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rebar in slab

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sparkmantoo

Member
Location
Virginia
i have read the articles and the posts about the ufer grounds and they were quite interesting and i have a question. if the rebar in a slab is new and accessible, does it have to be bonded to the rest of the grounding electrode system. the rebar that i am referring to is the steel that is embedded in the slab that reinforces the concrete, not the rebar that is placed in the footers. Art. 250.50 says " if available " all the electrodes SHALL be bonded together to form the grounding electrode system. in my opinion, if they are there and they are accessible before the concrete is poured we are required to bond them together as per the article. am i wrong in assuming this because we all know what assumptions are... they are the mother of all !@#$! ups. please respond.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: rebar in slab

Sparkmantoo,
The code does not say that the rebar in a slab is a grounding electrode. Only the rebar in a footing or foundation. See 250.52(A)(3). If the footing or foundation rebar is accessible, then you are required, by 250.50, to use it as part of the grounding electrode system.
Don
 

tom baker

First Chief Moderator & NEC Expert
Staff member
Location
Bremerton, Washington
Occupation
Master Electrician
Re: rebar in slab

Don isn't there a TIA from the NFPA stating the rebar doesn't have to be used even if accessible? The info on this is shown in the NFPA handbook.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: rebar in slab

Tom,
There was a formal interpretation a number of years ago that said you don't have to break the concrete to make the rebar accessible. I believe that under the current code, if the rebar is physically accessible when the electrician is on the job, that you are required to use the rebar as a grounding electrode. I don't remember a TIA on this subject.
Don
 

sparkmantoo

Member
Location
Virginia
Re: rebar in slab

this is interesting. on a lot of the slabs that i have seen poured, at the edge of the slab they slope the slab down about 18-24 inches as kind of like a footer which has steel in it which is also tied to the rebar that is in the slab. is this the same or is the footer or foundation that you are referring to seperate from the slab. also if the electrician chooses to be away from the job that day they set the steel in the foundation and they pour concrete over it, does that excuse the electrician from complying with art 250.50?
 

pierre

Senior Member
Re: rebar in slab

Sometimes the electrician is not hired until after the footings are poured, therefore the footings are not 'available' when he gets to the job. There are some municipalities that are requiring the 'Ufer' ground to be installed, and the inspector looks for it at the footing inspection.
The situation of the slab that is sloped at the edges as a footing is an interesting question. Are they deep enough to be effective?

Pierre
 

kqresq

Member
Re: rebar in slab

There is a difference between a "thickened edge" slab and a "monolithic foundation". If the building structure (framing, masonry, etc.) rests on it, it is a footing. Generally, thickened edges are only 3 or 4 inches thicker than the slab. This is done to allow anchor points in post tension slabs and/or to prevent "curling" of the slab edges. I have never seen a thickened edge exceed 12 inches.
 

hornetd

Senior Member
Location
Maryland
Occupation
Journeyman Electrician, Retired
Re: rebar in slab

When the building is constructed on a slab on grade isn't the slab the foundation?
--
Tom
 
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