The Informational Note following 250.53(A)(3) explains that this increases the efficiency in paralleling. When using multiple rod, pipe, or plate electrodes to meet the requirements of 250.53, they must be spaced at least 6 ft apart. The allowance to use only a single rod, pipe, or plate electrode when a resistance of 25 ohms or less to ground is obtained is now written as an exception to.
#CONCRETE ENCASED ELECTRODE CODE#
The Code requirements are now easier to understand and match the standard industry practice of driving two ground rods instead of testing the resistance of a single driven rod. These requirements were spread out in several different Code sections until the 2011 edition. 25 ohmsĪ long-standing rule says that a ground rod or pipe or plate electrode must have a resistance to earth of 25 ohms or less, or be supplemented by an additional electrode. thick, or a solid uncoated nonferrous metal plate at least 0.06 in. The electrode must be a bare or conductively coated iron or steel plate at least ¼ in. A 2011 Code change to 250.52(A)(7) clarifies that plate electrodes must be conductive. of surface to exterior soil is permitted as a grounding electrode. This dimension has been removed for listed rods, since this is an issue for the testing lab, not for the NEC.Ī plate electrode that exposes at least 2 sq ft. Previously, the Code also included a minimum diameter for listed rods. The minimum length for rod and pipe electrodes is 8 ft, and the minimum size for a rod is 5/8 in. Section 250.52(A)(5) contains the provisions for the use of rod and pipe electrodes. This is an important consideration in view of some of the modern building methods in use. In such a case, the concrete-encased electrode is not present, and another suitable electrode must be used. This note explains that when such materials are encountered that insulate the concrete from the earth, the "direct contact" with the earth required for the use of a concrete encased electrode has been lost.
2).Ī new informational note has been added to 250.52(A)(3) to clarify how a concrete-encased electrode is impacted by the use of insulation, vapor barriers, films, or similar items that separate the concrete from the earth. of concrete and located inside the concrete footing or foundation that is in direct contact with the earth ( Fig. These rebar or this conductor must be encased by at least 2 in. This is an electrode developed by using electrically conductive reinforcing bars or bare copper conductors not smaller than 4 AWG at least 20 ft in length. The requirements for a concrete-encased electrode, commonly called a "Ufer Ground" are included in 250.52(A)(3). The 2011 NEC no longer allows the structural metal to serve as a grounding electrode when supplemented by a ground rod. The concrete-encased electrode must comply with the requirements of 250.52(A)(3), and the hold-down bolts must be connected to the concrete-encased electrode by means of welding, exothermic welding, the usual tie wires used to secure the rebar in a footing, or other approved means ( Fig. The hold-down bolts securing the structural steel column that are connected to a concrete-encased electrode are considered to provide a satisfactory earth connection. When the structural metal is in direct earth contact for 10 ft or more, with or without concrete encasement, it is considered to be connected to the earth and is acceptable for use as a grounding electrode. The 2011 NEC has once again revisited the rule explaining when a structural metal building frame can serve as a grounding electrode. The use of structural metal as a grounding electrode is an issue that has been revised during several recent Code cycles.
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