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Joined: Aug 2001
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When I say THHN, I mean THHN and THWN. I just wanted to make the point that they both are OK to use in wrapped ridgid pipe underground.
[This message has been edited by aldav53 (edited 12-14-2001).]
The Golden Rule - "The man with the gold makes the rule"
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Air moves in and out of the conduit carrying with it water vapor. When the air cools in the conduit the water vapor condenses out leaving water in the conduit
My first encouter with a wic used on an outside Rigid run made this clear.
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As stated above THHN is not allowed in a wet location. Also as stated above most of us have not seen THHN that was not also rated THWN.
Again as stated above underground conduit is a wet location. It doesn’t matter if it’s PVC, Rigid or what ever. If you had conductors marked THHN only it would be a violation to install them in underground conduit.
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(Chiming in)
The individual conductors in type NM may be rated as THWN, but the overall cable assembly is not rated for wet locations. The paper filler will wick water like crazy.
THHN/THWN is not rated as wet location because of the nylon coating N. It is rated by the W. Type TW and type THW are both rated for wet locations, and don't have the nylon jacket.
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Electure, what do you mean when you say the paper in the NM cable will wick, even if it does get wet, the W rating on the jacket of the NM wire itself should protect it from the wet location.. right?
The Golden Rule - "The man with the gold makes the rule"
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aldav53,
It doesn't matter what the wire type is in the NM cable. 336-4(a) restircts NM cable to normally dry locations.
Don(resqcapt19)
Don(resqcapt19)
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And yes, I've seen it wick moisture and cause a volt-tic to give false "off" readings on live cable. (I learned the easy [non-violent] way by noticing that said cable was feeding a burning lamp...)
I must say that NM cable in conduit (outdoors) is one of the most common violations here... usually stuffed in 1/2" pipe (and sometimes with plumbing ells!)...
How'd they do it?
-Virgil
Residential/Commercial Inspector
5 Star Inspections
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2002 NEC should clear this up.
334.12 Uses not permited.
Types NM,NMC, and NMS
(A)d. Where exposed or subject to excessive moisture or dampness.
Definition of wet location covers, (Instalations underground.)
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Joined: Dec 2000
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Al,
Take apiece of NM cable. Put one end in a bucket of water. Come back the next day and the other end will be wet.
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ohhh water cooled conductors.....no derating
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