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Concrete-encased Electrodes and the Grounding Electrode System

Posted By Michael Johnston, Sunday, July 01, 2001
Updated: Wednesday, February 13, 2013

Most buildings or structures employ a structural design that includes a concrete footing or foundation, which connects the structure to the earth. For the building to be structurally sound and stable, a substantial foundation must be established to bring the structure out of the ground. Footings and foundations are typically constructed using concrete and reinforcing rods or bars for structural strength. The larger the building, the larger the footings or foundation will need to be to carry the structural load of the building. Concrete footings and foundations can vary from the elementary in design to the very complex. An example would be comparing a simple monolithic slab on grade for a single-family dwelling to a complex concrete and steel foundation for a multi-story high-rise structure. These structures have some commonalities; both include concrete and reinforcing bars, which establish a good structural connection to the earth and are permanent elements required for the construction of either building. The word "permanent” is a substantial word related to something established to be in place for a long period of time. This is a characteristic of the building footings and foundation that are expected to be in place and continue to exist as long as the building is required to remain standing.

Photo 1. Concrete-encased rebar

The Grounding Electrode System

A grounding electrode is defined as a conducting element that connects electrical systems and/or equipment to the earth. The lowest possible impedance connection to the earth is sought from the grounding electrode or grounding electrode system. Electrical systems and metal enclosures are grounded to limit the voltage on them due to contact with higher voltage lines; protect against lightning strikes; and to stabilize the voltage during normal operations. The grounding electrodes required to be used make up the grounding electrode system and are required to do so because they are inherent to the construction of the building. The grounding electrode system is the foundation of the electrical safety system. An effective, reliable grounding electrode or grounding electrode system is required to be used where electrical services and systems are employed.

Concrete-Encased Electrodes

The concrete-encased electrode is often referred to as a Ufer ground, although the word "Ufer” does not appear in the text of the Code. The concrete-encased electrode is described in Section 250-50(c) of the NEC, which reads:

(c) Concrete-Encased Electrode.An electrode encased by at least 2 in. (50.8 mm) 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 20 ft (6.1 m) of one or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than ½-in. (12.7-mm) diameter, or consisting of at least 20 ft (6.1 m) of bare copper conductor not smaller than No. 4. Reinforcing bars shall be permitted to be bonded together by the usual steel tie wires or other effective means.1

Most entities involved in the electrical industry, either as electrical contractors, designers, engineers or inspectors, agree that it is important to inspection departments and jurisdictions to strive for the most consistency and uniformity possible when enforcing the requirements of the Code. As used in Section 250-50, the word "available” can lead to inconsistency. The Code requires that if an electrode is available, then it must be used as part of the grounding electrode system. Sometimes, depending on how the section is interpreted, the word "available” and the word "existing” work against one another. The word "available” is not enforceable and according to the NEC Style Manual for 2000 should be avoided. The word "available” relative to the coordination of installation concrete encased electrode is a matter of a point in time when the building is being constructed. The issue of the word "available” being replaced with the term "if installed and present” is a concept that definitely is in need of further review.


Figure 1. Concrete-encased electrode

The IEEE papers written by H.G. Ufer confirm the validity and reliability of concrete-encased electrodes. History and data have proven the worthiness of the concrete-encased electrode. Numerous states and municipalities adopt local electrical amendments that amend the NEC by requiring a concrete-encased electrode to be part of the grounding electrode system. A current grounding electrode study has been under way for some time to monitor various grounding electrode connection resistance values to ground from season to season. Perhaps the data gathered from these grounding electrode studies might have an impact on the NEC requirements in future editions. The NEC is generally considered a minimum safety standard containing provisions that are considered necessary for safety. That means electrical installations must be installed at least in accordance with those rules.

Many interpret Part C of Article 250 to be a mandatory requirement to include the concrete-encased electrode if the building or structure is constructed with a footing. There are some regions where the effects of frost and frozen earth have some impact on the effectiveness of concrete-encased electrodes. There are also those who contend that lightning strikes can have a destructive effect on concrete-encased electrodes. IAEI is unaware of data that supports not using the concrete-encased electrode because lighting has a destructive effect on the concrete in some conditions or because of frost or frozen earth. Many claim that the impact to current industry practices relative to requiring a concrete-encased electrode on all new installations would create hardships for the construction industry.

The word "available” and the word "existing” work against each other where buildings are constructed without installing a concrete-encased electrode in the building footing. An example is where the building construction is started and all footings and foundations are completed before the electrical construction is started or the electrical contractor is onsite to install a concrete-encased electrode. If the footings are poured, then they are existing and no longer available. This appears to be a construction trade coordination problem, although a trade coordination issue in the field should not serve as a basis for allowing it to be installed only when there is availability or access to a foundation of a building or structure that is not poured. If the word "existing” were defined in the Code it might serve to eliminate a gray area between when trying to meet the intent of the word "available.” Proposed definitions for the word "existing” have been rejected in previous code cycles. Clearly the intent is not to require that existing building structural footings be disturbed to install a concrete-encased electrode. It should also be noted that in most cases, effectively grounded building steel is effectively grounded through the concrete-encased rebar. The concept of "if installed and present” is a valid one, and should be further studied.

The Code Requirements

Part C of Article 250 requires a grounding electrode system at buildings or structures. A closer look at Section 250-50 indicates that if any of the items permitted to be used for grounding electrodes are available, then they must be used and bonded together to form a grounding electrode system for the electrical service or electrical power distribution system for the building or structure. Section 250-50 reads, in part, as follows:

If available on the premises at each building or structure served, each item (a) through (d), and any made electrodes in accordance with Sections 250-52(c) and (d), shall be bonded together to form the grounding electrode system. The bonding jumper(s) shall be installed in accordance with Sections 250-64(a), (b), and (e), shall be sized in accordance with Section 250-66, and shall be connected in the manner specified in Section 250-70.

An unspliced grounding electrode conductor shall be permitted to be run to any convenient grounding electrode available in the grounding electrode system or to one or more grounding electrode(s) individually. It shall be sized for the largest grounding electrode conductor required among all the electrodes connected to it.2

Making the Best Decision


Photo 2. Concrete-encased electrode

There are many different discussions and interpretations of the term "if available” as used in this section. Some contend that if a building is constructed, then at some point during the construction, the concrete-encased electrode is required to be installed and made part of the grounding electrode system. This is one reason that many jurisdictions adopt local amendments to the NEC to require concrete-encased electrodes to be installed. This eliminates any doubt as to whether or not it is required. Many jurisdictions feel that it should not be viewed as a coordination problem between subcontractors on the jobsite. In contrast, there are those who feel that if the concrete footings or foundation is already in place prior to the electrical contractor’s presence on the construction site, access to the rebar system for establishing a concrete-encased electrode is not practical and, therefore, is unavailable. Is this the best approach? There are varying opinions on this question. The grounding electrode system is an important, vital part of the electrical distribution safety system and decisions relative to the grounding electrode system and what grounding electrodes are used as part of this system should be carefully considered.

Reliability and Effectiveness

With the grounding electrode serving as a major part of the safety system for buildings or structures, the grounding electrode or grounding electrode system sought for use in construction should have the characteristics of permanency and effectiveness whenever possible. When a building is constructed using a concrete- encased electrode as part of the grounding electrode system, it is without question one of the most reliable, permanent and effective. The installation of the concrete-encased electrode ensures that it usually will remain a permanent component of the grounding electrode system as long as the building footings or foundation are not disturbed. As for it’s effectiveness, the work and research by H.G. Ufer in the 1940s confirm the effectiveness of this type of electrode even in normally dry soil conditions. Every effort should be made to ensure that the safety system for the electrical installation in any occupancy is not compromised. CMP-5 acted on a proposal to the 2002 NEC to require the concrete-encased electrode to be used in the construction of new buildings. The proposal was rejected, but comments by the panel indicate that there are concerns about the concrete-encased electrode and how the word "available” is used in Part C that still need to be addressed. The concrete-encased electrode was inserted in the NEC based on its proven effectiveness and reliability through time.

"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.”3

For additional information on the research and the grounding electrode studies, refer to the IAEI Soares Book on Grounding. Many jurisdictions have local amendments to the National Electrical Code. Check with the local jurisdiction in your region if in doubt as to the requirements.

IAEI is very interested in receiving data and documented experiences relative to the destructive effects of lightning on concrete-encased grounding electrodes. IAEI encourages any organization or individual with such information to forward it to the international office. This information is valuable data and serves to develop and revise current codes and standards.

1 NFPA 70,National Electrical Code, 1999 Edition, Section 250-50(c). (Quincy, MA: National Fire Protection Association, Inc.), p. 70 – 88.

2 NFPA 70,National Electrical Code, 1999 Edition, Section 250-50. (Quincy, MA: National Fire Protection Association, Inc.), p. 70 – 88.

3 Soares Book on Grounding, 7th Edition. (Richardson, TX: International Association of Electrical Inspectors), p. 277.


Read more by Michael Johnston

Tags:  Featured  July-August 2001 

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