- How to position the grounding elements
- Down conductor
- Rod lightning rod
- Checking and monitoring the lightning protection system performance
- Overvoltage protection
- House electrical network audit
- Home protection (class B)
- Line protection (class C)
- Device protection (class D)
The article discusses the critical moments of organizing lightning protection with your own hands, which require special attention. It will be useful to know about them even if the lightning protection is done by third-party specialists.
To protect ourselves from the electrical discharge, which is lightning, we need to solve two problems. The first is to catch such a discharge. And second, send him to a safe place at home. This safe place is ground. We will start with him.
The photo shows perhaps the most popular grounding design for a small building. This design has three grounding conductors, which are located at the corners of an equilateral triangle. In fact, this is not a dogma. And the number of grounding conductors can be different, and their relative position too. The most important thing is that such a design provides reliable grounding. The most important grounding parameters are defined by such documents as PUE (Electrical Installation Rules, Chapter 1.7) and GOSTs (GOST 12.1.030-81 “Electrical safety. Protective grounding. Zeroing”, GOST R 50571.10-96 Part 5. Chapter 54. “Grounding devices and protective conductors “).
The main parameter that speaks about the ability of grounding to provide protection is the resistance, which should not be more than 4 ohms. You can find grounding structures that consist of only one grounding element. True, the deepening of such a conductor is usually at least 30 m, which is impossible to implement without special equipment on the site of a country house. Therefore, instead of one grounding element, several are taken. The number of elements and their depth are determined by specific conditions.
Based on the average conditions of our country, three grounding elements are usually used, which must be buried 3-5 m. It is worth noting that after installing such a structure, it is necessary to measure the resistance. If it is less than 4 ohms, then everything is fine. If it is more, then there is no need to be upset. One or more additional elements can be added to reduce resistance.
How to position the grounding elements
There is a simple rule that says that the distance between the grounding elements should be no less than twice the depth to which they are driven. This is the reason for the popularity of the equilateral triangle, this is the most compact accommodation option. In fact, if you comply with the requirement for the distance between grounding elements, then they can even be placed in a line.
The next most important issue is the choice of material. In principle, as logic suggests, you can use any conductor. However, we should consider not only the electrical parameters, but also how this material will behave in terms of reliability and safety. There are only three materials in PES: black steel, galvanized steel and copper. Therefore, it is better when choosing to limit yourself to them, and not take the risks of experimenters.
Depending on the material chosen, you must adhere to the minimum cross-sectional area requirements. So, for round black steel, the diameter should be at least 16 mm, for galvanized steel and copper – 12 mm. It is possible to use not only round grounding elements. You can take rectangular or even a corner. It is interesting that in the document the angle is indicated only for black steel. Black Steel Restrictions – 100mm Cross Section2 with a wall thickness of 4 mm. For galvanized steel 75 mm2 at 3 mm, and for copper 50 mm2 at 2 mm respectively.
When choosing a material, cost, availability and durability are usually evaluated. In terms of durability, it is not recommended to use fittings. The fact is that the upper layer of the reinforcement is hardened, which affects the electrical parameters. In addition, the reinforcement rusts faster. There is one more misconception. Now there are many means of protecting ferrous metals from corrosion. Therefore, it may be tempting to treat the grounding elements with such protection. It is forbidden to do this for a simple reason – such grounding will not work, but with this coating we isolate the grounding elements from the soil.
Having decided on the material, another question arises, how to correctly connect the individual grounding elements?
The connection must be reliable, last more than one year. In general, there is no single ideal solution. Welding is usually used for black steel. If you make a bolted connection, then each element will corrode, and the likelihood of a violation of conductivity only increases. True, the welded seam becomes the most vulnerable point in terms of corrosion. It is quite possible to treat it with a protective compound, this will not affect the resistance of the entire system.
Do not weld galvanized steel. At the seam, the protective layer will be broken. On the other hand, if you use special connectors, which are made of galvanized steel, then the connection will be protected from corrosion, which means that the reliability of operation will be ensured. They do the same with copper elements. There are also soldering technologies, but they are extremely rare and expensive. It is worth mentioning that stainless steel can also be used. It is also better not to weld it, but to use a bolted connection. And it should be noted that this material is not considered in the PES..
The material was selected, the connections were determined, you can proceed with the installation. You need to start with the markup. Choosing a place to place the grounding elements. Here you need to remember that the nearest grounding element must be at least 1 m from the foundation. It is also not necessary further, we still have to connect the grounding with the down conductor. In the places where the grounding elements are located, we dig holes 0.5–1 m deep, then we connect these holes with ditches of the same depth. Grounding elements approximately 3 m long can be hammered in with a sledgehammer. However, it all depends on the type of soil..
Next, we connect the vertical elements to each other. For connection, tape is usually used, just do not forget about the requirement for cross-sectional area and plate thickness. After the grounding assembly is completed, you need to check its integrity and organize a reliable connection with the down conductor. Then you need to cover it with earth, which it is desirable to compact.
Yes, before backfilling, it would be nice to measure the resistance. We’ll talk about how to do this below. In the meantime, remember that if the resistance is more than 4 ohms, you need to think about where to place another grounding element.
At first glance, the element is simple, but it is entrusted with the solution of the most important task – the delivery of an electric discharge from the lightning rod to grounding. The down conductor must be reliable and safe. Reliable – this means that when an electric current passes, it will not collapse, but safe – when an electric current passes, it will not harm both the house itself and the equipment that is placed in it. It is not difficult to make such a down conductor, but for this it is necessary to follow certain rules.
Let’s start with the material from which the down conductors can be made. The use of steel, copper and aluminum is permitted. The most commonly used round bar or wire. The cross-section of such a down conductor should not be less: for copper – 16 mm, for aluminum – 25 mm, for steel – 50 mm. Pay attention to aluminum. Direct bonding of copper and aluminum is not allowed. Therefore, it is better not to use them. And if you cannot do without it, then such a connection should be made through bolts made of neutral material. It can be noted that there are no restrictions on the use of steel. It is recommended to use galvanized steel to protect the down conductor from corrosion.
A down conductor is laid along the shortest distance between the lightning rod and grounding, horizontal or vertical straight lines. The number of connections in the down conductor must be minimized. And if such connections are necessary, then they must be reliable. Welding, brazing or bolting allowed.
The down conductor is attached directly to the walls. If they are made of non-combustible material, then the placement of down conductors is allowed not only on the wall, but also in the wall. If the wall is made of a combustible material, then there is a danger of fire; during the passage of an electric discharge, the down conductor can heat up to a dangerous temperature. Therefore, in the case of combustible materials, the down conductor is placed at a distance of at least 10 cm from the wall surface. Place down conductors away from windows and doors. If this is not possible for some reason, then a down conductor in high-voltage insulation should be used in this area. Do not place down conductors in downpipes.
The number of down conductors depends on the design of the protected object, the shape and size of the country house, and the required degree of protection. With the highest protection degree I, the average distance between the down conductors should be 10 m. With protection class IV, the average distance is 25 m. Several down conductors are parallel electrical connections, which means that the current flowing through each conductor will be less. As a result, a decrease in the heating of such a conductor during the passage of an electrical discharge, which reduces the risk of fire.
The presence of several down conductors also reduces another harmful effect of lightning. When an electric discharge passes through the down conductor, a strong electric field arises, which will cause an induced overvoltage in the networks and devices located in the house. It is clear that a decrease in the current in the conductor also reduces the strength of the electric field.
The rules allow the use of building elements as down conductors. It can be a metal frame of a building, other metal elements. Even the reinforcement of a building or a metal facade covering. The main thing is that the electrical continuity between the elements is reliable and durable. So, for example, for reinforcement it is considered sufficient if 50% of all horizontal and vertical bars are welded. The thickness of the facade coating elements must be at least 0.5 mm. Using only natural down conductors can be risky, but in combination with an equipped separate down conductor, you can get several down conductors at once, and therefore the benefits discussed above.
As down conductors, as well as grounding elements, it is impossible to use pipelines through which flammable substances are transported. In a country house, these are gas pipes and sewerage, since methane is released during the decomposition of feces and organic waste.
Rod lightning rod
Lightning rods can be purchased ready-made, or you can make yourself. The sizes and designs of rod lightning rods can be different. Thus, the length of finished devices is usually 2.5–15 m. It is important that the top of the peak of the air terminal is above the highest point of the structure. Additional masts can be used. The shape of the bar is not very important, the main thing is that the cross-sectional area corresponds to the norms. Different materials require a different minimum: copper – 35 mm2, aluminum – 70 mm2 and steel – 50 mm2.
It is believed that the thinner the tip of the air terminal lance is sharpened, the more efficiently it will work. On the other hand, if struck by lightning, a too thin tip will burn or shatter. And it will be much more susceptible to oxidative processes. Therefore, here you need to find a middle ground.
The lightning rod protects some space, which can be estimated as follows. We draw a straight line from the end of the air terminal to the ground, while the angle between the straight line and the air terminal is taken equal to 45 degrees. Taking a straight line as a generator, we build a protective cone. If the structure lies entirely inside this cone, then the house will be considered protected. If its individual parts protrude beyond the cone, then the protection will be insufficient, it is necessary to install an additional rod lightning rod. We build a new protective cone around it. If both cones cover a building, then the house is protected. If not, then we choose a place for one more rod lightning rod. We do this until the house is protected..
Checking and monitoring the lightning protection system performance
We organized grounding, installed a lightning rod, connected them with down conductors, the installation is finished. Now we need to check if our system will work. The electrical connection of individual elements and their connections can be checked with a conventional tester. But the grounding resistance cannot be checked with a simple tester..
Specialists can be invited to measure resistance. You can try to do it yourself, only for this you need a special device and a pair of additional electrodes. We will consider how to measure resistance, using the example of using the M-416 device, which is quite popular and easy to use..
Grounding meter М-416
Additional electrodes are usually supplied with the device. We arrange them in accordance with the scheme. Before measuring, the electrodes must be buried approximately 0.5 m.
Ground resistance measurement circuit: 1 – ground loop, 2 – ground level
Lightning protection requires regular monitoring. It is required to check its electrical integrity and monitor the grounding resistance. It is best to do this when the climatic conditions are the least favorable. The resistance will be maximum in two cases: in summer, when the warm dry weather was long, and in winter, in the coldest period. At this time, the level of soil moisture is minimal, respectively, the grounding resistance is maximum.
If the check shows that everything is normal, then we can assume that the external lightning protection is over. But this is only half the battle. It is also necessary to provide internal protection, which is called overvoltage protection..
There is no complete protection against thunderstorms. But in order to protect as much as possible from its effects, in addition to external protection, internal.
Earlier, we have already considered the case when an induced overvoltage may occur in home networks, which is caused by lightning that has hit the lightning rod. We even found a way to reduce the harmful effects. In fact, this is a rare case. More often, lightning affects the networks without even getting into the lightning rod. A lightning strike into a line that supplies electricity to a home can have tragic consequences, even if it happened a few kilometers from the house. It is from such an impact that we will try to protect ourselves..
House electrical network audit
The first thing to do is to audit the existing electrical network. The fact is that protection will be effective only when the internal electrical network is done correctly. Let’s start with the simplest. Let’s take the socket out of the installation box and see how many wires are connected to it. If there are two, then the network requires deep modernization. The thing is that the correct modern electrical network is three-wire: one wire for the phase, the second for the zero working, and the third for the zero protective. If only two wires are connected to the outlet, then this means that there is simply no zero protective.
There is a common and harmful misconception. An inexperienced electrician can make a discovery for himself – realizing that the working zero and the protective zero are still connected on the switchboard, it means that you can save money. From the point of view of the electrical circuit, nothing will change if the working and protective zeros are connected directly to the outlet. And even demanding household appliances that check for the presence of a protective zero will work in this case..
In old electrical installations, a protective zero was not provided; this situation can be considered a historical heritage. And when plugs with three contacts appeared, some electricians began to use this trick. In fact, such a decision is simply pointless. The main task of the protective zero is to protect against overvoltage and electric shock in the event of a worker failure. It is clear that if you short-circuit in the outlet, then there will be no protection. Therefore, it is necessary to check the input and metering board (input distribution device, ASU). Even with a single-phase connection, when there are only two wires at the input, it is already necessary to connect a protective zero at the input board. And from this shield, wire a separate protective zero, then we will get rid of an unreliable inheritance.
The next step in preparing the internal network will be to check, and if necessary, the organization of the potential equalization system. In general, potential equalization minimizes the harmful effects of leakage currents. Even under the most ordinary conditions, leakage currents have negative consequences. This is an electric shock, and accelerated corrosion of wires, and a possible overvoltage when the working zero burns out. In the case of overvoltage from lightning, the consequences can be even worse..
The regulatory documents define the procedure for constructing a potential equalization system. We have to connect this ground to the main ground of the house through the equipotential bonding system. This is done in the ASU shield, usually even before the electricity meter.
After such modernization, you can start organizing effective internal protection against surge overvoltage..
Home protection (class B)
The purpose of organizing overvoltage protection at this level is clear, it is necessary to protect the entire household electrical installation from direct lightning strikes into a building or power transmission line, as well as from induced overvoltage caused by such strikes. A protective device is installed in the ASU shield up to the electricity meter. Arresters are the most commonly used, although varistors can also be used. Most importantly, they meet the requirements for class B equipment.
Class B arrester
The main parameters are indicated on the body of the device. For such devices, the transmitted impulse current should be at least 10 kA, and the short-term one can reach 50 kA, the maximum voltage should be 2.0-2.5 kV.
Devices can be single-channel, as shown in the photo. This will be enough for a single-phase input. With three-phase input, it is more convenient to use three-channel devices.
A protective device is not installed between the working and protective zero at this level. The enclosure is designed to fit on a DIN rail. Material and construction requirement – fire and sparking outside the device housing must be excluded. A short circuit is not allowed even if the device fails.
Line protection (class C)
Devices of this level cannot protect against direct lightning strikes. They are designed for residual overvoltage, which remains after passing through the arrester at the input. Such a device is usually installed already in distribution boards. If there are several of them, for example, on each floor, then protective devices can be installed in each floor panel independently. At this level, it is better to use four channel devices. The fourth channel is used to set between working and protective zeros..
Arresters can be used at this level, although varistors are more commonly used. Usually their parameters are sufficient. For such devices, the transmitted pulse current must be at least 10 kA, and the short-term one can reach 40 kA, the maximum voltage must be 1.3 kV. Other requirements are similar to those of class B.
For the line protection to work correctly, the distance along the cable from the devices of the previous level must be at least 7-10 m, which provides a sufficient level of delay. In a small country house, a situation may occur that the distance will be less. Therefore, it is required to organize an artificial delay line, which is easy to do by installing a choke with an inductance of at least 12 μH. It is clear that a choke must be installed on each channel.
Device protection (class D)
This is the last layer of protection. Not required for all devices. For most, the two previous levels will be sufficient. Nevertheless, for the protection of some particularly sensitive and expensive devices, such protection is still advisable. Protective devices can be built into sockets, and autonomous.
Category D protective device
The device shown in the photo is connected directly to the outlet, and only then the device that requires protection is connected. They can be combined, in addition to overvoltage protection in the electrical network, they can additionally provide protection for low-current networks. The device shown in the photo has the ability to protect your home computer network.
By implementing external protection and overvoltage protection in a country house, we get the highest level of protection against thunderstorms currently available..