Electronics > Mechanical & Automation Engineering

best grounding washers?

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coppercone2:

--- Quote from: Stray Electron on December 20, 2022, 02:08:23 am ---
--- 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.

--- End quote ---

Ok to revisit this, based on what you said, the junction is washer starwasher bolt head. This means that the metal surface is being contacted by the regular washer.

I am thinking that if these were lockwire bolts, then you would not need the serrated washer (just mechanical). You don't think it has anything to do with the bottom of the screw electrically do you?

Why do you have the serrated washer between the bolt head and the regular washer? Is that just anti rotation ?

And from a non safety perspective, it still seems that there is a better EMI path through a bolt sitting on a washer rather then a bolt on a star washer on a washer. Less impedance.

So it sounds like you are saying that you only ever seen the star washer used for mechanical reasons in mil spec equipment.

If you got a bolt with a wider head, would you still desire the regular washer underneath?

I am also curious about penetrating thread locker (wicking) vs star washers for anti rotation. It seems that if its tightened already and it just wicks past the interfaces, then its a sealed thread, and the nut is better secured (electrically anti corrosion) to the nut.

But if course if you use a star washer, you can have grease on the thread. The bolt needs to be clean to mate with the nut for threadlocker. Then its a question of it is better to have a greasy thread interface and star washer for anti rotation or a clean thread interface with loc-tite with no star washer.

I wonder how to setup a experiment. Maybe a welded box with a antenna inside, secured in different ways, with a reciever outside. I bet its hard to measure though.

For instance this web page circles out the round washer for a lug.
https://www.unit3compliance.co.uk/spring-or-star-washers-for-earthing-stud/

But I bought some very reputable high current hardware from a professional manufacturer (german). They have a star washers, instead of the split ring, but do include a washer to protect the copper lug from the serrated washer. These guys seem to want a spring washer to cut into the lug.  ??? NASA also does not like the split ring washer. It seems that there is a school of thought that says you don't want any penetration of lug connectors.

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