This information is very timely since I am currently working on a project that requires varistors to ground. The varistors are not approved. How does one size the spark gap firing voltage and the fuse value? I am concerned with the fuse opening when the equipment sees a transient.
Also, if the equipment contains a circuit breaker, is the fuse necessary? Thanks, Jeff Jenkins Senior Regulatory Compliance Engineer Advanced Energy Industries, Inc. Fort Collins, CO USA 80525 Opinions are my own and not necessarily shared by Advanced Energy Industries, Inc. or its affiliates. -----Original Message----- From: Volker Gasse [mailto:ga...@de.ibm.com] Sent: Tuesday, December 15, 1998 3:34 AM To: emc-p...@majordomo.ieee.org Subject: RE: Varistors to ground The mentioned Cenelec decision is taken from the 'List of decisions from CENELEC Operational Staff Meeting for Electronic Equipment (OSM/EE)'. Here representatives from EU Testhouses meet to discuss interpretations of clauses in safety standards such as EN 60950 for IT products. These decisions are to be followed by all European testhouses. However, those decisions should be interpretations/clarifications to the existing standards, but not addition of new requirements. For EN 60950, Clause 1.5.1, Decision 98/2 states: 'A combination of a varistor in series with a spark gap (Gas-Tube) [between the mains and the protective earth] complying with Basic Insulation, and with a fuse will be accepted for a. Pluggable equipment Type B and permanently connected equipment: by all countries b. Pluggable equipment Type A: by all countries except DK, UK and SE. For pluggable equipment Type A two fuses are required.' (To be sure that even by non-polarized plugs a fuse is provided) This interpretation is an extension to a decision which was already issued in 1/94: 'If a Varistor is separately approved according to Publications IEC 601051-1 and IEC 601051-2, it can be accepted without a protective device. If a Varistor is not separately approved, a protective device against the short-circuit is required. Varistors tested according to CECC 42200 are considered as acceptable in the same way as tested to IEC 601051. Varistors between the mains and the protective earth cannot be accepted by the following countries: Pluggable equipment, type A: Austria, Belgium, Denmark, Finland, Norway, Sweden, United Kingdom.' The new decision is not part of the upcoming safety standard for IT products, IEC 60950 3rd edition, which is likely to be available beginning of next year. One of the reasons for requiring the spark gap in series with the varistor is a possible increase in leakage current if the varistor has been exposed to several mains transients. It should be noted, that IEC/EN 60950 does not require the use of transient suppressing components. Concerning the mit freundlichen Gruessen/ best regards Volker Gasse IBM Germany, Technical Relations/Product Safety, Tel: +49 7031-16-6796, Fax: -6916, e-mail: ga...@de.ibm.com Mail: 3114/7103-91, D-70548 Stuttgart, Germany ---------------------- Forwarded by Volker Gasse/Germany/IBM on 15.12.98 11:20 --------------------------- owner-emc-p...@majordomo.ieee.org on 15.12.98 02:11:00 Please respond to jeich...@statpower.com To: j...@bighorn.dr.lucent.com cc: emc-p...@majordomo.ieee.org Subject: RE: Varistors to ground John: Sorry I can't help, but I am interested in what replies you get. I also wonder what force the Decision carries. Is it a mandatory part of the Low Voltage Directive? How does it relate to the LVD or to the various EN's in force under the LVD? Thanks in advance for any light you can shed on these murky waters! Regards, Jim Eichner Statpower Technologies Corporation jeich...@statpower.com http://www.statpower.com Any opinions expressed are those of my invisible friend, who really exists. Honest. > -----Original Message----- > From: Boucher, John [SMTP:j...@bighorn.dr.lucent.com] > Sent: Monday, December 14, 1998 9:07 AM > To: 'emc-p...@ieee.org' > Subject: Varistors to ground > > All: > > I have received a copy of a CENELEC Decision (dated 6/98) regarding > the use > of varistors between mains conductors and ground. This particular > Decision > is written in a rather unclear fashion (at least its unclear to me...I > tend > to be rather literal in my interpretations of written requirements), > and I > am struggling with defining the actual requirements. > > If anyone out there has received this Decision, and believes they are > clear > about what the actual bottom line requirements are, please let me > know. I > have muddled through some of the issues, but need some confirmation on > a > couple of points (see the questions below). It may seem to some that > the > answers to these questions are straight-forward in the Decision, but I > have > studied this Decision (maybe too much) and find these points unclear. > > 1) Is this Decision only for pluggable equipment type A, or is the > spark-gap > / fuse requirement in effect for pluggable equipment type B as well? > > 2) Will Denmark, UK, and Sweden accept varistors to ground if the > circuit > contains a spark-gap and two fuses? > > 3) The installation instructions for our PABX systems include the > requirement for a permanently connected ground wire between the > equipment > ground and an approved building ground (this ground wire is in > addition to > the "green wire" lead in the AC mains). This wire is required for all > our > PABX systems (AC and DC powered systems, pluggable type A, type B, and > permanently connected systems). Does this permanent ground connection > provide an exemption to this Decision? > > If this Decision means DK, UK, SE will simply not accept varistors to > ground, then a lot of small pluggable type A equipment intended for > sale in > DK, UK, SE will have to either: 1) discontinue using varistors, or 2) > become > pluggable equipment type B (which would be onerous, given the IEC 309 > plugs > I've seen). > > > Thanks for the help. > > John Boucher > jpbouc...@lucent.com > > > --------- > This message is coming from the emc-pstc discussion list. > To cancel your subscription, send mail to majord...@ieee.org > with the single line: "unsubscribe emc-pstc" (without the > quotes). For help, send mail to ed.pr...@cubic.com, > j...@gwmail.monarch.com, ri...@sdd.hp.com, or > roger.volgst...@compaq.com (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
