Uzo machine purpose. The principle of operation of the ouzo and the connection diagram in a single-phase network

What does the RCD do? RCD is a residual current switch. He compares the current that went into the apartment with the current that returned from the apartment. If these currents are different, the RCD turns off the voltage.

In what cases is this property of the RCD useful? In cases of damage to the insulation of wires in electrical appliances. For example, inside a washing machine the insulation on a phase wire is damaged, causing it to touch the body. The RCD will immediately turn off the electricity, because the current that went into the apartment through the phase wire did not return to the RCD (from the machine body it returned to the panel via the “grounding” wire, bypassing the RCD, and therefore the incoming and outgoing currents through the RCD were different) .

If you handle electrical wiring carelessly. Here's a classic example. A man drills into the wall, leaning his bare foot on the battery, and gets into a phase wire. The current passing through the chain “metal drill body - arm - chest - leg - battery” causes cardiac paralysis and/or respiratory arrest. But if there is an RCD, then it will immediately “feel” that part of the current has not returned (the part that passed through the person and went into the battery). The voltage will be turned off so quickly that no harm will happen. Of course, the person will get an electric shock, but nothing more.

When handling electrical appliances carelessly. Here's a classic example. A man sits on the edge of the bathtub, and in the bathtub is his wife, insured for a decent amount. And he accidentally drops a radio receiver plugged into the socket into her water... I think the principle is clear - the current did not return to the RCD, but went through the pipes into the ground, etc. Note that the situation when part of the current does not return to the RCD is called “current leakage”.

When an RCD won't help

Alas, the RCD is not so intelligent as to distinguish what exactly is included in the electrical circuit - a person or a light bulb. If there is no current leakage, everything is fine. Why then is it believed that RCD significantly improves safety? Yes, because the vast majority of cases of electric shock are somehow associated with current leakage - a situation that the RCD recognizes. The likelihood of life-threatening situations (i.e. current passing through the chest) occurring without a leak is much lower.

How many RCDs do you need to have?

To ensure safety from electric shock, one for the entire apartment is enough. Another thing is the question of convenience. Of course, it is better if, in the event of any problem with electrical wiring or electrical appliances, only the corresponding line is turned off, and not the entire apartment is de-energized. More than one RCD, as a rule, can only be installed in an individual indoor panel, specially designed for this purpose. There is usually not enough space for this in the “native” shield on the landing.

When an RCD is used for a single line and current flows from it directly to the consumer, it must have a built-in maximum current limiter. If you install a simple RCD, then in the event of a short circuit it may fail. Or, with a long-term overcurrent, it will constantly heat up and eventually also deteriorate (for example, it will start to turn off for no particular reason). Such a device, i.e. An RCD and an “automatic device” in one housing costs 2 times more than a simple RCD. For example, branded devices cost about 50 and 100 dollars apiece, respectively.

Thus, if you see the inscription “40A” on a simple RCD, this does not mean that it will turn off at 60A, but it means that at 60A it will burn out after some time.

In what cases is the installation of an RCD inappropriate?

For example, in the case of old, dilapidated wiring. The ability of an RCD to detect current leakage can cause more problems than benefits if it begins to operate unpredictably. And with old wiring, this can start at any time (even when the RCD is turned on for the first time). Therefore in this situation best choice, perhaps, it will not be necessary to install an RCD in the power supply circuit of the entire apartment, but in places with increased danger, use sockets with a built-in RCD.

RCDs are divided into types:

AC - responsive to differential sinusoidal alternating current;
A - responsive to sinusoidal alternating and pulsating direct differential currents;
B - responsive to sinusoidal alternating, pulsating direct and direct differential currents.

Paragraph 7.1.78 of the PUE of the 7th edition states: “In buildings, RCDs of type “A” can be used, reacting to both alternating and pulsating fault currents, or “AC”, reacting only to alternating leakage currents. The source of pulsating current is, for example, washing machines with speed controllers, adjustable light sources, televisions, VCRs, personal computers, etc.”

The Temporary Guidelines for the use of RCDs in electrical installations of residential buildings (I. p. dated 04.29.97 No. 42-6/9-ET, clause 4.10) states:

“In residential buildings, as a rule, type “A” RCDs should be used, which respond not only to alternating currents, but also to pulsating fault currents. The use of RCDs of the “AC” type, which respond only to alternating leakage currents, is permitted in justified cases.”

It should be noted that in last years The number of electrical appliances with transformerless power supply has increased sharply.

Almost all personal computers, televisions, video recorders have switching power supplies, all the latest models of power tools, washing machines, sewing machines, and household kitchen appliances are equipped with thyristor regulators without isolation transformer. Various lamps are widely used - floor lamps, sconces with thyristor dimmers.

This means that the likelihood of a leakage of pulsating direct current, and, accordingly, injury to a person, has increased significantly, which was the basis for the introduction of type A RCDs into widespread practice.
In European countries, in accordance with the requirements of electrical standards, over the past few years there has been a widespread replacement of AC type RCDs with type A ones.
In our country, the widespread introduction of type A RCDs has also begun. Experienced designers, when carrying out important orders, include only type A RCDs in their projects.

The table shows oscillograms of currents in circuits containing various controlled and uncontrolled valve elements, and notes the possibility of using type A or AC RCDs in these circuits.

Type B RCDs are extremely rare; they are used in special industrial electrical installations with mixed power supply - alternating, rectified and direct currents.

Connection diagrams for RCDs in electrical installations of buildings

According to GOST R 50571.3-94 (clause 413.1.3.2), a necessary condition for the normal functioning of the RCD in the electrical installation of a building is the absence in the area of the RCD of any connections of the neutral working conductor N with grounded elements of the electrical installation and the neutral protective conductor PE.

In distribution boards of electrical installations with a TN-C-S grounding system, at the separation points of the PEN conductor, it is necessary to provide separate terminals or busbars for the zero working N and zero protective PE conductors.

Since damage and aging of insulation is possible in both phase and neutral working conductors, and the RCD reacts to a leak to ground from any of them, two- and four-pole circuit breakers should be installed on outgoing lines. Only in this case is it possible to find a faulty circuit, including a circuit with a leak from the neutral conductor, by switching on the lines one by one, without dismantling the input distribution device, and it is also possible to disconnect the faulty circuit to ensure the operation of the rest of the electrical installation.

In GOST R 50571.9-94 “Electrical installations of buildings. Part 4. Security requirements. Application of overcurrent protection measures" contains instructions on the implementation and protection of the zero working and zero protective conductors.

Clause 473.3.2 “Protection of the neutral working conductor” regulates the procedure for protecting the neutral working conductor from short circuit current.

Clause 473.3.2.1. TT and TN systems:

a) in cases where the cross-section of the neutral working conductor is at least equal or equivalent to the cross-section of the phase conductors, it is not necessary to provide devices for detecting short-circuit current in this conductor or for disconnecting it;

b) in cases where the cross-section of the neutral working conductor is smaller than the cross-section of the phase conductors, provision must be made for detecting a short circuit current in the neutral working conductor corresponding to its cross-section, with an effect on disconnecting the phase conductors. In this case, disconnecting the neutral working conductor is mandatory.

However, detection of short-circuit current in the neutral working conductor is not required if the following conditions are simultaneously met:

the neutral working conductor is protected from short circuits using a protective device for the phase conductors of the circuit;

the maximum expected current that can flow through the neutral working conductor in normal mode is significantly less than the value of the long-term permissible current of this conductor.

Note. The second condition is satisfied if the transmitted power is distributed as evenly as possible between the operating phases. For example, if the sum of the powers of electrical receivers connected between the phase and the neutral working conductor (lighting, plug sockets) is much less than the total power of the circuit in question. The cross-section of the neutral working conductor must be at least 50% of the cross-section of the phase conductor.

Clause 473.3.2.2. IT system.

IT systems generally should not have a zero working conductor. However, in cases where an IT system is used with a neutral working conductor, it is necessary to provide overcurrent detection devices in the neutral conductor of each circuit with the effect of disconnecting all live conductors of the corresponding circuit, including the neutral working conductor.

Such measures are not required if:

the neutral working conductor is reliably protected from short circuits using a device installed on the power side, for example at the input to the installation, in accordance with the rules specified in clause 434.3 of GOST 50571.5;

the circuit in question is protected using a residual current device that responds to differential residual current with a setting current of no more than 0.15 of the maximum permissible current of the neutral working conductor.

Such a device must disconnect all live conductors of the corresponding circuit, including the neutral working conductor.

If it is necessary to disconnect the neutral working conductor, then it must be disconnected after disconnecting the phase conductors, and turned on simultaneously with the phase conductors or earlier.

GOST R 50571.3-94 in clause 413 “Protection from indirect contact” formulates requirements for fulfillment protective grounding in the TT system.

Section 413.1.4. TT system.

Clause 413.1.4.1. All exposed conductive parts protected by one protective device, must be connected by a protective conductor to one grounding device. If several protective devices are installed in series, this requirement applies separately to each group of exposed conductive parts protected by each device.

The neutral point or, if one does not exist, the phase of the supply generator or transformer must be grounded.

Clause 413.1.4.2. The following condition must be met:

RАIa - 50 V, where: RА is the total resistance of the grounding conductor and the grounding conductor; Ia is the tripping current of the protective device.

If the protective device is a residual current device and responds to residual current, then Ia refers to the residual current protective device setting IDn.

If the protective device is an overcurrent protection device, then it must be:

or a device with an inverse time-current characteristic and Ia - a current value that ensures the device response time is no more than 5 s;

or a device with a current cut-off, and then Ia is the cut-off current setting.

In Fig. 1-11 show examples of electrical installation diagrams of buildings that meet the requirements of modern regulatory documents using RCDs (as an example, the ASTRO*UZO product range is taken).

In terms of efficiency, there is no real alternative to protective shutdown yet, as is clearly evidenced by the results of scientific research and the successful practice of using RCDs around the world.

In the coming years, RCDs will be the main and most radical electrical protective means, which means that the regulatory framework must develop and improve to meet the requirements of the time.


Fig.1. Electrical supply diagram for an apartment with a TN-S system. RCD F-3211 protects the lighting circuit, socket circuit and electric stove; RCD F-1111 protects the bathroom outlet circuit, separated into a separate line.	Rice. 2. Electrical supply diagram for an apartment in the absence of a PE protective conductor in the socket and lighting circuits. Recommended temporary solution for older housing stock.

Rice. 3. Electrical supply diagram for an apartment with an electric stove and recommended cross-sections of copper conductors	Rice. 4. Electrical supply diagram for an apartment with a gas stove with recommended cross-sections of copper conductors

Rice. 5. Electrical supply diagram for a building with three-phase input. Recommended in the absence of a three-phase load in order to provide redundant power supply to consumers.	Rice. 6. Workshop power supply diagram. It is recommended to use two- and four-pole RCDs for mixed (single- and three-phase) loads.

Rice. 7. Power supply diagram for a mobile building with a TT system. The use of this circuit is permitted only with mandatory protection of all circuits by residual current devices.	Rice. 8. An example of power supply for a two-room luxury apartment

Rice. 9. Electrical supply diagram for a cottage with the TN-C-S system (option 1). Recommended for single-phase input, completed full protection all group circuits.	Rice. 10. Electrical supply diagram for a cottage with the TN-C-S system (option 2). Recommended for three-phase input; two- and four-pole RCDs are used.

Rice. 11. Electrical supply diagram for a cottage with the TN-C-S system (option 3). With a large number of group circuits, it is recommended to use floor distribution boards - RShch1, RShch2, RShch3, as well as the use of lightning surge protection - surge arresters (for example, ASTRO*OPN-12/0.4).

Using a residual current device is a fairly relevant way to ensure the safety of the electrical network in the house. RCDs are usually used for human protection. This article will provide information about its purpose, operating principle and types of such equipment.

The main purpose of a residual current device is to protect a person from injury from alternating or direct current. If a faulty or damaged device is connected to the electrical network in a room, then if a person comes into contact with exposed conductors, he may be electrocuted. This equipment allows you to avoid electric shock when random contacts, and also protect the house from ignition of wiring due to current leakage.

The device is a mechanical switching device for stopping the supply of differential current under certain conditions. The RCD de-energizes the electrical network when a person (animal) touches the conductors of household appliances and equipment or the grounding contact. Triggering occurs both in direct contact with parts of the electrical installation and in indirect contact.

Switching off the RCD can also occur if the external insulation or contact of the conductors with the grounded body is damaged, if the grounding conductor and the working neutral are incorrectly changed, or if the phase wire is changed with the neutral working while touching them under voltage. A disconnection can occur due to a break in the working neutral conductor, which according to the diagram can be placed before and after the protective device, and when a person touches live parts of the device with a bare part of the body.

Kinds

Like all protective devices for electrical circuit, RCD has its own types. Due to their design and mechanics, devices can be electromechanical or electronic.

Electromechanical. Connecting such a device allows you to provide the circuit with higher reliability. The action of the electromechanical type of devices allows it to be widely used in buildings for various purposes, due to the ability of mechanics to work at any load in the electrical network. High price justified by the speed of response and long service life.

The main design elements are a relay, a magnetoelectric latch, and a transformer for zero-sequence voltage. Electronic. Design of this type equipment is very similar to electromechanical equipment, since it contains the same elements. However, the main magnetoelectric element is manufactured in the form of an electronic circuit.

The circuit itself consists of comparative elements, a filter, an amplifier and a rectifier. Thus, when an electronic type residual current device is connected to the network, its operation will depend on the line voltage. The residual current device can be connected according to a specific circuit to an electrical single-phase and three-phase power line.

Devices are classified according to their speed of reaction to a leak, according to the characteristics of the circuit break, according to the permissible load, according to the method of preventing short circuits and the type of housing installation. The choice of such a device should be based on its characteristics and the characteristics of the circuit.

Video “Operation principle and RCD diagram”

Principle of operation

The operating principle of protective equipment is based on comparing the potentials of the differential current that passes through it. To do this, the potential at its input and output is constantly measured. Ideally, after measurements, the sums of vector currents passing through the controlled conductors and should be equal to zero. So, with a single-phase electrical line circuit, the measurement is carried out on two conductors, and with a three-phase circuit, on three or more.

If the value of the flowing alternating current in the network differs from that entering the RCD, it will operate, de-energizing the room. Potential difference ranges can be standard for a certain type of equipment or have a range regulator to set an arbitrary value (of course, with a reasonable limitation). If a leak appears on the line (a person touches a phase wire or a decrease in the resistance of the external insulation of the cable), the vector sum of the incoming and outgoing current will be different. In this regard, the entire line will be de-energized.

So, when operating the equipment, we can identify the main element in its design - the differential current transformer. It is a core with a winding. The design also provides for preliminary testing. There is a special button on its body for testing the device. The operating principle of the test is an artificially created leakage charge. If everything is connected correctly and the residual current device itself is working correctly, then pressing the button will disconnect the power line branch.

It is a mistake to believe that in order to protect people from injury due to current leakage, automatic current breakers are installed on the housing of household appliances. For these purposes, the shields are equipped with a protective device. Having figured out the principle of operation of ouzo, you don’t have to fear for the lives of your loved ones and children.

The protection protects against the effects of current on the body when touching the body of the devices. If there is a leak of electricity, the magnitude of the current the machine will not react to. Another important defense job is keeping your home safe from fire.

Functional features of protection equipment

The body of the device is made of conductive material, as well as individual parts and even pipelines, sometimes proving dangerous to humans. A phase breaks through on them due to various wiring breakdowns and other reasons. This dangerous situation usually occurs in 2 cases:

The main task is that the leak must be immediately detected and the supply of electricity to this group of contacts must be stopped. And also to switch off when a person touches a bare wire and prevent fires in the building.

Important. The protection is triggered in the event of leaks, but you should remember that the housing of any household appliance will become deadly if, during installation, you confuse the phase and ground wires at the entrance to the building.

What should you pay attention to when choosing an RCD?

For the correct purchase and safety of your home, you need to pay attention to the following indicators:

Important. Regardless of the brand and manufacturer of the protection device and various markings, 2 main characteristics show the value of the operating and leakage current. These values are indicated regardless of the type of device and its price.

Operating principle of the protection device

The principle of operation of the protective device is the reaction of sensors when the incoming value of differential currents changes. An ordinary transformer can act as a current sensor. According to its design features, it is manufactured as a toroidal core. The magnetoelectric relay has a fairly significant sensitivity to leaks; on it we set a certain value for the device to operate.

Devices in which the operating principle of the ouzo is carried out with the installation of a monitoring relay are by far the most reliable and trouble-free. Even commercial electronic devices that control leakage using an electronic circuit are in some cases inferior to electromechanical devices.

The principle of turning off electricity to consumers in a device with a relay is based on its operation and the impact on the mechanism for interrupting the electrical circuit. It consists of 2 parts:

According to the device passport, a contact group is selected for the maximum current value in the network.
If an emergency occurs and your hand touches a bare area, a spring is provided to activate the device.

The serviceability of the protection can be checked using the “Test” button equipped on the device body. By pressing it, we create an artificial fault in the electrical network due to an electric current leak. The value is set sufficient to enable protection.

This in a simple way You can independently inspect and check the serviceability of the RCD without calling a technician or paying for his visit. This check is carried out at least once a month.

By measuring the values of the current and response time of the RCD, an electrician using a special device can carry out a more accurate check.

Correct operation of protection in different modes

How does ouzo work under normal conditions? Without leaks, the operating voltage, up to 12 V, flows towards and in parallel, while magnetic fluxes of the same magnitude are induced on the secondary winding of the transformer. They are equal to each other. This operation does not trigger the residual current device because the value of the current entering the secondary winding is zero.

Leakage current occurs when you accidentally touch a bare section of wiring or a device housing with a phase closed to it. In this case, the correct direction and magnitude of currents passing through the transformer are disrupted. On the secondary winding there is an imbalance in the current values, from which the relay is activated. It acts on the spring, and the supply of voltage to the network stops.

This is a simple explanation of the operation of an RCD; if necessary, there is enough information on the Internet to study this issue in more detail.

It must be remembered that the purpose of a residual current device is an additional measure for the safe use of electrical appliances. This device reacts to leakage current. For this reason, it is necessary to install RCDs together with automatic circuit breakers to disconnect the network in the event of a short circuit.

Probably, today there is no owner of an apartment or house who has not heard about residual current devices (RCDs) - what are they? This is the first question that is asked immediately when talking about this device. That is, everyone has heard that this is a protective device, but not everyone knows how it works, on what principle, what functions are assigned to it, what its main purpose is, or rather, few people know. Therefore, there is a need to understand it in general terms, without going into the jungle of electronics and electrics.

What does the RCD protect and from what?

Let's start with the fact that RCD began to be used quite recently. Literally twenty years ago it was not used anywhere, so even today it is not used in old houses. And the most important thing is that none of the owners of apartments and houses is going to install it. But in vain. Therefore, it is worth understanding the question of what an RCD is in electricians and what its role is in the safe operation of household appliances.

Many may say, why is a circuit breaker installed? Doesn’t the RCD repeat its functions? Doesn't repeat - that's for sure. Firstly, the circuit breaker installed in the switchboard is a protective device that opens the supply voltage when there is an overload or short circuit. That is, the machine protects the network itself. Secondly, an RCD is a device that protects people from the effects of current. How, that is, why do you need an RCD?

The thing is that any household appliances that we use every day, as well as electrical wiring, have a certain service life. After the latter, there is a high probability of failure of the insulation of electrically carrying areas. That is, the current begins to move not along a given circuit, but to the ground, if the conditions for connecting the wiring to the ground are created. In this case, the guide most often becomes the person himself.

For example, a standard situation is when the wiring in any household appliance (vacuum cleaner, washing machine, electric kettle, etc.) has broken, and the current begins to act on the body of the device (in fact, this is a bare live wire). If a person takes this device with one hand and stands barefoot on the wet floor, he will get an electric shock. And there are quite a lot of examples where not only the floor, but also other parts of the building or communication systems can become a conductor. It turns out that in everyday life you can get an electric shock unexpectedly, without knowing where it came from. And for this you don’t have to tinker with the socket. That is why, to avoid such troubles, a protective shutdown device is installed.

Of course, a grounding loop, if it is provided in an apartment or house, as well as installed sockets with grounding can save you from electric shock. But unfortunately, they are not installed everywhere, and grounding is not provided in all houses. So you can’t do without an RCD.

Attention! And one more point regarding the strength of the leakage current. It is small, so the machines do not respond to it.

That is, it turns out that the protective shutdown device is triggered if a leakage current appears. If a person grabs two bare wires protruding from the socket with both hands, it will certainly not work. Because in this case the person acts as a load, and the circuit breakers must respond to this. Now, probably, the main application of RCDs becomes clear.

How many RCDs are needed?

It is quite difficult to figure out the number of devices on your own. If you decide to use it in your own home, then invite a specialist to do this. Offhand, we can say that if you are the owner of a one-room apartment, then one device is enough. If the apartment is four-room (which means at least fifteen groups of sockets), then it is better to install five devices. Plus one more thing:

for all lighting;
on an electric hob;
to the water heater, if available.

Advice! All these devices will overload the home electrical network. Therefore, it is best to install differential circuit breakers instead of RCDs.

I would like to add that installing a residual current device is not always advisable. For example, if the house still uses old, dilapidated wiring, then the RCD will most likely disconnect the network for no reason all the time, since it will constantly react to dilapidated insulation, especially when the wires are under heavy load. In this case, it is recommended to use special sockets with small RCDs built into them. It is also better to install such sockets in places where there is an increased risk of leakage current.

Device marking

As for the markings, they are applied to the body of the device for ease of selection in terms of selecting it for operating conditions. The main characteristics of the RCD that you need to pay attention to:

rated current with unit ampere (A);
differential with the unit of measurement milliampere (mA), this is the leakage current;
the type of the device itself.

For example, the ratings may be indicated on the case: 50 A - in large font, below 300 mA - in small font. The type of device will also be indicated here in the form of a special icon. They are shown in the lower figure, where they are deciphered.

Please note that the electromechanical appearance of the device does not depend on the voltage value. This refers to its functionality. Electronic, on the contrary, is completely dependent on it. That is, the first one will definitely work even if there is no voltage in the network, the second one will never work without voltage.

Here on the case, usually on the side, the manufacturer must indicate the connection diagram of the device, which is a good hint for beginners who have decided to install the protection device and disconnect it from the network with their own hands.

So, marking makes it possible to do right choice, exactly matching the requirements of the operating conditions of the RCD. Anyone who understands it and calmly reads and understands what the abbreviation of the device means will accurately select the device for the needs of the electrical network. Especially when it comes to installation by sections.

There is another frequently asked question, which goes like this - how can you distinguish an electromechanical RCD from an electronic one? By appearance You won’t be able to tell it apart, so we advise you to look at the diagram printed on the body.

In the electromechanical diagram, the differential transformer (indicated by an icon that looks like a cigar, that is, a rectangle with rounded ends) is connected directly to the polarization relay (indicated by a square).
The electronic amplifier plate is installed between the transformer and the relay (it is in the form of a triangle in the diagram). By the way, it is this plateau that requires voltage, and it is this that has to be fed.

There is another option for how to distinguish the two types from each other. To do this, you will need a magnet, which needs to be moved a little along the RCD body: first along the front panel, then on the side. The main thing is that the device is turned on. If it turns off, then it is an electromechanical device, if not, then it is electronic.

Conclusion on the topic

So, in this article we tried to answer questions of concern to our readers related to the residual current device, and in particular, what is it and why do we need an RCD? The increasing infestation of household appliances has caused an increased occurrence of leakage current, which can cause electric shock to a person. And although the leakage current itself does not have much potential, and cannot kill a person, it is capable of causing him health-related problems. So you should pay attention to this device and be sure to install it in your own home or apartment. As they say, God protects those who are careful.

Without electricity it is impossible to imagine modern civilization. Progress has given people many electrical appliances that have made life much easier. So, now, when cleaning rooms, you don’t need to wave a broom, raising clouds of dust, but just turn on the vacuum cleaner; to boil a kettle, you do not need to inflate the samovar, but you can use an electrical appliance; ironing clothes is done without a massive charcoal iron, etc.

A feature of modern devices is their high power consumption, which requires modernization of the wiring that residents of houses and apartments have inherited since Soviet times. Anyone who has decided to take this step must have at least a general idea of what an RCD is. The residual current device, although not indispensable, significantly increases electrical safety. Today we will talk about why exactly a protective RCD is needed, and we will also explain in simple language the principle of its operation.

electrical safety

A mandatory element of any home electrical network (we will talk about this case later) is a circuit breaker. This device is mounted near the electric meter or in a special panel, and it is called an input device. Its task is simple: to perform switching, and also to interrupt the power supply without human intervention in the event of a sharp excess of the rated current (electromagnetic protection) or during a prolonged load above the permissible limits (thermal setting). A properly selected circuit breaker can prevent a wiring fire and partially protect a person from possible electrical injury. However, the protective functions are significantly expanded when another device is installed - an RCD. The installation points may coincide with the installation locations of conventional switches.

How does “classic” protection work?

In order to understand the purpose of a residual current device, let's present a simple example from life. The home electrical network is equipped with an automatic switch at the input, selected in accordance with the PUE. In any operating electrical appliance, insulation damage and a short circuit occur, as a result of which the current consumption increases to a value determined by the wiring features, and the electromagnetic release in the input switch registers this and breaks the circuit. It would seem, why do we need another RCD? But let’s imagine that due to damage in the iron, its metal parts are at dangerous potential. A person who is unlucky enough to touch such a device and a cast-iron heating radiator (bathtub, sink) at the same time will receive an electric shock flowing through the body to the “ground”.

Features of slot machines

Only specialists know that the protection of a class “C” switch will operate at 10 times the rated value; for “B” the situation is slightly better, and the response threshold will be half as large; Well, for class “A” the shutdown will occur when the nominal value is doubled. These are quite high values, and under certain circumstances, the “lucky” person has the risk of staying with the above-mentioned iron forever. If you consider that most apartments and houses are “protected” by C-class switches, then there is reason to think about your own safety. The result will be completely different if there is an RCD switch in the circuit.

Additional feature

Let's imagine the same situation, but we will supplement the machine with a residual current device (RCD). A person touches a conductive surface, and a current begins to flow through the body, which goes into the “ground”.

Its peculiarity is that, although the meter takes into account the ampere-hours consumed, and an electromagnetic field is created in the release coil, nothing is returned back to the network. The RCD machine just registers this and breaks the circuit. As a result, a person will feel an electric shock (the magnitude depends on the parameters of the device), but there will be no death.

For those people who are accustomed to using electric boilers to heat water, we recommend not only learning what an RCD is, but also installing this device as soon as possible. It is important to understand that although a residual current device makes the operation of equipment safer, it is not a panacea for all problems. And it cannot replace the need to use a protective grounding loop.

What is an RCD

A residual current device is an electromechanical device designed to improve electrical safety when using electrical equipment. Various designs are possible, but the most famous are solutions for mounting on a DIN strip, like modern single-pole circuit breakers. A plastic case, a shut-off tab and a button for checking the operation of the circuit - that’s all the RCD looks like. The heads of the clamping bolts are recessed in such a way that accidental contact with them is almost impossible. Installation of RCDs can be carried out in two ways: in the input panels, which protects the entire home electrical network, as well as on each line. In the second case, the protection is more effective. If funds are available, it is recommended to combine these two methods.

Physically, the connection is very simple: there are four bolt clamps on the body (for single-phase network), to the first two of which input wires are connected, and to the second, outgoing lines are screwed. That is, the RCD is installed in a circuit break. The only caveat: the contacts on the inlet are marked for zero and phase, which must be observed during installation for further correct operation. The simplest indicator allows you to identify a phase wire in a few seconds.

Operation

When studying what an RCD is, one cannot ignore the principle of its operation. Two lines pass through the entire device (zero and phase), which can be broken at any time by a trip electromagnet (the same system as the release in conventional switches). The current flowing through the lines induces an emf in the coil. Since its values in the phase and neutral wires are equal, there is potential in the coil, but there is no current - it is balanced. This is in the normal state of the protected circuit. Any leakage from a closed circuit causes the appearance of an induced current (tens of milliamps) and the activation of the shutdown electromagnet.

Looking at a real life example

Let's imagine that a person is taking a bath, the water for which is heated by an electric boiler. The socket for the heater is protected by an RCD. For some reason, the heating element breaks down the spiral onto the housing. Because of this, the entire mass of accumulated water is under dangerous potential, and voltage enters the bath through metal parts. If it is not dielectric and is installed on a conductive floor (most often this is the case), then current begins to flow to the “ground” through the heating element - water - bath circuit. A person, touching metal objects, is somehow included in the chain, falling under the influence of EMF.

While there was no damage to the heating element, the magnitude of the current flowing through the phase and neutral wires through RCD, were equal. That is, in simple terms, as much has come, so much has gone. After all, the circuit is closed. But as soon as a breakdown occurred and a third-party current flow path was formed, the equality ceased to hold, and more was supplied to the boiler than returned. The magnetic field that appears in the RCD coil activates the shutdown mechanism - and the circuit breaks. Everything is very simple. If the protection was carried out only by an electromagnetic release circuit breaker, then a circuit break would occur when the rated current value is exceeded by 2-3 times (for class A) or even 10 times (for class C). Needless to say, all this flow of electrons could come to a person if he was holding a shower hose in his hands and standing barefoot on a conductive floor?

There is also a three-phase RCD. In this device, not two wires pass through the coil, but four: one for each phase and zero. In this case, it does not matter how much load falls on each phase, the main thing is that the total incoming current is equal to the returning one.

Peculiarity

Earlier we said that an RCD cannot be a replacement for grounding. Let's imagine that a person touches the neutral and phase wires at the same time. Current will flow through the body, however, since there will be no leakage from the circuit, the RCD will not work. But when using a grounded circuit on the housings of electrical appliances, a dangerous potential cannot appear, since the current will immediately flow through the grounding wire into the ground, which will fix the machine and interrupt the power supply.