John, Very interesting. We'll have to keep this in mind.
We do have a dual pole contactor in the furnace circuit but the furnace also has a SSR for phase control. The contactor only opens and closes when the SSR is open (no current). The harmonic emissions from the phase control is why we have the large RF Line Filter. Thanks for the information. The Other Brian -----Original Message----- From: John Barnes [mailto:[email protected]] Sent: Tuesday, September 22, 2015 11:53 PM To: [email protected] Subject: Re: [PSES] Unexplained High Fallout of Power Supplies Brian, How is the furnace shut off? If you are using a contactor between the main line filter and the furnace, a phase line might open when it is carrying high current. The inductance of the line filter will try to keep this current flowing, generating a very-high kickback spike at the *output* of the line filter. Or, since the contacts in the contactor are unlikely to open/close at exactly the same time, a common-mode choke in the line filter can act as a transformer putting noise on the open phase(s) if only 1 or 2 phases are connected to the load. Some years ago, Bill Kimmel and Daryl Gerke wrote about a case where a 3-phase product had a contactor between a line filter and the load, which generated horrendous Conducted Emissions noise every time the contactor opened or closed, because of this transformer action. The solution was to replace the common-mode choke with 3 separate chokes, one for each phase line. John Barnes KS4GL, PE, NCE, NCT, ESDC Eng, ESDC Tech, PSE, Master EMC Design Eng, SM IEEE (retired) Lexington, KY http://www.dbicorporation.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 <[email protected]> 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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]> ________________________________ 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. To post a message to the list, send your e-mail to <[email protected]> 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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
