Lightning protection of buildings and structures without explosive zones. Do you need lightning protection? Lightning and its striking factors

This topic is very relevant for Belarusian designers. I planned to write it about two years ago. During this time, a lot of things have changed, there were several publications on this topic from leading experts in the country, but, nevertheless, I want to express my humble opinion.

As you know, in the Republic of Belarus, instead of RD 34.21.122, from November 1, 2011, TCP 336-2011 (Lightning protection of buildings, structures and utilities) was put into effect.

As soon as this TAP came out, I began to study it diligently. At that time, I was already beginning to realize what design really is.

Now I have accumulated a lot of which are created specifically for specific design tasks. But, in this list there is no program for calculating the need for a lightning protection device.

In fact, I have such a program, or rather even two.

My very first program with which I started creating my personal programs was called: The program looked like this:

By the way, my name is on the top. I made this program when this blog did not yet exist, and the link is to my old blog, which I have not been doing for a long time and on which I practiced site building skills. There were 3 versions of the program where I fixed my mistakes.

The program could be freely downloaded on the Internet at the forum. I am one of the first who made such a program and put it on the Internet. Now the download links do not work, because. this program is not up to date and in some cases may not produce completely correct results.

The fact is that at that time the experts did not yet require a calculation, and the program simply turned out to be unnecessary.

After some time, I made a program for myself, which I called: I do not distribute this program, I will not even review it, since there is an official program from the Ministry of Emergency Situations of Belarus: And she looks like this:

I came across this program quite by accident. I bring my calculation to an expert, and they tell me why you manually calculated everything if there is a program developed by the Ministry of Emergency Situations

Personally, I have never used this program until now, but the fact that the program does not work correctly is 100%. There is a good review of their program on the Internet, where they give a bunch of errors, I hope these errors have now been eliminated.

On the website of the Ministry of Emergency Situations of the Republic of Belarus you can download the version of the program from 04/08/2015.

Before proceeding with the calculation, you need to understand the essence of the calculation. The calculation is done in order to understand what measures need to be taken to protect the building and people from lightning strikes.

The most expensive thing that may appear is an external lightning protection device. I do the installation of surge arresters and a potential equalization system in almost every project.

Initially, you do not take any measures to protect against lightning strikes. After calculating how you have determined that your risk is higher than acceptable, you begin to add various measures, thereby reducing the corresponding coefficients.

The employees of the Ministry of Emergency Situations considered that it was enough to calculate only R1. I, as a designer, am very happy, because they made it easier for us to calculate, but why shouldn't we count R2? The most obvious error that catches the eye is that when calculating the risk, they sum up all intermediate values ​​from Ra to Rz. Not even in my first program.

The most important thing is that the expertise accepts it, and it will not be difficult to select the necessary coefficients. Although, there were cases (not for me) when the expert forced to make external lightning protection, despite the calculation that did not require it.

My personal opinion.

With this calculation, you need to do the following:

Risk calculation

This does not apply specifically to the MES program. There is very little meaning from all the calculations. All calculations can be adjusted to the desired results, since not all experts are well versed in this calculation. This was especially true at the beginning.

The most difficult thing that I had while developing the program was the calculation associated with the shielding of cables and the choice of appropriate coefficients. I stupidly adjust these values ​​​​to the desired result, since no one inside the building will shield the power cables.

I would like to ask a question to specialists, developers of TCP 336-2011: why did you not like table 1 in RD 34.21.122-87 (Instruction for lightning protection of buildings and structures)?

In my opinion, it is necessary to take this table and rework it. Add more objects.

For example:

School - III class.

Residential building 16 floors - IV class.

One-story house - MOH is not required.

It is quite realistic to list 100 objects in the table, on which to make decisions on external lightning protection. Moreover, one object must be brought in different cases: in the city, in the countryside, perhaps even depending on the height of the building.

This will save time for both the designer and the checking expert.

Next time I will check if all the mistakes that I made in the RMZ v.1.03 program have been corrected.

In this article, you can discuss other problems and questions on TCP 336-2011.

In St. Petersburg, it is customary to install active lightning rods. The entire installation takes about five hours (including driving deep ground electrodes). We ordered from a specialized company (StroyMaximum-STMX, read more on the website).
What prompted us to install professional lightning protection was the fact that in our cottage town (in the Priozersky district) for a little over two months, two houses with home-grown lightning protection burned down during a thunderstorm.
As the saying goes, God saves the safe.

In general, there is an interesting article: Statistics say that on a planetary scale, lightning strikes everything that is on the ground with an intensity of about a hundred beats per second! And about 2000 thunderstorms themselves rage on the planet at the same time. One of the results of this can be fires (only in our country, 7% of fires in residential buildings are caused by lightning)
Ask your friends who have recently built a country house if they have protected it from lightning. 90% of respondents will answer "no". The reason is ignorance of the possible consequences of such frivolity or a typical Russian "maybe". There are primary striking factors of lightning - this is a fire, destruction, as well as secondary ones - the drift of the induced potential, the appearance in the internal network of sources of consumption of electrostatic and electromagnetic induction. Lightning is a huge spark that has a complex trajectory. Only 25-30% of lightning goes from the cloud to the ground. Very often we see a lightning discharge that has arrived from somewhere on the side, and the place of its origin can be located several kilometers from the place of impact. External lightning protection
A lightning rod is a device of three main elements: a lightning rod that receives a lightning discharge; a current collector, which should direct the received discharge to the ground, and a ground electrode, which gives a charge to the ground. The lightning rod can be in the form of a metal pin (rod), stretched along the ridge of the roof of a metal cable or a metal mesh made of reinforcement with a mesh spacing of usually 6-12 m. protection (this is everything that fits into a cone, the height of which is determined by the height of the lightning rod, and the diameter of the base is equal to the triple value of the height) hit the selected objects. Quite often you can hear the opinion that a metal roof (for example, a metal tile) allows you not to worry about lightning protection. A very dangerous delusion! It is supported mainly by the sellers of metal tiles themselves. A metal roof can act as a lightning rod. However, such protection will not save you from "serious" lightning, since the calculated thickness of the roof sheets must be at least 4 mm (and who uses this?). Lightning simply burns through sheets of smaller thickness. If there are protruding elements on the roof (for example, metal chimneys), lightning rods are mounted on them, protruding 0.2 m above the upper edge and securely attached to the metal of the roof. Once again we remind you: buildings with a metal roof must be equipped with a lightning protection system.
In addition to "mechanical" lightning rods, there are "physical" ones. The ability to artificially create a column of ionized air has long suggested the use of a counter lightning leader as a kind of lightning rod. The first ionization devices were based on the use of a radioactive isotope. When voltage was applied to such a device, a column of ionized air appeared, to which the leader from a thundercloud closed. Later, these devices were transformed into safe lightning rods that no longer operate from radioactive isotopes, but with the help of electronics (ERICO, USA). The devices turned out to be quite effective, there is experience of their use in the Russian Federation. The undoubted advantages of such lightning rods include an excellent opportunity to preserve the architectural appearance of the building without distorting it with visible additions. Many of us have observed how often lightning discharges near various high objects, not always hitting them. But few people pay attention to the fact that near high objects lightning is observed somewhat more often than in other places. This pattern is explained by the fact that the "counter leader" from high objects, as it were, attracts leaders from the cloud not only strictly above its top, but also from the peripheral parts of the cloud. It turns out that any mast (for example, a cellular communication) objectively attracts a larger number of lightnings to its location zone. grounding
In any case, both for "external" and "internal" lightning protection, the role of grounding is very important. Let's return to our instructions. She strongly recommends grounding lightning rods on the foundation reinforcement of the house or, if this is not possible, burying electrodes in the ground (by the way, it is not always possible to ground on the foundation reinforcement, there are some limitations: if the foundation is waterproofed with epoxy-based compositions or if the soil moisture is less 3%). The electrodes must be deepened so as to reach the moist soil layers. We are talking about the so-called step voltage, which in the immediate vicinity of the ground electrodes can be very significant and life-threatening. During a thunderstorm, it is not recommended to be closer than five meters from the ground electrode of the lightning rod, so as not to fall under the action of step voltage and touch voltage.

A direct lightning strike into a building or structure and discharges from electrostatic induction of clouds and from electromagnetic induction of lightning current inside a building can strike people in it, cause fires and explosions, destroy stone and concrete structures, split wooden poles of overhead lines and damage insulation. Protection against atmospheric electricity must be organized in accordance with the Instructions for the installation of lightning protection of buildings and structures.
Depending on the presence and class of explosive zones in a given building, one of the three categories of lightning protection is required or lightning protection is optional at all.
Lightning protection category I is used for industrial buildings with explosive zones of classes B-Ia and B-II. All these are not rural objects.
Category II lightning protection is used for industrial buildings with zones of classes B-Ga, B-Ib and B-IIa (provided that they occupy at least 30% of the volume of the entire building, and if less, then either the entire building is protected by category III, or part of category II), as well as open installations with zones of class B-Ig. Lightning protection for these open installations is mandatory throughout the area, while category II lightning protection for buildings is required only in areas where there are at least ten thunderstorm hours per year. The division of the territory into areas with a different number of thunderstorms (thunderstorm hours) is given in the PUE and in the Instructions for the installation of lightning protection for buildings and structures. Category II lightning protection is performed for ammonia refrigerators, mills, factories or workshops for the production of animal feed, hay flour, TSM warehouses with gasoline, some fertilizers, pesticides.
For other industrial, residential and public buildings, lightning protection of category III should be built or not built at all, depending on the purpose and nature of the building, and sometimes also on the expected number of direct lightning strikes to this building per year.
This number is determined by calculation depending on the size of the building and the number of thunderstorm hours.
Regardless of the number of expected direct lightning strikes at 20 or more thunderstorm hours per year, category III lightning protection is constructed in the following cases: for outdoor installations of classes II ... III; for buildings of fire resistance degrees III ... IV - kindergartens, nurseries, schools and boarding schools, dormitories and canteens, recreational children's camps and rest homes; for hospitals, clubs, cinemas; for vertical exhaust pipes of boiler houses or industrial plants, water towers and silos at a height of more than 15 m from the ground. In areas with at least 40 thunderstorm hours per year, category III lightning protection is required for livestock and poultry buildings with fire resistance degrees III ... V: barns, calves and pigsties for at least 100 heads of all ages and groups of animals, stables for 40, sheepfold for 500 and poultry houses for 1000 heads (of all ages); for residential buildings - only at a height of more than 30 m (more than five floors), if they are located more than 400 m from the general array.
Category III lightning protection protects against a direct lightning strike and against the introduction of high potentials into the building through overhead electrical lines, as well as through other above-ground metal communications (trestle pipelines, overhead railways).
These communications, when entering the building and on the nearest support, are connected to grounding conductors with a resistance of not more than 30 ohms. At the input, you can use a grounding device to protect against a direct lightning strike.
On overhead electric lines with a voltage of up to 1000 V, passing through an open area or along a street with one-, two-story buildings (if the line is not shielded by tall trees or houses), insulator hooks or pins of phase wires are grounded (including street lighting lines ) and a neutral wire at least every 200 m with thunderstorms of 10 ... 40 hours a year and at least every 100 m with a greater number of thunderstorms (more often, for example, to the west of Moscow). The resistance of the grounding conductor should be no more than 30 ohms, it is made on supports with branches to the entrance to the building, where there can be many people (school, nursery, hospital, club), or to livestock buildings, warehouses, as well as on the final supports of the lines, if from them an input was made into any building. At the same time, the previous grounding should be no further than 100 m from the end support with grounding during thunderstorms of 10 ... 40 hours per year and no further than 50 m, if there are more of them.
When lightning surges appear on the wires of the line, the insulators overlap on the surface with an electric discharge to grounded hooks, and only relatively small surges penetrate the houses. Only approaching a few centimeters to the wiring during a thunderstorm can be dangerous, for example, when trying to turn on or off the light, radio. And in the absence or improper implementation of lightning protection, there were cases of people being struck at a distance of 2 m from the wiring or more.
All of the above applies to both wooden and reinforced concrete supports. For those reinforced concrete poles where lightning protective grounding is not required, the fittings, insulator hooks or pins and lamps are neutralized. A steel rod with a diameter of at least 6 mm is used as a grounding conductor, which is attached to the hooks with a wire bandage, and to the neutral wire with a clamp. On reinforced concrete supports, support reinforcement is used, to which the upper and lower ground outlets are welded for attaching grounding hooks and for connecting to the ground electrode. Lightning protection grounding on the line is done more often than repeated grounding of the neutral wire.
To protect against a direct lightning strike, rod or cable lightning rods are used. A rod lightning rod is a vertical steel rod of any profile, mounted on a support standing close to the protected object, or on a tree. The distance from the support to the building is not standardized, but it is desirable that it be at least 5 m. The cross-sectional area of ​​​​the rod, called a lightning rod, is usually at least 100 mm2, and the length is at least 200 mm It is connected to the grounding conductor with a down conductor made of steel rod with a diameter of at least 6 mm, but it can be used as down conductors for metal structures of protected buildings and structures with welding of their joints. These are metal trusses, columns, elevator rails, fire escapes.
For lightning protection, it is necessary to use as much as possible natural rod lightning rods: exhaust pipes, water towers and other tall structures located close to the protected object. Trees growing closer than 5 m from buildings of III...V degrees of fire resistance can be used as a support for a lightning rod, if a down conductor is laid on the wall of the building against a tree to the entire height of the wall, welded to the ground electrode of the lightning rod. However, it is allowed for any category of lightning protection to place lightning rods directly on the protected building without any additional measures. As a lightning rod, you can use a metal roof, grounded at the corners and along the perimeter at least every 25 m, or a grid of steel wire rod with a diameter of 6 ... grounded in the same way as a metal roof. Iron caps over chimneys or a wire ring specially applied to the pipe, if there is no cap, are attached to the grid or metal roof.
No special lightning rods are required if the roof covering consists of metal trusses or reinforced concrete, and the waterproofing and insulation are non-combustible (from slag wool, etc.). Farms are grounded.
It is possible to have one common grounding conductor for protection against a direct lightning strike, against the drift of lightning surges along overhead lines or other extended communications, and against electric shock. Chimneys of power plants and boiler houses or silos and water towers must have a lightning rod height above the chimney of at least 1 m. It is recommended to use a reinforced concrete foundation of the chimney or tower instead of a special artificial grounding device. For reinforced concrete pipes and towers, steel reinforcement serves as a down conductor, while for metal lightning rods and down conductors are not required at all.
On fig. 38 shows the protection zone of a single rod lightning rod with a height h. It is a circular cone with a vertex at a height h 0 1 and with a zone boundary at ground level in the form of a circle of radius r 0 . The horizontal section of the protection zone at a height h x is a circle with a radius r x . There is a narrower zone, in which the object is protected from a lightning strike with a probability of 99.5%, and a wider zone, where the probability of protection is 95%. Rural facilities generally require a wider protection zone. For it, the following relations take place: h 0 = 0.92h; r0 = 1.5h; r x \u003d 1.5 (h-h x / 0.92); h = 0.67r x + h x /0.92.

Rice. 38. Scheme of a single rod lightning rod and its protective zone

As grounding conductors for a lightning rod located on the roof of a protected building, it is possible to use ground electrode systems constructed for electrical safety reasons (repeated grounding of the neutral wire), and if they are far from the lightning rod or are absent at all (when power is supplied to the building via cables with plastic sheaths), then reinforced concrete the foundation of the building, connecting the down conductor from the lightning rod to the reinforcement of the foundation by welding. From each lightning rod on the roof ridge, two down conductors should depart along both roof slopes to their ground electrodes. If there is no reinforced concrete foundation, a special one is constructed in the form of two vertical rods with a diameter of 10 ... 20 mm and a length of 3 m, located at a distance of 5 m from each other and connected underground at a depth of at least 0.5 m with a steel strip with a cross section of at least 40x4 mm.
With a lightning rod in the form of a grounded metal roof or a mesh on a non-metal roof, the ground electrode is made in the form of a grounding steel strip 25x4 mm, laid on the edge along the building at a depth of 0.5 ... 0.8 m and at a distance of 0.8 m from the foundation. K all metal structures, equipment and pipelines located inside the building should be attached to these strips.
So that people and animals are not affected by step voltage, it is recommended to place concentrated lightning protection grounding conductors of all categories no closer than 5 m from roads and footpaths, from building entrances, in rarely visited places (lawns, shrubs). Down conductors should not pass near the doors or gates of livestock buildings. In case of forced placement of grounding conductors in frequently visited places, these places must be asphalted. For example, when placing a ground electrode along the barn wall, the width of the asphalt pavement must be at least 5 m from the walls.
Outdoor installations of class P-III, in which flammable liquids with a vapor flash point of more than 61 ° C are used or stored, are protected from a direct lightning strike as follows: the bodies of these installations or individual containers with a roof metal thickness of less than 4 mm are protected by a lightning rod (separately standing or installed on the protected structure), and the space above the gas pipes may not be included in the protection zone of the lightning rod. If the thickness of the roof metal is not less than 4 mm or, regardless of the thickness of the roof, the volume of individual tanks is less than 200 m3, then it is enough to connect them to the grounding conductors at least 50 m apart along the perimeter of the base.
Extended lightning rods (grounded cables made of stranded steel rope with a cross-sectional area of ​​at least 35 mm2) are used to protect long buildings from a direct lightning strike. Then the height of the cable lightning rod is considered to be the height of the cable above the ground in the place where it is closest to the ground as a result of sagging Нt, and the sag is taken equal to 2 m with a building length of up to 120 m, i.e. Nopor = Нt + 2. At the level earth Ro = = 1.7 Nt. At the height Hx (wall height) Rx = 1.7(Hm + Hx/0.92), and if Hx and Rx are given (for example, half the width of the building), then you can find Hm = 0.6 RxHx/0.92.
Small buildings with a degree of fire resistance III ... IV, located in rural areas with an average duration of thunderstorms per year of 20 hours or more, are allowed to be protected from a direct lightning strike in a simplified way compared to category III lightning protection in one of the following ways.
1. A tree growing at a distance of 3 ... 10 m from the building is used as a support for the lightning rod, if its height is at least 2 times higher than the height of the building, taking into account the pipes and antennas protruding above its roof. A down conductor is laid along the tree trunk, which should protrude above its top by at least 0.2 m. a depth of at least 0.5 m (they are also grounded in three other versions of simplified lightning protection. All connections are bolted, not welded). The main simplification in this option is the absence of a check whether the entire structure is included in the protection zone of the lightning rod.
2. If the roof ridge corresponds to the maximum height of the building, a cable lightning rod is suspended above it, which rises above the ridge by at least 0.25 m. The cable can be supported by wooden planks attached to the ends of the roof. With a building length of more than 10 m, down conductors from both ends of the cable are laid along the end walls or one roof slope from each end, and if the building is less than 10 m long, then only one end of the cable is grounded.
3. If a chimney rises above the ridge and other elements, a lightning rod is fixed on it, which rises above the chimney by at least 0.2 m. From it, one down conductor is enough for one roof slope.
4. The metal roof is grounded at one point, and all metal objects protruding above it are attached to the roof, and downpipes, metal stairs can serve as a down conductor, if they provide continuity of the electrical circuit.

Do you need lightning protection?

Lightning, atmospheric discharges are a constant and almost ubiquitous companion of people. Their terrifying power was presented to our ancestors as a manifestation of the will of the gods. In world science and practice, effective methods of protection against the consequences of atmospheric discharges have been developed. Lightning protection is a set of measures to protect the life and health of a person and his property. At the moment, lightning protection, as a set of norms, methods and means, is a dynamically developing part of world technology.

Lightning and its striking factors.

Atmospheric discharges have a crushing force and their various consequences pose a serious threat to human life and property.

There are several lightning theories, but the main thing is that a potential difference of up to 1000 kV in the clouds with respect to the earth's surface causes a monstrous discharge of up to 200kA, which is accompanied by flashes and thunder. The heating of the atmospheric discharge channel reaches 30,000 deg. The average duration of the discharge, the most common cloud-to-ground lightning strike, is approximately 60-100 µs. It is more convenient to analyze the variety of damaging factors and consequences using the example of a table.

From the above, we can conclude:

• lightning, lightning potential poses a real and diverse threat to human life and property.
• The human environment, as it becomes saturated with sensitive modern electronic equipment, has become extremely vulnerable to the effects of atmospheric and switching overvoltages.

As an example, the following statistics can be cited: over 25% of insurance payments in Germany account for damage from lightning and surges.

The need for lightning protection and surge protection is beyond doubt for everyone who has witnessed the consequences of atmospheric discharges.

A short list of problems related to the security of existing structures, the design and implementation of lightning protection of buildings in the territory of the Russian Federation.

At their core, the problems of Russian lightning protection are of a regulatory nature. The norms in force in the territory of the Russian Federation in the field of lightning protection do not fully reflect the achievements of modern science and technology. Effective methods and means of lightning protection are most fully presented in the IEC (International Electrotechnical Commission) standards and confirmed by wide practical application in industrialized countries.

For convenient perception of the text of the article, it is necessary to give the functional names of the basic sections of the lightning protection system adopted in international practice.

With a very generalized comparison of world and Russian standards, a number of fundamental conclusions can be drawn.

According to the section of external lightning protection:

• In contrast to the norms of the Russian Federation, the IEC standards have developed a detailed method of protection by applying lightning protection circuits (mesh) to complex roofs of buildings in combination with protection of protruding parts.
• The Russian guiding document "Instructions for the installation of lightning protection of buildings and structures" (RD 34.21.122-87) does not fix the world practice of using anti-corrosion materials and prefabricated elements, including ground electrodes and bolted connectors made of galvanized steel in grounding devices.
• The same instructions stipulate the unambiguous practice of receiving a lightning strike with a metal roofing. At the same time, in the IEC normative documents, this method is used only when there is no need to ensure the safety of this coating.

According to the section of internal lightning protection:

At the moment, the international concept of zonal surge protection for electrical installations of buildings, information and telecommunication systems, electronic equipment and terminal devices is practically outside the field of activity of Russian specialists.

• The IEC standards carefully developed rules and recommendations for the use of surge arresters in accordance with the zonal concept of internal lightning protection, as well as requirements for them. At the same time, the new edition of the PUE contains only a fragmentary indication of the need to install arresters on the input electrical cabinets during the air input of the supply line.
• The Russian standards have not developed a set of methods and means for protection against lightning and switching overvoltages of modern low-voltage networks, equipment and devices.

As a result, this is not an exhaustive list of the real problems faced by developers, contractors and property owners.

In the absence of practice of using prefabricated elements, it is possible to implement effective external lightning protection of cottages, estates and similar buildings only with the use of free-standing high rod lightning rods. As a rule, developers and owners are not satisfied with this decision, because. the architectural identity of the building is violated, and its implementation is associated with significant costs.

The use of a metal roofing (especially metal tiles) as a lightning rod can lead to deformation and destruction of the sheet material, as well as ignition of the underlying combustible materials of the roof structures.

Difficulties arise in the arrangement of external lightning protection on reconstructed industrial, public and administrative buildings. At such facilities, it is cheaper to perform external lightning protection and grounding, regardless of current-carrying building structures, than to determine their suitability and reconstruct. In conditions of practical unavailability of factory-ready elements on the market, it is difficult to effectively and economically implement lightning protection of these objects.

Parts of lightning protection and grounding devices made from improvised materials in construction conditions have, as a rule, a low durability, an insufficient degree of protection against a direct strike, and no means of protection against the brought and induced lightning potential.

Public and industrial buildings in urban areas that are protected from direct lightning strikes using conductive building structures, as a rule, are equipped with electrical installations without internal lightning protection devices. Owners and operating organizations may incur significant costs to eliminate the consequences and cover damage from lightning and switching overvoltages in networks.

Every year, expensive and sensitive to impulse voltage information technology equipment, telecommunications and automation systems are increasingly used in everyday life, management, industry and communications. Their uninterrupted operation and safety require complex and high-quality equipment to limit lightning and switching overvoltages with rules of application, installation and operation that are understandable to specialists.

Under these conditions, the subject of a possible reduction in the risks of insurance companies, and, accordingly, the size of tariffs for real estate and property insurers, is of great interest.

Experts offer you to create a new level of security for the houses you live in, which you build, equip and design. Complex equipment with system equipment of the leading German manufacturer OBO Bettermann is a time-tested effective solution for lightning and surge protection.

Lightning discharges can affect buildings and structures by direct impacts (primary impact), causing their direct damage and destruction, and secondary impacts through the phenomena of electrostatic and electromagnetic induction. During lightning strikes, high potential can be brought into buildings through overhead lines and various metal communications. The lightning channel has a high temperature (20,000 ° C and above), and when exposed to lightning, the resulting sparks and the heating of the combustible medium to the ignition temperature cause fires in buildings and structures.
The need for lightning protection of residential and public buildings and structures is established in accordance with the requirements of the Guidelines for the Design and Arrangement of Lightning Protection of Buildings and Structures (SN 305-69), based on their purpose, the intensity of lightning activity in the area of ​​their location, as well as the expected number of lightning strikes in year. The average thunderstorm activity in hours for one year is determined from the map given in CH 305-69 or based on data from local meteorological stations.

The following residential and public buildings and structures are subject to lightning protection:
1. Residential and public buildings or their parts, rising above the level of the general building array by more than 25 m, as well as stand-alone buildings with a height of more than 30 m, remote from the building array by at least 100 m.
2. Public buildings of III, IV, V degrees of fire resistance (kindergartens and nurseries, educational and dormitory buildings of schools and boarding schools, dormitory buildings and canteens of sanatoriums, recreation facilities and pioneer camps, dormitory buildings of hospitals, clubs and cinemas).
3. Buildings and structures of historical and artistic significance, subject to state protection as monuments of history and art.
Specified in paragraphs. 1 and 2, buildings and structures are subject to lightning protection if they are located in an area where the average thunderstorm activity is 20 or more thunderstorm hours per year. Buildings and structures specified in clause 3 are required to be provided with lightning protection throughout the territory of the USSR.
The above residential and public buildings and structures, according to SN 305-69, are subject to lightning protection according to category III, i.e. with a protection device against direct lightning strikes and against the introduction of high potentials through above-ground metal communications.

The magnitude of the impulse resistance of each grounding conductor from direct lightning strikes for residential and public buildings is assumed to be no more than 20 ohms.

Buildings are protected from direct lightning strikes by lightning rods, which consist of lightning rods that directly receive a lightning discharge, grounding conductors for diverting the lightning current to the ground, and a down conductor connecting the lightning rod to the ground electrode system. Lightning rods are divided according to their location into free-standing and installed directly on a building or structure; by type of lightning rod - rod, cable and special; by the number of lightning rods jointly operating on one structure - into single, double and multiple. If, for architectural reasons, the installation of lightning rods on a building is unacceptable, lightning protection of buildings can be carried out by applying a metal grounded mesh. To do this, use a steel wire with a diameter of 6-8 mm, which is fixed on the roof in the form of a rare mesh. The lightning protection mesh should have cells with an area of ​​\u200b\u200bno more than 150 m2, i.e., 12 x 12 or 6 x 24 m in size. This mesh is connected to ground electrodes at least in two opposite sides using down conductors made of the same wire and laid along the walls buildings. If the protected building is covered with roofing steel, then it is not necessary to arrange special lightning rods. Around the building along the eaves, it is necessary to lay a steel wire with a diameter of 6 mm and securely attach it to the metal roof at least every 15-20 m, and install current conductors from this wire to the ground electrodes. Down conductors are fastened to the roof with bolt clamps or by welding. Smoke and ventilation pipes protruding above the roof must be equipped with rod lightning rods made of steel wire with a diameter of 6-8 mm protruding 30 cm above the pipe and connected to a grounded roof. On metal pipes, the device of lightning rods is not required, but the pipes and the metal stretch marks that fasten them must be securely connected to the roof or ground electrode. Lightning rods of lightning rods are made of steel rods of various sizes and cross-sectional shapes with corrosion protection. The minimum area of ​​the lightning rod must be at least 100 mm2, which corresponds to round steel with a diameter of 12 mm, strip 35 X 3 mm, angled 20 x 20 x 3 mm or gas pipes with a flattened and welded free end. The lightning rod of a catenary wire lightning rod should be made of a steel multi-wire galvanized cable with a cross section of at least 35 mm2 (diameter 7 mm). Down conductors must be made of steel with a cross section of 25-35 mm2 using steel wire (wire rod) with a diameter of at least 6 mm or steel of flat, square and other profiles. The down conductor of a cable lightning rod must be made of a cable with a cross section of at least 35 mm2 or steel wire with a diameter of at least 6 mm.

In all cases, it is recommended to use metal structures of protected buildings and structures (columns, trusses, frames, fire escapes, metal guides for elevators, etc.) as down conductors. In this case, it is necessary to ensure the continuity of the electrical connection in the joints of structures and fittings, which, as a rule, is ensured by welding. Prestressed reinforcement of reinforced concrete columns, trusses and other reinforced concrete structures cannot serve as down conductors.

If the buildings have a top floor of metal trusses, the installation of lightning rods or the application of a lightning protection mesh is not required. In this case, the trusses are connected by down conductors to grounding conductors. In all cases, it is allowed to combine earthing switches for protection against direct lightning strikes, protective earthing of electrical equipment and a grounding electrode for protection against electrostatic induction.

If the building has a width of 100 m or more and is protected from direct lightning strikes by lightning rods installed on the building, lightning protection mesh or using a metal roof, then, in addition to external ground electrodes, additional ground electrodes should be installed to equalize the potential inside the building. These earthing switches are made in the form of long steel strips laid no more than 60 m apart and along the width of the building. The strips are accepted with a cross section of at least 100 mm2 and are laid in the ground at a depth of at least 0.5 m. Each ground electrode is connected with its ends to the outer contours of the ground electrode for protection against direct lightning strikes, and is also connected with a step of not more than 60 m to down conductors from lightning rods.

Depending on the location in the ground and the shape of the electrodes, ground electrodes are divided into the following types:
recessed - from strip or round steel. They are laid horizontally on the bottom of the pit in the form of extended elements or contours along the perimeter of the foundations;
vertical - from vertically screwed steel rods from round steel and driven rods from angle steel and steel pipes. Screwed-in electrodes are taken 4.5-5 m long, and driven-in 2.5-3 m. The upper end of the vertical ground electrode rises by 0.5-0.6 m from the ground surface;
horizontal - from strip or round steel. They are laid horizontally at a depth of 0.6-0.8 m from the earth's surface with one or more rays radiating from one point to which the down conductor is connected;
combined - combining vertical and horizontal ground electrodes into a common system.

The design of grounding conductors is adopted depending on the required impulse resistance, taking into account the specific resistance of the soil and the convenience of conducting work on their laying. In SN 305-69, typical designs of ground electrodes and the values ​​of their resistance to the passage of current are given. All connections of ground electrodes between themselves and with down conductors must be carried out only by welding with a welding step length of at least six diameters of the round conductors to be welded. Bolted connection can only be used when installing temporary ground electrodes.

Non-metallic vertical pipes of boiler houses and enterprises, water towers, fire towers with a height of 15 m or more are protected from direct lightning strikes. In this case, the magnitude of the impulse resistance of the ground electrodes is assumed to be 50 ohms for each TOKOOTEOD. For pipes up to 50 m high, one lightning rod and one external down conductor are installed. With a pipe height of more than 50 m, at least two lightning rods and down conductors are accepted, located symmetrically along the pipe. Pipes with a height of 100 m or more along the perimeter of the upper end are supplied with a steel ring with a cross section of at least 100 mm2, to which at least two down conductors are welded. The same rings are repeated along the height of the pipe every 12 m.
Metal pipes, towers and towers do not require the installation of separate lightning rods and down conductors, it is enough just to connect them to the ground electrode system.

Metal sculptures and obelisks (monuments of history and art) should be connected to grounding conductors with an impulse resistance of no more than 20 ohms.

The protection zone is the space around the lightning rod, in which the building or structure is protected from direct lightning strikes. Sufficient reliability of protection of an object from direct lightning strikes will be only if all its parts fall within this zone. The protection zone can be calculated analytically and graphically using formulas and nomograms. Protection zones can be formed by single, double and multiple rod lightning rods, as well as single and double wire lightning rods.

Rice. 4. Protection zone of four lightning rods in the plan

The height of lightning rods is determined by the nomogram quite accurately and does not require mathematical calculations. For example, to find the height of a double wire lightning rod in Fig. Figure 5 shows a nomogram constructed in such a way that the height of the lightning rods h is determined depending on the distance between the lightning rods a and on the value h0, which is the smallest height of the protection zone between two lightning rods (the height of the protected building) - r
The resulting height of the lightning rod supports must be increased by the height of the sling, depending on the span length. The nomograms given in SN 305-69 can also determine the height of single and double rod lightning rods, as well as single and double wire lightning rods up to 60 m high.

Protection against the drift of high potentials (atmospheric surges) is arranged as follows. On the external wires of power lines with a voltage of up to 1000 V, an overvoltage occurs from lightning strikes, and from the introduction of high potentials through the wires into buildings, fires can occur, accidents with people and animals can occur. This can be prevented by installing arresters, spark gaps (5-8 mm) on the lines or by grounding the hooks and pins of insulators of phase wires and wires of radio broadcasting, telephone and other networks. Such protection is mandatory for schools, nurseries, clubs, hospitals and other buildings with large crowds. Hooks on the power poles must be grounded with a down conductor made of wire with a diameter of 5-6 mm, wound around the hooks, and by connecting the neutral wire to the grounding descent with tinned bolt clamps.

If the inputs go to auxiliary premises (warehouses, sheds, etc.), then protection on the supports should be performed for every 5 inputs to consumers, alternating them with unprotected supports. The distance between protected supports should not exceed 200 m (5-6 spans). Entry into the building can be made from an unprotected support, provided that it will be at a distance of no more than 30 m from the protected support.

These protective measures may not be taken if the low voltage network is shielded from lightning strikes by tall trees, buildings, etc., or is located in areas not subject to lightning strikes. The possibility of refusing to perform the specified protection in each individual case should be decided by the operating or design organizations together with representatives of energy supervision organizations. To prevent the introduction of high potentials by radio antennas, it is necessary to lay a current conductor along each rack with one end connected to the ground electrode, and the other end located 10-12 mm from the antenna cable.

Protection of residential and public buildings from the secondary effects of lightning is not required.