Lightning Protection Systems

In most of the lightning protection systems used today, it is Franklin’s traditional design. Franklin-type lightning protection systems work on the principle that lightning must travel through a low impedance path to reach ground without damaging a building. Buildings are surrounded in a kind of Faraday cage to prevent electromagnetic interference. The building’s roof is protected by lightning rods and lightning conductors to prevent lightning from striking the building.

By intercepting lightning strikes and safely passing their high currents to ground, lightning protection systems prevent a building from being damaged by lightning strikes. There are a number of air terminals, bonding conductors, and ground electrodes in a lightning protection system that provide a low impedance path to the ground in case of a possible strike.

Structures are protected from lightning damage by lightning protection systems. Fires caused by lightning strikes can be minimized by lightning protection systems. Lighting protection systems provide a low-impedance path for the lightning current so that flammable structural materials are not heated. Lighting can literally explode porous and water-saturated material if heat produced from a high current turns the water into steam. That’s why lightning often shatters trees.

A lightning strike can be extremely energy intensive and electrically current intensive (currents can exceed 150,000 A). Additionally, lightning strikes are very rapid in their rise times, so no protection system can provide absolute protection. Even the divided lightning current can cause damage because it will follow every conductor to ground. Besides igniting a fire, side-flashes can tear apart brick, stone, or concrete, as well as injure people within a structure or building. Nevertheless, basic lightning protection systems have been proven effective for many years.

The wooden barn is a structure that can be struck by lightning. The lightning current transmitted through certain parts of the barn may cause the wooden structure and its contents to catch alight when lightning strikes it. Providing a conductive path between an air terminal and earth will allow most of the lightning’s current to follow the path of the lightning protection system with considerably less current passing through flammable materials.

Lightning protection can be achieved by bonding structural members to the earth. By burying its foundation in the ground, a metal flagpole can provide lightning protection on its own. A lightning strike, however, may completely incinerate the flag(s).

Lightning protection system with air terminals and “downleids” were originally thought to direct lightning’s current down into the earth for dissipation. In contrast, high speed photography clearly demonstrates that lightning is composed of both a cloud component and an oppositely charged component on the ground. Lightning caused by “cloud-to-ground” lightning usually occurs higher than the earth’s surface because these oppositely charged components meet to equalize unbalanced charges. Lightning protection systems attempt to mitigate the hazard caused by the heat generated by this electric current flowing through flammable materials by providing a low-resistance path for the lightning circuit.

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