I doubt that you are going to have much of a heat issue. I would make the trench at least 24" deep and put it in conduit. Go look at your shovel and measure how deep it goes every time you dig up a shovel full of dirt. You are going to be getting pretty close to 12" without trying very hard every time anyone digs a hole for anything.

18"- 24" is code depending on the particulars.

I thought that if it is only 20 amp and it is protected by GFCI before leaving building it could be at 12".

I thought that if it is only 20 amp and it is protected by GFCI before leaving building it could be at 12".

You are correct, but remember, that is a minimum cover. Deeper is always better.

I am comfortable at 12" in PVC, but is that allowed according to code?

Yes, still 12" if GFI before it goes underground.

I am curious as to how a chicken restaurant is getting by with only one 20A circuit.

In my area a "chicken house" is where the chickens are housed. 50' is really close if the supply is from a residence. The odor from chickens is not usually strong but distance helps.

Good point, Bus driver. The chicken house is about 250 feet from the house and about 50 feet from the barn. The barn has it's own subpanel. The wife wanted the chicken house closer to our house but I talked her out of it.

Any opinion on the conduit question?

You cannot put UF cable in conduit the whole way.
You can use conduit to protect the UF when it enters and exits the ground.

If you put in conduit pull separate wires.
Using rigid conduit can also get some relief on the burial depth.

From another discussion board:
I believe UF is allowed in conduit.

NEC2002 Article 340.10(1) says "For use underground, including direct burial..."

If you can't put it in a raceway underground, then what other methods are there besides direct burial?
__________________
Jim Dungar, P.E.
I hope this is what I meant to say.

From another contributor:
I don't know why it would be a "bad idea." It may not be a superbly good idea, but neither is it "bad."

The Code was in earlier time ambiguous about cable in conduit. In the 2005 Code (IIRC) they made a change in the wording to make sure that it is clear that cable is allowed in conduit.

That said, it would certainly be easier to run THWN in that conduit. Not to mention cheaper.

It seems that there is some debate.

Can someone answer my original question?

To answer your original question, put it in the conduit, that will provide physical protection for the wire and you have no danger of heat being a problem from the conduit. If you have this protected by a gfi it will be VERY safe.

Thanks. I just came in from from digging. After going through lots of tree roots I am down to 18".

In Canada we can put SE type cable in buried conduit as long as the cable is wet rated. Our rating for this type of cable is NMWU, meaning non-metallic wet underground.

brickeye, where in the code is UF cable not permitted in conduit?

Cables are only allowed in conduit systems if they are listed for that use in the article that covers the cable type.
Almost none are.

2008 code is at work.

The older versions were vague on cable in conduit, but around 2005 the code was changed to restrict use of cables in conduit systems to only cables listed for that use.

The restriction does NOT apply to short sections of conduit used only for physical protection.

Thanks Brick....I wasn't aware of the changes...mostly because I have never installed a cable assembley in a conduit system. I am, however called upon occasionally by realtors for overviews of HO installed wiring. Now I'll know if I see a new installation done this way, it's a no no.

"Cables are only allowed in conduit systems if they are listed for that use in the article that covers the cable type. "

Brick, I have to disagree here. Installations are only prohibited if specifically listed as such.
It doesn't have to specifically state something is permitted. It can be assumed.

For instance, UF cable is listed as permitted "For use underground, including direct burial in the earth."
It clearly states "including direct burial". What is the other underground option to direct burial?

Don't get me wrong. I do NOT use cable in conduit, and it kills me to see it done. But it is really not "prohibited".

I made a call and went with GFCI protected UF in conduit at 18". Code allows direct bury at 12" which IMO isn't as safe as what I did. I never do anything in the house that is against code, but in this case (chicken house) I did what I thought was going to be the better install. There is a lot of debate as to whether there will actually be more heat buildup in conduit versus just in the dirt. It sounds like dried out dirt has potential for heat build up as much as conduit. I don't like the idea of any unprotected cable unless it is at least 36" down. I will consider using THWN on my next project if I don't have a trencher.

Im not sure why everyone has a problem with using uf in this situation. The conduit run is not required but if added only improves the installation by adding a measure of physical protection to the run. In fact, it is just an extension of the protection you would provide where it enters and exits the ground. Heat build up caused by being in the conduit is not an issue. I had an inspector require a conduit run because of soil conditions once.