Frank, I have used coupling capacitors to bridge insulation several times in the form of frequency compensated voltage dividers and decoupling caps for opto - isolators. You will find in EN60950:1992 section 2.2.8.1 covers the subject. Other standards also often refer to "bridging" components. In EN60950 you may use a single approved "Y1" capacitor or two in series of other approved "U" and "Y" types.
However at times I find the Y1 caps to be of low tolerance and I need more precision. Suitable parts are generally not approved by any agency. In these cases I have tested the candidate capacitors as described in IEC 65 under section 14.2. You will need to perform all three required tests and store the test results in your technical file. The tests are a Surge (short test), Endurance (1500 hours) and a Humidity (21 days). A total of 30 parts. I find it prudent to perform the surge test prior to the others as it immediately screens out several capacitor types (for example Mica types). Also, it is not necessary to test every value capacitor you plan to use if they all appear on the same manufacturers data sheet and the values are not too far different. I never argue for parts that are more than a decade apart. But this may be up to your inspector. There are similar requirements for bridging resistors. Doug Powell Advanced Energy Industries, Inc. Ft. Collins, Colorado USA do...@ftc2.aei.com ---------- From: F.Goto To: emc-p...@ieee.org Subject: Coupling Capacitors &950 List-Post: emc-pstc@listserv.ieee.org Date: Tuesday, February 10, 1998 6:13AM I was wondering if anyone in the group has given serious thought to the testing requirements for coupling capacitors bridging insulation in EN60950(UL1950). One school of thought judges the measurements unnecessary, while another go through the whole routine of capacitance, voltage and frequency measurements (the same as Limited Current Measurements). Any help in this area would be appreciated. Sincerely, Frank Goto A-pex International Co., Ltd.(Safety Consultants) Tel. +81-596-24-6717 Fax. +81-596-27-5631
