[LazyPup]

As a plumber I will leave the wire sizing to the electrical experts however I am in full agreement with Speedy that I would prefer to see a PVC conduit and individual THWN conductors.

About a year ago I was working on a house sewer line from the structure to a septic tank. As I was digging the old sewer line up my shovel cut through the sheath of an unmarked buried cable running to a garden shed. When the shovel shorted out the wires it blew about an inch of the tip off my shovel and nearly caused me a heart attack.

Please, Please, Please, for the sake of us who make a living digging in the dirt, when you run a direct buried electrical service put it in conduit, and don't forget to run a "Red" marker tape indicating a buried electrical conductor.

You can get a roll of red plastic marker tape that is printed "Buried electrical line" at any good hardware or home supply center. Bury your line 18 or 24" deep, whatever your local code requires, then about a foot above the line lay a strip of the marker tape in the full length of the trench so that anyone digging in that area will hit the plastic tape first and be warned of the potential danger.