2005 Grounding Electrode system

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Re: 2005 Grounding Electrode system

Dave,
I don't agree. If there is 20' of rebar in the bottom of a footing that is in direct contact with the earth in a new building, that rebar must be used because it is "present". Just because you choose to add copper to the footing, does not make the rebar go away. If it is there, you are required under the 2005 wording to use it.
Don
 
Re: 2005 Grounding Electrode system

Bob,
I hope that you get an engineer's report before you go busting up any footings to get to an unlocated piece of rebar.
As a matter of fact, I think all job proposals should have a clause added as to put any of those issues onto the G.C.
Some type of 'we might have to bond it, but we aren't gonna find it.'
 
Re: 2005 Grounding Electrode system

New/Revised 2005 NEC Text:
250.50 Grounding Electrode System.
All grounding electrodes as described in 250.52(A)(1) through (A)(6) 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)(7) shall be installed and used.

2002 Text:
250.50 Grounding Electrode System.
If available on the premises at each building or structure served, each item in 250.52(A)(1) through (A)(6) shall be bonded together to form the grounding electrode system. Where none of these electrodes are available, one or more of the electrodes specified in 250.52(A)(4) through (A)(7) shall be installed and used.
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Don,
This is about a Concrete-Encased Electrode not rebar in a footer.
The code gives us the option of using rebar or copper to form the electrode. After 20' we have accomplished the requirement regardless of the material used.
When we say that rebar is required to be bonded and used as a GE, it gives the wrong impression and many think all of the rebar needs to be bonded together in every footer. The footers I have seen recently have rebar near the bottom and again near the top. The top rebar is not acceptable as an electrode and therefore does not need to be bonded to the bottom or the GE system.
 
Re: 2005 Grounding Electrode system

Dave
This was discussed at the Western Selectional meeting and the reply was that the exception was only to allow existing buildings to not have to use the re-bar that is not exposed, but in new construction if the footer has re-bar in it, it must be used as an electrode. this sparked a few questions by some who were there but they just said it would be up to the AHJ as to how it will be enforced. (via the building inspector or the electrical inspector) Also it was mention that it should be exposed and a listed connection be made. Not just a split bolt connection.

I have it on my recorder and I'll go back and listen to it again to be sure.

[ September 27, 2004, 02:19 AM: Message edited by: hurk27 ]
 
Re: 2005 Grounding Electrode system

Dave,
This is about a Concrete-Encased Electrode not rebar in a footer.
The code gives us the option of using rebar or copper to form the electrode. After 20' we have accomplished the requirement regardless of the material used.
Click to expand...
I still don't agree. If the footer has at least 20' of rebar in the bottom of the footing, under the 2005 code, that rebar must be used as a grounding electrode. The code wording says any electrode that is "present" must be used. If it (the rebar) is there it is present. The code does not give the option of using a length of copper in place of the rebar if the rebar is present. If you would install copper in addition to the rebar, then 250.50, requires that the copper be bonded to the rebar.
If there is no rebar in the bottom of the footing, then you have the option of creating your own concrete encased electrode and in this case you can use either bare copper or rebar.
Don
 
Re: 2005 Grounding Electrode system

Originally posted by wayne123:
What type of connection will have to be made if it is concrete ( cad weld, irreversible connections)?
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Yes
Edit: However there ar listed mechanical clamps for this purpose.

[ September 27, 2004, 12:57 PM: Message edited by: dereckbc ]
 
Re: 2005 Grounding Electrode system

This is how we inspect for the Ufer in our jurisdiction:

1. At foundation pour we ensure there is a Ufer made available (bent upwards out of the foundation so the electrician can access it after the pour)

2. If we blow it (forget to ensure the Ufer is available) then it's not available...that simple...a ground rod is used instead.

3. A listed clamp is used to secure the GEC to the Ufer.
 
Re: 2005 Grounding Electrode system

Dana,
That approach is fine under the 2002 code, but will not be acceptable under the 2005 code.
Don
 
Re: 2005 Grounding Electrode system

We danced this same dance nearly thirty years ago when the Code first introduced the concept of bonding all inherent grounding electrodes.

I believe Don's interpretation of the 2005 wording is correct and, in fact, that it was the original intent in 1978 too. Bonding was required for any potential "ufers." When the problems with that became obvious we got a "Formal Interpretation" that lasted 27 years. The intent though was to exclude ?existing buildings? - not foundations that were poured before the EC got there.

The fact that I agree with the Don's interpretation doesn't mean I agree with the Codes intent. There are a couple of other threads dealing with the actual safety purposes of a GES in the first place. My basic position is this: if bonding the rebar to the GEC isn?t necessary for "minimum" safety enough to require it for existing buildings, why is it anything but a design option at all? It?s like the ?existing work ? new work? requirements that passed away for conduit fill.

[ September 27, 2004, 11:49 AM: Message edited by: rbalex ]
 
Re: 2005 Grounding Electrode system

What type of connection will have to be made if it is concrete (Cad Weld, irreversible connections)?
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To be buried in concrete, the connector has to be listed for direct burial only.

The following is from the 2004 UL White Book for category KDER. "Ground clamps and other connectors suitable for use where buried in earth or embedded in concrete are marked for such use. The marking may be abbreviated "DB" (for "Direct Burial")." :D
 
Re: 2005 Grounding Electrode system

I had a few nice conversations with Chuck Mello and Mike Johnston, both on CMP 5 (Art. 250), while they were here in Utah for the IAEI NothWest section meeting.

It was quite clear that their intent was that the concrete encased electrode is more often than not the best electrode present at a building, and therefore it was to be used. Period. If that means chipping out concrete, well, so be it.
 
Re: 2005 Grounding Electrode system

There are alot of things we can do that are the "best" choice, but that is not the purpose of our code. (90.1(B))

What about the studies that have shown damage to concrete slabs and foundations from the effects of lightning? Many papers and articles I have read on the subject suggest supplementing the concrete-encased electrode with a ground rod to direct some of the energy away from the building. I kind of like the idea of sending lightning away from structures, even if that means my GES is less effective than another method.
 
Re: 2005 Grounding Electrode system

Originally posted by ryan_618:
If that means chipping out concrete, well, so be it.
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Well it will be interesting, the building inspectors and engineers will not want to see us chipping into footings just because the NEC CMP says so. :p

Originally posted by luke warmwater:
Bob,
I hope that you get an engineer's report before you go busting up any footings to get to an unlocated piece of rebar.
As a matter of fact, I think all job proposals should have a clause added as to put any of those issues onto the G.C.
Some type of 'we might have to bond it, but we aren't gonna find it.'
Click to expand...
Todd, I agree with you entirely, I would not even think of breaking into a footing without my office saying to do so, and I know they will not tell me to do that.

Bob
 
Re: 2005 Grounding Electrode system

chipping into a footing to expose rebar...?

How does one than provide proof to satisfy this requirement?

at least 6.0 m (20 ft) of one or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars rods of not less than 13 mm (? in.) in diameter
Click to expand...
Chip enough to expose 20', and than cap it with a cold joint, lol?
 
Re: 2005 Grounding Electrode system

Originally posted by bphgravity:
There are alot of things we can do that are the "best" choice, but that is not the purpose of our code. (90.1(B))

What about the studies that have shown damage to concrete slabs and foundations from the effects of lightning? Many papers and articles I have read on the subject suggest supplementing the concrete-encased electrode with a ground rod to direct some of the energy away from the building. I kind of like the idea of sending lightning away from structures, even if that means my GES is less effective than another method.
Click to expand...
What we do in the tilt-ups we wire is to drive a ground rod in the bottom of the footing, than loop the electrode though it, send one end up to the structural steel in the roof, leave at LEAST 20 in the footing, and bring the other end up to the MSB. All other grounding electrodes are than attached to the structural roof steel.
 
Re: 2005 Grounding Electrode system

Originally posted by sdbob:
Chip enough to expose 20', and than cap it with a cold joint, Lola?
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Your speaking sacrilege to the structural engineers I have worked with. :D
 
Re: 2005 Grounding Electrode system

"Herbert G. Ufer, in an IEEE Conference Paper, CP-61-978, describes an installation of made ground electrodes on twenty-four buildings in 1942, in Arizona, to meet a 5-ohm maximum value. The resistance values were checked bimonthly over an 18-year period, during which time no servicing was required.

"In 1960, the maximum reading was 4.8 ohms and the minimum, 2.1 ohms. The average value of the twenty-four installations was 3.57 ohms.

"The installations used 1/2-inch steel reinforcing rods set in a concrete footing. There were at two locations in Arizona. The first was near Tucson, Arizona, which is normally hot and dry during most of the year and has an average annual rainfall of 10.91 inches. The soil is sand and gravel. The second location was near Flagstaff, Arizona, where the soil is clay, shale gumbo and loam with small area stratas of soft limestone. The made electrodes were used as no water piping system was available.

"As a result of these installations and the 18-year test period, Mr. Ufer suggested that a No. 4 or larger copper wire be embedded in the concrete footing of a building and that test data be compiled further to verify the effectiveness. Based on this data, CMP-5 accepted a concrete-encased electrode commonly referred to as a "Ufer Ground." The concrete-encased electrode shall consist of at least 20 feet of bare copper not smaller than No. 4 AWG encased in 2 inches of concrete near the bottom of the footing or foundation."
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Formal Interpretation 78-4

Reference: Article 250.50

Question: Is it the intent of 250.50 that reinforcing steel, if used in a building footing, must be made available for grounding?

Answer: No.

Issue Edition: 1978
Reference: 250-81
Issue Date: March 1980
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Don,

We are not that far apart.
250.52 (A)(3) gives us the option of using rebar OR copper to make a Ufer Ground.
As I see your point of when rebar is in a footer it makes the footer a GE and therefore must be connected to the GE system. However, I maintain that the option is available that when there is a footer with rebar in it, one could add 20' of copper and satisfy the code.
One of the advantages of using 20' or more of 4AWG copper is it could be installed continuous with-out any clamps or cad welds. It could also be installed by the footer crew without worrying about the proper connections.
In the end, we still would have a "concrete encased electrode".
 
Re: 2005 Grounding Electrode system

Dave,
However, I maintain that the option is available that when there is a footer with rebar in it, one could add 20' of copper and satisfy the code.
Click to expand...
Even if you add the copper, the rebar is still a code required grounding electrode and would have to be bonded to the copper.
Don
 
Re: 2005 Grounding Electrode system

Bryan,
What about the studies that have shown damage to concrete slabs and foundations from the effects of lightning?
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The only time I've seen any documentation of this problem is for isolated foundations like for power poles and lighting standards. I have not read reports of damage to building foundations. Dereck has made posted some information on this problem in the past and as I recall, the problem can be eliminated by using double ties on the rebar and multiple bonding points to the rebar, as well as a connection to additional electrodes as you stated.
Don
 
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