Circuit breakers are devices whose task is to protect an electric line from the effects of a powerful current that can cause overheating of the cable with further melting of the insulating layer and fire. An increase in the current strength can be caused by too much load, which occurs when the total power of the devices exceeds the value that the cable can withstand in its cross section - in this case, the machine does not turn off immediately, but after the wire heats up to a certain level. With a short circuit, the current increases many times over a fraction of a second, and the device immediately reacts to it, instantly stopping the supply of electricity to the circuit. In this material we will tell you what types of circuit breakers are and their characteristics.
Circuit breakers: classification and differences
In addition to residual current circuit breakers, which are not used individually, there are 3 types of circuit breakers. They work with loads of different sizes and differ in their design. These include:
- Modular AB. These devices are installed in household networks in which currents of negligible magnitude flow. Usually have 1 or 2 poles and a width in multiples of 1.75 cm.
- Cast switches. They are designed to operate in industrial networks with currents up to 1 kA. They are made in a cast case, which is why they got their name.
- Air electric machines. These devices can be 3 or 4 poles and can handle currents up to 6.3 kA. They are used in electrical circuits with high power installations.
There is another type of circuit breakers for power grid protection - differential. We do not consider them separately, since such devices are conventional circuit breakers, which include an RCD.
Release types
The releases are the main working components of AB. Their task is to break the circuit when the permissible current value is exceeded, thereby stopping the supply of electricity to it. There are two main types of these devices, differing from each other in terms of the release principle:
- Electromagnetic.
- Thermal.
Electromagnetic-type releases provide almost instantaneous operation of the circuit breaker and de-energize a section of the circuit when an overcurrent of a short circuit occurs in it.
They are a coil (solenoid) with a core that is pulled inward under the influence of a large current and forcing the tripping element to operate.
The main part of the thermal release is a bimetallic plate. When a current that exceeds the rated value of the protective device passes through the machine, the plate begins to heat up and, bending to the side, touches the disconnecting element, which is triggered and de-energizes the circuit. The tripping time of the thermal release depends on the magnitude of the overload current passing through the plate.
Some modern devices are equipped as a supplement with undervoltage (zero) releases. They perform the function of switching off the AB when the voltage falls below the limit value corresponding to the technical data of the device. There are also distance releases, with which you can not only turn off, but also turn on AB, even without going to the switchboard.
The presence of these options significantly increases the cost of the device.
Number of poles
As already mentioned, the network circuit breaker has poles - from one to four.
It is not difficult to choose a device for a circuit according to their number, it is enough just to know where different types of AB are used:
- Single-pole networks are installed to protect lines that include sockets and lighting fixtures. They are mounted on a phase conductor without capturing a neutral conductor.
- The two-pole must be included in the circuit to which household appliances with a sufficiently high power are connected (boilers, washing machines, electric stoves).
- Three-pole networks are installed in semi-industrial scale networks, to which devices such as borehole pumps or equipment of a car repair shop can be connected.
- Four-pole AB allows you to protect electrical wiring with four cables from short-circuit and overloads.
The use of machines of different polarity is in the following video:
Circuit breaker characteristics
There is another classification of machines - according to their characteristics. This indicator indicates the degree of sensitivity of the protective device to exceeding the value of the rated current. The corresponding marking will show how quickly the device will react in the event of an increase in current. Some types of AB work instantly, while others will take a certain amount of time.
There is the following marking of devices according to their sensitivity:
- A. Switches of this type are the most sensitive and react instantly to increased load. They are practically not installed in household networks, protecting circuits with high-precision equipment with their help.
- B. These circuit breakers operate when the current rises with a slight delay. Usually they are included in the line with expensive household appliances (LCD TVs, computers and others).
- C. These devices are the most common in household networks. Their disconnection does not occur immediately after an increase in the current strength, but after a while, which makes it possible to normalize it with a slight drop.
- D. The sensitivity of these devices to increasing current is the lowest of all the listed types. They are most often installed in shields at the approach of the line to the building. They provide a safety net for the apartment machines, and if for some reason they do not work, they turn off the general network.
Features of the selection of machines
Some people think that the most reliable circuit breaker is the one that can handle the highest current, which means that it is he who can provide the maximum circuit protection. Based on this logic, an air-type machine can be connected to any network, and all problems will be solved. However, this is not at all the case.
To protect circuits with different parameters, it is necessary to install devices with appropriate capabilities.
Mistakes in the selection of AB are fraught with unpleasant consequences. If you connect a protective device designed for high power to a normal household circuit, then it will not de-energize the circuit, even when the current value significantly exceeds that that the cable can withstand. The insulating layer will heat up, then begin to melt, but the shutdown will not occur. The fact is that the current strength, which is destructive for the cable, will not exceed the nominal AB, and the device will "count" that there was no emergency. Only when the molten insulation causes a short circuit will the machine turn off, but by that time a fire may have already begun.
Here is a table showing the ratings of the machines for various power grids.
If the device is designed for less power than that which the line can withstand and which the connected devices have, the circuit will not be able to work normally. When the equipment is turned on, the AB will constantly knock out, and ultimately, under the influence of high currents, it will fail due to "stuck" contacts.
Clearly about the types of circuit breakers in the video:
Conclusion
The circuit breaker, the characteristics and types of which we have considered in this article, is a very important device that protects an electric line from damage by high currents. Operation of networks not protected by machines is prohibited by the Electrical Installation Rules. The most important thing is to choose the right type of AB, which is suitable for a specific network.
The danger posed by electric shock is known to everyone. Here you can also add the heating of the conductor, which occurs with a loose contact or short circuit. But without electricity, a person can no longer imagine his life, which means that ways are needed to tame this power. For this purpose, various protection devices were created, including automatic machines, the types of which we will consider today.
General characteristics of circuit breakers
Automatic devices are called devices that can open a circuit in the shortest possible time in the event of heating, short circuit or other emergency situations. With correctly selected parameters of the device, there is no doubt that it will react to the slightest excess of the norms and relieve the voltage from the line, thereby protecting not only the person himself, but also his property.
Circuit breakers can differ in their maximum current loads, the number of poles or the principle of operation. Anyone who has come across such equipment knows that the marking must be affixed to its case - B, C or D. The first type can be attributed to low-power devices, while the latter is used more often in industries where current loads are significant. For domestic use, choose the type with the C marking. The number after the letter is an indicator of the maximum current load, after which the device will trip. For example, a VA marked C16 will withstand 16 A without problems, but if the indicator is exceeded, it will open the circuit and remove the voltage.
Speaking about the types of electrical circuit breakers, three main ones can be noted:
- Difautomat.
Let's try to disassemble them in more detail in order to understand the purpose of protective devices.
Automatic switch: features, purpose
A device capable of opening a circuit in the event of a short circuit or network overload (excess of connected equipment). This is the main type of automaton, which has 2 contacts (phase input / output) and works on the principle of an electromagnet, consisting of a solenoid and a rod, as well as a bimetal plate. It turns out that at normal current load, the release operates in normal mode, but when it is exceeded, the rod is pushed out on the solenoid. He, in turn, rests against a bimetallic plate, which opens the contact.
These releases react not only to current overloads, but also to an increase in external temperature, therefore poorly stretched contacts can cause intermittent tripping. They also cope well with emergency shutdown in the event of a fire. But a more interesting type of electrical circuit breakers can be called an RCD.
Residual current devices: differences from VA
The principle of operation of the RCD has completely different functions. There are 4 contacts on the case, 2 of which are for the input / output of the phase conductor, and 2 for the neutral one. Such devices operate on the principle of potential difference. During normal operation of the circuit, the phase with zero is balanced and the RCD operates normally. However, even the slightest leakage current creates an imbalance and the device shuts down automatically. For human protection, this type of machine is better than VA.
Take, for example, the breakdown of a phase wire to the body of any household appliance. Almost everyone knows how unpleasant sensations arise when touching metal in such a case. In this situation, as soon as a person touches the device, the RCD will turn off the power, and the reaction of the device is much faster than that of VA. However, this type of automatic machine does not save from a short circuit - it simply does not react to a short circuit, continuing to work.
For those who want to understand the operation of the RCD in more detail, a short video is presented below.
Video on the topic "Residual current device"
It should be noted that both types of circuit breakers described above and performing completely different functions are optimally installed in pairs. Is it possible to get by with one device? Yes, easily.
Difautomat: what is it, how does it work?
Quite often people do not want to deal with unnecessary switching in the switch cabinet, and sometimes there is simply not enough space to install all the protection systems that were planned. After all, if you look at it, on the DIN rail the RCD takes 2 modular places plus a circuit breaker - in total 3. And if there are several power supply groups, besides, it is necessary to mount an input release, install an electricity meter? It turns out that you will have to give up any protection devices? Completely optional. Instead of RCD and VA, a difavtomat is installed, which combines the functions of both devices.
Such a device is capable of tripping on overcurrent, short circuit or leakage in the circuit. In size, it is similar to an RCD (for 2 places), and sometimes to a VA, which occupies one module. Often it is this factor that becomes decisive when choosing equipment, however, the differential machine also has its drawbacks. Its cost is higher than that of a VA or a residual current device, and if one of the parts fails, you will have to buy it entirely, while the release can be changed separately.
There is a lot of controversy among specialists, which is better - a separate defense or a combined one? Judging by the statistics, there are about the same number of supporters of difavtomats and their opponents. When solving this issue, one should proceed from the possibility of installation. And if a differential machine is chosen, you should not save on the purchase. It is better to buy a quality branded device than to periodically change cheap ones.
Finally
Protection of the power grid is necessary, anyone who has come across a similar issue will agree with this. But it is not enough just to buy the first device that comes along and connect it. It is necessary to carefully calculate all the necessary parameters, weigh the pros and cons in relation to this or that type of machine, and only then make a choice. The range of protective equipment for the home electrical network is quite wide, which means that the solution will not be easy. However, only an informed, thoughtful and correct choice will help protect the life and health of loved ones, as well as the safety of property.
The main types of machines. Types of electrical circuit breakers - modern technologies - advice for all occasions on the site
Surely many of us wondered why circuit breakers so quickly replaced outdated fuses from electrical circuits? The activity of their implementation is justified by a number of very convincing arguments, including the opportunity to buy this type of protection, ideally matching the time-current data of specific types of electrical equipment.
Doubt which machine you need and don't know how to choose the right one? We will help you find the right solution - the article discusses the classification of these devices. As well as important characteristics that you should pay close attention to when choosing a circuit breaker.
To make it easier for you to deal with the machines, the article material is supplemented with visual photos and useful video recommendations from specialists.
The automatic machine almost instantly turns off the line entrusted to it, which excludes damage to the wiring and equipment powered from the network. After a shutdown has been completed, the branch can be restarted immediately without replacing the safety device.
If you have knowledge or experience in performing electrical work, please share it with our readers. Leave your comments about the choice of a circuit breaker and the nuances of its installation in the comments below.
What is a circuit breaker?
Circuit breaker(automatic machine) is a switching device designed to protect the electrical network from overcurrents, i.e. from short circuits and overloads.
The definition of "switching" means that this device can turn on and off electrical circuits, in other words, make their commutation.
Circuit breakers are available with an electromagnetic release that protects the electrical circuit from short circuits and a combined release - when, in addition to an electromagnetic release, a thermal release is used to protect the circuit from overload.
Note: In accordance with the requirements of the PUE, household electrical networks must be protected from both short circuits and overloads, therefore, machines with a combined release should be used to protect household wiring.
Circuit breakers are divided into single-pole (used in single-phase networks), two-pole (used in single-phase and two-phase networks) and three-pole (used in three-phase networks), there are also four-pole circuit breakers (can be used in three-phase networks with TN-S grounding system).
The device and principle of operation of the circuit breaker.
The figure below shows circuit breaker device with combined release, i.e. having both an electromagnetic and a thermal release.
1,2 - respectively the lower and upper screw terminals for connecting the wire
3 - movable contact; 4 - arc-extinguishing chamber; 5 - flexible conductor (used to connect the moving parts of the circuit breaker); 6 - coil of the electromagnetic release; 7 - the core of the electromagnetic release; 8 - thermal release (bimetallic plate); 9 - release mechanism; 10 - control handle; 11 - clamp (for fixing the machine on a DIN rail).
The blue arrows in the figure show the direction of current flow through the circuit breaker.
The main elements of the circuit breaker are electromagnetic and thermal releases:
Electromagnetic release provides protection of the electrical circuit against short-circuit currents. It is a coil (6) with a core (7) located in its center, which is installed on a special spring, the current in normal operation passing through the coil according to the law of electromagnetic induction creates an electromagnetic field that attracts the core inside the coil, but the forces of this electromagnetic field do not enough to overcome the resistance of the spring on which the core is installed.
In the event of a short circuit, the current in the electrical circuit instantly increases to a value several times higher than the rated current of the circuit breaker, this short-circuit current passing through the coil of the electromagnetic release increases the electromagnetic field acting on the core to such a value that its pulling force is enough to overcome the resistance the springs, moving inside the coil, the core opens the movable contact of the circuit breaker, de-energizing the circuit:
In the event of a short circuit (i.e., with an instantaneous increase in current several times), the electromagnetic release cuts off the electrical circuit in a fraction of a second.
Thermal release provides protection of the electrical circuit against overload currents. An overload can occur when electrical equipment is connected to the network with a total power exceeding the permissible load of this network, which in turn can lead to overheating of the wires, destruction of the insulation of the electrical wiring and its failure.
The thermal release is a bimetallic plate (8). Bimetallic plate - this plate is welded from two plates of different metals (metal "A" and metal "B" in the figure below) with different coefficients of expansion when heated.
When a current that exceeds the rated current of the circuit breaker passes through the bimetallic plate, the plate begins to heat up, while the metal "B" has a higher expansion coefficient when heated, i.e. when heated, it expands faster than metal "A", which leads to bending of the bimetallic plate, bending it acts on the release mechanism (9), which opens the movable contact (3).
The tripping time of the thermal release depends on the amount of excess current of the mains of the rated current of the machine, the greater this excess, the faster the release will trip.
As a rule, the thermal release trips at currents 1.13-1.45 times higher than the rated current of the circuit breaker, while at a current exceeding the rated current by 1.45 times the thermal release will turn off the circuit breaker after 45 minutes - 1 hour.
The response time of the circuit breakers is determined by their
With any disconnection of the circuit breaker under load, an electric arc is formed on the moving contact (3), which has a destructive effect on the contact itself, and the higher the current to be switched off, the more powerful the electric arc and the greater its destructive effect quest. To minimize the damage from the electric arc in the circuit breaker, it is directed into the arc chute (4), which consists of separate, parallel-mounted plates, falling between these plates, the electric arc is split and extinguished.
3. Marking and characteristics of circuit breakers.
VA47-29- type and series of the circuit breaker
Rated current- the maximum current of the electrical network at which the circuit breaker is capable of operating for a long time without emergency shutdown of the circuit.
Standard values of rated currents of automatic switches: 1; 2; 3; 4; 5; 6; eight; ten; 13; 16; twenty; 25; 32; 35; 40; 50; 63; 80; 100; 125; 160; 250; 400; 630; 1000; 1600; 2500; 4000; 6300, Ampere.
Rated voltage- the maximum mains voltage for which the circuit breaker is designed.
PKS- ultimate breaking capacity of the circuit breaker. This figure shows the maximum short-circuit current that is able to turn off this circuit breaker while maintaining its operability.
In our case, the PKS indicated 4500 A (Amperes), which means that with a short-circuit current (short-circuit) less than or equal to 4500 A, the circuit breaker is able to open the electrical one and remain in good condition if the short-circuit current is. exceeds this figure, it becomes possible to melt the movable contacts of the machine and weld them to each other.
Tripping characteristic- defines the range of operation of the electromagnetic release of the circuit breaker.
For example, in our case, an automaton with the characteristic "C" is presented, its response range is from 5 · I n to 10 · I n inclusive. (I n - rated current of the machine), i.e. from 5 * 32 = 160A to 10 * 32 + 320, this means that our machine will provide instant circuit disconnection already at currents of 160 - 320 A.
Note:
- Standard response characteristics (provided by GOST R 50345-2010) are characteristics "B", "C" and "D";
- The area of application is indicated in the table in accordance with established practice, however, it may be different depending on the individual parameters of specific electrical networks.
4. Choice of circuit breaker
Note: For a complete methodology for calculating and selecting circuit breakers, see the article: "
Circuit breakers are devices that are responsible for protecting an electrical circuit from damage associated with the effect of a large current on it. Too strong a flow of electrons can damage household appliances, as well as cause overheating of the cable, followed by melting and ignition of the insulation. If the line is not de-energized in time, this can lead to a fire, Therefore, in accordance with the requirements of the PUE (Electrical Installation Rules), the operation of a network in which no electrical circuit breakers are installed is prohibited. AB have several parameters, one of which is the time-current characteristic of the automatic protective switch. In this article, we will explain how category A, B, C, D circuit breakers differ and which networks they are used to protect.
Features of the operation of circuit breakers
Whatever class the circuit breaker belongs to, its main task is always the same - to quickly detect the occurrence of excessive current, and to de-energize the network before the cable and devices connected to the line are damaged.
Currents that can pose a danger to the network are divided into two types:
- Overload currents. Their appearance most often occurs due to the inclusion of devices in the network, the total power of which exceeds that that the line can withstand. Another cause of overload is a malfunction of one or more devices.
- Overcurrents caused by short circuit. A short circuit occurs when the phase and neutral conductors are connected together. They are normally connected to the load separately.
The device and principle of operation of the circuit breaker - in the video:
Overload currents
Their value most often slightly exceeds the rating of the machine, therefore, the passage of such an electric current through the circuit, if it has not lasted too long, does not cause damage to the line. In this regard, instantaneous de-energization is not required in this case; moreover, the magnitude of the electron flux often quickly returns to normal. Each AB is designed for a certain excess of the strength of the electric current at which it is triggered.
The tripping time of the protective circuit breaker depends on the magnitude of the overload: with a slight excess of the norm, it can take an hour or more, and with a significant excess, it can take several seconds.
A thermal release is responsible for turning off the power under the influence of a powerful load, the basis of which is a bimetallic plate.
This element heats up under the influence of a powerful current, becomes plastic, bends and triggers the machine.
Short circuit currents
The flow of electrons caused by the short-circuit significantly exceeds the rating of the protection device, as a result of which the latter immediately trips, turning off the power. An electromagnetic release, which is a solenoid with a core, is responsible for detecting a short circuit and an immediate reaction of the device. The latter, under the influence of an overcurrent, instantly acts on the circuit breaker, causing it to trip. This process takes a split second.
However, there is one caveat. Sometimes the overload current can also be very high, but not caused by a short circuit. How is the apparatus supposed to distinguish between the two?
In the video about the selectivity of circuit breakers:
Here we smoothly move on to the main issue that our material is devoted to. There are, as we have already said, several classes of AB, differing in time-current characteristics. The most common of these, which are used in household electrical networks, are devices of classes B, C and D. Circuit breakers belonging to category A are much less common. They are the most sensitive and are used to protect high-precision devices.
These devices differ from each other in instantaneous tripping current. Its value is determined by the multiplicity of the current passing through the circuit to the rating of the machine.
Tripping characteristics of protective circuit breakers
The AB class, determined by this parameter, is indicated by a Latin letter and is affixed to the body of the machine in front of the number corresponding to the rated current.
In accordance with the classification established by the PUE, circuit breakers are divided into several categories.
Automatic machines of the MA type
A distinctive feature of such devices is the absence of a thermal release in them. Devices of this class are installed in the connection circuits of electric motors and other powerful units.
Overload protection in such lines is provided by an overcurrent relay, the circuit breaker only protects the network from damage as a result of short-circuit overcurrents.
Class A devices
Type A automata, as mentioned, have the highest sensitivity. The thermal release in devices with time-current characteristic A most often trips when the current exceeds the nominal AB by 30%.
The electromagnetic tripping coil de-energizes the network for about 0.05 seconds if the electric current in the circuit exceeds the nominal by 100%. If, for any reason, after doubling the strength of the electron flow, the electromagnetic solenoid does not work, the bimetallic release cuts off the power for 20-30 seconds.
The machines with the time-current characteristic A are included in the lines, during the operation of which even short-term overloads are unacceptable. These include circuits with semiconductor elements included in them.
Class B protective devices
Devices of category B have less sensitivity than those of type A. The electromagnetic release in them trips when the rated current is exceeded by 200%, and the trip time is 0.015 sec. The actuation of the bimetallic plate in a breaker with characteristic B with a similar excess of the AB rating takes 4-5 seconds.
Equipment of this type is intended for installation in lines that include sockets, lighting devices and in other circuits where there is no starting increase in electric current or has a minimum value.
Category C machines
Type C devices are most common in home networks. Their overload capacity is even higher than those previously described. In order for the solenoid of electromagnetic release installed in such a device to operate, it is necessary that the flow of electrons passing through it exceeds the nominal value by 5 times. The thermal release is triggered after a five-fold increase in the rating of the protection device after 1.5 seconds.
The installation of circuit breakers with a time-current characteristic C, as we said, is usually carried out in household networks. They do an excellent job of playing the role of input devices to protect the general network, while category B devices are well suited for individual branches to which outlet groups and lighting fixtures are connected.
This will allow observing the selectivity of the circuit breakers (selectivity), and with a short circuit in one of the branches, the entire house will not be de-energized.
Category D circuit breakers
These devices have the highest overload capacity. For the operation of an electromagnetic coil installed in an apparatus of this type, it is necessary that the electric current rating of the circuit breaker is at least 10 times exceeded.
In this case, the thermal release is triggered after 0.4 seconds.
Devices with characteristic D are most often used in general networks of buildings and structures, where they play a safety role. They are triggered if there was no timely power outage by circuit breakers in separate rooms. They are also installed in circuits with high starting currents, to which, for example, electric motors are connected.
Category K and Z protective devices
Automata of these types are much less common than those described above. Type K devices have a wide range of currents required for electromagnetic tripping. So, for an alternating current circuit, this indicator should exceed the nominal 12 times, and for a constant one - 18 times. The electromagnetic solenoid is triggered in no more than 0.02 seconds. The thermal release in such equipment can operate when the rated current is exceeded by only 5%.
These features are responsible for the use of K-type devices in circuits with an exclusively inductive load.
Devices of type Z also have different operating currents of the electromagnetic tripping solenoid, but the spread is not as great as in AB category K. 4.5 times the nominal.
Devices with characteristic Z are used only in lines to which electronic devices are connected.
Conclusion
In this article, we examined the time current characteristics of protective circuit breakers, the classification of these devices in accordance with the PUE, and also figured out in which circuits devices of various categories are installed. The information obtained will help you determine which protective equipment should be used on the network, based on what devices are connected to it.