Once it is intercepted by a lightning rod, it is conveyed to ground over the conductor system. If the entire structure is contained within the zone of protection of one or more lightning rods, the theory is that lightning should always attach to a rod in preference to the protected structure. Layout requirements for individual lightning rods call for the zone of protection of each one to overlap the zone of protection of an adjacent rod. They unintentionally comprised the lightning strike interception component of the first lightning protection systems. The purpose of these figurines was to frighten away lightning. If you look at an old Chinese building such as those found in the Forbidden City, you will notice a parade of small, fearsome looking figurines arranged along the edges. The ancient Chinese recognized that lightning was most likely to attach to corners and edges of a structure. Lightning rods are installed on the likely lightning strike locations on the structure. It consists of a system of lightning rods arranged around the perimeter of the structure, particularly on outside corners, with additional lightning rods in the center of the structure and on elevated features, such as stairway or elevator penthouses. This type of system basically just “gets in the way” of any strike to a protected structure and conveys the lightning energy to ground. They are simply membership organizations for manufacturers and installers. Organizations such as Lightning Protection Institute (LPI) and United Lightning Protection Installers (ULPI) are not. UL is the Nationally Recognized Testing Laboratory (NRTL – pronounced to rhyme with “turtle”) in the lightning protection industry. UL 96 covers Lightning Protection Components and UL 96A covers Installation Requirements. Underwriters Laboratories (UL) converts NFPA 780 into Standards for Safety materials and installation guidelines. NFPA 780 is the United States “Standard for the Installation of Lightning Protection Systems”. The first and oldest type of system is the Franklin lightning rod system as described in National Fire Protection Association NFPA 780. Let’s look at these systems in more detail. Lightning prevention systems described in more recent patents have not enjoyed general acceptance, and are the subject of much controversy. However, the systems described in these early patents never achieved general acceptance. Many of these patents addressed lightning protection for petroleum storage tanks. This system is based on patents going back to the 1830’s, including one issued in 1918 to Nikola Tesla. The third type of system claims to protect a structure by reducing the difference in potential between the cloud and ground sufficiently to prevent a strike or through creating a space charge above the structure, creating a shield through which lightning cannot travel. This technology was introduced by Ben Franklin, and goes back almost 250 years, essentially unchanged since then. That is why lightning protection is covered under the National Fire Protection Association standard, NFPA 780. It is helpful to remember that the primary purpose of a conventional lightning rod system is to keep the protected structure from burning down. As long as the entire protected structure is located within a lightning rod zone of protection, the claim is that lightning will always attach to a lightning rod and be harmlessly conveyed around the protected structure to ground, thereby sparing damage to the protected structure. Conventional lightning protection consists of a network of lightning rods interconnected by conductors leading to a grounding system. Think of it as a volume of space around a lightning rod wherein lightning will attach to that lightning rod in preference to anything else around it. The zone of protection is defined as the space adjacent to a lightning protection system that is substantially immune to direct lightning flashes. The first two types of systems protect structures by providing zones of protection over that structure. Lightning prevention systems – typically called Charge Transfer Systems (CTS) and/or Dissipation Array Systems (DAS).Lightning attraction systems – Early Streamer Emission (ESE) or Electronically Activated Streamer Emission (EASE) technology.Lightning interception systems – the common Franklin lightning rod technology.There are three common approaches to structural lightning protection, loosely grouped as follows : “May not the knowledge of this power of points be of use to mankind, in preserving houses, churches, ships, etc., from the stroke of lightning, by directing us to fix, on the highest parts of those edifices, upright rods of iron made sharp as a needle…Would not these pointed rods probably draw the electrical fire silently out of a cloud before it came nigh enough to strike, and thereby secure us from that most sudden and terrible mischief!” Ben Franklin.
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