When is it acceptable to use the rebar in concrete as a grounding electrode?

Using rebar in concrete as a grounding electrode is acceptable when it is in direct contact with the earth and properly bonded. This is because grounding electrodes must have a reliable path to earth to ensure that electrical faults can be effectively grounded, reducing the risk of electric shock or fire.

When rebar is embedded in concrete and in direct contact with the earth, it serves as an excellent grounding conductor due to its large surface area and conductive properties. Proper bonding is essential as it ensures that the entire structure is at the same electrical potential, which enhances safety and compliance with electrical codes.

The other options do not meet the necessary conditions for using rebar as a grounding electrode. For example, an unbonded rebar cannot effectively serve as a ground because it may not provide a continuous path to earth. Ignoring specified diameter sizes could compromise the effective grounding capability of the rebar, and if the rebar is installed in less than 2 inches of concrete, it may not provide sufficient protection and grounding efficiency.