I have added a large garage to my home. I currently have a 100 amp breaker panel and 100 amp meter base on the existing part, I have put a 200 amp meter combo on the far exterior (which is about 70') with a new 200 amp breaker panel back to back. I am putting a 100 amp breaker in the new 200 amp panel and running a service entrance cable from the existing 100 to the new 200 panel to this 100 amp breaker. My question is, what size service entry cable is needed to join these two panels that will supply the old 100 amp panel? Also, is aluminum safe or should I consider copper? All inside wiring is copper and this cable will be ran inside the garage. Some say if aluminum, it needs an inhibitor, some say that is only when connecting aluminum to copper, then I've read it can heat and be flamable. I am totally confused at this point.