contrex wrote:
If you want a fire or some electrocuted children, not to mention
voided insurance and a code violation citation, go right ahead. You
need to get your goddam wallet out and pay a qualified electrician.

Well that sounds a bit harsh. But I agree, I would not make any
underground connections. If I were you, I would do these few things.
1) Pull out the short wire, coil it up, and save it for another project.
2) Get a 250-foot roll of #12 UF Romex, and string that through the
pipe. "UF" means "underground feeder" - this wire is suitable for direct
burial in the ground, so the pipe simply adds some extra mechanical
protection against nicks and abrasion - and inadvertent digging.
3. When you assemble the pipe, make a waterproof seal at each joint,
and be sure that each end is terminated either indoors, or with a drip
loop and neck. This doesn't guarantee that the pipe won't get some water
in it - but if it does, the unspliced UF wire can handle it. Spliced
wire would be a disaster in this case.
4. When you bury the pipe, backfill the first 12" of depth of the
trench, then run yellow warning tape "WARNING - BURIED UTILITY LINE
BELOW" for the full length of the trench, then backfill the remaining 6"
up to grade.

By the way, 250 feet sounds like a whopper of a run for #12 wire. I
hope you aren't planning to use it at its nominal 20-amp rating? If you
need that sort of current, you ought to consider moving to #10.

Bill