Shutdown device. Types and principle of operation of the residual current device (RCD)

The requirement of reliable protection of a person from the damaging effects of current has always outstripped the possibilities of science and technology to create protective devices that satisfy this goal. Today, innovative developments in the electrical industry fully meet all the criteria for devices of this type. The article reveals the question of such a device as an RCD: what it is, its purpose, principle of operation, choice and application.

RCD stands for "residual current device"

Means and methods of electrical protection: modern devices and features of their work

As soon as the use of electric current entered our lives, it immediately became necessary to protect against its damaging effects on human health. First of all, this is the insulation of the conductive parts of the wiring and parts of the current receivers.

But complete isolation is impossible, since technological breaks and contact groups are present in any electrical circuit. There is always a possibility of violation (destruction) of the insulating layer of conductive elements and their mechanical damage, and most importantly - statistical regularity in violation of safety regulations, instructions and rules for the operation of electrical equipment, both at the production and household levels.

Electrical protection: isolation and grounding

One of the most effective ways to protect against the damaging effects of electric current is to organize a ground loop. The ground loop is an artificial conductor connection to the "ground" (the so-called PE-conductor) of neutral conductive cases or parts of electromechanisms, having a resistance of not more than 4 ohms. The listed elements of electrical equipment may be energized due to a short circuit to the body of the phase wire or lightning current.

The main purpose of the ground loop device is to exclude the possibility of electric shock to a person or animal in case of touching the body or part of the mechanism of electrical equipment that is energized due to a short circuit of the phase electric current.

Note! In AC networks with grounded neutral and voltage up to 1 kV (this is the format of residential power supply), grounding is not used as the main protection against electric shock from indirect contact, since it is not effective.

The passage of electric current through the human body in the event of an impact in a system with grounding (right) and without grounding (left)

The problem of the most effective protection against the effects of electricity on a person was solved by the so-called differential current devices (UDT) - this is a large segment of control and protective devices for various purposes and design features. The classification of the UDT segment is quite extensive: from the method of control, the type of installation and the number of poles, to the possibility of regulation and time delay of the breaking differential current.

Consider what an RCD is. The decoding of this abbreviation is a residual current device. The requirements for the installation and use of UDT are given in supplemented editions of the PUE - rules for the installation of electrical equipment and in a series of standards for electrical installations of buildings IEC 60364 and the impact of current on humans and livestock IEC 60479-1.

Historical background for the development of RCDs

Germany was an innovator in the development of RCDs. The first working sample of the protection device was designed and manufactured in the thirties of the last century. The smallest possible differential current transformer was used as a leakage current sensor, and a polarized magnetic relay with a sensitivity of 100 milliamps (mA) and a response time of no more than 0.1 seconds was used as a control element.

The threshold for fixing the differential current in the prototype was about 80 mA. It was impossible at that time to develop a control relay with a sensitivity of less than 80 mA due to the lack of materials with the required electromagnetic characteristics. And only in the middle of the twentieth century, a new design solution for the RCD was proposed. The design took into account the mechanisms to eliminate false positives from discharges during a thunderstorm and significantly increased the sensitivity to differential current up to 30 mA.

The overall dimensions of the RCD have also undergone changes: from the size of a parcel box to a modern format that can be installed on a DIN rail in modern electrical cabinets.

Technical experts in electrical and electronic engineering are already making predictions for the future. They firmly believe that systems such as protection against electric shock will soon be managed by artificial intelligence.

It will be able to perform not only measuring and control functions, but also performing video and audio monitoring of the object given to it, make instant decisions on any random situations and, if necessary, notify the rescue services.

RCD: what is it and how does it work

Residual current devices (RCDs) are among the most demanded of protective UDTs operating in domestic conditions. The RCD works as a protector of a person from electric shock and as a preventive mechanism to prevent accidental ignition of wiring cables and connected cords of electrical appliances.

The functional idea of ​​the device under consideration is based on the laws of electrical engineering, postulating the equality of the incoming and outgoing current in closed electrical circuits with active loads.

This means that the current flowing through the phase wire must be equal to the current flowing through the neutral wire - for single-phase current circuits with two-wire wiring and that the current in the neutral wire must be equal to the sum of the currents that flow in the phases for a three-phase four-wire circuit.

When in such a circuit, due to a person accidentally touching the non-insulated parts of the conductive elements of the circuit or upon contact of the bare part of the wiring (due to damage) with other conductive objects forming a new electrical circuit, the so-called current leakage occurs - the equality of the incoming and outgoing currents is violated .

This violation can be logged and used as a command to disable all electrical circuit. On this process, the RCD was designed. And the "leakage" current in the framework of electrical engineering began to be called differential current.

The RCD can detect very small "leakage" currents and act as a circuit breaker mechanism. Purely theoretically, the principle of operation of the RCD looks like this (where I in is the input current of the neutral wire, I out is the output current of the phase wire):

• I in = I out (balance of the system without violation, RCD in standby state);
• I in > I out (the balance of the system is disturbed, the RCD registers the appearance of a differential current and turns off the supply network).

RCD will definitely protect

When an RCD is installed in the power supply network, this means that protection is provided against:

• closing the phase wire to the body of the electrical appliance. In a large number of cases, these are the heating elements of washing machines, water heaters and heaters. Moreover, a breakdown can occur only when the thermal element is heated under the influence of current;
• improper wiring, when unscrupulous electricians wall up the “twisting” of wires in plaster without using a junction box. If the wall is wet, a differential current will leak from this twist into the wall and the RCD will de-energize the line all the time until the plaster is completely dry or the connections are properly repaired;

• improper installation in the electrical panel, when seemingly small, but "useful" changes made to the circuit change the current distribution and lead to a loss of high efficiency of the device. This will be discussed in more detail a little later.

RCD can work for reasons that are not evident from the first inspection of the connection diagram of household appliances. If you use a gas stove with electric ignition of gas, or a washing machine is connected by a hose in a metal case to a water tap, or when neighbors have grounded a water supply or heating system, then a current leakage will again occur in the electrical circuit, due to which it will work RCD. In such cases, rigorous engineering analysis is required.

Boundary conditions for RCD operation

Rules very often have exceptions. This principle has not bypassed the universal qualities of the considered protective shutdown device.

The RCD will not respond when a person or animal is energized, but no earth fault current will occur. Such a case is possible when touching simultaneously the phase and neutral conductors, which are under the control of the RCD, or with complete insulation with the floor. RCD protection in such cases is completely absent. The RCD cannot distinguish between the electric current passing through the human or animal body and the current flowing in the load element. In such cases, safety can be ensured by mechanical protection measures (full insulation, dielectric casings, etc.) or a complete de-energization of the electrical appliance before its technical inspection.

The RCD, which is completely dependent on the supply voltage of the network suitable for the object, is in working order only if the specified network is in full working order. The situation can become dangerous when the neutral wire breaks “above” the RCD, and the phase wire remains energized. Then, in the wiring, the phase wire can become a factor in electric shock, and the RCD, due to its own incapacity, will not be able to turn off the power to the network.

The RCD can “hang” in a standby state if the main contact rod in the solenoid is jammed or if the secondary winding fails. control device, and at the right time does not work. In order to check the operating condition of the RCD, there is a test mechanism. If you regularly test the device (and for this you just need to press the "T" - test button), the risk of RCD failure will be minimal.

Application and how to connect an RCD

RCDs received their main application in domestic conditions when used in electrical groups of bathrooms, kitchens and socket groups of a large number of connected devices and equipment. This does not mean that it does not make sense to use an RCD on a common incoming network. This selective scheme is dictated only by the efficiency of management and marketing expediency, since RCDs for small currents are much cheaper at the price of devices with higher power.

However, in some cases, if we consider hostels, clubs, etc., it will be more reliable to use a general selective RCD due to the massive and simultaneous use of almost all elements of electrical equipment. The selective type RCD differs from the usual one in the large delay time of the tripping differential current (i.e., the trip time) and is one of the most used devices. When a conventional local RCD is triggered in any circuit, the general selective RCD does not turn off all the wiring at once, but allows you to stop the power supply of only a separate group.

For example, if a breakdown of equipment insulation occurs at a disco and the case (for example, an amplifier) ​​is in contact with a phase wire, then at the moment the operator touches the amplifier, the local RCD trips and turns off only the amplifying equipment group, and the selective general RCD will not turn off all power and such groups as a common light, toilets and cafes will work as standard.

The mechanism for connecting an RCD to an existing network is similar to connecting a circuit breaker, with the only difference being that when two terminals are required on a single-phase machine, then four on an RCD.

If, when a person touches a bare section of a wire or a case of equipment under phase voltage, the electricity instantly turns off, it means that the RCD has worked.

Important! In AC systems, additional protection by means of RCDs should be provided for socket groups with a rated current up to 20A (washing machines, stoves, etc.) and mobile (portable) equipment and power tools with a rated current up to 32A, which are used outdoors.

The basic principles of the RCD mechanism and a comparative analysis of analogues

The physical processes occurring in the mechanisms of operation of many modern electromechanical or electronic devices may be completely incomprehensible to us. Not every person has knowledge of engineering and technical disciplines and, of course, is not able to understand and describe the physical basis of the principles of operation of a particular device. But the principle of use (rules of operation), built on security elements, makes it possible to use the most complex inventions in our daily life.

Related article:

Criteria for choosing fixtures. Types of overhead lighting fixtures. Types and prices of built-in models. Overview of LED chandeliers.

Each device has a technical passport, in which both the purpose and the principle of operation are always described in an understandable language, and whenever required, it prescribes installation, connection and proper operation measures. In our case, an attempt was made to describe the principle of operation of the trip protection device (RCD) most accessible way and give the reader the opportunity to make their own decisions in choosing one or another device, if necessary.

The principle of operation of the RCD and design features

To perform its protection function, the device consists of a differential current transformer minimized in size, a control “following” magnetoelectric relay, a control solenoid for the main contact group and additional diagnostic elements - the “Test” button and elements of triggering mechanisms.

The physical side of the work is as follows.

When the RCD is turned on (pressing the contact closure button), the solenoid turns on and holds the rod of the contact group in the same way as an electromagnet. Since at the same moment the terminals of the winding of the solenoid itself and the terminals of the supply wires come into contact. But in the power supply circuit of the solenoid, transit opening contacts are installed, which are controlled by a magnetoelectric relay and the relay is given the function of self-shutdown of the RCD.

The outgoing and incoming current of the network, flowing in the corresponding windings of the transformer, due to the produced EMF (electromotive force) creates two equal but oppositely directed magnetic fluxes in the magnetic circuit (core).

Due to the complete compensation of magnetic fluxes, no EMF occurs in the secondary winding wound on the core, which feeds the control relay, and the relay is in a passive state.

At the moment a person or animal touches the bare part of the phase wire or the case of any household appliance on which a phase breakdown has occurred, an additional differential current will flow through the incoming winding of the transformer.

Violation of the equality of the incoming and outgoing currents instantly creates an uncompensated magnetic flux in the core of the transformer. And as a result, the instantaneous appearance of EMF in the secondary winding connected to the relay as its power source.

The relay, having received power, immediately operates and turns off the power to the solenoid (the transit terminals open), which holds the main contacts in the closed position.

The contacts open, the solenoid de-energizes and releases the spring-loaded rod of the contact group, and the power supply to the network is interrupted. The more sensitive the control relay is to small values ​​​​of the differential current, the more effective the protective function of the RCD.

Note! Protective functions such as power outage during phenomena short circuit and current overload in the RCD are not provided. In practice, the installation of an RCD usually involves the sharing of an automatic switch ("machine"), directly designed for the possibility of a short circuit and current overload.

The correct connection diagram of the RCD and the machine. Mounting errors

Both devices have the same mounting design for installation in control panels for electricity metering and distribution. The task is reduced only to the correct connection to the mains and to each other:

1. The main option: central machine → metering → RCD.
2. Preferred: central machine → metering meter → RCD selective type → group machine → group RCD.

• in no case do not connect the neutral wire to the ground terminal after it has left the RCD. In this case, periodic occurrences of differential leakage current are possible, leading to false alarms;
• incomplete phase connection of the RCD. If the neutral wire from the mains passes in transit past the RCD, then the resulting current in the neutral wire will be perceived as differential, which will lead to a constant operation of the device;
• do not allow the connection of neutral wires of sockets that are under the control of the RCD with the ground wire (terminal). In this case, even an outlet not connected to the consumer will create a differential current;
• for group use of RCDs, jumpers of the neutral wire on the incoming terminals are not allowed. This will trip all RCDs at the same time.

Helpful advice!When connecting a four-pole. those. three-phase RCD into a similar network, it is necessary to strictly match the phase marking with the marking device terminals. Otherwise, the test mode will not be objective.

RCD analogues with advanced features

The market for RCDs (residual current devices) is very diverse. It should be distinguished from a number of analogues competing with RCDs the so-called differential machine, which belongs to the class of circuit breakers controlled by differential current - RCBO.

To answer in an accessible form the question: difavtomat, what is it? - it must be remembered that its main feature is the combination of the main function of the RCD and the circuit breaker. Also, the difference between RCD and differential automaton lies in the fact that the RCD itself requires protection against short circuits in the network and overcurrent (of course, this is why a circuit breaker is installed in a pair), and the difavtomat is able to protect itself.

It should be noted the entry into the market of new models of RCBOs - electronic and with an auxiliary power source. They differ from electromechanical designs by the presence of an electronic board with a differential current amplifier, which allows detecting leakages of the order of 10 mA and work even if the neutral wire of the incoming network is broken, when the phase wire remains energized. A conventional RCD or RCBO in such a situation, when a person comes into contact with an open phase section, will not work.

Another novelty in the line of differential current devices is the so-called multifunctional protection device. What is USM becomes clear from familiarization with its purpose. This device is used to completely turn off the equipment when the voltage parameters in the network go beyond the operating limits (less than 180V and more than 260V), as well as to protect operating equipment from "burning" windings and electronic elements of power surge devices. These jumps can be caused by electromagnetic impulses or short circuits of phase wires to zero in a three-phase network.

RCD or differential machine: how to distinguish and what to choose

There is no unambiguous algorithm that allows you to give preference to one or another device. The reason is the multivariate feature of the choice. Consider the main factors that influence the choice of RCD or RCBO.

Is it possible to place this or that device in the main panel. In practice, the overall overall size of the RCD and the circuit breaker is larger than the overall size of the difavtomat.

What is the purpose of making changes to the electrical circuit. If it is necessary to individually protect high-power equipment (kitchen stove, boiler, washing machine, etc.) from a possible “shock” by electric current, a differential machine is optimally suited, which clearly monitors the load current.

If it is necessary to protect against electric shock for any group of sockets or lighting lines, in which the power can be increased over time, it is advisable to use an RCD. The RCD has a large power reserve, and the differential machine, due to overload, will need to be replaced with a more powerful one.

Qualitative assessment. Practice has proven that devices that combine many functions of various devices are often inferior in quality to single devices. This also applies to such a multifunctional device as a differential machine, which is inferior in quality and service life to an RCD and a circuit breaker.

The breakdown situation. In a situation where the RCD or circuit breaker stops working, either one or the other device needs to be replaced. But when the differential machine does not work, even due to the failure of one of some functions, you have to replace it with a new one. In this case, the costs are much higher.

Supply stability. If the RCD fails, it is enough to install jumpers between the circuit breaker and the power supply network (bypass the RCD) and the power supply is restored. But if the difavtomat breaks down, you will need either a spare difavtomat or a spare circuit breaker. So a quick prompt resumption of power supply may be in question.

Helpful advice! If necessary right choice desired device differential current (RCD or RCBO), it is necessary to use an engineering approach and an economic assessment even when one or another type of device is already at hand.

The question remains on the external difference between the RCD and the RCBO.

Labeling of the title side of the device. Example 1: “ABV 16A 30 mA” - we have an RCD ABB (manufacturer “ABV”) with a rated current of 16 amperes and a lower differential current of 30 milliamps. Example 2: “CHNT C16 0.03A” - we have a difavtomat in front of us, manufacturer CHNT with a rated current of 16 amperes and a characteristic of an electromagnetic and thermal interrupter of class “C” at a differential current of 30 milliamps.

The indicated wiring diagram is on the title side. For RCDs, the diagram shows a differential transformer (oval loop), a control relay (square) with a loop on the oval contour, and a test circuit in the form of a dash-dotted line. For a difavtomat, the circuit is very similar to the RCD circuit, only there are additional figures in the form of a small arc and a stepped line - these are the designations that are different from the RCD, electromagnetic and thermal interrupter.

Application and installation of RCDs: designations on wiring diagrams

Most of the control and management devices installed in the power supply network have a small list of parameters necessary for their correct selection in the electrical circuit.

The choice of RCD is made according to the rated load current and the threshold for fixing the differential leakage current. Practice recommends a value not higher than 30 mA. The installation of the RCD in the electrical network is carried out on the basis of an engineering analysis of the elements existing in the network and the installation possibilities. The scheme for connecting the RCD to the network must take into account all possible switching errors and eliminate them. Only when properly connected to the power supply circuit, the RCD will ensure maximum efficiency in triggering the protective mechanisms of the device.

Selection parameters and connection diagram of RCD without grounding

Knowing the principle of operation of the RCD, with a standard two-wire electrical network, represented only by phase and neutral wires, which does not have a ground loop, it is possible and necessary to install an RCD in accordance with the protection requirements. The correctness and installation schemes of the RCD were discussed earlier.

The answer to the question of which RCD to put in the apartment is with a calculator in hand. It is necessary to sum up the power of the pieces of equipment and equipment installed in the apartment, and divide the sum by the number 220. Thus, in a rough approximation, we calculate the rated current, according to which the choice of RCD will be made. This calculation is based on the mathematical dependence of the electric power on the mains voltage (220V) and the current strength that occurs when the load devices are powered:

M = U x I,

where M is power, U is voltage, I is current.

Example: you want to select an RCD to protect a group of electrical appliances in a kitchen unit. This line contains the following appliances:

1. Electric 2000 W.
2. Microwave 1200W.
3. Food processor 700 W.
4. Refrigerator 800 W.
5. Small household appliances about 600 watts.

We summarize the power consumption: 2000 + 1200 + 700 + 800 = 5300 W. We calculate the current according to the formula: I \u003d M / U \u003d 5300/220 \u003d 24.09A. We select the closest RCD with a large value - 25A.

For an in-depth calculation of currents in the wiring lines, knowledge of the basics of higher electrical engineering is required.

In addition to the rated load current and the sensitivity threshold of the differential current, in some cases, when choosing an RCD, it is necessary to pay attention to one more criterion - the category of leakage current. In most cases, this applies to alternating and pulsed current in the network.

Connection diagram for RCDs and automata using the example of an apartment

AC category assumes the operation of the RCD in an alternating current environment of differential leakage. This category is the most common and can be used in all types of AC networks. In what cases the RCD is triggered - it was discussed above.

Category A has the lowest sensitivity threshold (about 10 mA) for differential current and is able to record a separate component of the current amplitude (the so-called half-wave). An RCD with this category of leakage current reacts not only to a variable current configuration, but also to a pulsed one. Such RCDs are gaining priority use, as more and more household appliances, especially lighting elements, are transferred to pulsed current power supplies.

The main trend of the European market is the expansion of the impulse equipment segment. This, of course, will lead to an increase in the number of pulse current RCDs used. But since active current receivers (full of alternating current) will remain in domestic use for a long time, RCDs of the AC category will occupy a fairly wide space on the market shelves.

Returning to the question of the absence or presence of a ground loop in the electrical network, it is necessary to emphasize that even in the presence of grounding, the organization of protection against electric shock by installing an RCD in the network is even more required.

The basic principles of the RCD connection scheme in a single-phase network have already been considered earlier. The circuit for connecting an RCD with grounding is no different from a circuit without grounding.

Helpful advice! If the electrical network has a ground loop, it is necessary to control and ensure the correct circuit when connecting the RCD, when not a single neutral wire in the electrical wiring should be paired with the wire (terminal) of the ground loop.

Graphic designation of the RCD on the power supply diagram

The main directive provisions included in GOST 2.755-87 ESKD “Conditional graphic symbols in electrical diagrams switching devices and contact connections ”and GOST 2.710-81 ESKD“ Alphanumeric designations in electrical circuits ”, a graphic and letter designation of such devices as an RCD is prescribed. But no strict prescriptions for the different designation of differential current devices have been presented.

As we already know, all differential current devices are represented by a breaker mechanism and a control element - a differential current transformer. Therefore, the designation of the RCD in the diagram is represented by two standard graphic symbols - a circuit breaker and a transformer that registers differential current. You can see the graphic designation of the RCD on single-line diagrams and other drawings.

Three-phase RCD connection diagram

This type of device is usually called a four-pole device and the specifics of its connection to a three-phase network are completely similar to the connection of a two-pole RCD. On the body of the device, the terminals for connecting the phase wires and the neutral wire are indicated. Also, a passport is attached to the device, which presents standard schemes for connecting a four-pole RCD to a three-phase network.

Different manufacturers sometimes have differences in the location of the zero terminal on the device case - on the right or on the left, and the connection of phase wires only requires matching the designation at the input and output.

Four-pole three-phase RCDs are used for high differential leakage currents and their main purpose is only to protect against ignition of electrical wiring. In order to organize the protection of people from electric shock, it is necessary to install two-pole single-phase RCDs on each individual group of equipment with leakage current adjustment equal to no more than 30 mA.

Lineup, manufacturers and prices of RCDs

The market segment of UDT products is represented by a number of foreign brand companies, as well as domestic manufacturers. To date, preference is given to brands from Italy, Poland, Germany and Spain, as their products have received the best consumer rating in terms of quality, reliability and price-quality ratio. The existing market for UDT differential current devices allows the production of a wide selection of various types of devices, providing a diverse range of products both in price and quality.

The table shows the products of the most common manufacturers of UDT and shows the market prices they offer:

As can be seen from the comparative table, the price of RCD 25A 30 mA (the most demanded on the market) depends on the manufacturer. So the price of RCD ABB 25A 30 mA is higher than Chinese counterparts, but lower than that of such manufacturers as Legrand or Schneider Electric. Taking into account such criteria as quality and cost, it is preferable to buy an RCD 25A 30 mA from ABB, and you can buy the necessary circuit breaker made in China or Legrand.

Helpful advice! Having decided to install an RCD in your home network, but having no experience in electrical installation of similar devices, use the services of a qualified electrician.

Summing up this excursion into the world of differential current devices, in particular, the residual current device (RCD), we will focus on the important points considered.

One of the most effective means of protecting humans and animals from the damaging effects of electric current is the installation of residual current devices (RCDs) in the power supply network.

The RCD has the function to respond to the differential leakage current that appears when a person comes into contact with a bare part of the wiring or the body of any electrical equipment. It may be under phase voltage due to damage to the insulation of the phase wire and its contact with the housing. Also, the RCD reacts to current leakage in places where the wiring insulation is damaged, when this can lead to heating and fire.

However, the RCD does not respond to short circuit phenomena in the wiring circuit and to excess current in the circuit. In this regard, it is necessary to install the device in tandem with a circuit breaker ("automatic"), which responds to a short circuit and power overload.

Most importantly, always follow the safety rules and caution when working with electrical appliances and machinery. As often as possible, visually inspect open current-carrying elements of electrical wiring and connected elements of current collectors.

Imagine the following - you have a washing machine installed in your bathroom. Whatever the well-known brand it is, devices of any manufacturer are subject to breakdown, and, for example, the most banal thing happens - the insulation on the power cord is damaged and the network potential appears on the machine body. And this is not even a breakdown, the machine continues to work, but it is already becoming a source of increased danger. After all, if they touch both the car body and the water pipe at the same time, we close the electrical circuit through ourselves. And in most cases it will be fatal.

To avoid these terrible consequences, they were invented RCD - residual current devices.

RCD- this is a high-speed protective switch that reacts to differential current in the conductors supplying electricity to the protected electrical installation - this is the “official” definition. In a more understandable language, the device will disconnect the consumer from the mains if there is a current leakage to the grounding conductor PE ("ground").

Let's look at the principle of operation of the RCD. For greater clarity, the figure shows its "internal" circuit diagram:

The main unit of the RCD is differential current transformer. In another way, it is called a zero-sequence current transformer. To make it easier for us and not to get confused in terms, let's call this node just a current transformer.

As can be seen from the figure, in this case it has three windings. The primary and secondary windings are included in the phase and neutral wires, respectively, and the third winding is connected to the starting element, which is performed on sensitive relays or electronic components.

The starting body is connected to the executive control device, which includes a power contact group with a drive mechanism. The test button is used to check and monitor the health of the RCD. Now imagine that a load is connected to the output of our circuit. Naturally, a current will immediately appear in the circuit, which will flow through the windings I and II. For further consideration of the principle of operation of the RCD, let's move on to a more visual diagram:

In normal mode, in the absence of leakage current, the circuit flows through the conductors passing through the window of the magnetic circuit of the current transformer. operating current loads. It is these conductors that form the back-to-back primary and secondary windings of the current transformer. These currents will be equal in magnitude and opposite in direction: I1 = I2. They induce equal but oppositely directed magnetic fluxes F1 and F2 in the magnetic core of the current transformer. It turns out that the resulting magnetic flux is zero, the current in the third (executive) winding of the differential transformer is also zero, and the starting element 2 is in this case at rest and the RCD is operating in normal mode.

When a person touches open conductive parts or the body of an electrical device, on which an insulation breakdown occurred along the phase (primary) winding of the current transformer, in addition to the load current I1, an additional current flows - (IΔ is indicated in the diagram), which is for the current transformer differential(difference: I1-I2= IΔ).

It turns out that our currents are unequal, therefore, magnetic fluxes are also unequal, which no longer compensate each other. Because of this, a current appears in the third winding. If this current exceeds the set value, then the starting body is activated, it affects the actuator 3.

The actuator, consisting of a spring drive, a trigger mechanism and a group of power contacts, opens the electrical circuit, as a result of which the installation is disconnected from the network. To carry out periodic monitoring of the health (operability) of the RCD, a test button 4 is provided. It is connected in series with the resistor. The value of the resistor is selected in such a way that the difference current is equal to the passport tripping leakage current of the RCD (we'll talk about the RCD parameters later). If, when you press this button, the RCD is triggered, then it is working properly. Typically, this button is labeled "TEST".

Three-phase residual current devices They work in much the same way as the single phase ones. In three-phase RCDs, four wires pass through the core window - three phase and zero. the simplest three-phase RCD is shown in the figure:

A three-phase RCD includes a switch 1, which is controlled by an element 2, which receives a trip signal from the secondary winding 3 of the current transformer 4, through the window of which the neutral working wire N and phase wires L1, L2 and L3 (5) pass.

If the load is equal in the zero and phase (or in three phase) wires, their geometric sum is zero (the current in the phase wire of a single-phase RCD flows in one direction, and the current in the neutral wire of exactly the same value flows in the opposite direction). Therefore, there is no current in the secondary winding of the current transformer.

In case of current leakage to the grounded housing of the electrical receiver, as well as in case of accidental contact of a person standing on the ground or on a conductive floor with a phase wire of the electrical network, the equality of currents in the primary winding of the current transformer will be violated, since, in addition to the load current, a leakage current will flow through the phase wire, and a current will appear in its secondary winding - just like the description of the operation of a single-phase RCD considered above. The current flowing in the secondary winding of the transformer acts on the control element 2, which, through the switch 1, disconnects the consumer from the mains. The appearance of a three-phase RCD is shown in the figure:

Consider practical schemes for switching on RCDs in switchboards.
RCD switching circuit for single-phase input. Here, a switching circuit with a divided zero (N) and "earth" (PE) bus is used. As you can see in the figure, the RCD (5) is installed after the introductory circuit breaker, and after it, circuit breakers are installed to protect and switch individual loops. Looking ahead, I want to note that the presence of a bunch of automatic - RCD is mandatory, since the RCD does not provide current protection, both thermal and short circuit. Instead of this "combination" - automatic - RCD, you can use one universal device. However, more on that later.

Scheme of switching on the RCD with a three-phase input. Unlike the previous scheme, both single-phase and three-phase consumers are protected here. In addition, a combination of zero and ground buses (PEN) is used. An electricity meter - an electric meter - is connected between the introductory machine and the RCD. As you remember from the reviews on metering schemes, all switching devices that are installed before the metering device are subject to mandatory sealing by the power supply organization. Therefore, the design of the introductory circuit breaker must provide for this possibility.

So far, we have only talked about electromechanical RCDs. But if you remember, I mentioned that sometimes there are electronic devices. In principle, an electronic RCD is built according to the same scheme as an electromechanical one.

Instead of a sensitive magnetoelectric element, a comparison device is used (for example, the most common example is a comparator). For such a circuit, you need your own built-in power supply - after all, you need to feed the electronic circuit with something.

The residual current has a very small value, therefore, it must be amplified and converted into a voltage level that is applied to. All this, of course, reduces the overall reliability of the device, in comparison with the electromechanical one, here is just the case - the simpler the better. And to be honest, I have not yet come across certified electronic RCDs at all. Therefore, I cannot say something good or bad about them. Therefore, let's leave aside electronic RCDs and dwell on one of the main points in considering electromechanical residual current devices - their parameters:

RCDs have the following main parameters:

network type - single-phase (three-wire) or three-phase (five-wire)

rated voltage -220/230 - 380/400 V

rated load current - 16, 20, 25, 32, 40, 63, 80, 100 A

rated breaking differential current - 10, 30, 100, 300 mA

type of residual current - AC (alternating sinusoidal current, sudden or slowly rising), A (similar to AC, additionally rectified pulsating current), B (alternating and direct), S (time delay, selective), G (similar to selective, only the delay time is shorter).

I want to note one important point regarding the parameters of the RCD. Many are misled by the rated load current printed on the device case, and it is taken as the same parameter as in the circuit breaker. However, this parameter in the RCD characterizes only its “current carrying capacity”, this expression may not be entirely correct, but I introduced it for the availability of the concept of the term “rated RCD load current”.

The RCD is not able to limit the load current and it must be protected from current overloads and short circuit currents by automatic switches, which just provide protection against both overcurrent and short circuit currents. The load current of the RCD should be selected so that it is one step (of the rated current range) greater than the rated current of the circuit breaker of the protected line. That is, if there is a load protected by a circuit breaker for a current of 16 Amperes, then the RCD should be selected for a load current of 25 Amperes.

Here a logical question arises - why not combine both the circuit breaker and the RCD in one housing, especially in the case when the RCD is involved in protecting only one power loop? After all, in this case, they still work "in pairs." This point was touched upon a little in the previous article. Well, the question is quite natural and such devices, of course, exist. They are called differential circuit breakers or simply differential automata.

In the figure you just see such a device. Here is a three-phase differential machine. As in a three-phase RCD, it has four clamps each - phase and zero, and a "TEST" button. If stops at it internal arrangement, it's hard to say anything new here. This is a circuit breaker and an RCD in one bottle.

The cost of diffusers is quite high. For example, three-phase models of well-known foreign manufacturers cost about 100 Euros. Relatively expensive. However, the AV + RCD bundle will have an approximately comparable cost, and instead of four standard 17.5 mm modules on a DIN rail (with a three-phase version), it will take eight. So in some cases, diffusers are still preferable, especially if there is a problem of free space in the switchboard.

How to check the operability of an RCD or differential automaton? We have already mentioned the "TEST" button. However, such a check is very superficial and does not always reflect the real essence of things. Therefore, for objective verification, test circuits or specialized devices are used.

Connecting an RCD (residual current device) is a generally accepted measure in world practice to improve the electrical safety of consumers. The number of human lives saved by RCDs goes into the millions, and the use of RCDs in the power supply networks of multi-apartment and private residential buildings, residential areas and industrial facilities prevents billions of damage from fires and accidents.

But Galen's rule: "Everything is poison and everything is medicine" is true not only in medicine.. Outwardly simple, RCD with thoughtless or careless use can not only prevent nothing, but also become a source of trouble. By analogy: someone built Kizhi with one ax, someone can build some kind of hut with them, but you can’t give someone an ax in their hands, they will chop off something for themselves. So let's get acquainted with the RCD in more detail.

Primarily

Any serious conversation about electricity is sure to touch on electrical safety rules, and for good reason. Electric current does not carry visible signs of danger, its effect on the human body develops instantly, and the consequences can be long and severe.

But in this case, we will not talk about the general rules for the production of electrical work, which are already well known, but about something else: RCDs fit very poorly into the old Soviet TN-C power supply system, in which the protective conductor is combined with neutral. For a long time it was not clear whether it fits at all.

All editions of the PUE unequivocally require: it is prohibited to install switching devices in the circuits of protective conductors. The wording and numbering of the paragraphs changed from edition to edition, but the essence is clear, as they say, even to the marabou bird. But what about the recommendations for the use of residual current devices? They are switching devices, and at the same time they are included in the gap of both the phase and ZERO, which is also a protective conductor?

Finally, in (PUE-7A; Electrical Installation Rules (PUE), 7th edition, with additions and changes, M. 2012), paragraph 7.1.80 still dotted i: “It is not allowed to use RCDs that respond to differential current , in four-wire three-phase circuits (TN-C system)”. Such a tightening was caused, contrary to previous recommendations, by recorded cases of electrical injuries WHEN ACTIVATED RCD.

Let's explain with an example: The hostess was washing, in the car it hit the heater body, as shown in the figure with a yellow arrow. Since the current distributes 220 V along the entire length of the heating element, something around 50 V will appear on the case.

This is where the following factor comes into play: the electrical resistance of the human body, like any ionic conductor, depends on the applied voltage. With its increase, the resistance of a person falls, and vice versa. Say, the PTB provides an absolutely reasonable calculated value of 1000 ohms (1 kOhm), with sweaty steamed skin or in a state of intoxication. But then, at 12 V, the current should be 12 mA, and this is more than the non-releasing (convulsive) current of 10 mA. Has anyone ever been hit by 12 volts? Even drunk in a saltwater jacuzzi? On the contrary, according to the same PTB 12 V is an absolutely safe voltage.

At 50-60 V on wet steamed skin, the current will not exceed 7-8 mA. This is a strong, painful blow, but the current is less than convulsive. You may need treatment for the consequences, but it will not come to resuscitation with defibrillation.

And now let's "defend" the RCD, not understanding the essence of the matter. Its contacts do not open instantly, but within 0.02 s (20 ms), and not absolutely synchronously. With a probability of 0.5, the ZERO contact will open first. Then, figuratively speaking, the potential reservoir of the heating element at the speed of light (literally) will be filled up to 220 V along its entire length, and 220 V will appear on the body, and the current through the body will pass 220 mA (red arrow in the figure). Less than 20ms, but 220mA is more than two instant killing 100mA values.

So, why not install RCDs in old houses? Still, it is possible, but carefully, with a full understanding of the matter. You need to choose the right RCD and connect it correctly. How? This will be discussed further in the relevant sections.

RCD - what and how

RCDs in electrics appeared simultaneously with the first power lines in the form of relay protection. The purpose of all RCDs remains unchanged to this day: to turn off the power supply in the event of an emergency. As an indicator of an accident, the vast majority of RCDs (and all household RCDs) use leakage current - when it rises above a predetermined limit, the RCD trips and opens the power supply circuit.

Then RCDs began to be used to protect against breakdown and fire of individual electrical installations. For the time being, for the time being, RCDs remained "fireproof", they reacted to a current that excluded the ignition of an arc between the wires, less than 1 A. "Fire" RCDs are produced and used to this day.

Video: what is RCD?

RCD-E (capacitive)

With the development of semiconductor electronics, attempts began to create household RCDs designed to protect a person from electric shock. They worked on the principle of a capacitive relay reacting to a reactive (capacitive) bias current; while the person works as an antenna. The well-known indicator-phase indicator with neon is built on the same principle.

RCDs-E have exceptionally high sensitivity (fractions of µA), can be made almost instantly triggered and are absolutely indifferent to grounding: a child standing on an insulating floor and reaching out with his finger to the phase in the outlet will not feel anything, and RCD-E will “smell” him and turn off the power until he removes his finger.

But RCDs-E have a fundamental drawback: in them, the flow of leakage current electrons (conduction current) is a consequence of the occurrence of an electromagnetic field, and not its cause, therefore they are extremely sensitive to interference. There is no theoretical possibility to “teach” the UZO-E to distinguish between a little hustler who has picked up an “interesting little thing” from a tram that has sparkled on the street. Therefore, UZO-E are used only occasionally to protect special equipment, combining their direct duties with a touch indication.

UZO-D (differential)

By “turning” the RCD-E “on the contrary”, it was possible to find the principle of operation of the “smart” RCD: you need to go directly from the primary electron flow, and determine the leakage by the imbalance (difference) of the total currents in the POWER conductors. If exactly the same amount flows from the consumer as it went to him, everything is in order. If there is an imbalance, it is leaking somewhere, you need to turn it off.

The difference in Latin is differentia, in English difference, therefore such RCDs were called differential, RCD-D. In a single-phase network, it is enough to compare the magnitudes (modules) of currents in the phase wire and neutral, and when an RCD is connected in a three-phase network, the full vectors of currents of all three phases and neutral. An essential feature of RCD-D is that in any power supply circuit, protective and other conductors that do not transmit power to the consumer must pass by the RCD, otherwise false alarms are inevitable.

It took quite a long time to create household RCDs. Firstly, it was necessary to accurately determine the value of the unbalance current, which is safe for a person with an exposure time equal to the RCD operation time. RCDs tuned to an imperceptible or smaller non-letting current turned out to be large, complex, expensive, and pickups “caught” only slightly worse than RCDs.

Secondly, it was necessary to develop high-coercivity ferromagnetic materials for differential transformers, see below. The radio ferrite was not suitable at all, it did not hold the working induction, and the UZO-D with iron transformers turned out to be too slow: the own time constant of even a small iron transformer can reach 0.5-1 s.

UZO-DM

By the 80s, the research was successfully completed: the current, according to experiments on volunteers, was chosen to be 30 mA, and high-speed differential transformers on ferrite with a saturation induction of 0.5 T (Tesla) made it possible to remove power from the secondary winding, sufficient to directly drive the breaker electromagnet. Differential electromechanical UZO-DM appeared in everyday life. Currently, this is the most common type of household RCD, so DM is omitted, and they simply say or write RCD.

Differential electromechanical RCD works like this, see the figure on the right:

The appearance with explanations of the designations on the case of a three-phase and single-phase RCD is shown in the figure above.

Note: using the “Test” button, the RCD is supposed to be checked monthly and every time it is turned on again.

An electromechanical RCD only protects against leakage, but its simplicity and "oak" reliability made it possible to combine an RCD and a current circuit breaker in one case. To do this, it was only necessary to make the breaker latch rod double and bring it into the current and RCD electromagnets. So there was a differential machine that provides complete consumer protection.

However, the difavtomat is not an RCD and an automatic machine separately, this should be clearly remembered. External differences (power lever, instead of a flag or a re-enable button), as shown in the figure, are only appearance. An important difference between an RCD and a differential machine affects when installing an RCD in power supply systems without protective grounding (TN-C, independent power supply), see the section below on connecting an RCD without ground.

Important: a separate RCD is designed to protect against leakage ONLY. Its rated current shows to what extent the RCD remains operational. RCDs for ratings of 6.3 and 160 A with the same unbalance of 30 mA give the same degree of protection. In difautomatic machines, the cutoff current of the machine is always less than the rated current of the RCD, so that the RCD does not burn out when the network is overloaded.

UZO-DE

In this case, "E" does not mean capacity, but electronics. UZO-DE are built directly into or in the electrical installation. The difference in currents in them is captured by a semiconductor magnetically sensitive sensor (Hall sensor or magnetodiode), its signal is processed by a microprocessor, and the circuit opens the thyristor. UZO-DE, in addition to compactness, have the following advantages:

1. High sensitivity, comparable to UZO-E, combined with the noise immunity of UZO-DM.
2. As a result of high sensitivity, the ability to respond to bias current, i.e., RCD-DE proactive, will turn off the voltage before it hits someone, regardless of the presence of grounding.
3. High speed: for the "buildup" of the RCD-DM, at least one half-cycle of 50 Hz is required, i.e. 20 ms, and at least one dangerous half-wave must pass through the body for the RCD-DM to work. RCD-DE is able to operate at a “breakdown” half-wave voltage of 6-30 V and cut it off in the bud.

The disadvantages of RCD-DE are primarily high cost, own power consumption (negligible, but when the mains voltage drops, RCD-DE may not work) and a tendency to failure - after all, electronics. Abroad, chipped sockets were widely distributed back in the 80s; in some countries their use in children's rooms and institutions is required by law.

We UZO-DE are still little known, but in vain. The bickering between mom and dad about the cost of a socket with "fool protection" is not comparable to the price of a child's life, even if an incorrigible vermin and troublemaker run amok in the apartment.

UZO-D indices

Depending on the device and purpose, main and additional indices can be added to the name of the RCD. According to the indices, you can make a preliminary selection of the RCD for the apartment. Main indices:

• AC - are triggered by the unbalance of the variable component of the current. As a rule, they are fire-fighting, for an unbalance of 100 mA, because cannot protect against short-term impulse leakage. Inexpensive and very reliable.
• A - react to the unbalance of both alternating and pulsating currents. The main version is protective for 30 mA unbalance. False trips / failures are possible in the TN-C system in any case, and in the TN-C-S with poor grounding and / or the presence of powerful consumers with significant intrinsic reactivity and / or switching power supplies (UPS): washing machine, air conditioner, hob, electric oven, food processor; to a lesser extent - dishwasher, computer, home theater.
• B - react to leakage current of any kind. These are either industrial RCDs of the "fire" type for 100 mA of unbalance, or built-in RCDs-DE.

Additional indices give an idea of ​​the additional functionality of the RCD:

1. S - selective in response time, it is adjustable within 0.005-1 s. The main area of ​​application is in the power supply of objects powered by two beams (feeders) with an automatic transfer switch (ATS). Adjustment of the response time is necessary so that when the main beam fails, the AVR has time to work. In everyday life, they are sometimes used in elite cottage settlements or mansions. All selective RCDs are fire, for an unbalance of 100 mA, and require the installation of protective 30 mA RCDs after them for a lower current, see below.
2. G - high-speed and ultra-high-speed RCDs with a response time of 0.005 s or less. They are used in children's, educational, medical institutions and in other cases when the "overshoot" of at least one striking half-wave is unacceptable. Exclusively electronic.

Note: household RCDs are most often not indexed, but differ in design and unbalance current: electromechanical for 100 mA - AC, they are also for 30 mA - A, built-in electronic - B.

PATTERN

Almost unknown to non-specialists, a type of RCD is not differential, triggered by current in a protective conductor (P, PE). They are used in industry, in military equipment and in other cases when the consumer creates strong interference and / or has its own reactivity that can “confuse” even UZO-DM. They can be both electromechanical and electronic. Sensitivity and speed for domestic conditions are unsatisfactory. A high quality serviced ground is required.

RCD selection

To choose the right RCD, the index is not enough. You also need to find out the following:

• Buy separately RCD with automatic or difavtomat?
• Select or calculate the cutoff value for extra current (overload);
• Determine the rated (working) current of the RCD;
• Determine the required leakage current - 30 or 100 mA;
• If it turned out that for general protection you need a “fire” RCD for 100 mA, determine how many, where and what kind of secondary “life” RCDs for 30 mA are required.

Separately or together?

In an apartment with TN-C wiring, you can forget about the difavtomat: the PUE prohibits, but ignore it, so the electricity itself will soon remind you. In the TN-C-S system, the difavtomat will cost less than two separate devices if the wiring is planned to be reconstructed. If the current machine is already standing, then a separate RCD that is coordinated with it in terms of operating current will be cheaper. Scriptures on the topic: RCD is incompatible with a conventional machine gun - an amateurish nonsense.

What overload to expect?

The cut-off current of the machine (extractors) is equal to the maximum allowable current consumption of the apartment (house), multiplied by 1.25 and added to the nearest higher value from the standard range of currents 1, 2, 3, 4, 5, 6.3, 8, 10, 13, 16 , 20, 25, 32, 35, 40, 50, 63, 80, 100, 125, 160, 250, 400, 630, 1000, 1600, 2500, 4000 and 6300 A.

The maximum current consumption of the apartment must be recorded in its data sheet. If not, you can find out in the organization operating the building (obliged to report by law). In old houses and new budget ones, the maximum allowable current is usually 16 A; in new ordinary (family) - 25 A, in business class - 32 or 50 A, and in suites - 63 or 100 A.

For private households, the maximum current is calculated according to the power consumption limit from the data sheet (the authorities will not miss it) at the rate of 5 A per kilowatt, with a coefficient of 1.25 and the addition to the nearest higher standard value. If the value of the maximum current consumption is directly stated in the data sheet, it is taken as the basis for the calculation. Conscientious designers on the wiring plan directly indicate the cut-off current of the main machine, so there is no need to count.

Rated current RCD

The rated (working) current of the RCD is taken one step higher than the cut-off current. If a difavtomat is installed, it is chosen BY THE CUT-OFF CURRENT, and the current rating of the RCD is inherent in it constructively.

Video: RCD or difavtomat?

Leakage current and general protection circuit

For an apartment with TN-C-S wiring, it will not be a mistake to take an RCD for an unbalance of 30 mA without much thought. A separate section will be further devoted to the TN-C apartment system, but clear and final recommendations cannot be immediately given for private houses.

According to paragraph 7.1.83 of the PUE, the operating (natural) leakage current should not exceed 1/3 of the RCD unbalance current. But in a house with electric underfloor heating in the hallway, courtyard lighting and electric heating of the garage in winter, the operating leakage current can reach 20-25 mA with a living area of ​​both 60 and 300 squares.

In general, if there is no greenhouse with electric heating of the soil, a heated water well, and the yard is illuminated by housekeepers, at the input after the meter it is enough to put a fire RCD with a rated current one step higher than the cut-off current of the machine, and for each consumer group - a protective RCD with the same rated current. But an accurate calculation can only be made by a specialist based on the results of electrical measurements of already finished wiring.

Calculation examples

The first is a new apartment with TN-C-S wiring ; according to the data sheet, the power consumption limit is 6 kW (30 A) . We check the machine - it costs 40 A, everything is OK. We take the RCD a step or two higher in terms of rated current - 50 or 63 A, it doesn’t matter - and for an unbalance current of 30 mA. We don’t think about leakage current: builders should provide it within the normal range, but if not, then let them fix it themselves for free. However, contractors do not allow such punctures - they know what smells like under the guarantee.

Second. Khrushchev, plugs for 16 A. We put the washing machine on 3 kW; the current consumption is about 15 A. To protect it (and protect it from it), you need an RCD with a rating of 20 or 25 A for 30 mA of unbalance, but 20 A RCDs are rarely on sale. We take an RCD for 25 A, but in any case, it is MANDATORY to remove the plugs, and put a 32 A machine in their place, otherwise the situation described at the beginning is possible. If the wiring clearly cannot withstand a short-term surge of 32 A, nothing can be done, you need to change it.

In any case, you need to submit an application to the energy service for the replacement of the meter and the reconstruction of the electrical wiring, with or without replacement. This procedure is not very complicated and troublesome, and a new meter with an indication of the status of the wiring will serve you well in the future, see the section on trips and malfunctions. And the RCD registered during the reconstruction will then allow free-of-charge calls for electricians for measurements, which is also very good for the future.

The third. A cottage with a consumption limit of 10 kW, which gives 50 A. The total leakage according to the measurement results is 22 mA, and the house gives 2 mA, the garage - 7, and the yard - 13. We put a common difavtomat on 63 A cut-off and 100 mA imbalance, we power the house with the garage separately through the RCD for 80 A nominal and 30 mA imbalance. In this case, it is better to leave the yard without its own RCD at all, but take the lamps for it in waterproof cases with a ground terminal (industrial type), and bring their earths directly to the ground loop, it will be more reliable.

RCD connection in the apartment

A typical RCD connection diagram in an apartment is shown in the figure. It can be seen that the general RCD turns on as close as possible to the input, but after the meter and the main (access) machine. The inset there also shows that in the TN-C system, the general RCD cannot be turned on.

If separate RCDs are needed for groups of consumers, they are turned on immediately AFTER the corresponding machines, highlighted in yellow in the figure. The rated current of the secondary RCDs is taken a step or two higher than that of “their own” machine: for VA-101-1 / 16 - 20 or 25 A; VA-101-1/32 - 40 or 50 A.

But this is in new houses, but in old ones, where protection is most needed: there is no land, the wiring is awful? Someone there promised to enlighten on the subject of connecting an RCD without earth. That's right, that's exactly what it came down to.

RCD without earth

Cited at the beginning of paragraph 7.1.80 exists in the PUE not in splendid isolation. It is supplemented with points explaining how, after all (well, there are no ground loops in our houses, no!) “Push” the RCD into the TN-C system. Their essence is as follows:

1. It is unacceptable to install a common RCD or difavtomat on an apartment with TN-C wiring.
2. Potentially dangerous consumers must be protected by separate RCDs.
3. The protective conductors of sockets or socket groups intended for connecting such consumers must be brought to the INPUT zero terminal of the RCD in the shortest way, see the diagram on the right.
4. RCD cascade connection is allowed, provided that the upper ones (closest to the RCD input) are less sensitive than the terminal ones.

A smart person, but unfamiliar with the intricacies of electrodynamics (which, by the way, many certified security electricians also sin) may object: “Wait a minute, what's the problem? We put a common RCD, start all PE at its input zero - and you're done, the protective conductor is not switched, grounded without ground! Yes, not so.

The electromagnetic field of the installation and the cord to it are also excluded from consideration. The first is concentrated inside the device, otherwise it will not pass certification and will not go on sale. In the cord, the wires pass close to each other, and their field is concentrated between them, regardless of frequency, this is the so-called. T-wave.

In an apartment with an increased fire hazard, it is permissible, with the obligatory presence of individual consumer RCDs connected according to the recommended circuit, to install a common FIRE RCD for 100 mA of unbalance and with a rated current one step higher than that of protective ones, regardless of the cutoff current of the machine. In the example described above, for Khrushchev, you need to connect an RCD and an automatic machine, but not a difautomatic! When the machine is knocked out, the RCD must remain in operation, otherwise the likelihood of an accident increases sharply. Therefore, the RCD at face value must be taken two steps higher than the machine (63 A for the disassembled example), and by unbalance - one step higher than the final 30 mA (100 mA). Once again: in difautomats, the RCD rating is made a step higher than the cut-off current, so they are not suitable for wiring without ground.

Video: RCD connection

Well, it's knocked out...

Why does the RCD work? Not how, it has already been described, but why? And what if it worked? Once knocked out, then something is wrong?

Right. You can’t just turn it on after a trip until its cause is found and eliminated. And you can find where something is “wrong” yourself without any special knowledge, tools and devices. A regular apartment electric meter will be of great help in this, unless it is completely antique.

How to find the culprit?

First, turn off all the switches, remove everything from the sockets. In the evening, you will have to use a flashlight for this; it is better to immediately attach a hook to the wall when installing next to the RCD and hang a cheap LED flashlight on it.

We turn off the access or main apartment machine. Doesn't turn on? Blame the electromechanics of the RCD; need to be sent in for repair. You can’t dig yourself - the device is vital, and after repair you need to check it on special equipment.

It turned on, but when the voltage was applied, it knocked out again with empty wiring? In the RCD, either the internal imbalance of the differential transformer, or the “Test” button is stuck, or the wiring is faulty.

We try to turn it on under voltage, looking at the counter. If the “Earth” indicator flashed at least for a moment (see fig.), or earlier it was noticed that it winks, there is a leak in the wiring. You need to take measurements. If the RCD is installed in the order of reconstruction of the wiring and is registered with the energy service, you need to call the municipal electricians, they are required to check. If the RCD is "self-propelled" - pay a specialized company. The service, however, is not expensive: modern equipment allows for 15 minutes. find a leak in the wall with an accuracy of 10 cm.

But before calling the company, you need to open and inspect the sockets. Insect excrement gives excellent leakage from the phase to the ground.

The wiring does not inspire fear, they even turned it off section by section with automatic machines, but does the RCD knock out “on empty”? Fault inside it. Both the imbalance and sticking of the “Test” most often cause not condensation or intensive use, but all the same “cockroach poop”. In Rostov-on-Don, a case was noted when in a perfectly well-groomed apartment in the RCD, a nesting place was discovered ... Turkestan earwigs, who knows how they got there. Hefty, with huge powerful cerci (tweezers on the tail), terribly angry and biting. In the apartment, they did not show themselves in any way.

The RCD trips when consumers are connected, but there are no signs of a short circuit? We turn on everything, especially potentially dangerous ones (see the section on the classification of RCDs by indices), we try to turn on the RCD, again looking at the meter. This time, in addition to the "Earth", the glow of the "Reverse" indicator is possible; sometimes it is denoted "Return", next. rice. This indicates the presence of high reactivity, capacitance or inductance in the circuit.

You need to look for a defective consumer in reverse order; by itself, it may not reach the RCD before tripping. Therefore, we turn on everything, then turn off the suspicious ones in turn, and try to turn them on. Turned on, finally? This is what it is, "reversible". For repairs, but not to electricians, but to "home appliances".

In apartments with TN-C-S wiring, it is possible that it is not possible to clearly determine the source of RCD operation. Then the likely cause is bad ground. Still retaining its protective properties, grounding no longer removes the higher components of the interference spectrum, and the protective conductors work as an antenna, similar to a TN-C apartment with a common RCD. Most often, this phenomenon is observed during periods of greatest drying and freezing of the soil. So what to do? It is obligatory to strain the building operator, let him bring the circuit to the norm.

About filters

One of the main sources of RCD malfunctions is interference from household appliances, and effective way to combat them - absorbing ferrite filters. Have you seen knobs - "bumps" on computer cords? This is what they are. Ferrite rings for filters can be bought at the radio store.

But for power ferrite absorbers, the magnetic permeability of the ferrite and the saturation magnetic induction in it are of decisive importance. The first should be at least 4000, and better - 10,000, and the second - at least 0.25 Tl.

The filter on one ring (at the top of the figure) can be built in with a "noisy" installation, if it is not under warranty, as close as possible to the network inlet. This work is for an experienced specialist, so the exact scheme is not given.

Several rings can simply be put on the power cord (in the figure below): from the point of view of electrodynamics, it doesn’t matter if the conductor is wrapped around the magnetic circuit or vice versa. In order not to cut the branded molded cord, you need to buy a plug, a socket block and a piece of a three-core cable. Ready-made power cords with ferrite noise absorbers are also sold, but it costs more than home-made prefabricated parts.

In our age of high technology, people are surrounded on all sides by a huge number of devices and devices that work with electricity. And the larger their number, the higher the likelihood of electric shock to a person. To avoid this, the RCD was invented. What it is and what it is for, we will describe in detail in this article.

Purpose

It is intended for a person from electric shock when touching the housing of electrical equipment (household electrical appliances), which, if the insulation was broken, turned out to be energized.

When RCD trips

Let's continue the story about RCD. What is it and how does it work? An electric current begins to flow through a person who touches the housing of an electrical appliance under voltage. When it reaches a value of 30 mA, the RCD turns off. As a result, the voltage is automatically disconnected from the damaged equipment. At the same time, a person does not feel anything, since painful sensations occur at much higher currents (from 50 mA). Lethal for humans is a current of 100 mA.

What does the RCD consist of?

Includes current transformer, (relay and break arm system), self-test circuit. More advanced devices contain in their design a system of electromagnetic and inversely dependent on the magnitude of the cut-off current (protection against and against overload).

The principle of operation of the RCD

What it is? How is this device powered? Now let's talk about all this in as much detail as possible. The RCD is based on current (CT). Phase and working neutral conductors pass through the current transformer. With normally operating equipment (with intact insulation), the magnitudes of the currents flowing through them are equal in magnitude, but reverse in direction. As a result, they induce CTs in the winding that are the same in magnitude but reverse in direction, which completely cancel each other out (there is no voltage at the ends of the CT secondary winding). If the insulation of the equipment is broken, part of the phase conductor current flows to the ground through the grounding conductor (if the instrument case is grounded) or through a person who has touched this electrical appliance. As a result of this, the amount of current flowing through the zero working conductor becomes less than the current flowing through the phase conductor. This leads to the fact that the magnetic fluxes in the transformer winding become different in magnitude. As a result, voltage appears at the ends of the CT winding. Through the relay connected to them, current begins to flow. When a difference of 30 mA is reached, a relay is activated, which activates a system of breaking levers. The equipment turns off.

Turning on the RCD

It is carried out only after identifying and eliminating the malfunction of the electrical equipment that led to the operation of the device by pressing the cocking levers.

Conclusion

In this article, we have introduced you in sufficient detail to the RCD: what it is, how it works and what it is used for. We hope you find this information useful.

RCD in any electrical circuit is a very important element. The main purpose of the RCD is to protect a person from electric shock when in contact with live parts. In addition, the RCD, the principle of operation of which will be discussed in this article, prevents the likelihood of fires that can be triggered by the ignition of electrical wiring.

In certain situations, the RCD, the principle of operation of which is quite simple, stops supplying voltage to the protected line. This happens if a person touches the current-carrying parts of electrical installations, and non-current-carrying elements, which, as a result of insulation breakdown, are energized. Another reason for opening contacts is the occurrence of current leakage to the electrical installation case or ground.

Consideration of the principle of operation of the RCD in general and on a specific example

When inexpensive apartments are rented from the developer, then all the electrics, including RCDs and diffusers, as well as wiring and circuit breakers, have already been installed. If you are building your own house or want to install an RCD in an apartment with your own hands, then you should know the principle of operation of this device and the rules for its installation.

RCD (the principle of operation is based on the detection of incoming and outgoing currents at the entrance to the system) can respond to minimal leakage and perform its protective function. To measure the leakage, a sensing element such as a differential transformer with three windings is installed in the device.

The principle of operation of the RCD can be easily understood with a specific example. If a person touches the current-carrying parts of the installation, or an insulation breakdown occurs on its case, the amount of current flowing through the phase wire will exceed the current in the neutral wire.

The total (final) flux of magnetic induction, in this case, will necessarily change, will differ from zero and will be the cause of current induction in the control winding. The relay to which the winding is connected will operate and the release of the contacts of the power protective device will be set in motion.

As a result of which a dangerous electrical installation is de-energized in a fraction of a second, it ensures the safety of human health.

Connecting an RCD to a single-phase network: basic rules

The RCD diagram is indicated on the body of the device and allows you to understand the principle of its operation, correctly connect the device to the electrical circuit protection circuit, avoiding incorrect operation of the device or its failure.

The RCD circuit, according to which it is connected to the power supply system, depends on various parameters and factors. In residential premises, as a rule, a single-phase version of electrical wiring with a rated voltage of 220 V is used.

Before installation, you need not only to understand the principle of operation of the RCD in a single-phase network, but also to familiarize yourself with the safety rules.

The principle of operation of the RCD and the wiring diagram imply the use of two wires of wiring connected to the input terminals, and two wires to the output of the device, connected to the corresponding output terminals. Install the device only when the power is off. Before installation, you need to make sure that there is enough space in the shield for the selected device.

And the wiring diagram is quite simple. There are several options for installing this device, but the principle, in general, remains unchanged.

The most common and affordable is the option in which the device is at the entrance to the house / apartment. The disadvantage of this option is that when the device is triggered, the entire living space is de-energized, and it is difficult to determine the cause of what is happening.

More expensive, however, very convenient is the connection option with the installation of several RCDs - in this case, each device will be responsible for a separate group of sockets or lighting.

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