Raceways In Concrete

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north star

Senior Member
Location
inside Area 51
&

Is NM cable allowed to be installed in a pvc raceway that
installed in a concrete foundation, ...actually encapsulated
in the concrete on top of the vapor barrier?

The application is for a new single family dwelling......GFCI rated
conductors installed in a pvc raceway, going to a Kitchen Island,
...located in the [ very humid ] Southeastern U.S.

What say ye learned folks?.....Type "NM" allowed, or UF required?
:cool:

&
 
Last edited:

jumper

Senior Member
UF.

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.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
Nope.

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.
 

jumper

Senior Member
&

Is NM cable allowed to be installed in a pvc raceway that
installed in a concrete foundation, ...actually encapsulated
in the concrete on top of the vapor barrier?


The application is for a new single family dwelling......GFCI rated
conductors installed in a pvc raceway, going to a Kitchen Island,
...located in the [ very humid ] Southeastern U.S.

What say ye learned folks?.....Type "NM" allowed, or UF required?
:cool:

&

missed that.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I think there is a good argument for the vapor barrier. If you are above the vapor barrier it may be okay however that really limits the coverage of the pvc in a 4" slab. In general we use uf in those cases.

If this is a basement slab then I would say no go but above grade maybe
 

north star

Senior Member
Location
inside Area 51
$

Dennis,

I cannot verify the actual location of the raceway in relation to the vapor barrier.
This IS a ground floor slab-on-grade type of concrete foundation.......If you have
some code sections & language to rebut the "on top of the vapor barrier"
installation, I WOULD like to read it, so I can communicate it to others.....This is
one more reason why I ask the experts on here and other Forums.


Chris,

It is the typical type of plastic visqueen installed underneath heated & cooled
areas, as required in the IRC.

$
 

dana1028

Senior Member
Condensation

Condensation

Given the above scenario: slab on grade, thin sheet of plastic [vapor barrier] installed under slab [to prevent moisture from 'wicking' through concrete into dwelling].

Conduit is installed in the concrete [cold compared to dwelling environment]. Are we saying the conductors that become heated from use [in the colder concrete environment] will not cause condensation inside the conduit?

In our area conduit in a concrete slab on grade [regardless of vapor barrier] is considered a wet location because of the condensation.

I have personally pulled conductors out of conduit installed in the same location as the OP describes [kitchen island, slab on grade] and found them wet.
 

Strife

Senior Member
Why not just flex both sides(3-4 feet at the most?) and pull THHN (which are rated THHW, THW WHATEVER)?

&

Is NM cable allowed to be installed in a pvc raceway that
installed in a concrete foundation, ...actually encapsulated
in the concrete on top of the vapor barrier?

The application is for a new single family dwelling......GFCI rated
conductors installed in a pvc raceway, going to a Kitchen Island,
...located in the [ very humid ] Southeastern U.S.

What say ye learned folks?.....Type "NM" allowed, or UF required?
:cool:

&
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
$

Dennis,

I cannot verify the actual location of the raceway in relation to the vapor barrier.
This IS a ground floor slab-on-grade type of concrete foundation.......If you have
some code sections & language to rebut the "on top of the vapor barrier"
installation, I WOULD like to read it, so I can communicate it to others.....This is
one more reason why I ask the experts on here and other Forums.


Chris,

It is the typical type of plastic visqueen installed underneath heated & cooled
areas, as required in the IRC.

$

The only code section is what Chris quoted but it does say in direct contact with the earth. Your installation does not fit that if it is on top of the vapor barrier. I guess I would have to decide whether or not there is likely to be condensation inside they pipe if there is a vapor barrier. I think there would not be but I am not certain. I guess that is a judgement call of the AHJ
 

kwired

Electron manager
Location
NE Nebraska
Given the above scenario: slab on grade, thin sheet of plastic [vapor barrier] installed under slab [to prevent moisture from 'wicking' through concrete into dwelling].

Conduit is installed in the concrete [cold compared to dwelling environment]. Are we saying the conductors that become heated from use [in the colder concrete environment] will not cause condensation inside the conduit?

In our area conduit in a concrete slab on grade [regardless of vapor barrier] is considered a wet location because of the condensation.

I have personally pulled conductors out of conduit installed in the same location as the OP describes [kitchen island, slab on grade] and found them wet.

Heat from conductors actually helps prevent condensation. Condensation happens when warm humid air hits the cooler environment below grade. You want to reduce condensation you need to seal the raceway so warm humid air can not migrate into the raceway. It may be difficult to prevent condensation completely. Some places will have more potential for condensation than others. Raceway under a building with conditioned air is likely to be a place with much less potential than one that is outdoors.
 

north star

Senior Member
Location
inside Area 51
~ ~ ~

The location of the SFD in question, is in the Southeastern U.S., where humidity
/ condensation is a problem.....If you were the AHJ, what would be your code
based position:
[1] no special wiring required, keep on installing the NM
conductors,
[2] change to THHW or UF type cable to err on the side of caution,
[3]
other?

For those that are interested, there IS another excellent Forum for the
discussion of codes.......Go to this link:


http://www.inspectpa.com/forum/forum.php

~ ~ ~
 
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