What wire to use underground?

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Old 05-12-09, 02:03 AM
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What wire to use underground?

What would be the best choice of wire to run in an underground conduit?

I am running electricity to my barn, have dug the trench and wonder what would be the best choice of wire to use. I know that there is direct burial wire but I do want to run the wire in conduit to protect it. Should I use, say, UF-B for further protection in case moisture forms in the conduit?

Here are the parameters.
- 50 foot run from house to barn
- Depth of trench 24
- Wire gauge: would prefer 10 (It is a 20 amp circuit but would prefer to use 10 gauge in case I decide to one day upgrade the rest of the circuit).
- Conduit: Intend to use the standard gray PVC, 1 or 1

Thanks
 
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Old 05-12-09, 05:06 AM
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Run individual wires in conduit. It is a real PITA to try and run UF-B, although it can be done. Go with the larger conduit if you have the option. You can never tell when you may want to upgrade service. You can do it easier that way. You may want to rethink your immediate needs as well. Will 20 amps be sufficient? Do you have any power tools running there? Will you need a welder later on? Just some food for thought.
 
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Old 05-12-09, 06:26 AM
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You would run THWN conductors in the proper size and colors in the conduit. You can pull them through with a fish tape.
 
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Old 05-12-09, 08:58 AM
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The W in THWN means waterproof.
 
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Old 05-12-09, 09:49 AM
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One more question...

Thanks for the info.

One more question came up: I want to also run a phone line and/or network cable (will most likely use the computer in the barn sometimes so would like to have DSL).

Should I run the phone line in a separate conduit? I dont know if code allows running the phone/data and power line in the same conduit, but in any case, Im also concerned that having the phone line run next to the power line for such a long stretch (50 ft) might induce crosstalk into the phone/data lines.

Also, should the telephone wire in the conduit be regular phone wire? Is there special phone/data wire for running in conduit underground?
 
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Old 05-12-09, 10:07 AM
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It should be a separate conduit at least 12" from the power conduit. A good way to do this is to dig the trench 24" deep; put in power conduit, backfill 12" put in data conduit, fill to grade.

You can buy underground / waterproof phone and data cables. Or just go with Wifi...
 
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Old 05-12-09, 06:02 PM
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I've had a piece of interior grade Category 4 wire in my low-voltage innerduct to my garage since 2001. It is still working fine. However, for best results you can get exterior grade category 5e.

Besides the conventional Schedule 40 conduit, you can get Schedule 80 for more protection with the trade-off of smaller interior diameter. There is also continuous innerduct and flexible PVC that is rated for burial. You will not find innerduct at retail stores, but it may be available from some supply houses.

My DSL comes in over a 5-pair shielded phone cable direct-buried next to a 200A feed with minimal separation - zero to two inches. Works fine. But more separation is better.

Also after you backfill to 6" below grade lay in CAUTION or DANGER tape to warn future diggers.
 

Last edited by ArgMeMatey; 05-12-09 at 06:05 PM. Reason: correct typo
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Old 05-20-09, 10:16 AM
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I am not being very successful at finding THWN wire. The usual stores (Home Depot, Lowes) do not carry it. I also called 4 electrical supplies and only 2 carried it, in 500ft spools only!
They all assure me that electricians routinely run THHN type cable underground in conduit.

Any thoughts?
 
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Old 05-20-09, 10:26 AM
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All of the home centers, hardware stores and supply houses carry THWN by the foot and by the spool, the clerks there probably just don't know they do.

Look closely at the fine print of the THHN insulation and it will also have a "THWN-2" rating, perhaps another couple ratings too.
 
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Old 05-20-09, 10:36 AM
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The clerk at the home center probably knows it as THHN, or just "wire". As Ben says, almost all THHN is dual rated as THWN. Just read the spec closely.

By the way, I'm not sure using #10 affords you any future flexibility, but I'd need to know more details to be sure.
 
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