So I bought a house about a year ago with old wiring, no grounds. The main breaker box is outside and its a square D all in one box. And its crammed full with tandem breakers. I have gone through the house and changed all my outlets to GFCI, as I cant afford to replace the wiring right now, but I would really like to take the first steps to a complete rewire and move and replace my box. The location I want is just below the outdoor box in the basement. My main question is whether or not I have to wire the new breaker box to the meter, or if I can go off the old box 200 amp breaker straight to the new box? Essentially having two 200 amp breakers parallel with each other. Is there any code against that? The main panel outside also has a 50 amp breaker at the bottom that goes to the garage, and I'd prefer to just keep that one out there, and relocate everything else.
Also as a side note, my box has a service disconnect at the top of the panel. This threw me for a loop when I went to replace some of my outlets for GFCI. I turned the main 200 amp breaker off, and checked power at outlets I was replacing and they were still hot. Some rooms didnt turn off until I turned the top service disconnect off. This entire system is weird. Also from what I gather that top service disconnect is rated to 50 amps and it has 80 amps of breakers attached to it. This is nuts!