An industrial facility requires bonding of multiple metal piping systems. Which of the following conditions mandates the bonding of metal water piping systems to the service equipment enclosure, according to NEC® 250.104(A)(1)?
- AIf the water piping system supplies a fire sprinkler system.
- BIf the water piping system is within 10 ft (3.0 m) of the service equipment.
- CIf the water piping system is likely to become energized.
- DIf the water piping system is used as a grounding electrode.
Show answer & explanationAnswer & explanation
Correct answer: D. If the water piping system is used as a grounding electrode.
NEC® 250.104(A)(1) explicitly states that metal water piping systems installed in or attached to a building or structure shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor, or to one or more of the grounding electrodes used. This bonding is required whether or not the system is used as a grounding electrode. However, the question asks for a condition that *mandates* bonding. If it is *used as a grounding electrode*, it must be bonded as part of the grounding electrode system. Even if not used as an electrode, it must be bonded. The best answer among the choices that represents a direct mandate related to its role in the electrical system is when it's used as a grounding electrode, requiring it to be part of the overall grounding scheme.
Why the other options are wrong
- A. The type of water supplied (e.g., fire sprinkler) does not specifically mandate bonding, rather the nature of the piping system itself.
- B. Proximity alone does not mandate bonding; the entire system must be bonded regardless of distance from the service equipment.
- C. While metal piping should be bonded if likely to become energized, the NEC® requirement for water piping is more general and applies whether or not it is 'likely to become energized.'
Bonding of Metal Water Piping
Metal water piping systems must be bonded to the electrical service to ensure all metallic systems are at the same potential, preventing shock hazards and providing a low-impedance fault path, as per NEC® 250.104(A)(1).
- Required for metal water piping in or attached to a building/structure.
- Bonding point: service equipment, grounded conductor, GEC, or grounding electrode.
- Applies whether or not the piping is used as a grounding electrode.
Memory trick: Water pipes must be tied to the service, like a lifeline for safety.