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Old 06-08-2008, 08:49 PM   #1
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conduit in slab grade


I am having a mono slab poured for a detached garge and was wondering if I will be ok w/ code putting a 2" conduit pipe thru slab to pull electrical from house.

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Old 06-09-2008, 08:34 AM   #2
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conduit in slab grade


You can certainly run conduit under a slab, or you can penetrate the slab vertically if you need to. It would need to be buried in a trench 4" below the bottom of the slab. You shouldn't run it horizontally through the slab, unless your slab is unusually thick.

Also, be sure that you use electrical conduit, not plumbing pipe. No conduit...Even glued PVC...Will remain watertight. You must not use type NM romex in this application. You have to use type UF wire, which is rated for burial.

If your conduit will be exposed vertically in the garage, or if it runs across the ground anywhere that is exposed and subject to physical damage, you must use schedule 80 PVC. For burial, regular schedule 40 will work fine.

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Old 06-09-2008, 11:28 AM   #3
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conduit in slab grade


Quote:
Originally Posted by thekctermite View Post
Also, be sure that you use electrical conduit, not plumbing pipe.
Excellent point. You will need to buy type DZYR grey electrical conduit (referred to as RNC in the NEC). The easy way to distinguish is that it will be stamped with a UL listing as opposed to an ASTM listing. This is not sold at the big boxes near me so you may have to get if from an electrical supply house.

KC-

I'm tending to disagree with you on the 4" though. According to Table 300.5 in the 2005 code book, I believe that the appropriate depth beneath the slab would be 18" since it will not be encased in concrete as it would seem to fall under the category of

One- and two-family dwelling
driveways and outdoor
parking areas, and used only

for dwelling-related purposes (copied directly from the code book)

Perhaps I'm mis-interpretting the code?

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Old 06-09-2008, 11:35 AM   #4
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conduit in slab grade


Quote:
Originally Posted by thekctermite View Post
If your conduit will be exposed vertically in the garage, or if it runs across the ground anywhere that is exposed and subject to physical damage, you must use schedule 80 PVC. For burial, regular schedule 40 will work fine.
In the past, I've made the transition to RGS conduit before emerging from the slab. Therein, you have a damage-proof install not to mention you can immediately terminate in a steel box.
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Old 06-10-2008, 08:23 AM   #5
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conduit in slab grade


Regarding my quote of the NEC in #3, I was incorrect. Per conversation with an electrician, this qualifies as "under a building" which requires 0." That being said, bury the conduit so that it is just visible above rough grade prior to pour so the inspector can see it.

Sorry for the misinformation!

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