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Old 03-17-2011, 12:28 PM   #1
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THHN loose wire thru buried conduit?


i am running 4 loose wires with 50A through 35 ft of buried conduit, from my basement to the shed. i know that XHHW is rated for direct burial but since this is not direct burial (using conduit), i was wondering if i can use THHN. it is cheaper and skinnier, i.e. should be easier to pull.

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Old 03-17-2011, 12:36 PM   #2
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THHN loose wire thru buried conduit?


Yes you can use THHN conductors, but they must be in a Rigid metal conduit, or nonmetallic conduit encased in not less than 3 inches of concrete.

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Old 03-17-2011, 12:40 PM   #3
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THHN loose wire thru buried conduit?


oh, i have PVC conduit but it is buried under concrete the whole way, except one 2 ft section
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Old 03-17-2011, 12:51 PM   #4
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THHN loose wire thru buried conduit?


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Yes you can use THHN conductors, but they must be in a Rigid metal conduit, or nonmetallic conduit encased in not less than 3 inches of concrete.

Mark
Could you please provide a code article that limits the OP to just these two choices? Why does the PVC need 3" of concrete?

Also the conductor insulation would need to have a W in the rating like THWN for the wet environment. It could not be just THHN.
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Old 03-17-2011, 12:53 PM   #5
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THHN loose wire thru buried conduit?


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Originally Posted by Jackofall1 View Post
Yes you can use THHN conductors, but they must be in a Rigid metal conduit, or nonmetallic conduit encased in not less than 3 inches of concrete.

Mark
Huh? You can bury conduit without concrete. IMC is also rated for burial and strangely enough, so is EMT although I would never suggest it as such.

Burial depth varies based on location and type of conduit.

and NO you cannot use THHN in underground conduit. While most THHN is also dual rated as THWN, not all of it is. You must have that W in there for it to be rated for wet conditions, which underground conduit is.

edit; and Jim beat me to the punch
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Old 03-17-2011, 12:59 PM   #6
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THHN loose wire thru buried conduit?


But just by 2 minutes. It took you longer to type the longer answer.
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Old 03-17-2011, 01:22 PM   #7
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THHN loose wire thru buried conduit?


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Could you please provide a code article that limits the OP to just these two choices? Why does the PVC need 3" of concrete?

Also the conductor insulation would need to have a W in the rating like THWN for the wet environment. It could not be just THHN.
You are correct THHN without the W is not acceptable, but most THHN wire produced is also rated THWN, as for the conduit I may have been looking under the wrong section, 300.50 Underground Installations (2) Other Nonsheilded Cables.

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Old 03-17-2011, 02:43 PM   #8
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THHN loose wire thru buried conduit?


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Originally Posted by Jackofall1 View Post
You are correct THHN without the W is not acceptable, but most THHN wire produced is also rated THWN, as for the conduit I may have been looking under the wrong section, 300.50 Underground Installations (2) Other Nonsheilded Cables.

Mark
You need to look to the regulation of the specific type of conduit to determine it's acceptable uses and limitations.
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Old 03-17-2011, 05:18 PM   #9
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THHN loose wire thru buried conduit?


I agree with Nap on that
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Old 03-17-2011, 10:57 PM   #10
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THHN loose wire thru buried conduit?


so before i start pulling the 4 wires through, what's the best technique? should i keep them as straight as possible to ease the pull (i have 3 90 deg turns over about 30ish ft and the conduit is 1") or is it better to intertwine them or braid them? i did pull my ADT security system wire thru today but that was a cakewalk because it was really skinny and the conduit was 0.5".
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Old 03-17-2011, 11:14 PM   #11
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THHN loose wire thru buried conduit?


NO do not braid or twist them.

For 35 feet you can possibly just push them in but I wouldn't bet on it. You need to use a pull rope and attach the wires to the rope.

especially since this is PVC conduit, use wire lubricant, and plenty of it.


and of course, it takes 2 people.
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Old 03-18-2011, 08:51 AM   #12
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THHN loose wire thru buried conduit?


For pulling, I used a mason's line with a bit of plastic bag tied to one end of the conduit. Had my son start shop vac at other end; air draft pulled string end with a bit of a plastic bag tied to the string (sort of acts like parachute to capture air)and done. This was about 40' with 2 elbows. I was amazed it worked.
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Old 03-18-2011, 09:27 AM   #13
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THHN loose wire thru buried conduit?


no interference problem with electric and security in same pipe?
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Old 03-18-2011, 09:39 AM   #14
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no interference problem with electric and security in same pipe?
Two conduits.

Quote:
i did pull my ADT security system wire thru today but that was a cakewalk because it was really skinny and the conduit was 0.5".
Can't fit the #6s in the 1/2" conduit.
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Old 03-18-2011, 09:47 AM   #15
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THHN loose wire thru buried conduit?


Post #10 OP has 1" buried

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