Lightning Protection Systems
Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
Showing changes from Rev 3
to Rev 4
in Lightning Protection Systems.
---
title: Lightning Protection Systems
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### A metal body of conductance located on the roof, such as a rooftop unit, exhaust fan, or metal vent, shall be bonded to the lightning protection conductor system where it is within the side-flash distance, and shall be provided with its own air terminal where it projects above the zone of protection.
−### The Contractor shall not assume that a metal appurtenance protects itself; a metal body that is part of the path can carry strike current into the building unless it is bonded into the external system. {note}
+### The Contractor shall not assume that a metal appurtenance protects itself; a metal body that is part of the path can carry strike current into the building unless it is bonded into the external system.
## Nonconductive Projections {toc}
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### NFPA 780 does not set a fixed maximum resistance for lightning grounding, because the function is to dissipate a transient rather than to clear a power fault, but a low and stable resistance reduces the ground potential rise during a strike. {note}
−### A maximum of 10 ohms is a common project target and is the recommended default. {note}
+### A maximum of 10 Ω is a common project target and is the recommended default. {note}
### The Engineer shall set a lower value for structures with sensitive electronics; where the measured value exceeds the target, the Contractor shall add electrodes or extend the ground ring and re-test.
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### All grounded media entering the structure — the electrical service ground, the metal water service, the metal gas piping, and the telecommunications and antenna grounds — shall be bonded to a common grounding point so that the entire structure operates as a single equipotential reference during a strike.
−### This common bonding is the practical expression of the principle that there shall be one ground potential, not several isolated ones, throughout the protected structure. {note}
+### This common bonding is the practical expression of the principle that there shall be one ground potential, not several isolated ones, throughout the protected structure.
# Surge Protective Device Coordination {toc}
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### Masts, flagpoles, antennas, and similar tall metal appurtenances that rise above the protected plane shall be either provided with their own air terminal and down conductor or bonded into the system as a strike-termination device in their own right, in accordance with NFPA 780.
−### A tall metal mast is itself a strike receptor and shall be treated as part of the conductor path, not as an object to be protected by terminals elsewhere on the roof. {note}
+### A tall metal mast is itself a strike receptor and shall be treated as part of the conductor path, not as an object to be protected by terminals elsewhere on the roof.
## Coordination with Other Trades {toc}
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## Where the Owner maintains rooftop equipment that is frequently relocated, the Owner may stock a small quantity of air terminals, bonding connectors, and conductor fittings of the installed type so that bonding can be restored after equipment is moved without compromising the certification.