Also keep in mind the NSF standards generally prohibit the use of external tooth star washers in food zones in food certified products. -Dave
From: Doug Powell [mailto:doug...@gmail.com] Sent: Wednesday, August 08, 2018 1:04 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] External toothed star washer used in earth connection 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<mailto: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<mailto: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<mailto:sdoug...@ieee.org>> Mike Cantwell <mcantw...@ieee.org<mailto:mcantw...@ieee.org>> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org<mailto:j.bac...@ieee.org>> David Heald <dhe...@gmail.com<mailto: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<mailto: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<mailto:sdoug...@ieee.org>> Mike Cantwell <mcantw...@ieee.org<mailto:mcantw...@ieee.org>> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org<mailto:j.bac...@ieee.org>> David Heald <dhe...@gmail.com<mailto: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>
