I need to join a new 100A feed on #2 aluminum wire to an existing #2 wire running from the panel. So this is actually #2 alum triplex in both cases plus a #8 bare copper ground. The junction will take place in an access panel in the wall where the two PVC conduits meet. What size junction box do I need for this? Is a juntion like this done with wire nuts the way a Romex juntion is? Does it matter what material the J-box is made of?