Subpanel vs breakers in main panel

[BeezFun]

I need two 120v, 20A circuits in a storage building that's 150' from the service panel in my house. Is there any reason to not just add two 20A breakers to my service panel, as opposed to putting a 40A subpanel in the storage building? In both cases I think I have to run the same wires: two #10 for hot, one #10 for neutral, and one #10 for ground. The only thing I see a subpanel buys me is a circuit breaker out in the storage building instead of up at the house.

 

[Lineman North Florida]

I'm not an inside electrician but I believe #12 is what is standard on a 20 amp circuit, as far as the sub-panel goes if you ever think you would need a little more than just the two 20 amp circuits you could up-grade, and if you live long enough you will want or need more, it's just human nature.

 

[pinetree10]

12 wire is used for 20 amp circuits and 10 wire is used for 30 amp circuits like a dryer plug. I can see why you're running 10 wire from your panel to the storage building though. With that much distance you increase the resistance on the wire just like you would increase the resistance on a long garden hose. You could run the 10 wire to the building and then use 12 wire inside the building. Just make sure you attach the 10 wire to a 20 amp breaker at your house panel and not a 30 amp breaker. Being an old electrician from the 1980s, I did the same thing for my detached storage building, which is 60 feet from my house. I don't intend to run much more than some fluorescent lights and a handful of receptacles to run things like a bench grinder, a leaf blower, or a garage door opener. I can see the argument for a sub panel if you want to run a welder or a large compressor and it would make future add-ons much easier because the panel is already there. I'm not current on the electrical code so there may be some working electricians out there who disagree with me. I'd be interested in knowing if there's some recent code against what I've done.

 

[BeezFun]

You could run the 10 wire to the building and then use 12 wire inside the building.

Yes, that's what I plan to do, I'll come into the building with 3/4" conduit into a 4" box and break out my two circuits using #12 in 1/2" conduit from there.

I don't intend to run much more than some fluorescent lights and a handful of receptacles to run things like a bench grinder, a leaf blower, or a garage door opener

Exactly what I'm doing

 

[Rock knocker]

More than one building or other structure
225.30 Number of supplies
Where more than one building or other structures is on the same property and under the same management, each additional building or other structure that is served by a branch circuit or feeder on the load side of the service disconnecting means shall be supplied by only one feeder or branch circuit unless permitted in 225.30(A) through (E). For the purpose of this section, a multi wire branch circuit shall be considered a single circuit

from the 2008 edition

 

[BeezFun]

from the 2008 edition

My vision is blurring trying to distinguish between branch circuits, feeders and services, but I think this says I can't use two circuit breakers in my main panel, I have to put a 40A breaker in my main service panel and run one multiwire branch circuit out to a 40A subpanel in the storage building. I think it also says I need a separate disconnect either inside or outside the storage building. Not sure what purpose that serves if I'm already required to have a breaker in my main service panel.

 

[Rock knocker]

Two 20A circuit breakers tied together and sharing a neutral should be legal as a MWBC as long as they are on opposite legs

 

[pinetree10]

This is why it's tough to stay up on the code when you don't do it every day. I interpreted it as you are permitted to run just one 20 amp circuit from your panel to the outside building. Otherwise you have to do what you described for more than one circuit. Am I correct that as long as it's kept to just one circuit then it's ok to use the 20 amp breaker in the house panel as the disconnect for the outside building?

 

[Rock knocker]

You are only allowed to run one single circuit to an out side detached building. But a MWBC properly tied together is considered a single circuit in this application

For the purpose of this section, a multi wire branch circuit shall be considered a single circuit

 

[BeezFun]

Two 20A circuit breakers tied together and sharing a neutral should be legal as a MWBC as long as they are on opposite legs

By "tied together", do you mean using a double pole breaker in the main service panel, and sharing a neutral?