Protective means of automation in electrical circuits protect a person from electric shock and prevent the impact of network disturbances on connected equipment. Some devices are similar in their functionality and cause a lot of controversy between users about giving preference to one of them. These devices include residual current devices (RCDs) and difautomatic devices. What they have in common, what are the differences, and what advantages do these or those products have, are described in this article.

Functional differences between devices

Initially, you should figure out what the device names mean:

• the second name of the RCD is a differential switch (VD);
• abbreviation of difavtomat AVDT - "A" automatic "B" switch "D" differential "T" current.

In both cases, there is the concept of "differential current", that is, leakage current. It appears when the electrical parts of the equipment are shorted to the case and can lead to injury to a person or a fire. RCDs and RCBOs provide protection against such manifestations, turning off the power supply when they are detected.

The difference between them lies in the fact that in addition to responding to leakage current, the difavtomat cuts off the voltage when significant overloads or short circuits occur. RCDs do not do this, therefore, in order to protect against short circuits, in circuits with their use, it is necessary to additionally install circuit breakers (AB), which are connected in series.

Design differences of automation equipment

Schematic diagrams of the internal structure of the protective equipment under consideration have much in common, but differ in the presence of individual elements that determine their functionality. To better understand the principle of operation of devices, you need to familiarize yourself with their designs.

The first is a residual current device. It consists of three parts:

• a module in which the analysis of the current passing through the phase wire and returning through the neutral conductor takes place;
• an executive relay that is triggered when discrepancies are detected in the current values ​​at the input of the consumer and at its output;
• test part, which serves to check the performance of the device.

Three-phase devices control the equality between the sum of the current values ​​\u200b\u200bof each phase and the current flowing through the neutral conductor.

The device of the difavtomat, in addition to elements similar to the RCD, provides for the presence of additional releases that respond to changes in temperature and electromagnetic field. This can be seen in the next image.

The thermal element of the difavtomat is triggered when the equipment is overloaded, and the electromagnetic element is triggered when overcurrents appear due to a short circuit. Thus, the RCBO provides protection both from leakage currents and from emergency modes.

Visual differences between protective devices

RCDs and differential automata are similar not only structurally, but also visually. Both have the same body size and configuration, an on/off switch, a "Test" button, and listings of specifications.

Abbreviation in the name of the device

This difference applies only to domestic products. As already mentioned, a residual current device can be referred to as a differential switch. Therefore, representatives of these models on their body will have the inscription "VD" or "RCD".

An alternative device is designated as "AVDT" (the decoding is already known to the reader).

Product marking according to the value of the operating current

Each device is designed to operate under rated load, that is, it is capable of passing current and voltage of a certain value. The manufacturer makes an appropriate entry about this on the front panel of the case. However, for a difavtomat, the rated current is set depending on the type and characteristics of the thermal and electromagnetic releases, therefore it is always indicated accompanied by the Latin letter “C”, “B” or “D”.

Thus, on the RCD, the rated current of 16 amperes is indicated as 16A, and the same indicator on the RCBO will look like C16.

Device diagram

Most models have an image of their circuit diagram on the body. The presence on it of the designation of a thermal and electromagnetic release indicates that the device is a difavtomat. They look similar to the following images:

Knowing about the listed distinguishing features, you can easily determine which of the devices is installed in a particular circuit. One or more of them will necessarily be obvious.

Connection diagrams for protective devices

The RCD cannot protect itself and the network it is connected to from overloads and short circuits, therefore, as an additional protection, it needs the use of circuit breakers.

In this case, the device is group and controls the entire electrical wiring of the house. To control each individual powerful consumer of electricity (boiler, stove, convector), its own RCD can be included in its circuit in series with the circuit breaker.

Differential machines are installed after the meter (electric meter) subject to certain conditions:

• it is not allowed to connect RCBOs in series with each other;
• it is impossible to use zero conductors coming out of other devices (phase and zero are taken from only one difavtomat);
• it is forbidden to combine output zeros for subsequent allocation.

Advantages and disadvantages of VD and RCBO

At first glance, it may seem that the advantages of difavtomatov over RCDs are quite obvious. But you can't jump to conclusions. It is not for nothing that well-known brands - manufacturers of automation equipment produce both types of protective devices, which are in equal demand.

For a fair assessment, the reader is invited to make a comparative analysis of the advantages and disadvantages of both devices, summarized for ease of perception in tables:

• When using RCD

• When using difavtomat

As you can see, each of the devices can be used with equal success. In some cases it is more convenient to use RCBO, in other situations it is more profitable to install an RCD. The final decision remains with the user.

Topical questions on the topic

Question: Will the use of the zeroing system cause false operation of protective automation?

Answer: This can only happen if the system is improperly arranged, that is, when the splitting of the common zero into a working zero and the PE conductor occurs after the RCD, and not before it. According to the rules, splitting should be done before entering the apartment shield.

Question: Why is it impossible to combine zero conductors after leaving difavtomatov on a common bus, for subsequent use of "0" in other circuits?

Answer: In this case, trips not related to the operation of the protected equipment may begin. For example, a RCBO is installed in a water heater circuit, and its "0" is also involved in another circuit. Accordingly, there will be a current difference between the input and output in the differential transformer, resulting in a trip, although there will be no leakage.

In conclusion, it should be noted that the considered means of automatic protection are not inferior to each other in terms of efficiency and can be successfully used when connecting various equipment. The main condition is compliance with the rules of installation and operation.

In the course of my work on electrical installation, one often hears the following question: what to choose - or? So let's find out which is actually better. Differential automatic or RCD.

I will tell you clearly. There is no correct answer to this question, because The choice between an RCD and a differential automaton depends on numerous factors.

But still, I will try to explain to you with examples and give you the opportunity to make your own choice.

Item 1. Free space in the dashboard

First of all, you need to determine the availability of free space on the DIN rail in your apartment panel.

You will ask why?

I answer, with a slight change (reconstruction) of the electrical wiring of your house, it is possible that the apartment shield will remain unchanged, and therefore your desires will not be able to come true for a simple reason - there is not enough space in the shield.

The differential machine takes up less space in the shield than the residual current device.

You all know that the RCD should protect against short circuit currents and line (group) overload. Therefore, together with each RCD, it is necessary to install a circuit breaker nearby, which will take up additional space in the shield.

Item 2. Purpose

What is your goal when installing a differential circuit breaker or residual current device?

There is nothing complicated here either.

If you need protection against electric shock of a specific electrical device (washing machine, jacuzzi bath, water heater, etc.), then you just need to install a differential machine with technical characteristics (rated load current, leakage current) of exactly the electrical device that You choosed.

If you need protection against electric shock of any group (line) of sockets, then in this case it is advisable for you to use an RCD rather than a differential machine.

Why? Yes, for a very simple reason.

In the event of a change in the load current (dynamic load), and this can happen elementarily. Nowadays, electrical appliances of increasing power are increasingly used (computer power supplies, plasma TVs, refrigerators, electric kettles, whirlpool baths, electric boilers, etc.).

Due to the increase in load (power), the differential machine will start to turn off due to overload and it will have to be changed to a higher rated current. In the case of an RCD, you only have to change the circuit breaker.

Think for yourself which is cheaper - differential machine or circuit breaker?

Item 3. Quality

At this point, I can say that most combined devices, and the differential machine is such (contains the functions of a circuit breaker and RCD) are of lower quality than special devices designed specifically for a specific purpose (RCD).

On this point, the advantage is on the side of the RCD.

Item 4 Repair and replacement

From the experience of operating electrical devices, I can say with confidence that nothing is eternal. Each device has its own lifespan. Therefore, in this paragraph, I will touch the condition of repair or replacement.

And again Residual current device takes precedence in front of the differential machine.

In the event of failure of the RCD or circuit breaker, either the RCD or the circuit breaker must be replaced. And if the differential machine fails, no matter for what reasons, it will have to be changed completely. From the financial point of view, these are completely different expenses.

Item 5. Power supply

Again, the advantage in this paragraph is on the side of the RCD.

In the event of a RCD malfunction and its replacement, the power supply of your house (apartment, cottage) can be temporarily restored by installing a jumper between the circuit breaker and the load.

In a similar situation with a differential machine, temporary power can be provided if you have another differential machine or circuit breaker in reserve.

Step 6. Reason for disabling

If for some reason your RCD has turned off, then the reason for the shutdown is obvious - a leakage current has appeared in the electrical wiring of your apartment.

If for some reason your circuit breaker protecting the RCD has turned off, then the reason for the shutdown is obvious - there is a short circuit or overload in the electrical wiring of your apartment.

If for some reason your differential machine has turned off, then the reason for the shutdown UNKNOWN. Either leakage current or short circuit.

Conclusion

In this article, I do not impose anyone in the use of a particular device.

What is preferable: a differential automaton or an RCD is decided by everyone independently, depending on the above personal observation.

One of the important components of life security is home security. This is especially true of home electrical wiring - an object of increased danger. Since modern apartments are equipped with a decent arsenal of various household electrical appliances, the power consumption of electricity in the apartment is quite large. Accordingly, the load on the electric cable also increases.

Why are protective shutdowns needed?

It is known that any material wears out over time and becomes unusable. The insulating properties of both home wiring and internal electrical appliance wires are lost over time. The resulting leakage of electricity, exposure of wires, oxidation can eventually lead to the most unpredictable consequences.

It is also possible that short circuits may occur due to faulty home wiring or electrical appliances, or due to negligence.

Due to the many electrical appliances used, including those with high power consumption, overheating of the electrical wiring of the home power network often occurs.

In the absence of protective devices, all these factors can lead to irreparable trouble or damage.

To protect yourself from trouble, you should install electrical protective devices: difavtomat (differential automatic device) or RCD (residual current device).

Before choosing which protective device to install, you should understand what they are, how they work, how the RCD differs from the differential automaton, which is preferable to choose, because the difference between the RCD and the difavtomat is significant.

Residual current device (RCD)

This device is designed to equalize the strength of the current going to the electrical appliance with the current coming out of the electrical appliance (along the neutral), by the difference between them it recognizes the leakage from the mains. When the difference reaches a value incompatible with human life (30 mA), the device turns off the voltage. As a result of the almost instantaneous operation of the device, the differential current flowing through the faulty insulation or through the human body does not have time to cause significant harm.

The RCD is not only able to protect a person from electric shock, but is also able to prevent a fire in the wiring due to overheating and malfunction, violation of integrity as a result of mechanical, thermal effects, and aging of the wire insulation.

How it works? Let's say the insulation of the phase wire is damaged inside the washing machine. If a person standing on a wet floor touches the body of the washing machine, the RCD will immediately turn off the voltage supply, determining that the current that has gone into the apartment has not returned via neutral to the residual current device, that is, the incoming and outgoing currents through the RCD are different.

RCD will also help in the following situation: for example, when drilling a wall with a bare foot resting on a heating battery, getting into the phase wire of the electrical wiring. The electrical circuit “drill - human body - battery” formed in this case can cause cardiac or respiratory arrest. But if there is an RCD, it will immediately “determine” that part of the current has not returned (the one that, having passed through the person, went into the battery). In this case, the voltage will also be turned off instantly. At the same time, even if a person receives an electric shock, it is not as strong as it could be.

In the absence of an RCD, any of these reasons can cause harm to a person that is incompatible with life. However, not in all cases, RCD can help. For example, if the home electrical wiring is old, dilapidated. In this situation, the RCD will trip constantly and cut off power due to constant leaks through faulty wiring, which will cause more trouble than good. Therefore, in such a situation, it is preferable to install an RCD pointwise, that is, install sockets with a built-in RCD.

Differential circuit breaker

Difavtomat differs in that this device works simultaneously as a circuit breaker and as a protective voltage shutdown device.

Difaavtomat is designed to protect against electric shock when touching current-carrying parts of electrical appliances or in the event of a differential current.

In such situations, the differential machine, as well as the RCD, instantly tripping, turns off the voltage in the network.

In addition, the difavtomat performs the functions of protecting electrical wiring from short circuits and overloads. This is due to the fact that the design of the difavtomat is similar to a conventional circuit breaker - it contains two releases:

• Thermal release, disconnects the power line in case of network overload.
• Electromagnetic release that trips when a short circuit occurs.

How does it all work?

1. As well as the RCD, the difavtomat detects differential current. Works similarly to the cases discussed above (examples with a washing machine and drilling a wall).
2. Operation of the electromagnetic release. Let's say a child pushed something conductive into the outlet, for example, a hairpin, or due to an insulation malfunction, the phase and neutral wires came into contact in the home network or in electrical appliances. In both cases, as a result of a short circuit, an electromagnetic release will operate.
3. Thermal release operation. Let's say a difavtomat with a nominal value of 16A is installed. They turned on several electrical appliances, with a total power significantly exceeding that allowed by the machine, for example, a 2-kilowatt heater, a kettle and an iron. Due to the heating of the wires, thermal protection will work, the electricity will immediately be turned off.

What is the difference between RCD and difavtomat

For homeowners, sometimes it does not matter what exactly they have installed: an RCD or a difavtomat. However, as we discussed their properties and purpose above, the difference between an RCD and a difavtomat is significant, and the level of safety of life and housing depends on what to choose.

Functional difference between RCD and differential automaton

1. The main function of the residual current device is to detect differential current in the network - leakage current. In the event of such a situation, first of all, a person may suffer by touching the metal case or parts of the damaged equipment. Also, when a differential current appears, the insulation of the electrical wiring can heat up, and this is one of the most common causes of household fires and fires. The presence of an RCD is capable of preventing trouble in these conditions.
2. The differential machine simultaneously performs the functions of both the circuit breaker and the previously considered RCD. That is, the functionality of the difavtomat is much wider: protection of the electrical network from short circuits, overload and the consequences of the occurrence of differential current.

Thus, the range of actions of the differential automaton is much wider than the narrowly directed action of the RCD.

When choosing what and where exactly to install, it should be remembered that the RCD, unlike the difavtomat, is not designed to detect overloads and short circuits. Some mistakenly believe that by installing an RCD, they are protected from everything - this is absolutely not the case.

How to visually distinguish an RCD from a difavtomat

At first glance, both devices are quite similar to each other: the case is similar, there is a switch, a “test” button, a diagram is shown on the case. But upon closer examination, you can find the difference between an RCD and a difavtomat: the circuits are different, different toggle switches, alphanumeric markings are also different.

One way to visually distinguish devices is current marking.

Marking in amperes, for example, 16A, is indicated on the case of the RCD. This indicates the rated current of 16A for which the device is designed. If at the beginning of the inscription there are letters B, C or D, and then a number, then this is a differential automaton.

Which is better: RCD or difavtomat? After reviewing the main characteristics, the choice, of course, will be made in favor of a differential machine. This is optimal if the house has a simple wiring diagram. If you have a large private house with a complex wiring diagram with many groups of wires designed for heavy loads, then it is better to use an RCD and a circuit breaker as a whole, which is separately installed on each of the existing groups.

What is the difference between a differential automat and an RCD? What are they protecting from? What type to choose in the apartment, in the kitchen? What is the difference between an RCD and a difavtomat? Examples of 4 differential protection markings.

TEST:

Mini-test on the safe use of RCDs.

1. What type of load is the protective device installed on?

A) washing machine

B) in a common line, in an apartment shield

1. What should be the trip current?

1. What type of RCD is used?

A) differential automatic

B) difrela and circuit breaker

1. From what will the differential protection in this design protect?

A) electric shock

B) from a fire

Answer options:

1. On the washing machine (A), we select an RCD with a trip threshold of 10 mA (A), with the type of RCD differential automatic (A). This threshold value protects against electrical injury (A).
2. A protection with a current differential value of 100 mA should be installed in the apartment shield (B). An RCD with a switch (B) will reduce the likelihood of a fire (B).
3. For a washing machine (A) with a threshold of 30mA (A), a differential relay with an automatic device (B) will protect against electric shock (A).

SIMPLE differences between a differential machine and a relay. We distinguish protection devices according to 4 features.

Video 1. This video describes how to distinguish a differential machine from a relay.

For example, a difrele and an IEK automatic machine are considered.

“Formula”Technical difference between RCD and difavtomat.

1st sign. The inscription on the body of the device. A differential switch means a difrele, and a differential current circuit breaker means a differential automatic (AVDT).

2nd sign. The presence of a letter (B, C, D or E - the speed of operation of the built-in switch) in front of the operating current value indicates a RCBO.

3rd sign. There is no conditional image of tripping due to overload and short circuit on the diagram.

4th sign. Previously, difavtomatov were larger in size. At present, this feature is not typical.

Designation of ouzo and difavtomat on the diagrams.

In order to understand the scheme of complex shields, you need to know how the protection devices are depicted in the diagram. As discussed above, the main device of the RCD was a residual current transformer that controls the opening contacts. It is placed on the symbol, fig. 5

Rice. 5. Single and double pole differential relay.

RCBO, as we have already discussed, has another active element - a circuit breaker. According to GOST 2.755-87 ESKD, it is designated by a rectangle on the NC contact (Fig. 6).

Rice. 6. RCBO in the diagram.

IMPORTANT! The given examples of designations are conditional, because normative documents not regulated.

Let's consider the conditional-graphic designations on the part of the real circuit (Fig. 7).

Rice. 7. RCD designation in an excerpt from a real project.

In this circuit, the differential relay is connected in the floor board after the circuit breaker and the meter. Following the rules of GOST 2.710-81, each element of a single-line network, in addition to the graphic, also has a letter designation t. In our case, the differential protection Q0 is of type F202.

What 2 dangers does RCD protect against?

1st danger.

There are quite a lot of network-operated devices in our homes. Everyone knows that electric current is dangerous to humans. Under normal conditions, electricity is not dangerous, because. housings of electrical appliances are insulated, and electric shock through the air is impossible. But there are two rooms in which the current poses an increased danger. In the bathrooms, a washing machine is installed, which has an electric motor and consumes significant power during operation. Also in the bathroom and in the kitchen there is a passage of current through the water. In this case (Fig. 1) a path for electricity through the human body is possible. Such a current, which is called leakage current (or differential current), does not lead to the operation of the circuit breaker in the shield, but is sufficient for severe electrical injury.

Rice. 1. If the phase wire (C) gets on the body of the washing machine, there is a danger of electricity passing (red line) through the human body to ground (PE).

2nd danger

Current, uncontrollably "leaking" from the mains, leads to heating of conductive parts and cause a fire.

The amount of electricity sufficient to cause injury and start a fire varies. To increase the safety of the wiring by eliminating these 2 dangers, RCD (diff protection) will help. Diffzashchita has a fire-fighting effect when installed on groups of consumers (apartment or floor electrical panel). In other cases, RCDs are included in the power supply circuit of a particular consumer.

Definition. Residual current device is a device used to protect people and electrical devices from differential current.

TOP 3 premises with mandatory installation of differential protection:

1. Rooms with high humidity.
2. With metal floors.
3. Rooms with devices having a conductive housing.

Marking. Designation on the case 5 main parameters.

In photo 1 - relay differential. On the front side of the device, next to the switch, you can see the parameter markings:

1. Operating current differential relay (16 A). The automaton associated with the differential relay must be of no less importance.
2. Short circuit current (3000) - the maximum value at which the relay retains its functionality.
3. Leak type. This relay will operate when an alternating differential current appears.
4. Operating alternating voltage and frequency in the network (230 V 50 Hz).
5. Rated operating current (30 mA) - the minimum leakage current at which the consumer will turn off.

IMPORTANT! Also on the case there is information about the operating temperature.

1. - the device can be installed outside heated rooms - up to minus 25 degrees.

3 schemes for connecting differential machines and RCDs.

Let's consider three characteristic schemes for connecting differential protection.

1. Connecting a differential relay to a separate consumer.

Let's say we want to improve the electrical safety of an individual, the most dangerous consumer, by turning it on through the RCD (Fig. 2). The consumer is a washing machine installed in the bathroom.

Rice. 2. Washing machine connection line. Red wire - phase L, blue - zero N, brown - protective earth PE.

IMPORTANT! The "TEST" button, when pressed, opens the consumer's power supply circuit. This button is used to test the operation of the device.

In Figure 2, the input power lines pass through the GA group machine, through the meter they are distributed to consumers. The washing machine is connected using an RCD and a separate circuit breaker AB installed in the phase wire L. A differential relay acts as a protective device in this circuit. Inside such a device, the wires L and N run inside the transformer T (These wires constitute the primary winding I). The secondary winding II is connected to the comparison circuit A. The comparison circuit controls the operation of the polarized relay P, which can open contacts K.

• Normal mode

Figure 2 shows the normal mode of operation - the washing machine is working correctly, there are no short circuits. All electricity passing through bus L returns through bus N. The current in winding II, which is equal to the difference in currents in the primary, is zero. The relay does not operate.

• Residual current and short circuit.

When the load fails, there is a leakage of electricity (yellow dotted line) inside the washing machine body. A residual current occurs in the transformer T of the protective device. Comparison circuit A through relay P disconnects the load from the network. In the event of a short circuit in the machine, the AB machine cuts off its line.

1. Connecting a differential machine to a common circuit.

Rice. 3. The introduction of a single RCD into the wiring.

Inside the inlet shield (Fig. 3 green dotted line) an RCD is installed - in this case, a differential automatic. Inside it, the phase conductor additionally passes through short-circuit protection (>I) and overload protection (t), as in a conventional circuit breaker. There will be a power outage for any reason for the appearance of a fire - excess consumption, short circuit in the load and the presence of differential current.

IMPORTANT! RCDs used as fire protection have a higher rated operating current.

1. We distribute differential protection by groups. DC and AC leakage.

If you install a separate differential machine for each load - each chandelier, computer, TV, air conditioner, washing machine, then you get the most expensive option. Using differential relays that respond to a certain leakage current, it will be possible to group consumers and reduce costs (Fig. 4)

Rice. 4. Loads are collected in groups. Protective grounding is conventionally not shown. After the counter, 50A circuit breakers are installed.

In Figure 4, a washing machine with a powerful AC motor is connected through an RCD for a current of 10mA. Other loads - sockets, lighting, a computer are fed through a differential relay with a threshold of 30mA. At the input, after the meter, a differential relay is switched on as a protective fire-fighting device.

How to avoid incorrect operation of the RCD?

1. Combining neutral conductors from different protections leads to false trips.
2. When connecting zero and ground, the RCD will not turn off the load at all, even if a leak occurs.

Answers to 5 frequently asked questions.

1. Our house does not have a separate protective earth line. Would it be useful to install a safety shutdown?

With such wiring, differential protection can protect against electric shock when touching both a faulty load and sewer or other metal pipes. If the insulation inside the device is damaged (short circuit to the case), the operation will not happen.

1. What operating time should be provided by differential protection?

All disconnect devices must turn off the consumer in the event of a leak in no more than 0.3 seconds. It is better to choose high-speed disconnect devices.

1. If fast protective devices are the best, why are delayed RCDs produced?

Such devices are installed on powerful consumers of electricity. When they are started or stopped, an uncontrolled leakage of electricity may occur.

1. The use of a protective shutdown is mainly advisory in nature. In what cases can you do without it?

The PUE discusses several cases of mandatory use of differential protection. The most characteristic is the protection of mobile residential trailers, outdoor power consumers.

1. And in what cases is RCD not recommended?

In cases where switching off can lead to a more dangerous result (installation on the alarm power line, medical devices)

When creating or reconstructing an intra-apartment or home electrical network, it is not enough to be limited only to laying wires (even if of the required section) and placing sockets and switches convenient for everyday use. Particular attention should always be paid to the safety measures for the operation of both the network itself and the household appliances connected to it. Sad statistics show that up to a quarter of all registered fires occur for reasons related to a malfunction or imperfection of household "electrical facilities". And in the reports of incidents, there continue to be reports of tragic cases from electric shock to people when using lighting fixtures or home appliances.

In order to protect both himself and his household, to ensure the safety of housing and all property in it, the owner is simply obliged to provide for the installation of special protection devices. Nowadays, several varieties of them are offered - these are circuit breakers that replaced fuses, residual current devices (RCDs) and differential ones. And for those who first dealt with this problem, the question often arises - what is better difavtomat or RCD? Let's try to answer it.

It is clear that taking on electrical installation on your own, without having the skills, is a gamble, and, sometimes even very unsafe for life. But it is useful for everyone to know such questions, although would from those considerations so that you can correctly plan the "budget" for the renovation of the home network. Yes, and it will be easier to communicate with an invited electrician, since many of these amateur craftsmen are big fans of “hang noodles” on ignorant owners in order to rip off extra money.

And in order to be able to compare a differential automaton with an RCD, it is probably necessary to have at least a little idea about their structure and functions.

Devices that ensure the safety of home electrical networks and their individual sections

What levels of protection should be provided in home electrical networks

To be absolutely precise, the heading in the title of the article is not quite correct. Let's put brevity aside and try to formulate it differently. So, what is better to use to provide the necessary levels of protection - a differential machine or a combination of a circuit breaker with a residual current device (RCD)? That is why the first illustration of the article is made as it is, and not otherwise.

Second Amendment. The question is not, probably, about what is better in terms of reliability in operation and ensuring the required security. Both options are equally effective, and they have to be compared according to completely different criteria, which will be discussed below.

But to start for those readers who do not have a clear enough understanding of the purpose of these useful devices should at least give some explanations on their design and operation.

So, what are the main "troubles" can expect consumer during the operation of home electrical wiring.

• Overload, that is, the situation when the total value of the load, simultaneously connected, exceeds the capabilities of the wires of the supply line. The reasons may be different. Very often, this is an ill-conceived connection of powerful household appliances to old wiring that does not meet modern requirements. The same thing can happen when several powerful devices are connected to one, even if it is a well-laid line, at the same time. It is no secret that many owners are too fond of using tees, and as a result, such a load falls on one outlet that the supply is simply unable to cope with.

As a result, this always leads to strong heating of the wires, causing melting of the insulation or even the plastic housings of sockets or household appliances. It is quite clear that such a situation can easily lead to an open fire.

The melting of the insulation, of course, becomes the cause of the appearance of a short circuit with all its "charms". A special danger of this phenomenon lies also in the fact that a violation of the integrity of the wiring can occur in a hidden area, and the consequences can be completely unpredictable.

By the way, overload mode sometimes happens and not through the fault of the owners. There are situations when malfunctions of consumption devices lead to such consequences. For example, an inter-turn short circuit in the winding of an electric motor or some partial violation of the integrity of the heating element of an electric heater.

So, it is quite obvious that an emergency shutdown system should be provided for when the line is overloaded.

• Short circuit. If for some reason there was a contact between the phase wire and zero (phase and ground), then the entire power of the network section is sharply concentrated in a very limited area. Of course, this leads to instantaneous high-temperature heating of the conductors, to the formation of an electric arc between them. And if the overload of the line gives some probability of an open fire, then a short circuit in most cases directly leads to it.

Even under conditions of timely protection operation, a short circuit can lead to a fire hazard. It's scary to even imagine how this state of emergency could end if the line remains switched on.

There are many possible reasons for a short circuit.

- It may be poor-quality or worn-out wiring insulation over time.

- It is clear that one of the frequent causes is the overload of the line already discussed above with the melting of the insulation.

— Accidental contact of foreign objects or substances with conductive parts.

- Carelessness, mistakes or completely illiterate actions during the installation of house lines.

- Gross violations of the rules for the operation of devices.

- Breakdowns of household appliances (for example, wear of electric motor bearings or mechanical damage to wires and contacts located inside) or failure of elements of electronic or electromechanical circuits of devices.

As can be seen from the above, it is simply impossible to predict all the reasons in advance. And, therefore, it is necessary to provide protection that would instantly break the power line in the event of a short circuit.

• leakage currents. This term can be figuratively understood as an electric current passing from to the "ground" along an unauthorized, that is, not intended for this and undesirable path.

This is explained by the fact that the insulation of conductive elements is far from always ideal in itself, that is, even in a completely new unworn condition. Plus, over time, it ages, somewhat wasting its dielectric qualities. The situation can be aggravated by periodic overloads of the lines, which have already been described. As a result, the electric current finds its way to spread - through the metal cases of household appliances, grounded pipes of heating or plumbing systems, along the reinforcing cage of reinforced concrete, and sometimes even along wet plastered wall surfaces. And when touching such objects or structures, a person can close the circuit through himself.

2 is a schematic representation of the insulation resistance.

3 - the metal case of a household appliance or a part of a building structure.

The main danger in domestic conditions is the possible defeat of a person by electric current. Probably, many have encountered the phenomenon when, when touching a washing machine or dishwasher, an electric stove or oven, and sometimes even plumbing fixtures, an unpleasant effect of electricity is felt. This is already a sign of extremely high danger!

Safe for humans at a voltage of 220 IN a current strength not exceeding 1.5 mA is considered - it is at such indicators that the effect is already beginning to be felt. At currents of the order of 2 ÷ 7 mA, convulsive reactions of the fingers and hands occur, and at 10 and above, a person is no longer even able to independently tear his hand away from the conductor (conductive surface). And the longer this contact, the lower the resistance of the human body, and the higher the likelihood of irreversible consequences.

Leakage currents are especially dangerous in rooms with high humidity - the conditions themselves contribute to high conductivity. And kitchens, and bathrooms in modern houses and apartments are literally crammed with electrical household appliances and appliances.

It is extremely difficult to deal with the occurrence of leakage currents. Moreover, no one is immune from the fact that a completely safe, for example, dishwasher will not become a source of real threat tomorrow. This means that a device is needed that could instantly turn off the power supply if, when touched with the device, the leakage current reaches dangerous values.

All three of these major hazards are taken into account when designing protection devices.

Circuit breakers

These compact, modular devices have replaced the once ubiquitous fuses - "plugs". The direct purpose is to protect the internal intra-apartment network or its dedicated section from overload and short circuit.

The purpose of this publication is not to discuss in detail the circuit breaker device, as well as other devices. Therefore, we restrict ourselves to a brief description and the principle of operation.

A modern circuit breaker has a modular design, enclosed in a compact plastic case. From the front there is a handle for turning on the circuit, from the back - a special groove with a latch - for fixing the switch on the DIN rail.

Any circuit breaker is designed for a certain rated load current. Its value must be indicated on the body of the device.

This is what modern circuit breakers look like inside

Contact closure is ensured when the handle is moved to the upper position. A special mechanical engagement device (a set of levers and stoppers) ensures fixation in this position.

But there are two levels of operation for opening contacts. One release has a bimetallic (thermal) principle of operation, the second - electromagnetic.

So, the passage of current through a conductor is always accompanied by the release of a certain amount of heat. If the value of the current passing through the circuit breaker exceeds the nominal value, then the bimetallic plate, heating up, begins to bend. At a certain level of bending, the contact release mechanism is activated, and the load line is de-energized.

The second, electromagnetic "line of defense" is short circuit protection. This is an induction coil. with a metal core located inside, held in the “working” position by means of a spring. That is, at normal current values, the induced electromagnetic field is not enough to move the core of this solenoid.

If a short circuit occurs on the line, then the value of the current passing through the switch increases many times over. Accordingly, the intensity of the electromagnetic field created by the induction coil also increases sharply. The core, overcoming the resistance of the spring, is drawn inward, thereby activating the free trip mechanism.

The opening of contacts at high current strength is accompanied by the formation of an electric arc. This is provided for in the design - a special chamber with metal plates crushes and extinguishes the arc, and the gas formed during its short burning is discharged through a special channel.

So, the circuit breaker will protect the line from overload above the nominal and from short circuit. He does not know how to deal with leakage currents.

Residual current device (RCD)

To protect against leakage currents, a completely different device is used. Its correct name is a differential switch (DV), and the operation of this device is based on comparing the current strength at the input and output.

The main "working body" of the RCD is a current transformer with a toroidal core, on which the windings are placed. Two of them are on the conductors L and N (let's conditionally call the input to the load and the output from it), equal in their parameters. And one more - control, connected either with an electromechanical relay or with an electronic key.

In the normal position, in the absence of leakage, the input and output windings create magnetic fluxes of equal magnitude, but directed in the opposite direction. Accordingly, they compensate each other, and the total magnetic flux in the toroidal core is zero.

If a leakage current appears (for example, a person touches a household appliance with damaged insulation), then the magnetic flux on the output winding becomes less than the input. There is no mutual compensation, and the resulting electromagnetic flux appears in the core, which induces an EMF on the control winding. The current that has arisen in it causes the operation of an electromechanical relay or an electronic key, breaking the load power supply circuit.

The response time of a serviceable RCD is usually within 0.2 ÷ 0.3 seconds.

Differential switches, depending on their type, can respond to AC or DC (pulse current) leakage. The characteristics of the device must indicate the nominal leakage current (that is, the difference between the input and output values) - usually it is 10, 30, 100, 300, 500 mA. For most household appliances, RCDs with a rating of 30 mA are selected, and if they are located in rooms with high humidity or in children's rooms - 10 mA. Differential switches with higher ratings already have a slightly different purpose - not to protect a person from electric shock, but to prevent the occurrence of emergency situations with high leakage and the likelihood of fire, that is, they are installed common on the input lines in switchboards.

We emphasize once again the feature - residual current devices set the necessary level of safety from the effects of leakage currents. But they are completely "helpless" with regard to power line overload and short circuit. Thus, the use of RCDs is mandatory in conjunction with circuit breakers. Only in this case will the necessary level of protection be provided.

Differential machines

These devices can be called the most advanced of those listed, since both the circuit breaker and the RCD are assembled in one case. And, the compactness of such difavtomatov (high-quality, of course, from leading manufacturers) does not affect the reliability of the protection created.

To be more precise, then the full name of these devices is a residual current circuit breaker (RCB). This abbreviation is very often placed on the front panel of the device.

In addition, the main characteristics are indicated on the differential machine itself or in its passport. This, by analogy with a circuit breaker, is the rated load current (with a letter index at the beginning, indicating the time-current characteristic of the device operation). And the value of the leakage current in mA, as it is accepted on the RCD.

It would seem - here it is, the optimal solution! However, not all so simple. Yes, the difavtomat will fully ensure the reliability of the line, but the expediency of installing it is sometimes in doubt. Therefore, in the next section of the article, we will just move on to a versatile comparison of the advantages and disadvantages of possible options: using an RCD in tandem with a circuit breaker or a differential circuit breaker.

What is better to put: RCD + circuit breaker or differential circuit breaker?

So, we proceed from the fact that the performance characteristics of the devices are equal, that is, they equally provide effective protection against the above emergency situations.

What take up more space?

Yes, let's start with the most obvious. Sometimes the dimensions of the switchboard do not allow ignoring this issue. And the installation of a more spacious cabinet is either completely impossible based on the dimensions of the available space, or is associated with serious repair and finishing work, which there is no desire to do.

Here - everything is simple. "Duet" circuit breaker + RCD will take 3 module-places on the DIN rail. And the differential automaton, which performs exactly the same functions, is only two.

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It seems to be empty. Perhaps so, but only if we are talking about protecting just one line. But a good host who cares about security will distribute the network over several dedicated lines. For example, a separate line to a washing machine (with a machine 16 A, RCD 25 A ΔI=30 mA), a group of sockets in the kitchen - (16 A, RCD 25 A ΔI=30 mA) and in the bathroom (10A, RCD 25A ΔI=10 mA).

If this scheme is implemented with automatic machine + RCD pairs, 9 module-places will be required on the din-rail of the switchboard. Quite a lot.

The same circuit, but with the use of differential automata, will require only 6 module-places, and for a small switchboard this difference is very noticeable.

By the way, at present, differential automata of even a single-module design can be found on sale. They are, of course, much more expensive, but they can significantly save space in the control cabinet.

What is easier in electrical installation?

This selection criterion is not so significant, but still.

In principle, the installation itself is not complicated in any case - all devices of this purpose have convenient screw terminals that provide reliable contact. Installing any switch on a DIN rail is also not difficult. The difference is only in the number of communication connections and in the greater "stuffing" of the cabinet's internal space with additional jumpers.

For comparison, the diagram below shows the switching of a pair of AB + RCD and a separate RCBO.

• So, in order to connect a pair of AV + RCD on a dedicated line, you must do the following:

- at the entrance automatic switch, a phase wire is connected. From the output, a piece of wire is switched to the input L of the RCD. And then, from the output terminal of the RCD - the phase wire goes to the payload.

- The zero wire is connected to the corresponding terminal N of the RCD, and then - the output towards the load.

Togo, six terminals and one jumper.

• To connect a differential machine to the circuit, it is enough to connect the corresponding wires to the L and N terminals at the input and output. Total - four terminals without any jumpers.

It is clear that the difference is small, and for an experienced installer, any of the options will not present any difficulties. Nevertheless, the circuit is simpler, and there are fewer jumper wires in the cabinet space.

Diagnosis of problems in the electrical network

Any of the protective devices under consideration is designed to operate, that is, to open the circuit in the event of certain malfunctions or emergencies. But here, let's say a trigger has occurred, and you need to determine its cause.

• If a pair of automatic + RCD is installed, then the problem that has arisen, at least, can be immediately localized. Everything is simple here: if the RCD worked, then a leakage current is observed on one of the household appliances. It is not so difficult to figure out which of them is “guilty” of this, especially if only some of the devices were connected to the network at the time of operation. If it worked, then you can sin either for network overload (after analyzing what worked at the time of shutdown), or for a short circuit, which usually makes itself felt by other signs.
• But if all the protective functions were assigned to the differential automaton, then “diagnosing” becomes much more difficult. It is necessary to consider all probable causes of operation.

In fairness, it should be noted that some models of differential automata are equipped with a kind of indicator that can indicate which of the circuits (by leakage or by overload) caused the protection to trip. But the cost of such RCBOs is certainly higher.

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Maintainability of the assembled circuit

You can never exclude the possibility that, for one reason or another, the protection device itself will fail. it will need to be replaced, and, alas, the differential automaton loses significantly by this criterion.

In the event of a breakdown of any of the devices in the RCD + AB bundle, it will be enough to replace only the faulty one - this will not affect the performance of the "partner". In the worst case scenario, the acquisition of each of them is much cheaper than buying a differential machine.

If it came out failure of any of the protection levels difavtomat, the device will have to be replaced completely. And this sometimes happens. For example, there are frequent trips seemingly for no reason, with a clearly non-congested network line. And the test button works quite normally, that is, the “built-in” RCD is working properly. Most likely, the problem lies in the thermal protection circuit (the bimetallic plate does not work correctly). But this will still require the purchase of a very expensive new RCBO.

Financial Issues

To a certain extent, we have already touched on this issue in the previous paragraph. But that was a force majeure situation. And now let's consider from the point of view of planning a "budget" for the creation or reconstruction of a home electrical network.

The acquisition of reliable protection devices (especially RCDs and RCBOs) is quite expensive. Especially if you focus on really high-quality products of leading brands. These include, for example, Schneider Electric, Legrand, ABB, General Electric, Siemens. The budget and, alas, not always justifying options include products "DEKraft", "IEK", "Kontaktor". There are also not known at all no brand, which should be treated with special biased caution, since the benefit in the cost of the purchase will be incomparable with the consequences that the incorrect operation of cheap automation can lead to.

So it’s worth thinking carefully about whether to purchase once and for a long time guaranteed high-quality devices, and after that “sleep well”, or go “on the path of least resistance”, but at the same time the owner will constantly “gnaw” a feeling of some kind of uncertainty.

Just as an example, to compare the costs of RCD + AV and RCBO, let's take the Legrand models with prices from a company store in Moscow.

Model name	Illustration	Rated current, maximum leakage current	Unit cost
DX³ series circuit breakers, single-module, single-phase, type C		6 A	185 rub.
		10 A	165 rub.
		16 A	157 rub.
		20 A	185 rub.
		25 A	165 rub.
Differential switches (RCD), two-module, 1 phase and neutral, AC type		16 A / 10 mA	3190 rub.
		25 A/30 mA	1136 rub.
		40 A/30 mA	1540 rub.
		63 A/30 mA	1660 rub.
Residual current circuit breakers, two-module, 1 phase and neutral, AC type		16A/10mA	4800 rub.
		16A/30mA	2290 rub.
		20 A/30 mA	2390 rub.
		25 A/30 mA	2390 rub.
		32 A/30 mA	3090 rub.
		40 A/30 mA	3390 rub.

Note: Prices are selective, for RCDs and RCBOs - a more affordable AC series, and only for example (in the context of covering the topic of this article).

In any case, the current prices must be specified at the place of purchase. By the way, the table shows prices for products of the original assembly, since licensed Chinese-assembled devices can be even cheaper.

Well, if there are prices before your eyes, and the scheme for distributing the general network into separate lines has already been clarified, it is easy to calculate the accounting itself. For example:

• A powerful household appliance has been purchased, say, a washing machine. It is supposed to stretch a separate power line to it, providing the necessary levels of protection.

Since the power of the machine is 2 kW, it will require a circuit breaker with a rated current of 16 A. The maximum leakage current to operate the protection will be 30 mA, since the device will be installed in a dry room (not in the bathroom).

We look at the price list and calculate:

- The cost of a circuit breaker for 16 A is 157 rubles.

- RCD with a rated current of 25 A (this indicator must be a step higher than the circuit breaker rating!) And with a leakage current of 30 mA - 1136 rubles.

In total - about 1300 rubles.

If you install a differential machine, then its cost at a rated current of 16 A and operation with a leakage of 30 mA is 2290 rubles.

It turns out almost 1000 rubles more expensive. But at the same time, as already mentioned, less space is occupied in the shield, installation is easier. In principle, at this level, the difference in total costs is not yet so tangible, and it is quite possible to accept both options. By the way, when laying single lines, many masters prefer just such a solution - a differential machine.

• Well, what if a shield is being mounted from which distribution is carried out, say, into six separate lines? Even the initial estimate shows that the difference in cost will already increase to six thousand or more. And this is already quite noticeable. It is easier to foresee a more capacious distribution cabinet in advance, having paid about 500 ÷ 600 rubles for it, and still remain in a significant gain, without losing at all in terms of security.

But that's not all. As a rule, RCDs are not installed on each line, as this looks too wasteful. Usually they are divided into groups of 2-3 lines with similar operational parameters. The safety of such a group will be provided by one RCD and individual circuit breakers. The cost of AB, as we can see, is low, so this approach gives a very impressive savings effect.

True, at the same time, it is not recommended to “enlarge” groups too much in order to further reduce costs. The fact is that the total current leakage on several lines, in principle, completely harmless individually, together can cause frequent protection trips for almost no apparent reason. In addition, a leak on any one device will cause a large number of lines to be disconnected at once, which is extremely inconvenient and in operation, in diagnostics faults. Agree, it's not pleasant to sit in darkness in the living roomif the RCD tripped, say, from a current leak on the dishwasher.

- six automatic switches 16A-6 × 157 = 942 rubles.

- three pieces of RCD 40 A / 30 mA (40 A, since two 16 A machines are connected) - 3 × 1540 = 4620 rubles.

In total: 942 + 4620 = 5562 rubles.

For comparison, you can determine the "unit cost" of one line - it is equal to 927 rubles. Significantly less than with a single connection.

If we replace the RCD with six differential machines with a nominal value of 16A / 30 mA, then the amount will be frightening: 6 × 2290 = 13740 rubles. It is clear that the "unit cost" of each line is equal to the price of the RCBO itself.

And there is nowhere to go - each line requires its own difavtomat. If we consider the breakdown of lines into groups, with the installation of one RCBO and two ABs to it, then in general it turns out to be complete nonsense. It turns out that the functionality of the difavtomat is curtailed, and it becomes an ordinary RCD. So isn't it easier and cheaper to install an RCD? After all, the effect will be the same.

By the way, pay attention to one more nuance. In the last two schemes considered, the use of differential automata did not give any gain in modulo-places. In both options, twelve seats are involved.

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In a word, when installing a shield with leads to several independent lines, it seems more expedient in terms of costs to use RCDs, broken down into groups, and “personal” circuit breakers for each line. Installing differential automata does not provide any advantages, but it is much more expensive.

So, in the publication, a comprehensive comparison was made of the advantages and disadvantages of using differential automata and “tandems” of RCD + circuit breaker as protection for electrical in-house or apartment lines. Everyone will draw conclusions for himself - there is enough information for this.

The article intentionally did not provide the rules and diagrams of electrical installation. This is very serious question that requires a separate detailed consideration. Here are some tips on where you can read about it.

The task of increased complexity and responsibility is the correct organization of household "electrical facilities"

It is better, of course, without having experience, not to undertake such work on your own, or at least do it under the supervision of a qualified electrician. To imagine how many events are to be held, and what numerous nuances should be taken into account, check out the detailed article on our portal. And one more voluminous publication is completely devoted to the rules.

And at the end of the publication, we suggest watching a video that is directly related to the topic of our conversation today.

Video: RCD or differential machine - which device should be preferred?