Does copper aluminum reaction occur only when there is current flow? Or regardless of current flow, when you have copper and aluminum touching you wil have current flow.

My main question is can i use regular wire nuts to connect aluminum and copper grounding wires or i need a an aluminum rated wire nut with the antioxidation?

Regards
Edward

With or without current, you still have oxidization due to dis-simular metal contact.

Not getting into the harder physics of it, but an electro-chemical reaction will rot the contact surfaces of the two. Aluminum on its own may do it in certain climates anyway.

And, ya, you need Al/Cu rated wire-nuts.

Edward,
Copper/Aluminium reaction, is caused by dampness, it set's up it's own Galvanic reaction that creates an EMF between the two dissimilar metals, thereby compounding the problem.
In an answer to your second question and in agreement with Mark (e57) use a bi-metallic crimping system, copper one side of a sleeve and Aluminium the other side and make sure you use the proper grease on the Al side.
We swear by them here, and we have some of the most rediculous atmospheres to work in.
(Salt air and the like).

Thanks Gents.