In the wiring at any time, various damage to electrical appliances can occur. To reduce the risk of electric shock hazards, household protective devices that perform various functions are used.
The circuit breaker, difavtomat and RCD in the complex increase electrical safety, quickly turn off emergencies, and save people from. However, they have serious differences in operation and design.
To analyze them, we first consider the types of possible faults in the electrical network that eliminate these devices. They may appear:
1.short circuit, which occurs when the electrical resistance of the load is reduced to very small values due to shunting voltage circuits with metal objects;
2.wire overload. Modern powerful electrical appliances cause large currents, which create increased heating of current-carrying conductors in poor-quality wiring. In this process, the insulation overheats and ages, losing its dielectric properties;
To worsen the situation with the appearance of malfunctions can:
old aluminum wiring, laid decades ago using obsolete technologies. It has long been exploited to the limit of its capabilities when powered by modern electrical appliances;
poor-quality installation and the use of coarse protective devices, even in a new electrical circuit.
To simplify the explanation of the differences in protective devices, we will consider only those devices that are designed for a single-phase network, because three-phase designs work in exactly the same way according to the same laws.
Differences of protective devices by purpose
Circuit breaker
The industry produces many varieties of it. They are designed to eliminate the first two types of noted faults. To do this, in their design are installed:
high-speed electromagnetic trip coil, which eliminates the emerging short-circuit currents and the system for extinguishing the resulting electric arc;
a time-delayed thermal release based on a bimetallic plate, which eliminates the resulting overloads within electrical circuits.
The circuit breaker for residential buildings is included in one phase conductor and controls only the currents passing through it. It does not react at all to emerging leakage currents.
Residual current device
RCD in a two-wire circuit is connected through two wires: phase and zero. It constantly compares the currents circulating in them and calculates their difference.
When the current leaving the neutral conductor corresponds in magnitude to that entering the phase wire, then the RCD does not turn off the circuit, it allows it to work. In the event of small deviations of these values that do not affect the safety of people, the residual current device also does not block the power supply.
The RCD removes voltage from the wires suitable for it in the event that a dangerous leakage current occurs inside the controlled circuit that can harm human health or operating electrical equipment. To do this, the residual current device is configured to operate when the current difference reaches a certain setting.
In this way, false alarms are excluded and opportunities are created for reliable operation of the protection to eliminate leakage currents.
However, the design of this device itself does not have any protection against the possible occurrence of short circuit currents and even overloads in a controlled circuit. This explains the fact that the RCD itself must be protected from these factors.
The residual current device is always connected in series with the circuit breaker.
Differential machine
Its device is more complex than that of a circuit breaker or RCD. During operation, it eliminates all three types of faults (short circuit, overload, leakage) that can occur in electrical wiring. The difavtomat has in its design electromagnetic and thermal releases that protect the RCD built into it.
The differential machine is made in one module, it has the functions of an automatic switch and a residual current device combined.
Considering all of the above, we can conclude that further comparison should be made between the characteristics of only two structures:
differential machine;
RCD protection unit with circuit breaker.
It will be technically justified and correct.
Differences in protection by operational characteristics
Dimensions
The modern modular design of devices with the possibility of mounting them on a din rail significantly reduces the space required for their installation inside an apartment or floor panel. But, even this technique does not always exclude the lack of space for equipping electrical wiring with new protective devices. RCDs with an automatic switch are made in autonomous cases and are mounted in two separate modules, and a difavtomat is only one.
This is always taken into account when creating an electrical work project in new homes and shields are selected even with a small margin of internal space for future circuit improvements. But when reconstructing wiring or minor repairs to premises, shields are not always replaced, and lack of space in them can become a problem.
Tasks in progress
At first glance, an RCD with a circuit breaker and a difavtomat solve the same issues. But, let's try to specify them.
Let's say that a block of several sockets is installed in the kitchen to power various devices of unequal power: a dishwasher, a refrigerator, an electric kettle, a microwave oven ... They turn on randomly and create a random load. In certain situations, the power of several operating devices may exceed the nominal value of the protections and create an overcurrent for them.
The installed difavtomat will have to be changed to a more powerful one. When using an RCD, it is enough to replace a cheaper circuit breaker.
When it is necessary to protect one electrical device connected by a separate, dedicated line, it is better to use a differential machine. Simply it should be selected according to the technical characteristics of a particular consumer.
Installation work
There are no big differences in attaching one or two modules to a din-rail. But when the wires are connected, the amount of work becomes more.
If the difavtomat and RCD cut into the phase and zero wires, then jumpers will also need to be laid to the circuit breaker to connect to the phase wire in series with the RCD. In certain cases, this can complicate the assembly of the circuit.
Quality and reliability
There is a certain opinion among some electrical practitioners that the durability and performance of protections depend not only on the factory assembly by their manufacturer, but also on the complexity of the design, the number of parts included in the design, the adjustment and refinement of their technologies.
The difavtomat is more complicated, it requires more operations to set up the interaction of parts, and on this point it can somewhat lose to RCD designs of the same manufacturer.
However, to apply this technique to all manufactured devices, to put it mildly, is not entirely correct, although many electricians abuse this. This is a rather controversial statement and it is not always confirmed in practice.
Maintainability and replacement
Breakdown can occur in any protective device. When it cannot be fixed on the spot, you will need to purchase a new device.
Buying a difavtomat is more expensive. In the case of RCD operation with a circuit breaker, one of the devices will remain intact and will not require replacement. And this is a significant cost savings.
In the event of a breakdown of any protective device, the consumers fed through it are turned off. In the event that the RCD is faulty, its circuits can be temporarily bypassed and powered through the circuit breaker. But, when the difavtomat is faulty, this will not work. It will need to be replaced with a new one or a circuit breaker delivered for a while.
Working conditions in different situations
The leakage current control circuit for an RCD and a differential automaton can be performed on a different element base using:
electromechanical relay design that does not require an additional power source for logic operation;
electronic or microprocessor technologies that require a power supply and a stabilized voltage from it.
They work in the same way in the normal state of suitable voltage circuits. But, as soon as a malfunction occurs in the circuit, for example, break the contact of one of the wires, say, zero, as they will immediately be visible. They work better and more reliably in the outdated two-wire circuit.
Determining the cause of a protection trip
After the RCD trips, it is immediately clear that leakage currents have occurred in the circuit and it is necessary to check the insulation resistance of the protected area.
When the circuit breaker has worked, the reason lies in the overload of the circuit or the resulting short circuit.
But after turning off the differential machine of most models, it will take longer to look for the reason for removing the voltage and deal with both the insulation resistance of the electrical wiring and the loads created inside the circuit. It is impossible to immediately determine the cause.
However, now it is possible to use expensive designs of difavtomatov with indicators of signaling the operation of a certain type of protection.
Differences in markings on the case
Despite the identical appearance of the RCD and difavtomat (identical case, "Test" button, manual switch lever, similar terminal blocks for installing wires), it is enough to simply deal with them according to the diagrams and inscriptions made on their front side.
The plates of the device always indicate the nominal values of its load and the controlled leakage current, the operating voltage in the wiring, and the internal connection of the elements.
For both devices, the diagrams show a differential current transformer and the circuits that it controls. The residual current device does not have circuit breaker overcurrent protections and they are not displayed. And they are shown on the body of the difavtomat.
Devices of domestic manufacturers are marked so that the buyer can easily navigate in the selected models. Right on the buildings you can see in a conspicuous place the inscription "Difavtomat". The RCD marking is found on the back wall.
The designation "VD" on the plate informs us that we have differential switch(correct technical name), which reacts exclusively to leakage currents and does not protect against overcurrent and short circuit. They are marked with RCD.
The inscription "AVDT" (circuit breaker differential current) begins with the letter "A" and emphasizes the presence of circuit breaker functions. In this way, a diphatomate is designated in the technical documentation.
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 shield
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 particular 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, Jacuzzi bathtubs, 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 that protects 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.
All electrical appliances are different from each other, but the devices can perform similar functions. Today we will discuss difautomats and RCDs, what is the difference and what is their principle of operation. First, we consider the question of what each of these devices is.
RCD, in simple terms, is a protected shutdown device installed in apartments and in places with the risk of a sudden change in electrical voltage. The advantages and functions of this device include the ability to recognize the difference and strength of the current. In the case when there is an increase in the current passing through the device, the system simply opens the network, which allows you to stop the circuit, as a result of the occurrence of a fire hazard or electric shock. Often this device consists of several elements, each of which is responsible for a specific function.
The differential circuit breaker has a significant difference from the RCD, but their task is similar. So, this device is a combination of an RCD and an ordinary machine into one. This equipment is used to prevent leakage of electricity, prevent short circuit and network overload.
Differential circuit breaker
This device contains thermal and modular protection, which creates the maximum comprehensive security against all possible dysfunctions.
Answering the question of how an RCD differs from a difavtomat, it is important to highlight that the first device performs a protective task only in the presence of voltage leakage from the wiring. Such equipment will be able to turn off the power directly at the moment of risk and the occurrence of a short circuit. The design of the device plays the role of a power relay in the electricity circuit.
The main part of homeowners does not give a damn what they have installed in the electrical box - a simple or differential machine. Relying on electricians of dubious qualifications when developing an electrical network project, such citizens risk getting problems in terms of electrical safety. Therefore, it makes sense to study the functional features and differences of the units that protect not only the networks of the house, but also the health of the residents themselves.
What are the differences in the principle of operation of a residual current device and a difavtomat
We will not consider in detail the design and operation of these devices. However, the information provided will be enough to figure out exactly what is installed in the shield and how secure it will be in the future. Of course, experienced electricians know such details thoroughly, but ordinary consumers will be interested. The topic is especially relevant in the implementation of the modernization of household electrical networks: repair of wiring, , shield installation.Outwardly, it is almost impossible to understand how an RCD differs from a residual current circuit breaker. They are similar, but perform different functions:
- Residual current device- comparing the amount of current suitable for the electric consumer and coming from it, the device determines the level of leakage. When the difference in current values reaches life-threatening scales (on average it is 30 mA), then the protective device will turn off the voltage. This not only saves a person from electrical injury when touching damaged equipment, but also effectively prevents a fire when the conductors are heated during a leak.
- Difamat- This is a unique design that combines an automatic machine and the already mentioned RCD. Thus, the differential machine provides protection for electrical wiring from overloads and short circuits, as well as from the occurrence of current leaks.
In general, the residual current device and the principle of operation of its circuit protects against electric shock and wiring leaks accompanied by fire. Many users find that by installing this switch, they are completely protected. Not at all, this is not so, unlike the difavtomat, it is not able to protect the network from overload and short circuits.
Speaking in an accessible language, such a switching device monitors the presence of current leakage from the main consumers. When the insulation is damaged, the circuit will react and shut down the network. However, RCD has a number of disadvantages:
- With the simultaneous inclusion of a number of powerful electrical consumers, an overload is created, and the unit will not work.
- If you connect the phase and zero while the residual current device is operating, i.e. organize a large short circuit, then the device will also not turn off the network.
- When the "neutral" is turned off, the element does not work, at this time there is voltage in the phase conductor, which is dangerous.
- The unit will not be able to work if the voltage in the network drops below the nominal value. The electronic type of devices is completely dependent on the availability of supply energy, their mechanism operates from a controlled network or an external power supply.
conclusions
The listed points are quite enough to understand how the RCD differs from the differential circuit breaker, without delving into the features of their design. Summing up, it is important to note that the residual current device is not able to protect the network from a short circuit or overload. Therefore, it is always included in the circuit in series with a conventional machine, so that one component protects against leaks, and the second against short circuits and overloads.
Using difavtomat, you can get rid of the described situations. It is guaranteed to turn off the network when a person directly touches energized equipment. Damage to the insulation and contact of current-carrying lines with the housing also causes this switching device to operate.
External factor: how does an RCD visually differ from a residual current circuit breaker
Outwardly, both devices are very similar: the case and switch, test button, specific designations are similar. But more attentive comrades will immediately find differences:
- The diagrams shown are different.
- Tumblers are different.
- Each device has its own letter designations.m
We studied the functional differences above, now let's look at electrical appliances visually.
Current marking
Any node of the circuit meets certain technical characteristics. For the devices that are considered here, the main parameters are considered to be the rated leakage current and the rated operating current. For example, let's take two switches rated for 16A:
- On the case of the RCD, only the number (rated current) and the unit of measurement - 16A are indicated in large characters.
- On the body of the difavtomat before the numbers there is a Latin letter, it can be B, C or D. For example, the letter C indicates the type of electromagnetic and thermal releases.
Image of electrical circuit
To understand the difference, it is not at all necessary to study the device of each residual current device and the principle of their operation, a close look at the circuit on the case is enough. At first glance, the images are similar, but we will not study the details of the circuitry - we will only determine the main differences: 
- The RCD circuit contains an oval, which indicates a differential transformer that responds to leakage. There is also an electromechanical relay that opens and closes the circuit, a contact group for connecting wires.
- On the difavtomat diagram, another designation is electromagnetic and thermal releases that respond to short-circuit and overload currents.
Now you can easily determine the type of device by looking at the schematic image on the case. If releases are shown, then this is clearly a differential machine.
Name
Some manufacturers, knowing about the problem that we are analyzing, write the name on the case:
- On the side plane of the residual current device, it is written - a differential switch (RCD).
- On the side of the body of the difavtomat it is written - a differential current switch (RCD).
Unfortunately, not all foreign products have such a marking, but Russian manufacturers, as a rule, apply the type of device. For the most part, the question of how a standard RCD differs from a residual current circuit breaker concerns foreign-made products.
Summing up the results
The cost of switching devices also differs, to a greater extent this applies to branded equipment. The price of a good difavtomat is slightly less than an RCD complete with a classic automatic. 
The quality of imported samples is an order of magnitude higher. Russian ones are also not bad, but they are inferior in such categories as response time, mechanical stability and case quality. In terms of reliability, these devices are in no way inferior to each other.
Given that the differential machine is a combined design, then among the shortcomings it is worth noting the difficulty of determining the cause of the shutdown. It is not clear what it was: current leakage, short circuit or overload. However, technologies are developing, some models of RCBOs are already equipped with a residual current trip indicator.
A positive feature of the difavtomat is ease of installation. Sometimes, especially in a tight shield, it is especially important to tighten two screws less. Moreover, this improves the build quality of the chain. However, in the event of a breakdown, the assembly must only be completely replaced.
When used in an RCD circuit paired with a conventional machine, the repair procedure is cheaper, because only one of the elements has to be changed. This point is important to consider when designing networks.
If we consider the elementary schemes of apartment wiring, then there is no fundamental difference in the choice. In a private house, you need to determine where it is more rational to insert a difavtomat, and where a residual current device. For example, in a boiler room or a workshop, the loads are large, therefore, there is a reason for an RCBO, and for socket lines, a set of an automatic machine and an RCD is enough.
The main difference between the RCD (it is sometimes called a difrele) and the difautomat lies in the decoding of the devices: the RCD is a shutdown protection device, the difavtomat is a differential (i.e., in this case, multifunctional) circuit breaker.
The technical principle of operation of the RCD, difavtomat
A protective device (RCD) is an electrical device, which includes a module for detecting the difference in currents that flow through the device. That is, if this difference does not correspond to the specified value, the contacts will open. To ensure this process, separate elements are included in the RCD that can detect, measure the differential current and “make a decision” about opening contacts. The last operation is performed by a disconnector that does not contain elements for protecting the electrical circuit from short circuits and overloads.
Difaavtomat, in fact, is a block in which an RCD and a disconnect device are combined. The machine protects the electrical circuit from current leakage (like an RCD) and at the same time interrupts the supply of electricity in the event of a short circuit (short circuit) or overloads. The performance of such functions is ensured by the presence of protection against overheating and overcurrents in the difavtomat, which guarantees the protection of the circuit and equipment.
The difference between difavtomat and RCD
The function of the protective device is to turn off the electrical circuit only in the event of a current leakage, i.e. it's just a device plugged into the network that needs protection. The RCD is a module that detects current leakage (for example, if the insulation is damaged) and instructs the power mechanism to turn off the circuit. At the same time, the RCD cannot protect the network from overloads or short circuits. Simply put, if a short circuit occurs in your wiring or all load standards are exceeded, all wires will burn out along with the RCD.
A differential machine is an electrical assembly that includes both current leakage protection and short circuit protection, plus overloads. At the same time, the difavtomat protects itself. Both devices can be distinguished visually. On the difrel there is a designation in large letters; for example, "16A", indicating the rated current. If on the body of the device there is a Latin letter in front of a large number, for example, “C16”, then you have a difavtomat in front of you (“C” characterizes the type of release designed for 16A). If the devices have designations in Russian, then “VD” will mean that you have an RCD, but if AVDT is written, then this is a “differential type circuit breaker”.
