Lightning rod

A lightning rod or lightning conductor (British English) is a metal rod mounted on a structure and intended to protect it from a lightning strike. If lightning hits the structure, it is most likely to strike the rod and be conducted to ground through a wire, rather than passing through the structure, where it could start a fire or cause electrocution. In technical documents, lightning rods are generally referred to as 'strike termination devices'. In a lightning protection system, a lightning rod is a single component of the system. The lightning rod requires a connection to the earth to perform its protective function. Lightning rods come in many different forms, including hollow, solid, pointed, rounded, flat strips, or bristle brush-like. All lightning rods must be made of conductive materials, such as copper and aluminum. Copper and its alloys are the most common materials used in lightning protection.

History The first proper lightning rod was assembled by Father Prokop Diviš, a Czech priest and scientist, who erected a grounded lightning rod in 1754. Diviš's design involved a vertical iron rod topped with a grounded wire, intended to attract lightning strikes and safely conduct them to the ground. His experimental apparatus, known as the weather machine predated Benjamin Franklin's more widely recognized experiments. Franklin then independently developed and popularized his own lightning rod design, which became widely adopted across Europe and North America. Franklin's contribution significantly advanced the understanding and application of lightning protection systems, although Diviš's earlier conceptual work remains an important milestone in the history of electrical safety engineering.

British Empire In what later became the United States, the pointed lightning rod conductor (not grounded), also called a lightning attractor or Franklin rod, was conceived by Benjamin Franklin in 1749 as part of his groundbreaking exploration of electricity. Although not the first to suggest a correlation between electricity and lightning, Franklin was the first to propose a workable system for testing his hypothesis. Franklin speculated that, with an iron rod sharpened to a point, "The electrical fire would, I think, be drawn out of a cloud silently, before it could come near enough to strike." Franklin speculated about lightning rods for several years before his reported kite experiment.

In the 19th century, the lightning rod became a decorative motif. Lightning rods were embellished with ornamental glass balls (now prized by collectors). The ornamental appeal of these glass balls has been used in weather vanes. The main purpose of these balls, however, is to provide evidence of a lightning strike by shattering or falling off. If after a storm a ball is discovered missing or broken, the property owner should then check the building, rod, and grounding wire for damage. Balls of solid glass occasionally were used in a method purported to prevent lightning strikes to ships and other objects. The idea was that glass objects, being non-conductors, are seldom struck by lightning. Therefore, goes the theory, there must be something about glass that repels lightning. Hence the best method for preventing a lightning strike to a wooden ship was to bury a small solid glass ball in the tip of the highest mast. The random behavior of lightning combined with observers' confirmation bias ensured the method gained a good bit of credence even after the development of the marine lightning rod soon after Franklin's initial work. The first lightning conductors on ships were supposed to be hoisted when lightning was anticipated, and had a low success rate. In 1820 William Snow Harris invented a successful system for fitting lightning protection to the wooden sailing ships of the day, but despite successful trials which began in 1830, the British Royal Navy did not adopt the system until 1842, by which time the Imperial Russian Navy had already adopted the system. In the 1990s, the 'lightning points' were replaced as originally constructed when the Statue of Freedom atop the United States Capitol building in Washington, D.C. was restored. The statue was designed with multiple devices that are tipped with platinum. The Washington Monument was also equipped with multiple lightning points, and the Statue of Liberty in New York Harbor gets hit by lightning, which is shunted to ground.

Lightning protection system

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