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.Father Procopius Diviš – The European Franklin https://www.astro.gsu.edu/~hal/Hujer/Misc/Articles/Article56.pdf 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
A lightning protection system is designed to protect a structure from damage from lightning strikes by intercepting them and safely passing their extremely high currents to ground. A lightning protection system includes a network of air terminals, bonding conductors, and ground electrodes designed to provide a low impedance path to ground for potential strikes.
Lightning protection systems prevent lightning strike damage to structures. Lightning protection systems mitigate the fire hazard that lightning strikes pose to structures. A lightning protection system provides a low-impedance path for the lightning current to lessen the heating effect of current flowing through flammable structural materials. If lightning travels through porous and water-saturated materials, these materials may explode if their water content is flashed to steam by heat produced from the high current. This is why trees are often shattered by lightning strikes.
Because of the high energy and current levels associated with lightning (currents can exceed 150,000 A), and the very rapid rise time of a lightning strike, no protection system can guarantee absolute safety from lightning. Lightning current divides to follow every conductive path to ground, and even divided current can cause damage. Secondary "side-flashes" can be enough to ignite a fire, blow apart brick, stone, or concrete, or injure occupants within a structure or building. However, the benefits of basic lightning protection systems have been evident for well over a century.NFPA-780 Standard for the Installation of Lightning Protection Systems 2008 Edition
Laboratory-scale measurements of the effects of lightning do not scale to applications involving natural lightning.Vernon Cooray (ed.) Lightning Protection, The Institution of Engineering and Technology, 2010, pp. 240–260, p 320 Field applications have mainly been derived from trial and error based on the best intended laboratory research of a highly complex and variable phenomenon.
The parts of a lightning protection system are air terminals (lightning rods or strike termination devices), bonding conductors, ground terminals (ground or "earthing" rods, plates, or mesh), and all of the connectors and supports to complete the system. The air terminals are typically arranged at or along the upper points of a roof structure. They are electrically bonded together by bonding conductors (called "down conductors" or "downleads"), which are connected by the most direct route to one or more grounding or earthing terminals. Connections to the earth electrodes must not only have low resistance, but must have low self-inductance.
An example of a structure vulnerable to lightning is a wooden barn. When lightning strikes the barn, the wooden structure and its contents may be ignited by the heat generated by lightning current conducted through parts of the structure. A basic lightning protection system would provide a conductive path between an air terminal and earth, so that most of the lightning's current will follow the path of the lightning protection system, with substantially less current traveling through flammable materials.
Originally, scientists believed that such a lightning protection system of air terminals and "downleads" directed the current of the lightning down into the earth to be "dissipated". However, high-speed photography has clearly demonstrated that lightning is actually composed of both a cloud component and an oppositely charged ground component. During "cloud-to-ground" lightning, these oppositely charged components usually "meet" somewhere in the atmosphere well above the earth to equalize previously unbalanced charges. The heat generated as this electric current flows through flammable materials is the hazard that lightning protection systems attempt to mitigate by providing a low-resistance path for the lightning circuit. No lightning protection system can be relied upon to "contain" or "control" lightning completely (nor thus far, to prevent lightning strikes entirely), but they do seem to help immensely in most lightning strikes.
Steel-framed structures can bond the structural members to earth to provide lightning protection. A metal flagpole with its foundation in the earth is its own extremely simple lightning protection system. However, the flag(s) flying from the pole during a lightning strike may be completely incinerated.
Most lightning protection systems in use today use the traditional Franklin design. The fundamental principle used in Franklin-type lightning protection systems is to provide a sufficiently low-impedance path for lightning to travel to ground without damaging the building.NFPA-780 Standard for the Installation of Lightning Protection Systems 2008 Edition – Annex B.3.2.2 This is accomplished by surrounding the building in a kind of Faraday cage. A system of lightning protection conductors and lightning rods are installed on the roof of the building to intercept any lightning before it strikes the building.
Russia The spire of the Leaning Tower of Nevyansk is crowned with a metallic rod in the shape of a gilded sphere with spikes. It acts as a lightning rod. This lightning rod is grounded through the rebar carcass, which pierces the entire building.
The Nevyansk Tower was built between 1721 and 1745, on the orders of industrialist Akinfiy Demidov. The Nevyansk Tower was built 28 years before Benjamin Franklin's experiment and scientific explanation. However, the true intent behind the metal rooftop and rebars remains unknown.
Europe The church tower of many European cities, usually the highest structure in the city, was likely to be struck by lightning. Peter Ahlwardts ("Reasonable and Theological Considerations about Thunder and Lightning", 1745) advised individuals seeking cover from lightning to go anywhere except in or around a church.Seckel, Al, and John Edwards, "Franklin's Unholy Lightning Rod ". 1984.
There is an ongoing debate over whether a "meteorological machine", invented by Premonstratensian priest Prokop Diviš and erected in Brenditz, (now Přímětice, part of Znojmo), Moravia (now the Czech Republic) in June 1754, does count as an individual invention of the lightning rod. Diviš's apparatus, according to his private theories, aimed to prevent thunderstorms altogether by constantly depriving the air of its superfluous electricity. The apparatus was, however, mounted on a free-standing pole and probably better grounded than Franklin's lightning rods at that time, so it served the purpose of a lightning rod.See the following two articles for conflicting views of this being an independent invention by Diviš: After local protests, Diviš had to cease his weather experiments around 1760.
Structure protectors
Lightning arrester
A lightning arrester is a device, essentially an air gap between an electric wire and ground, used on electric power systems and telecommunication systems to protect the insulation and conductors of the system from the damaging effects of lightning. The typical lightning arrester has a high-voltage terminal and a ground terminal.