I am interpreting 250.52 (a) (3) as saying that you could take a piece of #4 bare ground wire and attach it with a ground clamp to a 20ft piece of 1/2" rebar within the slab. You would of course leave enough #4 ground wire exposed to attach to your service. It isn't therefore necessary to run 20ft of #4 ground wire within the slab. Or am I wrong?
concrete encased ground
- Thread starter difowler1
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Lectricbota
Senior Member
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Last edited:
- Location
- Illinois
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- retired electrician
There has never been a requirement in the code that required you install #4 copper in the footing or foundation. That is an optional method of creating a concrete encased electrode. The rule says that if there is at least 20' of 1/2 or larger rebar in a footing or foundation that has direct earth contact, you must use that rebar as an electrode.
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- New Jersey
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To expand on what Don said if the rebar doesn't exist or is smaller than 1/2" you do not even need to use a CEE.
jxofaltrds
Inspector Mike®
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- Mike P. Columbus Ohio
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- ESI, PI, RBO
It is my understanding that if you have a vapor barrier as in a slab application, that a 20' section of the barrier must be removed to allow ground contact.
You must read 250.52(A)(3)(1&2) then if one of those applies the next paragraph applies.
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If the concrete encased electrode is separated by a vapor barrier then you don't need to use it or rip the vapor barrier. Look at information note in 2011
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- Placerville, CA, USA
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- Retired PV System Designer
Depending on the ease of installing other types of electrode and the objective need for a low impedance ground, it may be a good idea to modify the vapor barrier. But low impedance in a ground will still not make it a fault clearing path. And without knowing the long term consequences of modifying the vapor barrier it would be foolish to do that.
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- Illinois
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- retired electrician
Rebar or copper wire in a "slab" cannot be used as a grounding electrode.
- Location
- Illinois
- Occupation
- retired electrician
In general vapor barriers are installed under slabs and not under footings or foundations. No need to modify a vapor barrier under a slab as you cannot not create a concrete encased electrode in a slab.
jxofaltrds
Inspector Mike®
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- Mike P. Columbus Ohio
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- ESI, PI, RBO
Our 'host' (2005) at one time, I thought from watching the video, disagreed.
If I am incorrect please let me know.
Informational Note: Concrete installed with insulation, vapor
barriers, films or similar items separating the concrete
from the earth is not considered to be in ?direct contact?
with the earth.
This is why you MUST make a 20' section (my words) available.
- Location
- Placerville, CA, USA
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- Retired PV System Designer
Another way of looking at it is that if the local code requires a CEE, you have to come up with a suitable section of footing that does not have a vapor barrier on all earth contacting sides.
1. If you are not required to create a CEE, then the fact that none of the concrete footing is in earth contact is just fine.
2. And if you are required to connect to a CEE when present, then a footing with vapor barrier is not a CEE and you do not need to connect to it or break the vapor barrier.
3. On the other hand, if the footing has the right amount of rebar and is in direct earth contact but has no external access to connect to the rebar, then you do have a CEE and need to make the necessary modifications to connect to it except where the Code specifically says that you do not.
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- New Jersey
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- Journeyman Electrician
Pretty simple, if it qualifies as a CEE you must use it if it does not then you can either make a CEE or ignore it completely and use something else.
- Location
- Illinois
- Occupation
- retired electrician
There is no requirement to create an concrete encased electrode if one does not exist. If there a vapor barrier under concrete that would otherwise qualify for use as a CEE, you just don't have a CEE and will have to use other electrodes to satisfy the requirement for a grounding electrode.
jxofaltrds
Inspector Mike®
- Location
- Mike P. Columbus Ohio
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- ESI, PI, RBO
Informational Note: Concrete installed with insulation, vapor
barriers, films or similar items separating the concrete
from the earth is not considered to be in ?direct contact?
with the earth.
Now does that negate?:
250.50 Grounding Electrode System. All grounding electrodes
as described in 250.52(A)(1) through (A)(7) that are
present at each building or structure served shall be bonded
together to form the grounding electrode system. Where
none of these grounding electrodes exist, one or more of
the grounding electrodes specified in 250.52(A)(4) through
(A)(8) shall be installed and used.
The exception does not apply.
Exception: Concrete-encased electrodes of existing buildings
or structures shall not be required to be part of the
grounding electrode system where the steel reinforcing bars
or rods are not accessible for use without disturbing the
concrete.
- Location
- Illinois
- Occupation
- retired electrician
Remember the definition of the concrete encased electrode.
If the vapor barrier is there, the electrode does not exist and since it does not exist you can't use it.
The informational note just tells you that a vapor barrier prevents the concrete from being in direct contact with the earth.
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- Location
- New Jersey
- Occupation
- Journeyman Electrician
I agree, if the CE "electrode" doesn't quilify as an electrode then you are not required to use it. You can make one if you so choose but you're not required to do so.
jxofaltrds
Inspector Mike®
- Location
- Mike P. Columbus Ohio
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- ESI, PI, RBO
Don that is not a definition. It is a statement. Doesn't say IF it says shall.
Rob never said you had to make one.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
"... electrodes that are present ... shall be bonded...." is logically equivalent to "IF an electrode is present it shall be grounded."
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He may have said a 20' section without a vapour barrier would make it usable as a CCE or meet the definition of a CCE. I doubt he said you are compelled the NEC to do it.
The SHALL only counts IF it is one. If it is one is clearly defined.
Either you are saying a section of the vapor barrier must be removed or you are not.
There is no requirement to make something that does not meet the definition of a grounding electrode into something does.
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