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 email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
