Which of the following is not allowed to act as a concrete encased electrode?

• A. One 20-foot reinforcing bar (rebar)
• B. Four 6-foot reinforcing bars tied together with the usual steel tie wires
• C. Four 6-foot reinforcing bars welded together
• D. 20 feet of #6 AWG bare copper

Answer: (D)

Concrete-encased electrodes must be formed from steel reinforcing bars or other structural metal embedded in concrete, totaling at least 20 feet in length and with electrical continuity among the bars. The bars can be a single long piece or a group of pieces that are properly connected (welded or tied) to act as one continuous electrode. Bare copper, while a good conductor, is not listed as a permissible material for a concrete-encased electrode because it can cause galvanic corrosion with nearby steel in moist concrete, compromising both the electrode and the reinforcement. So a 20-foot piece of bare copper cannot serve as a concrete-encased electrode, whereas the configurations using steel bars—whether one 20-foot bar or multiple bars totaling at least 20 feet with appropriate connections—are acceptable.