Which material SHALL NOT be used as a bonding backbone conductor?

• A. Concrete Reinforcing Steel
• B. Copper
• C. Water
• D. Plastic

Answer: (A)

The backbone conductor for bonding must provide a continuous, low-impedance path that ties together all metal parts and equipment back to the grounding system. It should be a readily accessible, durable conductor with a known size and material so its reliability can be verified and maintained.

Concrete reinforcing steel fails this role because it is embedded in concrete and not guaranteed to form a continuous, inspectable bond path across the entire structure. Its connectivity can be compromised by cracks, corrosion, coatings, or changes in the concrete, making it unreliable for carrying fault currents or ensuring consistent bonding.

Copper, by contrast, is the standard bonding backbone due to its high conductivity and reliability. Plastic is an insulator and cannot serve as a bonding path, while water is not used as a backbone because its conductivity varies with impurities and moisture and it is not a dependable, protected bonding conductor.