I am looking to run a 100 amp subpanel to a new detached garage off of a 200amp main service in my basement. The planned load will be 15A fluorescent lights, 20A receptacles for power tools, 15A overhead door motors, 15A lights in the storage loft, 15A outdoor lights, and 20A GFI outlets. I will have 6 or 7 breakers in total (15/20A). I may potentially add a 30A double pole breaker for a ductless heating/cooling unit in the future. The install will require two ground rods outside the garage. Ground and neutral will not be bonded at the subpanel. The location of my property is in Southeastern CT. The total wire run will be approximately 125'. The run through my basement will be about 50' and then out the back of the house to the garage will be about 75', including up the outside wall and through LB to panel. I am reading online and getting electrical advice that underground conduit runs must be individual conductors of type THNN/THWN for wet and dry locations. I ideally wanted to run a single cable type without having to splice in a junction box. I planned to use 2-2-2-4 Aluminum SER which has type THNN/THWN inside the Romex. This would allow me to run cable in the basement with conduit or a raceway. The basement is unfinished. I have not seen any good explanation of why this wire would not be correct for this installation. Further complicating this for me is that I had a 25+ year licensed electrician come and state that this is exactly the wire that he would use. Even said that schedule 80 above grade is not needed, inspectors never check that it is 80 vs. 40. He is reputable and has been in business in the area for a long time. I plan to use 2" schedule 40 PVC below grade and schedule 80 above grade right to the LB. I can understand if PVC sizing is too small and posing a challenge or friction for the wire O.D. on the pull. Heat dissipation could then also be a problem, but if one uses adequate sized conduit I can not understand the reason to have to change wire types and complicate this. Interested in comments, thoughts, or suggestions.

My house has 400 amp electric service. From the meter there are two 200 amp disconnect/breakers on the exterior wall. Each disconnect feeds a separate 200 amp breaker panel in my garage. I'll call them panel A and panel B. The breaker panels are side by side separated by 16". I want to move one double pole 20 amp breaker from panel B to panel A. It is a 240 volt circuit for my well pump. Panel A has plenty of capacity to support the circuit. My question is this... when I pull the cable for this circuit out of panel B, it will be too short to reach the new breaker position in panel A. What is the correct way to add a few feet of cable to this circuit so I will have enough length to connect it in panel A?