I have room for four 20 amp breakers in my service panel. I want to run four 20 amp circuits to a detached building 100' away. Can I run four stranded #12 wires with one #12 for ground in poly pipe to the building? Is #12 large enough or will I need # 10? I plan on two lighting circuits, one kitchen circuit with microwave, refrig, no electric stove, Another circuit for freezer. Largest load is microwave at 1200 watts.

Actually, I do not believe that you can run four separate circuits. NEC Code requires that there is only one entry point.

You would be much better off running a feeder into a sub-panel into the detached building.

To correctly size the feeder, you will need to do a load calculation for the detached building.

If your detached building is going to have a kitchen, then you must provide two 20 A circuits. That's required by the 2008 NEC code. Receptacles serving the counter top, must be GFCI protected also.

Bathroom(s) will require GFCI protected receptacle outlets.

Might I suggest that you contact three or more licensed electricians to plan and bid this job.

Thanks Donf! I can do a subpanel. Believe me, if I could afford a contractor I'd let them do it, but a Rockafella I ain't (these days they probably say: a Warren Buffet I ain't).

Anyway, what I have gleaned from other posts is: a 60 amp feeder using #6, three conductors one ground with a 60 amp disconnect at subpanel, isolate neutral and ground bus, install a grounding rod for subpanel. I think that 60 Amps is way over kill as this is a 300 square foot cabin, far, far, far, from the maddening crowd. There are no 240v loads and if you turned everything on at the same time, total load would not exceed 3000 watts/25 amps. Could I do a 30 amp subpanel?