Ufer grounds
- Thread starter lsmith
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charlie
Senior Member
- Location
- Indianapolis
Re: Ufer grounds
As requested, "Section 250.52(A)(3) Concrete-Encased Electrode. An electrode encased by at least 50 mm (2 in.) of concrete, located within and near the bottom 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 (? 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."
As requested, "Section 250.52(A)(3) Concrete-Encased Electrode. An electrode encased by at least 50 mm (2 in.) of concrete, located within and near the bottom 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 (? 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."
charlie
Senior Member
- Location
- Indianapolis
Re: Ufer grounds
H. G. Ufer designed the "Ufer Ground" and spent many years convincing people that it was a very effective method of installing a grounding electrode.
H. G. Ufer designed the "Ufer Ground" and spent many years convincing people that it was a very effective method of installing a grounding electrode.
ryan_618
Senior Member
- Location
- Salt Lake City, Utah
Re: Ufer grounds
So...is it?Originally posted by charlie:
H. G. Ufer designed the "Ufer Ground" and spent many years convincing people that it was a very effective method of installing a grounding electrode.
charlie
Senior Member
- Location
- Indianapolis
Re: Ufer grounds
Yes, very.
Yes, very.
ryan_618
Senior Member
- Location
- Salt Lake City, Utah
Re: Ufer grounds
Charlie: thanks. I like to think that I have a decent knowledge of the code, but I'll be the first to admit that my knowledge of theory is quite lacking. Thanks again.
Charlie: thanks. I like to think that I have a decent knowledge of the code, but I'll be the first to admit that my knowledge of theory is quite lacking. Thanks again.
douglas34474
Member
Re: Ufer grounds
Just found this group. Hope you can help me out.
I design single family homes in Central Florida. I had one of my clients ask me about "Ufer Grounds".
He is adding a detached garage to his house and wants electric in it. The inspector failed him because he did not have a Ufer ground installed in the footer for the new garage. The existing system is grounded per Code.
My question is; does the Code require the Ufer ground in the addition?
I could see it on the original service, but I thought the system had to be grounded at the service panel. No sub-panel is being installed.
Thanks for your help.
Doug Cowan
Just found this group. Hope you can help me out.
I design single family homes in Central Florida. I had one of my clients ask me about "Ufer Grounds".
He is adding a detached garage to his house and wants electric in it. The inspector failed him because he did not have a Ufer ground installed in the footer for the new garage. The existing system is grounded per Code.
My question is; does the Code require the Ufer ground in the addition?
I could see it on the original service, but I thought the system had to be grounded at the service panel. No sub-panel is being installed.
Thanks for your help.
Doug Cowan
Re: Ufer grounds
Charlie, I have had about a hundred or so Ufer ground systems installed in fiber optic regenerator buildings and underground vaults.
Of those, we have had about 4 direct lightning strikes. With 3 of the direct strikes damage occurred to the concrete from the lightning vaporizing the moisture in the concrete causing it to crack or explode. Have you, or anyone else experienced this?
Charlie, I have had about a hundred or so Ufer ground systems installed in fiber optic regenerator buildings and underground vaults.
Of those, we have had about 4 direct lightning strikes. With 3 of the direct strikes damage occurred to the concrete from the lightning vaporizing the moisture in the concrete causing it to crack or explode. Have you, or anyone else experienced this?
douglas34474
Member
Re: Ufer grounds
dereckbc, thank you for the reply.
I did not think it was required. I believe the inspector is pushing a little to hard.
Again, thanks for the help.
dereckbc, thank you for the reply.
I did not think it was required. I believe the inspector is pushing a little to hard.
Again, thanks for the help.
karl riley
Senior Member
Re: Ufer grounds
Dereckbc, your experience with uffers leading to concrete "explosions" during lighning strikes makes me question their use as grounding electrodes, since the main function of these electrodes is lighning protection. Seems it leads to lightning destruction!
My take on uffer proponents is that they are still assuming that a "good ground" is for safety related to service voltage. This misunderstanding is so pervasive that it colors much of the discussion of grounding electrodes in this forum. Any opinions on this?
Karl
Dereckbc, your experience with uffers leading to concrete "explosions" during lighning strikes makes me question their use as grounding electrodes, since the main function of these electrodes is lighning protection. Seems it leads to lightning destruction!
My take on uffer proponents is that they are still assuming that a "good ground" is for safety related to service voltage. This misunderstanding is so pervasive that it colors much of the discussion of grounding electrodes in this forum. Any opinions on this?
Karl
- Location
- Illinois
- Occupation
- retired electrician
Re: Ufer grounds
Dereck,
I remember reading about an utility company study that showed no serious problems with the concrete when they use the rebar in pole bases for grounding, but I can't find it now.
Here are a couple of links to look at: polyphaser and amature radio site
Don
[ August 18, 2003, 04:19 PM: Message edited by: don_resqcapt19 ]
Dereck,
I remember reading about an utility company study that showed no serious problems with the concrete when they use the rebar in pole bases for grounding, but I can't find it now.
Here are a couple of links to look at: polyphaser and amature radio site
Don
[ August 18, 2003, 04:19 PM: Message edited by: don_resqcapt19 ]
Re: Ufer grounds
Karl & Don, I am already a step ahead of you. Since I read your last post I went over the specifications of the effected sites and found something that caught my eye. In the specs, or lack of them, the ufer ground was only specified to meet NEC requirements.
In the past I have talked to my consultants at XIT, Poly Phaser, and Burndy about the concrete damage. They all gave the same suggestion; that the GEC and rebar should be bonded together by either (depending on which rep I spoke with) an exothermic weld, or irreversible compression connectors. Since our specifications did not specify to that degree, I suspect the electrical contractor only installed a # 4 AWG in the bottom of the slab, without bonding to the rebar or only using tie wires.
Don, if you go to the Poly Phaser article you pointed too you will see that reflected in their white paper.
With my sites, the damage occurred where the # 4 AWG entered the concrete foundation for a distance of about 3 feet.
Karl, I am not ready to condemn the ufer ground yet. With all the sites I have, when tested they measure less than 10 ohms. This would lead an uninformed reader to believe it would be a good ground for lightning protection, but in reality, 10 ohms is no better than 100 ohms due to the inductance of the GEC and grounding conductors at high frequencies. I think the ufer would be a good electrode if it were installed by bonding all the rebar and GEC either with irreversible compression connectors or exothermic welds. The problem at least for residential is; who is willing to pay for that extreme of an specification?
Karl & Don, I am already a step ahead of you. Since I read your last post I went over the specifications of the effected sites and found something that caught my eye. In the specs, or lack of them, the ufer ground was only specified to meet NEC requirements.
In the past I have talked to my consultants at XIT, Poly Phaser, and Burndy about the concrete damage. They all gave the same suggestion; that the GEC and rebar should be bonded together by either (depending on which rep I spoke with) an exothermic weld, or irreversible compression connectors. Since our specifications did not specify to that degree, I suspect the electrical contractor only installed a # 4 AWG in the bottom of the slab, without bonding to the rebar or only using tie wires.
Don, if you go to the Poly Phaser article you pointed too you will see that reflected in their white paper.
With my sites, the damage occurred where the # 4 AWG entered the concrete foundation for a distance of about 3 feet.
Karl, I am not ready to condemn the ufer ground yet. With all the sites I have, when tested they measure less than 10 ohms. This would lead an uninformed reader to believe it would be a good ground for lightning protection, but in reality, 10 ohms is no better than 100 ohms due to the inductance of the GEC and grounding conductors at high frequencies. I think the ufer would be a good electrode if it were installed by bonding all the rebar and GEC either with irreversible compression connectors or exothermic welds. The problem at least for residential is; who is willing to pay for that extreme of an specification?
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: Ufer grounds
Dereck, a few years ago Mike Holt was trying to determine why ground rods were used a metal lighting poles. He or I could not find a standard to document why this practice started. One of the comments was a lighting strike to a metal lightig pole may damage the conrete, and the ground rod helps to minimize that.
Your statement about damage to ufer grounds from lighting is very revealing.
Erico has a Practical Guide to Grounding you may find usefull. One of the recommendations is the rebar and foundation anchors be bonded together.
You should be able to get a copy from your Erico (Cadweld) rep.
Dereck, a few years ago Mike Holt was trying to determine why ground rods were used a metal lighting poles. He or I could not find a standard to document why this practice started. One of the comments was a lighting strike to a metal lightig pole may damage the conrete, and the ground rod helps to minimize that.
Your statement about damage to ufer grounds from lighting is very revealing.
Erico has a Practical Guide to Grounding you may find usefull. One of the recommendations is the rebar and foundation anchors be bonded together.
You should be able to get a copy from your Erico (Cadweld) rep.
Re: Ufer grounds
Tom, if you click on the link Don gave for Poly Phaser and read the first three paragraphs you will notice a very similar circumstance. Although it is a radio tower instead of a lighting pole, it closely matches. What they are saying is since the anchor bolts were not bonded to the rebar, it is possible to heat the concrete enough to cause a problem.
The consensus I am hearing from consultants, factory reps (including Poly Phaser), and MHO is an Ufer ground and rebar should be bonded either by weld or compression connectors, and that an additional electrode should augment any Ufer ground.
Tom, if you click on the link Don gave for Poly Phaser and read the first three paragraphs you will notice a very similar circumstance. Although it is a radio tower instead of a lighting pole, it closely matches. What they are saying is since the anchor bolts were not bonded to the rebar, it is possible to heat the concrete enough to cause a problem.
The consensus I am hearing from consultants, factory reps (including Poly Phaser), and MHO is an Ufer ground and rebar should be bonded either by weld or compression connectors, and that an additional electrode should augment any Ufer ground.
pierre
Senior Member
- Location
- Westchester County, New York
Re: Ufer grounds
Dereck
I hope you do not think I am picking on you, I certainly am not. You seem to have a pretty good grasp on this subject. Anybody else that has something to say should join in and add to this thread.
My understanding and reading/research into this subject is limited to the last 2 or so years, I certainly am not an expert. I would like to learn more, so I am going to ask more questions.
Concrete, especially when wet has a hydrostatic characteristic. I am 'assuming' that is part of the reason for it being a good grounding electrode in conjunction with the rebar and/or copper in the bottom portion of the footing. Could those footings that resulted in 'exploding' have been in a dry location? I read and have downloaded some studies that have shown the damage caused by lightning in concrete footings to be exaggerated. I have also read the opposite, WHAT ARE WE TO BELIEVE? Your 'experience might be easier to believe, seeing as you actually experienced it.
With todays plumbing practices changing (plastic piping), installing to a grounding electrode that one can walk away from and truly forget about is not as easy as it once was. Therefore for new dwelling units, I would tend to install a Ufer ground and walk away satisfied that a plumber or the water department is not going to disconnect and possibly not reinstall it. I never use to see this, lately I have seen it several times in the last year.
Another question, I have asked this once before and was not satisfied with the answer.
We are seeing more and more sophisticated electronics in dwellings. We are also seeing more surge protection in the home to protect this equipment. Doesn't this make the grounding electrode important for more than overvoltage and lightning discharge?
Pierre
Dereck
I hope you do not think I am picking on you, I certainly am not. You seem to have a pretty good grasp on this subject. Anybody else that has something to say should join in and add to this thread.
My understanding and reading/research into this subject is limited to the last 2 or so years, I certainly am not an expert. I would like to learn more, so I am going to ask more questions.
Concrete, especially when wet has a hydrostatic characteristic. I am 'assuming' that is part of the reason for it being a good grounding electrode in conjunction with the rebar and/or copper in the bottom portion of the footing. Could those footings that resulted in 'exploding' have been in a dry location? I read and have downloaded some studies that have shown the damage caused by lightning in concrete footings to be exaggerated. I have also read the opposite, WHAT ARE WE TO BELIEVE? Your 'experience might be easier to believe, seeing as you actually experienced it.
With todays plumbing practices changing (plastic piping), installing to a grounding electrode that one can walk away from and truly forget about is not as easy as it once was. Therefore for new dwelling units, I would tend to install a Ufer ground and walk away satisfied that a plumber or the water department is not going to disconnect and possibly not reinstall it. I never use to see this, lately I have seen it several times in the last year.
Another question, I have asked this once before and was not satisfied with the answer.
We are seeing more and more sophisticated electronics in dwellings. We are also seeing more surge protection in the home to protect this equipment. Doesn't this make the grounding electrode important for more than overvoltage and lightning discharge?
Pierre
Re: Ufer grounds
Pierre, I will be happy to try to answer your questions.
The three sites I have witnessed the damage were located in Ashville, NC. Greenville, NC. and Melbourne, FL. These areas receive quite a bit of precipitation, so I doubt dryness was an issue.
The two NC sites are identical where they are fiber-optic regenerator buildings above ground, and the fiber enters from overhead distribution. The fiber is built into the static wire of a 345 KV transmission line. The fault entered via the fiber metallic sheath. At one site it cracked the concrete, and the other it blew out about 2 cubic feet chunk out of the foundation. The damage occurred where the # 4 AWG entered the foundation.
The Melbourne Fl site is again a fiber optic regenerator, but it is an underground vault referred to as a CEV. This site has the fiber ran under ground. The site was struck on the cover hatch as evident by the burn marks. The hatch cover was bonded to the inside ground halo system. Again the damage was where the # 4 AWG entered the wall of the structure. This damage caused some extra trouble because it broke the water seal, and allowed water to seep in the crack. The sump pumps kept it from becoming a problem, but the fix involved a lot of excavation and a lot of expense.
In all three sites we installed a ground ring, and the problem never has happened again. At the time I was mystified by the damage and asked a few consultants and reps (XIT, RO & Associates, Burndy, and Poly Phaser) if they have ever heard of the problem. They all responded that they have either heard of it or witnessed the problem. The consensus was that the rebar needed to be bonded by either compression connectors or exothermic welds, and the electrode cable needs to be bonded to the rebar in the same fashion. At the time construction was slow and still is, and I had other priorities so I moved on and forgot about it until I seen the thread pop up. So I went back through the construction specifications and found only minimum NEC requirements for the UFER ground. Or in other words no welding or compression connector were used to bond the rebar or GEC cable. Live and learn, next time I will specify if I need to use a UFER again.
TVSS is another subject all together. With respect to installing TVSS on AC services, the ground electrode impedance is not all that important because most AC surges occur on the primary side of the transformer and the surge is in the differential mode and not in the common mode. And if in the common mode the impedance of the GEC makes up the lump of the impedance rather than the electrode impedance itself. For example if the electrode impedance is say 5 ohms, and you have a GEC with a length of say 10 feet. A GEC of # 4 AWG @ length of 10 feet exhibits an impedance of about 2.6 K ohms @ 100 Mhz. 2.6 K ohms in series with 5 ohms is still 2.6 K ohms. Now raise the electrode impedance to 100 ohms in series with 2.6 K ohms and you still have 2.6 K ohms. Will that’s enough about TVSS for now. If you want to know more write me a e-mail or start another post with more specific questions and I will try to answer.
Dereck
Pierre, I will be happy to try to answer your questions.
The three sites I have witnessed the damage were located in Ashville, NC. Greenville, NC. and Melbourne, FL. These areas receive quite a bit of precipitation, so I doubt dryness was an issue.
The two NC sites are identical where they are fiber-optic regenerator buildings above ground, and the fiber enters from overhead distribution. The fiber is built into the static wire of a 345 KV transmission line. The fault entered via the fiber metallic sheath. At one site it cracked the concrete, and the other it blew out about 2 cubic feet chunk out of the foundation. The damage occurred where the # 4 AWG entered the foundation.
The Melbourne Fl site is again a fiber optic regenerator, but it is an underground vault referred to as a CEV. This site has the fiber ran under ground. The site was struck on the cover hatch as evident by the burn marks. The hatch cover was bonded to the inside ground halo system. Again the damage was where the # 4 AWG entered the wall of the structure. This damage caused some extra trouble because it broke the water seal, and allowed water to seep in the crack. The sump pumps kept it from becoming a problem, but the fix involved a lot of excavation and a lot of expense.
In all three sites we installed a ground ring, and the problem never has happened again. At the time I was mystified by the damage and asked a few consultants and reps (XIT, RO & Associates, Burndy, and Poly Phaser) if they have ever heard of the problem. They all responded that they have either heard of it or witnessed the problem. The consensus was that the rebar needed to be bonded by either compression connectors or exothermic welds, and the electrode cable needs to be bonded to the rebar in the same fashion. At the time construction was slow and still is, and I had other priorities so I moved on and forgot about it until I seen the thread pop up. So I went back through the construction specifications and found only minimum NEC requirements for the UFER ground. Or in other words no welding or compression connector were used to bond the rebar or GEC cable. Live and learn, next time I will specify if I need to use a UFER again.
TVSS is another subject all together. With respect to installing TVSS on AC services, the ground electrode impedance is not all that important because most AC surges occur on the primary side of the transformer and the surge is in the differential mode and not in the common mode. And if in the common mode the impedance of the GEC makes up the lump of the impedance rather than the electrode impedance itself. For example if the electrode impedance is say 5 ohms, and you have a GEC with a length of say 10 feet. A GEC of # 4 AWG @ length of 10 feet exhibits an impedance of about 2.6 K ohms @ 100 Mhz. 2.6 K ohms in series with 5 ohms is still 2.6 K ohms. Now raise the electrode impedance to 100 ohms in series with 2.6 K ohms and you still have 2.6 K ohms. Will that’s enough about TVSS for now. If you want to know more write me a e-mail or start another post with more specific questions and I will try to answer.
Dereck
karl riley
Senior Member
Re: Ufer grounds
Dereck, I am learning from your post. Please also give info as to how the 100 MHz is caused by the primary surge.
Karl
Dereck, I am learning from your post. Please also give info as to how the 100 MHz is caused by the primary surge.
Karl
Re: Ufer grounds
Karl, there are many types of surge events such as switching loads, primary to secondary contact, and lightning. I chose lightning to make a point about impedances at high frequencies. Lightning as you know is composed of frequencies from DC to GHz range. I chose 100 MHz because it is easy to work, makes the point, and my data tables list impedances of various wire sizes from 1, 10, 100, and 1000 MHz . I could have used 1 MHz which would have been 26 ohm’s, 10 MHz @ 260 ohms, and so on. Hope that helps.
Karl, there are many types of surge events such as switching loads, primary to secondary contact, and lightning. I chose lightning to make a point about impedances at high frequencies. Lightning as you know is composed of frequencies from DC to GHz range. I chose 100 MHz because it is easy to work, makes the point, and my data tables list impedances of various wire sizes from 1, 10, 100, and 1000 MHz . I could have used 1 MHz which would have been 26 ohm’s, 10 MHz @ 260 ohms, and so on. Hope that helps.
karl riley
Senior Member
Re: Ufer grounds
Thanks for info. It would be good to know the frequencies to expect in all the surge events that grounding electrodes are supposed to safely conduct to earth. If the main currents are in the kilo-Megaherz range, then what are we trying to achieve with our grounding electrodes and the GEC?
Karl
Thanks for info. It would be good to know the frequencies to expect in all the surge events that grounding electrodes are supposed to safely conduct to earth. If the main currents are in the kilo-Megaherz range, then what are we trying to achieve with our grounding electrodes and the GEC?
Karl
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