What is a “UFER “ground? This common question is worthy of a detailed explanation. “UFER” ground is slang for what the National Electrical Code (NEC) addresses as a concrete-encased grounding electrode. While the term “UFER” does not appear in the Code, it is used by many in the industry and is derived from the name of the engineer who created it as a solution to significant grounding problems discovered by the U.S. military.
The Code defines “grounding electrode” as “a conducting object through which a direct connection to earth is established.” An important feature is that the electrode is in direct contact with the Earth, making a connection. Without such a connection, there is no grounding. This article takes a closer look at what constitutes a concrete-encased electrode (UFER), when it is required, and installation techniques.
Details and description
NEC 250.52(A)(3) clearly specifies what constitutes a concrete-encased electrode. The concrete-encased electrode can be bare, zinc galvanized, or other electrically conductive, coated-steel reinforcing bars or rods of not less than ½ inch in diameter, installed in one continuous 20-foot length. If in multiple pieces, it can be connected by the usual steel tie wires, exothermic welding, welding, or other effective means to create a 20-foot or greater length.
A concrete-encased electrode can also be constructed using 20 feet or more of bare copper conductor not smaller than 4 AWG. Note that the 20 feet of conductive rods or bare wire used in creating a concrete-encased electrode establishes the connection to the concrete only. The combination of the concrete and the conductive component serve as the grounding electrode as clarified in the definition.
Grounding electrode system
Section 250.50 requires the use of all grounding electrodes to form the grounding electrode system. This includes all concrete-encased electrodes present at the building or structure. An exception to Section 250.50 relaxes this mandatory requirement for existing buildings and structures in which connecting the concrete-encased electrode could damage the structural integrity of the building or otherwise disturb the existing construction.
Because the installation of the footings and foundation is one of the first elements of a construction project and, in most cases, has been completed by the time the electric service is installed, this rule necessitates an awareness and coordinated effort on the part of designers and the construction trades to ensure the concrete-encased electrode is incorporated into the grounding electrode system during the placement of rebar and concrete footings. If a concrete-encased electrode is not present at the building or structure supplied, it is not required that a 4 AWG copper wire be used to form one, but it is an option.
The concrete-encased electrode has proven that it offers optimal performance and longevity. The footing or foundation of any building will typically be there as long as the building is. Because all of the rebar in the bottom perimeter of the building footing usually is tied together with tie wires, the electrode performs similar to a ground ring electrode, only it has much more surface area in the concrete connection to the earth. The footing is present around the bottom of the building perimeter, which means there is significant ground (earth) contact from concrete-encased electrodes.
Concrete retains moisture and is continuously absorbing moisture through the bottom of the footing. This keeps the connection between the footing and the earth effective. Also, the footing of a building is typically the largest grounding electrode in each building.
Herbert G. Ufer was an engineer at Underwriters Laboratories (UL) who assisted the U.S. military with ground-resistance problems at installations in Arizona. His findings in the 1940s proved the effectiveness of concrete-encased grounding electrodes. The military required low resistance ground connections (5 ohms or less) for lightning protection systems installed at its ammunition and pyrotechnic storage sites at the Navajo Ordnance Depot in Flagstaff and Davis-Monthan Air Force Base in Tucson.
Ufer developed the initial design for a concrete-encased grounding electrode that consisted of ½-inch reinforcing bars 20 feet in length placed within and near the bottom of 2-feet-deep concrete footings for the ammunition storage buildings. Test readings over 20 years revealed steady resistance values of 2 to 5 ohms, which satisfied the specifications of the U.S. government at that time.
This work eventually resulted in what we know as the concrete-encased electrode in the NEC. More details about Ufer’s research and findings are provided in his IEEE paper CP-978: “Investigation and Testing of Footing-Type Grounding Electrodes for Electrical Installations.”
Concrete-encased electrodes are required to be included in the grounding electrode system for buildings or structures. It is not optional.