It's also important to consider servicing operations. If servicing is intended on the unit while powered, considering the secondary as not isolated from primary (and so not evaluated as a safe circuit) is problematic.
On Tue, Sep 14, 2021 at 7:51 AM Pete Perkins < 00000061f3f32d0c-dmarc-requ...@ieee.org> wrote: > Amund, I support Rich’s approach. > > > > It does leave a lingering question, though. (removing my > rose colored glasses and putting on my dark, pessimistic glasses) > > > > Imagine a downstream case such as this: The unit works > well and is popular. A customer request comes to the manufacturer > something to the effect that the unit works well except does not provide > the full operational reliability in cases where there is significant EMC > generated in the use area; they ask for an output (USB , PoE, etc) so that > they can cable connect the unit for these applications. A (different) > company designer believes that this is easy to do and starts to work on > this project. If you are lucky, he consults the earlier safety lab report > to understand the details to properly implement this. > > Where in the report do you clearly state that the > requirements, including isolation/insulation (creepage and clearance) were > not evaluated and the ‘secondary’ is considered mains in a clear way? > > With this understanding the designer will know that the > full mains isolation/insulation will have to be done for the output circuit > since it wasn’t done for the mains/secondary interface initially. (Since, > reasonably often, the unit won’t meet the mains/secondary requirements in > some way and the manufacturer will not be willing to change it in this > redesign cycle.) > > If this is not clearly taken care of initially then the > process starts down the slippery slope of believing that everything was > completed earlier and not fully reviewed at the modification step. If not > caught by the designer then the test lab catch will be a major complication > in the project schedule. If not caught by the test lab (your associate > down the hall) then the product is inadequate and does not meet the > requirements of the standard; hopefully this gets caught in the review but > what if it doesn’t? > > > > My point is that simplifications need to be clearly stated > in the documentation for downstream users. Don’t leave anything to > chance. > > > > :>) br, Pete > > > > Peter E Perkins, PE > > Principal Product Safety & Regulatory Affairs Consultant > > PO Box 1067 > > Albany, ORe 97321-0413 > > > > 503/452-1201 <(503)%20452-1201> > > > > IEEE Life Fellow > > IEEE PSES 2020 Distinguished Lecturer > > www.researchgate.net <http://www.researchgate.net/Peter%20Perkins> search > my name > > p.perk...@ieee.org > > > > > > Entropy ain’t what it used to be > > > > *From:* Richard Nute <ri...@ieee.org> > *Sent:* Sunday, September 12, 2021 3:05 PM > *To:* EMC-PSTC@LISTSERV.IEEE.ORG > *Subject:* Re: [PSES] Creepage and clearance requirements > > > > > > > > Hi Amund: > > > > If no accessible conductive parts, then you can designate the secondary > circuits as part of the primary circuits, which means there is no need for > isolation between primary and secondary circuits. No creepage or clearance > requirements! OVC would not apply primary-to-(a primary) secondary. > > > > The plastic enclosure would probably constitute reinforced insulation > throughout. For electric shock, you would wrap in foil and measure touch > current. Should be comfortably below the limit. And, you would need to do > a dielectric test to the same foil at twice the voltage necessary for basic > insulation. Should easily pass. > > > > I have assumed the antenna is within the enclosure so no accessible > conductive parts. If the antenna is an accessible conductive part, then > the above scenario is not valid. > > > > Stay safe, and best regards, > > Rich > > > > > > > > > > *From:* Amund Westin <am...@westin-emission.no> > *Sent:* Sunday, September 12, 2021 10:16 AM > *To:* EMC-PSTC@LISTSERV.IEEE.ORG > *Subject:* [PSES] Creepage and clearance requirements > > > > IEC60950-1: > > > > How about the Creepage and clearance requirements for an AC driven radio > HUB device. > > > > - One input: 230VAC (direct into wall socket) > - No physical output ports, just radio communication. > - Insulated plastic enclosure (UL94 V-0) > > > > The Creepage and clearance requirements between primary and secondary > circuits, does it make any sense as long as the device has no cables and is > encapsulated by a plastic enclosure > > I understand that there should be some Creepage and clearance to withstand > OVC II (250V transient). > > > > Best regards Amund > > > > > > - > ---------------------------------------------------------------- > > 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://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>
