This article was posted 03/22/2006 and is most likely outdated.

The Use of Concrete-Enclosed Reinforcing Rods as Grounding Electrodes
 

 
Topic - Grounding and Bonding
Subject - The Use of Concrete-Enclosed Reinforcing Rods as Grounding Electrodes

March 22, 2006  

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The Use of Concrete-Enclosed Reinforcing Rods as Grounding Electrodes

 

The findings of Ufer that metal encased in concrete performs as an effective grounding electrode constitutes a major breakthrough in grounding technology. This has been recognized to the extent that copper wire embedded in the concrete footings of a structure is now an acceptable alternate to driven rods or pipe electrodes in the soil. This comes as a welcome relief from the condition of ineffective grounding by the use of water pipes due to insulated material or couplings and the antagonism of the proprietors of the water pipes.

 

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Comments

  • Ufer was the name of the radio(?) engineer who first came up with this solution around WWII. Tall radio towers built on high mountain points with rocky soild conditions seem to benefit rom this method as far as LIGHTNING protection concerned.

    To utilize the same method for electrical grounding raises several problems.

    In grounding systems there are always current flows present that are equalizing current flows between different potential due to several different reasons. This unpredictable current flow and the varying moisture content of the concrete, combined with the alkaline characteristics of the concrete will rpoduce galvanic interaction between the copper wire and steel rebar, eg. corrosion, in the structural rebars AND the grounding system itself. The performance and deterioration is unpredictable. The deterioration of the structural integrity can not be remedied.

    Due to concern about corrosion civil engineers sometimes specify epoxy coated rebars. In that case the rebars would be ineffective as a grounding media.

    The NEC suggest that when rebars are utilized as grounding that they should be "bonded together by the usual steel tie wires or other effective means". Again corrosion will have deterious effect on thse connections and bonding it together by other means is probably not a cost effective method.

    Lighting strikes had already demonstrated their destructive effect by striking the reinforcment and had blown concrete apart as predicted by another comment. That happened without intentionally trying to direct the lightning strike through the rebar.

    Unfortunately the NEC is in great error in not addressing cathodic interaction of dissimilar metals in grounding system and discloses it's fundamental defficiency in establishing rules without sound engineering and scientific background and backup. But that is a whole other discussion.....

    In short, fawgedeboutit.......

    Laszlo Weress

    • Reply from: ben jacks   
    Laszla, Your engineering discipline is correct about galvanic effects between dissimilar metals. The electrcial industry does use UL listed components to reduce such incident decay by using bronze alloy clamps between the copper conductor and #4 pickled steel rebar. Maybe you can elaborate and educate me further. Thankyou, Ben Jacks rbjpubs@earthlink.net

    Reply from: Mike Holt   
    Laszlo, you make a lot interesting comments. Do you have the research that supports your comments as it relates to concrete-encased steel rebar?

    Reply from: T.M.Haja sahib   
    lazla,Your assertion that lightning would blow away concrete is correct only when reinforcement bars are used as air terminations without any protrusions above concrete and as down conductors or when there is discontinuity.Otherwise things wlll work fine.

    Reply from: Ken Lillemo   
    T.M. so to summarize your comments, when everything is done well there will be no problem. I guess I could share your view, only as of now, I doubt this will often be the case.

    My concern is that the process of assembling rebar with wire ties is engineered to serve structural requirements, not electrical continuity or current capacity. Wire ties are only a temporary structure in the concrete. That wire ties last beyond the initial curing of the concrete or are electrically conductive is only by happenstance, not design.

    If we are going to make use of rebar for lightning protection, which requires a high current carrying capacity, then the rebar assembly should be engineered and the rebar assembly controlled for this new purpose. I think current rebar assembly standards are inadequate to safely carry tens of thousand Amperes of current.

    Once adequate rebar assembly standards are set we can address the next issue; are we going to make the concrete guys electrical subcontractors, or are we going to have the electricians fiddling around in the dirt before the concrete is poured?

    Cheers,

    Reply from: Mike Holt   
    Mr. T.M.Haja sahib is 100% correct. That's why the 2005 NEC requires steel rebars in the footer to be used as part of the grounding electrode system.

    Reply from: Mike Holt   
    Structural steel rebar in concrete footers is requied to be used as part of the grounding electrode system [250.50]. Studies by Mr Ufer in the 1960's and Mr. Ralph Lee in 1971 have show that steel rebar in concrete footers this is an excellent electrode. In addition, the Ground Resistance Study currently run by the NFPA also shows the positive value of steel rebar as an electrode.

    If you have a study to show otherwise, please let me know.
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