I have a temporary power pole about 75 ft from the small sub panel I'd like to install in my barn. Heat will be propane so the load will be minimal for barn/ small bathroom power.
I thought about buying 6/3 cable you can bury but the stuff is still quite expensive. One of the big box stores has a spool of 6/3 cable on sale at a big discount but it's not rated for outside use. The question is should I hold out for the cable you can bury or find another solution I can run in 1.5" plastic conduit? Amount of cable underground will be 50ft. Within about 2 years this will be pulled up and I'll run the barn power off the mains service from the house when it's built.
water gets into plastic conduit, so I would use the correct cabling and bite the cost. I would run pipe anyways, so you can replace the cable easily if needed. In fact, it may even be required, you will need a permit to do this work in most areas of the us/canada, so I would ask the inspecter whats required. When I roughed in any underground pipe in commercial electrical, it involved a layer of sand/gravel, then the conduit. Then grab a shop face, tie a long string onto a plastic bag in a small air bubble, and suck the bag through the pipe. Or for larger wire, use a thick rope, and lube it up with yellow wire lube (looks like butter).
I just did this myself 2 weekends ago.
You must have conduit, and like riverplace said - it is considered a wet location. You will need to use the correct wire. Specifically, THHWN, the W being necessary for wet locations. You'll need 4 conductors (wires), two hots, a neutral and a ground. The size of the wire depends on how much juice you need.
In the barn, you'll then need a subpanel with whatever breakers you intend to install.
You can get a nice 70amp subpanel quite cheap at Lowes, the squareD homeline works well. At the pole main box you install a dipole (220) breaker to feed the subpanel - for example 50amp.
You look at the NEC ampacity table to see what size wire you need.
http://www.okonite.com/engineering/nec-ampacity-tables.html
50amp requires #8 copper wire. You'll need 3 wires at #8, and the ground can be one up - number #10.
if by chance you decide you can get by with just a 30amp breaker, the wiring size would be #10, with a #12 ground.
I will stick with the proper under ground cable and use 1.5" conduit which I already have. 8 gauge will work so that could save me some money. Most if not all of the places around here don't carry 8/3 or 6/3 in stock as the biggest in stock is 10/3 which isn't enough.
Will be nice to get this done so I'm not plugging in an extension cord to run the barn lights.