Currently I have 200A electrical service that's brought to my house above ground and into the basement on the right side of the house, which feeds a 200A panel. I'm in the process of getting my service upgraded to 320A, which will be brought in underground and on the opposite side of the house.
It's an old house with mostly knob and tube wiring, so I will be eventually upgrading the electrical wiring throughout the house. But for the time being I need to complete this 320A upgrade (I'm working with the local electrical utility company, and have a permit which expires in a few months), while maintaining my existing electrical wiring. Since the new service will be on the opposite side of the house, I cannot simply re-wire all circuits to the new panel. What I'd like to do is temporarily use the existing 200A panel as a sub-panel to the new 320A/400A panel. The 200A panel obviously has its own 200A master breaker, so in theory it seems quite possible to wire the 200A panel as a circuit off of the new panel, assuming the correct gauge heavy duty wiring is used.
Is this temporary use of the existing 200A panel as a sub-panel possible? What steps would be involved to do this correctly?