Joe, Thanks for your very understandable explanation. I have read the sections you described in UL1950_3, however I still don't have a clear understanding of the difference between "basic" and "supplementary" insulation. John
-----Original Message----- From: [email protected] [mailto:[email protected]]On Behalf Of [email protected] Sent: Wednesday, October 14, 1998 10:06 AM To: [email protected] Subject: Re: Ground on Tip & Ring In a message dated 98-10-13, John Honeycutt writes: << It is unclear to me if connecting the midpoint of the series connected capacitors to the ground etch which connects to the PCB mounting bracket, which ultimately is attached to the computer chassis, violates safety in certain countries, i.e. Norway. >> John: If you connect the midpoint to chassis ground, your capacitors will bridge the safety isolation barrier. For equipment that is not permanently grounded (i.e., a typical PC), most countries require "basic" insulation per clause 6.2.1.2 of IEC 950. You can meet this requirement with a 1000 volt rms rated cap whose leads meet the creepage and clearance requirements. Norway and Sweden both require "supplementary" insulation, which imposes more stringent requirements. A conservative choice here would be to use a safety- rated Y1 cap, which IEC 950 specifically allows in clause 2.2.8.1 for bridging "reinforced" insulation. This would be overkill, but it would get the job done. Alternatively, I believe you could use a Y2 cap, which IEC 384-14 defines as suitable for bridging supplementary insulation. Y1 and Y2 caps are readily available in through-hole, ceramic disk form with radial leads. They are used in almost all switching power supplies that connect to the AC power mains, to reduce emissions. The only vendor I know that makes a surface mount Y1 cap is Murata Erie. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848
