I'm wiring my small detached garage and I need to know if I must install a sub-panel or can I just pull the circuits from the main panel? I only need 3 circuits: One 15A for lights, and the other two for 20A Receptacles. It's only about 70 ft from the main panel and I already have the necessary wire for the job. A sub-panel and grounding rod would probably double the cost of this project for me.

 

Code only permits one circuit to a detached building. One work-around would be to use 12-3 to run a multi wire circuit. It would double your available amps but count as only one circuit.

What actual loads will you have besides GD opener and lights. Any tools? If so what.

 

Just your standard work tools (drill, circ. saw, etc) and an 120v Air Compressor. How does pulling 12/3 count as only one circuit? I was planning on pulling a 12/3 for compressor(1 circuit) & receptacles(1 circuit) and a 14/2 for lights. I believe that's 3 circuits.

 

If only one tool will be on at a time, then you really only need one tool circuit.

A Multiwire Branch Circuit (MWBC) delivers the same power as two 20-amp circuits, but may be considered one circuit for purposes of this rule. So you'll get 4.8KW of power from this one circuit. Run a single 12/3 cable. No grounding rod required. You do, however, need a disconnect. This can be done simply by running the cable directly into a double-gang box with two switches. Then you can split the cable from there into two runs of 12/2. You can put all receptacles on one run, and perhaps a mixture of lights and receptacles on the other. You'll need a GFCI on each run.

You can then plan to not use the receptacles on the lighting circuit except in unusual circumstances where you need to run two tools simultaneously.

If you think that you might be tempted in the future to put in a refrigerator or freezer or large television or garage door opener or space heater or air conditioner or dust collection system or any 240-volt tools, you'd be much better off to put in the subpanel now.

 

Why? A compressor, even a 240v one, only needs 2-conductors.

 

What type of breaker would that require in my main? I'm guessing a double pole 20a.

Thank You for your help, btw.

 

Correct...................

 

Ray, I think you misread. Read the entire sentence.

 

Oh, multi wire for compressor and receptacles. But of course then he couldn't pull the 14-2 but I think he knows that now. Thanks for the correction.