http://www.ieee-pses.org/symposium http://www.emc2004.org/ -------------------------------------------------- At 08:50 PM 5/27/2004, Eric Meunier wrote:
I found that many components rated at 100VDC do not allow for the 1.4mm creepage specified in table 2L for the PCB land patterns and component body. Also, low voltage control circuits have much less than the 1.2mm creepage specified for 50VDC and below. Based on section 5.3.4 c), it seems that these spacing requirements can be waived where there is no risk of fire or damage to nearby Basic insulation. The PCB on which the components will be mounted is FR-4 rated V0. Hi Eric: In my experience, most test labs focus exclusively on the isolation barriers between different types of circuits, such as SELV-to-Hazardous, SELV-to-TNV, etc. A literal interpretation of 60950 would appear to require extensive analysis of the relative voltages among all the different nodes within a given circuit type, in order to ensure that the creepage, clearance, and dielectric withstand requirements are met for each and every combination. In practice, this type of analysis becomes quite complicated, and full compliance is seemingly impossible. Fortunately, I think that clause 5.3.4 (and possibly some similar exemptions elsewhere in the standard) are routinely used to bypass the detailed analysis within a given circuit type. I have not looked at these exemptions for several years, so the exact wording of the present clause 5.3.4 looks a bit different from what I recall. In particular, clause 5.3.4 seems to be limited to "insulation between a Secondary Circuit and an inaccessible conductive part that is earthed for functional reasons." My recollection is that these exemptions are more broadly applied for general evaluation of the internal aspects of any given circuit type. Perhaps the reference to clause 5.3.4 that appears in clause 2.10.1 is the reason that these exemptions are more broadly applied. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 (USA) [email protected] http://www.randolph-telecom.com <http://www.randolph-telecom.com/> ------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. IEEE PSES Main Website: http://www.ieee-pses.org/ To post a message send your e-mail to [email protected] Instructions for use of the list server: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
