For many code cycles NEC^® 250.52(A)(3) has permitted 20 or more feet of ½ inch or larger rebar, encased in at least 2 inches of concrete, and located horizontally within a concrete footing that is in direct contact with the earth to serve as a grounding electrode. From there, it is quite common to see the rebar bent 90 degrees and turned up into the stem wall as an extension for future connection to the grounding electrode conductor once the walls are built and the service has been installed.

On larger installations where rebar emerges from the footing and is stubbed up in a wall for example, if the rebar is being used as the conductor to interconnect other electrodes such as metallic water pipe to structural steel or to interconnect the grounding electrode conductor for multiple services as permitted in 250.58, this interconnection could require 3/0 AWG copper or 250 kcmil aluminum. The ½ inch rebar stub up has not been evaluated to be equal in size to specific size copper or aluminum conductors.

Section 250.53(C) makes it clear that rebar cannot be used as a conductor to interconnect other electrodes of a grounding electrode system.

Below is a preview of the NEC^®. See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2020 NEC^® edition of NFPA 70.

2020 Code Language:

250.53(C) Bonding Jumper. The bonding jumper(s) used to connect the grounding electrodes together to form the grounding electrode system shall be installed in accordance with 250.64(A), (B), and (E), shall be sized in accordance with 250.66, and shall be connected in the manner specified in 250.70. Rebar shall not be used as a conductor to interconnect the electrodes of grounding electrode systems.