Hi Jim:
If the equipment is permanently grounded, then you can put in a VDR/MOV between mains and ground. Think of a permanent ground as a reinforced safeguard, with no need for basic insulation (in my opinion). For cord-connected equipment, IEC 62368-1 will likely require a series circuit of VDR and gas discharge tube. The big problem with VDR/MOVs is that we don't know the energy that must be dissipated by the VDR/MOV. If the energy is high enough, the VDR/MOV will be destroyed and you will have arcs to ground. Have a Merry Christmas! Rich On 12/15/2010 13:06, JIM WIESE wrote: > Hey Rich, > > The reason for VDR's (MOV's) to ground is to prevent arcing to the > chassis for customers that demand either 6KV or 10KV lightning tests. > The products are permanently grounded so the arcing to ground is not a > safety hazard at those levels. The products easily pass the hipot > without the MOV's to several KV (well above the hipot level). > > The arcing at 6 or 10KV often functionally kills the supply or other > circuitry, which of course 60950 could not care less about > functionality. But other standards do. > > It sounds like IEC 62368 will mess up using MOV's to ground though as I > am not aware of MOV's rated several KV. > > 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) > [email protected] > > > -----Original Message----- > From: Richard Nute [mailto:[email protected]] > Sent: Wednesday, December 15, 2010 2:01 PM > To: JIM WIESE > Cc: [email protected] > Subject: Re: [PSES] IEC 60950-1 Ed. 2 Class A Pluggable equipment and > VDR bridging basic insulation. > > > > Hi Jim: > > > Thanks for your remarks. > > You CAN remove the VDR during hi-pot testing. > This is specified in 5.2.2: > > "To avoid damage to components or insulation > that are not involved in the test, > disconnection of integrated circuits or the > like and the use of equipotential bonding are > permitted." > > This is for the "type" test, not the "routine" > test. Nevertheless, your point is well taken. > > Also note that 5.2.1 specifies: > > "The electric strength of the SOLID INSULATION > used in the equipment shall be adequate." > > So, the hi-pot test only applies to solid > insulation. > > The other option is to specify the VDR at a higher > voltage than the hi-pot test voltage. > > Regarding VDRs, I don't know why any equipment > would need a VDR between mains and earth. The > requirements for clearance, creepage, and solid > insulations require an electric strength at least > as great as the expected transient overvoltage, > regardless whether a VDR is between mains and > earth or not. So, the VDR does not protect > anything against any voltage up to the required > electric strength of the equipment. > > The VDR *may* be useful to protect against > transient voltages exceeding the required electric > strength.n which case it will pass the hi-pot > test. > > In the new IEC 62368, the requirement is that any > VDR between mains and earth shall be rated greater > than the required electric strength. > > > Best wishes for the Christmas season, > Rich > > > > > > - ---------------------------------------------------------------- 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://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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
