I currently have an existing main panel with a 100 amp service. I would like to upgrade to a new 200 amp breaker box with a pass through to a 100 amp sub panel (existing). Problem is the pass through does not have a disconnect and the existing sub panel does not either. Which means i cannot shut off the feed between the new panel to the sub panel. Does anyone know where i can find a 200 amp breaker panel with a shut off for the 100 amp sub-panel in the main panel or will i have to use a 125 amp breaker to feed the sub-panel. I only need 8 spaces for breakers in the main panel.

You actually have to do a lot more thinking and planning.

1) Is there a Main Disconnect breaker in the Main Panel, or is there a disconnect switch before the service enters the main panel?

2) Will the sub panel be located within the same building as the main panel or in a remote building (detached garage)?

3) You will need a four wire feed from the main panel to the sub panel.

4) You have to install a breaker in the main panel to feed the sub panel.

5) You need a main disconnect switch at the sub panel or a breaker inside the sub panel to be a main cutoff or No more than six switches (breakers) to disconnect the entire load from the subpanel.

6) You must have the equipment grounding conductor isolated from the grounded conductor. The only place these two wires can be connected together is at the main panel or main disconnect switch.

There is much more to do, but we really need more information from you.