Internal structure of ouzo. RCD: operating principle, purpose, technical characteristics, RCD connection options

The abbreviation RCD is created from the phrase “Residual current device”, which defines the purpose of the device, which is to remove voltage from the circuit connected to it in the event of random insulation breakdowns and the formation of leakage currents through them.

Operating principle

To operate the RCD, the principle of comparing currents entering and leaving the controlled part of the circuit is used based on a differential transformer, which converts the primary values ​​of each vector into secondary values ​​strictly proportional in angle and direction for geometric addition.

The comparison method can be represented by ordinary scales or a balancer.

When balance is maintained, everything works normally, but when it is disturbed, the qualitative state of the entire system changes.

In a single-phase circuit, the phase current vector approaching the measuring element and the zero current vector leaving it are compared. Under normal operating conditions with reliable intact insulation, they are equal and balance each other. When a fault occurs in the circuit and a leakage current appears, the balance between the vectors under consideration is disrupted by its value, which is measured by one of the transformer windings and transmitted to the logic block.

Comparison of currents in a three-phase circuit is carried out according to the same principle, only the currents of all three phases are passed through a differential transformer, and an unbalance is created based on their comparison. In normal operation, the currents of the three phases are balanced during geometric addition, and if the insulation of any phase is damaged, a leakage current occurs in it. Its value is determined by the summation of vectors in the transformer.

Block diagram

The operation of a residual current device can be simplified block by block using a block diagram.

The imbalance of currents from the measuring element is sent to the logical part, which operates on the relay principle:

1. electromechanical;

2. or electronic.

It is important to understand the difference between them. Electronic systems are now rapidly developing and are becoming increasingly popular for many reasons. They have wide functionality and great capabilities, but require electrical power for the operation of logic and the executive body, which is provided by a special unit connected to the main circuit. If the electricity goes out for various reasons, then such an RCD, as a rule, will not work. The exception is rare electronic models equipped with this function.

Electromechanical relays use the mechanical energy of a charged spring, which is similar in principle to an ordinary mousetrap. For the relay to operate, a minimum mechanical force on the sensed actuator is sufficient.

Just as a mouse touches the bait of a prepared mousetrap, the leakage current that occurs when there is an imbalance in the differential transformer leads to the operation of the actuator and the disconnection of voltage from the circuit. For this purpose, the relay has built-in power contacts in each phase and a tester preparation contact.

Any type of relay has certain advantages and disadvantages. Electromechanical structures have been working reliably for many decades and have proven themselves well. They do not require external power, and electronic models are completely dependent on it.

It is now generally accepted that the most effective measure of protection against electric shock in electrical installations with voltages up to 1000 V is a residual current device (RCD).

Without objecting to the importance of this protection measure, most experts have been arguing for many years regarding the values ​​of the main parameters of the RCD - installation current, response time and reliability.This is explained by the fact that the parameters of the RCD are closely related to its cost and operating conditions.

Indeed, the lower the setting current and the shorter the response time, the higher the reliability of the RCD, the more expensive its cost.

In addition, the lower the setting current and the shorter the response time of the RCD, the stricter the requirements for the insulation of the protected area, since even a slight deterioration in it under operating conditions can lead to frequent, and in some cases long-term, false shutdowns of the electrical installation, thereby making it impossible to normal operation.

On the other hand, the higher the RCD setting current and the longer its response time, the worse its protective properties.

RCD design

The layout of a single-phase RCD is shown in the picture below.

In it, voltage is supplied to the input terminals, and a controlled circuit is connected to the output terminals.

The three-phase residual current device is made in the same way, but it controls the currents of all phases.

The picture shown shows a four-wire RCD, although three-wire designs are commercially available.

How to check the RCD

Any design model has a built-in functionality check function. For this purpose, the “Tester” block is used, which is an open contact - a button with a spring self-reset and a current-limiting resistor R. Its value is selected to create a minimum sufficient current, artificially simulating a leak.

When you press the “Test” button, the RCD connected to operation should turn off. If this does not happen, then it should be rejected, look for a breakdown and repair or replace it with a working one. Monthly testing of the residual current device increases the reliability of its operation.

By the way, the serviceability of electromechanical and individual electronic structures can be easily checked in the store before purchase. For this purpose, it is enough, when the relay is switched on, to briefly supply current to the phase or neutral circuit from a battery with any connection polarity according to options 1 and 2.

A working RCD with an electromechanical relay will work, but in the vast majority of cases electronic products cannot be checked this way. They need power for their logic to work.

How to connect an RCD to a load

Residual current devices are designed for use in power supply circuits using the TN-S or TN-C-S system with the connection of a protective zero PE bus in the electrical wiring, to which the housings of all electrical devices are connected.

In this situation, if the insulation fails, the potential arising on the housing immediately flows through the PE conductor to the ground and the comparison body calculates the fault.

In normal power supply mode, the RCD does not disconnect the load, so all electrical appliances operate optimally. The current of each phase in the magnetic circuit of the transformer induces its own magnetic flux F. Since they are equal in magnitude, but opposite in direction, they cancel each other out. There is no total magnetic flux and cannot induce an emf in the relay winding.

When a leak occurs, the dangerous potential flows to the ground through the PE protective busbar. An EMF is induced in the relay winding from the resulting imbalance of magnetic fluxes (currents in phase and zero).

The residual current device instantly calculates the fault in this way and de-energizes the circuit with power contacts in a split second.

Features of operation of an RCD with an electromechanical relay

Using the mechanical energy of a charged spring in some cases may be more profitable than using a special unit for electrical power supply of the logic circuit. Let's consider this using an example when the zero of the supply network is broken, and the phase is supplied.

In such a situation, the static electronic relays will not receive power and therefore will not be able to operate. At the same time, in this situation, the three-phase system experiences a phase imbalance and an increase in voltage.

If an insulation breakdown occurs in a weakened area, the potential will appear on the housing and will flow through the PE conductor.

In an RCD with an electromechanical protection relay, they will operate normally from the energy of a charged spring.

How does an RCD work in a two-wire circuit?

The undeniable advantages of protection against leakage currents in electrical equipment made according to the TN-S system through the use of RCDs have led to their popularity and the desire of individual apartment owners to install RCDs in two-wire systems not equipped with a PE conductor.

In this situation, the body of the electrical appliance is isolated from the ground and does not communicate with it. If an insulation breakdown occurs, the phase potential appears on the housing and does not drain from it. A person who has contact with the ground and accidentally touches the device is exposed to leakage current in the same way as in a situation without an RCD.

However, in a circuit without a residual current device, current can pass through the body for a long time. When the RCD is installed, it will sense a malfunction and turn off the voltage during the setting time within a fraction of a second, thereby reducing the degree of electrical injury.

Thus, the protection facilitates the rescue of a person when energized in buildings equipped according to the TN-C scheme.

Many home craftsmen try to independently install RCDs in old houses awaiting reconstruction to switch to the TN-C-S system. In this case, in the best case, they make a homemade grounding loop or simply connect the housings of electrical appliances to the water supply network, heating radiators, and iron parts of the foundation.

Such connections can create critical fault situations and cause serious damage. Work on creating a grounding loop must be carried out efficiently and controlled by electrical measurements. Therefore, they are performed by trained specialists.

Types of fastening

Most RCDs are made in a stationary design for mounting on a common Din-rail in an electrical panel. However, on sale you can find portable structures that are plugged into a regular electrical outlet, and the protected device is then powered from them. They cost a little more.

Electricity is one of the engineering systems that provides our comfort. But the same electricity carries a potential threat, so electrical networks must be as safe as possible. Ensures the safety of automatic protection devices. One of them is an RCD. What kind of device is this, what does it protect from, what is the principle of operation of the RCD - all this will be discussed in the article.

RCD is a residual current device(an alternative name is residual current switch, abbreviated as RCCB). Designed to turn off power in the event of an emergency that results in leakage current. This is possible in two cases: when the insulation breaks down to the ground and when a person touches live parts.

This picture will help to imagine the principle of operation of an RCD. The load is an incandescent lamp. The RCD compares the current before and after the load. If the difference exceeds the specified value, the device is triggered and opens the circuit

The principle of its operation can be compared to a scale with two bowls. The current in the circuit before and after the load is compared. As soon as one of the bowls outweighs, it means the current has found a “left” or bypass path. Most often, the workaround is through an insulation breakdown to the ground, or through the human body, also not to the ground. That is, part of the current “flowed” along this path. Hence the name - leakage current. The current did not flow through the laid wires, and this is dangerous. And the appearance of a leakage current is a signal to turn off the power. A relay in the RCD is triggered, breaking the contact and de-energizing the network. This is the principle of operation of an RCD described in simple words - for a better understanding of the purpose and principle of operation.

How to understand what leakage current is

A leakage current occurs when an insulation breakdown occurs on the housing (the wire is frayed, the heating element is “broken,” etc.). A leak is when you touch the body of a device that is energized. You touched with one hand and at the same time you are standing on a conductive floor without shoes or touching some other grounded object (central heating radiators, for example). Current will flow through your body, and it will “go” through the ground loop, since this is the path of least resistance. This will be the “workaround” path. As a result, the “returned” current will be less and the relay on the RCD will operate.

But, pay attention! Direct contact immediately with phase and zero is not our case. In this case, the body is perceived as a load rather than a leak. This is a normal situation and the protection will not work. Therefore, work with electricity with one hand, wearing dielectric shoes. And never touch zero and phase at once.

Connecting an RCD to the circuit increases safety. This is especially true for wet areas such as a bathroom.

Sometimes the protection reacts to unobvious things: neighbors are grounded in the wrong direction, a stove with piezo ignition is not grounded, a washing machine or dishwasher is connected with a metal braided hose to metal pipes. In general, there are many situations in which leakage current is generated. These are all also leakage currents, but they are the result of errors or violations. And the RCD also reacts to them. If outages occur for no apparent reason, they simply need to be identified. It’s not easy, but you shouldn’t ignore “false” shutdowns. The reason may be dangerous.

What does it look like

There is a switch on the front panel of the RCD that can be used to manually break the circuit or bring the device into working condition. There is also a “Test” button on the front panel, designed to test the functionality of the protection device. When it is pressed, a circuit containing a resistor is connected, which emits the occurrence of a leak. If the device is working properly, it will turn off the power - the “switch” will move down, opening the contact.

There are sockets for connecting wires at the top and bottom of the device. The wires supplying power are connected at the top, and the lines that go to the load or to downstream devices are connected at the bottom. Both phase wires and zero (neutral) pass through the RCD. That is, when triggered, the power is turned off completely.

There are inscriptions on the case that reflect the main parameters. The RCD is mounted on a DIN rail; for this purpose, there are special protrusions on the rear surface of the case. Fixation methods depend on the manufacturer. There are models that are simply hung, and others with fixation using a pressure valve.

How to ensure quality protection

Despite the obvious benefits of RCDs, you cannot do without a circuit breaker. The RCD does not respond to overcurrents (short circuits) or overload. It only monitors leakage current. So for the safety of the wiring, an automatic machine is also needed. This pair - an automatic machine and an RCD - is placed at the entrance. The machine is usually located before the meter, leakage protection is after.

Instead of a pair - RCD + automatic machine, you can use a differential automatic machine. These are two devices in one case. immediately monitors leakage current, short circuit, and overload. It is installed if there is a need to save space in the panel. If there is no such need, they prefer to install separate devices. It is easier to determine damage, cheaper to replace if it fails.

Operating principle of RCD

The protective shutdown device consists of a transformer, a relay and a disconnecting mechanism. The main working element of the RCD is a differential transformer with two primary windings and one secondary. It is he who compares the currents. The primary windings of a differential transformer have exactly the same parameters, but are connected towards each other. The current that goes to the load passes through one winding, and the current that returns from the load passes through the second winding.

When the line is in good condition, the currents flowing through both primary windings are equal, but have opposite signs. As a result, the electromagnetic fields they create cancel out. In such a situation, there are no induced currents in the secondary winding, the contacts are closed, and there is power.

As soon as a leak appears on the monitored lines, an excess appears in one of the primary windings (in the figure this is winding number 2). This leads to potential appearing on the secondary winding. When it reaches a threshold value (trip current), the relay is activated, cutting off the power. This is the principle of operation of an RCD.

In general, an RCD is a simple device, but very useful, since it is responsible for safety. For your safety and the safety of your children, we strongly recommend installing a residual current device in the switchboard.

Briefly about the parameters of the RCD

Despite the device not being too complicated, there are many parameters by which it is necessary to select an RCD. This:

All these parameters are selected when drawing up the circuit, since the cross-section of the wire, the connected load and many other details are important for selection. So first you need to decide on the number and power of consumers (light bulbs, large and small household appliances, heaters, etc.).

What is a fire protection RCD

Clever minds have figured out how to use the operating principle of RCDs not only to protect people from electric shock when the insulation is damaged. The same device can be used to prevent fires. Structurally, they are no different, they are simply designed for high leakage currents.

How does the RCD work in this case? As you know, when current flows, the temperature of the conductors increases. If the current is sufficient, the heat can be so great that it can cause a fire. If you install a device with a leakage current of 100 mA or higher at the entrance to the house, it will not save a person from electric shock, but it can even prevent the occurrence of a fire. How? It may well happen that one of the protection devices turns out to be faulty. The phase insulation will be damaged, which will sooner or later lead to a fire. It may happen that the damage occurs on the unprotected part of the lines. In this case, the fire protection RCD will turn off the power. This will mean that there is too much leakage and it is necessary to inspect the wiring: measure the insulation, check the heating, etc.

A fire protection device is installed after the meter. If we talk about the parameters, the minimum shutdown current is 100 mA. The type is better selective, but choose the exposure time yourself. Selectivity will save you from false positives. Below, after the fire protection RCD, protection is installed on the line, selecting the disconnecting leakage current depending on the type of load.

If you follow GOST, then the installation of protective devices on lighting lines located in rooms with normal operating conditions is not necessary. That is, “personal” RCDs and automatic machines do not need to be installed on the lines that lead to lighting.

Manufacturers

There is no official rating of RCD manufacturers, so you should rely on reviews from practicing electricians. As a rule, when assembling a “sophisticated” shield, experts recommend using products from three European companies:

• ABB (Swedish-Swiss company);
• Legrand (France);
• Schneider Electric (France).

In the catalogs of the above manufacturers, alternative names for residual current protection devices will be more often found. RCD - residual current switch (RCB). Difavtomat is an automatic residual current switch (RCCB).

The Schneider Electric company has developed a line of Easy9 devices belonging to the middle price segment.

Differential switch EASY 9 (RCD) 2P 63A 30mA (article EZ9R34263). Easy9 devices belong to the middle price segment, but at the same time they are distinguished by the quality, reliability and ease of use characteristic of equipment in the upper price segment

Many electricians are not satisfied with the quality of products from companies such as IEK, TDM, DEKraft, EKF.

Protective shutdown is especially important when a large number of different electrical appliances are used in the house. In this article we will look at residual current devices that are recommended and used in the construction of private houses. A diagram of the residual current device will be shown. Let's look at the question of what and when to use - an RCD or a differential automatic device (differential automatic machine). In addition, we will find out the main differences between residual current circuit breakers.

Types of circuit breakers

An important step in the organization of electrical safety are protective electrical devices or, as they are more often called, automatic devices. Conventionally, they can be divided into three types:

• automatic switches (AB);
• differential shutdown devices (RCDs);
• differential circuit breakers (DAB).

Figure 1. Circuit breaker

Fig 2. Residual current device (RCD)

Figure 3. Differential circuit breaker (DAB)

Operating principle of residual current devices

Automatic switches (AB), see Fig. 1, are installed to protect electrical wiring from overcurrents, and electrical consumers from short circuits. Overcurrent leads to heating of the conductor, which leads to fire of the wiring and its failure.

Residual current device (RCD) operating principle(Fig. 2). We install it to protect against electric shock in case of breakdown of the insulation of equipment and wiring. The RCD will protect us even if we touch open, uninsulated sections of wiring or equipment that are energized at 220 V and will prevent a fire from starting if the wiring is faulty.

If a current difference appears, the RCD turns off the voltage supply. It is necessary to select an RCD based on two parameters: sensitivity and rated current. Typically, for home purposes, an RCD with a sensitivity of 300 mA is chosen. The rated current is selected depending on the total power of electrical consumers and must be equal to or be an order of magnitude lower than the rated current of the input circuit breaker (AB), because the RCD does not protect against short circuits and overcurrents. A residual current device (RCD) is usually installed in the circuit after the meter to protect all wiring in the house, see fig. 4, 5. According to modern standards, the installation of an RCD is mandatory.

Rice. 4. RCD connection diagram

Rice. 5 Installation diagram for power supply to a house using an RCD

1 - sch distribution stream; 2 - neutral; 3 - w grounding ina; 4 - f aza; 5 - RCD; 6 - aw tomatic switch; 7 - pconsumer nutrition.

Differential circuit breakers (DAB) combine the functions of RCD and AV. The differential circuit breaker circuit is based on protecting circuits from short circuits and overloads, as well as protecting people from electric shock when touching live parts, see Fig. 6.

Rice. 6. Scheme of operation of DAV

These devices are widely used in household electrical networks (220/380 V) and in socket networks. A differential circuit breaker consists of a high-speed circuit breaker and a residual current device that responds to the difference in currents in the forward and reverse directions.

The operating principle of a differential machine. If the insulation of the electrical wiring is not damaged and there is no human contact with live parts, then there is no leakage current in the network. This means that the currents in the forward and reverse (phase-zero) load conductors are equal. These currents induce equal but counter-directed magnetic fluxes in the magnetic core of the DAV current transformer. As a result, the current in the secondary winding is zero and does not trigger the sensitive element - the magnetoelectric latch.

When a leak occurs, for example: when a person touches a phase conductor, the balance of currents and magnetic fluxes is disrupted, an unbalance current appears in the secondary winding, which triggers the magnetoelectric latch, which in turn acts on the release mechanism of the machine with the contact system.

To carry out periodic monitoring of the performance of RCDs and DAVs, a testing circuit is provided. When you press the "Test" button, a tripping differential current is artificially created. The activation of the protection devices means that it is generally in good working order.

Selecting a circuit breaker

Now, let’s decide in which case and which circuit breaker we should give preference to:

• To protect the wiring of the lighting network, from which all our lamps are powered, we select automatic circuit breakers (AB) with operating currents 16 A.
• The socket network in the house, which is used to turn on irons, table lamps, TV, computer, etc., must be protected by circuit breakers with differential protection (DAB).
• For the socket network, we choose a DAV with an operating current of 25 A and differential current shutdown 30 mA.
• To connect an air conditioner, dishwasher, electric oven, microwave oven and other powerful appliances that we need in everyday life, we need our own individual socket and, therefore, our own circuit breaker with differential protection. For example, to connect an electric furnace with a power of 6 kW, a differential circuit breaker with shutdown currents of 32 and 30 mA is required.

Please note, that all sockets must have a grounding contact. I recommend connecting power equipment, such as a grinding machine, to a circuit breaker. Since the entire network in our house is 220 V, we select the listed circuit breakers for the appropriate voltage.

Let's talk about the circuit breaker, which for safety reasons needs to be installed at the input. If we have protected all the outlet lines with circuit breakers with differential protection, then at the input we install an automatic circuit breaker (AB) with a rated current determined by the technical conditions and a single-line diagram of the project “Electrical equipment of a residential building”.

But it is possible, after the input circuit breaker (AB), to install a residual current device (RCD) with a differential protection current of 300 mA. See Fig. 5 for such a connection diagram. If we choose this protection option, then it does not oblige us to install differential circuit breakers for the outlet network, but simply install an automatic circuit breaker (AB), see the same fig. 5. This scheme is acceptable if we have only one socket line with a number of sockets. But it is completely irrational if we have a number of independent receivers plugged into individual sockets.

For example: You have a current leak on the body of the washing machine and you accidentally touch it. The differential protection will instantly work and the DAV of the washing machine will turn off. It will not be difficult for you to identify and eliminate the cause. Imagine how much work you need to do to find the reason for the RCD tripping at the input.

I would like to say that in the modern market of circuit breakers and RCDs there is a very large selection of devices, both domestic and foreign. It should be taken into account that domestically produced products are characterized by large overall dimensions, the ability to regulate current, lower price, and the service life in domestic conditions is almost the same.

Table 1. Comparison of the cost of circuit breakers

Conclusion

So, in the article we discussed the issues of electrical safety. They became especially relevant when a huge number of electrical appliances, consumer electronics and computers entered our home. The wiring carries a very high load and a protective shutdown is necessary. Modern technology is very expensive and demanding on the quality of networks. Therefore, you should not skimp on protective measures, because the cost of an RCD is not commensurate with the cost of the equipment in your home, and even more so with the cost of human life.

Please note: Prices are valid for 2009.

You can hear an opinion that disputes the need to install residual current devices (hereinafter RCDs). To refute or confirm it, it is necessary to understand the functional purpose of these devices, their operating principle, design features and connection diagram. Also an important factor is the correct connection, depending on the specific task. We will try to answer all questions regarding this topic as broadly as possible.

Functional purpose

According to the official definition, this type of device plays the role of a high-speed protective switch that responds to current leakage. That is, it is triggered when a circuit is formed between the phase and the “ground” (PE conductor).

Let's take a classic example: an electric water heater is installed in the bathroom. It works without problems for the warranty period and even more, then there comes a time when the body of one of the heating elements cracks and a breakdown of the phase to water occurs.

If in this case a circuit is formed: phase - man - earth, the load current will not be enough to trigger the electromagnetic protection; it is designed for a short circuit. As for thermal protection, its response time is much longer than the human body’s resistance to the destructive effects of electric current. The result need not be described; the worst thing is that in an apartment building such a boiler can pose a threat to neighbors.

In such cases, the presented device is the only effective way to provide reliable protection. It's time to consider its circuit diagram, design and principle of operation.

Device diagram

First of all, let us present a schematic diagram of the device, indicating its main elements.

Designation:

• A – Relay that controls the contact group.
• B – Differential CT (current transformer).
• C – Phase winding on the DTT.
• D – Zero winding on the DTT.
• E – Contact group.
• F – Load resistance.
• G – Button that starts testing the device.
• 1 – Phase input.
• 2 – Phase output.
• N – Neutral wire contacts.

Now let's explain how it works.

Operating principle

Let's say that a certain device with internal resistance Rn is powered from our protective device, while the body of the connected device is grounded. In this case, during normal operation, currents equal in value but different in direction will flow through windings I and II of the DTT.

Thus, the total value of i 0 and i 1 will be zero. Accordingly, the magnetic fluxes caused by the currents in the DTT will also be counter-current, therefore their total value will also be zero. Taking into account the above conditions, no current will be generated in the secondary winding of the DDT, therefore the relay controlling the contact group is not initiated. That is, the protective device will remain switched on.

Now let's consider a situation in which a breakdown occurred on the housing of the connected equipment.

As a result of the appearance of leakage current (i y) to ground, the balance of currents flowing through primary windings I and II will be disrupted. This will lead to the fact that the value of the magnetic flux will also become different from zero, which will cause the formation of current (i 2) on the secondary winding of the DTT (III), to which the relay that controls the contact group is connected. It will work and the connected equipment will be de-energized.

The test button on the device simulates current leakage through the resistor Rt, which makes it possible to verify the operation of the device. This check must be carried out at least once a month.

Design

The figure below shows a typical protective device with the top cover removed, which allows you to examine the main components of the structure.

Designations:

• A – The mechanism of the button that starts testing the device.
• B – Contact pads for connecting the phase input and neutral wire.
• C – Differential CT.
• D – Electronic board to amplify the current coming from the secondary winding to the level necessary to operate the relay.
• E – The lower part of the plastic case with standard DIN rail mounting.
• F – Arc chutes on the breaking group of contacts.
• G – Contact pads for connecting the phase output and neutral wire.
• H – Release mechanism (operated by relay or manually).

List of main characteristics

Having understood the design of the devices and their operating principles, let’s move on to the main parameters. These include:

• The type of electrical wiring being protected, it can be single-phase or three-phase. This parameter affects the number of poles (2 or 4).
• The rated voltage is 220-240 Volts for two-pole devices, 380-400 Volts for four-pole devices.
• The value of the rated current load, this parameter corresponds to that of circuit breakers (hereinafter referred to as AB), but has a slightly different purpose (will be discussed in detail below), measured in Amperes.
• Rated value of differential (breaking) current, typical values: 10, 30, 100 and 300 mA.
• Type of disconnecting current, accepted designations:

1. AC – Corresponds to sinusoidal alternating current. Both its slow increase and sudden manifestation are allowed.
2. A – To the previous characteristics (AC), the ability to monitor the leakage of rectified pulsating current is added.
3. S – Designation of selective devices; they are characterized by a relatively high response delay.
4. G – Corresponds to the previous type (S), but with less delay.

Now it is necessary to explain the meaning of the rated current parameter, since it raises some questions. This value indicates the maximum permissible current for this protective electromechanical device.

When selecting this parameter, it is necessary to take into account that it should be one step higher than that of AB on a given line. For example, if the AV is designed for 25 A, then it is necessary to install protective devices with a rated current of 32 A.

Please note that this type of device is not intended to be triggered by short circuits and overloads. If such an accident occurs, all the wiring will burn out and a fire will break out, but the device will remain turned on. That is why such protective devices must be used in conjunction with AV. As an option, you can install a differential circuit breaker, which is essentially also a residual current device, but equipped with a short-circuit and overload protection mechanism.

Marking

The marking is applied to the front panel of the device; we will tell you what it means using the example of a two-pole device.

Designations:

• A – Abbreviation or manufacturer’s logo.
• B – series designation.
• C – The value of the rated voltage.
• D – Rated current parameter.
• E – The value of the shutdown current.
• F – Graphic designation of the type of disconnecting current, can be duplicated with letters (in our case, a sinusoid is shown, which indicates the type of AC).
• G – Graphic designation of the device on circuit diagrams.
• N – Value of conditional short-circuit current.
• I – Device diagram.
• J – Minimum operating temperature (in our case: – 25°C).

We have provided standard markings that are used in most devices of this class.

Connection options

Before moving on to typical connection diagrams, it is necessary to talk about several general rules:

1. Devices of this type must be paired with an AB, as we mentioned above, this is due to the fact that the protective devices are not equipped with short-circuit protection.
2. The rated current of the protective device must be one step higher than that of the AB paired with it.
3. Do not confuse input and output contacts. That is, the input marked, as a rule, “1” should be supplied with a phase, and “N” - zero. Accordingly, “2” is the phase output, and “N” is zero.
4. The zero after the device should not be connected to the zero before it.

Now let's look at the simplest circuit, in which each line is protected against short circuits and leakage current.

In this case, everything is simple, an AB is installed at the input (A in Fig. 7) with a rated current of 40 A. After it there is a general device (B), it is also called a fire protection device. This device must have a leakage current of at least 100 mA, a rated current of at least 50 A (see paragraph 2 of the general rules indicated above). Next come two RCD-AB bundles (C-E and D-F). The rated current parameter for “C” and “D” is 16 A. For “E” and “F” this parameter should be one step higher, in our case it is 20 A. As for the value of the disconnecting current, for wet rooms this the indicator should be 10 mA, for other consumer groups - 30 mA.

This connection option is the simplest and most reliable, but also more expensive. It can still be used for two internal lines, but when their number is 4 or more, it makes sense to install one protection device per group AB. An example of such a scheme is given below.

As you can see in this diagram, we have one general (fire) protective device installed and four group ones for lighting, kitchen, sockets and bathroom. This connection option allows you to significantly reduce costs compared to a scheme where a bundle of RCD-AV is connected to each line. In addition, the necessary level of protection is provided.

In conclusion, a few words about the need for protective grounding. It is necessary for the normal functioning of the RCD. On the Internet you can find a switching diagram without PE (in fact, it is no different from the usual one), but it should be noted that it will only work if there is contact with batteries, cold or hot water pipes, etc.

Oleg Udaltsov

Eaton Power Distribution Components Product Specialist.

What is a residual current device

A residual current device, also known as an RCD, is a device installed in an electrical panel in an apartment or house to automatically turn off the power supply in the network in the event of a ground fault current.

Ground fault current occurs in wiring and/or electrical appliances when the insulation in them is broken for some reason or when exposed parts of the wires that should be secured in the terminals, for example inside household electrical appliances, touch the housing of the devices - and the current begins to “leak” in an undesirable direction.

This can lead to a fire due to overheating (first of the wiring or device, and then of everything around it) or to the fact that a person or pet will suffer from the current - the consequences can be extremely unpleasant, even death. But this will only happen if you touch a conductor or equipment body that is energized.

The main difference between an RCD and a conventional circuit breaker is that it is designed specifically to interrupt ground fault current, which the circuit breaker is not able to detect. An RCD can turn it off in a fraction of a second, before the moment when it becomes dangerous to a person or property.

Where and how much to install

For one- and two-room apartments - to the common electrical panel of the apartment. If the housing area is large, then in several local electrical panels distributed throughout the house.

An RCD will be required for the entire system for protection against, as well as for individual lines supplying groups of electrical appliances with a metal body (washing machine, dishwasher, electric stove, refrigerator, etc.) - for protection against electric shock. If a malfunction appears or an accident occurs, not the entire apartment will be de-energized, but only one line, so it will be easy to determine the culprit for tripping the RCD.

However, one must keep in mind: neither RCDs nor conventional automatic machines can save you from an electric arc or arc breakdown.

An electric arc can occur when, for example, the wire from an electric lamp is often pinched by a slamming door and the metal part of the wire inside is damaged. At the site of damage, a spark hidden from view will occur, accompanied by an increase in ambient temperature and, as a result, ignition of nearby flammable objects: first the wire sheath, and then wood, fabric or plastic.

To protect against such hidden threats, it is better to choose solutions that combine the functions of a machine, RCD and arc flash protection. In English, such a device is called arc fault detection device (AFDD), in Russia the name “arc fault protection device” (AFDD) is used.

An electrician may be able to include such a device in the design if you tell him that you need a higher degree of protection. For example, for a children's room, where a child can handle wires carelessly, or for groups of sockets for powerful electrical appliances with flexible wires that are prone to breaking.

It is equally important to install protection devices where wiring is laid openly and can be damaged. And also when planned, to avoid risks in case of accidental damage to hidden electrical wiring while drilling walls.

How to choose

A good electrician will recommend an RCD manufacturer and calculate the load, but you need to be sure that the recommendations are correct. And if you purchase everything yourself for repairs, then even more so you need to understand what to look for when choosing a device.

Price

Do not purchase a device in the lower price range. The logic is simple: the higher quality the components inside, the higher the price. For example, some cheap devices do not have burnout protection, and this can lead to fire.

A cheap device can be made of fragile materials and can easily break when you lift up the lever that is lowered when triggered. According to the standard, the RCD must be designed for 4,000 operations. This means that you will only have to make a choice once, but only if you have purchased a quality product. By purchasing a low-quality device, you put yourself and your loved ones at risk, not to mention material losses in the event of a fire.

Case quality

Pay attention to how tightly all parts of the device fit together. The front panel should be monolithic and not consist of two halves. The preferred material is heat-resistant plastic.

Device weight

Give preference to heavier devices. If the RCD is light, it means that the manufacturer has saved on the quality of internal components.

Conclusion

It is advisable to involve professionals to resolve issues related to electrical systems in the home. However, the responsibility should not be placed entirely on their shoulders. It is better to be guided by the proverb “Trust, but verify.” Having even basic knowledge of the subject and understanding the scenario for the future use of electrical appliances in the house, you can protect yourself and your loved ones from problems with electricity.