Fuses are traditionally used to protect electronic equipment. Usually they use thin bare conductors of a calibrated cross section, designed for a given burnout current. These devices work most reliably in high voltage alternating current circuits. With a decrease in the operating voltage, the efficiency of their use decreases. This is due to the fact that when a thin wire burns out in an alternating current circuit, an arc arises that sprays the conductor. The limiting voltage at which such an arc can occur is considered to be a voltage of 30 ... 35 6. With a low-voltage supply, the conductor simply melts. This process takes a longer time, which in some cases does not save modern semiconductor devices from damage.
However, fuses are still widely used in low-voltage DC circuits, where they are not required to increase their speed.
Where fuses cannot effectively solve the problem of protecting electronic equipment and devices from current overloads, they can be successfully used in circuits for protecting electronic devices from overvoltage.
The principle of operation of this protection is simple: when the supply voltage level is exceeded, a threshold device is triggered, arranging a short circuit in the load circuit, as a result of which the fuse conductor melts and breaks the load circuit.
The method of protecting equipment from overvoltage by forced blowing of the fuse is, of course, not ideal, but it has become quite widespread due to its simplicity and reliability. When using this method and choosing the optimal protection option, it is worth considering how fast the circuit breaker should be, whether it is worth blowing the fuse during short-term voltage surges or introducing a response delay element. It is also desirable to introduce an indication of the fact of a blown fuse into the circuit.
The simplest protective device, which allows you to save the protected electronic circuit, is shown in fig. 4.1. When the zener diode breaks down, the thyristor turns on and shunts the load, after which the fuse blows. The thyristor must be designed for a significant, albeit short-term current. It is completely unacceptable to use surrogate fuses in the circuit, since otherwise both the protected circuit, the power source, and the protective device itself may fail at the same time.

Rice. 4.1. The simplest surge protection

Rice. 4.2. Anti-jamming load protection circuit against overvoltage

An improved overvoltage load protection circuit, supplemented with a resistor and a capacitor, is shown in fig. 4.2. The resistor limits the current limit through the zener diode and the control transition of the thyristor, the capacitor reduces the likelihood of protection operation during short-term surges in the supply voltage.
The following device (Fig. 4.3) will protect radio equipment from failure in case of accidental polarity reversal or exceeding
supply voltage, which often happens when a generator malfunctions in a car.
With the correct polarity and rated supply voltage, the diode VD1 and the thyristor VS1 are closed, and the current through the fuse FU1 flows to the output of the device.

Rice. 4.3. Protection scheme for radio equipment with failure indication

If the polarity is reversed, then the diode VD1 opens and the fuse FU1 burns out. The EL1 lamp lights up, signaling an emergency connection.
With the correct polarity, but the input voltage exceeding the set level, set by the zener diodes VD2 and VD3 (in this case, 16 B), the VS1 thyristor opens and short-circuits the circuit, which causes the fuse to blow and the emergency lamp EL1 to light up.
Fuse FU1 must be rated for the maximum current consumed by the radio equipment.
Elements of GTL logic are usually operable in a narrow range of supply voltages (4.5 ... 5.5 B). If an emergency decrease in the supply voltage is not so dangerous for the “health” of the microcircuits, then an increase in this voltage is completely unacceptable, since it can damage all the microcircuits of the device.
On fig. Figure 4.4 shows a simple and fairly effective overvoltage protection circuit for 7777 devices, published in a Bulgarian magazine. The protection method is extremely simple: as soon as the supply voltage exceeds the recommended level by only 5% (i.e. reaches a value of 5.25 B), the threshold device will work and the thyristor will turn on. A short circuit current begins to flow through it, which blows the fuse FU1. Of course, surrogate fuses cannot be used as a fuse, since in this case the power supply protecting the thyristor circuit, and then the protected microcircuits, may fail.
The disadvantage of the device is the lack of indication of a blown fuse. This function is easy to enter into the device yourself. Examples of organizing an indication of a break in the supply circuit are also given in chapter 36 of the book.

Rice. 4.4. TTL chip protection circuit against overvoltage

Rice. 4.5. Scheme of an AC and DC surge protection device

A diagram of a device that, in the event of a power failure, will protect a TV, VCR, refrigerator, etc. from overvoltage, shown in fig. 4.5.
The protection operation voltage is determined by the voltage drop across the composite zener diode VD5 + VD6 and is 270 B.
Capacitors C1 and C2, together with resistor R1, form an RC circuit, which prevents the device from operating during surges in the network.
The scheme works as follows. At a network voltage of up to 270 V, the zener diodes VD3, VD4 are closed. Thyristors VS1, VS2 are also closed. With an operating voltage of more than 270 V, the zener diodes VD3, VD4 open, and the opening voltage is supplied to the control electrodes of the thyristors VS1, VS2. Depending on the polarity of the half-cycle of the mains voltage, the current passes either through the thyristor VS1 or through VS2. When the current exceeds 10 A, circuit breakers (plugs, fuses) operate, disconnecting electrical appliances from the mains. A load (not shown in the figure) is connected in parallel with the thyristors. You can check the performance of the device using LATR.
The device is operational and on direct current.

Rice. 4.6. Schematic diagram of self-locking surge protector relay

The overvoltage protection device (Fig. 4.6) compares favorably with the previous ones in that it does not cause irreversible damage to the protection element. Instead, at a voltage above 14.1 V, the zener diode chain VD1 - VD3 breaks through, the thyristor VS1 turns on and self-blocking, relay K1 is activated and disconnects the load circuit with its contacts.
It is possible to restore the initial state of the protection device only after the intervention of the operator - to do this, press the SB1 button. The device also goes into operational standby mode after a momentary power failure. Among the disadvantages of this protection device is its high sensitivity to short-term overvoltages.
The device (patent DL-WR 82992), the schematic diagram of which is shown in fig. 4.7, can be used to protect the load from unacceptably high output voltage. Under normal conditions, the transistor VT1 operates in a mode where the voltage between its collector and emitter is small, and a small power is dissipated on the transistor (the base current is determined by resistor R1). The resistance of the zener diode VD2 in this case is large and the thyristor VS1 is closed.

Rice. 4.7. Scheme of a semiconductor relay for protecting the load from overvoltage

When the voltage at the output of the device rises above a certain value, a current begins to flow through the zener diode, which leads to the opening of the thyristor. At the same time, the VT1 transistor closes, and the voltage at the output of the device becomes close to zero. The protection can only be disabled by turning off the power supply.
The described device must be included in the output circuit of the stabilizers so that the feedback signal is supplied from the circuit located behind the protection system. With a nominal output voltage of 12 V and a current of 1 A, the device can use the KT802A transistor, the KU201A - KU201K thyristor, and the D814B zener diode. The resistance of the resistor R1 should be 39 ohms (the power dissipation in the absence of an automation system that disconnects the stabilizer from the network is 10 W), R2 - 200 ohms, R3 - 1 kOhm.

The amount of electricity consumed by the population is increasing every year. A modern person cannot do without a washing machine, microwave oven, TV, refrigerator, air conditioner and other equipment. Unfortunately, the old apartment electrical wiring was not designed for such a large number of consumers. And for uninterrupted and long-term operation of household appliances, a stable power supply is necessary. Therefore, first of all, you need to check the condition of the wiring and make a partial or complete replacement. Wiring must be done competently, accurately and with high-quality materials.

The reason for the failure of household appliances can be both high voltage in the network and low. Sudden changes in electricity can also cause the equipment to become unusable.

There are several ways to protect against overvoltage. A high surge of energy can be triggered by lightning discharges. The easiest way to protect against lightning is to turn off all equipment from the network. However, it is not always possible to be at home. Therefore, to protect against overvoltage in a cabinet with an electric meter and circuit breakers, you need to install a surge arrester. With a three-phase power supply, the arrester is installed on each phase, that is, three arresters are needed.

A cheap and ineffective means of protection can be attributed to the usual. You should not buy the cheapest filter, because it will be an ordinary extension cord. As a rule, an interference filter, a fuse and a protective element are installed in the network. When the voltage rises above 260, the varistor abruptly changes its resistance and blows the fuse, turning off the connected equipment. A surge protector will not provide 100% protection.

Voltage drops can be caused by the deplorable state of transformer substations, electrical wiring in houses and porches. It is also impossible to exclude the human factor, when, as a result of the illiterate work of an electrician, the equipment in the whole house burns out.

Voltage stabilizers and uninterruptible power supplies (UPS) can be used to protect against overvoltage. There are advantages and disadvantages here. For a good stabilizer or high power UPS, you need to pay a round sum of money. But for powering expensive equipment, such protection is ideal.

To save money and protect your household appliances from power surges, it is recommended to install an AZM-40A voltage protection unit. When the voltage changes more than 265 volts or drops below 170 volts, the unit turns off all connected equipment. When the voltage level is restored, the protection unit will automatically connect the equipment after 2 minutes.

Another most affordable method of dealing with overvoltage is to install an RCD in conjunction with DPN-260 (overvoltage sensor). When the voltage rises, the DPN gives the command to the RCD to turn off the consumers. To supply electricity, you just need to turn on the RCD.

To have maximum protection, use all protection methods. Install surge arresters, voltage protection unit, voltage stabilizer, UPS and conventional surge protectors. After that, your equipment will be under reliable protection and you can sleep peacefully.

Overvoltage protection in the network is a very important measure that will not only extend the life of the electrical wiring, but also ensure the safety of its operation during power surges. If it occurs in the electrical network and there is no appropriate protection, household appliances fail, and this, in turn, is fraught with fire. Next, we will consider the main causes of overvoltage, as well as devices that will protect electrical wiring from the harmful effects of this phenomenon.

The main causes of occurrence

Most often, an overvoltage in a network of 220 and 380 Volts occurs for the following reasons:

1. on the supply line. The neutral conductor ensures the symmetry of the voltage in the phases of the supply network, with different loads in the phases. In the event of a zero break, the voltage in each of the phases changes depending on the difference in the loads in the phases: on a less loaded phase, it increases sharply up to 300 Volts or more, and on a more loaded phase, it drops sharply to values ​​below 200 V. Therefore, without surge protection when household appliances can fail almost immediately, and when electrical appliances will not work correctly. At the same time, there is a high probability of failure of electrical appliances, in the design of which there are electric motors (compressors).
2. Error when connecting to the electrical panel. If a three-phase input is made in the house and when connecting a single-phase 220 V wiring line, the conductor of the second phase was mistakenly connected instead of zero, then 380 V will appear in the outlet instead of 220 V.
3. There was an impulse voltage due to a thunderstorm entering the power line (which is why it is recommended to turn off all household appliances during a thunderstorm, as well).
4. Switching surges. In the event of emergencies in the electrical network: a short circuit on adjacent lines, an abrupt change in load due to disconnection (connection) of a section of the electrical network, accidents at power plants, which, depending on the magnitude, can adversely affect the operation of household electrical appliances .

Visual video example of the action of overvoltage

As you can see, many factors, including natural ones, affect a single-phase and three-phase network. Therefore, home wiring must be protected so as not to become a victim of an accident.

Surge Protection Devices

In the modern world, there are many different devices for surge protection in the network, which are easy to connect with your own hands. Consider devices that are used to protect against unwanted voltage surges.

Among the most useful for use in the house and apartment are:

1. . This device converts (stabilizes) the input voltage into a voltage of a given value. It is important to install a stabilizer if there are constant voltage drops in the network. It should be borne in mind that the stabilizer only works at a voltage that does not go beyond the permissible values ​​\u200b\u200bthat are indicated in its technical specifications. In the event of voltage surges above the permissible limits, the stabilizer may fail. Therefore, it is necessary with built-in overvoltage protection, and in the absence of such a function, install a voltage relay to protect it. About that, we talked in the corresponding article!
   
2. . This protective device, unlike CH, does not convert the input voltage. designed to disconnect home wiring from the electrical network in case of unwanted voltage drops (GOST 3699-82). The minimum and maximum voltage limits are set on the relay, and in the event of a jump above the set limits, the relay de-energizes the home electrical wiring, thereby protecting home electrical appliances. RN can be made as a modular device for installation in a switchboard (the well-known Barrier), built into an extension cord (power filter with the appropriate function), as well as in the form of an electrical plug (for example, ZUBR). We talked about that in a separate article.
   
3. Multifunctional protection device (UZM). This device can be installed in a switchboard instead of a voltage relay. UZM performs several functions, one of which is to protect the electrical network from voltage surges. About that, we told in a separate article.
   
4. Uninterrupted power supply unit. Again, I can confirm its effectiveness from my own experience. More than ten times the UPS saved my computer from a sudden shutdown when the voltage relay in the electrical panel was triggered. "Bespereboynik" has a low cost, so it is extremely necessary to buy such an option for overvoltage protection with a PC. In addition, most modern uninterruptible power supplies have a built-in stabilizer, which is especially important for computer equipment, which is more of all household appliances subject to the negative effects of surges. For information on how to choose a UPS, read our article:.
   
   
5. SPD. From impulse voltages (occur during a thunderstorm and can disable equipment) you can protect yourself by installing an SPD in the house. This device is quite popular today and is widely used both in everyday life and in production. In more detail about how and how it works, we told in a separate article, which we strongly recommend that you read. It should be noted that SPDs can also be called modular SPDs.
6. Contacting the energy service. The power supply organization, in accordance with the power supply contract, is obliged to provide a normal (within acceptable limits) voltage level of the electrical network in accordance with (IEC 60038:2009). Therefore, if you constantly have excessively low or, conversely, increased voltage, then you need to contact the supply organization with a corresponding complaint. It is most effective to handle a collective complaint, as single complaints are usually ignored. Contacting the supply organization is the only way to solve the problem if you experience strong voltage drops, since in this mode any CH will quickly fail.
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Quite often, breakdowns of electrical household appliances occur, because any electrical unit, when created, is designed to work with a certain level of electricity, i.e. on specific indicators of current strength and voltage in connection networks. Therefore, if these limits are exceeded, an emergency situation may occur.

The use of expensive home appliances, aggressive natural and atmospheric phenomena, and not too high a level of laying power lines make it vital for the owners of apartments and houses to take measures to protect against power surges in a private house and minimize possible consequences.

Where does overvoltage come from?

The planning and construction of many high-rise buildings a couple of decades ago was carried out without an eye to today's variety of household electrical equipment: microwave ovens, multi-chamber refrigerators, high-power irons and other electrically powered appliances. Therefore, the maxima of electricity consumption in the mornings and evenings adversely affect the operation of the entire electrical network in any home.

Electricity flowing through a cable or wire, unable to withstand such a load, contributes to their abnormal heating during the day and cooling in the evening. By virtue of the laws of physics, the conductor weakens as it becomes either wider or narrower. Contacts in the shield on the first floors or in a single input-distributing device in the house are noticeably weakened. Also, zero contacts can burn out, which leads to a voltage drop from 110 to 360 volts on all floors above the floor with burnt contacts.

An overvoltage in the electrical network can occur as a result of a lightning discharge in a power line, substation or house elements, while the current strength is simply huge, about 200 kiloamperes. When a lightning strikes a lightning rod and further passes along the ground loop, an electromotive force appears in the conductor materials, measured in kilovolts.

Also, welding or the simultaneous switching on of electrical appliances by many neighbors or the connection / disconnection of a powerful consumer can also cause a sharp power surge. To protect expensive electrical equipment and the entire private house, overvoltage protection in the network is necessary.

Features of protecting home electrical wiring

The organization of protection against emerging high voltage is one of the key issues when laying the electrical network in a residential building. It is carried out using special transformers and network filters. In many houses, circuit breakers are installed on the floor shields, which protect against electric currents during short circuits and temporary overloads.

When a high load is possible, all devices that protect networks from overvoltage must have devices for auto-shutdown and switches that respond to changes in current values. As a rule, the most reliable protection against such surges is placed on the input power wire, since it is this that is most affected during load peaks.

The surge protection scheme for the home electrical network is simple and multi-level. A simple one is mainly represented by an overvoltage relay in floor shields, and a multi-stage one (combined, protecting both from household power surges and from impulse ones, during thunderstorms) is an SPD, i.e. surge protection devices. Such devices are most often found in private homes.

Note! Electronic devices fail both due to increased and low voltage in the network (for example, refrigerators are hard to start, which negatively affects their further work).

The insulating layers of home electrical networks are usually designed for standard 220V, therefore, if the voltage increases many times, a spark jumps in the dielectric layer, which can provoke an electric arc and further fire.

To prevent negative consequences, the following protections are used, functioning according to the following principles:

• with a sharp unscheduled increase in voltage, the electrical circuit in the house or apartment is turned off;
• output of the received excess electrical potential from electrical appliances by transferring it to the ground circuit.

If the voltage rises slightly (for example, up to 380 volts), various stabilizers come to the rescue. However, their protective capabilities are rather limited - they are more designed to maintain the specified operating values ​​in the power grid.

When designing protection for a private house, various structural solutions and their technical characteristics are considered. It is necessary to take into account the principles of forming the base of surge arresters (surge arresters). For example, gas-filled arresters, after the pulse has passed, pass through themselves the so-called. follow current, the voltage of which is comparable to a short circuit. For this reason, they themselves can be a source of ignition, and they cannot be used for protection against electrical breakdown.

For home networks, a varistor protection device (semiconductor resistors) is most often used - rheostats composed of varistor "pills" from a mixture of zinc oxides, bismuth, cobalt and others. During normal operation of the power grid, such a circuit breaker allows microscopic leaks, and when a pulse of increased voltage passes, it is able to instantly switch to the “tunnel” mode and “lower” more than a thousand amperes in a very short period of time, since the resistance on this device decreases with increasing current strength, after which there is a quick return to regular "combat readiness".

Wiring resistance classes

All electrical appliances in domestic buildings are divided into four main categories, depending on the maximum withstand overvoltage:

• IV category - up to 6 kilovolts;
• Category III - up to 4 kilovolts;
• II category - up to 2.5 kilovolts;
• I category - up to 1.5 kilovolts.

In accordance with these categories, a protection system is built, which is abbreviated as ouzo (residual current device) with surge protection, for marketing purposes they are most often called limiters, and other names are used. Limiters are mounted in the direction of movement of a possible impulse. So, in the area from the inlet shield there is a 6-kilovolt impulse, in the first zone it is reduced by a surge suppressor to 4 kilovolts, in the next zone it drops to 2.5 kilovolts, and in the residential area with the help of an SPD of category III, the impulse potential is reduced to 1, 5 kilovolts. Protection devices of all classes function in a complex, consistently lowering the potential to normal values, which can be easily handled by the insulation of home electrical wiring.

Important! If at least one of the links of this protective chain fails, an electrical breakdown in the insulation may occur, which will lead to the failure of the final electrical appliance. Therefore, it is necessary to periodically check the serviceability of each element of the residual current devices.

The main devices of the protection system

One of the best ways to save the power grid from power surges is to install a stabilizer that is suitable for technical specifications. These are not cheap devices, and they are not always used, since the voltage in the networks is already quite stable.

Voltage control relays also help to eliminate instability in the network. In the event of a break in the neutral core and a short circuit in sagging cables, such a relay is able to turn on the protective functions even faster than the stabilizer, it takes only 2-3 milliseconds.

Such relays are very compact - for installation they require less space than stabilizers, they are easily placed on a simple din-rail, the cables are connected elementarily (unlike mounting stabilizers, when they are forced to wedge into the mains or install a special box for it). Stabilizers buzz noticeably, so it is undesirable to install them in residential premises, but the relays operate almost silently. In addition, devices that control the difference in electrical potentials consume very little electricity. The price of such relays is several times lower than those that have developed for stabilizers.

The principle of operation of the control relay is that with a constant supply of electric current, the device determines the potential difference and compares it with acceptable values. If the indicators are normal, the keys remain open, and the current continues to flow through the network. If a powerful impulse passes, the keys are instantly closed and the power supply to consumers is turned off. Such a quick and unambiguous response helps to secure all connected household appliances.

Additional Information. Return to normal mode occurs with some delay, adjustable by a timer. This is necessary so that large electrical appliances, such as refrigerators, air conditioners, and others, turn on in compliance with the rules and technical settings.

The relay is connected via a phase cable, while the null cable is included in the internal circuit for power supply.

There are two ways: end-to-end connection (in a straight line) or using a device - a contractor for communication. It is optimal to connect the relay mechanism before connecting the meter, which will also ensure its protection against overvoltage. However, if there is a seal on the meter, you will have to mount the relay behind it.

Impulse surges in the electrical network of private houses occur due to thunderstorms with lightning or switching surges. For the safety of electrical wiring, special SPD devices are used. As a rule, these are non-linear surge arresters (OPN), stabilizers and potential control relays. Of course, the arrangement of such a system is a costly undertaking, but its cost is much lower than expensive household appliances.

Video

A surge protection device (SPD) is a device designed to protect the electrical network and electrical equipment from surges that can be caused by direct or indirect lightning, as well as transients in the electrical network itself.

In other words SPDs perform the following functions:

— Lightning protection electrical network and equipment, i.e. protection against surges caused by direct or indirect lightning effects

— Surge protection caused by switching transients in the network associated with switching on or off electrical equipment with a large inductive load, such as power or welding transformers, powerful electric motors, etc.

— Remote short circuit protection(i.e. from overvoltage resulting from a short circuit that has occurred)

SPDs have different names: network surge arrester - OPS (OPN), impulse voltage limiter - SPE, but they all have the same functions and principle of operation.

1. Operating principle and protection device of SPD

The principle of operation of an SPD is based on the use of non-linear elements, which, as a rule, are varistors.

A varistor is a semiconductor resistor whose resistance has a non-linear dependence on the applied voltage.

Below is a graph of the resistance of the varistor against the voltage applied to it:

The graph shows that when the voltage rises above a certain value, the resistance of the varistor decreases sharply.

How it works in practice, let's look at the example of the following scheme:

The diagram simply shows a single-phase electrical circuit in which a load in the form of a light bulb is connected through a circuit breaker, an SPD is also included in the circuit, on the one hand it is connected to the phase wire after, on the other - to ground.

In normal operation, the circuit voltage is 220 Volts, at this voltage the SPD varistor has a high resistance measured in thousands of Megaohms, such a high resistance of the varistor prevents current from flowing through the SPD.

What happens when a high voltage pulse occurs in the circuit, for example, as a result of a lightning strike (thunderstorm impact).

The diagram shows that when a pulse occurs in the circuit, the voltage increases sharply, which in turn causes an instantaneous, multiple decrease in the resistance of the SPD (the resistance of the SPD varistor tends to zero), a decrease in resistance leads to the fact that the SPD begins to conduct electric current, shorting the electrical circuit to land, i.e. creating a short circuit that trips the circuit breaker and disconnects the circuit. Thus, the surge arrester protects electrical equipment from the flow of a high voltage pulse through it.

1. SPD classification

According to GOST R 51992-2011 developed on the basis of the international standard IEC 61643-1-2005, there are the following classes of SPDs:

SPD class 1 —(also referred to as ClassB) are used to protect against direct lightning effects (lightning strikes into the system), atmospheric and switching surges. They are installed at the entrance to the building in the input-distribution device (ASU) or the main switchboard (MSB). It must be installed for free-standing buildings in open areas, buildings connected to an overhead line, as well as buildings with a lightning rod or located next to tall trees, i.e. buildings with a high risk of being directly or indirectly affected by lightning. Normalized by pulse waveform 10/350 µs. The rated discharge current is 30-60 kA.

SPD class 2 —(also referred to as class C) are used to protect the network from the remnants of atmospheric and switching surges that have passed through the SPD of the 1st class. They are installed in local switchboards, for example, in the inlet panel of an apartment or office. They are normalized by pulsed current with a waveform of 8/20 µs. The rated discharge current is 20-40 kA.

SPD class 3 —(also referred to as ClassD) are used to protect electronic equipment from the remnants of atmospheric and switching overvoltages, as well as high-frequency interference passing through SPDs of the 2nd class. They are installed in junction boxes, sockets, or built directly into the equipment itself. An example of the use of SPDs of the 3rd class are network filters used to connect personal computers. Normalized by pulsed current with a waveform of 8/20 µs. The rated discharge current is 5-10 kA.

1. SPD marking - characteristics

SPD characteristics:

• Rated and maximum voltage- the maximum operating voltage of the network for operation under which the SPD is designed.
• Current frequency- operating frequency of the mains current for operation at which the SPD is designed.
• Rated discharge current(current waveform is indicated in brackets) is a current pulse with a waveform of 8/20 microseconds in kiloAmperes (kA), which the SPD is able to pass repeatedly.
• Maximum discharge current(current waveform is indicated in brackets) — the maximum current pulse with a waveform of 8/20 microseconds in kiloAmperes (kA) that the SPD is able to pass once without failing.
• Protection voltage level- the maximum value of the voltage drop in kilovolts (kV) at the SPD when a current pulse flows through it. This parameter characterizes the ability of the SPD to limit overvoltage.

1. SPD connection diagram

The general condition for connecting an SPD is the presence of a fuse on the side of the supply network or a fuse corresponding to the load of the network, therefore all the circuits presented below will include circuit breakers (SPD connection diagram in the switchboard):

Schemes for connecting SPDs (OPS, SPE) to a single-phase network 220V(two-wire and three-wire):

Schemes for connecting SPDs (OPS, SPE) to a three-phase network 3800V

Schematic diagrams of SPD connection are as follows.