I will actually be using less than 60 amps but the box has 100 amp breakers and rating. Do I need to go to a larger gauge simply because of the larger breakers or can I go smaller as for a 60 amp usage? I have a small compressor; 50 amp welder; may install a motorized garage door as a manual is there now. The lights were already in and are 6 long type fluorescent. The distance is 100 feet from home to garage and I am not sure if it will be above or underground. ( finances ). I am thinking of a temp service just for compressor and lights and save for the underground. I was using a 12/3 wire for lights and compressor but was just on ground. The contractor cut the underground wire that was there when be dug the basement. A trailer was here I I broke it up.. the renters had trashed it and the owner sold because of a divorce. I installed the breaker box and this was from the trailer. I followed code. Now no underground cable so will need some temp ideas and idea on the underground service.. I think I will need a 3" conduit or can I use the 2 for 100 at 60 amp? Thanks.. Earl

For a 100 amp feeder in conduit to a garage 100 feet away, you can use #3 copper, or #1 aluminum.