What size breaker and wire do I need for a subpanel in my shed?

Question

I am wanting to run power to my shed/workshop. I will have 8 outlets running table saw and such not everything at same time also will have shop lights and a separate 20 amp circuit for pool pump. What size breaker in main house panel should I use to connect to subpanel in shed that is approx. 90 feet from the main panel?

Answer 1

I've said it before, and I'll say it again. It's tough to beat a 60 ampere sub-panel. You might be able to get by with a 40 amp setup, but it's always nice to have future expansion possibilities.

At 90 ft., you're probably okay to use 6 AWG copper, or 4 AWG aluminum conductors. You'll have to pull four conductors, either through conduit or via a cable.

Since it's a separate structure, you'll need a grounding electrode system. Which you'll have to bond the grounding conductor from the feeder, and the grounding conductors within the building to. You'll keep the neutral conductors isolated from the grounding conductors, which will likely mean removing a bonding jumper within the panel.

Answer 2

Based on your question, since you will be having a subpanel, you want the breaker feeding the subpanel to be sized for the subpanel or slightly smaller. So if you purchase and install a 200A subpanel, then the breaker should be 200A. If you use a 125A subpanel, then use a 125A breaker. And so on...

If you are wondering on what size of subpanel, which I believe this is the question, then you add up the wattage (or amp draw) of each element or potential element to be used.

• 8 outlets * 1.5A = 12A
• Table saw * 15A = 15A
• Pool pump * 10A (guesstimate) = 10A
• Lighting (240W?) * 2A = 2A

Lighting is high depending on what you go with, but either way this runs up to only about 40A. Giving yourself some space, you still have plenty to work with a 60A panel and run it all. Outlets of course depend on what you plug in and such, but you know that.

So again, if you run with a 60A panel, then use a 60A breaker in your main.

I'd suggest giving yourself additional space though and install a 100A panel and main.