Grounding electrode conductor connections are an important part of any electrical safety system. These connections ensure the path to ground through any of the grounding electrodes identified in Section 250.52(A). At a recent training session, several questions came up about grounding electrode conductor connections to electrodes. Do they always have to be accessible? Do they have to be listed? How can you tell if they are suitable for concrete-encasement when the connection is made using a grounding clamp fastened to rebar? Answers to these questions follow, and the responses are based on the 2014 edition of the National Electrical Code (NEC).
In response to the first question, grounding electrode conductor connections to electrodes do not always have to be accessible. A couple exceptions provide practical relief from the accessibility requirements. Section 250.68 requires all accessibility for mechanical connections used to terminate a grounding electrode conductor or bonding jumper of the grounding electrode system. Exception 1 to 250.68 indicates that buried electrode connections and concrete-encased connections to electrodes shall not be required to be accessible. Exception 2 indicates that exothermic welded connections and irreversible connections to grounding electrodes that are encapsulated in fireproofing material are not required to be accessible. The exception applies not only to the connection but also the mechanical fastening means, such as a nut or bolt, that establishes the connection to the metal framing member.
A revision to the 2014 NEC in 250.68(C)(3) provides additional clarification for grounding electrode conductor connections to concrete-encased electrodes. This new list item indicates that the rebar can be extended from its location within the concrete to an accessible location above. This NEC change actually parallels a common industry practice to provide a means of connection to concrete-encased electrodes for instances where the contractor is not present on the construction project when the footings or foundations are poured in place. It is important to remember that, if the rebar emerges in a wall, an access panel or other access to the connection means must be provided if the connection is not exothermic or irreversible. Accessibility to grounding electrode connections provides the ability to verify the integrity of the connections and to perform and test procedures that might be required.
For the second question, the answer is yes. Generally, all grounding electrode conductor connections to electrodes are required to be listed. Grounding and bonding connections listed as grounding and bonding equipment have been evaluated for grounding electrode conductor performance. Section 250.70 indicates that the methods of connecting grounding electrode conductors to electrodes must be by exothermic welding, listed lugs, listed pressure connectors, listed clamps or other listed means. Exothermic welding processes are not required to be listed; however, while most exothermic welding kits are not listed, some are.
It is important to follow the manufacturer’s instructions when making exothermic welding connections. The size of the conductor, use of the right molds and intensity of the welds can affect the completed connection’s integrity.
Where the grounding electrode conductor tap concept is used in accordance with 250.64(D)(1), the grounding electrode conductor taps are required to be connected using the exothermic welding process, to be connections listed as grounding and bonding equipment, or be connected to an aluminum or copper busbar not less than ¼ inch thick and 2 inches wide. The connections to the busbar must be made using listed connections or the exothermic welding process. Where the common grounding electrode conductor tap method is used for multiple separately derived systems as permitted in 250.30(A)(6), any of the same methods above must be used for connecting the taps to the common grounding electrode.
For the third question, the answer is not as straightforward. Section 250.70 clarifies the methods of Code-compliant grounding electrode conductor connections. This rule requires grounding clamps to be listed for the material of the grounding electrode and the grounding electrode conductor. The grounding clamp must also be listed for direct soil burial or concrete-encasement. List items (1) through (4) provide the acceptable methods of connections. The NEC does not provide the information about a grounding clamp being identified for direct burial or concrete-encasement use. It just indicates that the clamp be listed for that use. The Underwriters Laboratories (UL) Guide Information for Electrical Equipment (UL White Book) in category KDER indicates that ground clamps marked for direct burial use will be identified using the words “direct burial” or the letters “DB” to indicate suitability for this use. It is interesting that ground clamps with these markings are also suitable for concrete-encasement. If a grounding electrode conductor is connected to a concrete-encased electrode using a clamp marked with “direct burial” or “DB,” it is acceptable for use if encased in concrete. This is a good example of information provided by UL that can be used to verify NEC compliance.