Generally bigger wires for Service Entrance, and Feeders yes, smaller wires for branch circuits no.....

What code ref. excludes alum. from being used as a branch circuit?

Brady,

I think that would be a Building Code requirement.

Bill

Have you seen any company manufacture aluminum branch circuit wiring? I don't think it is being manufactured anymore.

They used to use aluminum wiring in mobile homes years ago, but disimilair metal corrosion had caused a lot of fires and thats the main reason you dont see aluminum being used for anything under 2/0 anymore. There are a lot of breakers and recepticles manufactured that can accept both types of wires, but no one produces wire anymore out of aluminum. I dont know if it is against code, or just not practical anymore, but thats mainly why you dont see it.

You'll find good information and many links on aluminum wiring here:
http://www.inspect-ny.com/aluminum.htm