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-   -   THHN loose wire thru buried conduit? (http://www.diychatroom.com/f18/thhn-loose-wire-thru-buried-conduit-98693/)

amakarevic 03-17-2011 12:28 PM

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.

thanks

Jackofall1 03-17-2011 12:36 PM

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

amakarevic 03-17-2011 12:40 PM

oh, i have PVC conduit but it is buried under concrete the whole way, except one 2 ft section

Jim Port 03-17-2011 12:51 PM

Quote:

Originally Posted by Jackofall1 (Post 611357)
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.

nap 03-17-2011 12:53 PM

Quote:

Originally Posted by Jackofall1 (Post 611357)
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

Jim Port 03-17-2011 12:59 PM

But just by 2 minutes. It took you longer to type the longer answer.

Jackofall1 03-17-2011 01:22 PM

Quote:

Originally Posted by Jim Port (Post 611367)
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.

Mark

nap 03-17-2011 02:43 PM

Quote:

Originally Posted by Jackofall1 (Post 611385)
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.

windows77 03-17-2011 05:18 PM

I agree with Nap on that

amakarevic 03-17-2011 10:57 PM

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".

nap 03-17-2011 11:14 PM

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.

bob22 03-18-2011 08:51 AM

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.

tpolk 03-18-2011 09:27 AM

no interference problem with electric and security in same pipe?

Jim Port 03-18-2011 09:39 AM

Quote:

Originally Posted by tpolk (Post 611869)
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.

Jackofall1 03-18-2011 09:47 AM

Post #10 OP has 1" buried


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