Ned, I had this discussion with a TUV engineer way back in time. It is not in the UL or IEC standards specifically AFAIK. What the TUV guy asked me to do was consider the life of the product. The door hinge may have good (low) resistance today, but what will it be like in a few years? Hinges naturally get dirty, greasy, corroded over time. They are, by nature, not an air tight construction so dirt and corrosion will get inside. Then the contact points are no longer the low resistance you tested in the development stage. Since there is no standard coverage on this point, all you can do is the due diligence. Either explain it away with sound engineering reasoning (can't be done) or life test it (not practical). In this application, there is no common metal that will not corrode or oxidize when exposed to air and moisture, and no coating that will not wear through over time thus exposing those metals that will corrode or oxidize. And the fix is relatively painless, 6 inches of green yellow wire, two ring lugs, two lock washers and two nuts (or KEPS nuts with lock washers built in). The hard part is the two PEM studs, one in the door and one in the chassis.
I think the key here is the air tight connection of the door and the chassis to provide a reliable PE connection. BTW, since the hinge is a moving part, most hinges will move around to a point where the resistance will change dramatically, depending on hinge quality and age. Oh, and watch out for hinge mounting. We had a piano hinge mounted on a cover, but only after they painted the cover with no masking done! Good luck. Scott Ned Devine wrote: >Hi, > >I need some help. I told someone that you can not depend on mechanical contact only (i.e. in this case a door hinge) for protective earth. Even if it passes the test, it would still not be acceptable because it does not meet the construction requirements. He then asked me to show him were it said that in the standard (IEC 60950-1 or IEC 60601-1). I looked and could not find it. Am I just missing it, or is it not in the standards? > >There is a reference in CSA standards to C22.2 No. 0.4 that has the requirement, but I can not find a similar reference in UL or IEC standards. > > >Ned Devine >Program Manager III >Entela, Inc. >3033 Madison Ave. SE >Grand Rapids, MI 49548 > >Phone: 616 248 9671 >Fax: 616 574 9752 >e-mail: [email protected] >www.entela.com >1-800-888-3787 >Web: www.entela.com >Grand Rapids * Detroit * Boston * Toronto * Taipei > > > >This message is confidential and intended only for the individual to whom or entity to which it is addressed. If you are not the intended recipient or addressee, or an employee or agent responsible for delivering this message to the addressee, you are hereby notified that any dissemination, distribution, or copying, in whole or part, of this message is strictly prohibited. If you believe that you have been sent this message in error, please do not read it. Please immediately reply to sender that you have received this message in error. Then permanently delete all copies of the message. Thank you. > > > > >------------------------------------------- >This message is from the IEEE EMC Society Product Safety >Technical Committee emc-pstc discussion list. > >Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > >To cancel your subscription, send mail to: > [email protected] >with the single line: > unsubscribe emc-pstc > >For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [email protected] > >For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > >Archive is being moved, we will announce when it is back on-line. >All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc > > > > This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
