Switch phases Automatic three-phase principle of operation. Assignment, selection and connection of automatic phase switch. Modern devices are controlled by microcontrollers

Recently, network companies very often began to issue technical specifications for connecting private houses to three-phase networks with an allowed power of 15 kW. That is, three phases come to the house and further in the home shield, they are evenly distributed on single-phase consumers. Emergency situations where problems with one phase occurs. For example, a dangerous overestimated voltage may appear on the same phase or in general may for a long time the abyss of the phase. So all consumers will be disconnected, which were connected to it. Based on this, we can conclude that there is a possibility of disconnecting vital consumers, such as the controller of the heating and pumping boiler, security or fire alarm, refrigerator, etc. It can bring some problems for comfortable stay in the house and even in winter can defrost the heating system. Therefore, it is necessary to power the priority load in any way to reserve.

There is such a device as an automatic electronic switch phase PEF-319. He is produced by the enterprise "Novatek-Electro". It can solve the object described above. In this article, you will find a full description of the PEF-319, detailed photos, a connection scheme, and an example of assembling a shield with it for a boiler house of a private house.

So, the automatic electronic switch phase PEF-319 is designed to power the priority vital single-phase load from the three-phase network. He also protects consumers from hazardous voltage fluctuations. If we speak in other words, this device automatically controls the presence and quality of the input voltage on all three phases and switching the single-phase load on the priority phase, which is within the user-limit. That is, if there is a voltage in the phase "A" or came out for the set limits, then the PEF-319 will automatically fix and switch the load to another phase, the voltage of which is normal. If all phases are dangerous voltage or it will be absent, the device will turn off its output and give an error message. This will protect your equipment. It is worth considering that at least the switching between the phases is occurring very quickly in 0.2 seconds, but still the load can be deraid briefly and go to reboot. Therefore, for such consumers, the reboot of which cannot be allowed, it is necessary to install the UPS.

This is what the electronic switch phase switch PEF-319 looks like. Then goes a few of his photos from all angles.

In the shield, it takes 9 modules. All contacts for connecting wires are located below. PEF-319 is installed on a standard DIN rail. The maximum cross section of the connected wire is 6mm 2. Its contacts are very tightly included by the Pugv 1x6 fascinated by the NSHVI tip.

Latch one and plastic. Therefore, pull it carefully.

In this device, the built-in relays have contacts that can switch the maximum current 30a. Therefore, it is directly connected to a single-phase load of up to 6.6 kW. If the load power is more than 6.6 kW, then it must be connected through contactors (magnetic starters). Therefore, PEF-319 needs to be protected by a circuit breaker to 30A, i.e. on 25a. Unfortunately or there are no automata with a face value 30a. The instructions for the device says that the time-current characteristic of the circuit breaker must be "in". There is still a recommendation on the use of flexible (multi-breed) wires that need to crimp the TIPs of the NSHA. Here is a clipping out of the instruction ...

If you are interested in this device, then you're better download complete instructions on the Internet and read it.

By the way, it turns out. Network companies for connecting the house highlight the power of 15 kW. This is the nominal empty machine 25a. The PEF-319 phase electronic switch can switch the maximum current 30A. Accordingly, it can be freely used in private homes even on entering.

On the PEF-319 device there are control knobs. If you count them from left to right, then:

• handle 1 is regulated by the trigger threshold at minimum voltage;
• handle 2 adjusts the threshold of the response to the maximum voltage;
• handle 3 Adjusts the time for automatic re-inclusion;
• handle 4 adjusts the return time on the priority phase;

In the device, you can specify which phase to read the priority. This means that at rated voltage on all phases, the device will switch the load on the priority. Therefore, when using multiple PEF-319, you need to adjust the priority for different phases to eliminate the overload of the same phase.

Let us turn to the PEF-319 connection schemes. As it used to say that if the connected single-phase load has a power of up to 6.6 kW, then we can connect it directly. On the device 15 of the contacts that are all numbered. It commutes only phases. Zero PEF is needed only for its work and it connects to the latest contact "15". Even in the configuration there are two jumpers, which are set between contacts "2" - "7" and "5" - "10". A phase on a single-phase load comes from contact "4". Here is a visual PEF-319 connection scheme for direct. I think everything is clear on it.

If the connected single-phase load has a power of more than 6.6 kW, it is connected through magnetic starters. Here is a visual connection diagram of PEF-319 through contactors. It does not need to put jumpers. The PEF-319 device will control the rebels of the starters. Three phases from the machine that feed the load are connected to three different contactors. The same three phases from the output of contactors should be united. They all need to feed one common single-phase load, but not at once all at once. Therefore, all three phases from the output of the starters need to be connected to one common tire. It is possible to implement it in distribution blocks, for example, CBD-80 or more powerful. But this is how the probability of obtaining interfacial closure appears. Suddenly there will be two phases on this block, for example, when applied to the contacts of the device. From this, the PEF-319 provides protection. You need to hold the conductor from the contact "1" to this distribution unit. The diagram below is a purple line. Through this contact, the device controls the presence of voltage at the output of contactors. If the contact "1" has a voltage, then this means that it is also on the distribution unit, so the device will not switch to another phase. Switching between phases is possible in the absence of voltage on contact "1". This allows you to ensure that the contacts of the relay from the non-good phase are open.

If you have any questions about the diagram of connecting the PEF-319 phase switch of the PEF-319 switch, then specify them in the comments.

Now go to the example of the assembly of the shield using PEF-319. I was collected to order for a private house to boiler room. The shield has already left for St. Petersburg and pleases its owners)))

A few words by his scheme. Limiting automatic B20 on the boiler room is in the main shield. Therefore, there is a chopper on the introduction, so as not to produce several automatic machines with each other with the same rates. In a concrete case, it was decided to connect the entire boiler room through the PEF-319. After the electronic device there is a Uzo to 40A / 30MA type A, to which five 2-pole circuit breakers are connected. Two-pole machines were selected so that when the leakage occurs, it was possible to freely disable not a good line by turning off one automaton without disassembling the shield. The owner of the house is very often swimming, and his wife unscrew the zeros not with his hands somehow.

Staten jumpers I removed, as they were out of the rigid cable, and made them from the Wire of the Pugv 1x6. Here is the connection of the PEF-319 close-up.

Check the operation of the scheme. I have no three phases. Therefore, I filed one and the tight phase for all three contacts. The photo below shows that the green indicator "L1" is on. This means that now everything works from the first phase and it is considered a priority.

Checking I turned off in turns of the phase. After the device turned off the first phase, the device switched to the second. This signals the green indicator "L2".

Similarly, the PEF switched to the third phase. When the jumper returns to the place, the device moved to work from the "L1" phase. Those. That's right. So it should have happened.

Be sure to print color stickers for beauty and for a visual understanding of what machines are responsible for.

Stickers close-up. Here we have two controllers of two boilers, pumps, sockets and boiler room lighting.

Here is such a beautiful shield with us.

The cost of the PEF-319 phase switch for autumn 2017 is 3500-4000 rubles.

If you need a wheelchart, then I am ready to develop a scheme and collect it. When ordering assembly, we develop a scheme for free. To order, write a request to the mail This email address is protected from spam bots. You must have JavaScript enabled to view.

The phase switches are used to increase the reliability of single-phase consumers. At the inlet at the phase switch - three-phase, and at the output - single-phase voltage. In this article, consider automatic and manual phase switches.

Suppose you have three-phase input and there is a possibility of disappearing one or two phases. In such cases, you can make the schemes that will be automatically or manually switch the load on the working phase.

Automatic switches are needed if your consumers are very sensitive to power supply interruptions, it is often a phase disappearance, on rarely visited objects. For example, a country house.

Automatic phase switches.

Automatic switches are different.

As an example, consider the automatic switch phase PF-441.

As a rule, automatic phase switches must be applied together with contactors, because The rated current of the switch contacts is only 16a. For some loads, it may be quite enough.

PF-441 has a priority phase L1. If the voltage in phase L1 goes beyond (190-250) B, the phase switch switches the load from the L1 phase to the L2 phase or the L3 phase. When the voltage is restored on the L1 phase - switches the load back.

But, there are switches of phases that can be used without contactors: PF-40A, PF-60A, PF-80A.

The device is operational (capable of switching the load) If there are at least one phase at the input, provided that its voltage is not lower than 200 volts (for PF-40A), or 180 volts (for PF-60A and PF 80A).

Manual phase switches.

When searching for a manual phase switch, you need to pay attention to the required rated current. In my case, I needed a switch to 63a.

The only manual switch phase switch on 63a, which I managed to find - 4G cam switch. Moreover, it is not called as the phase switch.

Phase manual switch diagram - 4G63-108:

This manufacturer can select switches with the desired switching scheme from 10 to 100a. I did not find other analogues. Up to 40, something else can be found.

By the way, you can use as a manual phase switch. Upcoming 2 Switch 1R:

If you know other phase switches - add in the comments.

In modern networks to control the voltage in phases, protection against overvoltage and providing voltage supply of a certain size, a manual or automatic electronic switch phase is used. These devices are necessary for uninterrupted work technique and networks in general. In manual switches, set the parameters, and in the electronic system, the network itself is adjusted to the network.

Certain requirements for the functioning of various devices exist in almost any spheres of our life. It is possible to achieve the necessary indicators through several ways:

• using the automatic logging line - AVR (three-phase installations);
• aBR line with uninterruptible power blocks (single-phase installations);
• phase switch (single-phase installations).

Principle of operation and phase switcher device

In the general case, the phase switch is a device, the main task of which is the connection instead of the main phase of any other, which has a voltage close to nominal indicators, when the power line is disconnected or the voltage jump above the set limits.

The design of this device implies that three-phase meals are in its introductory terminals. At the same time, only one phase is received on the conclusion, the quality of the voltage is the closest to the testimony of the norm. The activation of the switch occurs in the case of a full phase disappearance or when pumps and power cuts. It is important to take into account the fact that a three-phase network is required for the operation of the phase switcher. In addition, as mentioned above, there are two types of such devices: automatic switches and models switched manually.

The principle of operation of the phase switch, for example, the PEF-301 models, is to enforce the power lines until the value is found, which has optimal voltage indicators. Switching is carried out by means of a microcontroller, which directs a relay group located inside the device housing.

Hand-made phase switch is more famous to many as a packet. This device is a cam mechanical switch (3-position). The modern industry offers other types of packets that differ in the number of switches, it all depends on the purposes and needs of the electrical network.

Rules for choosing equipment

When choosing an automatic phase switch, you should pay the following specifications of the device:

1. Permissible current parameters. This is the most important indicator when selecting a phase switch. You should not choose a model, the current parameters of which are significantly higher than the nominal nominal machine;
2. Adjustment functionality. As a rule, on budget models of three-phase switches, this functionality is generally absent. This indicates the absence of the possibility of adjusting the threshold of the minimum and maximum voltage of the power grid. In addition, in modern models of switches, manufacturers provide a timer that is configured by the user to perform an attempt to transition to the main phase through a certain time interval;
3. Indication and display of performance and instrument settings. Simple switches models have a minimal light indication. More modern devices are equipped with not only the segment indicator, but also the LCD display, which displays the basic parameters of the device settings, the voltage value, the phase to which is connected.

It often happens that the existing phase switch cannot perform the tasks. This problem can be solved:

• acquisition of a phase switch calculated on large current indicators;
• the switching switch (electromechanical), and it must be connected in such a way that the contactor or the coil starter can be connected to its output terminals.

Important! It is necessary to carefully examine the technical indicators of the equipment. There are big differences not only between household and industrial switches, but also in similar applying instruments.

Scope of application

Mainly the phase switch is used to connect the backup line of the power supply, which, in turn, guarantees uninterrupted functioning of the technique. Switching to the backup power line is automatically performed only at the moment if one of the transformer phases is overloaded.

The use of the phase switch in offices and production is used to ensure the operation of automated systems, tracking and control equipment, dispatching equipment, communications, ventilation systems.

In medicine, the phase switch is automatically used to work such equipment as life support devices, the walking plants for the storage of drugs.

In addition, the phase switch is used to continuously function in private homes and apartments, for uninterrupted work:

• gas boilers;
• security systems;
• modern house management complexes;
• video surveillance.

Connection features

After the necessary phase switch is purchased, it should be connected.

Note! Work on connecting and commissioning such equipment should be carried out by a specialist who has experience and permission to work with electricity and high voltage. Inaccuracies in connection and, accordingly, incorrect operation of the device can not only cause a circuit between phases, but also lead to an emergency, threatening health and human life.

By itself, the phase switch is a modular device installed on the necessary object into a specially intended panel by means of a din rail. The switch requires the installation of a three-phase switch (automation). Connecting the secondary circuits directly depends on the selected switch model and its technical parameters. As a rule, the corresponding scheme is indicated in the accompanying documentation.

As an example, consider the Algorithm for connecting the Digitop PS-63A switch, which is used for a single-phase load of 220 W or one phase in a three-phase network for industry and in everyday life. A microcontroller is used to adjust the voltage in the instrument. This element reflects voltage indicators on digital equipment indicators for each phase. Load exit goes through the relay.

The switch operates at the expense of controlled phases. By pressing the button, you can see the upper voltage limit at which the switches are triggered, and the network is deserved on the instrument. The specified values \u200b\u200bchange using the up and down buttons. Next, when you press the button, the lower shutdown parameters are shown. To work it is necessary:

• select the priority phase;
• set the time to delay the first inclusion (counting in seconds);
• denote the delay period to return to the required phase;
• set the delay period by lower value.

If necessary, you can reset the indicators to the factory by clicking on a specific button.

Attention! The functionality of the equipment depends on the specified indicators to automatically select the phases.

So, the phase switch is a functional and highly economical solution that can effectively improve the power stability. This is especially important for country real estate owners, where voltage jumps and simply interruptions with electricity are not uncommon.

Video

Uninterrupted operation of electrical appliances is always an urgent task for electricians and specialists in the field of energy supply. Uninterrupted work requirements are presented in production, medical institutions, security complexes and at home. Such a requirement can be performed in different ways: Using (ABR) from an additional line, ABR with uninterruptible power supplies or phase switch. The first option is most often used in three-phase installations, the second and third and in single-phase one. In fact, the switch between the phases is AUR, where additional lines are taken with one of the two unused phases of the usual three-phase network. However, this is said in general, let's consider the device and the principle of operation of the phase switch.

Device and principle of operation

The phase switch is a device that connects instead of the main phase any other, in which the voltage is closer to the norm when the main power supply disappears or goes out for the set limits. If you still do not understand why this device is needed, let's consider in more detail.

From the definition it follows that three-phase meals come to the introductory switch switch, and one comes out of it, the voltage quality is closer to all. The switch itself occurs when jumps, drawdowns or full disappearance of the main one. The choice of the main line is carried out depending on the specific option. From here it follows the restriction - the phase switch should operate in a three-phase network. It can also be used for the generator, but then you need to think about how to form a control pulse to run it. The device can be manual and automatic.

The principle of operation consists in crossing lines, until the time of which is the optimal parameters by switching the relay group with a microcontroller.

In addition to automatic phase switches, manual options are often found. The manual switch is a 3-position cam switch, sometimes it is called "Packet". It occurs on sale and 2-position and 4-position switch depending on the needs of the consumer.

The low-power mechanical models of the switches are not needed to switch the load, but to switch the measured voltmeter line. The switching order may differ, for example, 0-1-0-2-0-3, where 0 - all phases are disabled, and 1.2 and 3 is the number of the selected line. Powerful models are conveniently used for engine reversal or load connection, you can switch under voltage.

Be careful switch to 3 positions are not a fact that it will switch three phases, possibly its positions - 1-0-2, i.e. The first pair of contacts is closed, turned off and the second pair of contacts. Check out the documentation for it and check the switching scheme if there is no documentation - you can check with a conventional ring.

How to choose a switch phase

We looked at how the phase switch works, now let's find out what you need to watch when choosing automatic models. In addition to the power parameters in the PF add functions that simplify the process of setting up and operating.

The first and most important thing is current. In order for the phase switch to approach your power supply system, the main criterion to watch when choosing is a permissible current. Do not buy the device, the current of which exceeds the rated current of the introductory machine. Although it should provide a safe mode of operation, but it will not be superfluous to lead to a compliance with permissible current and power.

The second parameter - ability adjustment. On cheap switches, there is no possibility at all. It is not possible to set the magnitude of the minimum and maximum voltage in the power supply network, in which switching, select the priority phase. The minimum adjustment set is setting the minimum voltage at which the devices can work maximize. In more advanced models, you can adjust the time through which you need to try to switch to the main phase and other settings.

Third parameter - method of display and indication. In simpler models there is a LED indication, usually one LED on the phase and an additional indicator "Alarm". When the line is normal and the load is connected to it, the corresponding LED is lit, for example, in green, when the line is normal, but it is in the reserve - the LED flickering when there are problems on all lines - the "Accident" indicator is burning. In more advanced models, a seven indicator or LCD display is installed. Purpose of indicators: Display the voltage value, settings, and the priority phase are included. The least visual indication method is separate LEDs, and the most obvious - LCD display.

Fourth parameter - functional. The simplest PF has a set of pre-installed parameters of the supply network, taken as the norm, and seeks to stick to them. But each electrical appliance requires an individual approach to nutrition, it is usually 220 +/- 10% in, and in some cases the tolerance can be increased, or vice versa - reduced. In more advanced models, these values \u200b\u200bare mounted by turning screws or handles to the desired position, according to graduation. The most functional are models with display and sensory control. It should not be assumed that the simpler is the worse, it is often not worth overpaying money for functions that will not be useful.

If the power of your switch is not enough to provide needs, you can solve this problem in two ways:

1. Buy switch calculated for a larger current.
2. Install the electromechanical switch so that a coil or is connected to the output terminals of the phase switch. Thus, all load will fall on the power contacts of the latter.

Application area

Repeat that before ordering the switch, you need to know - for its operation you need 3 phases. Backup lines are taken precisely with additional phases. Between the phases, the voltage is 380 volts, it is called "linear", and between the phase and zero 220 volts, it is called "phase". They are interconnected, but within this article we will not deepen in. The main thing is that you understand that for connecting to the power grids you need a three-phase network of 380 volts.

As already mentioned, this device is applied to connect the backup line. It works only if one of the phases of the transformer is overloaded or there has occurred. In cases where a "bad" voltage is received on the entry, the voltage is needed to automatically enter the reserve on the other line, the phase switch in this situation will not help.

Power supply with continuous operation mode is carried out from the phase switch. I propose to consider the scope of use in visual examples.

In medicine:

• life support devices;
• refrigerators with medicines in pharmacies;

In production and in offices:

• automation tools;
• control and hardware tracking, recording signals;
• means of communication, stationary radio stations, dispatching equipment;
• ventilation systems;

• a gas boiler;
• protection system;
• cCTV;
• system "Smart Home";

Connection scheme

After purchase, you may have difficulty with how to connect the phase switch. If you do not have experience with electricity, it is better not to try, as you have to work with high voltage in a three-phase network - 380 volts. In addition, incorrect use and connection of such equipment can lead to a closure between the phases.

The phase switch is a modular device that is installed in the shield on the object on. A three-phase circuit breaker is installed in front of it. After installing the primary chain, we turn to the output. But how to connect the secondary chains depends on the model of the switch. The connection scheme is defined in a technical passport or other similar documentation and may differ from the manufacturer to the manufacturer.

The phase switch is a budget way to increase the stability of electricity supply, it is especially important that it may be outside the city in the cottage, in the country village, where there are interruptions with electricity. We talked about how to connect and where to install, as well as about all parameters of such devices. The choice of uninterrupted feed remains for you on the basis of the needs and budget.

The supply voltage does not always meet the requirements of consumers. If his jump occurs from 220 V to 250 V, it may fail the sensitive electrical appliances. As protection, you can use the phase switch here.

Variety of types of phase switches

Operating principle

The switch provides a phase selection, the voltage on which matches the set parameters. It itself connects to the three-phase network, and at the output one of the phases is connected to the loads. If the voltage on it goes for the specified range, the switch translates consumers to work from another phase.

Hand switches phase

The purpose of the application of devices is as follows:

• switching the supply network;
• running and stopping electric motors, inclusion of transformers and other devices.

The main goal of the mechanical switch is to create uninterruptible power supply of single-phase load and protect consumers from voltage jumps in the network.

Figure below shows a shift switch for 3 positions. Contacts (2), (4), (6) are connected to 3 phases, and the load is connected to a fixed contact.

Sketchy view of the 3rd positions of the switcher

Manual cam switches are used to switch the chains under voltage up to 380 V. They are used when the electrical appliances are turned on and off, as well as to create the main and control circuits. Devices have small dimensions, withstand short-term overloads and have a high switching ability. When the device is selected, it is important to pay attention to the rated current.

In many designs, manual switches are provided with a zero position in which the electrical chains remain open. This allows you to use them as switches.

Electronic phase switches

To protect single-phase consumers from voltage jumps in the network, an electronic device is best suited. It automatically goes to another line when the active line cannot work normally. The equipment serves to feed household and industrial load.

The automatic device of most types has the following installation parameters:

1. Minimum and maximum voltage limits. Especially important is the upper limit that should be properly exhibited. If it is too low, frequent responses will begin. At high values, the internal wiring will begin overheat. The priority phase (L1) of the switching device is selected. If there are no voltage jumps on it, the transition to the line (L2) or (L3) may not occur. If such a switching will occur, the device will continue tracking the priority line and when restoring the required voltage level, the load switch will occur. If the lower and upper voltage limits intersect in the range of 10-20 V deviations, the device will be unstable. Therefore, it is important to make the right choice of installations.
2. Return time - the interval during which the switch must automatically check the status of the previous power source to return to its original state. If it is normal, the return transition occurs. Otherwise, the following check will occur at the same time. The choice of return time makes the user based on the experience, needs and features of the power supply.
3. The inclusion time is a pause, after which the device attempts to turn on the power supply after the voltage is lost on all phases.

Manufacturers

Switches "Apator" series 4G

The Russian company "Apator" produces products of mass applications and made by special order. A wide range of products allows you to choose a suitable replacement of products from other manufacturers.

Switching schemes include the following options:

• the presence or absence of zero switch position;
• accelerated switching;
• multi-position switching with the number of poles from 1 to 8;
• group switching.

The position of the cam switch, as shown in the figure below, provides closure of the electrical circuit with upper movable contacts (3) and fixed (1). Conductors are clamped with screws (12).

The scheme of the structure of the company "Apator" based on cam mechanism

When the cam is rotated (2) by 90 0 counterclockwise, the upper rod (5) rises up under the action of the springs and open the chain. The lower rod rises up along with movable contacts, closing the bottom electrical circuit.

The cam mechanism has the following advantages:

• reliable switching;
• resistance to overload;
• small resistance of closed contacts;
• high speed of closure and opening contacts;
• small switching efforts;
• the ability to create numerous switching circuits by the same mechanism;
• long service life.

The device of the switches makes it easy to switch the electrical circuits without excess pressure on the handle. Her artificial braking is also inexpedient.

The company "Apator" manufactures special switches calculated on the rated current 100 A. High loads are provided by duplicating contacts. Devices can be used as key switches.

Switches "SOCOMEC SCP"

The "SOCOMEC SCP" manufacturer (founded in France) produces several types of devices. Multipole switches COMO C (mostly three, and four-pole) are most popular. Devices can safely switch and turn off load from 25 A to 100 A (Fig. A). Contact break - visible.

Different types of phase switches from the company "SOCOMEC SCP"

SIRCO VM Commut is a multi-pole manual switch (Fig. B) Provides the load of the load from two sources. The rated current is 65-125 A. when the apparent gap remains.

SIRCOVER M (Fig. B) is a ceremonic switch with manual control and several poles. The device provides a shutdown or power on the power supply to the load.

SPH-41 phases switch

The device provides a connection of a single-phase consumer to a three-phase four-wire network (manufacturer of Vektor LLC, Russia). The automatic device is installed after the meter, selects the most reliable phase parameters and connects the consumer to it. Then the voltage is controlled. The choice and installation of its upper and lower permissible limits is done in advance.

Switching phases automatically

The PEF-301 switch is shown in the figure below (Manufacturer of NPK "Electric Power Industry"). The device is designed to power a single-phase household and industrial load from the three-phase network. The device automatically selects the phase with the best parameters and connects the load to it. Consumers up to 3.5 kW are associated with a network through the device (Fig. A). The priority is the phase L1. When the voltage value is released for the trigger threshold, PEF-301 switches the consumer to another phase by contacts (7-8), (9-10), (11-12) at the output of the instrument.

For greater load power, the output contacts of the device are associated with magnetic starter coils, which control the power contacts of the voltage supply through the phase with the best characteristics (red, green and black in Fig. B).

Connection Schemes Automatic Phase Switch

3 phase switch. Video

The three-phase switch for the house is available in the video below.

The phase switch in the house or apartment can be set manual or automatic. The electronic phase switch provides maximum comfort, because it performs all the operation without interference and does not require constant control. One should only make the right setting of its operation, and it will reliably protect household electrical appliances.