Combining lightning protection and grounding loop. Instructions: grounding and lightning protection for a private house, dacha, cottage
The lightning protection circuit is complex system protecting an object from direct lightning strikes: lightning rod, down conductor, grounding. The classic scheme, proposed by Benjamin Franklin back in 1752, underlies all modern systems lightning protection. Proven technology combined with the latest equipment, professional design and installation provide almost one hundred percent protection against lightning damage!
Lightning protection circuit for buildings and structures
Lightning rods
- Rod lightning rod. Metal rods are installed on the roof or at the highest points. To increase the height of the structure, special metal masts are used. For large objects, it is recommended to install several free-standing rods around the perimeter with autonomous down conductors.
- Cable lightning rod. Lightning strikes a cable stretched between supports. The technology is suitable for extended objects. A typical example is power lines, which are protected with cable lightning rods.
- Lightning protection mesh. The system is mainly used on flat roofs: arranged throughout the entire area metal grid in increments of up to 5x5 m. It is worth noting that the mesh does not protect protruding objects, such as antennas or chimneys. That is why rods are also included in the lightning protection circuit, including them in a common circuit.
In addition to classical solutions, active lightning rods are used. The devices ionize the air and provoke a lightning strike. Thanks to this, it is possible to reduce the number of lightning rods and the overall height of the lightning protection circuit.
Down conductors
An aluminum or steel conductor, the main task of which is to transmit current from the lightning rod to the ground electrode. As a rule, external down conductors are installed on buildings, but in some cases, according to the RD instructions, the use of building structures, for example, reinforcement in reinforced concrete blocks. However, this is unacceptable in the presence of highly sensitive electronics: the electromagnetic field created during the passage of a discharge can damage the equipment.
A conductor with a cross section of 6 mm is used for the current conductor; all connections are welded. In places where human contact is possible, the cable must be insulated. In addition, there must be direct access to the down conductor for regular inspection.
Grounding
So, the lightning rod received the discharge and transmitted it along the down conductor to the ground electrode or ground loop - several vertical electrodes installed in the ground and connected to each other by a horizontal conductor. The sole purpose of a grounding device is to dissipate the resulting current into the ground. To save space, the contour is usually formed around the perimeter of the object, but no closer than 1 m to the foundation. The RD instruction requires the presence of at least 3 electrodes in the circuit, however, modern technologies offer the most effective solution: installation of a composite depth electrode. Thanks to immersion to a depth of up to 30 meters, installing one ground electrode is sufficient to achieve the required resistance threshold.
Calculation of lightning protection circuit
Correctly calculating and designing lightning protection are key tasks to ensure the safety of a building from direct lightning strikes. For complex objects, as well as systems exceeding 150 m in height, the calculation is performed using special computer programs. For all other buildings and structures, instructions SO 153-34.21.122-2003 provide standard formulas for calculations.
The protection zone for a circuit with rod lightning rods is a cone in which the highest point coincides with the top of the lightning rod. The protected object must fit completely within the protective cone. Thus, the protection zone can be increased by raising the lightning rod or installing additional rods.
The contour of cable lightning protection is calculated using a similar principle. In this case, a protective trapezoid is obtained, the height of which is the distance between the cable and the ground.
Ground loop resistance
Grounding resistance is measured in Ohms, and ideally should be equal to 0. However, in practice, the value is unattainable, therefore the maximum threshold is set for lightning protection - no more than 10 Ohms. However, the value depends on the soil resistivity, so for sandy soils, where this parameter reaches 500 Ohm/m, the resistance increases to 40 Ohms.
Combining the grounding loop and lightning protection
In accordance with paragraph 1.7.55 of the PUE for equipment and lightning protection of buildings of categories II and III, in most cases, general outline grounding. However, it is necessary to distinguish between types of grounding:
- Protective - for the electrical safety of equipment.
- Functional - necessary condition for the correct operation of special equipment.
It is prohibited to combine functional grounding with a protective or lightning rod grounding conductor: there is a risk of high potentials and failure of sensitive equipment.
In this case, you can combine the grounding for the lightning rod and the protection of electrical equipment or arrange it separately, but connect it to each other through a special clamp for potential equalization.
Designing lightning protection is a responsible and complex task. Trust the professionals to protect your home or office, contact the experienced specialists of our company! You can get advice on the website or by phone.
Here again we have to omit Instruction SO-153-34.21.122-2003, which does not contain any specific requirements for grounding lightning rods. Instruction RD 34.21.122-87 formally formulates the requirements, but they relate not to the value of grounding resistance, but to the design of grounding devices. For free-standing lightning rods we are talking about the foundations of lightning rod supports or a special grounding conductor, the minimum dimensions of which are shown in Fig. 7.
Figure 7. Minimum dimensions of a grounding conductor from horizontal stripe and three vertical rod electrodes according to RD 34.21.122-87
The standard does not contain any instructions on changing the size of the electrodes depending on the soil resistivity. This means that, according to the compilers standard design recognized as suitable for any soil. How much its grounding resistance R gr will change can be judged from the calculated data in Fig. 8.
Figure 8. Calculated value of the grounding resistance of a typical ground electrode from Instruction RD 34.21.122-87
A change in the value of R gr within almost 2 orders of magnitude can hardly be regarded as normalization. In fact, the standard does not contain any specific requirements for the value of grounding resistance, and this issue certainly deserves special consideration.
The Transneft JSC standard surprised us with a table of normalized grounding resistance values for lightning rods (Fig. 9), which the compilers completely copied from the latest edition of the PUE, where it applies to grounding conductors for overhead line supports of 110 kV and above. The stringent requirements of the PUE are quite understandable, since the grounding resistance of the overhead line support largely determines the magnitude of the lightning overvoltage on the linear insulation. It is impossible to find out the reasons for transferring these requirements to the grounding of lightning rods, especially since in high-resistivity soils they generally cannot be implemented using any reasonable designs. To demonstrate this, in Fig. Figure 10 shows the results of calculating a lightning rod ground electrode of an absolutely fantastic design. It represents completely metal structure square section, the side length of which is indicated on the x-axis. Two options have been calculated - with a depth of placement in the soil of 3 and 10 m. It is easy to verify that in soil with a resistivity ρ = 5000 Ohm m, the normalized value of 30 Ohm (R З /ρ = 0.006 m -1) will require filling the vicinity of the lightning rod foundation with metal with more than 50x50 m. The situation with an extended ground electrode is no better. Under the same conditions, to ensure the required grounding resistance, a horizontal bus more than 450 m long is needed.
| Equivalent specific | Maximum allowable resistance |
| More than 100 to 500 | |
| More than 500 to 1000 | |
| More than 1000 to 5000 | |
Table 9
Figure 10. To assess the possibilities of meeting the requirements of the Transneft standard using a concentrated grounding device
The requirements of the Gazprom standard are extremely specific. The grounding resistance of a free-standing lightning rod for protection levels I and II should be equal to 10 Ohms in soils with ρ ≤ 500 Ohm m. In higher-resistivity soils, it is allowed to use ground electrodes, the resistance of which is determined as
Recognizing the difficulty of producing such a relatively low ground resistance, the standard recommends chemical treatment or partial replacement of the ground. An assessment of the volume of recommended work in specific conditions deserves attention. It is easy to perform for the simplest situation, focusing on a hemispherical grounding electrode, the potential of which in a two-layer soil (regardless of what was done - chemistry or mechanical replacement of the soil) according to Fig. 11 is equal
Figure 11. To assess the grounding resistance in two-layer soil
Where exact value ground resistance is defined as
In the extreme case where chemical treatment or soil replacement has proven so effective that it resistivity dropped to almost zero
The expression allows us to estimate the processing radius r 1 from below. In the example under consideration, it turns out to be approximately 40 m, which corresponds to a soil volume of about 134,000 m 3. The obtained value makes us think very seriously about the reality of the planned operation.
Figure 12. Grounding resistance of a two-beam horizontal ground electrode depending on the thickness of the top treated soil layer
An assessment leads to a similar result for any other practically significant configuration of grounding electrodes, for example, for a two-beam grounding system made of horizontal busbars 20 m long. The calculated dependence in Fig. 12 allows us to evaluate how the grounding resistance of such a structure changes with variations in the thickness of the upper low-resistivity layer of the replaced soil. The required grounding resistance of 20 Ohms is obtained here with a thickness of the treated (or replaced) layer of 2.5 m. It is important to understand at what distance from the ground electrode the processing can be stopped. The indicator is the potential on the earth's surface U(r). A change in resistivity will cease to affect the result where the potential U(r) becomes much less than the potential of the grounding electrode U З = U(r 0).
2.2. For what purpose is a lightning rod grounded?
Please do not consider the section title trivial. Lightning rods have always been grounded since their invention, otherwise how could they conduct lightning current into the ground. Modern manuals say that grounding resistance should be provided safe drainage of lightning current. What danger and safety are we talking about? There is no excuse for this with platitudes. It’s probably worth remembering once again about overhead power lines. There, the grounding resistance determines the resistive component of lightning overvoltages that act on a string of insulators.
Lightning rods have nothing like this. Their lightning rod “without problems” accepts the potential of the grounding electrodes. The presence of finite grounding resistance does not in any way affect the ability of the lightning rod to attract lightning. The laboratory has repeatedly tried to monitor the influence of grounding resistance on this process, and each time to no avail. The explanation here is quite simple and obvious. Lightning never strikes a lightning rod. It is met and attracted to itself by the plasma channel of the counter discharge, which starts from the top of the lightning rod at electric field thundercloud and the charge of already forming lightning. This channel (it is called a counter leader) develops at a current of no more than tens of amperes. The voltage drop from such a weak current across the grounding resistance of the lightning rod is of little significance compared to the potential of the order of 10 7 -10 8 V, which is carried by lightning from a thundercloud. Indeed, with a grounding resistance of 10, 20, 100 or 200 Ohms, the voltage on the ground electrode from a current of ~ 10 A will still not exceed even 10 4 V - a value negligible compared to what lightning has.
A separate lightning rod, as is known, is used for the sole purpose of eliminating the spread of lightning current through the metal structures of the protected object. It is for this purpose that very specific distances from the lightning rod to the object by air and by ground are selected. Let's assume that they are chosen correctly and really exclude spark overlap. Nevertheless, the current enters the object’s grounding electrode and does so in a fairly significant proportion, especially when the function of its grounding is performed by the foundation of the protected structure, which is quite large in area. Calculated data in Fig. 14 show this share depending on the distance between the ground electrodes. At the lightning rod, it is made in accordance with the requirements of Instruction RD 34.21.122-87 in the form of a horizontal strip 10 m long with 3 vertical rods of 3 m each; the foundation of the object has dimensions of 50x50 m and is buried 3 m. Computer calculations were performed for homogeneous soil and for the case when the surface layer of the main soil to a depth of 2.5 m is replaced by a highly conductive one with a resistivity 50 times less. It is easy to verify that the insulation distance of 5 m, prescribed by the Transneft JSC standard, does little to prevent lightning current from penetrating the object through the ground, especially if it upper layer replaced or chemically treated. Even at a distance of 15 m, normalized by the Gazprom OJSC standard, the current in the facility’s ground electrode exceeds 50%.
Figure 14. The fraction of lightning current that penetrated into the object’s grounding electrode through the conductive connection with the lightning rod’s grounding electrode, depending on the distance between them
Here it is necessary to emphasize once again that any treatment of the top layer of soil, which reduces the grounding resistance, not only does not reduce the conductive connection between the lightning rod and the object, but significantly strengthens it, thereby increasing the share of the lightning current branched into the object.
It's time to once again raise the question of the goal of reducing grounding resistance. There remain two untouched aspects of the problem - the formation of spark channels and step voltage. The first question will be discussed below in a special section. As for the step voltage, it certainly depends on the design of the lightning rod grounding conductor and its grounding resistance. Calculation curves in Fig. Figure 15 demonstrates the dynamics of a decrease in step voltage with distance from a typical lightning rod ground electrode, prescribed by Instruction RD 34.21.122-87 (see explanations to Fig. 14).
2.3. How to design
The section again sets the task of meeting the requirements regulatory documents without unjustified material costs. This is all the more important because the quality external lightning protection The value of the grounding resistance of the lightning rod has little effect. In any case, it is not directly related to the dangerous effects of lightning that could lead to a catastrophic situation at a tank farm or any other hydrocarbon fuel processing facility. Most importantly, I would really like to avoid expensive chemical treatment or replacement of large volumes of soil and, without them, meet the requirements of industry standards for lightning protection.
It is advisable to create a ground electrode for each lightning rod separately only in soils with low resistivity, where even a standard design from RD 34.21.122-87 turns out to be quite capable. For example, with the recommended horizontal bus length of 12 m and 3 vertical rods of 5 m each, the grounding resistance in the soil with resistivity ρ is equal to
This means that at ρ ≤ 300 Ohm m the calculated value will not exceed 20 Ohm. With higher soil resistivity, 4 mutually perpendicular beams provide a good result. With a length of 20 m, each grounding resistance is equal to
and the installation of 5-meter vertical rods at the ends of each of the beams reduces this value to
The problem becomes serious when the soil resistivity significantly exceeds 1000 Ohm*m. Here, attention is drawn to the organization of a single grounding loop for all individual lightning rods. It is worth turning to Fig. again. 4, where protection is demonstrated tank farm 3 cables 100 m long, with a distance between parallel cables of 50 m. The combination of their supports with horizontal tires forms a grounding loop with two cells 100x50 m. Its grounding resistance when laying tires to a depth of 0.7 m ensures
which makes it possible to solve the problem in soil with a resistivity of up to 3000 Ohm*m, even following the requirements of the Gazprom standard. It is appropriate to note that the additional device of a local grounding conductor at each of the lightning rods has almost no effect on the grounding resistance of the formed circuit as a whole. Thus, the use of a foundation rack with metal reinforcement 5 m long and an equivalent radius of 0.2 m (R gr ≈ 0.1ρ [Ohm]) in a system of 6 racks as a local grounding conductor for each lightning rod reduced the total resistance of the grounding loop by only 6%. The reason for such a weak influence lies in the effective shielding of the rods by extended horizontal buses. By extending the horizontal busbars connecting the supports of lightning rods, it is possible to achieve a grounding resistance of about 20 Ohms even in soil with a resistivity of 5000 Ohms.
The reader has the right to interrupt the description of such rosy prospects, recalling that a long bus slowly enters the process of spreading pulse current due to its inductance. There is nothing to object to this. But at least two circumstances still act in favor of the proposed solution. Firstly, none of the mentioned standards require any specific values of pulsed grounding resistance, and secondly, in high-resistivity soils, the rate of penetration of pulsed current into the grounding bus is quite high and therefore the current value of grounding resistance R gr (t) = U gr (t)/i M (t) quickly takes on a steady value controlled regulatory requirements. As an example in Fig. Figure 16 shows the calculated dynamics of changes in the grounding resistance of a 200 m long bus between the lightning rod supports. It is accepted that the soil resistivity is 5000 Ohm*m, and its relative dielectric constant is 5 (taking this parameter into account is important when capacitive leakage into the soil is comparable to conductive leakage).
E. M. Bazelyan, Doctor of Technical Sciences, Professor
Energy Institute named after G.M. Krzhizhanovsky, Moscow
Useful materials:
Dear readers! The instructions are voluminous, so for your convenience we have made navigation through its sections (see below). If you have questions about the selection, calculations and design of grounding and lightning protection systems, please write or call, they will be happy to help!
Introduction - about the role of grounding in a private house
The house has just been built or purchased - in front of you is exactly the cherished home that you recently saw in a sketch or photograph in an ad. Or maybe you live in own home This is not the first year, and every corner in it has become native. Own yours personal home wonderful, but along with the feeling of freedom, in addition you get a number of responsibilities. And now we will not talk about household chores, we will talk about such a necessity as grounding for a private home. Any a private house includes the following systems: electrical network, water supply and sewerage, gas or electrical system heating Additionally, a security and alarm system, ventilation, and a “ smart House"etc. Thanks to these elements, a private home becomes a comfortable living environment modern man. But it really comes to life thanks to electrical energy, which operates the equipment of all the above systems.
The need for grounding
Unfortunately, electricity also has reverse side. All equipment has a service life, each device has a certain reliability built into it, so they will not work forever. In addition, during the design or installation of the house itself, electrical, communications or equipment, errors can also be made that can affect electrical safety. For these reasons, some electrical network may be damaged. The nature of accidents can be different: short circuits can occur that turn off circuit breakers, and breakdowns on the body may occur. The difficulty is that the breakdown problem is hidden. The wiring has been damaged, so the housing electric stove was under tension. If grounding measures are incorrect, the damage will not manifest itself until a person touches the stove and receives an electric shock. Electrocution will occur due to the fact that the current seeks a path into the ground, and the only suitable conductor is the human body. This cannot be allowed.
Such damage poses the greatest threat to human safety, because in order to detect it early, and therefore to protect against it, it is imperative to have grounding. This article discusses what actions need to be taken to organize grounding for a private home or cottage.
The need to install grounding in a private house is determined by the grounding system, i.e. the neutral mode of the power source and the method of laying the neutral protective (PE) and neutral working (N) conductors. The type of power supply network - overhead or cable - may also be important. Structural differences in grounding systems allow us to distinguish three options for power supply to a private home:
The main potential equalization system (BPES) combines all large current-carrying parts of the building, which normally do not have electrical potential, into a single circuit with the main grounding bus. Let's consider a graphic example of implementing a control system in an electrical installation of a residential building.
First, let's look at the most progressive approach to electrical power at home - the TN-S system. In this system, the PE and N conductors are separated throughout, and the consumer does not need to install grounding. You just need to connect the PE conductor to the main grounding bus, and then connect the grounding conductors to electrical appliances from it. Such a system is implemented both by cable and overhead line; in the case of the latter, an VLI (insulated overhead line) is laid using self-supporting wires(SIP).
But not everyone has such happiness because the old air lines transmissions use the old grounding system - TN-C. What is its peculiarity? In this case, PE and N along the entire length of the line are laid with one conductor, which combines the functions of both the neutral protective and neutral working conductors - the so-called PEN conductor. If previously it was allowed to use such a system, then with the introduction of the PUE 7th edition in 2002, namely clause 1.7.80, the use of RCDs in the TN-C system was prohibited. Without the use of an RCD, there can be no talk of any electrical safety. It is the RCD that turns off the power if the insulation is damaged as soon as it occurs, and not at the moment when a person touches the emergency device. To comply with everything necessary requirements, the TN-C system must be upgraded to TN-C-S.
In the TN-C-S system, a PEN conductor is also laid along the line. But, now, paragraph 1.7.102 of the PUE 7th ed. says that at the overhead line inputs to electrical installations, repeated grounding of the PEN conductor must be performed. They are carried out, as a rule, at an electrical pole from which the input is made. When re-grounding, the PEN conductor is divided into separate PE and N, which are brought into the house. The re-grounding norm is contained in clause 1.7.103 of the PUE 7th ed. and is 30 Ohm, or 10 Ohm (if there is a gas boiler). If grounding at the pole is not completed, you must contact Energosbyt, in whose department the electric pole, switchboard and entry into the consumer's home, and indicate the violation that must be corrected. If the distribution panel is located in the house, the PEN separation should be done in this panel and the re-grounding should be done near the house.
In this form, TN-C-S is successfully operated, but with some reservations:
- if the condition of the overhead line causes serious concern: the old wires are not in better condition, which creates a risk of breakage or burnout of the PEN conductor. This is fraught with the fact that there will be increased voltage on the grounded housings of electrical appliances, because the current path into the line through the working zero will be interrupted, and the current will return from the bus on which the separation was performed through the neutral protective conductor to the device body;
- If there are no repeated groundings on the line, then there is a danger that the fault current will flow into a single re-grounding, which will also lead to an increase in the voltage on the frame.
In both cases, electrical safety leaves much to be desired. The solution to these problems is the TT system.
In the TT system, the PEN conductor of the line is used as a working zero, and individual grounding is performed separately, which can be installed near the house. Clause 1.7.59 PUE 7th ed. stipulates the case when it is impossible to ensure electrical safety and allows the use of the TT system. An RCD must be installed, and its correct work must be provided by the condition Ra*Ia<=50 В (где Iа - ток срабатывания защитного устройства; Ra - суммарное сопротивление заземлителя). «Инструкция по устройству защитного заземления» 1.03-08 уточняет, что для соблюдения этого условия сопротивление заземляющего устройства должно быть не более 30 Ом, а в грунтах с высоким удельным сопротивлением - не более 300 Ом.
How to ground a house?
The purpose of grounding for a private home is to obtain the required grounding resistance. For this purpose, vertical and horizontal electrodes are used, which together must ensure the necessary spreading of current. Vertical grounding electrodes are suitable for installation in soft soil, while their burial in rocky soil is very difficult. In such soil, horizontal electrodes are suitable.
Protective grounding and lightning protection grounding are carried out in common; one ground electrode will be universal and serve both purposes, this is stated in paragraph 1.7.55 of the PUE 7th ed. Therefore, it will be useful to learn how to unify lightning protection and grounding. To clearly see the installation process of these systems, the description of the grounding process for a private house will be divided into stages.
A separate point should be made about protective grounding in the TN-S system. The starting point for grounding installation will be the type of power system. The differences in power systems were discussed in the previous paragraph, so we know that for the TN-S system there is no need to install grounding, the neutral protective (grounding) conductor comes from the line - you just need to connect it to the main grounding bus, and the house will be grounded. But one cannot say that a house does not need lightning protection. This only means that we, without paying attention to stages 1 and 2, can immediately move on to stages 3-5, see below
TN-C and TT systems always require grounding, so let's move on to the most important thing.
Protective grounding is installed at a pole or at the wall of the house, depending on where the PEN conductor is separated. It is advisable to locate the ground electrode in close proximity to the main ground bus. The only difference between TN-C and TT is that in TN-C the grounding point is tied to the PEN separation point. The grounding resistance in both cases should be no more than 30 Ohms in soil with a resistivity of 100 Ohm*m, for example loam, and 300 Ohms in soil with a resistivity of more than 1000 Ohm*m. The values are the same, although we rely on different standards: for the TN-C system 1.7.103 PUE 7th edition, and for the TT system - on paragraph 1.7.59 of the PUE and 3.4.8. Instructions I 1.03-08. Since there are no differences in the necessary measures, we will consider general solutions for these two systems.
For grounding, it is enough to drive a six-meter vertical electrode.
(click to enlarge)
This grounding turns out to be very compact; it can be installed even in the basement; no regulatory documents contradict this. The necessary actions for grounding are described for soft soil with a resistivity of 100 Ohm*m. If the soil has a higher resistance, additional calculations are required, seek help in calculations and selection of materials.
If a gas boiler is installed in the house, then the gas service may require grounding with a resistance of no more than 10 Ohms, guided by clause 1.7.103 of the PUE 7th ed. This requirement must be reflected in the gasification project.
Then, to achieve the standard, it is necessary to install a 15-meter vertical grounding conductor, which is installed at one point.
(click to enlarge)
It can also be installed at several points, for example, at two or three, then connected with a horizontal electrode in the form of a strip along the wall of the house at a distance of 1 m and at a depth of 0.5-0.7 m. Installation of the ground electrode at several points will also serve the purpose of lightning protection To understand how, let’s move on to its consideration.
Before installing grounding, you need to immediately decide whether the house will be protected from lightning. So, if the configuration of the ground electrode for protective grounding can be any, then the grounding for lightning protection must be of a certain type. At least 2 vertical electrodes 3 meters long are installed, united by a horizontal electrode of such length that there is at least 5 meters between the pins. This requirement is contained in paragraph 2.26 of RD 34.21.122-87. Such grounding should be installed along one of the walls of the house; it will be a kind of connection in the ground of two down conductors lowered from the roof. If there are several down conductors, the correct solution is to lay a grounding loop for the house at a distance of 1 m from the walls at a depth of 0.5-0.7 m, and at the junction with the down conductor, install a vertical electrode 3 m long.
(click to enlarge)
Now it’s time to find out how to make lightning protection for a private home. It consists of two parts: external and internal.
Carried out in accordance with SO 153-34.21.122-2003 “Instructions for the installation of lightning protection of buildings, structures and industrial communications” (hereinafter referred to as SO) and RD 34.21.122-87 “Instructions for the installation of lightning protection of buildings and structures” (hereinafter referred to as RD).
Buildings are protected from lightning strikes using lightning rods. A lightning rod is a device that rises above the protected object, through which the lightning current, bypassing the protected object, is discharged into the ground. It consists of a lightning rod that directly absorbs the lightning discharge, a down conductor and a grounding conductor.
Lightning rods are installed on the roof in such a way that a protection reliability of more than 0.9 CO is ensured, i.e. the probability of a breakthrough through the lightning rod system should be no more than 10%. For more information about what reliability of protection is, read the article “Lightning protection of a private home”. As a rule, they are installed along the edges of the roof ridge if the roof is gable. When the roof is mansard, hipped or even more complex in shape, lightning rods can be attached to chimneys.
All lightning rods are connected to each other by down conductors; the down conductors are connected to a grounding device that we already have.
(click to enlarge)
Installing all these elements will protect the house from lightning, or rather from the danger posed by its direct strike.
Protecting your home from surge voltages is done using an SPD. For their installation, grounding is necessary, because the current is diverted into the ground using neutral protective conductors connected to the contacts of these devices. Installation options depend on the presence or absence of external lightning protection.
- There is external lightning protection
In this case, a classic protective cascade is installed from devices of classes 1, 2 and 3 arranged in series. A class 1 surge protector is mounted at the input and limits the direct lightning strike current. A class 2 surge protector is installed either in the input panel or in the distribution panel, if the house is large and the distance between the panels is more than 10 m. It is designed to protect against induced overvoltages, it limits them to a level of 2500 V. If the house has sensitive electronics, then It is advisable to install a class 3 surge protector that limits overvoltages to a level of 1500 V; most devices can withstand this voltage. A class 3 surge protector is installed directly next to such devices. - There is no external lightning protection
A direct lightning strike into a house is not taken into account, so there is no need for a class 1 SPD. The remaining SPDs are installed in the same way as described in paragraph 1. The choice of SPD also depends on the grounding system, to be sure of the correct choice, contact for help.
The figure shows a house with installed protective grounding, an external lightning protection system and a combined SPD of class 1+2+3, intended for installation in a TT system.
Comprehensive home protection: protective grounding, external lightning protection system and
combined SPD class 1+2+3, intended for installation in a TT system
(click to enlarge)
Enlarged image of a switchboard with an installed surge protector for a home
(click to enlarge)
| No. | Rice | vendor code | Product | Qty |
| Lightning protection system | ||||
| 1 | ZANDZ Lightning rod-mast vertical 4 m (stainless steel) | 2 | ||
| 2 |  | GALMAR Holder for lightning rod - mast ZZ-201-004 to the chimney (stainless steel) | 2 | |
| 3 |  | GALMAR Clamp for lightning rod - mast GL-21105G for down conductors (stainless steel) | 2 | |
| 4 |  | GALMAR Copper-plated steel wire (D8 mm; coil 50 meters) | 1 | |
| 5 | GALMAR Copper-plated steel wire (D8 mm; coil 10 meters) | 1 | ||
| 6 |  | GALMAR Downpipe clamp for down conductor (tinned copper + tinned brass) | 18 | |
| 7 |  | GALMAR Universal roof clamp for down conductor (height up to 15 mm; galvanized steel with painting) | 38 | |
| 8 |  | GALMAR Facade/wall clamp for down conductor with raised surface (height 15 mm; galvanized steel, painted) | 5 | |
| 9 |  | |||
The need to electrically connect the grounding loop of lightning protection installed directly on the building with the grounding loop for electrical installations is prescribed in the current regulatory documents (PUE). We quote verbatim: “Grounding devices for protective grounding of electrical installations of buildings and structures and lightning protection of categories 2 and 3 of these buildings and structures, as a rule, should be common.” The 2nd and 3rd categories are the most common; the 1st category includes explosive objects for which increased lightning protection requirements are imposed. However, the presence of the phrase “as a rule” implies the possibility of exceptions.
Modern office and now residential buildings contain many life support engineering systems. It is difficult to imagine the absence of ventilation systems, fire extinguishing systems, video surveillance, access control, etc. Naturally, the designers of such systems have concerns that “delicate” electronics will fail as a result of lightning. At the same time, some doubts arise among practitioners about the feasibility of connecting the contours of two types of grounding and a desire arises “within the limits of the law” to design electrically unconnected groundings. Is this approach possible and will it actually improve the safety of electronic devices?
Why is it necessary to combine ground loops?
When lightning strikes a lightning rod, a short electrical impulse with a voltage of up to hundreds of kilovolts occurs in the latter. At such a high voltage, a breakdown of the gap between the lightning rod and the metal structures of the house, including electrical cables, may occur. The consequence of this will be the emergence of uncontrolled currents, which can lead to fire, failure of electronics and even destruction of infrastructure elements (for example, plastic water pipes). Experienced electricians say: “Give lightning a way, otherwise it will find it on its own.” This is why electrical grounding is mandatory.
For the same reason, the PUE recommends electrically combining not only the groundings located in the same building, but also the groundings of geographically close objects. This concept refers to objects whose groundings are so close that there is no zone of zero potential between them. The combination of several groundings into one is carried out, in accordance with the standards of PUE-7, clause 1.7.55, by connecting the grounding conductors with at least two electrical conductors. Moreover, conductors can be either natural (for example, metal elements of a building’s structure) or artificial (wires, rigid tires, etc.).
One common or separate grounding devices?
Grounding conductors for electrical installations and lightning protection have different requirements, and this circumstance can cause some problems. A ground electrode for lightning protection must discharge a large electric charge into the ground in a short time. At the same time, according to the “Lightning Protection Instructions RD 34.21.122-87”, the design of the ground electrode is standardized. For a lightning rod, according to this instruction, at least two vertical, or radial horizontal, grounding conductors are required, with the exception of category 1 of lightning protection, when three such pins are needed. That is why the most common grounding option for a lightning rod is two or three pins, each about 3 m long, connected by a metal strip buried at least 50 cm into the ground. When using parts produced by ZANDZ, such a ground electrode is durable and easy to install.
Grounding for electrical installations is a completely different matter. In a normal case, it should not exceed 30 Ohms, and for a number of applications described in departmental instructions, for example, for cellular communication equipment - 4 Ohms or even less. Such grounding electrodes are pins more than 10 m long or even metal plates placed at great depths (up to 40 m), where the soil does not freeze even in winter. It is too expensive to create such a lightning rod with two or more elements buried at tens of meters.
If the soil parameters and resistance requirements allow for a single grounding in the building for lightning rods and grounding of electrical installations, there are no obstacles to doing it. In other cases, various grounding loops are made for the lightning rod and electrical installations, but they must be connected electrically, preferably in the ground. The exception is the use of some special equipment that is particularly sensitive to interference. For example, sound recording equipment. Such equipment requires a separate, so-called technological grounding device, which is directly indicated in the instructions. In this case, a separate grounding device is made, which is connected to the building's potential equalization system through the main grounding bus. And, if such a connection is not provided for in the equipment operating manual, then special measures are taken to prevent people from simultaneously touching the specified equipment and metal parts of the building.
Electrical ground connection
A circuit with several electrically connected grounds ensures that different, sometimes conflicting, requirements for grounding devices are met. According to the PUE, grounding, like many other metal elements of the building, as well as equipment installed in it, must be connected by a potential equalization system. Potential equalization refers to the electrical connection of conductive parts to achieve equal potential. There are main and additional potential equalization systems. Grounding connections are connected to the main potential equalization system, that is, they are connected to each other through the main grounding bus. The wires connecting the grounding to this bus must be connected according to the radial principle, that is, one branch from the specified bus goes to only one ground.
In order to ensure safe operation of the entire system, it is very important to use the most reliable connection between the grounding and the main grounding bus, which will not be destroyed by lightning. To do this, you need to comply with the standards of PUE and GOST R 50571.5.54-2013 “Low-voltage electrical installations. Part 5-54. Grounding devices, protective conductors and protective potential equalization conductors” regarding the cross-section of the potential equalization system wires and their connections to each other.
However, even a very high-quality potential equalization system cannot guarantee the absence of voltage surges in the network when lightning strikes a building. Therefore, along with well-designed grounding loops, surge noise protection devices (SPDs) will save you from problems. Such protection is multi-stage and selective in nature. That is, a set of surge protection devices must be installed at the facility, the selection of elements of which is not an easy task even for an experienced specialist. Fortunately, ready-made SPD kits are available for typical applications.
conclusions
The PUE's recommendation on the electrical connection of all grounding loops in a building is reasonable and, if implemented correctly, not only does not create a danger to complex electronic equipment, but, on the contrary, protects it. In the event that the equipment is sensitive to lightning interference and requires its own separate grounding electrode, a separate process grounding can be installed in accordance with the manual supplied with the equipment. The potential equalization system, which combines disparate grounding loops, must provide a reliable electrical connection and largely determines the overall level of electrical safety at the facility, so special attention should be paid to it.
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Lightning protection and grounding are important elements of a private home. After all, protection from lightning not only prevents the loss of property, but also preserves the life and health of the inhabitants of the home.
The nature of lightning
Clouds are a collection of droplets of water and water vapor in the sky. The large size of clouds determines their location in different temperature zones. Therefore, temperatures in different layers of clouds can vary by 20-30 degrees. For example, while the temperature in the lower layer of a cloud may be -10 °C, in the upper layer it may be below -40 °C. This turns the water and steam into very small pieces of ice. Static electricity occurs due to contacts between crystals. Since the temperatures in different layers of the cloud are different, the electrical charges are also different, and therefore the cloud resembles a layer cake.
The current accumulated by the clouds is enormous. However, electricity is sooner or later discharged externally in the form of lightning, which, in essence, is a short circuit between conductors of different polarities.
Lightning is accompanied by roar, that is, thunder. Rolling thunder occurs as a result of the instantaneous penetration of a heated shaft of lightning through masses of air.
There are three types of lightning:
- directed towards the upper atmospheric layers;
- discharged inside layers with different charges - in one cloud or between neighboring clouds;
- with direction towards the earth's surface.
Since electricity always takes the shortest path, lightning strikes the highest parts of buildings and trees. The latter are natural lightning rods.
What is a lightning rod
A lightning rod is a device through which electricity is diverted to the ground, bypassing the protected object. The lightning rod is always located above the level of the protected object. The lightning protection device is an electrical conductor and, as it were, provokes lightning to strike it. Thus, a short circuit between the cloud and the earth's surface does not occur in an unexpected place, but precisely where it will be neutralized by lightning protection.
There are two types of lightning protection devices:
- Single lightning rods.
- Cable lightning rods, which are several cables stretched between individual lightning rods. This method of lightning protection is typical primarily for high-voltage power lines. In everyday life, such systems are used to protect large areas, where the cable is stretched along the perimeter of the site, or to protect extended buildings.
Lightning protection components
Lightning protection includes:
- lightning rod, which is a thin electrode with a sharp tip (mounted above the structure being protected);
- a current-carrying cable through which the current is carried to ground;
- grounding system.
Lightning rod
This part, as mentioned above, is designed to receive a lightning discharge. The optimal material for the manufacture of an lightning rod (as well as a ground electrode) is copper.
Note! It is not allowed to cover the lightning rod with paints and varnishes, because in this case the device will not be able to perform its function.
To organize lightning protection on the roof of a building, you can install small lightning rods, from half a meter to a meter long, on different sides of the roof and in the center. After this, they need to be combined into a single system and connected to the ground electrode.
The lightning rod can also be installed on the roof of a wooden building, on a chimney, or on a nearby tree. The device is placed on a wooden mast. If the house has a metal roof, directly grounding the roof may be sufficient.
Note! The higher the pantograph is located, the larger the protected area. However, this rule applies up to approximately 15 meters in height. At higher altitudes, the effectiveness of the device decreases.
Down conductor
To create a down conductor you will need a copper or aluminum cable with as large a cross-section as possible. The optimal solution would be a regular twisted aluminum wire used in the installation of overhead power lines. One end of the wire is attached to the lightning rod using couplings, crimp pipes or terminals, and the other end to the ground electrode. The wire must be positioned strictly vertically in order to use the minimum distance between the ground electrode and the lightning rod. The current-carrying cable can be insulated or laid through a specially created channel.
Grounding a private house
Correctly performed grounding is the basis for effective lightning protection of a building. There is a widespread belief that to arrange grounding, a steel rod connected by wire to a lightning rod and inserted into the ground is sufficient. This judgment is incorrect and lightning protection made in this way will not protect against natural disasters.
The instructions for installing grounding networks and lightning protection require strict adherence to a number of recommendations. The installation of grounding conductors is carried out according to the same principle as the grounding loop of a building. The best materials for lightning protection purposes are aluminum, brass, copper and other stainless metals. However, these materials are quite expensive, so steel can also be used. According to technical regulations (SNIP) for the operation of electrical installations and conductive parts, grounding conductors must be tested annually for mechanical damage and corrosion. If the diameter of the system elements has been reduced by more than half, they must be replaced.
You will also need not one, but several metal rods stuck into the ground. Moreover, although the number of rods is a calculated value, it is generally accepted that for a one-story or two-story house 3-4 rods are sufficient. The length of the rods should exceed by approximately 30 centimeters the depth of maximum freezing of the soil.
The rods are joined with an electrical conductor, usually aluminum, copper wire, or tinned steel plate. This creates a closed loop. Externally, the structure will resemble the letter “Ш”, dug into the ground.
Note! Tying the wire rods by hand or with pliers is not allowed. This cannot be done even in household grounding, much less in a lightning protection system.
Connections must be created by welding, using crimp sleeves or rigid twisting, that is, by cold welding of parts. Such connections are reliable, they are not subject to backlash and do not weaken over time. The assembled structure will look approximately as follows.
Important! Grounding for a lightning rod is necessary with a circuit. To do this, the lightning protection circuit is connected to the grounding circuit of the building.
The contours are joined with a steel strip. As a result of the work performed, the overall contour is strengthened, which has a positive effect on the safety of the building.
Ground electrode location
Both the down conductor and the grounding conductor must be located in a place that is inaccessible to children and pets. The ground electrode can be any large metal object, and the larger its contact area with the surface, the more effective it is. A mesh of reinforcement, a cast-iron bathtub, steel bed parts, etc. can be used as grounding conductors.
Water is an excellent conductor of electricity. Based on this, the ground electrode must be installed where the ground is damp. You can artificially moisten the grounding area, for example, by directing water runoff from the roof of the building there.
Note! In houses with running water and a centralized heating system, as well as in buildings connected to underground electrical networks, grounding is already available. Therefore, such objects do not need to install additional lightning rods.
Lightning rod protection zone
To calculate the protection zone, you can use the rule that the zone is close to a cone-like shape with a 45-degree angle at the top. If we are talking about a single cable lightning rod, the protection zone is similar to a prism with three sides, where the cable protrudes as an edge. The probability of a direct lightning strike in such areas is no more than 1%. Thus, if the lightning rod is located, for example, at a 10-meter height, the protective zone on the ground will also have a 10-meter diameter.
There is another way to calculate the protection zone. The formula used here is R = 1.732 h, where R is the diameter of the protective zone above the highest point of the building, h is the height from the highest point of the building to the peak of the lightning rod.
Calculation of protection zone
Thus, if the height of the house is 7 meters, and the upper end of the lightning rod is 3 meters above the highest point of the roof, the diameter of the protection zone will be 5 meters 20 centimeters. The result is a cone with a diameter at the base of 9 meters and a height of 10 meters.
Acceptance of lightning protection systems into operation
Lightning protection devices for construction sites are accepted by a special commission and put into operation by the building owner before the installation of valuable property on the premises. The composition of the acceptance commission is established by the customer of the facility. The acceptance committee consists of specialists in the following areas:
- electrical facilities;
- contractor;
- fire inspection;
The acceptance committee is provided with the following documentation:
- approved projects for creating lightning protection;
- acts for performing hidden work (installation of down conductors and grounding conductors that are inaccessible for visual inspection);
- acts of testing lightning protection devices against secondary effects of lightning and high potentials entering through metal communications (information on grounding resistance for lightning protection, results of monitoring work on installation of devices).
The acceptance committee checks the installation work performed on the arrangement of lightning protection systems.
Acceptance of lightning protection devices in new buildings is carried out using equipment acceptance certificates. The launch of lightning protection devices is carried out after the signing of the approval certificates of the relevant supervisory and control authorities of the state.
Upon completion of acceptance, passports for lightning protection systems and grounding conductor passports are issued, which are kept by the owner of the building or the person responsible for the electrical facilities.
Natural lightning rods
Different trees handle lightning diversion differently. The most suitable trees are birch, spruce and pine. However, in populated areas, birch is more suitable for lightning protection purposes, but people try not to plant conifers in close proximity to buildings, since their wood is more fragile.
The listed tree species have advantages over some other species due to their root system. The best grounding is provided by trees with the most extensive root system located shallow in the ground. It is best if the roots of such trees are partially located on the surface of the soil and fan out to the sides. When it hits a tree, the electric charge instantly reaches the root system and goes into the ground.
Important! Trees should be avoided during a thunderstorm, as the risk of being struck by lightning increases significantly.
Creating a lightning protection device is not very complicated, but requires a basic understanding of physical laws and compliance with technical regulations. If you do not have confidence in your own abilities, it is better to seek help from specialists.