NEC Section 250.68 provides the requirements on the physical connection of the grounding electrode conductor or bond jumper to the grounding electrode.

Under certain conditions, rebar in the footing may be used as the grounding electrode. It is common to see an additional length of rebar with a 90˚ bend connected to the rebar in the footing and extending above grade to provide a way to connect to it later after the slab is poured and the service is installed.

Section 250.68(C)(3) requires the additional rebar section to be continuous with the grounding electrode rebar (accomplished by bending a 90˚ angle in the rebar used for the electrode) or to be connected to the grounding electrode rebar by steel tie wires, exothermic welding, welding, or other effective means.

If someone measures correctly, the rebar stub up from the concrete encased electrode will end up right on the mark and centered inside the wall just under the electrical service. Once in a while someone misses their mark and the rebar stub up ends up emerging from the dirt outside the stem wall. According to the NEC^®, corrosion protection must be provided for just such an occurrence. If the rebar emerges from full concrete encasement into a wall bay then no corrosion protection is required. If the rebar happens to emerge from earth instead, corrosion protection is required.

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:

250.68(C) Grounding Electrode Conductor Connections. Grounding electrode conductors and bonding jumpers shall be permitted to be connected at the following locations and used to extend the connection to an electrode(s):

(1) Interior metal water piping that is electrically continuous with a metal underground water pipe electrode and is located not more than 1.52 m (5 ft) from the point of entrance to the building shall be permitted to extend the connection to an electrode(s). Interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building shall not be used as a conductor to interconnect electrodes of the grounding electrode system.

(2) The metal structural frame of a building shall be permitted to be used as a conductor to interconnect electrodes that are part of the grounding electrode system, or as a grounding electrode conductor. Hold-down bolts securing the structural steel column that are connected to a concrete-encased electrode complying with 250.52(A)(3) and located in the support footing or foundation shall be permitted to connect the metal structural frame of a building or structure to the concrete encased grounding electrode. The hold-down bolts shall be connected to the concrete-encased electrode by welding, exothermic welding, the usual steel tie wires, or other approved means.

(3) A rebar-type concrete-encased electrode installed in accordance with 250.52(A)(3) with an additional rebar section extended from its location within the concrete foundation or footing to an accessible location that is not subject to corrosion shall be permitted for connection of grounding electrode conductors and bonding jumpers in accordance with the following:

1. The additional rebar section shall be continuous with the grounding electrode rebar or shall be connected to the grounding electrode rebar and connected together by the usual steel tie wires, exothermic welding, welding, or other effective means.
2. The rebar extension shall not be exposed to contact with the earth without corrosion protection.
3. Rebar shall not be used as a conductor to interconnect the electrodes of grounding electrode systems.