I've just added a log cabin on my property. It came prewired and all I have to do is add the lights, outlets switches and run a service from my house. The building has 3 circuits as follows: Ckt #1 = (4) 15A outlets #12/2 wire with a ground Ckt #2 = (4) 15A outlets #12/2 wire with a ground Ckt #3 = (2) ceiling fans with lights (1) 100watt bulb each and (1) outside light 100watt max. The circuits terminate out the back of the building as 3 sets of wires. My plan is to mount a 4x4 exterior grade JB on the back wall drop 3 sets of direct burial wires down in a 2" piece of conduit to 10" below ground, then run in a 24" deep trench back to my house approximately 60 ft away. Once in the house through a hole in the foundation, I will connect the wires to a JB inside that has a single outlet on it. At this point I only plan to connect the 3 sets of #12 wires and grounds together in the outlet JB as I don't plan to put too much on the circuit. I may seperate them in the future. My question is, do I need to drop a ground at the building, or is grounding in the house enough? Also, does my plan sound okay at this point?