Splitting Service Equipment Across Two Enclosures
Your plan is still code compliant in the 17 version. I like copper but you may find aluminum easier to find and it is a little easier to bend even though it is a larger size. Make sure to use an anti oxide compound especially with aluminum, but I even use it with copper. Also make sure to properly torque the connections. I teach my apprentice’s to torque break loose and torque again 2-3 times each time the wires relax and are more secure. With large feeders I wiggle them back and forth then retorque it dose the same as releasing and retorqeing.