever activate, they always leave a permanent carbon track in the surface of the PCB. Given adequate time and humidity exposure, these tracks become conductive and leakage current can begin to increase dramatically. Eventually, this circuits will become permanently shorted. This the main reason for evaluating comparative tracking index (CTI) of insulating materials along with creepage evaluation. Best to simply use a glass or ceramic spark gaps which are inorganic and cannot produce carbon when arced (http://www.globalsources.com/manufacturers/Glass-Switching-Spark-Gap.html). thanks, –doug Douglas E Powell doug...@gmail.com<mailto:doug...@gmail.com> http://www.linkedin.com/in/dougp01 From: Kunde, Brian<mailto:brian_ku...@lecotc.com> Sent: Friday, September 06, 2013 9:56 AM To: EMC-PSTC@LISTSERV.IEEE.ORG<mailto:EMC-PSTC@LISTSERV.IEEE.ORG> Subject: [PSES] Spark Gap PCB Layout on AC Mains Our engineers are working on an AC Mains Distribution PCB. Like most electronic devices, we have seen the damage caused by lightning strikes. So we are increasing our creepage and clearance distances as wide as we can and still meet other requirements. But no matter what spacing you design to, there is a lightning bolt out there that will exceed the design and it will arc somewhere. So the question came up to whether it makes sense to deliberately make a weak spot, or an area where the clearance is slightly smaller to control where a lightning/surge pulse will arc and/or discharge, like a Spark-Gap. I have seen spark-gap lay outs on PC boards on I/O connectors; usually for ESD protection, but not on AC Mains. Is this a bad bad idea or something worth doing? Pros and Cons? Other suggestions?? Thanks to all for your help. The Other Brian ________________________________ LECO Corporation Notice: This communication may contain confidential information intended for the named recipient(s) only. If you received this by mistake, please destroy it and notify us of the error. Thank you. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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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://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
