What is a 'Ufer' Ground?
At a recent seminar, one of the attendees asked, "What is a 'Ufer' ground?"The National Electrical Code addresses a concrete-encased ground as a "Ufer" ground.The Code does not include the term "Ufer", but many in the industry use it.The name of the engineer who created it is Ufer.
The 2005 NEC defined the term as a conducting object through which a direct connection to earth is established.The definition shows that the electrode is in contact with the earth.Without a connection to the earth, there is no grounding.When it is required, and the installation techniques, let's take a closer look at what constitutes a concrete-encased electrode.
Section 250.52(A)(3) clearly states what constitutes a concrete-encased electrode.The concrete-encased electrode can be bare, zinc-galvanized, or other steel reinforcing bars or rods of less than 12 inch in diameter.It can be connected by steel tie wires, exothermic welding, or other means to create a 20-foot or greater length.A concrete-encased electrode can be constructed using 20 feet or more of bare copper conductor.The 20 feet of wire or rods used to create a concrete-encased electrode only establishes the connection to the concrete.The definition of the term states that the combination of concrete and the component that conducts electricity serves as the grounding electrode.
Section 250.50 requires the use of all grounding electrodes.All concrete-encased electrodes are included.There is an exception to Section 250.50 that relaxes the requirement for existing buildings and structures in which connecting the concrete-encased electrode could damage the structural integrity of the building.In most cases, the installation of the footings and foundation is done by the time the electric service is installed, so this rule necessitates an awareness and coordinated effort from designers and the construction trades to ensure the concrete-encase.If a concrete-encased electrode is not present at the building or structure, a 4 AWG copper wire can be used to form one.
The concrete-encased electrode has been proven to offer optimal performance.As long as the building is there, the footing or foundation will be there.The electrode acts like a ground ring because it has more surface area in the concrete connection to the earth than the bottom perimeter of the building.There is significant ground contact from concrete-encased electrodes around the bottom of the building perimeter.Concrete absorbs water through the bottom of the footing.The connection between the footing and the earth is ensured by this.The footing of a building is the most important part of the structure.
Herbert G. Ufer assisted the U.S. military with ground-resistance problems at installations in Arizona.The effectiveness of concrete-encased grounding electrodes was proved by Ufer in the 1940s.The military required low-resistance ground connections for its lightning protection systems, which were installed at its ammunition and pyrotechnic storage sites.The initial design for a concrete-encased grounding electrode consisted of 12 inch, 20-foot-long reinforcing bars placed within and near the bottom of 2 foot-deep concrete footings for the ammunition storage buildings.Steady resistance values of 2 to 5 ohms, which satisfied the specifications of the U.S. government at that time, were revealed by test readings over a 20-year period.The concrete-encased electrode in the NEC was the result of this work.More information about Ufer's research can be found in his October 1964 paper.
Michael is the executive director of standards and safety.He is a member of the NEC Correlating Committee.He can be reached at mj@necanet.org.