Electronics > Mechanical & Automation Engineering

best grounding washers?

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coppercone2:
why would you add it unless you had to? What does it bring to the table other then a useless component if its not being used to penetrate paint?

Stray Electron:

--- Quote from: coppercone2 on December 20, 2022, 01:03:13 am ---But read the document, they build stuff for the navy and they don't seem to recommend using a washer unless there is paint. I don't think this has anything to do with money. What it looks like is that it might be counter productive.

I think the idea is that
1) washer reduces bond area
2) washer allows for ingress of corrosive materials
3) grease is less secure

and they even seem to say that the washer is like a cheap-ass solution compared to stripping the paint and just bolting it.


And that document says that the washers are NOT approved by the ship yard, its a suggestion to use the washers to save man hour cost on paint stripping and masking planning! The entire point seems to be to convince the navy to use the washers to reduce costs.

--- End quote ---

   I worked for a company that made MIL equipment for the US Navy, the US Army, the US Army Missile Command, Canadian Forces and US Space Command. Those are just the End Users of programs that I personally worked on, but we also built items for the USMC, USAF and for the British military.  That said, I've never seen any kind of directive to use grounding washers over paint! In electrical devices we always used external tooth star washers on top of a flat washer and on a bare metal surface. Even on circuit boards that were conformal coated an area is left bare for each bolt and washer.  The idea of not using washers in any kind of military system in order to save money is simply ludicrous!  In many applications all nuts, bolts and washers were required to be replaced every time that they were removed. And further, NOTHING is grounded via screws and the like, EVERY electrical circuit has wired connections. Even the shield braid of coaxial cables have special crimped and soldered on connections to small wires and each of those wires is connected back to it's signal source (not a chassis ground!) Even the engine starters and the like in military aircraft and vehicles has WIRED power and power return (aka "ground") connections.  I also personally own two former US military vehicles both built in the 1950s and both of them are also built that way.  One is a x-Korean War USMC Forward Air Controller's jeep and packed full of both ground and aircraft radios so I have a LOT of experience with MIL electrical systems.

  I would REALLY like to see an kind of official directive to use washers as part of any kind of electrical circuit on top of a painted surface.

coppercone2:
well I will take that over a document that references cost 5000 times

thm_w:

--- Quote from: Stray Electron on December 20, 2022, 02:08:23 am ---  I would REALLY like to see an kind of official directive to use washers as part of any kind of electrical circuit on top of a painted surface.

--- End quote ---

Yes mil-spec is going to be stringent and not allow painted surfaces at all (below).
No directive would explicitly call out a painted surface that I can think of, but they could allow compliance by passing a high current earth test (10A+) within some resistance range.

Also for any sort of low voltage or RF application, where you've proven the device as built passes EMI testing, would be acceptable.



--- Quote ---3.2.6 Grounding requirements. A ground stud shall be provided on equipment. The ground stud shall provide the electrical ground connection to the chassis or frame and shall be mechanically secured to insure low resistance joints by soldering to a spot welded terminal lug or to a portion of the chassis or frame that has been formed into a soldering lug, or by use of a terminal by a screw, nut and lock washer. The ground stud shall be of a size to allow electrical connection of size AWG 10 wire. All hardware used for grounding or other
electrical connections shall be made from copper or copper alloys. Terminal luge shall be tin plated or hot tin dipped. Paint, varnish, lacquer, etc., shall be removed from the vicinity of the fastening point to insure metallic contact of the two surfaces. Corrosion protection shall be provided for all ground connections.
--- End quote ---

https://www.reddit.com/r/ECE/comments/468cx0/comment/d03uxo6/?utm_source=share&utm_medium=web2x&context=3
https://www.electricneutron.com/earthing-system/grounding-requirement-for-installation/
https://www.unit3compliance.co.uk/spring-or-star-washers-for-earthing-stud/

TimFox:
For assembling anodized aluminum T-slotted frameworks, there is special anodizing-breaking hardware to cut through the thick oxide surface to ensure electrical connection.
https://www.mcmaster.com/6812N216/

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