# Conduit depth concrete slab



## Gamit (Dec 30, 2009)

I need to provide a circuit for a kitchen island and you could of guessed that the kitchen is on a slab. I was looking at 300.5 and column 2 is rigid metal conduit and column 3 specifies without concrete encasement. So I eliminated those columns and column 4 I think would be the column to use but after looking at the locations the only one that mentions slab is exterior? Then after looking at the note number 2 mentions concrete envelope of 2 inches. Can someone explain how deep I would need to go with non-metallic so I can sleeve some 12/2 to the island?


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## Mr Rewire (Jan 15, 2011)

Gamit said:


> I need to provide a circuit for a kitchen island and you could of guessed that the kitchen is on a slab. I was looking at 300.5 and column 2 is rigid metal conduit and column 3 specifies without concrete encasement. So I eliminated those columns and column 4 I think would be the column to use but after looking at the locations the only one that mentions slab is exterior? Then after looking at the note number 2 mentions concrete envelope of 2 inches. Can someone explain how deep I would need to go with non-metallic so I can sleeve some 12/2 to the island?


 This would be under a building so 0


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## Gamit (Dec 30, 2009)

Mr Rewire said:


> This would be under a building so 0


I just noticed that! But 0 is unrealistic should be at least 1. Otherwise it would be exposed


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## RKRider (Feb 7, 2010)

The way I read it the table shows minimum cover requirements in inches so 0 inches means it can be in the slab, it isn't required to be under it.


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## Gamit (Dec 30, 2009)

RKRider said:


> The way I read it the table shows minimum cover requirements in inches so 0 inches means it can be in the slab, it isn't required to be under it.


That makes sense I was reading it as depth under slab thinking it needed a minimum cover requirement.


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## Mr Rewire (Jan 15, 2011)

I always tried to get the conduits in before the thermal barrier went down


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## tkb (Jan 21, 2009)

Gamit said:


> I need to provide a circuit for a kitchen island and you could of guessed that the kitchen is on a slab. I was looking at 300.5 and column 2 is rigid metal conduit and column 3 specifies without concrete encasement. So I eliminated those columns and column 4 I think would be the column to use but after looking at the locations the only one that mentions slab is exterior? Then after looking at the note number 2 mentions concrete envelope of 2 inches. Can someone explain how deep I would need to go with non-metallic so I can sleeve some 12/2 to the island?


I would be considered a wet location in the slab and you would not be able to use NM-B cable in the conduit, also inside the island cabinet would be subject to physical damage so NM-B cannot be used inside the cabinet.

You can use PVC-40 and THWN conductors in the slab and PVC-80 in the cabinet.


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## backstay (Feb 3, 2011)

tkb said:


> I would be considered a wet location in the slab and you would not be able to use NM-B cable in the conduit, also inside the island cabinet would be subject to physical damage so NM-B cannot be used inside the cabinet.
> 
> You can use PVC-40 and THWN conductors in the slab and PVC-80 in the cabinet.


The slab is a wet location only if it is in direct contact with the earth. Most slabs around here are poured on top of a vapor barrier and 2 inches of inslulation and have no contact with the earth.


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## piperunner (Aug 22, 2009)

Well if you install any wire underground in pvc rigid or imc conduit it better have wet rating the big w in the type of insulation wire used or its coming out .

This is feeders or branch now we have dual rated wire we use its both temp dual and wet or dry but bottom line if your inspector lets you install it without that wet rating marking the big w hes not a inspector .

Its in your code book in you wire types uses insulation just before wire ampacity tables .

If you install conduit underground in a slab dig a little so the 90 degree elbow does not stick up with its bend half in half out that will look like crap .

When it gets bent over by another trade its easyer to fixed when its straight up and not in the 90 bend .

It kinda helps the slab from cracking when you come up straight .


That vapor barrier doesnt apply if its on grade level one ground level its wet but thats florida .


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## backstay (Feb 3, 2011)

piperunner said:


> Well if you install any wire underground in pvc rigid or imc conduit it better have wet rating the big w in the type of insulation wire used or its coming out .
> 
> This is feeders or branch now we have dual rated wire we use its both temp dual and wet or dry but bottom line if your inspector lets you install it without that wet rating marking the big w hes not a inspector .
> 
> ...


If you read the definitions in the NEC, the slab has to be in direct contact. 

From the 2011 NEC
*Locations, Wet. *Installations underground or in concrete slabs or masonary in direct contact with the earth;

A lot of our slabs are completely surrounded by 2 inches of insulation(bottom and sides) because they are heated.


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## Gamit (Dec 30, 2009)

So if it's considered a wet location then I obviously can nit use NM cable so will pipe up closest wall to counter receptacle and use thwn


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## Gamit (Dec 30, 2009)

Gamit said:


> So if it's considered a wet location then I obviously can nit use NM cable so will pipe up closest wall to counter receptacle and use thwn


Or UF


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## RIVETER (Sep 26, 2009)

Two inches.


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## Gamit (Dec 30, 2009)

RIVETER said:


> Two inches.


Yea ? Where does it state that? Thanks


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## piperunner (Aug 22, 2009)

backstay said:


> If you read the definitions in the NEC, the slab has to be in direct contact.
> 
> From the 2011 NEC
> *Locations, Wet. *Installations underground or in concrete slabs or masonary in direct contact with the earth;
> ...



I guess someone better tell the inspector in florida because if it doesnt have a wet rating even installed in pvc conduit its not passing inspection .
Thats in concrete on the ground level . Above the barrier inside the pour 6 inch slab 2 inches above the bottom matt . 

As the conduit not touching the dirt will fill up with water or have damp or a wet problem always its never dry inside conduit .

Maybe its not wet or damp up north but it is in florida .


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## rnr electric (Jan 29, 2010)

piperunner said:


> I guess someone better tell the inspector in florida because if it doesnt have a wet rating even installed in pvc conduit its not passing inspection .
> Thats in concrete on the ground level . Above the barrier inside the pour 6 inch slab 2 inches above the bottom matt .
> 
> As the conduit not touching the dirt will fill up with water or have damp or a wet problem always its never dry inside conduit .
> ...


 My arguement with the inspector was that this is not in "direct contact". But rather laid on top of heavy guage plastic before the pour. BUT there is the argument for condensation, of which i agree..


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## piperunner (Aug 22, 2009)

rnr electric said:


> My arguement with the inspector was that this is not in "direct contact". But rather laid on top of heavy guage plastic before the pour. BUT there is the argument for condensation, of which i agree..


Well we never see it as a problem we just pull Thwn Thhw Xhhw its not really a cost issue or give a inspector a hard time but its nice to keep our local inspectors happy .

If you look at the code it says if it contacts earth that plastic is not going to stop water from flowing .

How long does that barrier last .

I think its different in some areas of electrical work were below sea level down here so i think were a little wet .


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## rnr electric (Jan 29, 2010)

piperunner said:


> Well we never see it as a problem we just pull Thwn Thhw Xhhw its not really a cost issue or give a inspector a hard time but its nice to keep our local inspectors happy .
> 
> If you look at the code it says if it contacts earth that plastic is not going to stop water from flowing .
> 
> ...


 yes, im also in fl. We both know where the water table starts:thumbsup:. The only reason i ever brought this up to him was for arguments sake,for the debate of interpratation, if you will. fortunately he is a good friend of mine and he doesnt get easilly offended when i do this.If i didnt know him so well i would never do this, and expect to pass next inspect


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## piperunner (Aug 22, 2009)

rnr electric said:


> yes, im also in fl. We both know where the water table starts:thumbsup:. The only reason i ever brought this up to him was for arguments sake,for the debate of interpratation, if you will. fortunately he is a good friend of mine and he doesnt get easilly offended when i do this.If i didnt know him so well i would never do this, and expect to pass next inspect


Well some actually check the insulation most jobs we do they look at the wire during pre power inspections and after a few miles of wire we dont want to get to that point lots of work its better to just comply with there rules .

Life goes on and the next job starts its been that way for some time now .

Were on good standings with most inspectors we know lots of them they are easy to talk with and most of them have worked for our company .

I knew them when they were electricians so we all get along well one big happy family you could say .

They do there job and we respect that .


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## rnr electric (Jan 29, 2010)

piperunner said:


> Well some actually check the insulation most jobs we do they look at the wire during pre power inspections and after a few miles of wire we dont want to get to that point lots of work its better to just comply with there rules .
> 
> Life goes on and the next job starts its been that way for some time now .
> 
> ...


 yes i agree, keep them happy. follow the rules and it normally works to your benefit,they inspect ours at pre-power also. the thing to remember is this, they usually interperet as we do in the field. But every now and then you will get one that got hired as a fluke and dont know his a$$ from his elbow. I actually had an inspector that wanted me to run a bond "From jacuzzi motor to the shower valve because it was all in PEX type plumbing and nowhere to bond" I told him he was insane and i would not do it. no kidding


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## nitro71 (Sep 17, 2009)

The minumum depth in this case is how deep is someone going to nail or drill into the slap. If it's not very far and doesn't have many bends in it could probably get some 12-2 UF sleeved through it. Depending on if you're sleeving in flex in the island there's really no advantage to not pulling some THHN.


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## Gamit (Dec 30, 2009)

nitro71 said:


> The minumum depth in this case is how deep is someone going to nail or drill into the slap. If it's not very far and doesn't have many bends in it could probably get some 12-2 UF sleeved through it. Depending on if you're sleeving in flex in the island there's really no advantage to not pulling some THHN.


It's not far and it's a kitchen. All I want to know is how deep does the conduit need to be regardless of what's going in it.


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## Mr Rewire (Jan 15, 2011)

Gamit said:


> It's not far and it's a kitchen. All I want to know is how deep does the conduit need to be regardless of what's going in it.


Try to get your conduit in before the slab gets poured it dosn't need to be buried. If you can't get it in before the slab you can saw cut the slab and lay it in the cut and use floor level path to cover it.


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## backstay (Feb 3, 2011)

piperunner said:


> I guess someone better tell the inspector in florida because if it doesnt have a wet rating even installed in pvc conduit its not passing inspection .
> Thats in concrete on the ground level . Above the barrier inside the pour 6 inch slab 2 inches above the bottom matt .
> 
> As the conduit not touching the dirt will fill up with water or have damp or a wet problem always its never dry inside conduit .
> ...


I didn't finish the code ref, if the slab is wet like say in a carwash or because of high water table then it is considered a wet location without being in direct contact with the earth.


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