At 01:44 PM 10/17/2007, you wrote: >Nearly two hundred years ago Oersted and Ampere figured out that if you >have >two conductors carrying current in the same direction, they would would >to pull >in close to each other whereas if you had two conductors carrying >current in >opposite directions, they would want to separate. The forces you are talking about are stationary magnetic forces around the traces. In DC, they have no bearing on where the current is flowing. In DC circuits, current follows the path of least resistance, which can be anywhere (or uniformly everywhere, perhaps) In AC circuits, there is a CHANGING magnetic field which induces a current in the opposite direction. These two currents will follow the path of least IMPEDANCE (re: inductance). As the frequency of change increases, the impedance distribution changes more sharply, with the lowest impedance path being where the currents are closest together. Thus, the current DENSITY within the conductors shifts to the path of lowest impedance (inductance.) The difference in the two effects you are concerned about is the difference between DC and AC. Doug Brooks _______________________________________________________________________________________________ Check out UltraCAD's PCB trace and impedance calculators 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