Please, are there any typical or range of Ohmic Values available for the 20' long 0.5" diameter steel electrode encased in concrete as included in NEC 2005 Art 250.52(A)(3) Concrete-Encased Electrode? Has anyone applied such a permitted electrode for grounding or measured its ground resistance? The typical ohmic values of the ground resistance could be used in the ongoing project conceptual phase.
NEC 2005 Art. 250.52(A)(3) Concrete-Encased Electrode
- Thread starter jbartos
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Re: NEC 2005 Art. 250.52(A)(3) Concrete-Encased Electrode
There is a 25 ohm maximum resistance permitted on one ground rod but not on the concrete encased electrode. Also if the CEE is used than a ground rod is not required.
There is a 25 ohm maximum resistance permitted on one ground rod but not on the concrete encased electrode. Also if the CEE is used than a ground rod is not required.
Re: NEC 2005 Art. 250.52(A)(3) Concrete-Encased Electrode
Are you talking about the resistance of the electrode itself, or the resistance to ground?
If you are talking about the resistance to ground, I would think it would vary a lot with the depth and size of the concrete.
Steve
Are you talking about the resistance of the electrode itself, or the resistance to ground?
If you are talking about the resistance to ground, I would think it would vary a lot with the depth and size of the concrete.
Steve
bphgravity
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Re: NEC 2005 Art. 250.52(A)(3) Concrete-Encased Electrode
In 1942, H.G. Ufer performed an 18 year study on the resistance of concrete-encased electrodes. At the end of the study in 1960, the average of 24 installations was 3.57 ohms, none every exceeding 4.8 ohms over the 18 years. The best reading was 2.1 ohms.
The study was performed in two soil types. One in dry sand and gravel, the other in moist clay, shale, gumbo, and loam.
Now for the important question. So what? What is the application you are installing that the ground resistance is so important?
In 1942, H.G. Ufer performed an 18 year study on the resistance of concrete-encased electrodes. At the end of the study in 1960, the average of 24 installations was 3.57 ohms, none every exceeding 4.8 ohms over the 18 years. The best reading was 2.1 ohms.
The study was performed in two soil types. One in dry sand and gravel, the other in moist clay, shale, gumbo, and loam.
Now for the important question. So what? What is the application you are installing that the ground resistance is so important?
bphgravity
Senior Member
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- Florida
Re: NEC 2005 Art. 250.52(A)(3) Concrete-Encased Electrode
Am I that predictable?
I actually think it is fantastic that concrete encased electrodes provide such a low resistance grounding system. I also think it is fantastic that electrons have a diamter of 1/12,700,000,000,000 inches and that Jupiter has a diamter of 86,000 miles, but I'm not completely sure how all these facts are usefull and have any real value.
Am I that predictable?
I actually think it is fantastic that concrete encased electrodes provide such a low resistance grounding system. I also think it is fantastic that electrons have a diamter of 1/12,700,000,000,000 inches and that Jupiter has a diamter of 86,000 miles, but I'm not completely sure how all these facts are usefull and have any real value.
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Re: NEC 2005 Art. 250.52(A)(3) Concrete-Encased Electrode
Bryan, those are some interesting facts, but I'm still giggling at "gumbo". Good word.
I thought Ufer was in the southwest, not Louisiana.
Bryan, those are some interesting facts, but I'm still giggling at "gumbo". Good word.
I thought Ufer was in the southwest, not Louisiana.
josefbartos
Member
Re: NEC 2005 Art. 250.52(A)(3) Concrete-Encased Electrode
Thank you to all contributors for their postings. Additional information for the usage of the posted ohmic values in Bryan's posting:
"In 1942, H.G. Ufer performed an 18 year study on the resistance of concrete-encased electrodes. At the end of the study in 1960, the average of 24 installations was 3.57 ohms, none every exceeding 4.8 ohms over the 18 years. The best reading was 2.1 ohms.
The study was performed in two soil types. One in dry sand and gravel, the other in moist clay, shale, gumbo, and loam.
Now for the important question. So what? What is the application you are installing that the ground resistance is so important??
is as follows:
///The project location and soil composition are known. The ground resistance is specified in the Specifications as: "Ohmic resistance between the equipment and the earth shall not exceed ten (10) ohms." The Project includes a large underground "Rebar Concrete Box" that will house Industrial/Commercial Rooms, and two light rail tracks (several hundred yard long). Since the rebars meet NEC "Concrete-Encased Electrode" requirements, grounding connection access to concrete rebars (Concrete-Encased Electrodes) have to be depicted on Project Drawings in terms of number of locations that would meet the specified ohmic value of 10 ohms or less. This is the normal and prudent electrical engineering, design and construction aspect.\\\
Thank you to all contributors for their postings. Additional information for the usage of the posted ohmic values in Bryan's posting:
"In 1942, H.G. Ufer performed an 18 year study on the resistance of concrete-encased electrodes. At the end of the study in 1960, the average of 24 installations was 3.57 ohms, none every exceeding 4.8 ohms over the 18 years. The best reading was 2.1 ohms.
The study was performed in two soil types. One in dry sand and gravel, the other in moist clay, shale, gumbo, and loam.
Now for the important question. So what? What is the application you are installing that the ground resistance is so important??
is as follows:
///The project location and soil composition are known. The ground resistance is specified in the Specifications as: "Ohmic resistance between the equipment and the earth shall not exceed ten (10) ohms." The Project includes a large underground "Rebar Concrete Box" that will house Industrial/Commercial Rooms, and two light rail tracks (several hundred yard long). Since the rebars meet NEC "Concrete-Encased Electrode" requirements, grounding connection access to concrete rebars (Concrete-Encased Electrodes) have to be depicted on Project Drawings in terms of number of locations that would meet the specified ohmic value of 10 ohms or less. This is the normal and prudent electrical engineering, design and construction aspect.\\\
Re: NEC 2005 Art. 250.52(A)(3) Concrete-Encased Electrode
I think that somebody forgot to add that the dry soil was in Arizona which is essentially a desert. The idea of the Ufer ground was to take advantage of the large contact area between concrete and soil as well as the depth of a basement.
You will get even better performance if the rebars in a footer that goes all the way around the building are bonded together. For a typical 30 foot by 30 foot house that gives you 120 square feet of soil contact. Compare to how for telegraphs that used a ground return the preferred electode was a 3 foot by 4 foot metal plate.
In the case of footers that have no rebars you should consider using a lot more than 20 feet of copper wire. Say two #4 copper wires for a 400 amp service comprising 2 Ufer grounds, 1 for each of the 200 amp service circuit breakers. This would avoid having to crimp or weld a tap if your inspector requires that for GEC taps rather than split bolts. Since you have 2 unbroken GECs you can bond them together with a split bolt.
[ May 19, 2005, 04:05 AM: Message edited by: mc5w ]
I think that somebody forgot to add that the dry soil was in Arizona which is essentially a desert. The idea of the Ufer ground was to take advantage of the large contact area between concrete and soil as well as the depth of a basement.
You will get even better performance if the rebars in a footer that goes all the way around the building are bonded together. For a typical 30 foot by 30 foot house that gives you 120 square feet of soil contact. Compare to how for telegraphs that used a ground return the preferred electode was a 3 foot by 4 foot metal plate.
In the case of footers that have no rebars you should consider using a lot more than 20 feet of copper wire. Say two #4 copper wires for a 400 amp service comprising 2 Ufer grounds, 1 for each of the 200 amp service circuit breakers. This would avoid having to crimp or weld a tap if your inspector requires that for GEC taps rather than split bolts. Since you have 2 unbroken GECs you can bond them together with a split bolt.
[ May 19, 2005, 04:05 AM: Message edited by: mc5w ]
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