Stainless steel bolts for electrical connections.

[Dave Plowman (News)]

Been a thread on a forum I read about a chap using stainless steel nuts and bolts on a kit car when doing the wiring, and had problems.

Difficult to be specific, but sort of implied he's used them to clamp a ground to the chassis where it would be normal to use ordinary steel nuts and bolts, and had a problem with corrosion very quickly (in a matter of weeks) resulting in a poor ground.

Now obviously if using a stud to distribute power, you'd use brass etc - but would it really make a difference when the bolt is merely holding two conducting surfaces together?

[meow2222]

With an ss bolt you get 2 problems

1. chrome oxide layer
2. dissimilar metals plus electricity

Just what impact those have I wouldnt know.

NT

[Dave Plowman (News)]

That's probably the one of interest.

Well, a typical ground connection on a car will be a plated brass ring terminal to the steel chassis. Most likely a steel nut welded to the back of the panel, and a steel bolt doing the clamping.

Is what I wondered if anyone could give chapter and verse on.

[Bob Minchin]

I'm no expert but a sailing friend often talks about the huge range of stainless grade and only a few are suitable for use in salt water. Stories include keels falling off due to using incorrect bolt grade.

So it seems there is scope for electrolytic problems with certain grades.

[Brian Gaff]

Perhaps he did not actually bolt the surfaces directly but put a nut in between so it was more like a terminal. That would cause corrosion I'd imagine. I found this out once many years ago on a lawn mower battery we used during the 3 day week back in the day, and I scuffled around to find some usable screws, and one must have been stainless, at least it was for about two weeks. :-) Brian

[harryagain]

Any two dissimilar metals plus none pure water =galvanic action=chemical saltsformed that don't conduct as well as metal.

So cars are a big no no due to the salt used on roads.

Always made worse if there is electrical current from exterior source.

So the worst thing he could possibly do.

Metals that are far apart in the reactivity series are the worst, eg zinc and copper/brass. But aluminim and zinc not as bad.

[Dave Plowman (News)]

Yes - that's what I did wonder. If it's merely used to clamp the terminal to a clean chassis there would surely be (near) zero current flow via the nut and bolt?