Exposed structural metal interconnected to form a metal building frame that is not intentionally grounded or bonded and is likely to become energized, shall be bonded to the _____.

• A. Service equipment enclosure or building disconnecting means
• B. Grounding electrode conductor where of sufficient size
• C. Grounded conductor at the service
• D. Neutral conductor

Answer: (A)

Bonding exposed structural metal that could become energized to the building’s grounding system creates a low-impedance path for fault current, ensuring the frame stays at earth potential and so a fault will trip the overcurrent device quickly. The correct point to make that bond is the service equipment enclosure or the building disconnecting means, because this is where the grounding electrode conductor terminates and where all grounding paths are tied together. This establishes a single bonding point and a reliable fault-path back to the source.

Bonding to the grounding electrode conductor alone can be part of the connection, but the recognized bonding location is at the service equipment enclosure or disconnecting means. Bonding to a neutral or to the grounded conductor is not appropriate for structural bonding (except for the prohibited, at-service-neutral bond), as it can create hazardous current paths and potential differences.