![CN Tower struck by lightning-Edit(Taxi)](https://upload.wikimedia.org/wikipedia/commons/0/09/CN_Tower_struck_by_lightning-Edit%28Taxi%29.jpg)
A lightning rod or lightning conductor (
British English
British English (BrE, en-GB, or BE) is, according to Oxford Dictionaries, "English as used in Great Britain, as distinct from that used elsewhere". More narrowly, it can refer specifically to the English language in England, or, more broadl ...
) is a
metal
A metal (from ancient Greek, Greek μÎταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, e ...
rod mounted on a structure and intended to protect the structure from a
lightning strike
A lightning strike or lightning bolt is an electric discharge between the atmosphere and the ground. Most originate in a cumulonimbus cloud and terminate on the ground, called cloud-to-ground (CG) lightning. A less common type of strike, ground- ...
. If lightning hits the structure, it will preferentially strike the rod and be conducted to ground through a wire, instead of passing through the structure, where it could start a fire or cause
electrocution
Electrocution is death or severe injury caused by electric shock from electric current passing through the body. The word is derived from "electro" and "execution", but it is also used for accidental death.
The term "electrocution" was coin ...
. Lightning rods are also called
finial
A finial (from '' la, finis'', end) or hip-knob is an element marking the top or end of some object, often formed to be a decorative feature.
In architecture, it is a small decorative device, employed to emphasize the apex of a dome, spire, towe ...
s, air terminals, or 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 earth to perform its protective function. Lightning rods come in many different forms, including hollow, solid, pointed, rounded, flat strips, or even bristle brush-like. The main attribute common to all lightning rods is that they are all made of conductive materials, such as
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...
and
aluminum
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...
. Copper and its
alloy
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductili ...
s are the most common materials used in lightning protection.
History
The principle of the lightning rod was first detailed by
Benjamin Franklin
Benjamin Franklin ( April 17, 1790) was an American polymath who was active as a writer, scientist, inventor, statesman, diplomat, printer, publisher, and political philosopher. Encyclopædia Britannica, Wood, 2021 Among the leading int ...
in
Pennsylvania
Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...
in 1749, who in subsequent years developed his invention for household application (published in 1753) and made further improvements towards a reliable system around 1760.
![Tesla's Lightning Rod](https://upload.wikimedia.org/wikipedia/commons/0/08/Tesla%27s_Lightning_Rod.jpg)
As buildings become taller, lightning becomes more of a threat. Lightning can damage structures made of most materials, such as
masonry
Masonry is the building of structures from individual units, which are often laid in and bound together by mortar; the term ''masonry'' can also refer to the units themselves. The common materials of masonry construction are bricks, building ...
,
wood
Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin ...
,
concrete
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...
, and
steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...
, because the huge
currents and
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...
s involved can heat materials to high temperature. The heat causes a potential for
structure fire
A structure fire is a fire involving the structural components of various types of residential, commercial or industrial buildings, such as barn fires. Residential buildings range from single-family detached homes and townhouses to apartments ...
, and its rapidity can lead to
explosive
An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An expl ...
damage as well.
Russia
A lightning conductor may have been intentionally used in the
Leaning Tower of Nevyansk. The
spire
A spire is a tall, slender, pointed structure on top of a roof of a building or tower, especially at the summit of church steeples. A spire may have a square, circular, or polygonal plan, with a roughly conical or pyramidal shape. Spires a ...
of the tower is crowned with a metallic rod in the shape of a
gilded
Gilding is a decorative technique for applying a very thin coating of gold over solid surfaces such as metal (most common), wood, porcelain, or stone. A gilded object is also described as "gilt". Where metal is gilded, the metal below was tradi ...
sphere with spikes. This lightning rod is
grounded through the
rebar
Rebar (short for reinforcing bar), known when massed as reinforcing steel or reinforcement steel, is a steel bar used as a tension device in reinforced concrete and reinforced masonry structures to strengthen and aid the concrete under tension. ...
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, which was usually the highest structure in the city, was likely to be hit by lightning. Early on, Christian churches tried to prevent the occurrence of the damaging effects of lightning by praying. 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.
There is an ongoing debate over whether a "metereological machine", invented by
Premonstratensian
The Order of Canons Regular of Prémontré (), also known as the Premonstratensians, the Norbertines and, in Britain and Ireland, as the White Canons (from the colour of their habit), is a religious order of canons regular of the Catholic Church ...
priest
Prokop DiviÅ¡ and erected in PÅ™ÃmÄ›tice (now part of
Znojmo
Znojmo (; german: Znaim) is a town in the South Moravian Region of the Czech Republic. It has about 33,000 inhabitants. Znojmo is the historical and cultural centre of southwestern Moravia and the second most populated town in the South Moravian ...
),
Moravia
Moravia ( , also , ; cs, Morava ; german: link=yes, Mähren ; pl, Morawy ; szl, Morawa; la, Moravia) is a historical region in the east of the Czech Republic and one of three historical Czech lands, with Bohemia and Czech Silesia.
The ...
(now the
Czech Republic
The Czech Republic, or simply Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. The ...
) in June 1754, does count as an individual invention of the lightning rod. Diviš's apparatus was, according to his private theories, aimed towards preventing 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. After local protests, Diviš had to cease his weather experiments around 1760.
United States
In what later became the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
, the pointed lightning rod conductor, also called a lightning attractor or Franklin rod, was invented by
Benjamin Franklin
Benjamin Franklin ( April 17, 1790) was an American polymath who was active as a writer, scientist, inventor, statesman, diplomat, printer, publisher, and political philosopher. Encyclopædia Britannica, Wood, 2021 Among the leading int ...
in 1752 as part of his groundbreaking exploration of
electricity
Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as describe ...
. 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.
![Drawing of a country store by Marguerite Martyn](https://upload.wikimedia.org/wikipedia/commons/4/4e/Drawing_of_a_country_store_by_Marguerite_Martyn.jpg)
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 vane
A wind vane, weather vane, or weathercock is an instrument used for showing the direction of the wind. It is typically used as an architectural ornament to the highest point of a building. The word ''vane'' comes from the Old English word , m ...
s. 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
Confirmation bias is the tendency to search for, interpret, favor, and recall information in a way that confirms or supports one's prior beliefs or values. People display this bias when they select information that supports their views, ignoring ...
ensured that 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
Sir William Snow Harris (1 April 1791 – 22 January 1867) was a British physician and electrical researcher, nicknamed Thunder-and-Lightning Harris, and noted for his invention of a successful system of lightning conductors for ships. It took ...
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
The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against Fr ...
did not adopt the system until 1842, by which time the
Imperial Russian Navy
The Imperial Russian Navy () operated as the navy of the Russian Tsardom and later the Russian Empire from 1696 to 1917. Formally established in 1696, it lasted until dissolved in the wake of the February Revolution of 1917. It developed from ...
had already adopted the system.
In the 1990s, the 'lightning points' were replaced as originally constructed when the
Statue of Freedom
The ''Statue of Freedom'', also known as ''Armed Freedom'' or simply ''Freedom'', is a bronze statue designed by Thomas Crawford (1814–1857) that, since 1863, has crowned the dome of the U.S. Capitol building in Washington, D.C. Originall ...
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 also was equipped with multiple lightning points, and the
Statue of Liberty
The Statue of Liberty (''Liberty Enlightening the World''; French: ''La Liberté éclairant le monde'') is a colossal neoclassical sculpture on Liberty Island in New York Harbor in New York City, in the United States. The copper statue, ...
in New York Harbor gets hit by lightning, which is shunted to ground.
Lightning protection system
![Atlas V 551 at Launch Pad 41](https://upload.wikimedia.org/wikipedia/commons/9/92/Atlas_V_551_at_Launch_Pad_41.jpg)
A ''lightning protection system'' is designed to protect a structure from damage due to
lightning
Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an average ...
strikes by intercepting such strikes and safely passing their extremely high
currents to
ground
Ground may refer to:
Geology
* Land, the surface of the Earth not covered by water
* Soil, a mixture of clay, sand and organic matter present on the surface of the Earth
Electricity
* Ground (electricity), the reference point in an electrical c ...
. A lightning protection system includes a network of air terminals, bonding
conductors, and ground
electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials ...
s designed to provide a low impedance path to ground for potential strikes.
Lightning protection systems are used to prevent
lightning strike
A lightning strike or lightning bolt is an electric discharge between the atmosphere and the ground. Most originate in a cumulonimbus cloud and terminate on the ground, called cloud-to-ground (CG) lightning. A less common type of strike, ground- ...
damage to structures. Lightning protection systems mitigate the fire hazard which 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 literally 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 be in excess of 150,000 A), and the very rapid
rise time In electronics, when describing a voltage or current step function, rise time is the time taken by a signal to change from a specified low value to a specified high value. These values may be expressed as ratiosSee for example , and . or, equivale ...
of a lightning strike, no protection system can guarantee absolute safety from lightning. Lightning current will divide to follow every conductive path to ground, and even the 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.
Laboratory-scale measurements of the effects of
ny lightning investigation researchdo 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, and 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
Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The flow of electric current creates a magnetic field around the conductor. The field strength depends on the magnitude of th ...
.
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 which 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 on most occasions of lightning strikes.
Steel framed structures can
bond
Bond or bonds may refer to:
Common meanings
* Bond (finance), a type of debt security
* Bail bond, a commercial third-party guarantor of surety bonds in the United States
* Chemical bond, the attraction of atoms, ions or molecules to form chemical ...
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.
The majority of lightning protection systems in use today are of the traditional
Franklin design.
The fundamental principle used in Franklin-type lightning protections systems is to provide a sufficiently low impedance path for the lightning to travel through to reach 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 Faraday cage or Faraday shield is an enclosure used to block electromagnetic fields. A Faraday shield may be formed by a continuous covering of conductive material, or in the case of a Faraday cage, by a mesh of such materials. Faraday cages ...
. 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.
Structure protectors
Lightning arrester
A lightning arrester is a device, essentially an air gap between an electric wire and ground, used on
electric power
Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. Standard prefixes apply to watts as with other SI units: thousands, millions and billions ...
systems and
telecommunication
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that ...
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.
In
telegraphy
Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas ...
and
telephony
Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunication services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is i ...
, a lightning arrester is a device placed where wires enter a structure, in order to prevent damage to electronic instruments within and ensuring the safety of individuals near the structures. Smaller versions of lightning arresters, also called
surge protector
A 'surge protector'' (or spike suppressor, surge suppressor, surge diverter, surge protection device (SPD) or transient voltage surge suppressor (TVSS) is an appliance or device intended to protect Electronics, electrical devices from voltage s ...
s, are devices that are connected between each
electrical conductor
In physics and electrical engineering, a conductor is an object or type of material that allows the flow of charge (electric current) in one or more directions. Materials made of metal are common electrical conductors. Electric current is gene ...
in a power or communications system, and the ground. They help prevent the flow of the normal power or signal currents to ground, but provide a path over which high-voltage lightning current flows, bypassing the connected equipment. Arresters are used to limit the rise in voltage when a communications or power line is struck by lightning or is near to a lightning strike.
Protection of electric distribution systems
In
overhead electric transmission systems, one or two lighter ground wires may be mounted to the top of the
pylons, poles, or towers not specifically used to send electricity through the grid. These conductors, often referred as to "static", "pilot" or "shield" wires are designed to be the point of lightning termination instead of the high-voltage lines themselves. These conductors are intended to protect the primary power conductors from
lightning
Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an average ...
strikes.
These conductors are bonded to earth either through the metal structure of a pole or tower, or by additional ground electrodes installed at regular intervals along the line. As a general rule, overhead power lines with voltages below 50 kV do not have a "static" conductor, but most lines carrying more than 50 kV do. The ground conductor cable may also support
fibre optic cables for data transmission.
Older lines may use
surge arresters which insulate conducting lines from direct bonding with earth and may be used as low voltage communication lines. If the voltage exceeds a certain threshold, such as during a lightning termination to the conductor, it "jumps" the insulators and passes to earth.
Protection of electrical substations is as varied as lightning rods themselves, and is often proprietary to the electric company.
Lightning protection of mast radiators
Radio
mast radiator
Mast, MAST or MASt may refer to:
Engineering
* Mast (sailing), a vertical spar on a sailing ship
* Flagmast, a pole for flying a flag
* Guyed mast, a structure supported by guy-wires
* Mooring mast, a structure for docking an airship
* Radio mas ...
s may be insulated from the ground by a
spark gap
A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the potential difference between the conduct ...
at the base. When lightning hits the mast, it jumps this gap. A small inductivity in the feed line between the mast and the tuning unit (usually one winding) limits the voltage increase, protecting the transmitter from dangerously high voltages.
The transmitter must be equipped with a device to monitor the antenna's electrical properties. This is very important, as a charge could remain after a lightning strike, damaging the gap or the insulators.
The monitoring device switches off the transmitter when the antenna shows incorrect behavior, e.g. as a result of undesired electrical charge. When the transmitter is switched off, these charges dissipate. The monitoring device makes several attempts to switch back on. If after several attempts the antenna continues to show improper behavior, possibly as result of structural damage, the transmitter remains switched off.
Lightning conductors and grounding precautions
Ideally, the underground part of the assembly should reside in an area of high ground conductivity. If the underground cable is able to resist
corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
well, it can be covered in
salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
to improve its electrical connection with the ground. While the electrical resistance of the lightning conductor between the air terminal and the Earth is of significant concern, the inductive reactance of the conductor could be more important. For this reason, the down conductor route is kept short, and any curves have a large radius. If these measures are not taken, lightning current may arc over a resistive or reactive obstruction that it encounters in the conductor. At the very least, the arc current will damage the lightning conductor and can easily find another conductive path, such as building wiring or plumbing, and cause fires or other disasters. Grounding systems without low resistivity to the ground can still be effective in protecting a structure from lightning damage. When ground soil has poor conductivity, is very shallow, or non-existent, a grounding system can be augmented by adding ground rods,
counterpoise (ground ring) conductor, cable radials projecting away from the building, or a concrete building's reinforcing bars can be used for a ground conductor (
Ufer ground The Ufer ground is an electrical earth grounding method developed during World War II. It uses a concrete-encased electrode to improve grounding in dry areas. The technique is used in construction of concrete foundations.
History
During World W ...
). These additions, while still not reducing the resistance of the system in some instances, will allow the
ispersionof the lightning into the earth without damage to the structure.
Additional precautions must be taken to prevent side-flashes between conductive objects on or in the structure and the lightning protection system. The surge of lightning current through a lightning protection conductor will create a voltage difference between it and any conductive objects that are near it. This voltage difference can be large enough to cause a dangerous side-flash (spark) between the two that can cause significant damage, especially on structures housing flammable or explosive materials. The most effective way to prevent this potential damage is to ensure the electrical continuity between the lightning protection system and any objects susceptible to a side-flash. Effective bonding will allow the voltage potential of the two objects to rise and fall simultaneously, thereby eliminating any risk of a side-flash.
Lightning protection system design
Considerable material is used to make up lightning protection systems, so it is prudent to consider carefully where an air terminal will provide the greatest protection. Historical understanding of lightning, from statements made by Ben Franklin, assumed that each ''lightning rod'' protected a
cone
A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex.
A cone is formed by a set of line segments, half-lines, or lines con ...
of 45 degrees. This has been found to be unsatisfactory for protecting taller structures, as it is possible for lightning to strike the side of a building.
A modeling system based on a better understanding of the termination targeting of lightning, called the Rolling Sphere Method, was developed by Dr Tibor Horváth. It has become the standard by which traditional Franklin Rod systems are installed. To understand this requires knowledge of how lightning 'moves'. As the
step leader of a lightning bolt jumps toward the ground, it steps toward the
grounded objects nearest its path. The maximum distance that each step may travel is called the ''critical distance'' and is proportional to the electric current. Objects are likely to be struck if they are nearer to the leader than this critical distance. It is standard practice to approximate the sphere's radius as 46 m near the ground.
An object outside the critical distance is unlikely to be struck by the leader if there is a solidly grounded object within the critical distance. Locations that are considered safe from lightning can be determined by imagining a leader's potential paths as a
sphere
A sphere () is a Geometry, geometrical object that is a solid geometry, three-dimensional analogue to a two-dimensional circle. A sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...
that travels from the cloud to the ground. For lightning protection, it suffices to consider all possible spheres as they touch potential strike points. To determine strike points, consider a sphere rolling over the terrain. At each point, a potential leader position is simulated. Lightning is most likely to strike where the sphere touches the ground. Points that the sphere cannot roll across and touch are safest from lightning. Lightning protectors should be placed where they will prevent the sphere from touching a structure. A weak point in most lightning diversion systems is in transporting the captured discharge from the lightning rod to the ground, though. Lightning rods are typically installed around the perimeter of flat roofs, or along the peaks of sloped roofs at intervals of 6.1 m or 7.6 m, depending on the height of the rod. When a flat roof has dimensions greater than 15 m by 15 m, additional air terminals will be installed in the middle of the roof at intervals of 15 m or less in a rectangular grid pattern.
Rounded versus pointed ends
![Pointed Lightning Rod](https://upload.wikimedia.org/wikipedia/commons/c/cd/Pointed_Lightning_Rod.jpg)
The optimal shape for the tip of a lightning rod has been controversial since the 18th century. During the period of political confrontation between Britain and its American colonies, British scientists maintained that a lightning rod should have a ball on its end, while American scientists maintained that there should be a point. , the controversy had not been completely resolved.
It is difficult to resolve the controversy because proper controlled experiments are nearly impossible, but work performed by
Charles B. Moore, et al., in 2000 has shed some light on the issue, finding that moderately rounded or blunt-tipped lightning rods act as marginally better strike receptors. As a result, round-tipped rods are installed on most new systems in the United States, though most existing systems still have pointed rods. According to the study,
In addition, the height of the lightning protector relative to the structure to be protected and the Earth itself will have an effect.
Charge transfer theory
The charge transfer theory states that a lightning strike to a protected structure can be prevented by reducing the electrical potential between the protected structure and the thundercloud. This is done by transferring electric charge (such as from the nearby Earth to the sky or vice versa).
[, Richard Ralph Zini, et al., Non-contaminating lightning protection system. Claim one and claim ten.] Transferring electric charge from the Earth to the sky is done by installing engineered products composed of many points above the structure. It is noted that pointed objects will indeed transfer charge to the surrounding atmosphere and that a considerable electric current can be measured through the conductors as ionization occurs at the point when an electric field is present, such as happens when thunderclouds are overhead.
In the United States, the National Fire Protection Association (NFPA) does not currently endorse a device that can prevent or reduce lightning strikes. The NFPA Standards Council, following a request for a project to address Dissipation Array
mSystems and Charge Transfer Systems, denied the request to begin forming standards on such technology (though the Council did not foreclose on future standards development after reliable sources demonstrating the validity of the basic technology and science were submitted).
Early streamer emission (ESE) theory
![Lightning Rod Meteora](https://upload.wikimedia.org/wikipedia/commons/c/c6/Lightning_Rod_Meteora.jpg)
The theory of early streamer emission proposes that if a lightning rod has a mechanism producing ionization near its tip, then its lightning capture area is greatly increased. At first, small quantities of radioactive isotopes (
radium-226
Radium (88Ra) has no stable or nearly stable isotopes, and thus a standard atomic weight cannot be given. The longest lived, and most common, isotope of radium is 226Ra with a half-life of . 226Ra occurs in the decay chain of 238U (often referre ...
or
americium-241
Americium-241 (, Am-241) is an isotope of americium. Like all isotopes of americium, it is radioactive, with a half-life of . is the most common isotope of americium as well as the most prevalent isotope of americium in nuclear waste. It is com ...
) were used as sources of ionization between 1930 and 1980, later replaced with various electrical and electronic devices. According to an early patent, since most lightning protectors' ground potentials are elevated, the path distance from the source to the elevated ground point will be shorter, creating a stronger field (measured in volts per unit distance) and that structure will be more prone to ionization and breakdown.
AFNOR, the French national standardization body, issued a standard, NF C 17-102, covering this technology. The
NFPA also investigated the subject and there was a proposal to issue a similar standard in the USA. Initially, an NFPA independent third party panel stated that "the
arly Streamer Emission
The Arly () is a 32.1 km long river in the Departments of France, departments of Savoie and Haute-Savoie, France. It is a tributary of the Isère (river), Isère, which it joins at Albertville.
Towns crossed by the river
* Megève
* Praz-sur ...
lightning protection technology appears to be technically sound" and that there was an "adequate theoretical basis for the
arly Streamer Emission
The Arly () is a 32.1 km long river in the Departments of France, departments of Savoie and Haute-Savoie, France. It is a tributary of the Isère (river), Isère, which it joins at Albertville.
Towns crossed by the river
* Megève
* Praz-sur ...
air terminal concept and design from a physical viewpoint".) The same panel also concluded that "the recommended
FPA 781 standardlightning protection system has never been scientifically or technically validated and the Franklin rod air terminals have not been validated in field tests under thunderstorm conditions".
In response, the American Geophysical Union concluded that "
e Bryan Panel reviewed essentially none of the studies and literature on the effectiveness and scientific basis of traditional lightning protection systems and was erroneous in its conclusion that there was no basis for the Standard". AGU did not attempt to assess the effectiveness of any proposed modifications to traditional systems in its report. The NFPA withdrew its proposed draft edition of standard 781 due to a lack of evidence of increased effectiveness of Early Streamer Emission-based protection systems over conventional air terminals.
Members of the Scientific Committee of the
International Conference on Lightning Protection (ICLP) have issued a joint statement stating their opposition to Early Streamer Emission technology. ICLP maintains a web page with information related to ESE and related technologies. Still, the number of buildings and structures equipped with ESE lightning protection systems is growing as well as the number of manufacturers of ESE air terminals from Europe, Americas, Middle East, Russia, China, South Korea, ASEAN countries, and Australia.
Analysis of strikes
Lightning strikes to a metallic structure can vary from leaving no evidence—except, perhaps, a small pit in the metal—to the complete destruction of the structure.
[Rakov, et al., ''Lightning: physics and effects'', p. 364] When there is no evidence, analyzing the strikes is difficult. This means that a strike on an uninstrumented structure must be visually confirmed, and the random behavior of lightning renders such observations difficult.
There are also inventors working on this problem, such as through a
lightning rocket A lightning rocket is a rocket that unravels a conductor, such as a fine copper wire, as it ascends, to conduct lightning charges to the ground. Lightning strikes derived from this process are called "triggered lightning."
Design
A conducting li ...
. While controlled experiments may be off in the future, very good data is being obtained through techniques which use radio receivers that watch for the characteristic electrical "signature" of lightning strikes using fixed directional antennas. Through accurate timing and triangulation techniques, lightning strikes can be located with great precision, so strikes on specific objects often can be confirmed with confidence.
The energy in a lightning strike is typically in the range of 1 to 10 billion
joule
The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied ...
s. This energy is released usually in a small number of separate strokes, each with duration of a few tens of microseconds (typically 30 to 50 microseconds), over a period of about one fifth of a second. The great majority of the energy is dissipated as heat, light and sound in the atmosphere.
Aircraft protectors
Aircraft are protected by devices mounted to the aircraft structure and by the design of internal systems. Lightning usually enters and exits an aircraft through the outer surface of its
airframe
The mechanical structure of an aircraft is known as the airframe. This structure is typically considered to include the fuselage, undercarriage, empennage and wings, and excludes the propulsion system.
Airframe design is a field of aerospa ...
or through a
static discharger
Static dischargers, also called static wicks or static discharge wicks, are devices used to remove static electricity from aircraft in flight. They take the form of small sticks pointing backwards from the wings, and are fitted on almost all civi ...
s. The lightning protection system provides safe conductive paths between the entry and exit points to prevent damage to
electronic equipment
The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...
and to protect flammable fuel or cargo from
sparks.
These paths are constructed of conductive materials.
Electrical insulators are only effective in combination with a conductive path because blocked lightning can easily exceed the
breakdown voltage
The breakdown voltage of an insulator is the minimum voltage that causes a portion of an insulator to experience electrical breakdown and become electrically conductive.
For diodes, the breakdown voltage is the minimum reverse voltage that mak ...
of insulators.
Composite material
A composite material (also called a composition material or shortened to composite, which is the common name) is a material which is produced from two or more constituent materials. These constituent materials have notably dissimilar chemical or ...
s are constructed with layers of wire mesh to make them sufficiently conductive and structural joints are protected by making an electrical connection across the joint.
Shielded cable
A shielded cable or screened cable is an electrical cable that has a common conductive layer around its conductors for electromagnetic shielding. This shield is usually covered by an outermost layer of the cable. Common types of cable shieldi ...
and conductive enclosures provide the majority of protection to electronic systems. The lightning current emits a magnetic pulse which
induces
Electromagnetic or magnetic induction is the production of an electromotive force (emf) across an electrical conductor in a changing magnetic field.
Michael Faraday is generally credited with the discovery of induction in 1831, and James Cler ...
current through any loops formed by the cables. The current induced in the shield of a loop creates magnetic flux through the loop
in the opposite direction. This decreases the total flux through the loop and the induced voltage around it.
The lightning-conductive path and conductive shielding carry the majority of current. The remainder is bypassed around sensitive electronics using
transient voltage suppressor
A 'surge protector'' (or spike suppressor, surge suppressor, surge diverter, surge protection device (SPD) or transient voltage surge suppressor (TVSS) is an appliance or device intended to protect electrical devices from voltage spikes in alt ...
s, and blocked using electronic filters once the let-through voltage is low enough. Filters, like insulators, are only effective when lightning and surge currents are able to flow through an alternate path.
Watercraft protectors
A lightning protection installation on a
watercraft
Any vehicle used in or on water as well as underwater, including boats, ships, hovercraft and submarines, is a watercraft, also known as a water vessel or waterborne vessel. A watercraft usually has a propulsive capability (whether by sail, ...
comprises a ''lightning protector'' mounted on the top of a
mast or superstructure, and a ''
grounding conductor'' in contact with the water.
Electrical conductor
In physics and electrical engineering, a conductor is an object or type of material that allows the flow of charge (electric current) in one or more directions. Materials made of metal are common electrical conductors. Electric current is gener ...
s attach to the protector and run down to the conductor. For a vessel with a conducting (iron or steel) hull, the grounding conductor is the hull. For a vessel with a non-conducting hull, the grounding conductor may be retractable, attached to the
hull, or attached to a
centerboard.
Risk assessment
Some structures are inherently more or less at risk of being struck by lightning. The risk for a structure is a function of the size (area) of a structure, the height, and the number of lightning strikes per year per mi
2 for the region. For example, a small building will be less likely to be struck than a large one, and a building in an area with a high density of lightning strikes will be more likely to be struck than one in an area with a low density of lightning strikes. The National Fire Protection Association provides a risk assessment worksheet in their lightning protection standard.
The
International Electrotechnical Commission
The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
(IEC) lightning risk-assessment comprises four parts: loss of living beings, loss of service to public, loss of cultural heritage, and loss of economic value.
Loss of living beings is rated as the most important and is the only loss taken into consideration for many nonessential industrial and commercial applications.
Standards
The introduction of lightning protection systems into standards allowed various manufactures to develop protector systems to a multitude of specifications. There are multiple international, national, corporate and military lightning protection standards.
*
NFPA-780: "Standard for the Installation of Lightning Protection Systems" (2014)
*M440.1-1, Electrical Storms and Lightning Protection, Department of Energy
*AFI 32-1065 – Grounding Systems, U. S. Air Force Space Command
*FAA STD 019e, Lightning and Surge Protection, Grounding, Bonding and Shielding Requirements for Facilities and Electronic Equipment
*
UL standards for lightning protection
** UL 96: "Standard of Lightning Protection Components" (5th Edition, 2005)
** UL 96A: "Standard for Installation Requirements for Lightning Protection Systems" (Twelfth Edition, 2007)
** UL 1449: "Standard for Surge Protective Devices" (Fourth Edition, 2014)
*
IEC
The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
standards
** EN 61000-4-
IEC 61000-4-5 "Electromagnetic compatibility (EMC) – Part 4-5: Testing and measurement techniques – Surge immunity test"
** EN 62305/IEC 62305: "Protection against lightning"
** EN 62561/IEC 62561: "Lightning Protection System Components (LPSC)"
ITU-T K Series recommendations "Protection against interference"
*
IEEE
The Institute of Electrical and Electronics Engineers (IEEE) is a 501(c)(3) professional association for electronic engineering and electrical engineering (and associated disciplines) with its corporate office in New York City and its operation ...
standards for grounding
** IEEE SA-142-2007: "IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems". (2007)
** IEEE SA-1100-2005: "IEEE Recommended Practice for Powering and Grounding Electronic Equipment" (2005)
* AFNO
NF C 17-102: "Lightning protection – Protection of structures and open areas against lightning using early streamer emission air terminals" (1995)
*
GB 50057-2010 Design Code for Lightning Protection of Buildings
*AS / NZS 1768:2007: "Lightning protection"
See also
*
Apollo 12
Apollo 12 (November 14–24, 1969) was the sixth crewed flight in the United States Apollo program and the second to land on the Moon. It was launched on November 14, 1969, by NASA from the Kennedy Space Center, Florida. Commander Pete Conra ...
– A Saturn V rocket that was struck by lightning shortly after liftoff.
*
James Otis Jr.
James Otis Jr. (February 5, 1725 – May 23, 1783) was an American lawyer, political activist, colonial legislator, and early supporter of patriotic causes in Massachusetts at the beginning of the Revolutionary Era. Otis was a fervent opponent ...
– Contemporary of
Ben Franklin
Benjamin Franklin ( April 17, 1790) was an American polymath who was active as a writer, scientist, inventor, statesman, diplomat, printer, publisher, and political philosopher. Encyclopædia Britannica, Wood, 2021 Among the leading intel ...
, killed at doorway by lightning in
Andover, Massachusetts
Andover is a town in Essex County, Massachusetts, United States. It was settled in 1642 and incorporated in 1646."Andover" in ''The New Encyclopædia Britannica''. Chicago: Encyclopædia Britannica Inc., 15th ed., 1992, Vol. 1, p. 387. As of th ...
on May 23, 1783.
*
Ground (electricity)
In electrical engineering, ground or earth is a reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the Earth.
Electrical circuits may be conne ...
*
Grounding kit
*
Lightning
Lightning is a naturally occurring electrostatic discharge during which two electric charge, electrically charged regions, both in the atmosphere or with one on the land, ground, temporarily neutralize themselves, causing the instantaneous ...
*
Lightning rod fashion
*
''The Autobiography of Benjamin Franklin''
*
Václav Prokop Diviš Václav () is a Czech male first name of Slavic origin, sometimes translated into English as Wenceslaus or Wenceslas. These forms are derived from the old Slavic/Czech form of this name: Venceslav.
Nicknames are: VaÅ¡ek, VaÅ¡Ãk, Venca, Venda
For ...
(1698–1765) – Constructor of the first grounded lightning rod, in
PÅ™ÃmÄ›tice u Znojma during 1750–1754.
References
Citations
Sources
* Vladimir A. Rakov and Martin A. Uman,
Lightning: physics and effects'. Cambridge University Press, 2003. 698 pages. .
* J. L. Bryan, R. G. Biermann and G. A. Erickson, "Report of the Third-Party Independent Evaluation Panel on the Early Streamer Emission Lightning Protection Technology". National Fire Protection Association, Quincy, Mass., 1999.
* Kithil, Rich. "More on lightning rods...", Lightning Safety Home Page, Message #402. May 8, 2000. (Response to C. B. Moore) Originally at: https://portishead-plumbing.co.uk/
*
*
*
*
* Carpenter Jr., Roy B.
Preventing Direct Strikes.
External links
.
USA Today
''USA Today'' (stylized in all uppercase) is an American daily middle-market newspaper and news broadcasting company. Founded by Al Neuharth on September 15, 1982, the newspaper operates from Gannett's corporate headquarters in Tysons, Virgini ...
, June 10, 2002.
*
Federal Aviation Administration
The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...
,
FAA-STD-019d, Lightning and surge protection, grounding, bonding and shielding requirements for facilities and electronic equipment".
National Transportation Library
The National Transportation Library (NTL) maintains and facilitates access to information necessary for transportation decision-making in government and coordinates with public and private transportation libraries and information providers to impr ...
, August 9, 2002.
* Kithil, Richard,
Lightning Rods: Recent Investigations. National Lightning Safety Institute, September 26, 2005.
* Kithil, Richard,
. National Lightning Safety Institute, September 26, 2005.
* Kithil, Richard,
. National Lightning Safety Institute, September 26, 2005.
* Nailen, Richard L.,
Lightning controversy goes on, The Electrical Apparatus, February 2001.
page
*
John Scoffern
John Scoffern (1814–1882) was an English surgeon and popular science writer.
Life
He was born in Dutson, Cornwall, the son of William Scoffern (1783–1854) and his wife Wilmot Crocker, was educated by the Rev. John Couch Grylls at Saltash. He ...
, ''
Orr's Circle of the Sciences
''Orr's Circle of the Sciences'' was a scientific encyclopedia of the 1850s, published in London by William Somerville Orr.
William S Orr & Co.
William S. Orr & Co. was a publisher in Paternoster Row, London. It put out the '' British Cyclopà ...
''
Atmospheric Electricity—Theory of Lightning-rodsW. S. Orr 1855.
* February 1919 Popular Science article about Lightning Arresters and how they were used in early AC and DC power distribution systems, "Electrical Devices and How They Work, Part 14: Lightning Arresters",
Popular Science
''Popular Science'' (also known as ''PopSci'') is an American digital magazine carrying popular science content, which refers to articles for the general reader on science and technology subjects. ''Popular Science'' has won over 58 awards, incl ...
monthly, February 1919, 5 unnumbered pages, Scanned by Google Books: https://books.google.com/books?id=7igDAAAAMBAJ&pg=PT17
"Do lightning rods really work?", The Straight Dope August 24, 2001
*''
Scientific American
''Scientific American'', informally abbreviated ''SciAm'' or sometimes ''SA'', is an American popular science magazine. Many famous scientists, including Albert Einstein and Nikola Tesla, have contributed articles to it. In print since 1845, it i ...
'',
Protection From Lightning, 06-Aug-1881, pp.88
{{Authority control
Lightning
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Czech inventions
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