In message <63056535adcf774b87d41a999d9a7f2b23732...@bct1e2k301.americas.tsp.ad>, dated Tue, 21 Dec 2010, "Goedderz, Jim" <[email protected]> writes:
>Is there any additional response to Pat's inquiry? I would also like to >know the justification of a VDR/gas discharge tube connection in the >primary circuit. > >It would be useful to have that available. Some information became available very recently. This is not a standard or even an official interpretation of a standard. I suppose it is advice having a strong provenance: TC108 position on varistors having connection to the mains, also identified as voltage dependent resistors (VDR) and metal oxide varistors (MOV). During the recent TC108 meetings in Seattle, October 2010, the use of varistors having connection to mains circuits was discussed. There seemed to be different opinions and interpretations regarding the requirements contained in several of the TC108 standards. This INF document is intended to clarify the current interpretation of TC108 on those aspects where agreement has been reached. Some issues are still under discussion and these will be explained as soon as possible. Existing requirements not addressed below remain applicable. The following statements are supported by the experts and the management of TC108 on the application of varistors in the IEC 60065, IEC 60950-1 and IEC 62368-1 standards. -------------------------------------------------- Compliance with IEC 61051-2 Where a varistor is used in connection with the mains, it shall comply with IEC 61051-2. The combination pulse test of IEC 61051-2:1991, Am 1:2009 (2.3.6, Table I group 1 and Annex A), including consideration of the nominal mains voltage and overvoltage category, should be allowed as an alternative to the requirements in the current standards. Protection of varistors Where a varistor is used in parallel with the mains connection, it should be protected against temporary overvoltages, overloads or short circuits. Details can be found in IEC 60950-1, clause 1.5.9.2. Varistors in series with a GDT (for all types of equipment, including 'normal' Pluggable Type A equipment) Where a varistor in series with a GDT is used to bridge BASIC INSULATION, the following applies: – the varistor has to comply with IEC 61051-2 as indicated in the standards; and – the GDT has to comply with: • the electric strength test for BASIC INSULATION; and • the external CLEARANCE and CREEPAGE DISTANCE requirements for BASIC INSULATION. It should be noted that the use of a VDR in series with a GDT to bridge reinforced insulation was also discussed. So far, no agreement was reached within IEC TC108. -------------------------------------------------- It should be noted that each of the mentioned standards is currently being revised under the TC 108 maintenance procedures and these clarifications will be introduced in the relevant standards as deemed necessary. -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK Plural: data, criteria. Singular: datum (different meaning: use 'data element' for a single item), criterion. 'Effect' is a noun, 'affect' is a verb (except in psychiatry). - ---------------------------------------------------------------- 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]>
