Let me second the words of Chris. I too, have seen the kinds of destruction to which he refers. I have done failure analysis on power controllers where the traces were ripped up leaving the board looking like a rat's nest. There were two kinds of faults that seemed to cause very similar results. One was where the 12 or 24 KV distribution line fell onto (contacted) the 240/480 drop and the other was caused by lightning strikes. The biggest cause and effect appeared to be from magnetostrictive action. The more inductance the more the effect. Even worse than the damage to PCB was the damage to RFI filters. I saw one tar filled filter explode spewing hot flaming tar. It made UL's hot flaming oil test look tame.
Fred Townsend DC to Light [email protected] wrote: >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! :-) > >Memories... > >Chris Dupres > > > > > > > >*******************Internet Email Confidentiality Footer******************* >The contents of this e-mail message (including any attachments hereto) are >confidential to and are intended to be conveyed for the use of the >recipient to whom it is addressed only. If you receive this transmission in >error, please notify the sender of this immediately and delete the message >from your system. Any distribution, reproduction or use of this message by >someone other than recipient is not authorized and may be unlawful. > >- >---------------------------------------------------------------- >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 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 ______________________________________________________________________
