Traces heat by I^2*R loss. Traces cool by several means. Trace temperature is determined by the where the equilibrium is between the heating and cooling effects. 20us is so short there is effectively no cooling. In fact, there is negligible cooling for the first few seconds after a step-function pulse is applied. Studies suggest that trace equilibrium occurs (95% to 99%) after about 4 to 5 minutes. It gets half way to equilibrium in about 30 seconds. So you are looking at a fusing effect, not a trace current/heating effect. UltraCAD has an article specifically on fusing effects on PCB traces ( Fusing Current: When Traces Melt Without a Trace!) on it web site. Go to http://www.ultracad.com/article_outline.htm and look under the Trace Current/Temperature/Power/Resistance: heading. UltraCAD also has a calculator that specifically addresses fusing effects (among other things). You can find it at http://www.ultracad.com/calc.htm under the heading UCADPCB.exe. (This calculator will also take skin effect into consideration, if anyone cares!) The calculator suggests that a 20us time frame is so short that trace width is not an issue (it is actually beyond the range of the calculator!) The calculator would suggest that for a 100us pulse and .5 Oz trace, the fusing width is about 8 mils. That means if you want the trace to FAIL (so as to trigger a controlled system shutdown after a catastrophic failure) you would size the trace somewhat narrower than this. If you want it to survive this pulse, you would size it somewhat larger, say 20 to 30 mils. Doug Brooks At 04:51 AM 9/15/2009, Deepak V.L wrote: >Dear Experts, >Could someone please guide me how to select a trace width for carrying a >100A surge current for 20us over a PCB trace ? > > >Thanks in advance, >Deepak > >------------------------------------------------------------------ >To unsubscribe from si-list: >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >or to administer your membership from a web page, go to: >//www.freelists.org/webpage/si-list > >For help: >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > >List technical documents are available at: > http://www.si-list.net > >List archives are viewable at: > //www.freelists.org/archives/si-list >or at our remote archives: > http://groups.yahoo.com/group/si-list/messages >Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > Check out our resources at http://www.ultracad.com ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu