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Grounding Rebar

 
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Old 01-03-2009, 05:31 PM   #1
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Grounding Rebar


when pouring a footing who would usually do the grounding of the rebar, the mason or an electrician?
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Old 01-03-2009, 06:08 PM   #2
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Re: Grounding Rebar


Rebar is not grounded. It can be used as a ground.

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Old 01-03-2009, 06:14 PM   #3
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Re: Grounding Rebar


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Originally Posted by tkle View Post
Rebar is not grounded. It can be used as a ground.
WWHHOOAAAA there pardner.

If the rebar fits the bill as described in the NEC, it MUST be utilized as a grounding electrode. It is commonly called a Ufer ground (after the man the engineered it in 1946 (I think) in Arizona or some other dry desolate western state)

and I would strongly suggest an electrician do it so it is correct.

what I do is tell them to stick the end of one of the rebars out in a location I choose so I can attach to it later.

but to further make a point, the rebar is grounded by virtue it is inside moist, mineral bearing concrete which is in contact with the earth. That is why it is used as an electrode; it is already grounded.
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Old 01-03-2009, 06:21 PM   #4
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Re: Grounding Rebar


On new construction we, (the footing crew), will provide and put in place a solid copper wire that serves as the Ufer Ground.

We make sure it exits the concrete in the correct location and with sufficient length to reach the electrical panel.

On remodels/additions it is usually not required.
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Old 01-03-2009, 06:35 PM   #5
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Re: Grounding Rebar


Quote:
Originally Posted by nap View Post
WWHHOOAAAA there pardner.

If the rebar fits the bill as described in the NEC, it MUST be utilized as a grounding electrode. It is commonly called a Ufer ground (after the man the engineered it in 1946 (I think) in Arizona or some other dry desolate western state)

and I would strongly suggest an electrician do it so it is correct.

what I do is tell them to stick the end of one of the rebars out in a location I choose so I can attach to it later.

but to further make a point, the rebar is grounded by virtue it is inside moist, mineral bearing concrete which is in contact with the earth. That is why it is used as an electrode; it is already grounded.
The rebar is concrete enclosed. It does not attached to ground. The ground is attached to it.
http://www.mikeholt.com/mojonewsarch...r~20030914.htm

...and yes. I leave it to the electrician.

Last edited by tkle; 01-03-2009 at 06:37 PM.
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Old 01-03-2009, 07:14 PM   #6
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Re: Grounding Rebar


Hey, I just had something similar answered. Should be the electrician who installs it, but most times there is no electrician when I am building and pouring foundations so I install it. Mag tells me use #4 and you can't go wrong.
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Old 01-03-2009, 07:20 PM   #7
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Re: Grounding Rebar


Quote:
Originally Posted by tkle View Post
The rebar is concrete enclosed. It does not attached to ground. The ground is attached to it.
http://www.mikeholt.com/mojonewsarch...r~20030914.htm

...and yes. I leave it to the electrician.
the Ufer is considered a concrete encased electrode. what is attached to an electrode is a GEC (grounding electrode conductor).

as a matter of fact, a ground rod is not even required when there is a Ufer ground. A rod is a supplemental electrode required when other electrodes are not used or available.

you are really misinterpreting what the link you provided states.
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Old 01-03-2009, 07:21 PM   #8
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Re: Grounding Rebar


Quote:
Originally Posted by tgeb View Post
On new construction we, (the footing crew), will provide and put in place a solid copper wire that serves as the Ufer Ground.

We make sure it exits the concrete in the correct location and with sufficient length to reach the electrical panel.

On remodels/additions it is usually not required.
so, what do you use to attach the GEC to the rebar?

and on remodels; it is not required to damage existing concrete so as to be able to attach. A ufer ground is only required to be utilized when new 'crete and bar is used.
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Old 01-03-2009, 07:33 PM   #9
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Re: Grounding Rebar


Quote:
Originally Posted by nap View Post
so, what do you use to attach the GEC to the rebar?

and on remodels; it is not required to damage existing concrete so as to be able to attach. A ufer ground is only required to be utilized when new 'crete and bar is used.
We do not "attach" the copper to the steel, it is simply encased in the concrete. I don't know if it's right or wrong, that's the way it is done here, inspected and approved.

Here is where I got my knowledge on Ufer.
Attached Files
File Type: doc ufergrnd.doc (28.5 KB, 1021 views)
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Old 01-03-2009, 07:38 PM   #10
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Re: Grounding Rebar


Quote:
Originally Posted by tgeb View Post
We do not "attach" the copper to the steel, it is simply encased in the concrete. I don't know if it's right or wrong, that's the way it is done here, inspected and approved.

Here is where I got my knowledge on Ufer.
that is why you leave it for the electrician. It has to be attached to the rebar and a proper attachment device has to be used.

and it may get approved that way but has the inspector ever actually seen this or simply seen the GEC hanging out of the concrete? It is not legit nor legal.

this is where you need to get the specific requirements:http://www.constructionbook.com/2008...nec-code-2008/

Last edited by nap; 01-03-2009 at 07:40 PM.
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Old 01-03-2009, 07:59 PM   #11
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Re: Grounding Rebar


Quote:
Originally Posted by nap View Post
the Ufer is considered a concrete encased electrode. what is attached to an electrode is a GEC (grounding electrode conductor).

as a matter of fact, a ground rod is not even required when there is a Ufer ground. A rod is a supplemental electrode required when other electrodes are not used or available.

you are really misinterpreting what the link you provided states.
The link vaguely explains why rebar not being grounded poses no threat to the concrete. The question was about grounding the rebar when placing a footing.. There is no reason for this.
Other that that we're saying the same thing. The ufer is the ground.
Also copper reacts to the alkali in the concrete.
http://www.psihq.com/iread/ufergrnd.htm
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Old 01-03-2009, 08:00 PM   #12
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Re: Grounding Rebar


Quote:
Originally Posted by nap View Post
that is why you leave it for the electrician. It has to be attached to the rebar and a proper attachment device has to be used.

and it may get approved that way but has the inspector ever actually seen this or simply seen the GEC hanging out of the concrete? It is not legit nor legal.

this is where you need to get the specific requirements:http://www.constructionbook.com/2008...nec-code-2008/
Yes, the inspectors do actually look at, and comment on the copper wire as it is laying in the open footer prior to the concrete pour. The same inspectors also do the electrical inspections.

In fact we had an instance last summer where the wire left out of the footer got cut, the inspector made us dig a trench minimum 10 feet long and lay a cooper wire in it, hold it off the soil with stakes, he looked at it and then we poured concrete around it. No rebar in the trench.

I will make it a point to ask about this on the next one we do.
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Old 01-04-2009, 11:07 AM   #13
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Re: Grounding Rebar


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Originally Posted by Chris Johnson View Post
Hey, I just had something similar answered. Should be the electrician who installs it, but most times there is no electrician when I am building and pouring foundations so I install it. Mag tells me use #4 and you can't go wrong.
That's what I was thinking. I'll just clamp the wire to the rebar and let it run wild, have the electrician hook it up latter. Saves a trip by the electrician.
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Old 01-04-2009, 11:27 AM   #14
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Re: Grounding Rebar


You need to know what code cycle they (AHJ) are using before you can answer this question. But if your using it it should be attached to the rebar not just laying in the concrete.
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Old 01-04-2009, 04:01 PM   #15
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Re: Grounding Rebar


My understanding was the connection had to be exposed. Perhaps a void during concrete placement along with heat and cold cycles or a reaction due to the ph factor could result in a poor connection. I thought all electric connections had to be accessible for that matter. I don't know, other just being a dumb mason I have studied electrical codes in school but that was in 85'.
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Old 01-04-2009, 04:56 PM   #16
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Re: Grounding Rebar


Our inspectors require the connection to be accessible. The rebar in the footing is all connect by lapping and wrapping all the joints with tie wire. One piece of rebar is bent up to extend into a wall cavity. The connection to the grounding wire must be accessible. Generally we screw a mud ring to a stud in front of the connection and put a blank cover on it.

At the time of the final inspection the inspector will check to insure that connection is accessible. He will remove the blank cover to check the connection. If the connection is improper or not accessible we will get a correction notice.
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Old 01-04-2009, 10:38 PM   #17
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Re: Grounding Rebar


As a flatwork guy, I had to ask why there was a piece of rebar sicking up out of the footing in the basement. Here, they leave a piece of rebar that is tied to the grid of rebar in the footing sticking up in the basement, and I finish around it. Then they, as I was told "bond" the rebar that is left sticking up.
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Old 01-04-2009, 10:48 PM   #18
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Re: Grounding Rebar


Quote:
[=tkle;570085]The link vaguely explains why rebar not being grounded poses no threat to the concrete.
right. what they are talking about is what happens when lightning strikes and uses this ground. Many guys think it will blow a hole in the concrete. You link states that has not been supported.

Quote:
The question was about grounding the rebar when placing a footing.. There is no reason for this.
yes, I know and yes, there is a reason and it is a CODE requirement. The rebar inside of the concrete is the grounding electrode, just like a ground rod is or metal pipe in the ground. As I said before, when you have a Ufer grounding electrode, you need no other grounding electrodes other than a water pipe bond. You do not even need a rod. None, nada, zip.


Other that that we're saying the same thing.
Quote:
The ufer is the ground.
No. The ground is the ground. The Ufer is the grounding electrode.


Quote:
Also copper reacts to the alkali in the concrete.
and that is why you must use a listed means of attachment between the copper and the rebar.


from your link:


Quote:
When bonded to the electrical ground, building steel, etc., the buildings reinforced floor and foundation become part of the building grounding system. The result is a much improved grounding system with a very low overall resistance to earth reference.

Quote:
]If Ufer grounding alone was enough, the manufacturers of ground rods would go out of business. But a Ufer ground alone it is not adequate.
this is not true. Code accepts this plus a water pipe bond (which in many situations offers nothing since the use of plastic pipe) to be all the grounding electrodes needed


Quote:
Few buildings, even those under construction today are built to take advantage of the Ufer ground. It is common to see the use of "Ufer grounding" in military installations, computer rooms, and other structures with very specific grounding specifications. It is not common in most industrial plants, office buildings and homes. More common today is grounding to national and local electrical codes.
the Ufer IS code required, if available.


Quote:
This will involve one or more driven ground rods connected (bonded) to the neutral wire of the electrical service entrance. The purpose of this bond is what is known as life safety ground. It is used for many other things but the code required life safety ground is why it is there to begin with
this is where this article goes really bad. Ground, and with that I mean actual bond to earth ground, is not a life safety system. It provides a means for a reference to ground and a path for objectionable currents to be drained, if experienced due to lightning or a higher voltage system contact.
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Old 01-04-2009, 10:51 PM   #19
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Re: Grounding Rebar


Quote:
In fact we had an instance last summer where the wire left out of the footer got cut,
he should have made you dig out to the rebar and attach

Quote:
the inspector made us dig a trench minimum 10 feet long and lay a cooper wire in it, hold it off the soil with stakes, he looked at it and then we poured concrete around it. No rebar in the trench.
that's fine and dandy other than this is the improper way to make a concrete encased electrode. He would have been better off having you lay bar in the concrete and bonding to it but the problem is, there is a required length of rebar, and diameter, to be present before the Ufer is required to be included in the GES.

Quote:
I will make it a point to ask about this on the next one we do.
I don't know if I would bother. It sounds like he really doesn't know what he is doing concerning this.
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Old 01-04-2009, 10:54 PM   #20
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Re: Grounding Rebar


Quote:
Originally Posted by tkle View Post
My understanding was the connection had to be exposed. Perhaps a void during concrete placement along with heat and cold cycles or a reaction due to the ph factor could result in a poor connection. I thought all electric connections had to be accessible for that matter. I don't know, other just being a dumb mason I have studied electrical codes in school but that was in 85'.
It does not have to be exposed. The inspector may be requiring that in your area so he can see the bond. If you have him inspect the bond before the concrete it poured, there should be no problems.

Like I said, you do have to use a bonding method listed for use in concrete. I typically cadweld the copper to the rebar.

I'm not trying to be an ass here guys. I am merely telling you what the code requires and the reasons behind it, as best as I can. If I came across any other way, I apologize. I simply wanted your installs to be proper. If they aren't, there is really no reason to even bother with them.

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Last edited by nap; 01-04-2009 at 10:57 PM.
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