Is there a maximum length for a electrical line from my 400 amp service panel to a 200 amp service panel in my detached garage. I would like to run the cable through the attic and outside then to the garage and the 200 amp panel. The detached garage is approximately 10 feet from the house.
Thanks

To properly calculate voltage drop, three variables are needed,one, the load in amperage, two, the entire length of the cable from point to point, and three, the size wire planned to be installed.

Since the building is only 10 feet away from the main building, there is no concern for worry as long as the feeder is no smaller than #4/0 aluminum or #2/0 copper.