Jeff: In the military product area, using star washers for a ground path is not acceptable. The theory is that the stars only dig in at tiny point-contacts, and the crenelations leave voids where possibly corrosive contaminants may collect. At those point contacts, the current density can get really high if you get a power fault current or a lightning stroke.
The preferred bonding technique is to use a bolt with a split washer under the head, and then a flat washer under the split washer, then the two metal surfaces, then another flat washer and then the nut. (Seems to me that another split washer should go between the last flat washer and the nut, but I've been told that that's un-necessary over-kill.) If you need a star washer to cut into the mating surfaces, then that really means that the surfaces are not properly prepared to begin with. Besides, the current path should be between the mating surface faces, not from one face through a washer to a bolt head through the bolt shank to the nut to a washer to the other material face. Would it be possible to use a conductive chemical surface treatment rather than painting? Although I have little experience with conductive paint, I would think that the organic vehicle would be non-conductive, and would never be completely eliminated from the dried film. Regards, Ed ------------------------ From: "JENKINS, JEFF" <[email protected]> Subject: Conductive Paint, Round 2 Date: Tue, 13 Apr 1999 13:03:04 -0600 To: 'emc-pstc' <[email protected]> > I need to clarify my earlier question on conductive paint. We bond our > enclosure panels together with screws. We use external-tooth starwashers > between the screws and sheet metal to achieve a reliable, protective-earth > bond. On our painted panels, we mask the paint so that the starwasher makes > good contact with the metal. We are now considering using conductive paint > without masking, but we would still use starwashers. I don't see how this > could be a problem, but it's not something I've seen done before and so I'd > like your input. > > Thanks again, > > Jeff Jenkins > Senior Regulatory Compliance Engineer > Advanced Energy Industries, Inc. > Fort Collins, CO USA 80525 > > Opinions are my own and not necessarily shared by Advanced Energy > Industries, Inc. or its affiliates. -------------------------- Ed Price [email protected] Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA. USA 619-505-2780 List-Post: [email protected] Date: 04/13/1999 Time: 15:51:31 Military & Avionics EMC Services Our Specialty Also Environmental / Metrology / Reliability -------------------------- --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
