I recently upgraded my service to 200 amp,30 slot panel. I currently have fifteen 20 Amp single pole breakers in this panel and two 30 amp double pole breakers intalled. I have eleven spare slots. I am finishing my basement and the panel will be in the finished part so I will not have access to it if I need power. I want to add a subpanel in the unfinished part of my basement in case I need power in the future. I might add my house is a small cape code 1500 square feet plus basement.

What is the maximum size subpanel I can run off this 200 Amp panel?

I believe you DO NOT tie the nuetral to the ground in the new subpanel. Is this correct?

At one time this house had a water pump installed and there was a small fused panel by the pump. The owner tied in a garbage disposal, and an outside motion light to this box, the pump is gone now. This fuse panel is currently one of the existing 20 amp breakers in the main panel.

Should I run a another smaller say 4 slot subpanel in addition to the one above or just run a new circuit out of the above subpanel and tie the light and garbage disposal together in an electrical box where the existing feud box is?

Before you can determine the size and configuration of the subpanel, you must do a load calculation to make sure you get the correct amperage to the subpanel.

Then you will need the proper size Breaker for the cable from the main panel to the subpanel.

You will need a cable sized for the amperage needed along with a equipment grounding conductor.

You can install two types of panels. 6 or less breaker positions (No main cut off switch required). Or for a subpanel with more than six breaker positions you will either need a Main Cut Off Switch or a main breaker in the subpanel that will power to the panel.

The maximum breaker for your panel may be 100 or 125A. You CAN put a 200 A main breaker sub panel where the main breaker is used as a disconnect. It can be supplied by say a 100 or 125 A breaker from the main panel. Wire size is based on the feeding breaker size.

So this means, you can have a 100-125A feed and a 100 to 200 A main breaker sub-panel.

When main breaker sub panels are used, usually a ground bar kit is required to be purchased and the green neutral to ground bond screw is removed.

It's a misconception that the sum of the breaker amperage in the panel be equal to the main breaker size.

4 wire feeds are required and neutral and grounds are isolated in the sub panel.

I would run a 100 a sub panel, you do not bong the neutrals and grounds together keep them separated, you can run a 4 AMG copper or 2AMG alum.

For a subpanel, you cannot use NEC table 310.15 (B) 6, where #4 Cu is allowed.

Must use Table 310.16, and # 3 copper or # 2 aluminum is the smallest wire allowed.