N.E.C. 250 - Concrete encased electrode

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NMCB13

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To my understanding that for new construction the EC is required to install a Ufer ground using # 4 AWG and connected to a 20 ft. length of rebar. Ok I got that, than the connection is completed to the meter pan. Now (assuming) that the concrete encased electrode is installed correctly and therefore you have a proper ground. What about the plastic barrier that is installed between the earth and the concrete? Would that not impeed the grounding method?

I also have seen that on some new homes here in FLorida, the EC connects the grounding electrode to a vertical rebar in the wall, is this acceptable?
 
NMCB13 said:
To my understanding that for new construction the EC is required to install a Ufer ground using # 4 AWG and connected to a 20 ft. length of rebar. Ok I got that, than the connection is completed to the meter pan. Now (assuming) that the concrete encased electrode is installed correctly and therefore you have a proper ground. What about the plastic barrier that is installed between the earth and the concrete? Would that not impeed the grounding method?

I also have seen that on some new homes here in FLorida, the EC connects the grounding electrode to a vertical rebar in the wall, is this acceptable?
Click to expand...
Pretty straightforward.
If the concrete slab is not in direct contact with the earth, then it is not a CEE. If the plastic extends only under the central part of the slab but not under the perimeter foundation or footings, then it is a CEE.
Other things that will interfere with concreted being a CEE are Integrated Insulating Forms if they do not leave a substantial portion of the bottom surface in conact with the dirt, a gravel bed under the entire concrete structure, and waterproofing coatings adhered to the outer wall of the foundation.

In the case of vertical walls, as long as the rebar in the wall is properly bonded (deliberately tied to other rebar as described in the code) down to rebar in the foundation or footings, then you have a valid CEE. In fact, the code just requires the rebar mesh you bond to to be part of the same continuous mass of concrete that is in earth contact, not necessarily the rebar which is in the underground and contacting part of that mass of concrete.
Common sense should be enough to guide you in this if you know what the contractor did to create the CEE you are bonding to.
If you are of an experimental nature, you can use some of the standard techniques for testing ground electrode resistance to measure the resistance of a Ufer/CEE ground.
Just not the ones that are based on the assumption that the ground under test is located at a specific point.
 
I ran into an interesting situation on my job the other day. I told the builder 4 times not to forget about the concrete encased electrode. Well I went by the job and lo and behold the footers were poured. I got angry but then I realized I have an out.

This particular job has almost the entire side of the house underground. Full basement and about 6 or so feet of the first floor is below grade. Since the rebar is stubbed up from the footers and they will be pouring a concrete foundation wall I can just connect to the rebar in the wall as that is connected to the footer rebar.


Now if there were plastic down under the footer I wonder if those walls would still be okay as they usually treat the walls for water penetration which would impede the effectiveness of the concrete encased electrode. I realize it would not meet the letter of the code but I am curiopus if it would still be better than a ground rod.
 
Dennis Alwon said:
I realize it would not meet the letter of the code but I am curiopus if it would still be better than a ground rod.
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IMHO it would be better than a ground rod only if a substantial area of concrete (maybe 10 sq.ft. or more?) is in direct earth contact. (i.e about the size you would use for plate electrode.) But that could be distributed over a wide area of the concrete, not necessarily directly under the rebar you are connected to.
If you only have a few sq.ft. or less total, made up of poor seams in the plastic, etc. I would have to say no.
 
It is required in Florida even though there is plastic under the concrete. The plastic does not extend up the outside of the footer to the finished grade therefor it is in contact with the dirt. The connection is different depending on who is inspecting. In Lee county, the rebar is turned up in the block wall near the meter location and the rebar is painted green. A 3" or so hole is knocked in the block allowing access the required acorn ground clamp. 2 gang mud ring and a 2 gang blank plate and your good to go. Other places allow you to go into the garage framed wall and do the same thing. EGC needs to be no larger than #6.
 
GoldDigger said:
IMHO it would be better than a ground rod only if a substantial area of concrete (maybe 10 sq.ft. or more?) is in direct earth contact. (i.e about the size you would use for plate electrode.) But that could be distributed over a wide area of the concrete, not necessarily directly under the rebar you are connected to.
If you only have a few sq.ft. or less total, made up of poor seams in the plastic, etc. I would have to say no.
Click to expand...
There would be an area about 15' x 40' under ground - at least on one side of the wall anyway.
 
Dennis Alwon said:
There would be an area about 15' x 40' under ground - at least on one side of the wall anyway.
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As long as the underground area is on the outside surface of the wall, that should do it. ;)
And as long as there is no moisture barrier applied to that outside wall surface (as mentioned above.)
 
Dennis Alwon said:
I assume you mean gec not egc . Are you saying the grounding electrode conductor does not need to be larger than a #6 to the concrete encased electrode?
Click to expand...

I know you believe that you understand what you think I said but I'm sure you realize that what you heard is not what I meant. I'm getting dyslexia the older I get.
 
N.E.C. 250 - Concrete encased electrode

GoldDigger said:
Pretty straightforward.
If the concrete slab is not in direct contact with the earth, then it is not a CEE. If the plastic extends only under the central part of the slab but not under the perimeter foundation or footings, then it is a CEE.
Other things that will interfere with concreted being a CEE are Integrated Insulating Forms if they do not leave a substantial portion of the bottom surface in conact with the dirt, a gravel bed under the entire concrete structure, and waterproofing coatings adhered to the outer wall of the foundation.

In the case of vertical walls, as long as the rebar in the wall is properly bonded (deliberately tied to other rebar as described in the code) down to rebar in the foundation or footings, then you have a valid CEE. In fact, the code just requires the rebar mesh you bond to to be part of the same continuous mass of concrete that is in earth contact, not necessarily the rebar which is in the underground and contacting part of that mass of concrete.
Common sense should be enough to guide you in this if you know what the contractor did to create the CEE you are bonding to.
If you are of an experimental nature, you can use some of the standard techniques for testing ground electrode resistance to measure the resistance of a Ufer/CEE ground.
Just not the ones that are based on the assumption that the ground under test is located at a specific point.
Click to expand...
Reply: The vapor barries extends up to the top (or close to) the footer. So the concrete encased electrode is not a true CEE. Also I do not think the vertical rebar is ited to the rebar stub up. I say this because no mason is going to install the block with a 9 foot rebar installed.
 
NMCB13 said:
Reply: The vapor barries extends up to the top (or close to) the footer. So the concrete encased electrode is not a true CEE. Also I do not think the vertical rebar is ited to the rebar stub up. I say this because no mason is going to install the block with a 9 foot rebar installed.
Click to expand...

the vertical bars are tied to the footer bars per code.
 
Cavie said:
the vertical bars are tied to the footer bars per code.
Click to expand...
In a poured concrete wall, yes. But if the OP is talking only about the rebar in a concrete block wall, that may not happen. Which would in turn require the GEC to go the rebar step-up directly.
Earthquake codes may also affect the way the rebar in a wall is configured.
 
Cavie said:
I know you believe that you understand what you think I said but I'm sure you realize that what you heard is not what I meant. I'm getting dyslexia the older I get.
Click to expand...
You're so old you didn't answer my question. Why is #6 the largest needed for a concrete encased electrode and not #4
 
Dennis Alwon said:
I ran into an interesting situation on my job the other day. I told the builder 4 times not to forget about the concrete encased electrode. Well I went by the job and lo and behold the footers were poured. I got angry but then I realized I have an out.

This particular job has almost the entire side of the house underground. Full basement and about 6 or so feet of the first floor is below grade. Since the rebar is stubbed up from the footers and they will be pouring a concrete foundation wall I can just connect to the rebar in the wall as that is connected to the footer rebar.


Now if there were plastic down under the footer I wonder if those walls would still be okay as they usually treat the walls for water penetration which would impede the effectiveness of the concrete encased electrode. I realize it would not meet the letter of the code but I am curiopus if it would still be better than a ground rod.
Click to expand...

Do you know for certain the stubs out of the footer are tied to the rebar in the footer? I have often seen those stuck in the mud after the footer is poured and if that is the case they are not tied to any rebar in the footer. They are typically installed for horizontal movement reinforcement purposes and not for vertical movement purposes.
 
kwired said:
Do you know for certain the stubs out of the footer are tied to the rebar in the footer? I have often seen those stuck in the mud after the footer is poured and if that is the case they are not tied to any rebar in the footer. They are typically installed for horizontal movement reinforcement purposes and not for vertical movement purposes.
Click to expand...

Depending on the rest of the construction, the stubs up out of the footer may be bent up ends of the horizontal rebar, in which case there is no need to tie it at all if that one length of rebar is 20' or longer.

In places where earthquake protection is mandatory, the down ties are threaded rods with some sort of expanded end, and if connected to the rebar will only be supported by it but not necessarily tied to it electrically.

If you can find out from the workers who poured it what they did, that would set your mind at ease.
 
GoldDigger said:
Depending on the rest of the construction, the stubs up out of the footer may be bent up ends of the horizontal rebar, in which case there is no need to tie it at all if that one length of rebar is 20' or longer.

In places where earthquake protection is mandatory, the down ties are threaded rods with some sort of expanded end, and if connected to the rebar will only be supported by it but not necessarily tied to it electrically.

If you can find out from the workers who poured it what they did, that would set your mind at ease.
Click to expand...

I could see that for places where earthquake is more common.

Most of time when I have been around when a footing is poured they pour the footing then stick vertical rods in before concrete sets. This makes it easier to strike the footing and the main purpose of the rods is to help with lateral movement reinforcement, no vertical movement is expected. I know we did exactly that when we built my house - I was there helping.
 
4# is the largest required for any service & most will follow the practice to avoid problems if an upgrade is needed. Maybe his reference was towards a 200A service. I prefer the base footer & always ask to see the specific verticle steel tied to the base. Once that is done technically the grid of the wall with steel ties in order to extend the ufur near the service location. IMO keep it simple by tying a 4# to the footer.
 
kwired said:
Do you know for certain the stubs out of the footer are tied to the rebar in the footer? I have often seen those stuck in the mud after the footer is poured and if that is the case they are not tied to any rebar in the footer. They are typically installed for horizontal movement reinforcement purposes and not for vertical movement purposes.
Click to expand...

I believe they legally have to be however I do know for sure as I asked both the builder and the concrete guy. I have also seen the same concrete company do other jobs and they were done exactly as stated so I am pretty comfortable with it.

This company I have worked with for 30 years and they do very high end homes and high end quality construction.
 
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