A journeyman is inspecting a lightning protection system on a commercial building. Which of the following is an acceptable component for a lightning protection grounding electrode system, according to generally accepted lightning protection standards like NFPA 780, often referenced by NEC® 250.106?
- AThe building's structural steel frame, if not connected to the electrical ground.
- BThe building's electrical service grounding electrode system.
- CAn isolated metal flagpole adjacent to the building.
- DA dedicated lightning rod with an unbonded driven ground rod.
Show answer & explanationAnswer & explanation
Correct answer: B. The building's electrical service grounding electrode system.
NFPA 780, which the NEC references for lightning protection, emphasizes the importance of bonding the lightning protection grounding electrode system to the building's main electrical service grounding electrode system and other metallic systems to prevent side flashes and equalize potential. An isolated flagpole or unbonded ground rod would create potential differences and increase risk.
Why the other options are wrong
- A. The building's structural steel frame, if effectively grounded and bonded to the electrical ground, can be used as part of the grounding electrode system for lightning protection, but if *not connected* to the electrical ground, it creates an isolation hazard.
- C. An isolated metal flagpole would not provide a proper ground path for lightning and could become a hazard if struck.
- D. A dedicated lightning rod must have its grounding electrode bonded to the building's electrical service grounding electrode system to prevent dangerous potential differences during a lightning strike.
Lightning Protection Grounding
Lightning protection grounding electrodes must be integrated and bonded with the building's main electrical grounding electrode system and other metallic systems to create an equipotential plane and safely dissipate lightning energy, preventing side flashes.
- Based on NFPA 780 standards.
- Requires bonding to the electrical service ground.
- Aims to prevent dangerous potential differences (side flashes).
Memory trick: Lightning needs a unified path, not isolated islands.