THHN under slab

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sticko

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I was going to pull THHN in pvc installed under floor slab. Then I saw here that the installation was considered outside of the building. Does this mean that the pvc is in a "wet" location and I need to use an insulation type with a "w"? If so, what code article can I find this?
 
sticko said:
I was going to pull THHN in pvc installed under floor slab. Then I saw here that the installation was considered outside of the building. Does this mean that the pvc is in a "wet" location and I need to use an insulation type with a "w"? If so, what code article can I find this?
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Yes a conduit underground is a wet location.

Take a look at the definition of wet location.

"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 weather."

Also take a look at 310.8(C) for types of conductors allowed to be used in a wet location.

Chris
 
sticko said:
I was going to pull THHN in pvc installed under floor slab. Then I saw here that the installation was considered outside of the building. Does this mean that the pvc is in a "wet" location and I need to use an insulation type with a "w"? If so, what code article can I find this?
Click to expand...
Definition:
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 weather.

Then look at 110.11.

Then go to 310.8(C):
(C) Wet Locations. Insulated conductors and cables used in wet locations shall comply with one of the following:
(1) Be moisture-impervious metal-sheathed
(2) Be types MTW, RHW, RHW-2, TW, THW, THW-2, THHW, THWN, THWN-2, XHHW, XHHW-2, ZW
(3) Be of a type listed for use in wet locations
 
Most if not all THHN is 'dual rated' as THWN or THWN-2, along with other rating. Check the label. This might rended the 'wet or not' question moot.

My understanding is that in most areas, conduit in slab is considered a wet location.

The only code sections that I recall that talk about conduit in or below a slab as being 'outside' have to do with service conductors and the requirement that they be protected nearest the point of entry into the building.

-Jon

P.S.
Talk about simultaneous posting. I wrote the above in a separate editor, refreshed to see if anyone else had posted, hit reply, and bang! there were the other answers.

I forgot about 'definitions', and agree with the above.
 
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charlie said:
It is amazing to me how many posts are made at almost the same time. Looking at the bright side, Chris and I agree on this one. ;)
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I know, it happens to me all the time (Im a slow typist:D).

I usually agree with you Charlie.:)

Chris
 
sticko said:
I was looking at 310.8. But I didnt think to look at art. 100 for definition. Again I'm humbled. Thanks.
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Your welcome.:)

Don't be humbled, I'm just a code geek without a life.:D

Chris
 
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