Copper Ground System on Metal Roof

As far as I know this is not acceptable. But I can't find a source for it. Or am I wrong? Has anyone got a source

Yes, but percentage is a factor too. Copper is more noble than aluminum, but the sheer volumn of a metal roof, versus the small amount of copper in contact with it will generally prevent any issues. And it's all relevant to how much water is involved. Since the wire is along the ridge, it doesn't get the volumn of water necessary to get electrolosis up and running.

Typically copper is incompatible with other metals, most especially aluminum. This is because of their different ionic compositions. Putting them together causes galvanic corrosion, where one of the metals ends up eating through the other metal. The grounding copper should have some kind of barrier between it and the other metal so that they aren't in direct contact with each other. The simplest way would be to coat the copper with plastic epoxy.

Me too. Steel, tin, aluminum, leaded copper and copper.

I meant "Steel Roofs"

BTW, we have grounded metal roofs all over this state. :)

Why not? I've reinstalled ground rods and cable on several. My metal carport is grounded too.