I have a duplex with 2 - 100 amp panels mounted adjacently in one basement.
I want to install a sub panel 30 feet away to give tenant access to their own panel.
Original main panels are square-d 1976ish.
I was planning on installing a new 100amp disconnect to replace the main, then use a main lug subpanel 30 feet away.
1. Would the original main breaker be fine as the disconnect? (old 1976). I will be able to drag all the original main panel circuits to the new subpanel, but that will leave all my circuit breaker knockouts open and the main buss exposed.
2. I would like to run the sub feed wire under the joists in conduit rather than drill (old home/butchered joists) What size copper or aluminum wire size do I use? Conduit?
You can use your existing panel to power your sub, and you can use a main lug panel. You know better than to leave an energized electrical install open, and no one here will tell you different. If you feed the sub panel with conduit, why would you need to leave it open anyway? One suggestion that I will offer is the use of a trough or junction box near the panel. Take the circuits that are feeding the unit and get them into the trough or J box. Run your conduit to the sub to feed the circuits and voila! How much/what size conduit depends on how many circuits and what ampacity those circuits are. Never hurts to leave a spare home run in there either. Keep us posted