Hi Ted, Thanks for your reference! I downloaded the 1st doc document successfully but failed to reach the 2nd document. Can you do me a favor sending a copy to me.
Thanks and regards, Scott On Thu, 9 Aug 2018 at 03:00, Ted Eckert < 000007cf6ebeab9d-dmarc-requ...@ieee.org> wrote: > These references are in relation to ship building, but may be of interest > to anybody who wants to look at star tooth washer bonding in detail. > > http://www.public.navy.mil/navsafecen/Documents/afloat/Surface/Rsrcs/References/MIL-STD-1310H.PDF > > https://nsrp.org/wp-content/uploads/2015/10/Deliverable-2011-452-Improved_Bonding_Grounding_Final_Report-Ingalls_Shipbuilding.pdf > > The second link even includes a table showing the torque required to > penetrate paint with various washers. (See table 2) > > Ted Eckert > Microsoft Corporation > > The opinions expressed are my own and do not necessarily reflect those of > my employer, the Navy, the ship-building industry or or the American > Association of Manufacturers of Internal and External Tooth Washers. > > -----Original Message----- > From: Brian O'Connell <oconne...@tamuracorp.com> > Sent: Wednesday, August 8, 2018 10:30 AM > To: EMC-PSTC@LISTSERV.IEEE.ORG > Subject: Re: [PSES] External toothed star washer used in earth connection > > 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://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.linkedin.com%2Fin%2Fdougp01&data=02%7C01%7Cted.eckert%40microsoft.com%7Cde232d4406a343b52e2808d5fd569820%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636693470724048869&sdata=k4YiuXJYCkjT3v7o1QwVjbOiPSEhEezB7YqpexM3h8w%3D&reserved=0 > 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. 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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>
