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lightning rod
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18 مهر 1401
  • What is a lightning rod?

    Lightning rod, a metal rod (usually copper) that protects the structure from lightning damage by cutting off electricity and directing their current into the ground. Since lightning tends to strike the highest object in the vicinity, the rods are usually located at the top of the structure and along its ridges. They are connected to earth by low impedance cables. In a ship, water is used as a substitute for land. Lightning rods are available in various shapes including hollow, solid, pointed, round, flat strips or even brush-like. The main common feature of all lightning arresters is that they are all made of conductive materials such as copper and aluminum. Copper and its alloys are the most commonly used materials in lightning protection. Due to the high energy and current levels associated with lightning strikes (currents can exceed 150,000A), and the extremely fast rise time of a lightning strike, no protection system can guarantee absolute safety against lightning strikes. The lightning current is divided to follow any conductive path to ground, and even the divided current can cause damage. Secondary “side flashes” can be sufficient to ignite a fire, blow away brick, stone, or concrete, or injure occupants inside a structure or building. However, the benefits of lightning protection systems have been evident for over a century.

    The parts of a lightning protection system are: air terminals (lightning rods or surge termination devices), bonding conductors, ground terminals (earthing rods or “earthings”, plates or mesh), and all connections and supports to complete the system.

    Most lightning protection systems in use today are of the traditional Franklin design. The basic principle used in the Franklin type lightning arrester system is to provide a path of sufficient impedance for the lightning to pass through and reach the ground without damaging the building. This is done by surrounding the building in a kind of Faraday cage. A system of lightning protection conductors and lightning arresters is installed on the roof of the building to intercept any lightning before it hits the building.

    History of the lightning rod

    The principle of the lightning rod was first described by Benjamin Franklin in Pennsylvania in 1749, who in the following years developed his invention for home use (published in 1753), and around 1760 made further improvements to a Reliable system did. As buildings get taller, lightning becomes more of a threat. Lightning can damage structures made of materials such as: masonry, wood, concrete, and steel, because the huge currents and voltages present can heat the materials to high temperatures. The heat creates the potential for fire in the structure, and its velocity can also lead to explosive damage.

    Russia

    A lightning rod may have been deliberately used in the Noyansk Leaning Tower. The crown of the tower is crowned with a metal rod in the shape of a globe gilded with clusters. This lightning rod is connected to the ground through the carcass of the rebar, which pierces the entire building.

    The Noyansk Tower was built between 1721 and 1745 by the order of the craftsman Akinfi Demidov. Noyansk Tower was built 28 years before Benjamin Franklin’s experiment and scientific explanation. However, the true purpose of the metal roof and rebars remains unknown.

    Europe

    The church tower of many European cities, which was usually the tallest building in the city, was likely to be struck by lightning. In the early days, Christian churches tried to prevent the destructive effects of lightning by praying. Peter Ahlvards (“Sane and Theological Considerations on Lightning”, 1745) advised people seeking cover from lightning to go anywhere except in or around a church.

    United States

    In what later became the United States, the pointed lightning conductor, also called the lightning rod or Franklin rod, was invented by Benjamin Franklin in 1752 as part of his groundbreaking discovery of electricity. Although not the first to propose a connection between electricity and lightning, Franklin was the first to propose a workable system for his experiment and hypothesis. Franklin surmised that “by means of a sharpened iron rod, I suppose the electric fire would be quietly drawn out of the cloud before it came near enough to strike.”

    In the 19th century, the lightning rod became a decorative motif. Lightning rods were decorated with ornamental glass balls (now prized by collectors). The ornamental charm of these glass balls is used in weather vanes. But the main purpose of these balls is to provide evidence of lightning strikes by breaking or falling. If a missing or broken orb is discovered after a storm, the property owner should inspect the building, ground rods and wires for damage.

    Bullets of solid glass were sometimes used in a way that was claimed to prevent lightning from striking ships and other objects. So, the theory goes, there must be something about the glass that repels lightning. Therefore, the best way to prevent lightning from hitting a wooden ship was to bury a small ball of solid glass at the tip of the topmost mast. The random behavior of lightning combined with observer confirmation bias ensured that the method gained good validity even after the development of the marine lightning rod soon after Franklin’s initial work.

    The first lightning rods on ships were to go off when lightning was predicted and had a low success rate. In 1820 William Snow Harris invented a successful system for fitting lightning protection to wooden sailing ships, but despite successful trials beginning in 1830, the British Royal Navy did not adopt the system until 1842.

    In the 1990s, the “Lightning Points” as originally constructed were replaced by the reconstruction of the Statue of Liberty atop the United States Capitol in Washington, DC. The statue is designed with several devices whose tip is made of platinum.

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