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 On 12/15/2010 11:27, JIM WIESE wrote: > 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) > [email protected] > > - ---------------------------------------------------------------- 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]>
