It has become the norm for all of us that in the distribution boards of residential buildings, it is mandatory to install incoming circuit breakers, modular circuit breakers for outgoing circuits, RCDs or differential circuit breakers in rooms and equipment where possible current leaks are critical (bathrooms, hob, washing machine, boiler ).
In addition to these mandatory switching devices, almost no one needs to explain why a voltage control 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. At the same time, you don’t need to think that increased voltage gets into the wiring due to an unscrupulous electrician.
Natural phenomena that do not depend on the qualifications of electricians are quite possible. A tree simply fell and broke the neutral wire. 
Also, do not forget that any overhead line becomes obsolete. And even the fact that a new line has been connected to your house using a self-supporting insulated insulation system, and everything in your house is installed according to the rules, does not guarantee that everything is fine at the supply transformer substation itself - the transformer substation. 
There, the zero on the busbar may also oxidize or the contact on the transformer pin may burn out. No one is immune from this.
That is why all new electrical panels are no longer assembled without UZM or RN of various modifications. 
As for surge voltage protection devices, or SPDs for short, most here have doubts about the need to purchase them. Are they really that necessary, and is it possible to do without them?
Such devices appeared quite a long time ago, but still 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 in their minds is: “I installed a surge voltage relay, why do I need another SPD?”
No voltage relay will save you from this, but will most likely burn out along with all other equipment. At the same time, the SPD does not protect against small differences of tens of volts or even hundreds. 
For example, devices for installation in home panels, assembled on varistors, can only operate when the change reaches values above 430 volts.
Therefore, both LV and SPD devices complement each other.
Protecting your home from thunderstorms
A thunderstorm is a spontaneous phenomenon and it is still not very easy to calculate it. In this case, lightning does not have to hit the power line directly. It is 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 equipment failure, this is also fraught with the development of a fire.
Even when lightning strikes relatively far from overhead lines, pulse surges occur in the networks, which damage the electronic components of home appliances. A modern electronic meter with its filling may 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:
All these wires take on the consequences of a lightning strike. That is, all your kilometers of wiring receive a gigantic interference, from which no voltage relay can save you.
The only thing that will help and protect all the equipment, costing several hundred thousand, is a small box called an SPD. 
They are installed mainly in cottages, and not in high-rise apartments, where the supply to the house is made with an underground cable. However, do not forget that if your transformer substation is not powered by a 6-10 kV cable line, but by an overhead overhead line or overhead line (SIP-3), then the effect of a thunderstorm on medium voltage can also be reflected on the 0.4 kV side. 
Therefore, do not be surprised when, during a thunderstorm in your high-rise building, many neighbors’ WiFi routers, cordless phones, televisions and other electronic equipment simultaneously fail.
Lightning can strike a power line several kilometers from your home, but the impulse will still arrive at your outlet. Therefore, despite their cost, all electricity consumers should think about purchasing an SPD. 
The price of high-quality models from Schneider Electric or ABB is approximately 2-5% of the total cost of rough electrics and an average switchboard. In total, this is not such a huge amount of money.
SPD classes
Today, all surge voltage devices are divided into three classes. And each of them plays its role. 
The first class module dampens the main impulse; it is installed on the main input panel.
After the largest overvoltage has been extinguished, the residual impulse is taken over by a class 2 SPD. It is mounted in the distribution panel of the house. 
If you do not have a Class I device, there is a high probability that the entire impact will be taken by the II module. And this could end very sadly for him.
Therefore, some electricians even discourage customers from installing impulse protection. Motivating this is that since you cannot provide the first level, then you should not spend money on it at all. There will be no point.
However, let's see what not a familiar electrician says about this, but the leading company for lightning protection systems, Citel: 
That is, the text directly states that class II is mounted either after class 1 or AS A STANDALONE DEVICE.
The third module directly protects a specific consumer.
If you do not want to build all this three-stage protection, purchase SPDs that are initially designed to work in three zones 1+2+3 or 2+3. 
Such models are also produced. And they will be the most universal solution for use in private homes. However, their cost will certainly scare off many.
Electrical panel diagram with SPD
The circuit diagram of a distribution board that is well-equipped from the point of view of protection against all voltage surges and surges should look something like this.
At the input in front of the meter there is an input circuit breaker that protects the metering device and the circuits inside the panel itself. Next is the counter. 
Between the meter and the input machine there is an SPD with its own protection. The electricity supply organization can, of course, prohibit such installation. But you can justify this by the need for surge protection for the meter itself.
In this case, it will be necessary to mount the entire circuit with the devices in a separate box under a seal in order to prevent free access to exposed live parts up to the meter. 
However, here the issue of replacing the triggered module and breaking the seals will arise. Therefore, agree on all these points in advance.
After the metering device there are:
If there are no questions with the usual components when assembling 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 install them in street shields.
The second important point is the connection diagrams. Manufacturers may produce different models to suit different 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.
Connection diagrams
Here are the basic SPD connection diagrams depending on the design of the grounding systems using the example of models from Schneider Electric. Connection diagram for a single-phase SPD in a TT or TN-S system: 
The most important thing here is not to confuse the connection location of the N-PE insert cartridge. If you plug it into a phase, you will create a short circuit.
Diagram of a three-phase SPD in a TT or TN-S system: 
Connection diagram for a 3-phase device in the TN-C system: 
What should you 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 device terminal to the grounding busbar, the total length of the conductors should be no more than 50cm! 
And here are similar diagrams for surge protectors from ABB OVR. Single-phase option: 
Three-phase circuit: 
Let's go through some of the schemes 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 the phase and the ground.
Each phase is connected through an independent device and operates independently of the others. 
In the TN-S network version, 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 brunt of the blow falls on him. 
That is why, when selecting and connecting the N-PE SPD option, individual characteristics for the pulse current are indicated. And they are usually greater than the phase values.
In addition, do not forget that thunderstorm protection is not only a properly selected surge protector. This is a whole complex of events.
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 grounding loop. 
One corner or pin driven into the ground to a depth of 2 meters will clearly not be enough here. A good ground resistance should be 4 ohms.
Operating principle
The operating principle of the SPD is based on attenuating 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 onto the ground loop, thereby saving expensive equipment from a destructive impulse.
Determining the status of the protection device is quite simple:
However, do not enable the module with the red flag. If there is no spare one, then it is better to dismantle it altogether.
An SPD is not always a disposable device, as some people think. In some cases, class 2 and 3 models can fire up to 20 times!
Circuit breakers or fuses in front of the SPD
To maintain uninterrupted power supply in the house, it is also necessary to install a circuit breaker that will turn off the surge protector. The installation of this machine is also due to the fact that at the moment the pulse is removed, a so-called accompanying current arises.
It does not always allow the varistor module to return to the closed position. In fact, it does not recover after being triggered, as in theory it should.
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 is triggered and de-energizes the protective module. Uninterrupted power supply to the house continues.
Remember that this machine does not primarily protect the arrester, but your network.
At the same time, many experts recommend installing not even a machine, but modular fuses as such protection. 
This is explained by the fact that the machine itself during a breakdown is exposed to a pulsed current. And its electromagnetic releases will also be under increased voltage.
This can lead to breakdown of the trip coil, burning of contacts and even failure of the entire protection. In fact, you will find yourself unarmed in the face of a short circuit.
Therefore, installing an SPD after a machine is much worse than after fuses.
There are, of course, special automatic switches 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 choose the GG type.
They are capable of protecting over the entire range of overcurrents relative to the rated ones. That is, if the current has increased slightly, GG will still turn it off at a given time interval.
There is, of course, a minus to the circuit with a machine or PC directly in front of the SPD. We all know that thunderstorms and lightning are long-term, not one-time phenomena. And all subsequent impacts may be unsafe for your home. 
The protection had already worked the first time and the machine gun was knocked out. And you won’t even guess about it, because your power supply was not interrupted.
Therefore, some people prefer to install an SPD immediately after the input circuit breaker. So that when triggered, the voltage in the entire house is turned off. 
However, there are pitfalls and rules here too. 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 circuit breakers mounted in front of surge protection devices: 
If you think that the lower the nominal value of the machine is installed, the more reliable the protection will be, you are mistaken. The pulse current and voltage surge can be of such magnitude that they will lead to the circuit breaker tripping even before 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 comes into operation instantly.
Connection errors
1 The most common mistake is installing an SPD in an electrical room with a poor grounding circuit.There will be no sense in such protection. And the very first “successful” lightning strike will burn both all your devices and the protection itself. 
Check the technical documentation of the surge protector and consult with an experienced electrician responsible for electrical equipment, who should be aware of what grounding system is used in your home. 
Surge suppressor is one of the most widely known high-voltage devices used to protect the network.
To begin with, it is worth explaining why, in principle, pulse overvoltages occur and why they are dangerous. The reason for the appearance of this process is a disturbance in the atmospheric or switching process. Such defects are quite capable of causing enormous damage to electrical equipment that is exposed to such influence.
Here it is worth giving an example of a lightning rod. This device does an excellent job of diverting a strong discharge striking an object, but it will not be able to help in any way if the discharge enters the network through overhead lines. If this happens, then the very first conductor that gets in the way of such a discharge will fail, and can also cause a breakdown of other electrical equipment that is connected to the same electrical network. Elementary protection is to turn off all devices during a thunderstorm, but in some cases this is impossible, and therefore devices such as surge arresters were invented.
If we talk about conventional means of protection, then their design is somewhat worse than that of surge arresters. In the usual version, carborundum resistors are installed. An additional design is the spark gaps, which are connected to each other in a series manner.
Surge suppressors also contain elements such as nonlinear transistors. The basis for these elements was zinc oxide. There are several such parts, and they are all combined into one column, which is placed in a special case made of a material such as porcelain or polymer. This ensures completely safe use of such devices, and also reliably protects them from any external influences.
It is important to note here that the main feature of the surge suppressor is the design of zinc oxide resistors. This design allows you to greatly expand the functions that the device can perform.
Like any other device, an arrester has a basic characteristic that determines its performance and quality. In this case, this indicator was the amount of operating voltage that can be supplied to the terminals of the device without any time limitation.
There is one more characteristic - conduction current. This is the value of the current that passes through the device under the influence of voltage. This indicator can only be measured under conditions of actual use of the device. The main numerical indicators of this parameter are capacity and activity. The total value of this characteristic can reach several hundred microamps. Based on the obtained value of this characteristic, the performance of the surge suppressor is assessed.
To make this device, manufacturers use the same electrical engineering and design techniques that are used to make other products. This is most noticeable when examining the dimensions and materials used to make the case. The appearance also has some similarities with other devices. However, it is worth noting that special attention is paid to such things as the installation of a surge suppressor, as well as its further connection to general consumer-type electrical installations.
There are several requirements that apply specifically to this class of devices. The surge arrester housing must be completely protected from direct human contact. The risk of the device catching fire due to possible overloads must be completely eliminated. If the element fails, this should not result in a short circuit in the line.
The main purpose of nonlinear surge suppressors is to isolate electrical equipment from atmospheric or switching overvoltages. This device belongs to the group of high-voltage devices.
These devices do not have such a section as the spark gap. If we compare the operating range of an arrester and a conventional one, the limiter is able to withstand deeper voltage drops. The main task of this device is to withstand these loads without time limits. Another significant difference between a surge suppressor and a conventional valve one is that the dimensions, as well as the physical weight of the structure in this case are much lower. The presence of such an element as a lid made of porcelain or polymers has led to the fact that the inside of the device is reliably protected from external environmental influences.
The design of this device is somewhat different from a conventional surge arrester. In this embodiment, a column of varistors is used, which are enclosed in a tire. To create a tire in this case, it is no longer porcelain or polymers that are used, but a fiberglass pipe onto which a shell of tracking-resistant silicone rubber is pressed. In addition, the varistor column has aluminum leads that are pressed on both sides and also screwed inside the pipe.
Equipment > Modular devices
Surge suppressors
Modern individual construction sites (cottages, country houses, etc.) require the use of increased electrical safety measures. This is due to the high energy saturation, branching of electrical networks and the specific operation of both the facilities themselves and the electrical equipment. When choosing a power supply scheme, type of RCD and distribution panels, you should pay attention to the need to use surge protection devices ( SPD ), which should be installed before the RCD.
Surge suppressors (SPDs) are designed to protect internal distribution circuits of residential and public buildings from lightning and switching overvoltages.
Structurally, the limiters are made in the form of standard modules 18 mm wide for installation on a mounting rail and consist of a base - a contact block and a replaceable functional module. The replaceable module contains a solid-state composite varistor made of zinc carbide and a mechanism for visual monitoring of the degree of “wear” of the varistor with an “emergency” fuse.
Zinc carbide has the property of almost instantly reducing its resistance by thousands of times when a voltage exceeding the maximum permissible value appears at the terminals of the replaceable module.
Checking the serviceability of the limiter
Check the serviceability of the limiter during operation as follows:
- check the degree of “wear” using a visual indicator (if the indicator is darkened by more than 3/4, then it must be replaced);
- disconnect the limiter from the supply network and connect it to a 1000 V megger;
- measure the resistance of the limiter, which should be in the range of 0.1...2 mOhm. If the limiter resistance is outside the specified range, the limiter must be replaced.
Technical specifications
Parameter |
0PS1 V (I) |
0PS1 S (II) |
0PS1 D (III) |
Rated operating voltage, V |
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Maximum operating voltage, V |
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Rated discharge current 8/20 μs, kA |
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Maximum discharge current 8/20 µs, kA |
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Protection voltage level, no more than, kV |
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Classification voltage, V |
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Number of poles |
1, 2, 3, 4 |
1, 2, 3, 4 |
1, 2 |
terms of Use |
UHL4 |
UHL4 |
UHL4 |
Cross-section of connected wires, mm sq. |
4...25 |
4...25 |
4...25 |
dimensions
Electrical circuits
Sources of surge voltages
In the summer, a lightning discharge into an overhead line causes overvoltages of tens of kilovolts, which are in the nature of traveling waves with a high steepness and a rise time from zero to a maximum of 1.0...8.0 μs. If a discharge enters the internal distribution network of a building, it can cause breakdown, ignition of insulation and failure of electrical equipment. Similar consequences can be caused by switching overvoltages that occur during switching at substations or during startup and shutdown of powerful electrical consumers.
Using OPS1 you can create very effective and long-term protection of an object. One of the main conditions for this is the presence of a grounding loop, and for industrial premises - a potential equalization system; because, despite its short duration, a lightning discharge carries significant energy. The maximum peak discharge current can reach 100 kA, and in the absence of potential equalization, dangerous step voltages are quite possible. A three-stage protection system inside the building allows you to smoothly reduce a dangerous overvoltage impulse “along the way” towards the consumer to a safe value by selecting and “draining” part of the energy into the ground by fast-acting arresters of each stage. When installing arresters, it should be taken into account that sequential (selective) operation of the protection stages will be ensured if the distance between the stages along the overhead and cable circuits is at least 7...10 m. In this case, when a traveling discharge wave appears, the inductance of the circuit section will be create the necessary delay time constant for the voltage rise.
The distance from the arresters installed in the consumer's subscriber panel to the most remote load should not exceed 30 m.
Connection to the phase and neutral buses in all three stages is made before the switching equipment and residual current equipment. The length of the conductors connecting the arresters to the PEN or PE conductor must be minimal, and their cross-section must be at least 25 mm2.
Classification of electrical equipment according to resistance to overvoltage
Characteristic |
Rated impulse withstand voltage, kV |
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Special equipment that, being connected to existing electrical installations of buildings, requires additional surge protection devices. SPDs may be built into Category 1 equipment or located between that equipment and the rest of the electrical installation (for example, personal computers that are connected to the mains supply through extension cords with built-in SPDs). |
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Equipment that is connected to existing electrical installations in buildings by means of socket outlets and other similar connectors (for example, household electrical appliances, electronic devices, portable tools). |
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Equipment installed inside buildings that forms part of the building's specific electrical installation and is accessible to the general public and untrained personnel. Examples of such equipment are distribution boards, wiring, switches and sockets, electric stoves. |
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Equipment installed close to the electrical installations of buildings (inside or outside) in front of the main distribution board, which can be an input distribution device for multi-story buildings or an apartment panel for individual buildings (for example, electric meters, primary overcurrent protection devices). |
Areas of application 0PS1 in accordance with the classification voltage
Class 0PS1 |
Purpose and installation location 0PS1 |
I (B) |
The first stage of protection against direct or indirect lightning discharges in power lines at the entrance to the facility. Installed at the entrance to the building in the input distribution device (IDU) or in the main distribution board (MSB) |
II (C) |
The second stage of protection of the internal distribution circuits of the facility from lightning discharges and switching overvoltages. Installed in distribution boards. |
III (D) |
The third stage of protection of the facility’s electrical equipment from residual lightning and switching overvoltages. Installed in close proximity to electrical consumers (electrical appliances). |
Installation of surge protectors in the TN-C-S 220/380 V network
In order to reliably protect an object from the effects of any type of overvoltage, it is first necessary to create an effective grounding and potential equalization system with a TN-S or TN-C-S power supply system. This is important not only from the point of view of protection against surge voltages, but also to protect people from electric shock (it is possible to use an RCD). The next step should be to install protective devices. When installing protective devices, it is necessary that the distance between adjacent protection stages be at least 10 m along the power cable.
Compliance with this requirement is very important for the correct operation (coordination of operation) of protective devices. When a pulsed lightning overvoltage occurs in a power cable, due to an increase in the inductive resistance of the metal conductors of the cable when a current pulse flows through them, a voltage drop occurs on them, which is applied to the first protection cascade. In this way, its priority operation is achieved (the necessary time delay in the rise of the overvoltage pulse at the next protection stage is ensured).
Volt-ampere characteristics
A feature of the current-voltage characteristic of a varistor is the presence of a section of low currents (from zero to several milliamps), in which the operating point of the varistor is located, and a section of high currents (up to thousands of amperes), which in some cases is called a tunnel.
The tunnel section largely determines the functional properties and, in particular, the constraint voltage, i.e. the maximum pulse voltage affecting the protected electrical equipment when it is shunted with a varistor. One of the characteristics of a varistor is the classification voltage (Ucl). The classification voltage is indicated at a current of 1.5 mA.
If your home has a lot of expensive household appliances, it is better to take care of organizing comprehensive electrical protection. In this article we will talk about surge protection devices, why they are needed, what they are and how they are installed.
Many people have been familiar since childhood with the fuss of unplugging household electrical appliances at the first sign of an approaching thunderstorm. Today, the electrical equipment of city networks has become more advanced, which is why many people neglect basic protection devices. At the same time, the problem has not disappeared completely; household appliances, especially in private homes, are still at risk.
The nature of the occurrence of pulse overvoltages (OS) can be natural and man-made. In the first case, IP occurs due to lightning striking 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 strike radio towers and lightning rods connected to the main grounding circuit, in which case an induced overvoltage appears in the household network.
1 - remote lightning strike on power lines; 2 - consumers; 3 - ground loop; 4 - close lightning strike to power lines; 5 - direct lightning strike to the lightning rod
Man-made power sources are unpredictable; they arise as a result of switching overloads at transformer and distribution substations. With an asymmetrical increase in power (only in one phase), a sharp voltage surge is possible; it is almost impossible to foresee this.
Pulse 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 overvoltages up to 1000 V, these occur most often. At a higher voltage, failure of the power supplies is guaranteed; insulation breakdown in the wiring of the house is also possible, which leads to multiple short circuits and fire.
The SPD, depending on the protection class, may have a semiconductor device based 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 protective grounding through a varistor or two electrodes with a strictly regulated gap.
During a voltage surge, even a very short one, the current passes through these elements and spreads along the grounding or is compensated by a sharp drop in resistance in the phase-zero loop (short circuit). After the voltage stabilizes, the arrester loses its capacity, and the device operates in normal mode again.
Thus, the SPD closes the circuit for a while so that the excess voltage can be converted into thermal energy. In this case, significant currents pass through the device - from tens to hundreds of kiloamperes.
Depending on the causes 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 PI reaches its maximum value, the second is the time it takes for it to fall to nominal values. As you can see, the second type of overvoltage is more dangerous.
Class I devices are designed for protection against power surges with a characteristic of 10/350 μs, which most often occur during a lightning discharge in power lines closer than 1500 m to the consumer. The devices are capable of briefly passing current from 25 to 100 kA through themselves; almost all Class I devices are based on arresters.
Class II SPDs are focused on IP compensation with a characteristic of 8/20 μs, the peak current values in them range from 10 to 40 kA.
Protection class III is designed to compensate for overvoltages with current values less than 10 kA with an IP characteristic of 8/20 μs. Protection class II and III devices are based on semiconductor elements.
It may seem that installing only Class I devices as the most powerful is enough, but this is not the case. The problem is that the higher the lower threshold of the throughput current, the less sensitive the SPD is. In other words: at short and relatively low IP values, a powerful SPD may not work, and a more sensitive one will not cope with currents of such magnitude.
Devices with protection class III are designed to eliminate the lowest voltages - only a few thousand volts. They are completely similar in characteristics to the protection devices installed by manufacturers in power supplies for household appliances. In case of backup installation, they are the first to take on the load and prevent the operation of the SPD in devices whose service life is limited to 20-30 cycles.
A complete list of requirements for organizing protection against power supply is set out in IEC 61643-21; mandatory installation can be determined using 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, installing a class I surge protector 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 supports, PEN conductor and metal load-bearing elements, installation of a lightning rod with a separate grounding loop, installation potential equalization systems.
An easier way to assess risk is to compare the cost of unprotected household appliances and security devices. Even in multi-storey buildings, where overvoltages have very low values with a characteristic of 8/20, the risk of insulation breakdown or failure of devices is quite high.
Most surge protectors are modular and can be installed on a 35 mm DIN rail. The only requirement is that the shield for installing the SPD must have a metal casing 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 electrical network. Another parameter is the maximum limiting 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. The phases and protective conductor are connected to the upper terminals of the SPD, and the neutral conductor is connected to the lower terminals.
SPD connection example: 1 - input; 2 - automatic switch; 3 - SPD; 4 - grounding bus; 5 - ground loop; 6 - electricity meter; 7 - differential automatic; 8 - to consumer machines
When installing several protective devices with different protection classes, their coordination is required using special chokes connected in series with the SPD. Protective devices are built into the circuit in ascending order of class. Without approval, more sensitive SPDs will take the main load and fail earlier.
Installation of chokes can be avoided if the length of the cable line between devices exceeds 10 meters. For this reason, class I SPDs are mounted on the façade even before the meter, protecting the metering unit from overvoltages, and the second and third classes are installed, respectively, on the ASU and floor/group switchboards.
A residual current device (RCD) is a device that protects a person from electric shock and also prevents damage to electrical receivers. The principle of operation of the device is simple: it compares the currents in the phase and neutral wires. If they are equal, then the network is operating normally and the device does not respond. As soon as a difference in values appears due to the fact that less current flows through the zero than the phase current, which indicates a leak, then the device immediately (in less than 0.1 sec) operates, disconnecting the power receiver from the network.
Circuit breakers may not respond to small leakage currents that are dangerous to human health and life, and network grounding, although it protects, will not save the equipment. That's why they install an RCD. A current of 0.1 A is considered fatal to humans.
The RCD response current, i.e. the difference in phase and zero, is 0.03 A.
In everyday life, it is not advisable to use more sensitive RCDs due to the fact that the device can often turn off the voltage for no apparent reason. In order to understand the connection principle, you need to know which wires go to the apartment.
Namely:
The risers on each floor carry phases, a neutral wire and grounding to the distribution panels. The panels are equipped with additional circuit breakers that disconnect the network in the event of a short circuit. From the machines to each apartment there is 1 phase, neutral and ground wire. In the apartment, wiring laid in the wall is connected to each socket and to the lighting outlets.
Installing an RCD in a single-phase network is not difficult. The device has 2 input terminals and 2 outputs. Phase and neutral are placed in the input terminals, respectively, without touching the ground wire. The wires passing through the device exit through the output terminals and are drawn directly to the electrical energy receiver. The device itself should be connected after the automatic shutdown. The devices from ABB have proven themselves to be the most effective.
The device is often equipped with a digital indicator, which serves to visually monitor the voltage level of the connected network. The COICOP09I indicator is often used for these purposes.
A two-wire network implies the presence in the apartment of only a phase and a neutral, without ground. Today, this type of wiring is used only in old Soviet buildings or some private houses.
In a two-wire network, there are several ways to connect an RCD:
Each option has both pros and cons. The first one will cost less, because... 1 device is purchased, but in case of a leak, it will turn off all devices in the house, which will cause discomfort. Determining which equipment caused the outage will be problematic. The option with several protection devices is somewhat more expensive and will take up more space in the distribution panel. This scheme will be more reliable and accurate.
Now it’s worth considering some schematic solutions for installing an RCD.
A diagram where the RCD is divided into separate consumption groups (bathroom, kitchen, bedrooms, and sometimes can also be used specifically for lighting) will look like this: the phase and neutral wires after the circuit breaker are divided into power supply for the electricity consumption groups.
Each set of wires (phase-zero) goes to a separate group.
Here they install a separate RCD for each group, passing wires through the input and output terminals. Place separate ABs for each group. The neutral wires of each group are output to the neutral buses.
Connection diagram with a common RCD:
Sometimes, after the machine, a surge suppressor (SVP) can be installed, protecting wiring and equipment from lightning discharges and induced communication surges. This device is installed between phase or neutral and ground. In this case, the RCD is installed after ONE, providing complete, multi-stage protection not only for humans, but also for electrical appliances and wiring.
Modern buildings are subject to mandatory grounding. Only old buildings have the old model of power supply and do not have grounding. To avoid accidents. in such areas an RCD is simply necessary. The house can be connected to either 1 or 3 phases. The choice of protection devices depends on the number of phases. An RCD in a private house with one phase can also be installed with options - one RCD, several devices that disconnect different groups.
A private plot is distinguished by the fact that it can have not only a house building, but also:
Each of these buildings represents a separate group of energy consumers, because they contain not only lighting, but also other parts that consume electricity and, sometimes, in large quantities, for example, a pump for pumping water into a pool or heat guns in a barn in winter.
On a private site with one phase, it would be correct to choose a connection diagram from several RCDs and circuit breakers.
If a private house has a three-phase network, then special protection devices are used to protect it. They disconnect one specific phase in case a fault occurs. The remaining phases continue to operate normally. The load must be evenly distributed among the phases to avoid voltage imbalance.
This method is not very rational, but, nevertheless, it is sometimes used. This method is used for sequential installation of an initial single-phase network, to which 2 more electrical components are then added for a general protective function.
It is very important in this case that the phase is connected to the current conductor through which the RCD will be tested in operating condition.
To do this, the resistance of each phase and zero is called. In this case, the power contacts must be turned on and the test button must be pressed. It should be noted that this action must be carried out on a dismantled RCD in the absence of voltage.
A three-phase RCD, which is connected to a single-phase network, has 3 circuits:
Due to the fact that the contacts will be broken, the resistance at 2 terminals will be equal to infinity. And one will show the resistance value of the resistor, which limits the current. It is to this terminal that you will need to connect.
