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Old 12-10-2011, 03:25 PM   #1
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cee placement technique


My building plan calls for a poly vapor barrier under the slab. I had planned a 20' cee tied to the bottom of my beam steel and swing the 1/2" rod up into the corner of the building where the panel will be. However I found this:

7. 250.52(A) Electrodes Permitted for Grounding

The rule explaining when a structural metal frame can serve as a grounding electrode has been changed again, and the requirements for concrete encased electrodes, ground rods, and ground plates have been clarified.
250.52 Grounding Electrode Types.
(A) Electrodes Permitted for Grounding.
(1) Underground Metal Water Pipe Electrode. Underground metal water pipe in direct contact with the earth for 10 ft or more can serve as a grounding electrode.
(2) Metal Frame Electrode. The metal frame of a building/structure can serve as a grounding electrode when it meets at least one of the following conditions:
(1) At least one structural metal member is in direct contact with the earth for 10 ft or more, with or without concrete encasement.
(2) The bolts securing the structural steel column are connected to a concrete encased electrode [250.52(A)(3)] by welding, exothermic welding, steel tie wires, or other approved means. (click here to see Fig. 7)
(3) Concrete-Encased Electrode. At least 20 ft of either (1) or (2):
(1) One or more of bare, zinc-galvanized, or otherwise electrically conductive steel reinforcing bars of not less than in. diameter, mechanically connected together by steel tie wires, welding, or other effective means, to create a 20 ft or greater length.
(2) Bare copper conductor not smaller than 4 AWG.
The reinforcing bars or bare copper conductor must be encased by at least 2 in. of concrete located horizontally near the bottom of a concrete footing or vertically within a concrete foundation that’s in direct contact with the earth.
If multiple concrete-encased electrodes are present at a building/structure, only one is required to serve as a grounding electrode
Note: Concrete containing insulation, vapor barriers, films or similar items separating it from the earth isn’t considered to be in “direct contact” with the earth.


My particular concern is the last sentence. Should I tell my foundation crew to delete lining the bottom of the beam trench on the perimeter of the building? I think I can live with that if the foundation building inspector will allow that deletion. I've don't think I've ever seen a building that didn't line the entire bottom shell of the the foundation. If that's the case then the CEE is improper and unusable.



What should I do?

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Last edited by n175h; 12-10-2011 at 03:58 PM.
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Old 12-10-2011, 03:45 PM   #2
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cee placement technique


The CEE is usually palced in the building footings which usually have no vapor barrier. Is your building a slab only with no footings?

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Old 12-10-2011, 03:50 PM   #3
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cee placement technique


Quote:
Originally Posted by brric View Post
The CEE is usually palced in the building footings which usually have no vapor barrier. Is your building a slab only with no footings?
Slab with footings. General accepted practice is to line the floor of the footings. We are in a very humid climate, and this is done regularly. I've attached a slab beam drawing. the liner is supposed to lay into the bottom of the trench.
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cee placement technique-slab-beams.jpg  
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Old 12-10-2011, 03:52 PM   #4
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cee placement technique


you dont have a valid CEE if there is a VB under the entire footer and slab
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Old 12-10-2011, 04:09 PM   #5
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cee placement technique


I'll have to ask the inspector to allow me to leave out 20' of vapor barrier from the corner of the slab where the CEE will be located. If he won't then I'll just have to beat in a ground rod, I guess.
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