Code Change Summary: The rules pertaining to using hold down bolts as a component in the grounding electrode system have been relocated.

Hold-down bolts are often used to secure a structural steel column to the concrete floor. Sometimes they are “wet set” as the concrete is being poured, or in other cases, they are installed and tie-wired to the rebar in the footing before concrete is poured like in the image.

If the hold-down bolts are tie-wired to a portion of foundation or footing rebar that qualifies as a concrete encased electrode, and done in accordance with 250.68(C)(2), they are permitted to extend the metal structural frame of a building to the concrete encased grounding electrode. A wet set hold down bolt might hold things together pretty well but it cannot be relied upon as a part of the grounding electrode system.

In the 2014 NEC^®, these requirements were found in 250.52(A) which is really a section meant to describe the actual grounding electrodes themselves rather than items like hold-down and anchor bolts which are permitted to be used as an extension to reach the grounding electrode if done properly. These hold-down bolts function more like a grounding electrode conductor which is why the requirements for them were relocated to 250.68(C) pertaining to grounding electrode conductors.

Below is a preview of Article 250. See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC^® edition of NFPA 70.