Electrical – How to add a main shutoff breaker to sub panel

Yes, you can. The systematic computer programmer in me even thinks it's a good idea, allowing a "star" topology for electrical distribution.

1. You will need 4 wires, as others have mentioned.

2. Keep the ground and neutral separate in the subpanels. The only place they should be bonded is in the main panel.

3. You will need ground rods at the new location. Yes, it's redundant, but it's still required.

4. The wire feeding the new subpanel must be protected from overcurrent by an appropriately-sized breaker. It can be at either end - in the old subpanel or in the new subpanel - or at both ends. It's up to you, but if only using one, I slightly prefer the upstream location, so that I can easily kill power to the feeder wire. If using both, 1 must be sized for the conductor, and the other can be that size or larger -- convenient if you buy a panel with a 100A breaker preinstalled.

5. While there are wires rated for direct burial, it's good that you're planning to use conduit. Oversize the conduit for ease of pulling wires, and minimize bends. While you have the trench open, run a second conduit for future expansion (ethernet? gas? macerator?). May as well run a water line, too, so you can have a sink.

6. Most electric kitchen stoves are installed on 240V/50A circuits. If you're installing something like that, then I suggest a 60A subpanel. That gives you plenty of headroom to install lighting, a small point-of-use electric hot water heater, and some convenience receptacles. Those will come in handy when doing maintenance in the area.

7. Aluminum wire is usually much cheaper than copper, but harder to work with. It's stiffer. You must use 1 size larger than with copper. The ends must be protected from corrosion with anitoxidant goop. The lugs must be torqued correctly. Some people think you should retorque the lugs on some schedule. Last time I bought wire, I wanted 8ga copper, but 2ga aluminum was 1/2 the price, so going with Al was worth it.

You may feed a 14-50 outlet directly from your main panel since there are unused breaker slots available. Use the correct breaker of course, and correct conductor type/size for the load. Do not forget voltage drop and temperature ratings when choosing cable.

You do not need to add another sub-panel for a single outlet.

Do not expect the code book to tell you what you can do. It's there to tell you what you can't.