In response: > I have a couple of questions regarding this standard: > (I have the 1992 version) It's time to upgrade to current versions. Check: http://www.iec.ch/cgi-bin/procgi.pl/www/iecwww.p?wwwlang=E&wwwprog=cat-d et.p&wartnum=027973 for the latest version still in the process of being adopted by some countries. Even if you have your product certified to older standards, I would recommend review to this latest IEC standard by your approval agency.
> Table 16 specifies maximum temperature RISE for components, > surfaces,... What are the assumptions here? Are they assuming > an ambient of room temperature (25 deg C)? Which would mean > that a rubber handle could become as warm as 25 deg C + 50 deg C > which is 85 deg C? This seems high to me. (Typo? 75 deg C?) Pay attention to the references in the text (in your standard the reference to 1.4.7) currently to 1.4.12. The idea is, the permissible rise is that permittted when tested at a 25 debree ambient. The allowable maximum under (25 + 50) is the maximum allowed under the operating conditions of your equipment. That is, if you permit your equipment to be operated at a 60 degree ambient, the rise would have to be limited to 15 degrees. The current standard has been rewritten to clearly show these limits rather than rise. > This would be even worse under high temperature ambients. For > instance, our products are typically specified to operate in > ambients up to 45 deg C. In this ambient temperature, Table 16 > would appear to allow an absolute temperature of 45 deg C + 50 > deg C for an absolute temperature of 95 deg C!!!!! This seems > high to me. Any thoughts? With a 45 degree D ambient, the allowable rise would be 30 degrees C. Note that for capacitors, you can use the temperature established by a component standard, in this case IEC 60384-14. Refer to the manufacturer for ratings. > I am planning on using high voltage hold-up capacitors in a high > Voltage bus application (200VDC). The capacitors are aluminum > electrolytic, radial leaded, PCB mount with a safety vent. > Nichicon The capacitors will be the tallest components on a > PCB within a metal chassis. The metal cover going over them will > be grounded. Do I need to leave a clearance distance over the > top of these capacitors for the safety vent to operate? Do I need > to leave a clearance between their top and the grounded cover > for dielectric withstand reasons? If the grounded cover is > within a few thousandths of an inch of the capacitor tops, do I need > to put some kind of mylar sheet in between insulate it from the > capacitors? (assuming that the cover could be bent to touch the > capacitors.) You need to determine the insulation needed between the cap and the cover with regard to the type needed (probably BASIC in this case) and its related parameters, working voltage, transient rating, pollution degree, etc. The insulation provided on the caps needs to be evaluated with regard to these requirements to determine if more is needed. The equipment needs to be evaluated (possibly by test) with regard to the safety consequences of a failure to properly vent if you have a design which blocks the designed vents. If the cap can explode or otherwise fail without exposing people to physical risk and compromising electrical insulation, you can probably get away with blocked vents. Keep in mind, a failure which results in compromising only one of two levels of insulation or protection is an acceptable condition. Keep in mind there are several other requirements applying to capacitors, e.g. clauses 1.5, 2.1.1.7, 4.7.1. Bob Johnson ITE Safety ------------------------------------------- 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
