I am going to run power to my unattached shop (15'x24')from my existing 200A main which is about an 80' run. I am planning on the following: (1)50A 220v outlet to run an smal AC stick welder, (1) 20A circuit for lighting inside and out. I am planning on having an upright refrig/freezer, and will use an 8000 or 10,000 BTU window unit AC on occassion, as well as a few extra outlets on the inside and one on the outside. I was figuring at least two if not three 20A circuits for outlets. I will also run on occassion a 6.5hp air compressor and various power tools. Do these circuits seem reasonable?

My main question is the size of my feed. I was planning on a 100A or 125A subpanel. Should I run #2 THHN copper from the main or can I get away with #4? I am going to drive a ground rod at the building, and was thinking 1 1/4" conduit.

Which subpanel would be best?
What feeder wire size?

Thanks,

I would install a subpanel with a 100A main breaker, fed by 2-2-2-4 mobile home feeder cable in 1.5" conduit, protected by a 70 or 90A breaker in the main panel.

The subpanel will need a separate grounding terminal and an isolated neutral terminal. You will need 1 or 2 ground rods driven at the shop, connected with at least a #6 Cu wire to the grounding terminal of the subpanel.

Thanks, but I have one more question. why do I need a 4 wire feeder if i am going to drive ground rods at the site. I thought I only needed two hots and a neutral, then of course the ground, grounded at the building.

Thanks,

The ground rod does not provide a fault path back to the main service panel, it is only for dissipation of high voltage spikes such as lightning or contact with the POCO high voltage lines. The 4th wire for the subpanel is your fault path.