The correct placement of surge arresters in the power line is essential for the correct operation of the designed surge protection system.
As noted earlier, when organizing surge protection systems for power electric power equipment, limiters are mounted in the following places:
- outside the construction site, in lightning protection zone 0B, at the input of power cables to devices (more often these are class II arresters, sometimes class I);
- at the point of transition of power cables through the wall of the building (depending on the level of threat, these are class I or II limiters) - in a cable connection, grounded by the shortest path to the grounding device;
- inside the construction site:
- in local switchboards (depending on the level of threat, these are class II or III arresters);
- close to protected devices (more often these are class III arresters, sometimes - class II, in terms of too low rated current of class III arresters, most often 16 A).
It must be emphasized here that of all the locations of surge arresters proposed in section 443 of IEC 60364-4, the only correct location is in a cable connection, provided that the connection is in the wall of the building to be protected.
Placement of restrictors in the overhead line:
In the case of placing arresters in an overhead line, one should not forget about the possibility of penetration of overvoltage shocks to the power cable on the route "overhead line pole - building", which makes this placement useless.
Placement of restraints inside the building:
1.6. Short circuit resistance
Surge arresters must be protected against the effects of short-circuit current. From its switching circuit (parallel connection with respect to the terminals of the protected circuit), it follows that any action of the surge arrester subsequently causes a short-circuit current to flow in the protected line. For this reason, the manufacturer must state when and which fuse should be used in series with the surge arrester in order to guarantee adequate short-circuit current resistance of the fuse-surge arrester circuit.
When determining the need to use additional protection of the surge suppressor with a fuse connected in series, one should compare the rated currents I F1 of the phase fuses of the protected circuit with the allowable current I DOP that can flow in the surge suppressor circuit (recommended by the manufacturer). Depending on the results of such a comparison, the scheme should be used:
- I F1 ≤ I DOP - without additional protective fuse (fig.1.3.a),
- I F1 > I DOP - containing an additional fuse F2 connected in series with surge arresters (Fig. 1.3.b).
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1.7. Surge arrester connection diagrams
Depending on the grounding system of the power supply network, one of the types of connection of surge arresters, shown in fig. 1.4, 1.5 or 1.6.
In a TT network system, it is possible to use 4 typical surge arresters or a so-called 3+1 system (3 surge arresters + 1 N-PE arrester). Such connection systems concern arresters of classes I and II.
In the case of class I arresters, systems with additional fuses connected in series with the arresters must be used. The use of fuses is not necessary if the relevant conditions described in section 1.6 are met.
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If your home has a lot of expensive household appliances, it is better to take care of organizing a comprehensive protection of the power grid. In this article, we will talk about surge protection devices, why they are needed, what they are and how they are installed.
The nature of surge voltages and their impact on technology
Since childhood, many have been familiar with the fuss of disconnecting household electrical appliances from the network at the first sign of an impending thunderstorm. Today, the electrical equipment of urban networks has become more advanced, which is why many people neglect elementary protection devices. At the same time, the problem has not completely disappeared; household appliances, especially in private homes, are still at risk.
The nature of the occurrence of impulse overvoltages (IP) can be natural and man-made. In the first case, lightning strikes occur due to lightning strikes into overhead power lines, and the distance between the point of impact and consumers at risk can be up to several kilometers. It is also possible to hit radio masts and lightning rods connected to the main ground loop, in which case an induced overvoltage appears in the household network.
1 - remote lightning strike in power lines; 2 - consumers; 3 - ground loop; 4 - close lightning strike in power lines; 5 - direct lightning strike into the lightning rod
Man-made IP are unpredictable, they arise as a result of switching overloads at transformer and distribution substations. With an asymmetric increase in power (only in one phase), a sharp jump in voltage is possible, it is almost impossible to foresee this.
Impulse voltages are very short in time (less than 0.006 s), they appear systematically in the network and most often pass unnoticed by the observer. Household appliances are designed to withstand surges up to 1000 V, these appear most often. At a higher voltage, the failure of power supplies is guaranteed, and insulation breakdown in the wiring of the house is also possible, which leads to multiple short circuits and a fire.
How SPD is arranged and how it works
SPD, depending on the protection class, may have a semiconductor device on varistors, or have a contact arrester. In normal mode, the SPD operates in bypass mode, the current inside it flows through a conductive shunt. The shunt is connected to the protective ground through a varistor or two electrodes with a strictly standardized gap.
During a voltage surge, even a very short one, the current passes through these elements and spreads along the ground or is compensated by a sharp drop in resistance in the phase-to-zero loop (short circuit). After the voltage stabilizes, the arrester loses its capacity, and the device again operates in normal mode.
Thus, the SPD closes the circuit for a while so that the excess voltage can be converted into thermal energy. At the same time, significant currents pass through the device - from tens to hundreds of kiloamperes.
What is the difference between protection classes
Depending on the causes of the occurrence of IP, two characteristics of the increased voltage wave are distinguished: 8/20 and 10/350 microseconds. The first digit is the time during which the IP gains its maximum value, the second is the time it takes to fall to nominal values. As you can see, the second type of overvoltage is more dangerous.
Class I devices are designed to protect against IP with a characteristic of 10/350 µs, most often occurring when lightning strikes in power lines closer than 1500 m to the consumer. The devices are capable of briefly passing through themselves a current from 25 to 100 kA, almost all class I devices are based on arresters.
SPDs of class II are focused on compensation of IP with a characteristic of 8/20 µs, peak current values in them range from 10 to 40 kA.
Protection class III is designed to compensate for surges with current values less than 10 kA with a characteristic IP 8/20 µs. Protection class II and III devices are based on semiconductor elements.
It may seem that it is enough to install only class I devices, as the most powerful ones, but this is not so. The problem is that the higher the lower threshold of the forward current, the less sensitive the SPD. In other words: with short and relatively low IP values, a powerful SPD may not work, and a more sensitive one will not be able to cope with currents of this magnitude.
Protection class III devices are designed to eliminate the lowest SI - only a few thousand volts. They are completely similar in characteristics to protection devices installed by manufacturers in power supplies for household appliances. In case of redundant installation, they are the first to take on the load and prevent SPD operation in devices, the resource of which is limited to 20-30 cycles.
Is there a need for an SPD, risk assessment
A complete list of requirements for the organization of protection against IP is set out in IEC 61643-21, you can determine the mandatory installation according to the IEC 62305-2 standard, according to which a specific assessment of the degree of risk of a lightning strike and the consequences caused by it is established.
In general, when supplying power from overhead power lines, the installation of a class I SPD is almost always preferable, unless a set of measures has been taken to reduce the impact of thunderstorms on the power supply mode: re-grounding of poles, PEN-conductor and metal bearing elements, a lightning rod with a separate potential equalization systems.
An easier way to assess risk is to compare the cost of unprotected appliances and security devices. Even in multi-storey buildings, where overvoltages are very low with a characteristic of 8/20, the risk of insulation breakdown or failure of devices is quite high.
Installation of devices in the main switchboard
Most SPDs are modular and can be mounted on a 35mm DIN rail. The only requirement is that the shield for installing the SPD must have a metal case with a mandatory connection to the protective conductor.
When choosing an SPD, in addition to the main performance characteristics, you should also take into account the rated operating current in bypass mode, it must correspond to the load in your mains. Another parameter is the maximum clamping voltage, it should not be lower than the highest value within the daily fluctuations.
SPDs are connected in series to a single-phase or three-phase supply network, respectively, through a two-pole and four-pole circuit breaker. Its installation is necessary in case of soldering of the spark gap electrodes or breakdown of the varistor, which causes a permanent short circuit. Phases and a protective conductor are connected to the upper terminals of the SPD, and zero to the lower terminals.
SPD connection example: 1 - input; 2 - automatic switch; 3 - SPD; 4 - ground bus; 5 - ground loop; 6 - electricity meter; 7 - differential machine; 8 - to automatic machines of consumers
When installing several protective devices with different protection classes, they must be coordinated using special chokes connected in series with the SPD. Protective devices are built into the circuit in ascending order of class. Without coordination, more sensitive SPDs will take on the main load and fail earlier.
The installation of chokes can be avoided if the length of the cable line between devices exceeds 10 meters. For this reason, SPDs of class I are mounted on the facade even before the meter, protecting the metering unit from surges, and the second and third classes are installed, respectively, on the ASU and floor / group shields.
Any electrical equipment is created to work with a certain electrical energy, depending on the current and voltage in the network. When their value becomes more than the designed norm, then an emergency mode occurs.
Protection is designed to prevent the possibility of its formation or eliminate the destruction of electrical equipment. They are created for specific conditions of the occurrence of an accident.
Features of protection of home electrical wiring from high voltage
The insulation of a household electrical network is calculated for a voltage limit slightly above one and a half kilovolts. If it increases more, then a spark discharge begins to penetrate through the dielectric layer, which can develop into an arc that forms a fire.
To prevent its development, protections are created that work according to one of two principles:
1. disconnecting the electrical circuit of a house or apartment from high voltage;
2. removal of dangerous overvoltage potential from the protected area due to its rapid redirection to the ground contour.
With a slight increase in the voltage in the network, they are also called upon to correct the situation. But, for the most part, they are created to maintain the operating parameters of the power supply in a limited range of its regulation at the input, and not as a protective device. Their technical capabilities are limited.
In home wiring, the voltage may rise:
1. for a relatively long period, when zero burns out in a three-phase circuit and the neutral potential shifts depending on the resistance of randomly connected consumers;
2. short-term impulse.
The voltage control relay successfully copes with the first type of malfunction. It constantly monitors the input parameters of the network and, when they reach the upper setpoint, disconnects the circuit from power until the trouble is eliminated.
The causes of the appearance of short-term overvoltage impulses can be two situations:
1. simultaneous disconnection of several powerful consumers on the supply line, when the transformer substation does not have time to instantly stabilize the system;
2. a lightning strike of lightning into the electrical equipment of a power line, substation or house.
The second variant of the development of the accident represents the greatest danger than in all previous cases. The strength of the lightning current reaches enormous values. With average calculations, it is taken at 200 kA.
When it hits the lightning rod and normal operation of the lightning protection of the building, it flows through the lightning rod to . At this moment, in all nearby conductors, according to the law of induction, an EMF is induced, the value of which is measured in kilovolts.
It can appear even in wiring disconnected from the network and burn its equipment, including expensive TVs, refrigerators, computers.
Lightning can also strike an overhead power line supplying a building. In this situation, the line arresters work normally, extinguishing its energy to the ground potential. But they are not able to completely eliminate it.
Part of the high-voltage impulse through the wires of the connected circuit will spread in all possible directions and will come to the input of the residential building, and from it to all connected devices in order to burn their weakest points: electric motors and electronic components.
As a result, we got two options for damage to expensive household electrical equipment of a residential building during the normal elimination of the consequences of a lightning strike into the lightning rod of our own building or a power transmission line by regular protection. The conclusion suggests itself: it is necessary to install for them automatic protection against impulse discharges.
Types of surge arresters for home wiring
The range of such protections is created for work in different conditions, differs in design, materials used, work technology.
Principles of formation of the element base of arresters
When creating overvoltage protections, the technical capabilities of various design solutions are taken into account. For gas-filled arresters, it is characteristic that after the end of the passage of the discharge pulse, they support the flow of additional current, close in magnitude to the short-circuit load. It is called follow current.
Arresters that provide a follow-up current of the order of 100÷400 amperes can themselves become a source of fire and do not provide protection. They cannot be installed to protect insulation from breakdown between any phase, working and protective zero. Models of other types of arresters work quite reliably inside a 0.4 kV network.
In home wiring, overvoltage protection received priority varistor devices. Under normal operating conditions of an electrical installation, they create very small leakage currents up to several milliamps, and during the passage of a high-voltage pulse, the voltages are transferred as quickly as possible to the tunnel mode, when they are able to pass up to thousands of amperes.
Classes of insulation resistance of home electrical wiring to impulse overvoltages
The electrical equipment of residential buildings is created in four categories, which are designated by Roman numerals IV÷I and are characterized by the maximum allowable overvoltage of 6, 4, 2.5 and 1.5 kilovolts. Under these zones, surge protections are designed.
In the technical literature they are called SPD, which stands for surge protection device. Manufacturers of electrical equipment for marketing purposes have introduced a more understandable definition for the general population - limiters. Other names can be found on the Internet.
Therefore, in order not to get confused in the terminology used, it is recommended to refer to the technical characteristics of the devices, and not just to their name.
The main parameters of the relationship between insulation resistance categories and building hazard zones and the use of three SPD classes for them will help to understand the figure below.
He demonstrates that in the section from the transformer substation along the power line to the input shield, a pulse of 6 kilovolts can come. Its value must be reduced by a class I surge arrester in zone 1 to four kV.
The zone 2 switchboard operates a class II arrester, reducing the voltage to 2.5 kV. Inside a living room with zone 3, a class III SPD provides a total pulse reduction of up to 1.5 kilovolts.
As you can see, all three classes of limiters work in a complex manner, sequentially and in turn reduce the overvoltage impulse to a value acceptable for electrical wiring insulation.
If at least one of the components of this chain of protection turns out to be faulty, then the entire system will fail and an insulation breakdown will occur on the final device. They must be used comprehensively, and during operation it is required to check the serviceability of the technical condition at least by external inspection.
Selection of varistors for different classes of surge arresters
Equipment manufacturers supply SPD devices with models of varistors selected according to current-voltage characteristics. Their type and operating limits are shown in the corresponding graph.
Each protection class has its own voltage and opening current. You can install them only in their place.
Principles of formation of circuits for switching on surge arresters
To protect the power supply line of an apartment, various principles for connecting an SPD can be used:
1. in phase;
2. out of phase;
3. combined.
In the first case, the longitudinal principle of protection of each wire against overvoltage relative to the ground contour is performed, and in the second case, it is transverse between each pair of wires. Based on the collection of statistical data on the processing of faults and their analysis, it was found that the occurring anti-phase impulse overvoltages create more damage and are therefore considered the most dangerous.
The combined method allows you to combine both previous methods.
Options for connecting surge arresters for the TN-S grounding system
Scheme with electronic SPDs and arresters
In this scheme, SPDs of all three classes eliminate overvoltage impulses between the phases of the line and the operating zero N along the “wire-wire” chains. The function of reducing common-mode overvoltages is assigned to arresters of a certain class due to their connection between the working and protective zero.
This method makes it possible to galvanically separate PE and N from each other. The position of the neutral of a three-phase network depends on the symmetry of the applied loads in phases. It always has some potential, which can be from fractions to several tens of volts.
If power supplies with a pulsed load are operating in the system, then high-frequency noise can be transmitted from them through the potential equalization and grounding circuits through the PE conductor to sensitive electronic devices, interfering with their operation.
The inclusion of arresters in this case reduces the impact of these factors due to better galvanic isolation than electronic arresters on varistors.
Circuits with electronic SPDs in protection classes I and II
In this scheme, protection against surge voltages in the input and distribution boards is performed only by electronic surge arresters.
They eliminate all common mode overvoltages (any wires relative to the ground loop).
In class III, the previous circuit with an electronic surge arrester and a surge arrester works, providing protection (wire-wire) for the end consumer.
Peculiarities of using various models of surge arresters, taking into account the sequence of operation of cascades
When operating stages of protection against impulse overvoltage, their coordination and coordination is required. It is carried out by removing steps along the cable at a distance of more than 10 meters.
This requirement is explained by the fact that when a high-voltage pulse with a steep waveform enters the circuit, a voltage drop occurs due to the inductive resistance of the cores. It is immediately applied to the first cascade, causing it to work. If this requirement is not met, then steps are shunted when the protection does not work properly.
The subsequent protection cascades are connected according to the same principle.
When, according to the design features of the equipment, it is located close, then additional isolating pulse-type chokes are artificially included in the circuit, creating a delay chain. Their inductance is adjusted in the range of 6÷15 microhenries, depending on the type of power input used in the building.
A variant of such a connection with a close location of the input and switchboards and remote installation of end consumers is shown in the diagram.
When mounting a throttle on such a system, one should take into account their ability to work reliably under the loads created, to withstand their limit values.
For ease of maintenance, surge protection, together with throttling devices, can be placed in a separate protective shield that connects the input device in series with the main switchboard at home.
One of the options for such a design for a building made according to the TN-C-S grounding system is shown in the diagram below.
With this installation, all three classes of limiters can be placed in one place, which is convenient for maintenance. To do this, it is necessary to install isolating chokes in series between the protection stages.
Structurally, the input device, main switchboard and protective shield with this method of mounting the circuit should be located as close as possible.
The combined location of the SPD and chokes in one place - the protective shield, makes it possible to prevent overvoltage impulses from reaching the equipment of the main switchboard, in which the PEN conductor is separated.
Connecting power cables to the main switchboard has some peculiarities: they must be laid along the shortest paths, avoiding joint contact for sections of the protected circuit and without protection.
Modern manufacturers are constantly modifying their SPD designs using built-in pulse isolating chokes. They allowed not only to place the protection stages at a close distance along the cable, but also to combine them in a separate unit.
Now on the market, taking into account the implementation of this method, SPD designs of combined classes I + II + III or I + II have appeared. A different range of models of such arresters is produced by the Russian company Hakel.
They are created for different grounding systems of the building, they work without installing additional protection levels, but they require the fulfillment of certain technical installation conditions along the length of the connected cable. In most cases, it should be less than 5 meters.
For the normal operation of electronic equipment and to protect it from high-frequency interference, various filters are produced, which include SPDs of class III. They need to be connected to the ground loop through a PE conductor.
Features of protection of complex household appliances from overvoltage impulses
The life of a modern person dictates the need to use various electronic devices that process and transmit information. They are quite sensitive to high-frequency interference and impulses, they do not work well or even fail when they appear. To eliminate such failures, individual grounding of the device case, called functional, is used.
It is electrically separated from the protective PE conductor. However, if a lightning strike strikes the lightning protection between the grounds of the building or line and the functional electronic device, a discharge current will flow along the ground loop, caused by the applied high-voltage overvoltage pulse.
It can be eliminated by equalizing the potentials of these circuits by installing a special arrester between them, which will equalize the potentials of the circuits in case of accidents and provide galvanic isolation in everyday operating conditions.
Hakel also specializes in the production of such arresters.
Additional requirement for the protection of arresters against short circuits
All SPDs are included in the circuit for equalizing the potentials between its various parts in critical situations. At the same time, it should be taken into account that they themselves, despite the presence of built-in thermal protection of varistors, can be damaged and become a source of a short circuit that develops into a fire.
Protection on varistors can fail if the rated voltage is exceeded for a long time, associated, for example, with zero burnout in a three-phase supply network. Arresters, unlike electronics, are not supplied with thermal protection at all.
For these reasons, all SPD designs are additionally protected by fuses operating during overloads and short circuits. They have a special complex design and are very different from models with a simple fusible link.
The use of circuit breakers for such situations is not always justified: they are damaged by lightning impulses when the power contacts are welded.
When using the SPD protection circuit with fuses, it is necessary to observe the principle of creating its hierarchy using selectivity methods.
As you can see, in order to ensure reliable protection of home electrical wiring from surge surges, it is necessary to carefully approach this issue, analyze the likelihood of accidents in the design scheme, taking into account the operating grounding system, and select the most suitable surge arresters for it.
For all of us, it has become the norm that in the switchboards of residential buildings, it is mandatory to install introductory circuit breakers, modular automatic circuit breakers, RCDs or differential automatic devices for rooms and equipment where possible leakage currents are critical (bathrooms, hob, washing machine, boiler ).
In addition to these mandatory switching devices, almost no one needs to explain why a voltage monitoring relay is needed.
SPD or voltage relay
Everyone started installing them everywhere. Roughly speaking, it protects you from 380V instead of 220V going into the house. In this case, you do not need to think that the increased voltage enters the wiring due to an unscrupulous electrician.
Natural phenomena are quite possible that do not depend on the qualifications of electricians. A tree fell corny and cut off the neutral wire. 
Also, do not forget that any VL becomes obsolete. And even the fact that a new SIP line was brought to your house, and everything was installed in your house according to the rules, does not guarantee that everything is fine at the supply transformer substation itself - KTP. 
There, zero can also be oxidized on the bus bar or the contact on the transformer stud can burn out. Nobody is immune from this.
That is why all new switchboards are no longer assembled without UZM or LV of various modifications. 
As for surge protection devices, or SPDs for short, the majority here have doubts about the need to purchase them. But are they really needed, and is it possible to do without them?
Such devices appeared a long time ago, but so far no one is in a hurry to install them en masse. Few ordinary consumers understand why they are needed at all. 
The first question that arises for them is: “I installed a voltage surge relay, why do I need another SPD?”
No voltage relay will save you from this, but most likely it will burn out along with all other equipment. At the same time, the SPD does not protect against small drops of tens of volts or even a hundred. 
For example, devices for mounting in home shields, assembled on varistors, can only work when the change reaches values above 430 volts.
Therefore, both RH devices and SPDs complement each other.
Thunderstorm protection at home
A thunderstorm is a natural phenomenon and it is still not particularly possible to calculate it. In this case, lightning does not have to fall directly into the power line. Enough to hit next to her. 
Even such a lightning discharge causes an increase in the voltage in the network to several kilovolts. In addition to the failure of equipment, this is also fraught with the development of a fire.
Even when lightning strikes relatively far from the overhead line, impulse surges occur in the networks, which disable the electronic components of home appliances. A modern electronic counter with its filling can also suffer from this impulse. 
The total length of wires and cables in a private house or cottage reaches several kilometers.
This includes both power circuits and low current:
- security alarm
All these wires take on the consequences of a lightning strike. That is, all your kilometers of wiring receive a giant pickup, from which no voltage relay can save.
The only thing that will help and protect all the equipment, costing several hundred thousand, is a small box called an SPD. 
They are mounted mainly in cottages, and not in apartments of high-rise buildings, where the connection to the house is made by an underground cable. However, do not forget that if your transformer substation is powered not by a 6-10kv cable line, but by an overhead power line or overhead line (SIP-3), then the influence of a thunderstorm on medium voltage can also be reflected on the 0.4kv side. 
Therefore, do not be surprised when during a thunderstorm in your high-rise building, many neighbors simultaneously fail WiFi routers, cordless phones, TVs and other electronic equipment.
Lightning can strike a power line several kilometers from your home, but the impulse will still fly to your outlet. Therefore, despite their cost, all consumers of electricity need to think about buying SPDs. 
The price of quality models from Schneider Electric or ABB is approximately 2-5% of the total cost of rough electrics and the average switchboard configuration. All in all, it's not that big of a deal.
SPD classes
To date, all surge protection devices are divided into three classes. And each of them plays a role. 
The first class module extinguishes the main impulse, it is installed on the main input board.
After the largest overvoltage has been extinguished, the residual impulse is taken over by the SPD of the 2nd class. It is mounted in the switchboard of the house. 
If you do not have a class I device, there is a high probability that the entire impact will take the module II. And this can end very sadly for him.
Therefore, some electricians even dissuade customers from installing impulse protection. Motivating this by the fact that since you cannot provide the first level, then you should not spend money on it at all. There will be no sense.
However, let's see what not a familiar electrician says about this, but Citel, a leading company in lightning protection systems: 
That is, the text directly says that class II is mounted either after class 1, or AS A STANDALONE DEVICE.
The third module protects a specific consumer directly.
If you have no desire to build all this three-stage protection, purchase SPDs that initially come with the calculation of work in three zones 1 + 2 + 3 or 2 + 3. 
Such models are also produced. And they will be the most versatile solution for use in private homes. However, their cost will certainly scare away many.
Scheme of electrical panel with SPD
The scheme of a switchboard that is well-equipped in terms of protection against all voltage surges and surges should look something like this.
At the input in front of the meter there is an introductory circuit breaker that protects the meter and circuits inside the shield itself. Next is the counter. 
Between the meter and the introductory machine there is an SPD with its own protection. The power supply company can, of course, prohibit such installation. But you can justify this by the need for surge protection and the meter itself.
In this case, it will be necessary to mount the entire circuit with devices in a separate box under a seal in order to prevent free access to bare current-carrying parts to the metering device. 
However, the issue of replacing the failed module and breaking the seals will become acute here. Therefore, coordinate all these points in advance.
After the meter are:
- voltage relay UZM-51 or equivalent
- simple modular machines
If there are no questions with the usual components when completing such a shield, then what should you pay attention to when choosing an SPD?
For operating temperature. Most electronic types are designed to operate at ambient temperatures down to -25C. Therefore, it is not recommended to mount them in street shields.
The second important point is the wiring diagrams. Manufacturers may produce different models for use in various grounding systems. 
For example, it will no longer be possible to use the same SPDs for TN-C or TT and TN-S systems. You will not achieve correct operation from such devices.
Wiring diagrams
Here are the main schemes for connecting SPDs, depending on the design of grounding systems, using the models from Schneider Electric as an example. Wiring diagram of a single-phase SPD in a TT or TN-S system: 
The most important thing here is not to confuse the connection point of the N-PE plug-in cartridge. If you plug it into a phase, you will create a short circuit.
Scheme of a three-phase SPD in a TT or TN-S system: 
Wiring diagram for a 3-phase device in a TN-C system: 
What do you need to pay attention to? In addition to the correct connection of the neutral and phase conductors, the length of these same wires plays an important role.
From the connection point in the terminal of the device to the ground bar, the total length of the conductors must be no more than 50cm! 
And here are similar schemes for SPDs from ABB OVR. Single phase option: 
Three-phase circuit: 
Let's go through some schematics separately. In the TN-C circuit, where we have combined protective and neutral conductors, the most common protection solution is to install an SPD between phase and ground.
Each phase is connected through an independent device and operates independently of the others. 
In the variant of the TN-S network, where the neutral and protective conductors have already been separated, the circuit is similar, but here an additional module is mounted between zero and ground. In fact, the entire main blow falls on him. 
That is why, when choosing and connecting the N-PE SPD, individual characteristics for impulse current are indicated. And they are usually larger than the phase values.
In addition, do not forget that lightning protection is not only a properly selected SPD. This is a whole range of activities.
They can be used both with and without lightning protection on the roof of the house. 
Particular attention should be paid to a high-quality ground loop. 
One corner or pin hammered into the ground to a depth of 2 meters will obviously not be enough here. A good ground resistance should be 4 ohms.
Operating principle
The principle of operation of the SPD is based on the attenuation of the voltage surge to a value that the devices connected to the network can withstand. In other words, this device, even at the entrance to the house, dumps excess voltage on the ground loop, thereby saving expensive equipment from a destructive impulse.
Determining the status of the protection device is quite simple:
- green indicator - the module is working
At the same time, do not enable the module with a red flag. If there is no spare, then it is better to dismantle it altogether.
SPD is not always a disposable device, as some people think. In some cases, class 2.3 models can fire up to 20 times!
Circuit breakers or fuses before SPD
To maintain uninterrupted power supply in the house, it is also necessary to install an automatic switch that will turn off the ultrasonic device. The installation of this machine is also due to the fact that at the time of the withdrawal of the pulse, the so-called follow current occurs.
It does not always allow the varistor module to return to the closed position. In fact, it does not recover after being triggered, as it should have been in theory.
As a result, the arc inside the device is maintained and leads to a short circuit and destruction. Including the device itself. 
In the event of such a breakdown, the machine operates and de-energizes the protective module. Uninterrupted power supply to the house continues.
Remember that this machine primarily protects not the arrester, but your network.
At the same time, many experts recommend installing not even an automatic machine, but modular fuses as such protection. 
This is explained by the fact that the machine itself during the breakdown is under the influence of a pulsed current. And its electromagnetic releases will also be under increased voltage.
This can lead to a breakdown of the trip coil, burning of the contacts, and even failure of the entire protection. In fact, you will find yourself defenseless in the face of a short circuit.
Therefore, installing an SPD after a circuit breaker is much worse than after a fuse.
Of course, there are special circuit breakers without inductors, which have only thermal releases in their design. For example Tmax XT or Formula A. 
However, considering this option for cottages is not entirely rational. It is much easier to find and buy modular fuses. In this case, you can make a choice in favor of type GG.
They are able to protect over the entire range of overcurrents relative to the nominal. That is, if the current has grown slightly, GG will still turn it off at a given time interval.
Of course, there is also a minus of the circuit with an automatic device or a PC directly in front of the SPD. We all know that thunder and lightning is a continuous, not a one-time phenomenon. And all subsequent strikes may not be safe for your home. 
After all, the protection had already worked for the first time and the machine knocked out. And you will not even guess about it, because your power supply has not been interrupted.
Therefore, some prefer to install an SPD immediately after the introductory machine. So that when triggered, the voltage is turned off throughout the house. 
However, it also has its own pitfalls and rules. The protective circuit breaker cannot be of any rating, but is selected according to the brand of the SPD used. Here is a table of recommendations for choosing automatic devices mounted in front of surge protection devices: 
If you think that the lower the nominal value of the machine will be installed, the more reliable the protection will be, you are mistaken. Impulse current and voltage surge can be of such magnitude that they lead to the operation of the circuit breaker, even before the moment when the SPD operates.
And accordingly, you will again be left without protection. Therefore, choose all protective equipment wisely and according to the rules. SPD is a quiet, but very timely protection against dangerous electricity, which is activated instantly.
Connection errors
1 The most common mistake is installing an SPD in a switchboard with a poor ground loop.There will be no sense from such protection. And the very first “successful” lightning strike will burn you both all the devices and the protection itself. 
Check the technical documentation of the SPD and consult with an experienced electrician responsible for electrical services, who should be aware of what kind of earthing system is used in your home. 
One of the devices from the series "to be or not to be?"... he is in the metering board - are surge arresters ⚡⚡⚡ They are also called SPD, SPE, OPS-1 ... etc. There are countless of them, they come in different classes, there are different manufacturers. To install or not to install, the connection diagram of such a device, we will cover all this in this article!
First, I will talk about the surge arresters that I use to install in my customers' metering boards. I stopped my choice on a device called OIN-1 from the Energomera JSC concern.
SPE-1 side view
The main criterion for choosing this limiter for me was the availability of a supplier in the warehouse and the price, the latter criterion is of greater importance, because. in my opinion, the need to install such products is extremely small, but more on that later. For comparison, a set of limiters OIN-1 JSC "Energomera" for three phases costs about 900 rubles, the closest "competitor" is OPS-1 3R D from IEC costs around 3500. The functions performed by these limiters are exactly the same, and if there is no difference, why should you pay more?!
As for SPD, SPE, OPS connection diagrams and other similar devices. In the metering board, they are connected from the lower terminals of the introductory machine, and the output and the limiter go to the GZSH bus, in our case it is a pass-through block.
Wiring diagram for surge arrester from the lower terminals of the introductory machine using NShVI-2 lugs
As a GZSH in our metering board there is a pass-through block. This feed-through unit is re-grounded using the grounding conductor.
Since the limiter is in the connection diagram up to the meter, it must be sealed. In our case, using a plastic box.
General form
The connection scheme for surge arresters SPD, OPS-1, SPE and others is identical for other manufacturers. The only difference is that if you take a three-pole limiter, then its output conductor is already assembled from three into one.
Based on my experience, I can say that not all network organizations in the technical conditions for applicants have such a requirement to install surge arresters. I met such a requirement in the Nizhny Novgorod region and in the Krasnodar Territory.
Let's first touch on the practical part of the question. To understand whether to set or not to set, you need to understand what can be the source of such an overvoltage, and there are only two of them:
1.lightning strike, both direct and close
2.switching surge.
In order to understand whether or not to install a limiter for protection against impulse (lightning) overvoltages, you need to know what wire the trunk is made to, to which our metering panel will be connected. If the trunk is made with a bare wire, there is a probability of a lightning strike, if it is self-supporting insulated (SIP), the probability of a lightning strike is extremely small. In addition, you need to keep in mind in which region we will install our metering board. Below is a map with the number of thunderstorm hours per year:
As we see on this map in the north of the country, there is a very small number of thunderstorm hours and the limiter in our metering board will simply take up space and will not perform useful functions. The further south, the greater the number of thunderstorm hours per year and the higher the probability of the first overvoltage source.
As for switching surges. These overvoltages occur during operational switching at substations. The closer we are to our substation, the higher the probability of a switching overvoltage.
For myself, I made a choice not in favor of installing surge arresters, since my main line is made with SIP wire, and the site is located on the edge of the village where there are no large substations and the number of lightning hours in our region is small.
As we can see on the general view of the metering board, due to the installation of the limiter, we did not have enough space to install the outlet and the automatic outlet. Of course, you can buy a case with larger sizes, but again, it will cost more for us. And in my opinion, a socket with a machine in the metering board is much more useful than a surge arrester.
Let's now look at the legal side of the issue.. I would like to make a reservation right away that I do not have a legal education and these are only my thoughts that arose while studying regulatory documents.
Indeed, in the PUE there is clause 7.1.22 where it is said that surge arresters should be installed at air input, but clause 7.1 says that chapter 7 applies to - "residential buildings listed in SNiP 2.08.01-89 "Residential buildings"(this SNIP covers the design of residential buildings (apartment buildings, including apartment buildings for the elderly and families with wheelchair users, hereinafter referred to as families with disabilities, as well as hostels), up to and including 25 floors.); public buildings listed in SNiP 2.08.02-89 "Public buildings and structures"(with the exception of buildings and premises listed in Chapter 7.2) (this SNIP applies to the design of public buildings (up to 16 floors inclusive) and structures, as well as public premises built into residential buildings. When designing public premises, built-in in residential buildings and built-in-attached to them, you should additionally be guided by SNiP 31-01-2003.); administrative and household buildings, listed in SNiP 2.09.04-87“(This SNIP applies to the design of administrative and residential buildings 1 height (according to SNiP 21-01-97) up to 50 m, including the attic floor, and premises of enterprises.). All these SNIPs refer to apartment buildings, administrative buildings, public and other buildings. Those. paragraph 7.1 does not indicate that paragraph 7.1.22 applies to individual residential buildings.
In addition, in accordance with Decree of the Government of the Russian Federation of December 27, 2004 N 861 (as amended on July 28, 2017)
25(1). In the technical conditions for applicants provided for in paragraphs 12.1 and 14 (individuals up to 15 kW, that is, our case) of these Rules, the following must be indicated:
a) connection points that cannot be located further than 25 meters from the border of the site on which the applicant's connected objects are (will be) located;
a(1)) maximum power in accordance with the application and its distribution for each point of connection to the power grid facilities;
(Item “a(1)” was introduced by Decree of the Government of the Russian Federation of 04.05.2012 N 442)
b) justified requirements for strengthening the existing electrical network in connection with the connection of new capacities (construction of new power lines, substations, increase in the cross-section of wires and cables, replacement or increase in the power of transformers, expansion of switchgear, modernization of equipment, reconstruction of electric grid facilities, installation of control devices voltages to ensure the reliability and quality of electric energy), mandatory for execution by the grid organization at its expense;
c) requirements for electrical energy (power) metering devices, relay protection devices and devices that provide control of the maximum power value;
d) distribution of responsibilities between the parties for the fulfillment of technical specifications (measures for technological connection within the boundaries of the site where the applicant's power receiving devices are located are carried out by the applicant, and technological connection measures up to the border of the site where the applicant's power receiving devices are located, including the settlement of relations with by other persons, carried out by the network organization).
(paragraph “d” as amended by Decree of the Government of the Russian Federation of September 24, 2010 N 759)
(see text in previous edition).
Those. in the technical specifications of the applicants there should be no requirements for devices limiting impulse overvoltages. It is possible if only to pull "their ears" as "relay protection devices" which such devices are not.
Now we know both the practical issues of installing limiters and the legal ones. The choice is always yours! For myself, I have already made this choice!
Don't forget to visit YOUTUBE and put your finger up at the video about SPD, SPE, OPS.
It is very easy to buy a reliable metering board - you just need to send an application using the communication channels convenient for you!
