Chris, interesting discussion I had today with UL. Per UL 1012, Clause 28A.1.7 "With respect to evaluating spacings, spacings between uninsulated parts of different circuits shall be based on the highest of the circuit voltages" Per Clause, primary spacings between the traces of earth ground and secondary are required. But what really got me was there was no reference in terms of rating components in this case, such as the proposed cap. Interesting dilemma
-----Original Message----- From: Maxwell, Chris [mailto:[email protected]] Sent: Tuesday, December 19, 2000 12:54 PM To: 'Ed Eszlari'; [email protected]; [email protected] Subject: RE: Spacings Issue I don't get this one? And I'm not ashamed to ask the questions that confuse me. Maybe some of the more safety oriented people can shed some light on this subject. (See Ken's original email at the bottom.) Capacitors between secondary circuits and chassis ground needing to meet High Voltage isolation requirements? I can only think of a few of scenarios where high voltage safety testing of secondary caps might apply. One would be if your "secondary" is still carrying lethal voltages with enough energy to be considered "hazardous". The other would be if your primary to secondary isolation doesn't include double insulation or equivalent. Another case would be TNV circuits. But TNV circuits aren't "secondaries". They are their own class of potentially lethal circuits that I consider much like a primary. There may be other instances, such as high voltage measuring circuits ... In my experience, our secondaries are considered "SELV" (if their ground is floating) or "SELV-E" (if they reference Earth ground) because they carry non-lethal voltages, have low energy and they are isolated from primaries and TNV with double insulation. We have all sorts of capacitors that reference these SELV secondaries to chassis ground. We never once think about their high voltage withstand and/or isolation. These products have been safety tested at a third party lab with no problems. So what gives? Maybe Ken has a secondary that violates one of these principles (either voltage, energy or isolation)? Maybe that is why his agencies are considering short circuit testing? I especially wonder why they would short primary to secondary. I could only see a reason for this if there was no double (or, in some cases, re-inforced) insulation from primary to secondary. My understanding is that shorting double insulation constitutes a double fault test. The safety standards that I am familiar with require only single fault testing. Is there something that I'm missing here? Happy Holidays! Chris Maxwell, Design Engineer GN Nettest Optical Division 6 Rhoads Drive, Building 4 Utica, NY 13502 PH: 315-797-4449 FAX: 315-797-8024 EMAIL: [email protected] > -----Original Message----- > From: Ed Eszlari [SMTP:[email protected]] > Sent: Tuesday, December 19, 2000 9:34 AM > To: [email protected]; [email protected] > Subject: Re: Spacings Issue > > > > Hello Ken, > > First of all the "floating secondary ground" (if not connected directly to > earth) should be treated as part of the secondary circuit which in many > cases will require reinforced insulation to the primary circuit according > to the working voltage measured. Next, in most applications, the > secondary circuitry can be cap coupled to earth ground and does not > require basic insulation spacings for a primary circuit. I have seen > equipment which incorporates TNV circuitry that does require supplemental > insulation spacing at the primary working voltage from the TNV to earth > due to Nordic Country deviations. I believe this is required due to poor > earthing in these countries, and the thought is that if the safety earth > was removed, reinforced insulation will remain between the primary > circuitry and the TNV (basic + supplemental = reinforced). This is the > information I had received in the past, but maybe some others in the group > can provide you with more information. > > Ed > > >From: "Matsuda, Ken" > >Reply-To: "Matsuda, Ken" > >To: [email protected] > >Subject: Spacings Issue > >Date: Mon, 18 Dec 2000 18:37:22 -0500 > > > > > > > >Hello Group, > > > >A circuit uses a floating ground in the secondary, and caps are used for > >protection from the secondary outputs to earth ground. The question is, > >under spacings requirements, would the secondary have to meet the high > >voltage requirements for spacings for primaries due to this earth ground. > > >A few agencies have expressed desires to short the primary to secondary > and > >require the the secondary to meet primary voltage spacings to this earth > >ground trace. > > > >Any help would be greatly appreciated. And thanks again for all your > >opinions > > > > > > > >Thanks, > > > >Ken Matsuda > > > >------------------------------------------- > >This message is from the IEEE EMC Society Product Safety > >Technical Committee emc-pstc discussion list. > > > >To cancel your subscription, send mail to: > > [email protected] > >with the single line: > > unsubscribe emc-pstc > > > >For help, send mail to the list administrators: > > Jim Bacher: [email protected] > > Michael Garretson: [email protected] > > > >For policy questions, send mail to: > > Richard Nute: [email protected] > > > > > > _____ > > Get your FREE download of MSN Explorer at <http://explorer.msn.com> > > > ------------------------------------------- This message is from the IEEE > EMC Society Product Safety Technical Committee emc-pstc discussion list. > To cancel your subscription, send mail to: [email protected] with the > single line: unsubscribe emc-pstc For help, send mail to the list > administrators: Jim Bacher: [email protected] Michael Garretson: > [email protected] For policy questions, send mail to: Richard Nute: > [email protected] ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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