GES not spelled out in plans

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Electromatic

Electromatic

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Master Electrician
I'm so used to the dirt worshipers specifying extreme electrode systems that now I'm not given that, I'm doubting myself.

This project is a slab on grade, block (CMU) building (no structural steel). Power comes in as a feeder from another building (480V, 3Ø) to a 480V panel then immediately to a 480/208 transformer to a 208/120 panel. There is no electrode system shown in the riser/one-line. The only mentions of the GES are in a specification note saying,

"PARTICULAR ATTENTION IS CALLED TO NEC ARTICLE 250.32(B)(1) (INCLUDING EXHIBIT 250.19)
WHERE A REMOTE BUILDING IS FED FROM SERVICE EQUIPMENT OF ANOTHER BUILDING."

and a transformer connection diagram showing a connection to,
"NEAREST GROUNDING ELECTRODE
PER 2017 NEC 250.30 (A) (4),
INCLUDING EXCEPTION NO. 1"

In addition, the incoming water line is not metal, and the slab will be poured with a fiber reinforcement mix--no rebar.
I'm thinking of throwing ≥20' of bare #4 Cu in the slab and calling it a day. Does that seem right? Is that still legitimate with a vapor barrier under the slab?

Thanks in advance.
 
A piece of wire used as a CEE in the slab is not code compliant unless there is a footing.
 
Yeah, that makes sense. I'm wondering what my options are, then.
The CMU is on a footing. They've installed the block so far up to top-of-slab level and have moisture-barriered the outside of the block. If the slab goes up to the CMU, would the 20' of bare copper in the slab count then? There are pieces of rebar spaced out among the block webs that will be grouted. Can I tie several of them together to create an electrode? I don't want to penetrate the block now for exterior ground rods; could I drive/lay a couple in the dirt under the slab?
 
To be compliant a CEE must be in a footing which is in contact with dirt.

A slab is not a footing.
 
Electromatic said:
Yeah, that makes sense. I'm wondering what my options are, then.
The CMU is on a footing. They've installed the block so far up to top-of-slab level and have moisture-barriered the outside of the block. If the slab goes up to the CMU, would the 20' of bare copper in the slab count then? There are pieces of rebar spaced out among the block webs that will be grouted. Can I tie several of them together to create an electrode? I don't want to penetrate the block now for exterior ground rods; could I drive/lay a couple in the dirt under the slab?
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Just do this the easy and simple way. two ground rods 6 feet apart with a #6 wire to them.
 
Is there any reason I can't drive/lay the rods in the dirt under the slab? Since they've already installed the moisture barrier on the exterior block, I don't want to make a penetration through the block to exterior rods.
 
Electromatic said:
Is there any reason I can't drive/lay the rods in the dirt under the slab? Since they've already installed the moisture barrier on the exterior block, I don't want to make a penetration through the block to exterior rods.
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the code generally requires rods be driven vertically.

maybe you could install a plate type electrode under the slab.
 
petersonra said:
I think if you read carefully the requirements for a CEE in the NEC, you would come to the conclusion that rebar in any slab would not count as a CEE.
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I have read the requirements for a CEE in the NEC. I do not reach that conclusion because that is not what the NEC says.

When the foundation is a slab, and when that slab foundation has metallic components encased by at least 2" of concrete, and the slab or a portion of it is direct contact with the earth, then those metallic components in the slab foundation would qualify as a CEE.
 
david luchini said:
I have read the requirements for a CEE in the NEC. I do not reach that conclusion because that is not what the NEC says.

When the foundation is a slab, and when that slab foundation has metallic components encased by at least 2" of concrete, and the slab or a portion of it is direct contact with the earth, then those metallic components in the slab foundation would qualify as a CEE.
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when would a slab ever be a foundation?

the slab and foundation could all be cast together as a single piece, which is not unheard of, but that does not make the slab a foundation.
 
david luchini said:
When a slab is the foundation...then in the slab.
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Except for a DIY shed, I don't think I have seen a slab in significant contact with dirt. They are usually poured over a gravel base, several inches thick, and separated by a vapor barrier or insulation.
 
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jim dungar said:
Except for a DIY shed, I don't think I have seen a slab in significant contact with dirt. They are usually poured over a gravel base, several inches thick, and separated by a vapor barrier or insulation.
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Worked on an apartment building recently where the foundation was a reinforced slab beneath the entire building. Foundation walls and piers were built up from there. The ground floor slab was several feet above the foundation slab.

Have also seen monolithic slab foundation that get thicker toward the outside walls. The outside portion is in contact with earth, while the inner portion is on a gravel base.

Both of those slab types are foundations .
 
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