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Old 09-28-2012, 01:23 PM   #16
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how deep should PVC conduit be in slab?


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Originally Posted by Gac66610 View Post
So you (a long with others) are saying that PVC can not be used in concrete?
I read Notes 2, and 5, both say minimum of 2" concrete, so how would a slab be any different?
Note 2 relates only to raceways not approved for direct burial. PVC is not one of those, so note 2 is irrelevant. Note 5 applies only when installing exterior conduit over rock, which is not what you're doing, so it's also irrelevant. The table entry for burial-rated conduit under a building is directly applicable here if you place the conduit under the slab. The earth under a slab qualifies as both "exterior", i.e. not within the building, and also as "under a building". So you would need no concrete encasement and could lay the pipe right under the slab.

However, placing PVC conduit inside an interior slab is a situation not addressed by this table, I think. It is not "buried", and it is inside the building envelope. I believe the only applicable rule would be that the conduit must be suitably protected from damage, just like any other conduit inside a building. Unless someone can find a different code provision that specifically applies to this, I would say a conduit located within a concrete slab only has to be below the surface, or however deep is necessary to protect it from damage.

As a practical matter, it's a bad idea to place any embedded objects within about 1/2" of the surface of a slab during a pour because it tends to cause cracking and spalling later (1.5-2" cover over rebar is a standard spec). More cover is needed to avoid problems when doing a patch like this. Make sure you undercut the sides so the patch is locked into the slab, and use a high slump mix with fine aggregate. Or maybe a pourable grout if it's a really narrow patch.

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Old 09-28-2012, 02:42 PM   #17
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how deep should PVC conduit be in slab?


Quote:
Originally Posted by Gac66610 View Post
So you (a long with others) are saying that PVC can not be used in concrete?
I read Notes 2, and 5, both say minimum of 2" concrete, so how would a slab be any different?
Again, Note 2 refers to "Raceways approved for burial only where concrete encased". PVC does not require concrete encasement.

Note 5 refers to raceways in "rock". The OP is installing PVC under or in a slab. Therefore, neither note applies.
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Old 09-28-2012, 05:07 PM   #18
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how deep should PVC conduit be in slab?


The 50mm or 2 inches is what's required to meet the requirements of mechanical protection. Probably depends on the inspector as to how they interperet possible mechanical damage. In my neck of the woods we go down far enough that we can get a sold layer on top that won't crack and be done with it.

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