THHN In Conduit Outside

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  #1  
Old 11-18-14, 10:06 AM
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THHN In Conduit Outside

Does someone know the code number on no longer using THHN in conduit outside and the year it was changed? When I've written that in the past I just went by what was written here but I have been asked for more info.
 
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  #2  
Old 11-18-14, 11:00 AM
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Article 310

Ray, check out article 310 in the 2014 NEC, I can't remember the last time we have used THWN.
Geo
 
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Old 11-18-14, 11:05 AM
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I see. Thank you for the correction. You are saying conduit outside but not underground is not a wet location.
 

Last edited by ray2047; 11-18-14 at 11:28 AM.
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Old 11-18-14, 07:07 PM
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If outside conduit would not be considered a wet location, but a dry location, NM-B cable could be used outside in conduit, right? I don't have a copy of the 2014 NEC.
 
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Old 11-18-14, 07:36 PM
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Without checking I believe it says outdoors and underground is a wet area.
 
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Old 11-18-14, 07:48 PM
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I think PCboss is correct, but if there is a change in the 2014 NEC it's possible that outdoor conduit MIGHT be just a damp location where underground conduit would be a wet location.
 
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Old 11-19-14, 04:09 PM
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Not sure if this helps. It's from the 2014 NEC.

300.9 Raceways in Wet Locations Abovegrade

Where raceways are installed in wet locations abovegrade, the interior of these raceways shall be considered to be a wet location. Insulated conductors and cables installed in raceways in wet locations abovegrade shall comply with 310.10(C).
 
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Old 11-19-14, 04:32 PM
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The article just posted would rule out NM and THHN outside.
 
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Old 11-19-14, 06:14 PM
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There appears to be no actual definition (article 100) for wet location,how ever underground is considered wet but conduits above grade are only considered wet if they are in areas such as dairies,carwashes etc.in which case the equipment must be set off the surface by 1/4".
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Old 11-19-14, 06:41 PM
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Article 100 has a definition for Location, Wet.
 
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Old 11-19-14, 07:15 PM
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Of course another question is how easy is it to buy THHN. Isn't most of the wire sold marked THHN/THWN and in reality just THWN with the added specification?
 
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Old 11-19-14, 07:28 PM
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2014 NEC Location, Wet
Installations underground or in concrete slabs or masonry in direct contact with the earth; in locations subject to saturation with water or other liquids, such as vehicle washing areas, and in unprotected locations exposed to the weather.
 
  #13  
Old 11-19-14, 09:35 PM
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in unprotected locations exposed to the weather.
That makes sense, such as under a roof, but outside. A good example would be under a roof at a loading dock, but still outside. That area would be a damp location and NM cable would still not be allowed even in conduit.
 
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Old 11-20-14, 04:07 AM
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Ray, I think you hit on a point. It seems Southwire is classifying their THHN and THWN-2 in the same breath. So is their THHN adaptable to wet locations? Their literature says so. Just wondering.
 
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Old 11-20-14, 04:17 AM
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The wiring is probably dual rated for both categories.
 
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Old 11-20-14, 07:51 AM
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The wiring is probably dual rated for both categories.
I cannot recall seeing any THHN that wasn't dual rated as THWN.
 
  #17  
Old 11-21-14, 08:41 AM
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How about these ratings? THHN ,THWN ,MTW ,AWM. Same conductor.
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Old 11-21-14, 09:00 AM
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Pretty common, it has all the properties to meet all those categories.
 
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Old 11-21-14, 10:04 AM
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Pretty much since the advent of full synthetic wire insulations like PVC, nylon and polyethylene there is not a whole lot of difference between the types of wire out there. I have recently seen a plain "TN" (no HH, no W) ground wire which a low voltage contractor was using as a bonding conductor between various equipment. The shade of green was unusual it caught my eye so I looked more closely -- I assume just some cheap imported wire they bought online somewhere. Anything you get from a reputable source will likely carry several ratings.
 
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