Considering that screws can be added to PCBs explicitly to contact a power trace (for instance, to accept a spade lug from the power cord), if this screw passes the requirements for that, everything should be OK.
Orin On Thu, 7 Oct 2010 19:43:36 +0000 Richard Nute <[email protected]> writes: > Hi Mark: > > > > let's assume there are 120VAC traces on the top layer of the PCB > (AC comes > > in from a detachable power cord) Right next to the trace (<1mm) > > > > there is a plastic stand with metal screw (washer build-in) in it. > metal > > washer lays on top of the AC trace, separated only by the mask. > > > > Screw is not connected to any grounds or circuits or any other > conducted > > part. It is untouchable to the user side. > > > > Is where any safety concern? Product is evaluated under 60950. One > thing > > came to my mind, is a plastic standoff, probably should be able to > support > > high voltage? is it valid concern? any others? > > The solder mask is NOT a suitable safety insulation > (because its purpose is that of a solder mask). > > Therefore, you must consider that the screw is connected > to the the PCB 120-volt trace. > > Now, you must evaluate the safety based on the screw > being part of the mains circuit. That means you must > evaluate the clearance and creepage distances from the > screw to other parts of the equipment. And, you must > evaluate the plastic standoff as a solid insulation, > including distance through insulation as specified in > 60950-1. > > > Best regards, > Richard Nute > Product Safety Consultant > San Diego > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. To post a message to the list, send your > e-mail to <[email protected]> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > Graphics (in well-used formats), large files, etc. can be posted to > that URL. > > Website: http://www.ieee-pses.org/ > 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]> > > - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ 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]>
