A solar technician is performing a final inspection of a roof-mounted PV array before commissioning. They notice that the grounding conductor from the PV array frame is connected directly to a copper cold-water pipe on the roof. What is the primary concern with this grounding method?
- AThe connection point is exposed to weather and will corrode.
- BIt violates NEC requirements for rapid shutdown of PV systems.
- CThe cold-water pipe is not a suitable equipment grounding conductor.
- DThe pipe may not have a continuous metallic path back to the service entrance.
Show answer & explanationAnswer & explanation
Correct answer: D. The pipe may not have a continuous metallic path back to the service entrance.
While a cold-water pipe can sometimes be part of a grounding electrode system, connecting directly to it on the roof has a primary concern: its metallic continuity back to the service entrance grounding electrode conductor is often unreliable. Sections of the pipe could be non-metallic (e.g., PEX), or metallic pipe could be interrupted by non-conductive fittings (e.g., dielectric unions, plastic valves). NEC requires a continuous, reliable metallic path for equipment grounding, which a utility water pipe cannot guarantee without verification. It is not an approved grounding electrode for a PV system's equipment grounding conductor.
Why the other options are wrong
- A. Corrosion is a concern for any outdoor connection, but the primary issue is the *reliability* of the grounding path itself.
- B. This grounding method is unrelated to rapid shutdown requirements, which address DC conductors and array voltage during emergencies.
- C. A cold-water pipe *can* be part of a grounding electrode system if it meets specific NEC requirements, but it's not a suitable *equipment grounding conductor* for the PV array without a verified continuous metallic path.
PV Equipment Grounding Reliability
Ensuring a continuous, low-impedance metallic path from all non-current-carrying metal parts of the PV system back to the main service grounding electrode system.
- Prevents electric shock hazards by safely clearing ground faults.
- Requires dedicated equipment grounding conductors or approved metallic raceways/racking.
- Utility water pipes are generally not reliable for equipment grounding due to potential interruptions.
Memory trick: Grounding must be sound and true, a continuous path for safety too!