Hi all, At first I thought the discussion concerning simple current carrying capability. Now I'm wondering if Brian was thinking about fusing current of traces (destruction point). Maybe this will help: http://www.ultracad.com/articles/fusing.pdf
Pat Lawler SL Power Electronics Corp. [email protected] wrote on 02/06/2007 05:56:16 AM: > Just another two pee's worth of accumulated wisdom from way back in my > Sewage days... (don't ask) > We used 'ASTA certified' motor control centres, rated at 80kA fault > currents, where the 2" x 1/4" copper bus bars were quite capable of tearing > themselves away from their mountings on the occasion of a digger out on > site going straight through a feed to a sludge pump. Fault currents of > that magnitude on all three lines of a bus bar system exceeded the > strength of the plastic bus bar holders. (>800 Newtons rings a bell) > Similarly, on a mains distribution PCB for use on small instrumentation > pumping systems, we had two 1/4" tracks, one on either side of the PCB, > Single phase, 240V, protected by a 32A Circuit Breaker. The PCB was > furnished with about ten or so IEC 240V 16 amp outlets. The inevitable > happened, a short circuit, line to neutral, and the long mains tracks tore > themselves off the board before the trip operated, to leave them hot > looking, but flapping around in space like skipping ropes. I suspect there > was significant heating of the track, i.e. adhesive softening, before this > happened, but even so - not at all what we expected. I suspected EM > forces, but we simply went to hard wired after that, so never followed it > up. > > The breakers were Motor start types, with a longer thermal response time, > and DOL breaking capacity was 9kA. > > If a PCB track is used as an Earth, it must be expected to take a fault > current of about 9kA until the fuse/breaker protection operates (mS). > Happily, it'll only be a single conductor with no adjacent magnetic field > to drive against - unless the mains conductor is very close by - like our > Motor Distribution board example. Once again, a mechanical problem! :-) - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
