What is a circuit breaker?
Circuit breaker(automatic) is a switching device designed to protect the electrical network from overcurrents, i.e. against short circuits and overloads.
The definition of "switching" means that this device can turn on and off electrical circuits, in other words, switch them.
Circuit breakers come with an electromagnetic release that protects the electrical circuit from short circuits and a combined release - when, in addition to the electromagnetic release, a thermal release is used that protects the circuit from overload.
Note: In accordance with the requirements of the PUE, household electrical networks must be protected from both short circuits and overload, therefore, to protect home electrical wiring, machines with a combined release should be used.
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 a 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 electromagnetic and thermal release.
1.2 - respectively, the lower and upper screw terminals for connecting the wire
3 - moving contact; 4 - arc chute; 5 - flexible conductor (used to connect the moving parts of the circuit breaker); 6 - electromagnetic release coil; 7 - the core of the electromagnetic release; 8 - thermal release (bimetallic plate); 9 - release mechanism; 10 - control handle; 11 - latch (for mounting 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 mounted 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, however, 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 greater 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 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 by several times), the electromagnetic release switches 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 allowable 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 soldered 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 exceeding 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 the curvature of the bimetallic plate, bending it acts on the release mechanism (9), which opens the moving contact (3).
The response time of the thermal release depends on the magnitude of the excess current of the power supply network of the rated current of the machine, the greater this excess, the faster the release will operate.
As a rule, the thermal release is triggered at currents 1.13-1.45 times the rated current of the circuit breaker, while at the current 1.45 times the rated current, the thermal release will turn off the machine after 45 minutes - 1 hour.
The operating time of 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 disconnected current, the more powerful the electric arc and the greater its destructive air. action. To minimize the damage from the electric arc in the circuit breaker, it is directed to the arc chute (4), which consists of separate, parallel plates, falling between these plates, the electric arc is crushed and damped.
3. Marking and characteristics of automatic switches.
BA47-29— type and series of circuit breaker
Rated current- the maximum current of the electrical network at which the circuit breaker is able to operate for a long time without emergency shutdown of the circuit.
Standard values of rated currents of circuit breakers: 1; 2; 3; four; 5; 6; eight; ten; 13; 16; twenty; 25; 32; 35; 40; fifty; 63; 80; 100; 125; 160; 250; 400; 630; 1000; 1600; 2500; 4000; 6300, Amp.
Rated voltage- the maximum mains voltage for which the circuit breaker is designed.
PCS- 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 performance.
In our case, the PKS is indicated as 4500 A (Amps), 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 exceeds this figure, it becomes possible to melt the moving contacts of the machine and weld them to each other.
Tripping characteristic- determines the operating range of the electromagnetic release of the circuit breaker.
For example, in our case, an automatic machine with a 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 \u003d 160A to 10 * 32 + 320, this means that our machine will provide instant circuit shutdown already at currents of 160 - 320 A.
Note:
- The standard response characteristics (provided by GOST R 50345-2010) are characteristics "B", "C" and "D";
- The scope is indicated in the table according to established practice, however, it may be different depending on the individual parameters of specific electrical networks.
4. Circuit breaker selection
Note: Read the full methodology for calculating and selecting circuit breakers in the article: "
Circuit breakers are devices that provide wiring protection under short circuit conditions, when a load is connected with indicators exceeding the set values. They should be chosen with special care. It is important to consider the types of circuit breakers, their parameters.
Automatic machines of different types
Characteristics of machines
When choosing a circuit breaker, it makes sense to focus on the characteristics of the device. This is an indicator by which you can determine the sensitivity of the device to a possible excess of current values. Different types of circuit breakers have their own marking - it is easy to understand from it how quickly the equipment will respond to excess current values to the network. Some switches respond instantly, others activate over a period of time.
- A - marking, which is affixed to the most sensitive models of equipment. Automatic machines of this type immediately register the fact of overload and quickly respond to it. They are used to protect equipment characterized by high accuracy, but in everyday life they are almost impossible to meet.
- B - characteristic, which have switches that operate with an insignificant delay. In everyday life, switches with the appropriate characteristic are used together with computers, modern LCD TVs and other expensive household appliances.
- C - a characteristic of automata, which are most widely used in everyday life. The equipment begins to function with a slight delay, which is enough for a delayed response to registered network congestion. The network is turned off by the device only if it has a fault that really matters
- D is a characteristic of switches that have a minimum sensitivity to exceeding current indicators. Basically, such devices are used as part of the supply of electricity to the building. They are installed in shields, almost all networks are under their control. Such devices are chosen as a fallback option, since they are activated only if the machine does not turn on in time.
All parameters of circuit breakers are written on the front
Important! Experts believe that the ideal performance of circuit breakers should vary within certain limits. Maximum - 4.5 kA. Only in this case, the contacts will be under reliable protection, and current discharges will be discharged in any conditions, even if the established indicators are exceeded.
Types of machines
The classification of circuit breakers is based on their types and features. As for the types, we can distinguish the following:
- Rated breaking capacity - this is the resistance of the contacts of the switch to the effects of currents with high rates, as well as to the conditions in which the circuit is deformed. Under such conditions, the risk of burning increases, which is neutralized by the appearance of an arc and an increase in temperature. The higher the quality and durability of the equipment material, the higher are its corresponding abilities. Such switches are more expensive, but their characteristics fully justify the price. Switches have a long service life, do not require regular replacement
- Rating calibration - we are talking about the parameters in which the equipment operates in normal mode. They are installed at the stage of equipment production, and are not regulated already in the process of its use. This characteristic allows you to understand how strong overloads the device can withstand, the period of time of its operation in such conditions
- Setpoint - usually this indicator is displayed as a marking on the equipment case. We are talking about the maximum current values in non-standard conditions, which, even with frequent shutdowns, will not have any effect on the functioning of the device. The setting is expressed in current units, marked with Latin letters, digital values. The numbers, in this case, display the face value. Latin letters can be seen in the marking only of those machines that are made in accordance with DIN standards
This article continues a series of publications on electrical protection apparatus- circuit breakers, RCDs, difautomats, in which we will analyze in detail the purpose, design and principle of their operation, as well as consider their main characteristics and analyze in detail the calculation and selection of electrical protection devices. This cycle of articles will be completed by a step-by-step algorithm, in which the complete algorithm for calculating and selecting circuit breakers and RCDs will be briefly, schematically and in a logical sequence considered.
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Well, in this article we will understand what a circuit breaker is, what it is intended for, how it works and consider how it works.
Circuit breaker(or usually just “automatic”) is a contact switching device that is designed to turn on and off (i.e. for switching) an electrical circuit, protect cables, wires and consumers (electrical appliances) from overload currents and from short circuit currents.
Those. The circuit breaker performs three main functions:
1) circuit switching (allows you to turn on and off a specific section of the electrical circuit);
2) provides protection against overload currents by turning off the protected circuit when a current exceeding the allowable current flows in it (for example, when a powerful device or devices are connected to the line);
3) disconnects the protected circuit from the supply network when large short-circuit currents occur in it.
Thus, the automata simultaneously perform the functions protection and features management.
According to the design, three main types of circuit breakers are produced:
— air circuit breakers (used in industry in circuits with high currents of thousands of amperes);
— molded case circuit breakers (designed for a wide range of operating currents from 16 to 1000 Amperes);
— modular circuit breakers , the most known to us, to which we are accustomed. They are widely used in everyday life, in our houses and apartments.
They are called modular because their width is standardized and, depending on the number of poles, is a multiple of 17.5 mm, this issue will be discussed in more detail in a separate article.
We, on the pages of the site, will consider exactly modular circuit breakers and residual current devices.
The device and principle of operation of the circuit breaker.
The thermal release does not operate immediately, but after some time, allowing the overload current to return to its normal value. If during this time the current does not decrease, the thermal release trips, protecting the consumer circuit from overheating, melting of the insulation and possible ignition of the wiring.
An overload can be caused by connecting powerful devices to the line that exceed the rated power of the protected circuit. For example, when a very powerful heater or electric stove with an oven is connected to the line (with a power exceeding the calculated power of the line), or several powerful consumers at the same time (electric stove, air conditioner, washing machine, boiler, electric kettle, etc.), or a large number at the same time included appliances.
Short circuit the current in the circuit instantly increases, the magnetic field induced in the coil according to the law of electromagnetic induction moves the solenoid core, which activates the release mechanism and opens the power contacts of the circuit breaker (i.e. moving and fixed contacts). The line opens, allowing you to remove power from the emergency circuit and protect the machine itself, the wiring and the shorted electrical appliance from fire and destruction.
The electromagnetic release is activated almost instantly (about 0.02 s), unlike the thermal release, but at much higher current values (from 3 or more nominal current values), so the wiring does not have time to heat up to the melting temperature of the insulation.
When the circuit contacts open, when an electric current passes through it, an electric arc occurs, and the greater the current in the circuit, the more powerful the arc. The electric arc causes erosion and destruction of the contacts. To protect the contacts of the circuit breaker from its destructive action, the arc that occurs at the moment of opening the contacts is directed to arc chute (consisting of parallel plates), where it is crushed, damped, cooled and disappears. When the arc burns, gases are formed, they are discharged outward from the body of the machine through a special hole.
The machine is not recommended to be used as a conventional circuit breaker, especially if it is turned off when a powerful load is connected (i.e. at high currents in the circuit), as this will accelerate the destruction and erosion of the contacts.
So let's recap:
- the circuit breaker allows you to switch the circuit (by moving the control lever up - the machine is connected to the circuit; moving the lever down - the machine disconnects the supply line from the load circuit);
- has a built-in thermal release that protects the load line from overload currents, it is inertial and works after a while;
- has a built-in electromagnetic release that protects the load line from high short-circuit currents and works almost instantly;
- contains an arc quenching chamber, which protects the power contacts from the damaging effects of an electromagnetic arc.
We have analyzed the design, purpose and principle of operation.
In the next article, we will look at the main characteristics of the circuit breaker that you need to know when choosing it.
See The design and principle of operation of the circuit breaker in video format:
Useful articles
It is easier and cheaper to prevent the fire-hazardous consequences of destruction than to complain bitterly about the measures not taken. Prevention of ignition of the electrical network consists in the installation of protective equipment. In the last century, the function of protecting against short circuits and against the danger of overload was entrusted to porcelain fuses with replaceable fuses, then to automatic plugs. However, due to a significant increase in the load on power lines, the situation has changed. It's time to replace outdated devices with reliable machines. In order for the choice of a circuit breaker to end with the acquisition of a device with the appropriate characteristics, information about a number of electrical nuances is required.
Why do we need automatics?
Circuit breakers are devices designed to protect the power cable, more precisely, its insulation from melting and integrity violations. Automatic machines do not protect the owners of equipment from shock and do not protect the equipment itself. For these purposes, an RCD is equipped. The task of the automata is to prevent overheating, which accompanies the flow of overcurrents to the entrusted section of the circuit. Thanks to their use, the insulation will not be melted and damaged, which means that the wiring will operate in normal mode without the threat of fire.
The operation of circuit breakers is to open the electrical circuit in the event of:
- the appearance of TKZ (further short-circuit currents);
- overload, i.e. passage through the protected section of the network of currents, the strength of which exceeds the permissible operational value, but is not a TKZ;
- a noticeable decrease or complete disappearance of tension.
The automata guard the section of the chain following them. In other words, they are set on the input. They protect the lines of lighting and sockets, the mains for connecting household equipment and electric motors in private homes. These lines are laid with a cable of various sections, because equipment of different capacities is powered by them. Therefore, to protect network sections with unequal parameters, protection devices with unequal capabilities are needed.
If you want to know how to install socket boxes, we advise you to read the article
It would seem that it is possible without too much trouble to purchase the most powerful automatic shutdown devices for installation on each of the lines. The step is fundamentally wrong! And the result of it will lay a direct "path" to the fire. Protection against the vagaries of electric current is a delicate matter. Therefore, it is better to learn how to choose a circuit breaker, and install an apparatus that breaks the circuit when a real need arises.
Attention. An oversized circuit breaker will carry currents that are critical to the wiring. It will not turn off the protected section of the circuit in a timely manner, due to which the cable insulation will melt or burn.
Automatic machines with underestimated characteristics will also present a lot of surprises. They will endlessly break the line when the equipment is started and eventually break due to repeated exposure to too large currents. Contacts are soldered, which is called "sticky".
The design and principle of operation of the machine
It will be difficult to make a choice without understanding the circuit breaker device. Let's see what is hidden in a miniature box made of refractory dielectric plastic.
Releases: their types and purpose
The main working bodies of automatic switches are releases that break the circuit in case of exceeding the standard operating parameters. The releases differ in the specifics of their action and in the range of currents to which they must respond. Their ranks include:
- electromagnetic releases, almost instantly responding to the occurrence of TKZ and "cutting off" the protected section of the network in hundredths or thousandths of a second. They consist of a coil with a spring and a core, which is drawn in by the action of overcurrents. Retracting, the core strains the spring, and it makes the release device work;
- thermal bimetal releases acting as an overload barrier. They undoubtedly also react to TKZ, but they are required to perform a slightly different function. The task of thermal counterparts is to break the network in the event that currents pass through it that exceed the maximum operating parameters of the cable. For example, if a 35A current flows through the wiring intended for transportation of 16A, the plate consisting of two metals will bend and cause the machine to turn off. Moreover, she will courageously “hold” 19A for more than an hour. But 23A will not be able to “endure” for an hour, it will work earlier;
- semiconductor releases are rarely used in household machines. However, they can serve as a working body of a protective switch at the input to a private house or on the line of a powerful electric motor. The measurement and fixation of the anomalous current in them is carried out by transformers, if the device is installed on an AC network, or choke amplifiers, if the device is connected to a DC line. Disconnection is carried out by a block of semiconductor relays.
There are also zero or minimum releases, most often used as an addition. They disconnect the network when the voltage drops to any limit value specified in the data sheet. A good option are remote releases that allow you to turn off and turn on the machine without opening the control cabinet, and locks that fix the “off” position. It is worth considering that equipping with these useful additions significantly affects the price of the device.
Automatic machines used in everyday life are most often equipped with a well-functioning combination of an electromagnetic and thermal release. Devices with one of these devices are much less common and used. Nevertheless, combined-type circuit breakers are more practical: two in one is more profitable in every sense.
Extremely important additions
There are no useless components in the design of the circuit breaker. All components work diligently in the name of a common safety cause, these are:
- an arcing device mounted on each pole of the machine, of which there are from one to four pieces. It is a chamber in which, by definition, the electric arc that occurs when the power contacts are forced to open is extinguished. Copper-plated steel plates are located in parallel in the chamber, dividing the arc into small parts. The fragmented threat to the fusible parts of the machine in the arc extinguishing system cools down and completely disappears. Combustion products are discharged through gas outlet channels. An addition is a spark arrester;
- a system of contacts subdivided into fixed, built into the housing, and movable, pivotally attached to the semi-axes of the levers of the opening mechanisms;
- calibration screw, with which the thermal release is adjusted in the factory;
- a mechanism with a traditional inscription "on / off" with the corresponding function and with a handle intended for implementation;
- connection terminals and other devices for connection and installation.
Here is what the process of extinguishing the arc looks like:
Let's dwell a little on the power contacts. The fixed version is brazed with electromechanical silver optimizing the electrical durability of the switch. When an unscrupulous manufacturer uses a cheap silver alloy, the weight of the product decreases. Sometimes silver plated brass is used. “Substitutes” are lighter than standard metal, therefore a high-quality device of a reputable brand weighs somewhat more than the “left” counterpart. It is important to note that when replacing the silver soldering fixed contacts with cheap alloys, the resource of the machine is reduced. It will withstand less cycles of turning off and then turning on.
Decide on the number of poles
It has already been mentioned that this protection device can have from 1 to 4 poles. Choosing the number of poles of the machine is as easy as shelling pears, because it all depends on its purpose of use:
- a single-pole machine will perfectly cope with the protection of lighting lines and sockets. Mounted only on the phase, no zeros!;
- a two-pole switch will protect the cable that feeds electric stoves, washing machines and water heaters. If there are no powerful household appliances in the house, they put it on the line from the shield to the entrance to the apartment;
- a three-pole device is required for three-phase wiring equipment. This is already semi-industrial scale. In everyday life, there may be a line of a workshop or a borehole pump. A three-pole device must not be connected to a ground wire. He must always be in full combat readiness;
- four-pole circuit breakers are used to protect four-wire wiring from fire.
If it is planned to protect the wiring of an apartment, bath, house with the help of two-pole and single-pole circuit breakers, a two-pole device is installed first, then a single-pole device with a maximum rating, then in descending order. The principle of "ranking": from a more powerful component to a weak, but sensitive one.
Marking - information for reflection
We figured out the device and the principle of operation of the machines. Learned why. Now let's boldly proceed to the analysis of the markings affixed to each circuit breaker, regardless of the logo and country of origin.
The main reference point is the denomination
Because the purpose of acquiring and installing the machine is to protect the wiring, then first of all you need to focus on its characteristics. The current flowing through the wires heats the cable in proportion to the resistance of its current-carrying core. In short, the thicker the core, the greater the current can pass through it without melting the insulation.
In accordance with the maximum value of the current transported by the cable, the rating of the automatic shutdown device is selected. You don’t need to calculate anything, the interdependent values \u200b\u200bof electrical installation devices and wiring by caring electricians have long been summarized in the table:
Tabular information should be somewhat adjusted according to domestic realities. The prevailing number of household sockets is designed to connect a wire with a core of 2.5 mm², which, according to the table, implies the possibility of installing a machine with a rating of 25A. The real value of the outlet itself is only 16A, which means you need to buy a circuit breaker with a rating equal to the rating of the outlet.
A similar adjustment should be made if there is any doubt about the quality of the existing wiring. If there is a suspicion that the cable cross-section might not correspond to the size specified by the manufacturer, it is better to play it safe and take an automatic machine, the nominal value of which is one position less than the table indicator. For example: according to the table, an automatic machine for 18A is suitable for protecting the cable, but we will take it for 16A, because we bought the wire from Vasya on the market.
Calibrated characteristics of the nominal value of the device
This characteristic is the operating parameters of the thermal release or its semiconductor counterpart. It is a coefficient, by multiplying by which we get the current strength during overload, which the device may or may not hold for a certain period of time. The value of the calibrated characteristic is set during the production process, it is not subject to adjustment at home. Pick it up from the standard range.
The calibrated characteristic indicates how long and what kind of overload the machine can withstand without disconnecting the circuit section from the power supply. Usually these are two numbers:
- the smallest value indicates that the machine will pass current with parameters exceeding the standard for more than an hour. For example: a 25A machine will pass a current of 33A for more than an hour without disconnecting the protected section of the wiring;
- the largest value is the limit beyond which the shutdown will occur in less than an hour. The device indicated in the example will quickly turn off at a current of 37 or more amperes.
If the wiring runs in a strobe formed in a wall with impressive insulation, the cable will practically not be cooled during overload and the accompanying overheating. So, in an hour, the wiring can be badly damaged. Maybe no one will immediately notice the result of the excess, but the service life of the wires will be significantly reduced. Therefore, for hidden wiring, we will look for a switch with minimal calibration characteristics. For the open version, you can not particularly get hung up on this value.
Setpoint - indicator of instantaneous operation
This figure on the case is a characteristic of the operation of the electromagnetic release. It indicates the limiting value of the anomalous current strength, which, with repeated shutdowns, will not affect the performance of the device. It is normalized in units of current, and is indicated in numbers or Latin letters. With numbers, everything is extremely simple: this is the face value. But the hidden meaning of the letter designations is worth finding out.
Letters are affixed on machines made according to DIN standards. They denote the multiplicity of the maximum current that occurs when the equipment is turned on. A current that is several times higher than the operating characteristics of the circuit, but does not cause a shutdown and does not render the device unusable. It is simpler, how many times the switching current of the equipment can exceed the rating of the device and cable without threatening consequences.
For circuit breakers used in everyday life, these are:
- AT- designation of automata capable of responding without their own damage to currents exceeding the nominal value in the range from 3 to 5 times. Very suitable for equipping old buildings and rural areas. They are not often used, therefore for the distribution network they are most often a custom item;
- FROM- designation of these protective equipment, the operating range of which is in the range from 5 to 10 times. The most common option, in demand in new buildings and new country houses with autonomous communications;
- D- the designation of switches that instantly break the network when a current flows with a force exceeding the nominal value from 10 to 14, sometimes up to 20 times. Devices with such characteristics are needed only to protect the wiring of powerful electric motors.
There are variations abroad, both up and down, but they should not be of interest to the average owner of domestic property.
Current limiting class and its meaning
This is brief, because most of the devices offered by the trade belong to the 3rd class of current limitation. Occasionally meets the 2nd. This is an indicator of the speed of the device. The higher it is, the faster the device will respond to TKZ.
There is a lot of information, but without it it will be difficult to choose the right circuit breaker and protect property from unwanted fires. Information is also needed for those who will order the installation of protection devices. After all, not every electrician who positions himself as a great specialist should be unconditionally trusted.
An electric machine, or circuit breaker, is a mechanical switching device, by means of which it is possible to manually achieve a de-energization of the entire electrical network or a specific section of it. This can be done in a house, apartment, country house, garage, etc. Moreover, such a device is equipped with the function of automatically turning off the electric cable in case of emergency: for example, in the event of a short circuit or overload. The difference between such circuit breakers and conventional fuses is that after operation they can be turned on again with the button.
Automata (automatic switches) are what came to replace conventional traffic jams, i.e. fuses in a ceramic case, where the overcurrent protection was a blown nichrome wire.
Unlike cork, machine - reusable device, and its protection functions are separated. Firstly, protection against overcurrents (short circuit currents or short circuits), and secondly, protection against overload, i.e. the mechanism of the machine breaks the load circuit when the operating current of the machine is slightly exceeded.
According to these functions, the circuit breaker contains two types of breakers. Magnetic quick release short circuit protection with arc quenching system (response time in milliseconds) and slow thermal disconnect with a bimetallic plate (its reaction time is from several seconds to several minutes, depending on the load current).
Classification of electric machines
There are several typical circuit breakers: A, B, C, D, E, K, L, Z
- BUT– for breaking long circuits and for protecting electronic devices.
- B- for lighting networks.
- FROM- for lighting networks and electrical installations with moderate currents (current overload capacity is twice that of B).
- D– for circuits with inductive loads and electric motors.
- K– for inductive loads.
- Z– for electronic devices.
Main criteria for choosing a circuit breaker
Limiting short-circuit current
This indicator must be taken into account immediately. It means the maximum current value at which the electric machine will work and open the circuit. Here the choice is not great, since there are only three options: 4.5 kA; 6 kA; 10kA.
When choosing, one should be guided by the theoretical probability of a high short-circuit current. If there is no such probability, then it will be enough to purchase a 4.5 kA automatic machine.
Machine current
Accounting for this indicator is the next step. We are talking about the required nominal value of the operating current of the electric machine. To determine the operating current, you need to be guided by the power that is supposed to be connected to the wiring, or by the value of the allowable current (the level that will be maintained in normal mode).
What do you need to know when determining the parameter in question? It is not recommended to use machines with an overestimated operating current. Just in this case, the machine will not turn off the power during overload, and this can cause thermal destruction of the wiring insulation.
The pole of the machine
This is perhaps the simplest indicator. To choose the number of poles for a switch, you need to proceed from how it will be used.
So, a single-pole machine is your choice if you need to protect the wiring that goes from the electrical panel to sockets and lighting circuits. A bipolar switch is used when it is necessary to protect all wiring in an apartment or house with single-phase power. Protection of three-phase wiring and load is provided by a three-pole circuit breaker, and four-pole ones are used to protect four-wire power.
Characteristics of the machine
This is the last indicator that you need to pay attention to. The time-current characteristic of the circuit breaker is determined by the loads that are connected to the protected line. When choosing a characteristic, the following are taken into account: the operating current of the circuit, the rated current of the machine, the cable capacity, the operating current of the switch.
In the event that it is necessary to connect small starting currents to the power supply line, i.e. electrical appliances, characterized by a small difference between the operating current and the current that occurs when turned on, preference should be given to the tripping characteristic B. For more serious loads, characteristic C is chosen. Finally, there is one more characteristic - D. if you intend to connect powerful devices with high starting points. What devices are we talking about? For example, about the electric motor.
RCD classification
The RCD responds to differential current, i.e. the difference between the currents flowing in the forward and reverse wires. A differential current appears when a person touches a protected circuit and a grounded object. RCDs to protect people are selected for current 10-30 mA , fire RCDs - for a current of 300 mA. The latter protects the entire wiring system, and in case of fire, leakage currents usually occur earlier than short-circuit currents.
Residual current devices protect people from electric shock.
The choice of RCD is difficult because it is a more complex device than an automaton. For example, there is difavtomatami- devices that combine an automatic machine and an RCD. RCDs are also subdivided according to the type of execution into electronic and electromechanical. Experience has shown that it is better to use electromechanical RCDs. They are better protected from false positives and from breakdowns.
By number of poles RCDs are divided into:
- bipolar for 220 V circuits;
- four-pole for 380 V circuits.
According to the terms of operation on the:
- AC- responding only to alternating sinusoidal differential current.
- BUT- responding both to alternating sinusoidal differential current and to direct pulsating differential current.
- AT- responding to alternating sinusoidal differential current, to direct pulsating differential current and to direct differential current.
By the presence of a delay on RCDs without delay for general use and with a time delay of type S. According to the current characteristic (diphautomats) on B, C, D. And, finally, according to the rated current.
You should be aware that if the conventional Residual Current Device and the machine are in series in the same circuit, then the machine must be at a lower current than the RCD. Otherwise, the RCD may be damaged, because. the machine breaks the load circuit with a delay.
In conclusion, it must be said that you should choose devices from well-known companies: ABB abb, GE POWER, siemens siemens, LEGRAND and others at least certified in Russia. It is better to choose electromechanical RCDs, because. they are much more reliable than electronic ones. Instead of a tandem of an RCD and an automatic machine, it is better to choose a difavtomat, this will make the design of the shield more compact and reliable. The current characteristics must be selected depending on the wiring used. The operation current of automata and difavtomatov must be less than the maximum allowable cable currents.
For copper three-wire cables, the following data can be given for the correspondence of the cross section of the cable conductors in square millimeters and the currents of the machines:
- 3 x 1.5mm 2 - 16 Amps;
- 3 x 2.5 mm 2 - 25 A;
- 3 x 4 mm 2 - 32 Amps;
- 3 x 6mm 2 - 40 A;
- 3 x 10 mm 2 - 50 Amps;
- 3 x 16 mm 2 - 63 A.
We hope that after reading all the material it will be easier for you to understand the design and construction of electrical wiring.
The history of the creation of the RCD
The first residual current device (RCD) was patented by the German company RWE in 1928, when the principle of current differential protection, previously used to protect generators, lines and transformers, was applied to protect a person from electric shock.
In 1937 Schutzapparategesellschaft Paris & Co. manufactured the first operating device based on a differential transformer and a polarized relay, which had a sensitivity of 0.01 A and a speed of 0.1 s. In the same year, with the help of a volunteer (an employee of the company), an RCD was tested. The experiment ended successfully, the device worked well, the volunteer experienced only a mild electric shock, although he refused to participate in further experiments.
All subsequent years, with the exception of the war and the first post-war years, intensive work was carried out to study the effect of electric current on the human body, the development of electrical protective equipment and the improvement and implementation of protective shutdown devices.
In our country, the problem of using residual current devices first arose in connection with the electrical and fire safety of schoolchildren about 20 years ago. It was during this period that they developed and put into production UZOSH (UZO school) for the equipment of school buildings. Interestingly, RCDs of this type are still installed in school buildings, although due to outdated technologies, these devices no longer fully meet modern electrical and fire safety requirements.
Another event that exacerbated the problem of installing an RCD was the reconstruction of the Rossiya Hotel in Moscow after the infamous fire, which was caused by the most ordinary short circuit. The fact is that the principles of power supply were violated during the construction of this hotel complex. Several tragic incidents that led to the death of service personnel forced the hotel management to schedule the installation of residual current devices in order to ensure electrical and fire safety.
At that time, such installations were produced only for industrial use. One of the defense enterprises was entrusted with developing a protective shutdown installation for domestic purposes. But they did not have time to prevent the tragedy, and the fire that arose as a result of a short circuit in the Rossiya Hotel led to numerous victims. After the fire, during the restoration of the building, work was carried out to install an RCD in each room. Since domestic RCDs were manufactured in a very short time and had flaws, they gradually began to be replaced by devices from SIEMENS (Germany).
By this time, our electrical engineering enterprises also began to think about the problem of producing household protective shutdown devices. So, the Gomel plant "Electroapparatura" and the Stavropol electrical plant "Signal" developed and began to produce household protective shutdown devices. And since 1991-1992, the mass introduction of protective shutdown devices in housing construction began, at least in Moscow.
In 1994, the standard "Power supply and electrical safety of mobile (inventory) buildings made of metal or with a metal frame for street trading and public services" was adopted. Technical requirements". In the same year, a decree of the Moscow government was issued on the introduction of an RCD, which prescribed the mandatory equipping of new buildings in Moscow with protective shutdown devices.
In 1996 came out Letter of the Main Directorate of Civil Service of the Ministry of Internal Affairs of Russia dated 05.03.96 No. 20 / 2.1 / 516 « On the use of residual current devices (RCD)". And the Moscow government made another decision to improve the reliability of power supply to the entire housing stock, regardless of the year of construction. We can say that from that moment the legalized mass introduction of RCDs in housing construction began.
At present, the areas of application of RCDs are already clearly defined, a number of regulatory documents are in force that regulate the technical parameters and requirements for the use of RCDs in electrical installations of buildings. Today, the RCD is an indispensable element of any switchboard, all mobile objects are equipped with these devices without fail (residential trailer houses on camping sites, shopping vans, catering vans, small temporary outdoor electrical installations, arranged on the squares during the festive festivities), hangars , garages.
An RCD connection option that provides the safest operation of electrical wiring. In addition, RCDs are built into socket blocks or plugs through which power tools or household electrical appliances are connected, operated in especially dangerous, humid, dusty, with conductive floors, etc., rooms.
When assessing the risk that determines the sum insured, insurance companies must take into account the presence of RCDs on the insurance object and their technical condition.
Currently, there are an average of two RCDs for every inhabitant of developed countries. Nevertheless, for many years, dozens of companies have consistently produced these devices of various modifications in significant quantities, constantly improving their technical parameters.
These are the main indicators should be considered when choosing a circuit breaker. Accordingly, if you know all the necessary data, then the choice will not be difficult. It remains only to take into account the latest criterion - the manufacturer of the machine. What does it affect? It is obvious that on price.
Indeed, there is a difference. Thus, well-known European brands offer their circuit breakers at a price that is twice the cost of domestic counterparts and three times the price of devices from the South-Eastern countries. Also, the presence or absence of a switch with clearly defined indicators in the warehouse depends on the choice of a particular manufacturer.
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