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  • What is ouzo? RCD in electrical engineering - what is it? Video: residual current device

What is ouzo? RCD in electrical engineering - what is it? Video: residual current device

The abbreviation RCD stands for residual current device. This mechanism, as well as the machine, are protection devices. Why do we also need RCDs if there are circuit breakers? The fact is that the insulation of the wires wears out over time. In addition, even new wiring can be damaged accidentally as a result of mechanical stress.

Contacts on electrical equipment are weakened in the absence of regular inspection. All this leads to current leakage. And because of this, sparking and fire are formed.

It is possible that a person may touch a bare phase wire. Or young children, being curious, may stick something foreign into an electrical outlet. And then the current will flow through the human body. The magnitude of this current can be slightly more than 100mA.

Simple automatic machines for such a small current will not work, because... they are designed to disconnect overload currents and short-circuit currents, and this is several tens and even hundreds of amperes. Meanwhile, even a small current of several tens of milliamps can have a negative impact on a person.

For example, in order for a machine with a nominal value of 16A to work, the current that passes through it must exceed 18A. That is, the current is at least 13% more than the rated current of the machine itself.

Moreover, the machine will not turn off immediately, but after a time exceeding 1 hour (according to its current characteristics). That is why they developed and implemented an RCD.

Another important aspect when choosing to use an RCD is the grounding system in the house. If your house has (3 phases and zero), then the question of why install an RCD in the panel should not even arise. In fact, this is the only effective and economical measure to ensure the safe operation of all wiring and electrical devices.

RCD parameters

By what main parameters is RCD characterized? The two most important of them are:

  • ⚡ rated differential breaking current (or leakage current)
  • ⚡ rated load current

In 220-380V home electrical wiring networks, in order to protect a person from the effects of electric current, an RCD with sensitivity or differential is used. shutdown current 10mA and 30mA. In order to protect against fire, you need to choose an RCD with a sensitivity of 100mA or more.

If you have only one or two groups of electrical wiring at home, you can install one RCD with a current of 30 mA.

It will play the role of both fire protection and will be able to protect you from electric shock.

Operating principle

What does an RCD consist of? The design of the RCD itself is made of dielectric. A small current transformer is mounted inside. It has three windings.

  • ⚡ control winding
  • ⚡ two primary windings

The primary windings are connected opposite each other. Through the first, current flows to the load, through the second (which is formed by the neutral conductor), the current flows in the opposite direction (away from the load).

What makes the RCD trip? In a normal situation, when there is no short circuit or damage to the insulation, all currents flowing in the windings are the same in magnitude, but flow in different directions. When they flow, they create a transf in the core. current mutually balancing magnetic fluxes. Therefore, the summing magnetic flux will be zero and the RCD will not work.

What happens when the insulation is damaged and a leakage current is generated? What happens is that the current in the phase conductor will not be equal to the current in the neutral conductor. That is, to the current that flows through the phase, a leakage current will be added. Since the currents will be different, the magnetic fluxes will be induced differently. And the total magnetic flux will not be equal to zero. Consequently, an electric current will be induced in the control winding.

At the moment when such current exceeds the value of 10-30-100-300 mA (depending on the RCD used), the power contacts of the device will be switched off under the action of the release and the electrical equipment with wiring will be de-energized.

The same thing happens if a person accidentally touches exposed live parts or an uninsulated equipment body with damaged insulation. Current begins to flow through our body into the ground. A current difference appears in the conductors, and as a result, a current is induced in the control winding. Then the release is triggered and the power contacts are disconnected.

To check the RCD you need to use the TEST button. You press it and artificially create a leakage current. A working residual current device must turn off immediately when this button is pressed.

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 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 out 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 a 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. An essential feature of the RCD-D is that in any power supply circuit, the 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 simply say or write 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 automatic machine appeared, providing complete protection for 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 below the section 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 magnetosensitive 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 the RCD-DE are, first of all, high cost, its own energy consumption (negligible, but if the network voltage drops, the RCD-DE may not work) and the tendency to failure - it is electronic 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 own 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 indices give an idea of ​​the additional functionality of the 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 imbalance 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 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 ignore it, and 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 to 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 grounding 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 out 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. What should I 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 an effective way to combat them is 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 they cost more than a homemade one assembled in parts.

There is probably no owner of an apartment or house today 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 then 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 panel is a protective device that opens the supply voltage network when an overload or short circuit occurs. 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 circuit, if 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:

  1. rated current with unit ampere (A);
  2. differential with the unit of measurement milliampere (mA), this is the leakage current;
  3. 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 make the 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? You can’t tell it apart by its appearance, 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 is an RCD needed? 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.

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

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

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

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

How to understand what leakage current is

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

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

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

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

What does it look like

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

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

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

How to ensure quality protection

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

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

Operating principle of RCD

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

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

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

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

Briefly about the parameters of the RCD

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


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

What is a fire protection RCD

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

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

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

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

Manufacturers

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

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

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

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

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

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

In homes, factories, and enterprises, electrical equipment is always equipped with wiring, as well as devices and loads, and all this is insulated with a shell. Probably, many people know that in electrics there is such a residual current device as an RCD. But how it actually works and what it is, and indeed what it is for, is known to a small number of people.

What is an RCD

This device is in electrical serves for safety living beings, it protects against electric shock in case of minor damage to the insulation of electrical devices. If the insulation is broken, then current “flows” through elements capable of conducting current and metal devices. When the permissible current leakage value is exceeded, the RCD immediately reacts by turning off phases in areas that are damaged, or by turning off the entire controlled circuit.

should detect a leak current “to ground” and instantly disconnect the network when it occurs. Current leakage is detected by the difference between the output current from the residual current device and the current returning to it through the neutral. If the magnitude of these currents is equal and they are opposite in direction, then everything is in order with the network. If a leak occurs, then the current, having passed, for example, through a person or animal that touched the wire, will pass into the ground and then return through the neutral to the RCD, but the value will be less than the output current. A transformer with a ring core detects this difference, which is formed between the outgoing and returning current.

Installation of RCD also prevents fire in case of poor quality wire connections and worn insulation. In such cases, the RCD immediately blocks the power supply to the entire building if it detects a significant current leak in the circuit, thereby preventing a short circuit and the formation of a flame.

An electric shock protection device will also protect against overcurrent. To do this, you just need to install a fuse, i.e., a circuit breaker, in front of the residual current device. And if several lines are connected at once, this should be done! It is also important to know that the absence of a fuse in the RCD does not exclude a current short circuit.

This protection device should be installed in circuits with possible current leakage and where there is a danger of electric shock to a person. The kitchen and bathroom in residential apartments and houses are such places. These places have humidity, they are equipped with a large number of electrical appliances, small space. In this regard, all sockets and electrical appliances in the house must be protected by installing an RCD.

Installation of the device provides that fuses or circuit breakers will be installed along with it, providing it with protection against overloads. The residual current device can be mounted in a chain of different electrical panels, on floors to protect individual devices, and in apartment panels.

Based on the following criteria, it is carried out device selection:

It is important to remember that the residual current device is only additional means of protection in apartment electrics or apparatus production. Its installation does not exclude the possibility of electric shock due to small short circuits between the neutral and the phases and the occurrence of a fire, but still significantly increases the level of safety of the devices.

Device classification

There are a large number of types of residual current devices, as well as subtypes. Divided according to the following criteria:

According to the method of action:

By installation method:

  • Stationary devices
  • Portable devices

By number of poles:

  • single pole
  • bipolar
  • three-pole
  • four-pole

Depending on the availability of protection against overloads and overcurrents:

  • There is protection
  • No protection

Depending from regulation of the disconnecting differential current:

  • There is regulation
  • No regulation

Depending on durability:

  • No resistance to impulse voltage
  • There is resistance to impulse voltage

Depending on the network they are divided into:

  • Electronic RCDs
  • Electromechanical RCDs

Connection errors

If you are not an electrician and have never been involved in this matter, then you may experience common errors when connecting this device. These include: connecting the phase from above and zero from below; parallel connection on the neutral protection side from different RCDs; connection to a 1-phase network of a four-way RCD; substitution of zeros; connecting a load whose conductor is connected to the working neutral conductor or to live parts that are open; connection to the neutral of another device or to the zero lead before the load RCD.

In some cases, when the device is connected to electricity, the residual current device will trip. In others it may work without load, in others the test button will work. It is possible that the RCD will stop working altogether.

Installing a residual current device

The most common scheme is connection in a single-phase network two-pole RCD. Of course, before connecting, you should turn off the voltage and make sure that the RCD is working. You can see the connection diagram in its passport, as well as on the body of the product itself. Using this diagram, you can easily determine where you need to connect the neutral and where the phase. The process itself is not difficult, but the connection of the neutral must be clearly controlled; markings on the terminals will help with this. The residual current device is connected after the meter and the circuit breaker.

We have discussed in detail what an RCD is in electrical engineering. You also need to know that the condition of the residual current device, that is, its functionality, should be checked every month. And after installing the RCD, its functionality must be checked by an electrician.