Concrete encased electrode
- Thread starter steve66
- Start date
- Status
- Location
- New Jersey
- Occupation
- Journeyman Electrician
IMO no if you mean a horizontal slab. A slab is not a footing nor a foundation.
IMO Yes if a floating slab. (not slab between footings/walls…)I see no depth requirement in NEC.
The handbook notes make it quite clear this is acceptable (we all know how much weight that carries…)
Makes me wonder how well a floating slab performs as a CEE sitting on four feet of frost.:-? (Only applies to those of us up here in the hinterland, ya know.)
The handbook notes make it quite clear this is acceptable (we all know how much weight that carries…)
Makes me wonder how well a floating slab performs as a CEE sitting on four feet of frost.:-? (Only applies to those of us up here in the hinterland, ya know.)
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- Location
- Logan, Utah
engy said:IMO Yes if a floating slab. (not slab between footings/walls?)I see no depth requirement in NEC.
The handbook notes make it quite clear this is acceptable (we all know how much weight that carries?)
Makes me wonder how well a floating slab performs as a CEE sitting on four feet of frost.:-? (Only applies to those of us up here in the hinterland, ya know.)
What do you mean by "floating slab"?
I have both the 2005 and the 2008 NEC handbook and neither one appears to show a slab as a CEE.
I agree with Trevor, a concrete slab is not a footing or a foundation.
Chris
- Location
- Logan, Utah
engy said:
What you describe is called a monolithic slab in my area and the thicked edges that contain rebar are footings.
The pictures in Exhibit 250.22 and 250.23 show something that may be a monolithic footing and slab, but the thickness is not known.
If you are connecting to the rebar in a "floating slab" as you describe then I believe that you are OK as the edges of that slab are footings.
What I meant with you can't use a slab would be an unreinforced floor slab typically no thicker than about 4 inches.
Chris
Exhibits 250.29 and 250.31 in the 2008 handbook seem to show a CCE in a similar slab.
The reason the question popped up is in reagard to a greenhouse that has a concrete slab under part of the building, but no other footings or foundations. I'm not sure if it is thickened on the edges, but it probably is.
So does this building need a CCE or not?
Then I have one more question that the Architect needs to answer - is there a moisture barrier between the concrete and the ground??
Steve
The reason the question popped up is in reagard to a greenhouse that has a concrete slab under part of the building, but no other footings or foundations. I'm not sure if it is thickened on the edges, but it probably is.
So does this building need a CCE or not?
Then I have one more question that the Architect needs to answer - is there a moisture barrier between the concrete and the ground??
Steve
A/A Fuel GTX
Senior Member
- Location
- WI & AZ
- Occupation
- Electrician
raider1 said:
Chris....What if the monolithic slab had no rebar? Could I still lay a #4 in the bottom of the thickend edge and have an adequate CEE or would I have to place the #4 suspended within the concrete to meet the 2" reference in 250.52(A) (3)?
steve66 said:
The question is NOT does it need one. The question is does it have one.
steve66 said:
I recall from a previous thread, that the consensus was "who cares", because the poly would not act as an insulator anyway. (and the code does not seem to care, or at least account for...)
earshavewalls
Senior Member
Here in LALA land (California), most use the entire reinforcement system, which is tied together, to act as one grounding electrode/ufer. The code just says that you CAN use this method, and that if it is available, you must use it. If you must break up concrete to get to it, you don't have to use it.
An example of a "foundation" that is not a typical footing is a mat foundation (see ACI 318), or a Post-tensioned foundation. These sometimes, but not always, have a grade beam or thickened slab area at the perimeter and sometimes running through the slab at other locations NOT on the perimeter. These are still considered "footings" in the sense that they perform the same function of a footing, which is to support the structure above. IF you have reinforcement that is accessible during construction, you must use it as one of the grounding electrodes in 250.52.
An example of a "foundation" that is not a typical footing is a mat foundation (see ACI 318), or a Post-tensioned foundation. These sometimes, but not always, have a grade beam or thickened slab area at the perimeter and sometimes running through the slab at other locations NOT on the perimeter. These are still considered "footings" in the sense that they perform the same function of a footing, which is to support the structure above. IF you have reinforcement that is accessible during construction, you must use it as one of the grounding electrodes in 250.52.
- Location
- Logan, Utah
A/A Fuel GTX said:
If the monolithic slab had no rebar, but the edges were thickened to act as a footing (not all footings require rebar this is a building code issue) then I would say you would be OK to install 20' of #4 and call it a CEE. You would have to suspend the #4 at least 2" to meet the requirement that the #4 be encased by at least 2" of concrete.
JMHO,
Chris
- Location
- Logan, Utah
engy said:
I must have missed that thread, it has always been my contention that the footing or foundation need to be in direct contact with the earth and that a vapor barrier would cause and issue as it would separate the footing or foundation from the earth.
Chris
I have to agree with Raider on the moisture barrier. The code says the concrete must be in contact with the earth. And a slab with a moisture barrier would not be in contact with the earth. (A footing might be different - I don't think a moisture barrier would wrap around the entire footing. But I know very little about footings and concrete.)
This is a new building, and 250.50 says:
"All grounding electrodes as described in 250.52A1 through A6 that are present at each building or structure served shall be bonded together to form the grounding electorde system."
So if it has rebar that works for a CCE, then it must be connected to the grounding system.
See the exception to 250.50 for existing buildings.
Steve
This is a new building, and 250.50 says:
"All grounding electrodes as described in 250.52A1 through A6 that are present at each building or structure served shall be bonded together to form the grounding electorde system."
So if it has rebar that works for a CCE, then it must be connected to the grounding system.
See the exception to 250.50 for existing buildings.
Steve
- Location
- Massachusetts
earshavewalls said:
Here in MA if it is a new footing that has rebar in it you must use it.
If the GC went ahead and allowed the pour without getting an EC to make GEC connection and have it inspected the GC will have to break some concrete.
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