It really happens in white goods. They want to streamline the process using toothed star washer. I fully agree your point and will read the reference book later to understand it in greater detail. IPC is generally for normal electronic assembly and did not remember any reference for earthing connection.
What is CSA engineering manual for 60950-1? Is it explanatory note for 60950-1 requirements? Thanks and regards, Scott On Thu, 9 Aug 2018 at 01:44, Brian O'Connell <oconne...@tamuracorp.com> wrote: > Am not aware that it is "common to use external toothed star washer to > cut through the paint". It has been my experience that NRTLs, SCC members, > NBs, and the Vulcan Science Academy look askance at such construction, and > tend to require a paint-free zone for electrical power ground bond stuff. > > Agree with Doug that IPC610 does not say much about safety, other than > that clearance (does not mention creepage) is part of the design > considerations and shall be determined by other standards (but does > reference the min spacing table from IPC2221). Another thing that IPC610 is > careful to do is to not use star/toothed washers as examples of hardware > securement - only the split lock washer is used in construction examples. > > The lock washer should not interface between the bolt head and the metal, > the lock washer should be between the head and a flat washer. A decent > example of reliable ground bond construction can be found in the CSA > engineering manual for 60950-1. And 40A ground bond test for all, and all > for one. > > Brian > > > > From: Doug Powell [mailto:doug...@gmail.com] > Sent: Wednesday, August 08, 2018 10:04 AM > 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 > 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) > 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>
