Pete, this is incredible info for me personally. But what's more intriguing are very few responses this question produced. It seems like then a question raised on a voltage matter, it will get much more researched and UL, IEC will get every spec, test and procedure how to deal with overvoltage, surge, hi-pot, clearances, creepages and so on. when it comes to current, almost nothing. section 5.3 says do the short circuit test and you can relay on circuit breaker for secondary backup protection. Really? by the time it gets to the circuit breaker it is all over with 900A going through UL/TUV/CB/CE/GS certified adapter which explodes like there is no tomorrow. How many people, even HW engineers, realize or understand breaking capacity of the fuse, not fuse rating/tripping/opening point, but how much current fuse can clear before it gets destroyed? You do not want metal fuse to gets blown to pieces inside your product. Isq2/t anyone? Adapter vendor picks 3.15A fuse for 0.2A device, claiming surge, inrush current and over life derating to avoid nuisance tripping and it has 35A breaking capacity. Little solder ball on one of the diodes and boom. Although 1.2 parts per million, but does anyone wants to take a chance? Again, went through all of the testing/certs and all short tests being performed and documented. Put the short on the cap behind the inductor, and it will raise voltage/arcing even higher driven by huge inductance, prolonging the event. I know I do not have extensive expertise in power supplies design and fuse ratings/regulations, but you would expect people on a different committees would get together and discuss it. Would you? Or is it one of those stones better kept unturned? Mark > From: [email protected] > To: [email protected]; [email protected] > Subject: RE: IEC 60950-1 short circuit test criteria > Date: Wed, 20 May 2009 15:52:21 -0700 > > Mark, Brian et al, > > Without trying to deal with all of the issues that this question > raises, I would like to comment on just one aspect from my experience. > > In the North American distribution system the short circuit current > that can be expected from the usual 115V domestic & commercial outlet is on > the order of 7000A. Because of this fuses and circuit breakers providing > protection for these circuits must comply with a 10,000A breaking capacity. > > > In my other life I remember testing a current measurement product > subjected to this 10kA current which produced a surprising failure that > provided ionized/arcing fire from the front panel which ate up the 3AG > instrumentation fuse proposed along with the panel connector and several > inches of the lead wire coming into the product. Needless to say the design > engineer then recognized the inadequacy of the small fuse and designed the > product to accommodate the proper breaking capacity fuse (which was quite a > bit larger). Experience is a great teacher; unfortunately we sometimes > forget too fast. > > br, Pete > > Peter E Perkins, PE > Principal Product Safety & Regulatory Consultant > Tigard, ORe 97281-3427 > > 503/452-1201 fone/fax > [email protected] > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > Graphics (in well-used formats), large files, etc. can be posted to that URL. > > Website: http://www.ieee-pses.org/ > Instructions: http://listserv.ieee.org/request/user-guide.html > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <[email protected]> > Mike Cantwell <[email protected]> > > For policy questions, send mail to: > Jim Bacher: <[email protected]> > David Heald: <[email protected]>
________________________________ Windows Live™: Keep your life in sync. Check it out. <http://windowslive.com/explore?ocid=TXT_TAGLM_BR_life_in_synch_052009> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]>
