Revised Text:
250.52 A (3) Concrete-Encased Electrode. An electrode encased by at least 50 mm (2 in.) of concrete in contact with earth, installed as specified in 250.53(I)1 or 2. Where multiple concrete-encased electrodes are present at a building or structure, it shall be permissible to bond only one into the grounding electrode system.
Proposed Text:
250.53(I) Concrete-Encased Electrode. The electrode shall be installed and constructed so that it be encased by at least 50 mm (2 in.) of concrete, located horizontally for a length of 20’ within 4” of earth, or vertically for a length of 20’ within 4” earth, or combination thereof within that portion of a concrete foundation, footing or pier that is in direct contact with the earth, by one of the following methods.
(1) Constructed of at least 6.0 m (20 ft) of one or more bare, zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 13 mm (? in.) in diameter. Where multiple reinforcing bars are used they shall be permitted to be bonded together by the usual steel tie wires or other effective means and require two or more points of connection. Corrosion protection shall be used for any exposed portions of steel reinforcement bars or rods in wet or damp locations. Such corrosion protection shall be hot-dipped zinc galvanized, or approved electrically conductive permanent coating suitable for the conditions, and done prior to the pouring of concrete, and be continuous from a point at least 2” inside the concrete, and extend to the exposed end.
(2) Constructed of at least 6.0 m (20 ft) of bare copper conductor not smaller than 4 AWG. Where copper conductor is used as a concrete-encased electrode, exposed portions of the electrode shall comply with 250.64(B), and may be used as a grounding electrode conductor if complying with 250.64(F) and continuous within the concrete.
For purposes of 250.68 (A), any exposed portion of the electrode shall be considered part of the concrete-encased electrode for it entire length, if continuous to the qualifying portion(s). Connections to any exposed portion of concrete-encased electrode (copper conductor or reinforcing rods) shall comply with 250.70. Where connection to the grounding electrode conductor is not encased, it shall be accessible.
Substantiation:
Relocates specific details of, and expands on guidance for the installation, construction of, and connection to Concrete-Encased Electrodes to 250.53 where similar guidance on other electrodes is located, and serves to clarify the previously worded version of 250.52(A)3.
The wording “near the bottom” in 250.53(A)3 implied no maximum distance from earth within horizontal or vertical portions of foundations footings or piers.
Adds guidance for connection of multiple steel reinforcement bars or rods if used as the material for the electrode.
Adds guidance for corrosion protection, and installation of exposed steel reinforcement bars or rods if used as the material for the electrode.
The revised text also clarifies use, connection to, and installation of copper conductor as a concrete-encased electrode. As well as, its popular dual use of the un-encased portion as both a grounding electrode, and grounding electrode conductor. Which may be superior in that it may provides fewer (if any) points of connection failure, and lower impedance.
Current wording of 250.52(A)3 is in direct conflict with 250.68 in many interpretive views that regard exposed portions of the concrete-encased electrode as a non-qualifying location for connection to the concrete-encased electrode. The added text clarifies this possible conflict that may otherwise place the connection to the concrete-encased electrode beyond inspection or repair unnecessarily if interpreted in this method.
As well clarifies that copper conductor, if used as the concrete encased electrodes need not be continuous, and may be connected to as would be allowed in 250.68(A). and 250.70.
