Rick, I have worked with European requirements for the last 5 years now and often design equipment with black oxide coatings. In order to insure proper Protective Earth (PE) grounding we routinely coat our sheet metal parts with a zinc finish overall and then follow black oxide using a masking layer on the CAD drawings. I have found no way to get around the requirement. Therefore I must agree that excluding the paint from the area of concern is a good idea. A star washer will not always displace the paint to the side of the tooth and can remain behind as a contaminant at the point of contact.
Additionally I use the star washer between the ring lug on the wire and follow with locking hardware to secure the connection. Doug Powell [email protected] ---------- From: [email protected] To: [email protected]; Rick Busche Subject: Re: Bonding of structures List-Post: [email protected] Date: Tuesday, June 03, 1997 2:07PM Rick: I would assume that the main concern is damage to the protective paint layer which gets ripped open and may give access to moisture with potential for corrosion. That is, if you paint the bare steel without any protective coating. If you used zinc plating (or similar) in the first place, no question should arise, although damage to the plating due to the bite of the washers and possible damage to the plating due to slippage of the washer may keep the debate going.. You are right in assuming that the toothed washer provides gas-tight contact (specify a minimum torque requirement before this can gets opened!) but in my opinion, damage to the paint would negate this over time. The way I see it, the question boils down to money (as usual): are you willing to engage in a protracted argument "my expert vs. your expert", or would it be cheaper to not paint the areas of concern and provide some selective plating? Another cheap way would be to put some spray paint on the screws after everything has been tightened down, which may lead again to arguments as above. Please let me know how this ends. Bogdan M. Matoga [email protected] ______________________________ Reply Separator _________________________________ Subject: Bonding of structures Author: Rick Busche <[email protected]> at Internet List-Post: [email protected] Date: 6/2/97 16:43 I have a projector assembly which is essentially a large metal structure (frame) with a metal projector platform which swivels for purposes of maintenance. The structure is painted steel, with pressed in bronze bushings at all motion points each of which have been measured at significantly less than 0.10 ohms. Arguably, there is no guarantee that these structures will remain bonded at these levels over time and bonding wires (braid, with crimped ring lugs) have been added across the pivot points. These wires are secured to the structure using a toothed washer and screw. The intent of the toothed washer is to bight through the paint to ensure conductivity. My customer's safety officer (in Europe) is now insisting that the paint must be ground off to bare metal and coated with Zinc paint prior to affixing the lug to the structure. I am concerned that this is an excessive requirement. It has been my understanding that the toothed washer (and the screw for that matter) creates a gas tight connection which is acceptable for all bonding requirements. I would be interested in hearing from the group regarding this bonding issue. I can find no standard or specification which disallows this biting washer or requires Zinc paint. Any comments would be appreciated. Rick Busche [email protected]
