Yet another lively discussion! I throw in with the camp that is convinced that reliable grounding, over time, cannot rely on a hinged part.
The corporate compliance engineer, in a properly structured engineering development community, will be able to exert his or her will by simply not signing off on the release of such product. By properly structured, I mean that someone from the regulatory compliance group signs off on all product releases and modifications. May catch a little (a little) heat for this decision, but that comes with the territory, and you have a pretty thick skin by now anyways, right? The product safety engineer working for an evaluating agency will need to stick neck out a little (a little), and advise the client that this construction is not considered reliable, and will not approve or accept this construction. Hopefully, said agency has a bulletin, application guide, or some-such that backs up this opinion. At any rate, an agency issuing authorization to apply a mark has discretion in its interpretation of the standard, and may apply requirements outside of the standard, if deemed necessary; it's their mark, after all. Standards be damned, I think common sense dictates that this is NOT a safe practice, and, after all, the bottom line is product safety, whether it is plainly stated in black & white in a particular standard or not. Doug Massey Product Safety Engineer Advanced Compliance Solutions Ph. (770) 831-8048 FAX (770) 831-8598 Visit our web home at http://www.acstestlab.com From: [email protected] [mailto:[email protected]] On Behalf Of GARY MCINTURFF Sent: Monday, November 17, 2003 11:06 AM To: [email protected]; [email protected] Subject: RE: Grounding Morning Ed, This is stated much better than commercial with the ... reliabily and permanent ... but still has the weakness of a test that is performed when the product is new and which it will likely pass; 0.1 ohm resistance or the application of the test current. After time as the hinge "ages" it may fail the same test, because of corrosion, wear etc. So the problem becomes that when we compliance types - who generally recognize this weakness have our feet put to the fire all we can do is run the test. When it passes the bean counters etc, say good drop the strap and we are left with no recourse but to drop the permanent ground. Running salt or corrosion tests is usually out of the question because of the cost and time - this things going out the door. So unless the standards actually say a hinge cannot be relied upon as a ground and as long as higher powers insist it isn't needed there isn't much that can be done from the regulatory standpoint - and I think that is what the original poster was getting at. Usually through just plain being obnoxious about it, I insist the strap go in when the application requires it but for the bean counting literists of the world its a struggle to accept. Gary >From: "Price, Ed" <[email protected]> >Reply-To: "Price, Ed" <[email protected]> >To: "'[email protected]'" <[email protected]> >Subject: RE: Grounding >Date: Mon, 17 Nov 2003 07:06:30 -0800 > > > > >-----Original Message----- > >From: Gary McInturff [mailto:[email protected]] > >Sent: Friday, November 14, 2003 10:46 AM > >To: 'Crabb, John'; Ned Devine; IEEE EMC/Product Safety (IEEE, > >EMC/Product Safety) > >Subject: RE: Grounding > > > > > > > >John, > > You are correct, but you have just presented the > >conundrum of the > >thread. > > "Reliably grounded" can be determined through test - 25 > >or 30 amps > >for a minute. A new hinge will likely pass that test. A "used" one may > >likely fail because of the corrosion and wear discussed by > >others. So the > >conundrum is do you test to get through the standard or do you use the > >standard to help you design something which hopefully remains safe. > > Personally, I don't like hinges for grounds - PE or > >earth and for > >the very cost sensitive it can be a real issue with the > >management guys and > >bean counters. > > Gary > > > > >FWIW, military practice doesn't allow grounding through a hinge. > >MIL-HANDBOOK-454A, Paragraph 4.5.2.2 says "Ground connections to shields, >hinges, and other mechanical parts should not be used to complete >electrical >circuits." It goes on to also say "...the ground should be continuous and >permanent." > >Paragraph 4.5.2.3 specifically addresses hinged panels and doors, saying >"Hinges or slides should not be used for grounding paths. Panels and doors >containing meters, switches, test points, etc., should be attached or >hinged >in such a manner as to insure that they are at the same ground potential as >the equipment in which they are mounted, whether in a closed or open >position. A ground should be considered satisfactory if the electrical >connection between the door or panel and the system tie point exhibits a >resistance of 0.1 ohm or less and has sufficient capacity to insure the >reliable and immediate tripping of equipment over-current protection >devices." > >Of course, this isn't a commercial requirement, but it defines what the >military thinks is necessary to avoid problems. > >Ed > >Ed Price >[email protected] WB6WSN >NARTE Certified EMC Engineer & Technician >Electromagnetic Compatibility Lab >Cubic Defense Applications >San Diego, CA USA >858-505-2780 (Voice) >858-505-1583 (Fax) >Military & Avionics EMC Is Our Specialty _________________________________________________________________ Is your computer infected with a virus? Find out with a FREE computer virus scan from McAfee. 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