The purpose of ouzo is in electrical engineering. RCD is an abbreviation that can save you from a short circuit

How the RCD works:

All RCDs belong to the category of electronic protective equipment. However, in terms of its functionality, the residual current device differs significantly from standard circuit breakers. What is their difference, and how does an RCD work in comparison with an automatic machine?

Everyone knows that over time, wire insulation ages. Damage may occur, and the contacts connecting live parts gradually weaken. These factors ultimately lead to current leakage, which causes sparking and further fire. Often, people may accidentally touch such emergency phase wires that are under voltage. In this situation, electric shock poses a serious danger.

Purpose of RCD

Residual current devices must respond to even minor short-term current leaks. This is their main difference from circuit breakers, which operate only during overloads and short circuits. Automatic machines have a very high time-current response characteristic, while an RCD operates almost instantly, in the presence of even the most minimal leakage current.

The main purpose of the RCD is to protect people from possible electric shocks, as well as to prevent dangerous current leaks.

Operating principles of RCD

From a technical point of view, any RCD is a high-speed switch. The operating principles of the residual current device are based on the response of the current sensor to the changing current flowing in the conductors. It is through these conductors that current is supplied to the electrical installation, which is protected by the RCD. A differential transformer is wound onto the core, which is a current sensor.

To determine the response threshold of an RCD having a certain current value, a highly sensitive magnetoelectric relay is used. The reliability of relay structures is considered quite high. In addition to relay ones, electronic device designs have now begun to appear. Here the threshold element is determined by a special electronic circuit.

However, conventional relay devices seem to be more reliable. The actuation of the actuator is precisely carried out using a relay, as a result, a rupture occurs electrical circuit. This mechanism consists of two main elements: a contact group designed for maximum current and a spring drive that breaks the circuit in the event of an emergency.

To check the serviceability of the device, there is a special circuit inside it that artificially creates a current leak. This triggers the device and makes it possible to periodically check its serviceability without calling specialists to carry out electrical measurements.

The direct operation of the RCD is carried out according to the following scheme. A situation should be considered where the power supply system is operating normally and there are no leakage currents. The operating current passes through the transformer and induces magnetic fluxes directed towards each other and equal in magnitude. When they interact, the current in the secondary winding of the transformer has a zero value, and the threshold element does not operate. When a current leak occurs, an imbalance of currents in the primary winding occurs. Because of this, a current appears in the secondary winding. Thanks to this current, the threshold element is triggered, and the actuator is activated and de-energizes the controlled circuit.

From a technical point of view, the residual current device consists of a fire-resistant plastic housing. On its back there are special locks for installation on an electrical panel. In addition to the elements already discussed, an arc suppression chamber is installed inside the housing, which neutralizes the electric discharge arc. Clamps are used to connect the wires.

RCD operation parameters

For the right choice device response settings, you should remember the danger of alternating current for humans. Under its influence, cardiac fibrillation occurs when contractions are equal to the frequency of the current, that is, 50 times per second. This condition causes a current starting from 100 milliamps.

Therefore, the settings at which the RCD is triggered are selected with a margin of 10 and 30 milliamps. The lowest values ​​are used in high-risk areas, such as bathrooms. The highest settings are 300 mA. RCDs with such settings are used in buildings, protecting them from fires due to damaged circuits.

When choosing an RCD, the rated current, required sensitivity and number of poles are taken into account, in accordance with the phases of the supply network. It is necessary to check the degree of thermal stability of the device, as well as the ability to turn it on and off, based on the calculated network parameters.

The rated current value for the RCD must be higher than that of the machine. A lower current rating of the machine will protect the RCD from damage in the event of a short circuit in the circuit.

How to connect an RCD

All terminals on the RCD body are marked with the corresponding letters. Terminal N is for the neutral wire, and L is for the phase wire. Therefore, they must be connected to their own terminals.

Also, it is necessary to take into account the position of the entrance and exit and under no circumstances change their places. The entrance is located at the top of the device. The power wires running through the input machine are connected to it. The output is located at the bottom of the RCD and the load is connected to it. If you confuse the position of the input and output, then false triggering of the residual current device or its complete failure may occur.

Installation of RCDs is carried out together with conventional circuit breakers. Thus, devices installed together provide protection not only from short circuits and overloads, but also from leakage currents. At the same time, the RCD itself, which is connected behind the input machine, is protected.

Connecting a residual current device in an apartment or private house has its own characteristics. For apartments where a single-phase network is used, the RCD connection diagram is assembled as follows, following a certain sequence: input machine => electricity meter => RCD itself with a leakage current of 30 mA => the entire electrical network. For consumers with high power It is recommended to use your own cable lines with the connection of separate residual current devices.

In large private houses, connection diagram protective devices differs from apartments due to its specifics. Here, all devices are connected as follows: input circuit breaker => electricity meter => input RCD with selective action (100-300 mA) => circuit breakers for individual consumers => RCD for 10-30 mA for individual groups of consumers.

RCD errors when connecting

Correct connection of protective devices is the key to reliable operation of the entire electrical network.

Any electrical network must have a protection device, but not everyone knows what an RCD is and what the principle of its operation is. The decoding of the abbreviation looks like this - residual current device.

This low-voltage electrical device is designed to turn off the protected section of the circuit when a differential current exceeds the rated value for this device.

In our article we will try to analyze in detail the design and principle of operation of RCDs, consider the existing varieties and understand what information the marking of residual current devices contains.

The RCD ground loop device is a PE conductor of neutral conductive housings or parts of electrical mechanisms with a resistance not exceeding 4 Ohms.

If a leakage current occurs, these equipment elements may be energized, which poses a danger to human and animal life in contact with them, as well as to property in general.

To save from electrical injuries is the calling of survey devices. When a leakage current is detected, they turn off the voltage.

The greatest danger lies in the fact that such disturbances in the circuit are invisible and, in rare cases, noticeable, when you can feel a slight electric shock when touching the device.

The main reason for this phenomenon is a violation of the insulating layer of the wiring. Uncontrolled processes can cause great harm, which is why protective equipment is becoming increasingly popular in domestic environments.

The impact of conductive networks on the human body can result in disastrous consequences. This problem was solved with the help of RCD control devices belonging to the protective segment. Basic requirements for installation and use are described in IEC 60364

The use of RCDs is most widespread with alternating current and neutral line grounding, as well as with voltage levels up to 1 kW in the household power supply format.

RCD design

Optional features of the protective mechanism will help you understand the principle of operation of the RCD, namely the reproducible response of the device to current leakage.

Key operating units include:

• transformer differential sensor;
• trigger - a mechanism that breaks an incorrectly functioning electrical circuit;
• control block.

Opposite windings are connected to the sensor - phase and zero. During normal operation of the network, these semiconductor elements form magnetic fluxes in the core that have the opposite direction in relation to each other. Due to this, the magnetic flux is zero.

The transformer consists of a closed steel core, on which two coils are placed: the primary one is connected to the alternating current source, the secondary one is connected to the load. The number of times the transformer increases the AC voltage, the same number of times the current decreases

An electromagnetic type relay is connected to the secondary winding wound on the magnetic core of the transformer. If the network meets standard operating conditions, it is not used.

When a current leak occurs, the entire operation changes dramatically. The phase and neutral conductors begin to pass different amounts of current. Now the power value and direction of the magnetic fluxes on the transformer core will also have different parameters.

A current appears in the secondary turns and when the specified values ​​are reached, the electromagnetic relay is activated. It is paired with a release mechanism. This connection reacts at the right moment and disconnects the electrical network.

According to fire safety requirements, control checks of the differential protection device are carried out regularly, at least once a month. For this purpose, the device has a special “TEST” button.

The testing unit is represented by a resistance mechanism - a certain load connected to bypass the differential sensor. This element simulates current leakage and thus checks the functionality of the device. We talked in more detail about verification methods.

The operating principle of the RCD is as follows: supplying current from the phase line to the control resistance and then to the neutral wire, bypassing the sensor.

This creates conditions for different current indicators at the input and output of the device. This imbalance should lead to the startup of the shutdown unit.

Depending on the developers, the circuit design may vary, but the principle used in the operation of the RCD will be identical for all models.

The principle of operation of the protective mechanism

Let's consider why you need to use an RCD. The functioning of the protective device is based on a measuring method.

The incoming and outgoing parameters of the currents flowing through the transformer are recorded. If the first value is greater than the second, this means that there is a current leak in the electrical circuit and the device reproduces a shutdown. If the parameters are identical, the device does not work.

In a two-wire system, the differential device does not operate if a current of equal strength passes through the phase and neutral wires. If there is a difference in these values, it means there is an insulation breakdown in the network and the protective mechanism will turn off the damaged section

For a better understanding, let's consider how an RCD will work in a household distribution panel with a two-pole system.

The input two-wire wire (phase and neutral) is connected to the upper terminal blocks. Phase and neutral are connected to the lower terminal blocks, laid to the load area, for example, to the power outlet of a boiler or electric kettle. Protective grounding of the device will be carried out by cable, bypassing the RCD.

In standard operating mode, the movement of electrons is carried out along the line-phase from the incoming cable to the electric heater of the boiler/kettle, flowing through the differential protection device. They move back to the ground again through the RCD, but along the neutral line.

If a person touches the body of a current-carrying device, on which a potential has appeared due to a breakdown, in this situation the current leakage will pass through the human body, to which the device reacts almost instantly by turning off the power system

For example, the insulation in the heating element of the device was damaged. Thus, through the water inside, the current will be partially conducted by the housing, and then will go into the ground through the wiring of the protective device.

The remaining current will return along the neutral line through the RCD. However, its strength will become less by the amount of leakage compared to the incoming one.

The difference in indicators is calculated by a differential transformer. If the number is greater than the permitted value, the device instantly reacts and breaks the circuit.

The feasibility of using RCDs

Let's consider why you need to use an RCD and from what negative impact factors the device provides protection.

First of all, a phase short circuit to the electrical equipment housing. Mainly, problem areas include heating elements of heaters and washing machines. It is worth noting that breakdown occurs only when the heat-generating part is heated under the influence of current.

Also if the wires are connected incorrectly. For example, if twists without a terminal box are used, which are subsequently recessed into the wall and covered with a layer of plaster. Since the surface has high humidity, this twist will be a breakdown that will leak into the wall.

The differential protection mechanism in this case will constantly de-energize the line until the area is completely dry or until the connecting node is redone.

Automatic protection is effectively used in everyday life: in electrical groups for the bathroom, kitchen and sockets, with a large number of powered devices. The ideal option is when this type of device is installed on each group of sockets

The scope of application of survey devices is quite diverse - from public buildings to large-scale enterprises. They complete electrical structures and circuits intended for reception and distribution: switchboards in residential buildings, current supply systems for individual consumption, etc. The main thing with this is to do it right.

Types of devices and their classification

Development companies endow their products with diverse capabilities, which must be taken into account when determining the required type of RCD, based on the specific operating conditions of the electrical network.

In order to ordinary consumer managed to select the necessary residual current device from the variety of models offered, a classification system was created based on the following characteristics:

• operating principle;
• type of differential current;
• time delay of disconnecting differential current;
• number of poles;
• installation method.

Classification #1 - by inclusion method

There are only two switching methods - electromechanical and electronic. In the first case, the machine will turn off the power to the damaged line, regardless of the network voltage. The main working body is a toroidal core with windings.

When a leak occurs, a voltage is generated in the secondary circuit to activate the polarization relay, which leads to activation of the shutdown mechanism.

Electromechanical type devices do not require external voltage. The source for their operation is the differential current on the fault line

The functioning of a device with electronic filling is completely dependent on additional voltage, i.e. external power required. Here the working body is an electronic board with an amplifier.

Inside such a mechanism there are no additional sources that accumulate energy, so the circuit uses electricity from the external network to operate and, if there is no voltage, the device will not break the circuit.

Determining the type of device: solder two wires to the terminals of an AA battery. Turn on the RCD and connect it to the input of the protective block, and the next one to the output. The lines are connected to one pole. If the device turns off, this means that the electromechanical type is presented; if not, it is electronic

An example of the operation of an electronic RCD installed on a line with a socket from which a microwave oven is powered: a break in the zero phase has occurred, in addition to this, during the same period a malfunction occurs in the microwave wiring and a phase short circuit occurs to the housing, i.e. it has dangerous potential.

If you touch the stove, the electronic type of protection will not be activated, because no power supply. It is precisely because of unreliability in comparison with its electromechanical analogue that this device has become less widespread.

Classification #2 - by type of leakage current

All models of manufactured safety circuit breakers are additionally divided by the load current passing through the device. They process voltage of a given oscillation format.

The rated operating voltage is indicated on the housing of all devices and in the passport. This parameter must correspond to the rated current range of the electrical equipment.

The AC type will be activated when an alternating leakage voltage instantly appears in the controlled circuit or when it increases in waves. These devices are marked with the inscription “AC” or the symbol “~”.

The most suitable form factor for domestic use is UZO-AS. The model is the cheapest of devices of similar action. In the passport for electrical engineering, manufacturers often indicate a specific model of circuit breaker suitable for this product.

Type A is triggered by the instantaneous formation of an alternating or pulsating breakdown current in the controlled circuit, or by their slow increase.

This mechanism can be used in any of the situations presented. The abbreviation “A” or symbol is marked on the body of the machine, as in the graphic image in a rectangle.

Most often, the A-type is connected to a circuit where load regulation is reproduced by cutting off the top of the sinusoid, for example, adjusting the speed of motor rotational movements with a thyristor converter.

Subtype B RCDs are effective for reproducing the reaction in a subordinate electrical circuit of direct, alternating or converted (rectified) leakage current.

This is expensive equipment intended for industrial facilities. They are not used in domestic conditions.

The presented tripping protection devices of type A, B and AC are designed for an activation time of 0.02-0.03 s.

Classification #3 - by type of time delay

This classification distinguishes between two types: S and G. Type S automatic protection can be characterized by a selective format reaction. The response time delay corresponds to the range of 0.15-0.5 s. It is advisable to choose it in the case of group connection of an RCD.

Scheme of an apartment panel with two load groups, where two different types of protective devices are connected: AC or A, and S

According to the diagram, the panel contains two load groups in the form of sockets No. 1 and No. 2, to which a type A RCD is connected, and a second circuit breaker - S - is connected to the entrance of the room.

If a breakdown occurs in one beam, the input device is activated only when the collective device does not fulfill its function and does not turn off the defective section.

Selectivity of circuit break activation can be achieved using another method - through leakage current settings. This method is most widespread.

Scheme of an apartment panel with two load groups, where two different types of protective devices are connected: AC with a breakdown setting, and the second A, but with a higher value

Let's take a circuit similar to the previous one and modify it in this way: we select a group automaton of the AC type only with a diftoka setting of 0.03 A, and at the input there will be a similar device with only 0.1 A.

There are situations when the differential current in the fault circuit exceeds the rated settings of the two protection devices. For the first circuit, selectivity will not be impaired, but in the second, any of the connected devices can supply the cutoff current.

The G form factor device is also represented by a selective triggering principle and has a shutter speed of 0.06-0.08 s. All described selected types are designed for exposure to extreme currents - up to 15 kA.

Some RCD models have a system for adjusting the diforgan setting, others do not have this capability. However, the second version is suitable for domestic purposes.

The limiting current is an important selection parameter because This is precisely what ensures safety.

For example, in rooms with high humidity, electrical appliances are powered by connecting disconnect devices to the circuit with a setting of 0.01 A. For standard living conditions - 0.03 A.

To organize fire safety of buildings - 0.1-0.3 A. We recommend that you familiarize yourself with the tips and subtleties of its installation.

Classification #4 - by number of poles

Due to the fact that the automatic device operates on the principle of comparing the magnitudes of current passing through it, the number of poles of the machine will be identical to the number of current-carrying lines.

A two-pole RCD is designated as 2P. It is included in single-phase circuit to ensure human protection and prevent possible reasons fire.

Marking of four-pole RCDs is 4P. They are designed to work in a three-phase network. An installation combination is also possible, for example, a device with four poles is connected to a two-wire network.

However, this will not realize the full potential of the device, which is economically unprofitable.

When installing a circuit breaker, it is worth considering the possibility that the load current may exceed the maximum operating values ​​of the device. Therefore, an additional circuit breaker with a rated voltage no greater than the operating current of the safety system is installed

Classification #5 - according to the method of installation of the device

Since differential protective devices come in a variety of housings, they can be used as stationary or portable.

In the second case, the device is equipped with an extension cord. Devices that are fixed on a DIN rail, which is placed either in the corridor or in the apartment.

There are also options for the type and RCD plug. In both the first and second cases, any electrical device connected through such a mechanism does not pose a danger to humans if it breaks down.

Full decoding of marking values

The name of the developer company must be on the device body. This is followed by standardized markings indicating the serial number.

To decipher the abbreviation we will use the following example: [F][X]00[X]-:

• [F]– residual current device;
• [X]– performance format;
• 00 – digital or alphanumeric designations of the series;
• [X]– number of poles: 2 or 4;
• – characteristics by type of leakage current: AC, A and B.

The nominal parameters of the device will also be indicated here, which you need to pay special attention to when choosing.

Explanation of the abbreviation: 1 – brand; 2 – device type; 3 – selective species; 4 – compliance with European standards; 5 – rated operating current and setting; 6 – maximum alternating operating voltage; 7 – rated current that the device can withstand; 8 – differential making and breaking capacity; 9 – electrical diagram; 10 – manual performance check; 11 – switch position marking

The maximum parameters for which the devices are designed include: voltage Un, current In, differential value of circuit opening current IΔn, ability to turn on and off I'm switching capacity during short circuits Icn.

The main markings must be located in such a way that they remain visible after installation of the device. Some parameters may be marked on the side or on the rear panel, visible only before installation of the product.

Outputs intended only for connecting the neutral wire are designated by the Latin symbol “ N" The disabled RCD mode is indicated by the symbol “ ABOUT" (circle), included - short vertical bar " I».

Not every product is marked with optimal environmental temperature indicators. In those models where there is a symbol, this means that the operating range is from -25 to + 40 °C; if there are no symbols, this means standard indicators from -5 to +40 °C.

The use of an RCD is a profitable and correct solution not only from the point of view of economy, but, from the point of view of fire safety, and human protection.

Do you still have questions about the operating principle or classification of residual current devices? Or do you want to supplement the presented material with useful information? Please write your clarifications in the comments block, ask questions - experts and competent visitors to our site will try to answer you as thoroughly as possible.

– a protective shutdown device that cuts off the supply of current to the circuit in the event of a leak to the ground and thereby protects against electric shock. This type of electrical equipment is used where it is not possible to connect to grounding, and this is not only in everyday life, but also in production, where current leakage through a metal case is also a very common phenomenon.

Some manufacturers equip their equipment with an RCD, so the user does not have to separately purchase and install it.

Residual current devices– this is electrical protective equipment designed to operate in alternating current networks of 220 and 380 volts, in single-phase and three-phase circuits. The device is made of non-flammable PVC housing and is designed for the flow of current of various sizes.

RCDs are produced with a leakage current limit with ratings according to the standard:

• 10 mA;
• 30 mA;
• 100 mA;
• 300 mA;
• 500 mA;

Another device parameter– this is the rated load current that the device can transit through itself.

Application area

Since the devices are used for protection, it is advisable to use them wherever electrical devices operate that are not equipped with protection from unauthorized access, that is, where accidental touch is possible.

In industry, a grounding loop is used for these purposes, however, in most residential buildings built during the Soviet period, it is absent, and before the RCD became widely available, apartment residents exposed themselves to danger.

The same applies to office electrical networks, server rooms and other premises where electrical equipment is used and there is no grounding bus.

RCDs are used in electrical networks of 220/380 volts to prevent electrical injuries when a phase breaks through to the housing.

In most cases, the appearance of potential on the housing does not lead to a malfunction, therefore, to a person ignorant of electrical safety issues, it may seem that there is no danger.

The device can be installed in front of a specific device or at the entrance to the apartment, depending on the need.

Device

Do not confuse RCD and, there are significant differences between them in design, principle of operation and purpose:

1. AB Designed to supply or disconnect loads, protect against short circuits and overheating.
2. designed to prevent leakage currents and protect against electric shock.
3. AB reacts to the release of heat during the passage of large currents and short-circuit currents.
4. reacts to leakage current and does not protect the circuit from short circuits and overheating.

However, very often you can find a design in the form of an automatic machine and an RCD in one housing, which is quite convenient, especially if the equipment is located in a small panel. You can also purchase each device separately.

The operation of the RCD is based on the use of a differential current transformer having three windings - two primary windings connected in series to the phase and neutral wire and one secondary, from which the polarized relay is powered.

It can be electromechanical or electronic, which is why a distinction is made between electronic and mechanical EO devices. When there is no leakage current, the primary windings are not excited.

If a ground leak occurs through the housing, the current in the windings increases, which leads to the appearance of voltage in the secondary winding that supplies the polarized relay. The latter activates the spring mechanism and cuts off the consumer from the network simultaneously in zero and phase.

Where is it installed?

Protection devices are installed in the electrical panel, or immediately before the load, but only after the electrical energy metering unit. Last option, as a rule, is used in technological rooms, and for loads without a stationary power cord.

Usually, an installation is used to cut off a specific load, since an RCD installed at the input will turn off the entire electrical network.

Installation order, starting from the counter:

1. Circuit breaker.

When installing a combined instrument, there is no need to maintain this sequence.

Types and classification

It is customary to distinguish three types of RCDs according to the type of differential leakage current, for which the corresponding markings are applied to the body:

1. AC– sinusoidal variable, sudden or increasing.
2. A– sinusoidal alternating, sudden, or increasing and rectified pulsating.
3. IN– variable and constant.

Devices are classified according to the following parameters:

1. In terms of resistance to impulse voltage:
   • disconnecting the current if available;
   • surge voltage resistant;
2. According to the method of action:
   • without auxiliary power;
   • connected to auxiliary power;
   • with power supply and automatic shutdown in case of power failure;
3. By installation method:
   • stationary, ;
   • portable, with flexible extension cords;
4. By number of poles:
   • two-wire with one pole;
   • bipolar;
   • three-wire, two-pole;
   • three-pole;
   • four-wire three-pole;
   • four-pole;
5. By type of overload protection:
   • equipped with overload protection;
   • without protection;
6. If possible, regulation:
   • not adjustable.
   • with smooth adjustment;
   • with step adjustment;
7. Technical specifications:
   • for single-phase circuits;
   • for three-phase circuits;

Selection criteria and cost

When purchasing an RCD, the value of the leakage current is taken into account, as well as the rated load current for which the circuit breaker was designed. However, for the protection device, given value should be chosen an order of magnitude higher than that of the machine.

The fact is that the diffavtomat is quite expensive equipment and, as a rule, it is cheaper to purchase a model without a shutdown function in the event of a short circuit.

Selected in accordance with the procedure described above, it will not fail if a short circuit occurs and the switch de-energizes the circuit. For residential premises, it is recommended to install difavtomats with a leakage current of no more than 30 mA, since a higher value is already life-threatening.

This equipment, even for domestic installation, is quite expensive, which can be explained by several reasons.

The main one is the presence of a differential transformer; it is made of expensive materials and accounts for up to 50% of the total cost.

The greater the number of poles in the device, the more expensive it is; in addition, the design of the relay matters - electromechanical or electronic, as well as the presence of additional options.

The brand name also plays a role. For example, a 30 mA device for installation at home from the Russian company IEK can be purchased for an average of $10. From the world famous French Legrand it is at least twice as expensive.

How to install and connect correctly?

Installation and installation of any electrical equipment requires appropriate qualifications, especially if it concerns safety equipment.

To work you will need:

1. Phillips screwdriver.
2. Voltage indicator, .
3. Assembly knife.
4. Connecting wires.
5. A hammer drill, a drill and a housing for the RCD - if the installation is carried out directly near the consumer.

Stages of work

Installation near the consumer:

1. Marking the installation location of the housing and drill holes for installation.
2. Mounting the housing and connect the wires.
3. Checking the absence of voltage in the phase, we strip the wires with a knife and insert them into the corresponding connectors marked L and N, strictly observing the polarity, as indicated in the diagram.
4. The RCD is fixed on a DIN rail in the case, after which you can apply voltage and check the operation by pressing the “TEST” button

Installation in electrical panel:

1. Find the required pair of wires and determine the polarity.
2. Power off and clean the conductors.
3. Install the RCD on the DIN rail and connect the wires to the corresponding connectors, observing the polarity.
4. Turn on power and test the work.

Modern protection devices are designed in such a way that it is impossible to make a mistake in installation. The main mistake is made at the calculation stage; as a rule, it is an incorrect choice of the operating current limit relative to the parameters of the circuit breaker.

If this value is lower or corresponds to that for which the AV is designed, then the protection device fails and, in most cases, cannot be restored.

When working with household electrical appliances, there is always a danger of electric shock when touching metal parts that accidentally become energized. To avoid electrical injury, you must immediately disconnect the device from the network.

This task is successfully performed by residual current devices (RCDs). Currently, different types of such devices are produced with a wide range of technical parameters for use in single-phase and three-phase networks.

Principle of operation

Mains voltage is supplied to electrical appliances through two wires, one of which is neutral and the other phase. The neutral wire is connected to the ground, and the phase wire contains an alternating voltage of 220 V. During normal operation of the equipment, a current of the same magnitude flows in each wire, but different in direction.

If a person touches the exposed phase wire, a current will begin to flow through his body, which will be shorted to the ground. This current is called leakage current. In the phase wire, the total current immediately increases by the amount of the leakage current, and in the zero wire it remains at the same level.

The RCD, using a differential transformer, detects the difference that has arisen and instantly breaks the network contacts. The shutdown happens very quickly, in a split second, and there is no critical hit.

Such RCDs are called “protective type” and are available for different leakage currents: 6, 10, 30 mA. For normal premises, 30 mA devices provide reliable human protection. In areas with increased danger (bathrooms, damp basements), devices with lower leakage current are more suitable.

Leakage currents arise over time in the wiring due to deterioration of insulation. They can reach significant levels, especially in large houses with a distributed electrical network, and cause fire. To prevent fires, they install 100-300 mA RCDs, which are called “fire departments”.

It must be taken into account that all these devices respond only to the occurrence of leakage current. They do not protect the network from short circuits, because during a short circuit there is no current imbalance in the neutral and phase conductors, although it increases into unacceptable thousands of times. To protect the network from short circuits, they are used, which should always be installed together with an RCD.

Types of RCD

The industry produces electromechanical and electronic RCDs. Both designs are based on a differential transformer, but in the second version, the imbalance of currents is amplified by an electronic circuit.

Due to this, electronic RCDs are more sensitive and quickly disconnect equipment from the network. But for their work they require power, which in some situations may disappear, and then the protection will not work. Electromechanical devices do not require voltage and always operate. Therefore, they are considered more reliable, although not as fast.

If the connected electrical equipment does not contain its own power supplies, voltage regulation and conversion devices, then the leakage currents that may arise in them will be sinusoidal in nature (as is the supply voltage). AC type RCDs protect against such alternating currents.

In more complex devices, for example, in washing machines with variable speed control or in computers, leakage currents can be of a unipolar pulse nature. In this case, it is necessary to install type A protective devices.

The most popular and cheapest are AC type RCDs. But recently it has been recommended to use type A. In medical institutions with complex equipment, type B devices are installed, which respond not only to alternating sinusoidal and pulsed ones, but also to direct leakage current.

The indices S and G, present after indicating the device type, indicate that the network shutdown will occur with a slight delay. Such instances are used in protection circuits with the sequential connection of several RCDs (for example, fire and protective) so that they respond to the occurrence of leakage currents with a time delay.

Both electromechanical and electronic RCDs are produced for single-phase and three-phase networks. The former have an operating voltage of 230 V, the latter - 400 V. The standard degree of protection is IP 20, the operating temperature range is -25...+40 degrees.

Marking

The device passport and the front side indicate:

• Operating voltage(230 or 400 V);
• The rated current at which the RCD remains operational. Standard values: 16, 25, 32, 40, 50, 63 amperes;
• The setting current is the leakage current at which the device is triggered. Typical values: 6, 10, 30, 100, 300, 500 mA;
• Device type AC, A, B or symbols in the box: sinusoid (AS), square wave and sinusoid (A), square wave, sinusoid, straight line (B);
• Additional indexes S or G;
• Type electromechanical or electronic.

General selection rules

Selecting suitable equipment is always a complex and ambiguous process, with several options. Key points to consider:

1. The RCD is always turned on together with the circuit breaker. The rated current must be one step higher than the rated current of the circuit breaker. For example, if the circuit has a 16 A switch, then the RCD should be 25 A.
2. In accordance with the house power supply diagram(apartments) for each RCD, the required setting current and type (A, AC with the necessary indices) are indicated. In most cases, fire RCDs are chosen with a current of 100 mA, and protective ones - 30 mA.
3. Which device should you prefer?- electronic or electromechanical - a matter of taste.

Connection and operation rules

For modern three-wire electrical networks such as TN-S and TN-C-S, protective devices are installed in the input panel together with a circuit breaker. For a small apartment with a small number of consumption sources, one device is enough.

If the apartment is large, then consumers are divided into groups. Each group has its own RCD. For each group, select the type of device (A, AC, B) with the calculated rated current and leakage current. One fire switch is installed at the entrance with a leakage current of 100–300 mA and, possibly, with a delay in response time.

In private houses, they most often install one common one - a fire RCD (AC type, leakage current 100-300 mA, especially if the wiring is old) and for each group of consumers - a protective one (leakage current 30 mA), with a separate circuit breaker.

The leakage current is calculated depending on the length of the wiring, the number and type of electricity consumers (heated floors, heating boilers, bathhouses). For places with high humidity - bathrooms, baths, damp basements, the leakage current is chosen lower - 10 mA.

In apartments with old two-wire TN-C networks (without grounding), residual current devices can only be installed on a separate outlet or group of outlets, which include the most dangerous consumers of electricity. The easiest way to solve this issue is by using special chip sockets or portable RCDs that are plugged directly into the socket. Such devices are much more expensive than stationary ones and are not yet widespread.

RCDs are not installed in circuits that require 24/7 constant connection. These circuits include fire and security alarms. Failure of the device leads to immediate shutdown of the alarm system, which is unacceptable.

After connecting, be sure to conduct a performance test by pressing the special button with the “T” icon. If the RCD is in order, it will turn off the network.

If the RCD is disconnected, you cannot turn it on immediately. First, you need to unplug all electrical appliances from the sockets, and only then turn on the RCD. If it doesn’t work, then you need to look for equipment that has a leak. If it works, then the leak may be in the wiring or the device itself may be broken. There are special devices for searching for leaks in wiring. The device is checked and repaired only in specialized workshops.

• Control testing of all installed RCDs should be carried out at least once a month.
• If a person touches the phase and neutral wires at the same time, the RCD will not protect him or turn off the network. All electrical work (repairing sockets, switches, replacing light bulbs) is safe to carry out only when the voltage is turned off.
• RCD is the old name, now it is more correct to call it a “differential switch”.
• The industry produces difavtomats, which in their functions completely replace the RCD and circuit breaker. Some people prefer to install it because of its low cost and ease of installation. However, there is a drawback to such a replacement. When the combined device is triggered, the reason for the network shutdown is unclear: either a short circuit occurred, or leakage currents appeared. When using the RCD and circuit breaker separately, the reason is immediately visible. If the circuit breaker has tripped, then a short circuit has occurred; if the RCD has tripped, a leakage current has occurred.
• Although chip sockets- an expensive pleasure, it’s still worth equipping a children’s room with them.
• Life depends on the quality of protective devices. You should only purchase certified products from trusted sellers.

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

But Galen’s rule: “Everything is poison and everything is medicine” is true not only in medicine. Outwardly simple, an RCD, if used thoughtlessly or carelessly, 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 it, but someone cannot even be given an ax in their hands, they will chop off something for themselves. So let's get to know the RCD in more detail.

First of all

Any serious conversation about electricity will inevitably 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-lasting and severe.

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

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

Finally, in (PUE-7A; Rules for the construction of electrical installations (PUE), 7th edition, with additions and amendments, M. 2012), paragraph 7.1.80 still dotted the i’s: “It is not allowed to use RCDs that respond to differential current , in four-wire three-phase circuits (TN-C system).” This tightening was caused, contrary to previous recommendations, by recorded cases of electrical injuries WHEN THE RCD was activated.

Let's explain with an example: The housewife was doing the laundry; the heating element in the machine broke through on the body, as shown in the picture with the yellow arrow. Since 220 V current is distributed along the entire length of the heating element, there will be something around 50 V on the body.

The following factor comes into play here: The electrical resistance of the human body, like any ionic conductor, depends on the applied voltage. As it increases, human resistance decreases, and vice versa. For example, the PTB provides an absolutely justified 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 V? Even completely drunk in a jacuzzi with sea water? 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 won’t go as far as resuscitation with defibrillation.

Now let’s “defend ourselves” against the RCD, without 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 to 220 V along its entire length, and on the body there will be 220 V, and a current of 220 mA will pass through the body (red arrow in the figure). Less than 20 ms, but 220 mA is more than two instantly killing 100 mA values.

So, is it impossible to install RCDs in old houses? It’s still 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 electrical engineering 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. The vast majority of RCDs (and all household RCDs) use leakage current as an indicator of an accident - when it increases above a specified limit, the RCD trips and opens the power supply circuit.

Then RCDs began to be used to protect individual electrical installations from breakdown and fire. For the time being, RCDs remained “fire-proof”; they responded to a current that prevented the ignition of an arc between the wires, less than 1 A. “Fire” RCDs are produced and used to this day.

Video: what is an RCD?

UZO-E (capacitive)

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

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

But RCD-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 of “teaching” UZO-E to distinguish a little scoundrel who picked up an “interesting thing” from a tram that sparkled on the street. Therefore, RCD-E is used only occasionally to protect special equipment, combining its direct responsibilities with touch indication.

UZO-D (differential)

By “turning” the RCD-E “the other way around,” we were able to find the operating principle of the “smart” RCD: you need to go directly from the primary flow of electrons, and the leakage is determined by the imbalance (difference) of total currents in the POWER conductors. If exactly the same amount flows away from the consumer as went to him, everything is in order. If there is an imbalance, there is a leak somewhere, you need to turn it off.

The difference in Latin is differentia, in English difference, which is why such RCDs were called differential, RCD-D. IN single-phase network It is enough to compare the magnitudes (modules) of currents in the phase wire and the neutral, and when connecting an RCD in a three-phase network, the total current vectors of all three phases and the neutral. Essential feature of UZO-D– 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 RCD-Ds. Firstly, it was necessary to accurately determine the amount of unbalance current that is safe for humans with an exposure time equal to the response time of the RCD. RCD-D, configured for an imperceptible or smaller non-releasing current, turned out to be large, complex, expensive, and picked up interference only slightly worse than the RCD-E.

Secondly, it was necessary to develop highly coercive ferromagnetic materials for differential transformers, see below. Radio ferrite was not suitable at all, it did not maintain working induction, and RCD-D with transformers on iron 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, based on experiments on volunteers, was chosen to be 30 mA, and high-speed ferrite differential transformers with a saturation induction of 0.5 Tesla (Tesla) made it possible to remove power from the secondary winding sufficient to directly drive the breaker electromagnet. Differential electromechanical RCD-DMs have appeared in everyday life. Currently, this is the most common type of household RCD, so DM is omitted, and they say or write simply RCD.

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

The appearance with explanations of the symbols on the housing 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 housing. To do this, it was only necessary to make the breaker lock rod double and insert it into the current and RCD electromagnets. This is how a differential machine appeared, providing full protection consumers.

However, a difavtomat is not an RCD or an automatic machine separately, this should be clearly remembered. External differences (power lever, instead of a flag or a restart button), as in the picture, are only appearances. An important difference between an RCD and a differential circuit breaker is reflected when installing an RCD in power supply systems without protective grounding(TN-C, autonomous 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 value the RCD remains operational. RCDs with ratings of 6.3 and 160 A with the same unbalance of 30 mA provide the same degree of protection. In difavtomats, the cut-off 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, the “E” does not stand for capacitance, but for electronics. UZO-DE are designed to be built directly into an electrical installation. The current difference in them is detected by a semiconductor magnetically sensitive sensor (Hall sensor or magnetodiode), its signal is processed by a microprocessor, and the circuit is opened by a thyristor. UZO-DE, in addition to compactness, has the following advantages:

1. High sensitivity, comparable to UZO-E, combined with noise immunity of UZO-DM.
2. As a consequence of high sensitivity, the ability to respond to displacement current, i.e., the RCD-DE is proactive, will turn off the voltage before it hits someone, regardless of the presence of grounding.
3. High performance: to “stimulate” 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 capable of triggering at a voltage of the “breakdown” half-wave of 6-30 V and cutting it off in the bud.

The disadvantages of UZO-DE are primarily high price, its own energy consumption (negligible, but if the network voltage drops, the RCD-DE may not work) and the tendency to failure are electronics after all. Abroad, chip sockets became widespread back in the 80s; in some countries their use in children's rooms and institutions is required by law.

In our country, UZO-DE is still little known, but in vain. The bickering between mom and dad about the cost of a “foolproof” outlet is not comparable to the cost of a child’s life, even if an incorrigible mischief and troublemaker is rampaging through the apartment.

UZO-D indices

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

• AC - triggered by an imbalance in the alternating current component. They are carried out, as a rule, as fire protection, for an unbalance of 100 mA, because cannot protect against short-term pulse leakage. Inexpensive and very reliable.
• A - react to imbalance of both alternating and pulsating currents. The main design is 30 mA imbalance protection. False alarms/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 self-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 imbalance, or built-in RCDs-DE.

Additional indexes provide insight into additional functionality RCD:

1. S – time-selective response, it is adjustable within 0.005-1 s. The main area of ​​application is in the power supply of facilities powered by two beams (feeders) with an automatic transfer switch (ATS). Adjustment of the response time is necessary so that when the main beam disappears, the ATS has time to operate. In everyday life they are sometimes used in elite cottage communities or mansions. All selective RCDs are fire protection, for an unbalance of 100 mA, and require the installation after themselves of protective 30 mA RCDs for a current of a lower stage, see below.
2. G – high-speed and ultra-fast 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 “breakthrough” of at least one damaging half-wave is unacceptable. Exclusively electronic.

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

PATTERN

A type of RCD almost unknown to non-specialists is non-differential, triggered by current in the 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 an RCD-DM. They can be either electromechanical or electronic. Sensitivity and performance for domestic conditions are unsatisfactory. A high quality maintained grounding is a must.

RCD selection

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

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

Separately or together?

In an apartment with TN-C wiring, you can forget about the automatic switch: the PUE prohibits it, but if you ignore it, the electricity itself will soon remind you. In the TN-C-S system, the difavtomat will cost less than two separate devices if reconstruction of the wiring is planned. If the current circuit breaker is already installed, then a separate RCD matched with it in terms of operating current will be cheaper. Writings on the topic: RCD is incompatible with a conventional machine gun - amateurish nonsense.

What overload should I expect?

The cutoff current of the machine (extracts) is equal to the maximum permissible current consumption of the apartment (house), multiplied by 1.25 and added to the nearest higher value from the standard series 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 registration certificate. If not, you can find out from the organization operating the building (obliged to report by law). In old houses and new budget ones, the maximum permissible current is usually 16 A; in new regular (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 technical passport (the authorities will not let you register it) at the rate of 5 A per kilowatt, with a coefficient of 1.25 and addition to the nearest higher standard value. If the data sheet directly states the value of the maximum current consumption, it is used as the basis for the calculation. Conscientious designers directly indicate the cut-off current of the main circuit breaker on the wiring plan, so there is no need to count.

RCD current

The rated (operating) current of the RCD is taken one step higher than the cut-off current. If a difavtomat is installed, it is selected according to the CUT-OFF CURRENT, and the current rating of the RCD is built into it structurally.

Video: RCD or difavtomat?

Leakage current and general protection circuit

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

According to clause 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 an electric heated floor 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 ​​60 and 300 square meters.

In general, if there is no greenhouse with electrically heated soil, a heated water well, and the yard is illuminated by housekeepers, at the input after the meter it is often enough to install a fire RCD with a rated current one step higher than the cut-off current of the machine, and for each group of consumers - 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 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 is at 40 A, everything is OK. We take the RCD a step or two higher in rated current - 50 or 63 A, it doesn’t matter - and for an unbalance current of 30 mA. We don’t think about the leakage current: the builders must provide it within normal limits, but if not, let them fix it themselves for free. However, contractors do not allow such mistakes - they know what the warranty smells like.

Second. Khrushchevka, 16 A traffic jams. We set the washing machine to 3 kW; current consumption is about 15 A. To protect it (and protect against it) you need an RCD with a rating of 20 or 25 A for 30 mA imbalance, but 20 A RCDs are rarely on sale. We take a 25 A RCD, but in any case, it is MANDATORY to remove the plugs and install a 32 A machine instead, 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 to replace the meter and reconstruct the electrical wiring, with or without replacement. This procedure is not very complicated and troublesome, and a new meter with an indication of the wiring status will serve you well in the future, see the section on errors and malfunctions. And the RCD registered during reconstruction will then allow you to call electricians for free for measurements, which is also very good for the future.

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 set the common difavtomat at 63 A cutoff and 100 mA imbalance, we power the house and garage separately through an RCD at 80 A nominal and 30 mA imbalance In this case, it is better to leave the yard without its own RCD, but take the lamps for it in waterproof cases with a grounding terminal (industrial type), and connect their grounds directly to the ground loop, this will be more reliable.

Connecting an RCD in an apartment

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

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

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

RCD without ground

Section 7.1.80, quoted at the beginning, does not exist in splendid isolation in the PUE. It is supplemented with points explaining how (well, there are no grounding loops in our houses, no!) to “shove” an RCD into the TN-C system. Their essence boils down to the following:

1. It is unacceptable to install a general RCD or a circuit breaker in 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 connected to the INPUT zero terminal of the RCD in the shortest possible way, see the diagram on the right.
4. Cascade activation of RCDs is allowed, provided that the upper ones (closest to the electrical input RCDs) are less sensitive than the terminal ones.

A smart person, but unfamiliar with the intricacies of electrodynamics (which, by the way, many certified power electricians are guilty of) may object: “Wait, what’s the problem? We install a common RCD, connect all PEs to its input zero - and you’re done, the protective conductor is not switched, we are grounded without a ground!” Yes, but not so.

We also exclude the electromagnetic field of the installation and the cord to it from consideration. The first is concentrated inside the device, otherwise it will not pass certification and will not go on sale. In a 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 general FIRE RCD with a 100 mA imbalance and with a rated current one step higher than that of the protective ones, regardless of the cut-off current of the machine. In the example described above, for Khrushchev, you need to connect an RCD and an automatic machine, but not a automatic machine! When the machine is knocked out, the RCD must remain in operation, otherwise the likelihood of an accident increases sharply. Therefore, the RCD in terms of its rating must be taken two steps higher than the machine (63 A for the disassembled example), and in terms of unbalance - one step higher than the final 30 mA (100 mA). Once again: in automatic machines the rating of the RCD is made one step higher than the cut-off current, so they are not suitable for wiring without ground.

Video: connecting an RCD

Well, it’s knocked out...

Why does the RCD trip? Not how, this has already been described, but why? And what to do if it works? If it's knocked out, does that mean something is wrong?

Right. You can’t just turn it on after it’s triggered until its cause is found and eliminated. And you can find where things are “wrong” yourself without any special knowledge, tools or equipment. An ordinary apartment electricity 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 to do 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 entrance or main apartment automatic machine. Doesn't turn on? The electrical mechanics of the RCD are to blame; needs to be sent in for repair. You can’t dig around yourself - the device is vital, and after repair it needs to be checked using special equipment.

It turned on, but when the voltage was applied, it went out again with empty wiring? In the RCD, there is either an 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 meter. If the “Ground” indicator flashes at least for a moment (see figure), or it was previously noticed that it was winking, there is a leak in the wiring. Measurements need to be taken. If the RCD is installed in order to reconstruct the wiring and is registered with the energy service, you need to call municipal electricians, they are required to check. If the RCD is “self-made”, pay a specialized company. The service, however, is not expensive: modern equipment allows you to do it in 15 minutes. Find a leak in the wall with an accuracy of 10 cm.

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

The wiring does not inspire concern, they even turned it off section by section with automatic machines, but the RCD trips “on empty”? The fault is within it. Both imbalance and sticking of the “Dough” are most often caused not by condensation or intensive use, but by the same “cockroach poop”. In Rostov-on-Don, there was a case when in a perfectly well-kept apartment in the UZO a nest was discovered... of Turkestan earwigs, who knows how they got there. Hefty, with huge powerful cerci (pincers on the tail), terribly angry and biting. They did not show themselves in any way in the apartment.

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

You need to look for a defective consumer in the reverse order; on its own, it may not reach the RCD before it triggers. Therefore, we turn on everything, then turn off the suspicious ones one by one, and try to turn them on. Has it finally turned on? This is what he is, “reverse”. For repairs, but not for electricians, but for “household appliances.”

In apartments with TN-C-S wiring, it is possible that it is not possible to clearly determine the source of the RCD triggering. Then the likely cause is bad soil. While still maintaining protective properties, grounding no longer removes higher components of the interference spectrum, and the protective conductors act 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? I am obliged to strain the building operator, let him bring the circuit up to standard.

About filters

One of the main sources of failures in the operation of RCDs is interference from household appliances, and effective way to combat them - absorbing ferrite filters. Have you seen the “knobs” on computer cords? This is what they are. Ferrite rings for filters can be purchased at a radio store.

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

A filter on one ring (above in the figure) can be built into a “noisy” installation, if it is not under warranty, as close as possible to the network input. This work is for an experienced specialist, so the exact diagram 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 whether the conductor is wound around the magnetic core or vice versa. In order not to cut the proprietary molded cord, you need to buy a plug, a socket block and a piece of three-core cable. Ready-made power cords with ferrite noise absorbers are also sold, but these cost more than a homemade one assembled in parts.