In message <[email protected]>, dated Mon, 5 Feb 2007, "Kunde, Brian" <[email protected]> writes >Our CAD guys just want a current value for the PE so they can plug into >their computer and it will make the trace width wide enough to handle >the current. So is X2 the fault current enough? I thought the article I >mentioned above recommended X3 or X4.
I don't recommend using a rule of thumb 'safety factor' for this, because it isn't that difficult to carry out tests, and that's much more impressive in your safety technical file for the LVD. I guess UL might like it, too. There are several factors that can affect the results. The time that the protective device takes to clear the fault is obviously one, but another is the temperature of the board before the fault occurs. The fault current induces thermal shock in the board, so normal temperature considerations are not valid. If the adhesive between track and board vaporizes, the track lifts off in places and is deprived of any heat-sinking there, so it can get very hot indeed very quickly. Bends in the track act as heat concentrators (non-uniform current distribution). I suggest you print some test boards with the track configuration you want to use, with a selection of track widths, and carry out fault-current tests, using the protective device intended for the product, of course. Keep a safe distance. Wear eye-protection. If you underestimate the required track width a lot, you may need ear-protection as well. (;-) -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk There are benefits from being irrational - just ask the square root of 2. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - 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 ______________________________________________________________________
