Hi Doug, Very interesting about oxygen free connection for long term reliability!
Thanks and regards, Scott On Thu, 9 Aug 2018 at 01:03, Doug Powell <doug...@gmail.com> wrote: > I have used IPC guidance in the past and while they have many good things > to say, the primary aim is for reliability. Product safety is considered > but of secondary importance in my view. Based on IPC workmanship standards > and the requirements of product safety standards combined, best practice > is to not rely on the star to cut through paint. If you study such > connections by disassembling, you will see a bit of paint or a single paint > chip at the bottom of the holes created by the star points. This is a > resistance point which may degrade over time. I much prefer to have the > metal surface spot faced or masked, conductive coatings excepted. The > purpose is to provide and oxygen free connection so the long term corrosion > effects are negligible. I believe the product liability directive in > Europe requires 10 years from the date when the product is put into > service. A safety earth connection seldom carries much current during its > life and may be called into service for full fault current at any time > during that period. > > Fastener torque should be high enough to secure the fastener just short of > deforming or crushing the star or other connective parts. This may take > some experimentation with a few test samples. Experimental test results > always supercede the tables and calculations found in the International > Fastener Institute (IFI) books. I use stars only for safety grounding and > not for conductors carrying very much current such as mains; steel makes a > comparatively poor conductor. Although there are some steep pitch stars > made of phosphor bronze and are suitable for high current connections. > External tooth has not been mandatory in the safety standards I use, but > the modern GTD tolerancing methods used by mechanical engineers often > result in fairly large holes. An internal tooth star may not engage the > metallic surface correctly. > > Best of luck, Doug > > -- > > Douglas E Powell > doug...@gmail.com > https://www.linkedin.com/in/dougp01 > > Sent from my Android on the Verizon 4G LTE Network > *From:* scott...@gmail.com > *Sent:* August 8, 2018 7:22 AM > *To:* EMC-PSTC@LISTSERV.IEEE.ORG > *Reply-to:* scott...@gmail.com > *Subject:* [PSES] External toothed star washer used in earth connection > > Notice that it is common to use external toothed star washer to > cut through the paint on metal enclosure instead of removing the paint for > earthing. The connection effectiveness may be affected with following > things > > - Sharpness of teeth on washer (some toothed washers are single sided > instead of 2-sided) > - Material of washer > - Paint thickness > - Screw torque > > Is there any standard to give the guidance of minimum requirement for this > purpose? > > Thanks and regards, > > Scott > - > ---------------------------------------------------------------- > > 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 < > emc-p...@ieee.org> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.org/ > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe) <http://www.ieee-pses.org/list.html> > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <sdoug...@ieee.org> > Mike Cantwell <mcantw...@ieee.org> > > For policy questions, send mail to: > Jim Bacher <j.bac...@ieee.org> > David Heald <dhe...@gmail.com> > - ---------------------------------------------------------------- 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 <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
