I want to upgrade my load centre panel that currently has a 100 amp main breaker w to 200 amp one along with the 100 amp service shutoff. The main is about 20' from the inside 100 amp fused shutoff connected with NMD-7 3/3. The meter base is outside on the opposing wall of the shutoff and is rated 200 amp. The shutoff and meter base are connected via conduit so i can't easily see the wire gauge. Do i need to replace the NMD-7 3/3 wire? Can i replace the main panel with a 200 amp and change the 100 amp service shutoff at a later date?
You can use a 200 A panel with 100 A service with no problem; it's done quite regularly. You can just put a 100 A main breaker on it (saving the 200 A one it may have come with for later). A lot of times the 200 A panels are cheaper, have more slots, and/or are just physically bigger (easier to work in), which is why they are used even if the service is less than 200 A.