The purpose of the Lightning Rod Report or ADPS (Atmospheric Discharge Protection Systems) Report is to provide information regarding the current conditions of the ADPS installation, in accordance with the requirements of NBR 5419/2015 of ABNT – Brazilian Association of Technical Standards.
The ADPS Report must be based on the understanding that a atmospheric discharge protection systems is designed to safeguard a structure by intercepting lightning strikes and conducting their (extremely high) currents safely to the ground. An effective ADPS should consist of a network of air terminals, down conductors, and grounding electrodes designed to provide a low-impedance path to earth.
The Lightning Rod Report should also be prepared with a focus on installation safety, as atmospheric discharge protection systems help mitigate the fire risk posed by lightning, particularly in explosive atmospheres. An ADPS offers a low-impedance path for lightning current with the goal of reducing the thermal effects caused by high-current flow through structural materials (which may be flammable). If lightning flows through porous, water-saturated materials, these materials may literally explode if the water content is turned into vapor by the heat generated from the current.
A lightning rod is a device used in electrical power systems and telecommunication systems to protect insulation and conductors from the damaging effects of lightning. A typical lightning rod has a high-voltage terminal and a ground terminal. When a lightning surge travels along a power line to the lightning rod, the surge current is diverted, in most cases, safely to ground.
If surge protection is missing or fails, lightning strikes to an electrical system can result in tens of thousands of kilovolts, potentially damaging transmission lines, destroying transformers, and compromising sensitive electrical or electronic equipment.
Key Considerations Regarding the Operation of an ADPS:
– Lightning is a natural phenomenon that is completely unpredictable in terms of both its electrical characteristics (current intensity, duration) and the destructive effects it can cause when it strikes buildings.
– Nothing can be done to prevent lightning from striking a certain region. There is no “long-distance attraction”, these systems are primarily receptors. Thus, internationally adopted solutions focus solely on minimizing destructive effects by establishing preferred interception points and providing a safe path to conduct lightning current to the ground.
– The design and maintenance of lightning protection systems are governed internationally by the IEC (International Electrotechnical Commission) and locally by organizations such as ABNT (Brazil), NEPA (United States), and BSI (United Kingdom).
– Only projects developed in compliance with these standards can be considered efficient and reliable. However, no system can offer 100% protection, even compliant installations are subject to occasional failures. The most common damage includes chipped facade surfaces or corners of buildings.
The ADPS, commonly known as a lightning rod, involves much more than simply placing metal rods at the highest points of a building, such as on rooftops, tanks, or antennas, and connecting them to the ground with metallic conductors.
An ADPS design based on the NBR 5419 technical standard ensures a significant reduction in the harmful effects of lightning and provides better protection for people and structures. While the installation of a lightning protection system is essential for safeguarding electrical and electronic equipment, installation alone is not sufficient, periodic inspection reports are also required.
The primary function of the ADPS is to direct and safely dissipate atmospheric discharges (lightning) into the ground. These discharges are caused by electrically charged clouds due to friction and movement. It is important to emphasize that lightning protection systems do not attract lightning, they only dissipate the discharges once they occur, thereby helping to prevent damage to buildings and protect occupants.
Its function is to receive lightning strikes that hit the top of a building and distribute the current through the down conductors. It is composed of metallic elements, usually masts or properly sized conductors.
The lightning protection system is divided into three main parts:
– Air termination system,
– Down-conductor system, and
– Earth termination system.
The air termination system may include Franklin rods (lightning rods) or other types of capture devices. The number and positioning of lightning rods are determined by the building’s dimensions, its width, length, and height relative to the ground.
Currently, technical standards allow the tip of a metal pipe to serve as a lightning rod. Likewise, a metallic tower can be considered a valid air terminal. Essentially, any metallic part that could be struck by lightning must be considered in the ADPS design, and thus naturally acts as a lightning receptor. Examples include: flashings, chimneys, metal tanks, guardrails, helipads, ladders, steel structures of warehouses, metal roof tiles, antenna masts. In some cases, the designer may not install a separate air termination system, as the existing metallic structures already serve this function, they are simply integrated into the down-conductor and grounding systems. Another effective method to create a robust air termination system is to install bare copper cables with a cross-section of 35 mm² around the entire perimeter of the building, along with transverse cables to form a large Faraday cage. Alternatively, aluminum tapes with a minimum cross-section of 70 mm² may be used, all in accordance with the NBR 5419:05 lightning protection standard.
The down-conductor subsystems of a lightning protection system can be made of bare copper cables with a cross-section of 16 mm² for buildings up to 20 meters in height. For taller structures, bare copper cables of 35 mm² or aluminum tapes of 70 mm² must be used, with all down-conductors interconnected by equipotential bonding rings every 20 meters, as required by the NBR 5419:05 standard. Structural steel columns, provided that electrical continuity is ensured, can also serve as natural down-conductors, which reduces costs associated with copper or aluminum conductors and improves system maintenance, since these elements are less prone to vandalism or theft.
In many lightning protection installations, the use of aluminum tapes, structural steel, or reinforced concrete is advisable due to the frequent theft of copper conductors. Another important recommendation is that each building should have at least two down-conductors, even for small constructions. For larger structures, such as shopping centers, logistics warehouses, or large industrial plants, with widths greater than 40 meters, multiple down-conductors should be installed within the protected volume.
The grounding subsystems of a lightning protection system can be composed of the steel structures within the foundations, such as footings, columns, and tie beams of the buildings, whether it is the foundation of a condominium, club, industrial plant, church, farm, countryside property, or even a simple residence. The amount of metal present in reinforced concrete foundations is typically substantial and protected against corrosion because it is embedded in concrete, which is hygroscopic and has high electrical conductivity, often greater than that of fertile garden soil, which is considered one of the most conductive types of soil used in lightning protection system designs.
Another way to achieve effective grounding, whether for lightning protection systems or electrical systems, is through the use of high-coating ground rods, meaning rods with a 254-micron copper layer over a round steel bar measuring at least 2.40 meters in length and 5/8” in diameter, commonly known as copperweld rods. According to technical standards, a minimum of two rods must be driven into the ground. Additional rods should be installed as needed to ensure effective dissipation of electrical currents into the soil from the lightning protection system’s capture subsystem.
To determine this measurement, thermometer-type meters are used. These instruments simulate a lightning strike on a smaller scale, and then compare the residual voltage that the soil is able to dissipate through the lightning protection system’s grounding subsystem.
These conductors receive the currents distributed by the air termination system and quickly direct them into the ground. For taller buildings, they also serve the purpose of intercepting side strikes, thus taking on the function of an air terminal. In such cases, the conductors must be properly sized for this dual role. At ground level, down conductors should be interconnected using bare copper cable.
Grounding rings perform two important functions. The first is to equalize the potentials of the down conductors, thereby minimizing the electric field within the building.
The second function is to receive lateral lightning discharges and distribute them to the down conductors. In this case, the rings must also be dimensioned as part of the air-termination system.
They receive the electric currents from the down conductors and dissipate them into the ground. They also serve to equalize the potential of the down conductors and the ground itself, requiring special attention in areas with frequent pedestrian access, to minimize step voltages in these locations. A preliminary soil resistivity survey is essential for properly sizing the grounding grid.
At the ground level and ring level, the grounding of the following systems must be interconnected:
– The utility company’s neutral,
– The telecommunications provider’s grounding,
– Grounding for electronic equipment and elevators (including elevator guide rails),
– Metallic fire and gas pipelines (including the gas meter housing when present),
– Water and sump pump piping, etc.
To accomplish this, a strategically located main equipotential bonding box must be installed and connected to the grounding grid. Every 20 meters in height, additional secondary bonding boxes should be installed, connected to the structural reinforcement bars and linked by a vertical conductor to the main grounding box.
The connection to the equipotential bonding box as well as to the metallic piping may be done using 16mm² bare copper wire, before laying the concrete subfloor of the apartments located at the ring levels. The bonding of different metallic pipes can be done using nickel-plated perforated tape (bimetallic), which enables connections between different types of metals and pipe diameters, and also reduces inductance due to its flat surface.
Special structures with inherent explosion risks, such as those containing flammable gases, generally require the highest level of protection.
For other types of structures, it must first be determined whether an ADPS is mandatory or not.
In certain locations, the use of a ADPS is essential, such as: locations with large gatherings of people; sites where essential public services are provided, such as power substations; areas with high lightning density; structures of historical and cultural value; isolated structures taller than 25 meters.
The selection of the protection level for an ADPS can be made according to the following criteria: The average expected annual frequency of lightning strikes on a structure.
There are three basic types of methods for protection against lightning surges:
This method consists of determining the protection volume provided by a cone, whose generatrix angle varies according to the desired protection level and the height of the structure. The Franklin method is recommended for use on very tall structures with small horizontal surface areas, where a small number of air terminals (lightning rods) can be used, making the design economically efficient.
This method is based on the theory that the magnetic field inside a conductive cage is null.
It consists of surrounding the upper part of the structure with a mesh of bare electrical conductors, with the spacing between them determined by the desired protection level. Unlike the Franklin method, the Faraday method is recommended for structures with relatively low height but large horizontal surface areas. However, according to NBR 5419/01, for buildings taller than 60 meters, the Faraday method is mandatory.
Some Recommendations for Installing the Faraday Method:
. The standard recommends installing vertical air terminals or lightning rods with heights between 30 to 50 cm, spaced 5 to 8 meters apart along the conductors of the mesh;
. Horizontal conductors should cover the entire perimeter of the structure;
. Natural or non-natural down conductors can be used:
Natural: parts of the building structure, such as: angles (metal brackets); metal pipes; metal bars;
Non-natural: conductors and/or busbars specifically installed for this purpose;
. Grounding:
– At least one ground rod per down conductor;
– All ground rods must be interconnected, forming a closed loop (ring);
– There should be a single grounding system for the entire installation;
– The grounding resistance must be less than 10 ohms;
. If the lightning protection system is intended for critical applications, the Faraday cage is the best option, provided that all recommendations of the technical lightning protection standard are followed. The Faraday cage has the advantage of better shielding the protected volume, especially when the reinforced concrete structure or metal framework naturally forms multiple Faraday cages, thereby reinforcing the lightning protection system. The principle of the Faraday cage is to provide shielding of the protected volume against incoming and outgoing electromagnetic waves, as long as the cage is properly grounded and connected to the ADPS system. For calculation and design purposes, lightning is considered to be composed of strong electromagnetic waves, typically in the megahertz range.
Also known as the rolling sphere method, the Electrogeometric Method is based on defining the protection volume provided by ADPS air terminals, which can include rods, cables, or even a combination of both. It is highly effective for tall structures and/or buildings with complex architectural shapes.
This is the most recent method, and it involves “rolling” a fictitious sphere, with a radius determined by the desired level of protection, over the entire building. Any point where the sphere touches the structure is considered a potential lightning strike point and must be protected with metallic elements connected to the grounding system.
Standardization
To ensure the safety and efficiency of the system, the design must always comply with the guidelines of NBR 5419 from ABNT (Brazilian Association of Technical Standards), as well as Ordinance 598 from the Ministry of Labor and Employment (MTE) issued in 2004, which amends the regulations related to electrical installations and services under NR10.
There are also state decrees that integrate the ADPS with fire safety and panic prevention systems.
In addition, there are Technical Guidelines issued by the Fire Department, according to each state’s regulations, which further ensure the safety of the projects, reinforcing the importance of the ADPS inspection report.
1. Define the protection level to be adopted;
2. Check the possibility of using natural elements;
3. Add metallic conductors to the capture subsystem around the building perimeter and in distributed meshes according to the following tables;
4. Use tall masts with Franklin rods to provide localized protection for antennas and other structures on the building’s top;
5. Distribute the down conductors, one at each vertex of the building, with maximum distances according to the table. Protect the conductors against mechanical damage up to a height of 2.20 m;
6. Install bonding rings every 20 meters from the ground, interconnecting the down conductors;
7. Equalize all metallic elements within 0.5 m of these components;
8. Install a grounding ring made of bare copper cable, buried 0.5 m deep. At each down conductor, install a high-layer copper-coated rod connected to the grounding ring and the down conductor via exothermic welding. This is the most practical grounding system;
9. Perform potential equalization as previously mentioned, at ground level and at each bonding ring level.
Observations:
1. All metallic structures (chimneys, guardrails, staircases, etc.) must be equipotentially bonded and interconnected with the lightning protection system;
2. Measurement boxes must be used to decouple the grounding system for testing purposes;
3. Buried connections must be made by welding or compression. Mechanical connections must be housed in ground-type boxes and protected with caulking compound. Caulking compound is a high-consistency product designed to seal joints or gaps against dust, moisture, etc.;
4. All metallic piping that crosses the grounding ring must be interconnected to it. Pipes with cathodic surface protection via impressed current must be equipotentially bonded using surge protection devices (SPDs);
5. Only components made of steel with hot-dip galvanized protection are permitted; electroplated protection is prohibited;
6. Copper-coated rods must have a copper layer thickness of 254 microns (0.254 mm), with rod diameters of 1/2″, 5/8″, and 3/4″.
– Down conductors and intermediate ring conductors can be fixed directly to the building’s façade or embedded beneath the plaster;
– Down conductors should be distributed along the perimeter of the building according to the required protection level, preferably positioned at main corners;
– For buildings over 20 meters high, the down conductors and horizontal intermediate rings must have the same cross-sectional area as the air-termination conductors due to potential lateral strikes;
– To minimize aesthetic impact on façades and terraces, flat copper conductors may be used;
– The grounding mesh should consist of a bare copper cable (#50 mm²), buried 0.5 meters deep and interconnecting all down conductors;
– “Copperweld” type grounding electrodes must be of high-layer copper (254 microns); low-layer electrodes are not permitted;
– Buried connections should preferably be made using exothermic welding. If compression connectors are used, they must be housed in a ground inspection box for protection and maintenance;
– All metal fittings must be hot-dip galvanized; electroplated galvanization is strictly prohibited;
– Potential equalization must be carried out at ground level and every 20 meters in height, interconnecting all grounding meshes, metallic risers, and the building’s structural elements;
– It is important to note that gas piping with cathodic protection must not be directly bonded to the system. In this case, a spark-gap type surge protection device (SPD) must be installed;
– It is recommended to properly seal all holes made during the ADPS installation to prevent future water infiltration;
– Use stainless steel nuts, washers, and bolts along with nylon anchors to extend the system’s durability.
The concept of using reinforced concrete rebar as a means of conducting and dissipating lightning currents in down conductors originated from the use of such metallic structures in grounding systems.
In Brazil, the use of structural Atmospheric Discharge Protection System (ADPS) is regulated by standards. According to the 2015 revision of the NBR 5419 standard, there are two main options for such systems. The first is to use the reinforcement bars of the concrete structure as natural down conductors, provided that electrical continuity of the vertical reinforcement in the columns is ensured. The second option involves the addition of a hot-dip galvanized steel bar to the existing reinforcement. This method is detailed in a specific annex of the standard and outlines the requirements for its use. This bar, commonly referred to as a “re-bar” (reinforcement bar), is intended to ensure continuity from the ground level to the top of the building. It is favored by professionals who implement ADPS systems due to the challenge civil construction contractors face in ensuring vertical electrical continuity of the rebar, as this is not structurally necessary and thus not commonly considered during construction.
Regardless of whether the additional bar is used, the standard requires that at least 50% of all rebar intersections (in columns, slabs, and beams) be tightly tied with twisted steel wire. These bindings must be repeated on every slab and for all columns that form part of the building structure.
More important than a low-resistance grounding system (as measured by the four-point Wenner method, per NBR 7117:81), is the proper potential equalization of all grounding systems. This includes implementing a single ground system (Boat Theory) and installing a main equipotential bonding bar, as required by the low and medium voltage technical standards (NBR 5410 for electrical installations). The use of aluminum in the soil for lightning or electrical grounding systems or even for simple interconnections is strictly prohibited by technical standards.
A well-designed lightning protection system operates by draining as much of the lightning discharge current into the ground as possible. The greater the percentage of current diverted to the ground, the more efficient the system will be. It is important to note that no ADPS system is capable of conducting 100% of a lightning discharge. The system’s function is to equalize the potential (voltage) between the cloud and the ground. When a charged cloud passes over an ADPS installation, a descending leader (lightning strike) or ascending leader may strike the structure, effectively creating a massive short circuit that produces a high-energy spark or arc (lightning flash).
The most effective lightning protection system is one that evenly distributes the lightning current to the ground through multiple down conductors, minimizing differences in potential between the conductors and at ground level.
In summary, the main cause of damage to electronic equipment and injuries from lightning is the residual voltage that remains in the ground or between metallic parts of a building and the ground. For this reason, standards such as NBR 5419:05 and NBR 5410 emphasize the need to bond all metallic parts and equipment enclosures to the ADPS. This includes all protective conductors, metal structures, and grounding wires. It is similar in principle to the old “ground wire” used in electric showers when pipes were metallic, everything must be at the same potential (the same ground).
The scope of IEC 62305-3 covers the design, installation, inspection, and maintenance of a ADPS for structures, without limitation on height. It also defines measures for the protection of living beings against injuries caused by touch and step voltages.
According to this IEC standard, the design of an ADPS can be broken down into the following components: installation of an external lightning protection system, installation of an internal lightning protection system or adoption of measures to reduce potential hazards.
In the sections that follow, each of these topics is discussed based on IEC 62305-3.
Installation of an External Lightning Protection System
An external ADPS project can be implemented by dividing the solutions into the following subsystems:
– Air-Termination System: Responsible for receiving atmospheric discharges (lightning strikes).
– Down-Conductor System: Responsible for conducting the current from the lightning strike, received by the air-termination system, down to the earth-termination system.
– Earth-Termination System: Responsible for conducting and dissipating the current from the lightning strike into the ground.
Air-Termination System
The air-termination system can be implemented through:
– Air rods (masts)
– Catenary wires
– Mesh conductors
– Natural metallic components of the structure, provided they meet the minimum thickness and other requirements set by the standard
The air-termination conductors should preferably be placed at the most exposed points of the structure, such as edges and corners, following one or more of the following positioning methods:
– Protection angle method
– Rolling sphere method
– Mesh method
The protection angle method is limited to structures with simplified shapes and is restricted in its application for tall structures (limited to a maximum height of 60 meters).
The rolling sphere method is applicable to any situation, from simplified to complex-shaped structures.
The mesh method is suitable for flat-roofed structures, such as large industrial buildings with significant horizontal extension.
For structures taller than 60 meters, special attention must be given to protecting against lateral lightning strikes.
The minimum positioning requirements for each method are specified in the standard, according to the selected protection level.
Down-Conductor System
The down-conductors, in order to minimize the likelihood of damage during a lightning strike, should be arranged to ensure the shortest possible distance between the lightning strike point (air-termination system) and the ground (earth-termination system). The following characteristics must be observed:
– Provide multiple paths for the lightning current to descend
– Be as short as possible
– Allow equipotential bonding with the conductive parts of the structure
The down-conductor system may consist of dedicated metallic conductors installed for this purpose or may use the structure’s own components, provided that the requirements and minimum thicknesses specified in the standard are met.
Earth-Termination System
The earth-termination system is essentially composed of electrodes buried in the ground. The standard recommends an earthing system with resistance lower than 10 ohms, but it emphasizes that the geometry and interconnections of the earthing system are more important than the resistance value itself. Therefore, from the perspective of lightning protection, an interconnected earth-termination system with adequate geometry is the most advisable. The low-frequency grounding resistance value serves as a reference, but it does not represent the performance of the grounding system in the face of lightning discharges, which are impulsive phenomenon.
According to the standard, the earth-termination system can follow two basic topologies:
– Type A, which consists of horizontal and vertical conductors buried in the ground and connected to each down-conductor.
– Type B, which consists of conductors buried at least 80% of their length below ground level, forming a closed loop around the structure. This type may also consist of a mesh (grid) system installed below the entire footprint of the structure, formed either by dedicated conductors or by the building’s structural reinforcement bars.
The installation of the internal protection system aims to prevent dangerous sparking inside the structure that could cause damage to installations and transfer hazardous potentials.
Dangerous sparking can be avoided in two basic ways:
– Equipotentialization;
– Electrical insulation.
The following subsections detail each method for minimizing hazardous potentials.
Equipotentialization
The installation of the equipotential subsystem is achieved by interconnecting the ADPS with the following parts of the structure:
– Metallic components.
– Internal systems.
– External conductive elements connected to the structure.
Equipotentialization can be implemented through the following methods:
Directly, using electrical conductors, when the element to be bonded to the ADPS can be directly connected to the earth potential.
Indirectly, through surge protective devices (SPDs), when the element cannot be directly connected to earth potential.
Electrical Insulation
Electrical insulation of the metallic parts of the structure and the ADPS must be provided by maintaining a distance d between the parts, which should be greater than the minimum separation distance.
The vicinity of the down conductors of the ADPS can develop hazardous potentials that may cause harm to humans through two phenomena:
– Step voltage
-Touch voltage
The following sections present the concepts and implications outlined in the Standard [8] for these two hazards. Hazard refers to the risk to human beings caused by these dangerous potentials.
Step Voltage
The potential difference experienced between a person’s feet is defined as step voltage.
The IEC Standard states that the vicinity of the down conductors of an ADPS is favorable for the development of step voltages, even when the ADPS has been designed in compliance with the Standard.
According to the standard, the hazard is reduced if:
– The probability of the presence of people near the down conductors is very low.
– The resistivity of the surface layer of soil within 3 meters around the down conductor is greater than 5 kΩ·m.
If neither of these conditions is met, protection measures must be implemented following the directives below:
– Equipotentialization through a mesh grounding system.
– Physical access restriction and/or installation of warning signs to minimize the likelihood of people entering the 3-meter area around the down conductors.
Touch Voltage
A person in contact with an object at a different potential from the point where their feet are grounded may be subject to a voltage that causes current to flow through their body. This voltage is known as touch voltage.
The IEC Standard warns that down conductors of a ADPS are favorable points for the development of touch voltages.
According to the standard, the hazard is reduced if:
– The probability of the presence of people near the down conductors is very low.
– The down conductor subsystem is of the natural type, consisting of several columns with assured electrical continuity.
– The resistivity of the surface layer of soil within 3 meters around the down conductor is greater than 5 kΩ·m.
If none of these conditions are met, protection measures must be implemented according to the following directives:
– Insulation of exposed down conductors for impulses of 100 kV (1.2/50 µs waveform).
– Physical restriction and/or installation of warning signs to prevent the down conductors from being touched.
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