I am not positive, but I think this is just a North American glitch (UL/CSA). I think internationally you could make the justification that Rich pointed out that it is inherently safe and on these products skip a final AC hipot. So what if line and neutral are shorted to ground (other than for functionality reasons). The MOV's will short the line and neutral to ground at a couple hundred volts anyway and could fail short permanently.
If it is the case that internationally it isn't a problem, yet somehow domestically it becomes a safety hazard only due to the follow-up services required ac hi-pot aspect, something seems wrong. It just doesn't seem to hold water from a technical basis. 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: Kunde, Brian [mailto:[email protected]] Sent: Thursday, December 16, 2010 8:17 AM To: [email protected] Subject: Re: [PSES] IEC 60950-1 Ed. 2 Class A Pluggable equipment and VDR bridging basic insulation. Here is another clunky suggestion. What if you put your Surge Suppressor circuit after a dual pole circuit breaker that is only energized when the device is powered up. That way, the VDR is out of the circuit during the Hipot test, but in-circuit during the Surge Immunity test. This brings up a good point in regards to production hipot testing. Some of our instruments have double pole relays, so during hipot those downstream circuits do not get tested. So those circuits have to be individually hipot tested before the side panels are installed. As you said, this goes against the intent of the production hipot test, but what else can you do? You do the best you can. If an inspector disagrees, have him give you the solution. The Other Brian -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of JIM WIESE Sent: Wednesday, December 15, 2010 5:18 PM To: [email protected] Cc: [email protected] Subject: RE: [PSES] IEC 60950-1 Ed. 2 Class A Pluggable equipment and VDR bridging basic insulation. Thanks Rich, Your first paragraph is what I tried with the safety lab to no avail as they still required a factory hipot, which requires disassembly or some other form of clunky workaround as Brian mentioned. Brian's method could be feasible in some cases from the safety perspective to remove the MOV for the hipot, but lousy if you need a low impedance reliable path for thousands of amps of lightning current. It also is not feasible in most cases for potted or OSP sealed telecom equipment. Merry Christmas, 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 4:06 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: 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. 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