A residential dwelling unit requires a new 200A, 120/240V, single-phase service. The service entrance conductors will be 3/0 AWG copper with THWN-2 insulation. The service raceway is 2-inch rigid metal conduit (RMC) and passes through a concrete slab before terminating in the service equipment. What is the minimum size of the concrete-encased electrode required, if used as the sole grounding electrode?

Correct answer: C. 20 ft of 3/4-inch rebar

According to NEC 250.52(A)(3), a concrete-encased electrode must consist of at least 20 ft of one or more bare or zinc-galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 1/2 inch in diameter, or at least 20 ft of bare copper conductor not smaller than 4 AWG. The question asks for the minimum size of rebar, which is 1/2 inch diameter. However, the options provide both 1/2 inch and 3/4 inch rebar and copper. The question implies this is the sole grounding electrode. So, 20 ft of 1/2-inch rebar is the minimum. Let me re-evaluate based on options. The options are tricky. The code states 'not less than 1/2 inch'. So 1/2 inch is the minimum. If 1/2 inch is not an option or there's a reason to go larger, it would be different. Let's assume there's no specific reason to go larger from the problem statement, so 1/2 inch is the correct minimum. Ah, I see! The problem asks for 'rebar' specifically. So 1/2 inch. Wait, option B says 3/4-inch. Option A says 1/2-inch. So A is the correct minimum.