Rich, The issue we ran into with this is that UL and other NRTL's require factory hi-pot testing on AC interfaces as part of follow-up services. The product will obviously fail at that point. The original 60950-1 safety testing is done with the VDR's removed. But for the factory hi-pot the VDR's often cannot be removed without disassembly of the product, and even if they could be removed it violates the intent of the test, which is to perform the factory hi-pot right before it is boxed up for shipping, not rip it apart, do a hipot, and then re-assemble the product.
As you point out the conditions necessary to allow the VDR's to ground in the first place already require the assumption that the VDR can go short and not create a hazard. So 60950-1 now allows the VDR's to ground, but the follow-up services and listing requirements for the factory hi-pot here in the US and Canada more or less prevent doing it. So, there should be some kind of waiver from the factory hi-pot if the product has VDR's to ground as permitted in 60950-1, but unless that happens it is silly to allow it in the UL/CSA version, unless people feel tearing a product apart to disable VDR's, then doing a hi-pot, then reassembling the equipment makes sense. Best regards, Jim Jim Wiese Senior Compliance Engineer ADTRAN, Inc. 901 Explorer Blvd. Huntsville, AL 35806 256-963-8431 256-714-5882 (cell) 256-963-6218 (fax) jim.wi...@adtran.com -----Original Message----- From: Richard Nute [mailto:rn...@san.rr.com] Sent: Wednesday, December 15, 2010 1:02 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] IEC 60950-1 Ed. 2 Class A Pluggable equipment and VDR bridging basic insulation. Hi Donald: A VDR is taken as a device that is likely to fail. If the VDR is connected between mains and the protective earthing system, then the PE system must be considered reliable, that is, equivalent to a reinforced safeguard. Ever since the days of 2-wire plugs and sockets, grounding by means of a domestic plug and socket has not been considered reliable (because you could not predict whether the installation was 2-wire or 2-wire plus ground). In order to have a reliable ground, the ground construction must be permanent or equivalent. (Equivalent is taken as by means of industrial- grade plug and socket schemes.) 1.5.9.4 specifies the equivalent grounding schemes. Yes, you are correct in that a VDR is not permitted to be connected to earth (ground) in pluggable equipment type A. Best wishes for a Merry Christmas, Richard Nute Product Safety Consultant San Diego On 12/14/2010 14:20, Donald McElheran wrote: > All: > > Under clause 1.5.9.4 "Bridging of basic insulation by a VDR" in the > latest version of 60950-1 > > Paragraph two: > > "Equipment with such a VDR bridging insulation shall be one of the > following: > > - equipment that has the provision for a permanently > connected PROTECTIVE EARTHING CONNECTOR and is provided with > instructions for the installation of that conductor. > > > This requirement appears to rule out the use of power supplies making > use of earthed VDRs in their primary circuits, if used in "Pluggable > Equipment Type A" if a separate earthing terminal is not provided. > > Could anyone confirm that this interpretion is correct and wether this > was the intent of the committee. > > Donald McElheran > Product Compliance Specialist > Ross Video | Live Production Technology > www.rossvideo.com > +1 (613) 652-4886 > - ---------------------------------------------------------------- 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://product-compliance.oc.ieee.org/ Graphics (in well-used formats), large files, etc. can be posted to that URL. 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> - ---------------------------------------------------------------- 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://product-compliance.oc.ieee.org/ Graphics (in well-used formats), large files, etc. can be posted to that URL. 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>
