Most consumers do not care what is in front of them: RCD (residual current device) or difatomat (differential circuit breaker). But when developing electrical network projects for private houses or apartments, this issue has a certain significance.
In general, the problems that our citizens have with organizing the protection of their own homes in terms of electrical safety are significant. But what can we say if in many remote areas such things as “bugs” in traffic jams are still the norm?
Recently, one of my acquaintances asked me a question: what is on my dashboard? RCD or difavtomat. How to distinguish them. Since the problem, in a professional opinion, is very acute, we offer you a small educational program on this topic, including for electricians, especially young ones.
This knowledge will allow you to understand exactly what “lives” in your switchboard: an RCD or a circuit breaker, why place it there and how much it will help, or why it will save you in the future?
An experienced electrician, who has more than one short circuit under his belt, may even be offended by such questions! However, among young people, little attention is paid to theory, although consumers ask such questions all the time. And now I will tell you several options.
The difference between an ouzo and a differential machine according to its functional purpose
If you look at the RCD and the difavtomat, then in appearance these two devices are very similar to each other, but the functions they perform are different. Let's remember what functions the RCD and the differential circuit breaker perform.
The residual current device is triggered if a differential current appears in the network to which it is connected - a leakage current. When a leakage current occurs, the first person to be harmed is the person who touches the damaged equipment. In addition, when a leakage current appears in the electrical wiring, the insulation will heat up, which can lead to fire.
Therefore, RCDs are installed to protect against electric shock, as well as damage to electrical wiring in the form of leaks that are accompanied by fire. For more details on how this device works, see the article on the principle of operation of an RCD.
Now let's look at the differential machine. This is a unique device that combines both a circuit breaker (more understandable to the population as a “machine”) and the previously discussed RCD. Those. a differential circuit breaker can protect your wiring from short circuits and overloads, as well as from leaks associated with the previously described situations.
Now the main point where everyone starts to get confused: remember that the RCD, unlike the automatic circuit breaker, does not protect the network from overload and short circuit. And most consumers think that by installing an RCD, they are protected from everything!
In simple terms, an RCD is simply an indicator that monitors leakage and that current does not flow past your main consumers: electrical appliances, light bulbs, etc. If somewhere in the network the insulation is damaged and a leakage current appears, the RCD reacts to this and turns off the network.
If you turn on all electrical appliances (heaters, hair dryers, irons) at the same time, that is, deliberately create an overload, the RCD will not work. And the wiring, if there are no other protection devices, rest assured, will burn out along with the RCD. If, when the RCD is turned on, you connect phase and zero and get a huge short circuit, then the RCD will also not work.
Why do I mean all this, I just want to draw your attention to the fact that since the RCD does not protect the network from overloads and short circuits, you will probably agree with me that it itself needs to be protected. That is why the RCD is always connected in series with the machine. These two devices work in pairs, so to speak: one protects against leaks, the other against overloads and short circuits.
By using a difavtomat instead of an RCD, you get rid of the situations described above: it will protect against everything.
Let's sum it up, the main thing difference between RCD and difavtomat is that the RCD does not protect the network from overloads and short circuits.
Visual difference between ouzo and difavtomat
In fact, there are a lot of external signs by which it is easy to distinguish an RCD from a difavtomat. Look at the picture. Visually, these two devices are very similar: the case is similar, the switch, the “test” button, some kind of circuit on the case and incomprehensible letters.
But if you are more meticulous, you will notice: the circuits are different, the toggle switches are different, the letters will not be repeated. Which of these devices is an RCD, and which is a difavtomat?
Above we looked at the functional differences between these devices, now we’ll look at What is the difference between an RCD and a difavtomat? visually - so to speak, the differences are noticeable to the naked eye.
1. Marking by rated current
One way to visually differences between RCD and difavtomat This is a current marking. On any device, its technical characteristics are indicated. For the devices that we are considering, the main characteristics are the rated operating current and rated leakage current.
If only a number (the value of the rated current) is indicated in large letters on the body of the device, this is an RCD. In our picture this is a device of the VD1-63 brand.
The number 16 is indicated on its body. This means that the device is designed for a rated current of 16 (A). If at the beginning of the inscription there are the Latin letters B, C or D, and then there is a number, then this is a differential machine. For example, the AVDT32 difavtomat has the letter “C” in front of the rated current value, which indicates the type characteristics of electromagnetic and thermal releases.
Read it carefully again and remember. If it is written "16A" - this is an RCD, the rated current of which should be no more than 16 amperes. If it is written “C16”, this is a diffautomatic device, where the letter “C” is a characteristic of the releases “built-in” into the device, designed for a rated current of 16A.
2. Electrical diagram shown on the device
On the housing of any actuating or protective devices, the manufacturer always applies its circuit diagram. On RCDs and differential circuit breakers they are really similar.
We will not list now everything that is depicted there (this is the topic of a separate article), but we will only highlight the main differences. In the diagram, the RCD is an oval, which denotes a differential transformer - the heart of the device, responding to leakage currents and an electromechanical relay, which closes and opens the circuit, power contacts for connecting wires, etc.
In the diagram of the difavtomat, in addition to all similar elements, the designations of the thermal and electromagnetic releases are distinctive, which react to overload and short circuit current.
Therefore, looking at the connection diagram, which is shown on the case, you now know how they differ. If the diagram shows a thermal and electromagnetic release, this is a differential circuit breaker. This is the schematic difference between RCD and difavtomat.
3. Name on the device body
If you, as a simple consumer, find it difficult to remember, What is the difference between an RCD and a difavtomat?, we inform you: knowing about the problem that the article is devoted to, many manufacturers, so that buyers do not get confused, specifically write the name of the device on the case.
On the side surface of the RCD body it is written - differential switch. On the side surface of the difavtomat case it is written - residual current circuit breaker. Although such inscriptions are not applied on all products, as a rule, I have not seen such markings on Russian manufacturers, and not on all foreign products.
4. Abbreviation on the device
Basically the question how to distinguish an RCD from a difavtomat is set for foreign-made products. If we are talking about domestic products, then there are no questions at all.
On such devices, as a rule, it is written in Russian that this is an RCD (VD) or a differential automatic circuit breaker.
Let me remind you that residual current devices (RCDs) are now correctly called differential switches (SD). Differential circuit breaker - also known as an automatic differential current switch (RCBO).
Let's summarize how to distinguish an ouzo from a difavtomat
By price parameters RCDs and difavtomats are different. This is especially true for imported products. A normal automatic device costs a little less than an RCD included with a regular automatic device.
The quality of imported devices is higher. Domestic ones are also quite good, but they lose in such important characteristics as response time, they are inferior in the reliability of mechanical parts, and they are simply inferior in the quality of housings.
In terms of operational reliability, these two devices are in no way inferior to each other.
Since the difavtomat is a combined device, one of the disadvantages of operation I would note is that when it is triggered, it is difficult to determine what caused the shutdown: overload, short circuit or current leakage. True, the device is developing: some automatic machines are equipped with differential current trigger indicators.
A positive aspect of RCBOs is ease of installation: it is important for an electrician to tighten a couple of screws less in a cramped mounting box. On the other hand, this increases the reliability of the circuit: the fewer connections, the better. But if the device breaks, it must be completely replaced.
In the case of using an RCD in conjunction with a machine gun, the repair process looks cheaper: either one element or another is changed. This must be taken into account when designing your networks, taking into account the risk of certain negative events and their possible frequency.
If we talk about simple apartment wiring diagrams, it doesn’t matter You choose RCBO or RCD+automatic. If we talk about a large private house, then you need to look at which lines to connect to the automatic circuit breaker (for example, a boiler room or utility unit: there are more different loads, which means there are more risks), and which ones to connect to a pair of RCDs + circuit breakers (lighting lines, groups of sockets) .
You can come up with a lot of options for implementing circuits with these devices, the main thing is that you understand and remember why you are doing it.
Not everyone knows what an RCD is, much less a differential circuit breaker. And these are very necessary and important devices that will solve the problem of electrical safety in the house.
RCD- residual current device, also called differential switch ( VD). By monitoring the wiring if any leaks occur, the RCD turns it off. At the same time, without protecting the electrical wiring from overloads or short circuits.
RCDs are used:
- To ensure human protection from direct and indirect electric shock;
- To prevent fire hazards due to current leakage.
Most devices have a metal body. A washing machine, microwave oven, electric oven, and other household appliances may conduct current due to their malfunction.
Wear, mechanical or thermal effects lead to disruption of the conductor insulation, and a short circuit to the metal body of the equipment may occur. In this case, a phase equal to the mains voltage will appear on the housing. Surely everyone has ever felt 
The RCD must be protected by a circuit breaker or fuse. It works if if electrical wiring is used with a protective conductor PE (phase, neutral, ground)
Working in tandem with a machine, it turns out that one device protects against leaks, and the other against overloads.
Without using a grounding system, a person will feel only a short-term shock, equal to the response time of the RCD.
When faulty wiring is used or poor quality installation is carried out, a fire may occur. The RCD will prevent this situation by disconnecting the network. You need to select an RCD with a response setting from 300 to 500 (mA)
Sometimes, the outlet line may be overloaded, and experts recommend purchasing an RCD with a rating one order of magnitude higher than the rated current of the protection device. For example, the input device for an apartment has an indicator of 50 (A), respectively, we install the RCD according to the indicator of 63 (A).
There is a standard range of rated residual currents in RCDs: 6 (mA), 10 (mA), 30 (mA), 100 (mA), 300 (mA) and 500 (mA).
What is a differential machine
In simple terms, a difavtomat is an automatic differential current switch ( RCBO). This device combines the capabilities of an RCD and a circuit breaker. It turns out, two in one.
The difavtomat is used for:
- Protection of the electrical network from overload and short circuit;
- Preventing all kinds of leaks associated with faulty electrical wiring, household appliances and human exposure to voltage.
Types of RCDs and automatic devices
RCDs and difavtomats are divided according to the following criteria:
1.By type of differential current leakage
- Type AC, in which the device instantly responds to an alternating current leak;
- Type A, triggered by AC and DC leakage, a universal option, but more expensive;
- Type IN, which is used for industrial facilities.
2. By time delay
- Selective type S, which is connected when several RCDs are used in a line, and which is triggered if a group RCD turns off;
- Type G it is also selective and has a time delay for operation of 0.06-0.08 (s).
The manufacturer indicates all designations of types of RCDs and automatic devices on the housing
3. By trigger type
- Electromechanical- do not depend on the network, and the source of their operation will be differential current;
- Electronic- depend on the mains voltage, and to operate they need an external source. Manufacturers build an electromagnetic relay into it, thereby disconnecting the load circuit.
4.By number of poles
- Bipolar- used in a single-phase network to prevent fire. Available for rated voltage 230 (V);
- Four-pole- for a three-phase network. Designed for a nominal voltage of 400 (V).
5. By design
- Portable - installed in place of the outlet or connected to it, and household appliances are connected to them;
- Stationary.
How to choose the right RCD and difavtomat
These devices are very similar, but the manufacturers immediately indicate what is in front of you on the front side or on the side of the cover. In stores you will find devices from companies such as IEK, EKF, TDM, ABB, Legrand, Schneider Electric and others.
Their price range may vary depending on the type of work and design. For example, portable RCDs are easy to use, and their price is higher than stationary ones. And a good automatic device costs less than an RCD included with a conventional automatic machine. But the repair process when a RCD with a machine breaks down will be cheaper, since either one or the other element is changed. If the automatic machine breaks down, you will have to replace it entirely. But, ease of installation and reliability of the chain give it an advantage.
When choosing, you need to look at the device’s passport and fire safety certificate, as counterfeits are often found.
You should also pay attention to:
- Labeling. If the rated current value is indicated on the body without other symbols and letters, this is an RCD. If the current value is preceded by a letter B, C or D- This is a differential machine.
- Scheme. Take a careful look at RCD: The oval indicates a differential transformer. On the diagram difavtomat In addition to the oval, you can see the winding of electromagnetic and thermal releases, which reacts to short circuits and overloads. It's simple.
Advice. Choose a difavtomat in those areas where the voltage is high - boiler room, utility unit. RCD + automatic - lighting lines, groups of sockets. If we talk about apartment wiring, then there is no fundamental difference in what to choose.
Bathrooms and bathhouses are places of increased danger, so it is worth using an RCD installation there with a differential current of 10 (mA), with a separate line. When a line is combined, for example, with a corridor, an RCD with a setting of 30 (mA) should be used.
R.S.
Among our readers, there are probably experts who have a deeper knowledge of the intricacies of this issue. We will be glad and grateful if you leave some corrections and clarifications in your comments.
- 40 % deaths Due to household problems with electricity, it occurs among children under 9 years of age.
- 50 % fires occurs due to a short circuit.
- 12 people die every day from fires in residential premises.
- 10 million apartments in Russia are at risk of problems with electricity.
Tragedies occur for many reasons, but the main one is the neglect of protective automation at the planning stage of the home electrical network.
Currently, three levels of protection against electrical problems are used: circuit breakers (CBs), residual current devices (RCDs), differential circuit breakers (DCCBs).
Circuit breakers
They break electrical circuits during a short circuit or increased load on the wiring.
It is important to know: AVs protect against fire and short circuit, but do not protect against electric shock!
Circuit breakers are installed in the distribution board. They group household appliances by power and location in the house. For example, a group of ten incandescent lamps of 100 W each consumes a total current of 1000 W and 4.5 A (the current is also summed up). This means that for this group you need to use a circuit breaker with a rated current of no more than 6 A. If during an accident the load increases above 6 A, the circuit breaker will turn off the damaged section.
It is recommended to install a separate circuit breaker for each power consumption group. For example, for a group of overhead lighting in the kitchen, for a dishwasher or washing machine, for kitchen sockets, etc. This is convenient: if a problem occurs in one of the network sections, it will be that one that will turn off, and not the entire apartment.
The table below shows an example of selecting circuit breakers and RCDs from the Schneider electric Easy9 series, based on consumer power, rated current and type of shutdown.
RCD
When any electrical appliance is turned on, the current in the network increases briefly (inrush current). For some appliances it is smaller (kettle), for others it is larger (refrigerator). This function of the machine prevents false alarms when turning on/off current consumers.
Click on the image to expand the table
An RCD - an automatic shutdown device - saves you from electric shock. This is the second level of security. For example, for a number of reasons, a current leak occurs, and the metal body of the washing machine becomes energized. The body is insulated, and nothing terrible will happen until a person touches it - then the current will pass into the “ground” through the person’s body and cause serious injury. But if an RCD is used to connect the washing machine, then at the moment a current leak appears on the machine body, the automation will operate, the circuit will break and the danger will be eliminated. If a person accidentally touches a live part of the electrical network, the RCD will also turn off the power to that circuit before the person receives an electric shock, thereby saving life and health.
The main criterion for choosing an RCD is its sensitivity to leakage currents (indicated on the housing in mA). The most sensitive ones are 10 mA, these are installed in wet rooms and children's rooms. In other domestic premises, it is customary to use 30 mA devices (see table).
Fire protection RCDs, which have a lower sensitivity to leakage currents - usually 100 or 300 mA, deserve a separate discussion. Such RCDs are installed, as a rule, at the very beginning of the electrical network and prevent situations where a significant leakage current can heat, for example, the sheath of a wire or part of the wall along which this wire is laid and cause a fire. Lower sensitivity allows you to organize coordinated operation with other RCDs installed below and avoid false shutdowns of the electrical network.
Differential circuit breakers
Difavtomats combine the functions of an RCD and a circuit breaker. They are universal devices that protect against both short-circuit current and overload, as well as electric shock (or fire). This solution is more compact than a machine and an RCD separately. This arrangement makes it possible to reduce the size of the electrical panel while providing the required level of protection. In addition, in some cases, the use of automatic machines is MANDATORY. For example, current regulatory documents require the use of a difavtomat at the input of the electrical network of wooden houses.
Now you understand this issue and know how to protect your loved ones and your home. But! When choosing equipment, be sure to consult a specialist! Schneider Electric engineers will be happy to assist you.
The impact of electricity has a detrimental effect not only on human life and health, but also on the entire number of consumers who, without proper protection, fail. Differential protection devices have become widespread. Which is better: ouzo or differential automatic? To answer this question, it is necessary to study them in detail, and then draw conclusions.
Residual current devices
When laying electrical wiring or upgrading it, circuit breakers are not enough. The main criterion is electrical safety, because electricity not only has useful properties, but can also lead to huge problems (financial difficulties, threats to health and life).
To protect electrical wiring, devices and devices, specialized devices are used, which are called differential current devices. They protect not only from current leakage and from exceeding the electrical parameters of the network, but also from short circuits. This is a necessary measure, because you cannot control electricity while, for example, at work. This often leads to equipment failure, accidental fires and fires.
Nowadays, differential automatic devices and RCDs have become widespread. And many people are very concerned about ouzo or difavtomatic - what to choose?
Troubles when using home wiring
Before you begin choosing a differential protection model, you need to find out from what adverse factors the electrical network should be protected.
The main problems of an unsecured network:
Danger at home- electric shock to a person. For example, when touching a pump or microwave oven, the unpleasant effect of current on the human body is felt. This is where the danger lies, because today there will be a weak blow, and after a while the phase will cause a breakdown in the body of the product.
According to electrical safety regulations, a voltage of 220V and a current of 1.5mA are safe for humans. At currents up to 7 mA, convulsive phenomena are felt, and at 10 mA a person is no longer able to tear his hand away from the current-carrying part.
But these values in real life differ significantly. It all depends on the resistance of the human body and the method of touch. Body resistance depends on many factors, here are some of them: air humidity, moisture on the floor, shoes, clothing, genetic characteristics, nutrition and even mood.
Criteria for choosing differential protection
In order to clarify the next problem of choice (difavtomatic or ouzo - which is better?), it is necessary first of all understand their operating principle, scope of application, design features, occupied space, cost, difficulty of repair and connection, troubleshooting, ease of installation.
Design and installation features
For home use, single-phase ouzos are usually used and have a bipolar design. They must be used together with a circuit breaker, because the ouzo protects the electrical network or circuit section from leakage currents, and the circuit breaker protects from overloads and short circuits. This design occupies 3 modules in the panel.
Ordinary single-phase automatic circuit breaker made in 2-module, but there are models that are produced in a single-module design. If there are several difavtomats or several ouzos, then the space savings will be significant.
It is not difficult to install an ouzo or difavtomat - convenient clamps allow you to do this without problems, but there are some nuances here too.
For comparison, diagram 1 shows the switching of a pair of ouzo with an automatic machine and a difavtomat. Therefore, connecting the difavtomat is much simpler.
Scheme 1 - Scheme for comparing the switching of an ouzo+automatic machine and a difavtomatic machine
Diagnostics and maintainability of circuits
Each of the differential protection devices under consideration is designed for circuit break if triggered. To find out the reason why the operation occurred, it is necessary to carry out some diagnostics.
When a pair is installed (uzo and circuit breaker), the problem that has arisen can be immediately identified. When the ouzo was triggered, a current leak occurred on some line. If the circuit breaker has tripped, then there is an overload or short circuit in the electrical network.
But if the automatic transmission is installed, identifying the cause becomes more difficult. Some expensive models are equipped with a special indication that indicates leakage or overload.
Default protection devices may also fail. For example, with frequent triggering for no reason or with a clearly overloaded line. In this case, the thermal protection circuit is most likely faulty (malfunction of the bimetallic plate). In the case of a pair of RCD and AV, as a rule, 1 element fails, which can be replaced, which is cheaper than purchasing a breaker.
Operating principle of RCD and difavtomat
An RCD is used to identify and protect against leakage currents. The principle of operation is based on comparing the magnitudes of currents (incoming and outgoing).
Figure 1 - RCD (Residual current device or differential switch)
RCD device:
- Toroidal transformer with 2 primary windings and one control winding.
- Electromechanical relay (key).
The control winding is connected to the switch, and during normal operation of the device, the currents on the 2 primary coils create magnetic fluxes. Moreover, these coils are wound in opposite directions. When added together, these magnetic fluxes give a resulting magnetic flux in the core equal to zero. However, when a leakage current appears, this rule is violated, and a magnetic flux is formed on the control coil due to a difference in magnetic fluxes other than zero. This magnetic flux causes the switch to operate and the circuit opens. The response time of the RCD (differential switch) is in the range from 0.2 to 0.3 seconds.
Particularly widespread 30 mA devices, and in rooms with high humidity - 10 mA.
A difavtomat or automatic differential current switch (RCCB) combines an RCD and an AV (automatic circuit breaker).
Figure 2 - Difavtomat
Absolutely all RCBOs are superior to RCDs in response speed (0.04 seconds) and allow you to quickly turn off power to sections of the circuit during voltage surges over 250V.
Price
Solving this issue is quite simple. The cost of a pair of RCD and AV is lower than the cost of the automatic device itself. After all, if any element of this pair fails, it is necessary to replace the AV or RCD (cheaper than changing the automatic circuit breaker). It is advisable to immediately purchase high-quality devices, because the stingy pays twice. And when purchasing a high-quality differential protection device, fewer problems arise. The best brands are Schneider Electric, General Electric and ABB.
An example showing how to select a particular device.
A powerful device (15A and 1.5 kW) was purchased, to which a separate power supply line must be connected. For this case, you will need a 16A AV and an RCD (30mA). It is necessary to add up the costs of the devices and compare the resulting cost with the price of the RCBO. If it is necessary to install protection on 8 lines, each of which consists of 4 groups for a pair of RCD and CB: 6 AV * (cost of one CB) + 3 RCD * (cost of 1 RCD).
Nothing can be done for automatic machines, since 8 of them are needed (1 RCBO per 1 line). We calculate the amounts and find that installing RCBOs is much more expensive.
Main advantages and disadvantages
Having clarified the differences between the two differential protection devices, it is possible to formulate a number of advantages and disadvantages.
However, it is quite difficult to find out, because you need to be guided by the specific situation and the parameters of the electrical wiring lines, as well as the devices connected to this network.
The main disadvantages of the difavtomat:
- Diagnostic problem: it is difficult to diagnose the reason for the device’s operation, although there are expensive models that provide this function.
- Financial side: it costs more than an RCD and if it fails, you need to buy a new one.
Disadvantages of RCD:
- High response time relative to RCBOs.
- Takes up more space during installation.
- Must be used together with AB.
Advantages of the automatic machine:
- High response speed.
- Ease of installation.
- Takes up less space in the box.
Advantages of RCD with AV:
- Relatively low price.
- Easy diagnostics.
- Better maintainability.
If we take into account that the reliability of RCD+AV and RCBO is the same (low-cost options are not considered), then the main criterion for choosing a device is, first of all, its cost. After all, everything depends on financial capabilities.
Key aspects to consider when choosing:
- Installation and connection diagrams: not particularly difficult.
- Diagnostics: when connecting the RCBO, finding the cause is not a problem, because there is a light indication.
- There is no need to save on a spacious shield; perhaps someday you will need to draw another line, which also needs to be protected.
Thus, when choosing a specific differential protection device, you need to think about everything, draw up a rough plan for dividing the power supply lines of a residential premises, decide on consumers, calculate the total possible power of consumers for each line and, based on the financial situation, make the final choice. The main difference and main criterion is the price, but you should not save, because this is your safety, as well as minimizing financial problems.
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