Lightning protection systems for structures are typical […]
Lightning protection systems for structures are typically not a requirement of national building codes, although the Standards may be adopted by the authority having jurisdiction for general construction or specific occupancies.
There are five elements that need to be in place to provide an effective lightning protection system.
Strike termination devices must be suitable to accept direct lightning attachment and patterned to accept strikes before they reach insulated building materials.
Cable conductors route lightning current over and through the construction, without damage, between strike terminations at the top and the grounding electrode system at the bottom. The below grade grounding electrode system must efficiently move the lightning to its final destination away from the structure and its contents.
Bonding or the interconnection of the lightning protection system to other internal grounded metallic systems must be accommodated to eliminate the opportunity for lightning to sideflash internally.
Finally surge protection devices must be installed at every service entrance to stop the intrusion of lightning from utility lines, and further equalize potential between grounded systems during lightning events.
When these elements are identified properly in the design stage, incorporated into a neat workmanlike installation, and no changes to the building occur, the system will protect against lightning damage. Elements of this passive grounding system always serve a similar function, but the total design is specific for each particular structure.
Copper, copper alloys (including brass and bronze), and aluminum are the basic system component materials. They serve the best combination of function for current carrying and weathering. Since aluminum materials have slightly lower current carrying capability and mechanical strength than similar sized copper products, listed and labeled materials for lightning protection include larger physical size parts. For example to be considered equivalent, a minimum size air terminal would be ½” diameter in aluminum, versus 3/8” diameter in copper.