250.52(A)(3) Direct Contact

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chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
This is from Mike's August 7th's newsletter.

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Q10. Is a Ufer ground required if there is a vapor barrier under the concrete of the footing?
A10. If a moisture/vapor barrier is installed under a concrete footer, then the steel rebar can?t be part of a concrete-encased electrode. The concrete must be in contact with the earth in order to qualify as an electrode [250.52(A)(3)].
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So a gentleman I'm working with was questioning my use of a CEE in a slab with a visqueen membrane under it. This is what the typical south Florida slab looks like.

View attachment 2128

View attachment 2129

Now notice that although there is visqueen under the pour, once the forms are stripped and site is backfilled to grade, the sides of the footers will be in direct contact with the earth. Also the many cuts around the plumbing and electrical bring the slab and footers into direct contact with the earth.




BTW, the new thumbnail format is much better. Nice job people.
 

iaov

Senior Member
Location
Rhinelander WI
I'd agree with you Chris.My question would be is there (and I know there is no number given in the Book) is there some percentage/square footage that has to be in direct contact for it to be considered an effective ground.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
iaov said:
I'd agree with you Chris.My question would be is there (and I know there is no number given in the Book) is there some percentage/square footage that has to be in direct contact for it to be considered an effective ground.
Great question, but at this point I believe we both know the answer is there is no number.

The gentleman that brought this up was just at Mike's continuing ed here and Mike suggested to cut a 20' slice into the vapor barrier. Would that not defeat the purpose of the barrier? Would that not violate the building code that requires the barrier?
 

iaov

Senior Member
Location
Rhinelander WI
You ask awefully tough questions. I think when the plumbers are putting holes in the barrier, technically they are probably violating a building code too.My guess is that a 20' slit in it will not provide as much contact as you will get from the back filling,etc.The realy big question here may be How well do you know the inspector and have you bought him a coffee recently.:smile:
 

resistance

Senior Member
Location
WA
Then it goes back to the AHJ.

The definition of: "direct contact with earth"
needs a ruling

Rather a portion of
or fully
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
chris kennedy said:
Great question, but at this point I believe we both know the answer is there is no number.

The gentleman that brought this up was just at Mike's continuing ed here and Mike suggested to cut a 20' slice into the vapor barrier. Would that not defeat the purpose of the barrier? Would that not violate the building code that requires the barrier?

Chris what I do is install 20 foot of copper in the footer and tie it to the rebar. Solves any problems. I have never seen a vapor barrier under a footer. Why??
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
LarryFine said:
Same here. I believe the vapor barrier is part of the pad's construction, but not the footing's.
Take a close look at the pics Larry. It runs under the slab and down into the footers.

FWIW, I have done this install many times and have never been flagged. I also showed an inspector Mikes answer yesterday during a slab inspection and he agrees with me. That footer is in contact with the earth. Simple as that.
 

iaov

Senior Member
Location
Rhinelander WI
chris kennedy said:
Take a close look at the pics Larry. It runs under the slab and down into the footers.

FWIW, I have done this install many times and have never been flagged. I also showed an inspector Mikes answer yesterday during a slab inspection and he agrees with me. That footer is in contact with the earth. Simple as that.
That is all that counts!!:grin:I've never seen vapor barrior under footings either. Are they in the footings or under?
 

acrwc10

Master Code Professional
Location
CA
Occupation
Building inspector
chris kennedy said:
Take a close look at the pics Larry. It runs under the slab and down into the footers.

FWIW, I have done this install many times and have never been flagged. I also showed an inspector Mikes answer yesterday during a slab inspection and he agrees with me. That footer is in contact with the earth. Simple as that.

By the time the concrete gets hosed into the footing there will be alot less plastic in the way of "Direct contact" with the earth. Even with the plastic quite abit of the footer is contacting the earth on the side and edge of the bottom.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
iaov said:
That is all that counts!!:grin:I've never seen vapor barrior under footings either. Are they in the footings or under?

The barrier is under the footers but in 12 to 24 inches of the vertical sides of the footers are in contact.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
buckofdurham said:
I think the NEC says 10' in direct contact with earth.
Buck, I don't see that.

250.52(3) Concrete-Encased Electrode. An electrode encased by at least 50 mm (2 in.) of concrete, located horizontally near the bottom or vertically, and within that portion of a concrete foundation or footing that is in direct contact with the earth, consisting of at least 6.0 m (20 ft) of one or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 13 mm (1/2 in.) in diameter, or consisting of at least 6.0 m (20 ft) of bare copper conductor not smaller than 4 AWG. Reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means. Where multiple concrete-encased electrodes are present at a building or structure, it shall be permissible to bond only one into the grounding electrode system.
 

jimport

Senior Member
Location
Outside Baltimore Maryland
Occupation
Master Electrician
250.52(3) Concrete-Encased Electrode. An electrode encased by at least 50 mm (2 in.) of concrete, located horizontally near the bottom or vertically, and within that portion of a concrete foundation or footing that is in direct contact with the earth, consisting of at least 6.0 m (20 ft) of one or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 13 mm (1/2 in.) in diameter, or consisting of at least 6.0 m (20 ft) of bare copper conductor not smaller than 4 AWG. Reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means. Where multiple concrete-encased electrodes are present at a building or structure, it shall be permissible to bond only one into the grounding electrode system.

This may sound like splitting hairs but the electrode is in the bottom and the side walls of the footer would be the parts in direct earth contact. This seems to contradict the part stating "within that portion of a concrete foundation or footing".

During the Code update class here it was stated that NO barrier was allowed under footer if you were trying to use it for a ufer due to lack of direct contact. YMMV.
 

RUWired

Senior Member
Location
Pa.
Hey Chris, did you read 250.52(A)3,...exception 1

Where a nonconductive vapor barrier is placed beneath the more than 20' of rebar or 20' of not less than # 4 awg bare, one additional ground rod shall be required.
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