I read in !emc-pstc that Rich Nute <ri...@sdd.hp.com> wrote (in <200204262205.paa10...@epgc264.sdd.hp.com>) about 'EMC and Class 2 equipment', on Fri, 26 Apr 2002: > > > >Hi John: > >> >Ground connections is usually nice to have when dealing with EMC. But what >> >about EMC and a class 2 (double insulation) power supply (shall comply >> with >> >MIL-STD-461E) ..... I'm thinking on, what to do with the regularly >> Y-caps, >> >does it really have any meaning with these caps when ground is absent? >> >> No, it has no meaning. A Y-cap is earthed/grounded at one end. If there >> is no earth/ground, there is no Y-cap, by definition. > >No. > >According to IEC 384 (1981) > > "Capacitor of Class Y > > "A capacitor of a type suitable for use in situations where > failure of the capacitor could lead to danger of electric > shock."
That was the formal definition in the component standard 20 years ago. Now we have sub-classes Y1 to Y4. Y capacitors can be used in locations where neither side is grounded, but in the OP's context, grounding is involved. > >A Y-cap can be used between primary and secondary of a Class II >product and it is still designated a Y-cap. Such construction >is not uncommon for EMC suppression in Class II products. How does that suppress emissions? It seems to me that they would be encouraged. > >Y-caps of relatively small values are also used across the >isolation barrier of a modem, e.g., from TNV circuits to SELV >circuits. In such applications, the Y-cap is not connected to >the primary circuit and is not connected to ground. It is a >signal-carrying component used in a situation where failure of >the capacitor could lead to danger of electric shock (from the >telephone line). I can't find any Y-rated components of the type you imply. What values are involved? -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
