Originally Posted by
James Duffin
You should know that a bolted connection is required.
I do know that, but originally we were not discussing 'how the connection was made'.
The sheet-metal screw has very little metal to metal contact so it it no allowed. The paint is not an issue in this application.
Paint is not a good conductor, and the paint needs to be removed when that bolted connection is made, because that bolted connection is made, not by contact between the bolt and the inside of the hole (as you said, even a sheet metal screw which cuts into the metal is a poor connection there, much less a bolt through a drilled hole), but is made by compressing the terminal (for the bond wire) to the metal between the terminal and the washer under the bolt head/washer&nut.
Unless you scrape the paint off, all you are doing is clamping terminal-to-paint and bolt/washer-to-paint, using the metal only to hold the paint in place.
That connection is unlike a ground screw in a box or panel enclosure. First, those have metal which is thinker, and their holes are threaded, for use with threaded screws, and the connection between the threaded screw and the metal is the electrical connection, because it is so much better than a sheet metal screw into metal.
If you've even seen one of those connections take a hit, you will notice the scorch arc mark all around the head of the terminal where the arc burned through the paint to make more contact when the threads could not carry the current load.
Those connections are not required to have the paint scraped off, because they are threaded and have what has been deemed 'adequate' metal-to-metal contact at the threaded ground screw itself.
