Important EMI consideration: Two Y-caps in series = lower capacitance, twice the parasitics, less filtering, and thus more conducted EMI.
There is no free lunch: "Bomb-proof" Y cap design = reduced EMI performance, unfortunately. I agree with the statements that Y caps are exceedingly reliable and that the need to put them is series is slim. The only applications that I am aware of that *don't* use Y-caps are those that have extremely high requirements for leakage current such as some classes of medical devices. (I am humbled by the ability of our medical device compliance colleagues to meet all the regulatory requirements without these Y-caps.) ...Marko From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of rn...@san.rr.com Sent: Monday, January 14, 2008 1:18 PM To: 'Brian O'Connell' Cc: emc-p...@ieee.org Subject: RE: Y1 cap info Hi Brian: > While our design technically conforms to the requirements of > 60950-1, I do > not feel 'right' about a single component bridging either > primary/secondary, or primary/floating metal in a Class II > unit until I > can learn more about Y1 cap reliability and typical failure > modes, so I > have no information for a case-by-case basis. Stress and reliability requirements for Y-capacitors are specified in IEC 60384-14 and UL 1414. If the capacitors are certified, these standards are quite good at getting reliable parts. Study the standards, and you may feel better about using a single Y1 cap. Y1 capacitors are rated for reinforced insulation, and can be used in Class II equipment between mains and accessible parts, including SELV. I've had no hesitation in using certified Y1 caps in such applications. And, I've had no failures of certified Y1 or Y2 caps. Since EMC requirements came into effect, virtually every product has employed certified Y1 or Y2 caps. This is a very good base for judging reliability. I'm not aware of any Y-cap field failure problems. For typical failure modes, contact your Y-cap manufacturer. Failure modes are likely unique to each manufacturer. If you are still concerned about reliability, and if cost is not an issue, use two Y caps in series. Y2 caps are rated for basic or supplementary insulation. Or, to be super-conservative, use two Y1 caps in series. Best regards, Rich - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.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 emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.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 emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
