Hello all, I'm new to this so excuse me if I am redundant but I couldn't find this questions anywhere else.

I have a 125 amp sub panel in my garage. It was previously wired before I purchased the house. The old service in the house was 100amp - since then it's been upgraded to a 200 amp service. My problem is the 200 amp box is in a different location than the 100 amp service and I cannot reach the wires to this new box. The garage is all wired, all I need is the main wires to get to that 200 amp box.

Here is my dilemma: Aluminum wire is run underground from the garage to the basement of the house - it's 2AL USE burial wire. How can I get this to my service? I've never spliced anything larger than 8 ga and that was quite the ordeal. This may be a dumb questions but can I put a disconnect in there and use that as a junction? If so what size disconnect? Or do they make a junction 'device' I could use?

Another thing - on the old service there was no breaker for this sub panel - it seems like it was just wired right off the service coming in. I may be wrong but don't I need to put a 125amp breaker on my 200 amp service?

Any help would be greatly appreciated.