According to Joey :
Hi all,

I'm running electric to a new shop building underground for about
185 feet. I'm considering using aluminum tri-plex #4 or #6 inside
1" PVC buried about 2 feet. I'll be running a 120V air compressor,
an arc welder, and a 120V window A/C but not all at the same time.
The reason I'm looking at the aluminum tri-plex is the cost which
is .70/.85 cents a foot in my area. Is this the best and least
expensive way to do this job ? I'm doing it myself so I'm not
worried about code but I will have sufficient breakers on both
ends. Any suggestions/ideas please ?

When we wired our detached garage (100A, 120' worth of sub feed),
it would have cost about $700 in copper versus $300-ish in Al.

#3 Al triplex versus #4 Cu NMW (aka US UF).

In our area (Canadian codes), you can direct bury NMW (no conduit
or other protection) as long as it's 24" underground (goes to 30"
under driveways/roads). You can subtract 6" from the depth if you
put it in CSA-rated PVC tubing. (I don't think the NEC permits
PVC tubing of any kind, has to be real conduit).

We used a PVC sleeve under the driveway, but not under other parts
because the trench was 24" thruout.

Given the price difference, we went with the aluminum. Haven't
regretted it. But it does have to be carefully done exactly
to code (grease etc).
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.