I've had personal experience with lightning coupled transients to the secondary, strong enough to burn out an office Mr Coffee pot. Interestingly, if you have a transformer in the coupling path and the windings are oriented to normally invert a sine wave, the transient will likely not be inverted. This is because the coupling is through inter-winding capacitance and not the transformer core flux. This can usually be simulated with the IEC 61000-4-5 test as well.
-Doug Laporte, Colorado USA doug...@gmail.com LinkedIn <https://www.linkedin.com/in/coloradocomplianceguy/> (UTC -07:00) Mountain Time (US-MST) On Fri, Dec 2, 2022 at 3:17 PM Richard Nute <ri...@ieee.org> wrote: > > > > > Hi Steve: > > > > Mains circuits are subject to lightning and switching transients both > line-to-neutral and line/neutral-to-ground. The transients are normal; to > prevent insulation breakdown and consequential electric shock, the electric > strength of mains-to-ground and mains-to-other circuits insulations must > exceed the expected transient voltages. (Electric strength requirements > based on transient voltages are specified in IEC 60664-1, supported by > research by Stimper.) > > > > The mains transients can be capacitively coupled to secondary circuits, > depending on the configuration of the isolation scheme. In most cases, the > isolation scheme and the impedance of the secondary circuit attenuates the > transient voltage to near zero. This point seems to be recognized by IEC > 60101-1. > > > > Then, as Brian Kunde has said, secondary circuit devices such as relays, > solenoids, and switching can generate transients in the secondary > circuits. In most cases, such transient voltages are small and are > attenuated by the secondary source impedance. > > > > IEC 60601-1 has a similar requirement, although it includes clearance > requirements for no-transient secondary circuits. IEC 62368-1 does not > have such a requirement. I wonder what evidence or research supports > transient voltages in secondary circuits? > > > > Best wishes for the holiday season, > > Rich > > > > *From:* Steve Brody <sgbr...@comcast.net> > *Sent:* Thursday, December 1, 2022 12:51 PM > *To:* EMC-PSTC@LISTSERV.IEEE.ORG > *Subject:* [PSES] Secondary creepage/clearance > > > > I have a client who has a secondary pwb that has traces and vias that may > have 100 vdc on them adjacent to ground. > > > > Per 61010-1 there is a requirement for spacing and/or dielectric test, > both depending on what the mains voltage is. > > > > The question is why is the mains voltage a consideration or concern if the > 100vdc secondary voltage is several layers of impedance and circuitry from > the mains? > > > > Is it a concern that a surge on the mains would trickle down to the > secondary circuit, or is there another reason/rationale? > > > > I suggested that a dielectric test per Table 6 [in A1] would suffice and > put the issue to rest for this product, but the question from the designers > remains as to why is it a concern in the standard of what the mains voltage > is. > > > > Is there anything in the standard, that I haven't found, that does not > require Table 6 to be followed if there is no way for a mains surge to > impact the secondary voltage? > > > > I look to the experts for an explanation. > > > > Thanks, > > > > Steve Brody > > sgbr...@comcast.net > > C - 603 617 9116 > > - > ---------------------------------------------------------------- > > 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 > > 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: > Mike Cantwell <mcantw...@ieee.org> > > For policy questions, send mail to: > Jim Bacher <j.bac...@ieee.org> > David Heald <dhe...@gmail.com> > ------------------------------ > > To unsubscribe from the EMC-PSTC list, click the following link: > https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1 > - > ---------------------------------------------------------------- > > 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 > > 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: > Mike Cantwell <mcantw...@ieee.org> > > For policy questions, send mail to: > Jim Bacher <j.bac...@ieee.org> > David Heald <dhe...@gmail.com> > ------------------------------ > > To unsubscribe from the EMC-PSTC list, click the following link: > https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1 > - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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