The requirement for "secondary protection" is based on the results of Type Tests for components that are across the line, and the requirements found in 1.5.9.2. The assumption is that the component is rated to be used across mains, and the box is Class I construction.
The best result for a surge is that when the varistor (MOV) conducts, the fault current has a low-Z path to the current interrupt device (input fuse) which quickly opens. In this case, the 'additional' protection is provided by a typical input fuse. Brian > -----Original Message----- > From: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf > Of Spencer, > David H > Sent: Wednesday, December 15, 2010 4:12 PM > To: Bill Owsley; EMC-PSTC@LISTSERV.IEEE.ORG; oconne...@tamuracorp.com > Subject: RE: OT A BIT........ [PSES] IEC 60950-1 Ed. 2 Class > A Pluggable > equipment and VDR bridging basic insulation. > > My safety people are telling me that part of Ed. 2 also > requires that VDR's line to line ( or line to neutral) have > secondary protection. > Either a fuse, gas tube, or double insulated cap. They > have been with great gusto been pulling out the VDR's or > replacing them with fused versions. > > From an EMC aspect, we never know when a VDR (from now on > MOV) goes bad. > > SO.... > > with respect to line to line (neutral) MOV's only and Ed.2 > > Do MOV's need a secondary protection? > > thanks for any comments > > Regards > > David Spencer > EH&S EMC Engineer > Xerox Corp > Is the VDR rating for 62368 conformity a working voltage or > surge rating ? - ---------------------------------------------------------------- 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>
