All, This email is a sanity check.
We deal mainly with EN 61010-1 for our products. THIS QUESTION DEALS WITH HAZARDOUS/SELV SEPARATION WHERE THE HAZARDOUS VOLTAGE IS ON ONE LAYER AND SELV IS ON ANOTHER LAYER. >From EN 61010-1, we get a "through insulation" distance of about 0.016" when we consider our hazardous working voltages for a particular design. I remember some discussion on this topic from before which stated that smaller layer to layer distances are permissable as long as two conditions are met: 1. Each layer of the PCB laminate used must have a dielectric strength such that it could pass the hipot test even in a small thickness (for instance 0.001"). This isn't a big problem, given that most PCB material has a dielectric strength of several thousand volts per 0.001" 2. More than two layers of this laminate must be used between PCB layers. The reason for this was given as "pinholes". A layer of fiberglass that is .001" thick can withstand hipot; but there is a finite chance that there could be some pinholes in it. If more than two layers of .001" fiberglass are used; then the probability that the pinholes in all of the layers could line up becomes infinitesimal. Confusing? How about an example: What if I were to specify a circuitboard with .006" layer to layer spacing between an SELV layer and a hazardous layer? Obviously, this is less than .016". Furthermore, the drawing would specify to the PCB maker that they must use at least three layers of laminate to make this spacing, for instance, three sheets of .002" fiberglass? Can anybody shoot holes in this design from an EN 61010-1 perspective? BONUS QUESTION: WHAT ABOUT HAZARDOUS/SELV SEPARATION BETWEEN TRACES ON THE SAME, ***INTERNAL*** LAYER? I am assuming that I would have to apply the 0.016" distance between an SELV and hazardous trace on the same internal layer. Can anybody see a problem with that? Thanks in advance for any assistance. Chris Maxwell | Design Engineer - Optical Division email [email protected] | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
