Hello fellow Homologator's: I have a question about Y capacitors used to bridge Supplementary or Reinforced insulation. The IEC 384-14 standard addresses this. My question relates specifically to bridging these barriers in ITE equipment, and application of the IEC 950 standards.
1) Is there a minimum distance through insulation requirement called out in the IEC 384-14 standard? A few people I have talked to say there is, but I have not been able to find it. (Maybe one of the other IEC 384 standards?) 2) The creepage and clearance distances called out in IEC 384-14 and IEC 950 are not the same. The 384-14 standard calls out larger external creepage and clearance distances for the caps than application of the 950 standard would. For example, table VII in IEC 384 calls out a minimum 4.0mm creepage distance, and the IEC 950 (table 6) standard would call out a minimum creepage of 2.5mm assuming material group III. How does one resolve this discrepancy when laying out the board? UL's standard response would probably be that the end-product standard takes precedence, in this case UL 1950. But what about Europe (EN 60950)? Australia (AS/NZS 3260)? 3) Every decision I have seen for EN 60950 product using Y caps to provide a supplementary barrier specifies a minimum of Y2 capacitor. Why can't a Y3 capacitor be used? Does this have to do with concerns about the overvoltage category? The reasoning does not seem to be clearly spelled out anywhere I have looked. The only difference between Y3 and Y2 capacitors that I can see is that the Y2 capacitor is subject to surge testing before the applicable endurance test, and the Y3 capacitor is not. Therefor, it would seem to me that a proper choice of capacitor would depend on the types of transients and surges that one would see, but this is not clearly spelled out in the 384-14 standard anywhere that I have seen. Do any other standard apply? Anyone with experiences using these types of capacitors in ITE equipment, your comments would be most appreciated!! Thank you for your help! Mel Pedersen Midcom, Inc. Homologations Engineer Phone: (605) 882-8535 [email protected] Fax: (605) 886-6752
