In a message dated 96-07-24, Brent Taira writes: >Is anyone aware of an agency approved Y1 capacitor (IEC 384-14, 1993 edition) >that is stable at high temperatures (X7R)? > >One more item - a VDE Engineer had informed me that I needed to use either 3 - >VDE 565-1 or 2 - VDE 560-2 approved capacitors in series between primary and >secondary (Reinforced Insulation). Could anyone provide insight into this? >Perhaps, I did not argue strongly enough?
Brent: The precise safety requirements for capacitors that bridge reinforced insulation have always confused me, and I do not claim to be an expert on this subject. However, I am under the impression that the Panasonic ECK-DNS series is suitable for bridging reinforced insulation. Values up to 1000 pF have a fairly stable temperature characteristic. I think that the notion of placing multiple caps in series stems from the reference to "insulation in thin sheet material" as described in subclause 2.9.4. Here, you can circumvent the requirement for 0.4 mm distance through insulation by using either two or three independent layers of insulation. Each capacitor can be viewed as a "thin sheet" of insulation. In the case of the Panasonic ECK-DNS series, I believe that the thickness of the dielectric exceeds 0.4 mm, so a single capacitor is sufficient. You may be interested to know that draft Amendment 4 to IEC 950 adds a subclause (2.2.8.1) that explicitly addresses bridging capacitors. It says that reinforced insulation can be bridged by any of the following: 1) A single capacitor that complies with IEC 384-14: 1993, subclass Y1 2) Two series caps that each comply with IEC 384-14: 1981, class U or Y 3) Two series caps that each comply with IEC 384-14: 1993, subclass Y2 or Y4 This amendment is not yet official, but it probably serves to show the direction that things are headed. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc.
