Hello friends. The topic of the post is types and types circuit breakers(automatic machines, AB). I also want the results of the crossword puzzle tournament.
Types of machines:
Can be divided into AC switches, direct current and universal, operating at any current.
Design - there are air, modular, in a molded case.
Rated current indicator. The minimum operating current of a modular machine is 0.5 Amperes, for example. Soon I will write about how to choose the right rated current for a circuit breaker, subscribe to the blog news so as not to miss it.
Voltage rating is another difference. In most cases, AVs operate in networks with a voltage of 220 or 380 Volts.
There are current-limiting and non-current-limiting.
All switch models are classified by the number of poles. They are divided into single-pole, double-pole, three-pole and four-pole circuit breakers.
Types of releases - maximum current release, independent release, minimum or zero voltage release.
Speed of operation of circuit breakers. There are high-speed, normal and selective automatic machines. They are available with or without a time delay, independent or inversely dependent on the current response time delay. Characteristics can be combined.
They differ in the degree of protection against environment— IP, mechanical influences, conductivity of the material. By type of drive - manual, motor, spring.
By the presence of free contacts and the method of connecting conductors.
Types of machines:
What does type AB mean?
Automatic circuit breakers contain two types of circuit breakers - thermal and magnetic.
Magnetic quick release switch designed to protect against short circuit. The tripping of the circuit breaker can occur in a time from 0.005 to several seconds.
The thermal breaker is much slower, designed to protect against overload. It works using a bimetallic plate that heats up when the circuit is overloaded. Response time ranges from a few seconds to minutes.
The combined response characteristic depends on the type of connected load.
There are several types of AV shutdown. They are also called types of time-current shutdown characteristics.
A, B, C, D, K, Z.
A– used for breaking circuits with long electrical wiring, serves as good protection for semiconductor devices. They operate at 2-3 rated currents.
B- For lighting network general purpose. They operate at 3-5 rated currents.
C– lighting circuits, electrical installations with moderate starting currents. These can be motors, transformers. The overload capacity of the magnetic circuit breaker is higher than that of type B switches. They operate at 5-10 rated currents.
D– used in circuits with active-inductive loads. For electric motors with high starting currents, for example. At 10-20 rated currents.
K– inductive loads.
Z– for electronic devices.
It is better to look at the data on the operation of switches of types K, Z in the tables specifically for each manufacturer.
That seems to be all, if there is anything to add, leave a comment.
Circuit breakers are devices that provide protection for wiring in short circuit conditions when connecting a load with values exceeding the established values. They should be selected from special attention. It is important to consider the types of circuit breakers and their parameters.
Vending 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 possible excess current values. Different types circuit breakers have their own marking - it is easy to understand how quickly the equipment will respond to excess current values to the network. Some switches respond instantly, while others activate over a period of time.
- A is a marking that is affixed to the most sensitive equipment models. Automatic machines of this type immediately register the fact of overload and promptly respond to it. They are used to protect equipment characterized by high accuracy, but it’s almost impossible to meet them in everyday life
- B is a characteristic possessed by switches that operate with an insignificant delay. In everyday life, switches with corresponding characteristic used together with computers, modern LCD TVs and other expensive household appliances
- C is a characteristic of machines that are most widely used in everyday life. The equipment begins to function with a slight delay, which is sufficient for a delayed response to registered network overloads. The network is switched off by the device only if it has a fault that really matters
- D - characteristic of switches with minimal sensitivity to excess current. Basically, such devices are used to supply electricity to a building. They are installed in panels and control almost all networks. Such devices are chosen as a backup 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 part
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 under any conditions, even if the established values are exceeded.
Types of machines
The classification of circuit breakers is based on their types and features. As for types, we can highlight the following:
- Rated breaking capacity - we are talking about the resistance of the switch contacts to the effects of high currents, as well as to conditions in which deformation of the circuit occurs. Under such conditions, the risk of burning increases, which is neutralized by the appearance of an arc and an increase in temperature. The higher quality and durable the equipment is made of, the higher its corresponding capabilities are. Such switches are more expensive, but their characteristics fully justify the price. Switches last a long time and 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 production stage of the equipment, and are not regulated during its use. This characteristic allows you to understand how strong overloads the device can withstand, the period of time it operates in such conditions
- Setpoint - usually this indicator is displayed as a marking on the equipment body. It's about about the maximum current values in non-standard conditions, which, even with frequent shutdowns, will not have any effect on the operation of the device. The setting is expressed in current units, marked in Latin letters, digital values. The numbers, in this case, reflect the denomination. Latin letters can be seen in the markings of only those machines that are manufactured in accordance with DIN standards
From the very beginning of the emergence of electricity, engineers began to think about the safety of electrical networks and devices from current overloads. As a result, many have been designed different devices, which are distinguished by reliable and high-quality protection. One of the latest developments is electric automatic machines.
This device is called automatic because it is equipped with a function to turn off the power in automatic mode in the event of short circuits or overloads. Conventional fuses must be replaced with new ones after tripping, and the circuit breakers can be turned on again after eliminating the causes of the accident.
Such a protective device is necessary in any electrical network circuit. A circuit breaker will protect a building or premises from various emergency situations:
- Fires.
- Electric shocks to a person.
- Electrical wiring faults.
Types and design features
Need to know information about existing types circuit breakers in order to correctly select the appropriate device during purchase. There is a classification of electric machines according to several parameters.
Breaking capacity
This property determines the short circuit current at which the machine will open the circuit, thereby turning off the network and devices that were connected to the network. Based on this property, machines are divided into:
- 4500 ampere circuit breakers are used to prevent power line faults residential buildings old building.
- At 6000 amperes, they are used to prevent accidents during short circuits in the network of houses in new buildings.
- At 10,000 amperes, used in industry for protection electrical installations. A current of this magnitude can occur in the immediate vicinity of a substation.
The circuit breaker trips when a short circuit occurs, accompanied by the occurrence of a certain amount of current.
The machine protects electrical wiring from damage to insulation by high current.
Number of poles
This property tells us about the greatest number wires that can be connected to the machine to provide protection. In the event of an accident, the voltage at these poles is switched off.
Features of machines with one pole
Such electrical circuit breakers are the simplest in design and serve to protect individual sections of the network. Two wires can be connected to such a circuit breaker: input and output.
The purpose of such devices is to protect electrical wiring from overloads and short circuits of wires. The neutral wire is connected to the neutral bus, bypassing the machine. Grounding is connected separately.
Electrical machines with one pole are not input, since when it is disconnected, the phase is broken, and the neutral wire still remains connected to the power supply. This does not provide 100% protection.
Properties of machines with two poles
In cases where an emergency requires complete disconnection from the electrical network, circuit breakers with two poles are used. They are used as introductory ones. In emergency cases, or in the event of a short circuit, all electrical wiring turns off at the same time. This makes it possible to carry out repair and maintenance work, as well as work on connecting equipment, since complete safety is guaranteed.
Two-pole electrical circuit breakers are used when it is necessary to have a separate switch for a device operating on a 220-volt network.
A machine with two poles is connected to the device using four wires. Of these, two come from the power supply, and the other two come from it.
Three-pole electrical circuit breakers
In an electrical network with three phases, 3-pole circuit breakers are used. The grounding is left unprotected, and the phase conductors are connected to the poles.
The three-pole circuit breaker serves as an input device for any three-phase load consumers. Most often, this version of the machine is used in industrial conditions to power electric motors.
You can connect 6 conductors to the machine, three of which are phases of the electrical network, and the other three coming from the machine and provided with protection.
Using a four-pole circuit breaker
To provide protection for a three-phase network with a four-wire system of conductors (for example, an electric motor connected in a star circuit), a 4-pole circuit breaker is used. It plays the role of an input device for a four-wire network.
It is possible to connect eight conductors to the device. On the one hand - three phases and zero, on the other hand - the output of three phases with zero.
Time-current characteristic
When devices that consume electricity and electrical network operate in normal mode, then normal current flow occurs. This phenomenon also applies to electric machines. But, if the current increases for various reasons above the rated value, the circuit breaker is triggered and the circuit is broken.
The parameter of this operation is called the time-current characteristic of the electrical machine. It is a dependence of the operating time of the machine and the relationship between the actual current passing through the machine and the rated current value.
The importance of this characteristic lies in the fact that it ensures smallest number false alarms on the one hand, and current protection on the other hand.
IN energy industry There are situations when a short-term increase in current is not associated with an accident, and the protection should not operate. The same thing happens with electric machines.
The time-current characteristics determine after what time the protection will operate and what current parameters will arise. The greater the overload, the faster the machine will operate.
Electric machines marked “B”
Automatic switches of category “B” are capable of switching off in 5 - 20 s. In this case, the current value ranges from 3 to 5 rated current values ≅0.02 s. Such machines are used to protect household devices, as well as all electrical wiring of apartments and houses.
Properties of machines marked “C”
Electrical circuit breakers of this category can turn off in 1 - 10 s, at 5 - 10 times the current load ≅0.02 s. These are used in many areas, most popular for houses, apartments and other premises.
The meaning of the marking "D" on automatic
Automatic machines with this class are used in industry and are made in the form of 3-pole and 4-pole versions. They are used to protect powerful electric motors and various three-phase devices. Their operation time is up to 10 seconds, while the operation current can exceed the rated value by 14 times. This makes it possible to use it with the necessary effect to protect various circuits.
Electric motors with significant power are most often connected through electrical machines with characteristic “D”, because starting current is high.
Rated current
There are 12 versions of the machines, which differ in the characteristics of the rated operating current, from 1 to 63 amperes. This parameter determines the speed at which the machine turns off when it reaches limit value current
Based on this property, the machine is selected taking into account the cross-section of the wire cores and the permissible current.
Operating principle of electric machines
Normal mode
At regular work machine, the control lever is cocked, current flows through the power wire at the top terminal. Next, the current flows to the fixed contact, through it to the moving contact and through a flexible wire to the solenoid coil. After it, the current flows through the wire to the bimetallic plate of the release. From it, the current passes to the lower terminal and further to the load.
Overload mode
This mode occurs when the rated current of the machine is exceeded. The bimetallic plate is heated by a high current, bends and opens the circuit. The action of the plate requires time, which depends on the value of the passing current.
The circuit breaker is an analog device. There are certain difficulties in setting it up. The tripping current of the release is adjusted at the factory using a special adjusting screw. After the plate has cooled, the machine can function again. The temperature of the bimetallic strip depends on the environment.
The release does not act immediately, allowing the current to return to its nominal value. If the current does not decrease, the release trips. Overload can occur due to powerful devices on the line, or the connection of several devices at once.
Short circuit mode
In this mode, the current increases very quickly. The magnetic field in the solenoid coil moves the core that activates the release and disconnects the power supply contacts, thereby removing the emergency load of the circuit and protecting the network from possible fire and destruction.
An electromagnetic release acts instantly, which is different from a thermal release. When the contacts of the operating circuit open, an electric arc appears, the magnitude of which depends on the current in the circuit. It causes destruction of contacts. To prevent this negative effect, an arc chute is made, which consists of parallel plates. In it, the arc fades and disappears. The resulting gases are discharged into a special hole.
The main difference between these switching devices and all other similar devices is the complex combination of capabilities:
1. maintain rated loads in the system for a long time by reliably passing powerful flows of electricity through its contacts;
2. protect operating equipment from accidental malfunctions electrical diagram due to the rapid removal of power from it.
Under normal equipment operating conditions, the operator can manually switch loads with circuit breakers, providing:
different power plans;
changing the network configuration;
removal of equipment from operation.
Emergency situations in electrical systems ah arise instantly and spontaneously. A person is not able to quickly react to their appearance and take measures to eliminate them. This function is assigned to automatic devices built into the switch.
In the energy sector, it is common practice to divide electrical systems by type of current:
constant;
variable sinusoidal.
In addition, there is a classification of equipment according to voltage:
low voltage - less than a thousand volts;
high voltage - everything else.
For all types of these systems, their own circuit breakers are created, designed for repeated operation.
AC circuits
Based on the power of transmitted electricity, circuit breakers in alternating current circuits are conventionally divided into:
1. modular;
2. in a molded case;
3. power air.
Modular designs
The specific design in the form of small standard modules with a width that is a multiple of 17.5 mm determines their name and design with the possibility of installation on a Din rail.
The internal structure of one of these circuit breakers is shown in the picture. Its body is entirely made of durable dielectric material, eliminating .
The supply and output wires are connected to the upper and lower terminals, respectively. To manually control the state of the switch, a lever with two fixed positions is installed:
the top one is designed to supply current through a closed power contact;
the lower one ensures a break in the power supply circuit.
Each of these machines is designed for long-term operation at a certain value (In). If the load becomes greater, then the power contact breaks. For this purpose, two types of protection are placed inside the case:
1. thermal release;
2. current cut-off.
The principle of their operation makes it possible to explain the time-current characteristic, which expresses the dependence of the response time of the protection on the load current passing through it or an accident.
The graph presented in the picture is shown for one specific circuit breaker, when the cut-off operating zone is selected at 5÷10 times the rated current.
During the initial overload, a thermal release made of , which, with increased current, gradually heats up, bends and acts on the tripping mechanism not immediately, but with a certain time delay.
In this way, it allows small overloads associated with short-term connection of consumers to resolve themselves and eliminate unnecessary shutdowns. If the load provides critical heating of the wiring and insulation, then the power contact breaks.
When an emergency current occurs in the protected circuit, capable of burning the equipment with its energy, the electromagnetic coil comes into operation. With an impulse, due to the surge of the load that has arisen, it throws the core onto the disconnecting mechanism in order to instantly stop the over-the-top mode.
The graph shows that the higher the short circuit currents, the faster they are switched off by the electromagnetic release.
The household automatic PAR fuse works on the same principles.
When large currents break, an electric arc is created, the energy of which can burn out the contacts. To eliminate its effect, circuit breakers use an arc-extinguishing chamber that divides the arc discharge into small streams and extinguishes them due to cooling.
Cut-off ratio of modular structures
Electromagnetic releases are configured and selected to work with certain loads because when started they create different transient processes. For example, when turning on various lamps, a short-term surge of current due to the changing resistance of the filament can approach three times the nominal value.
Therefore, for the socket group of apartments and lighting circuits, it is customary to choose automatic switches with a time-current characteristic of type “B”. It is 3÷5 In.
Asynchronous motors, when spinning a rotor with a drive, cause large overload currents. For them, machines with characteristic “C” are selected, or - 5÷10 In. Due to the created reserve of time and current, they allow the engine to spin up and be guaranteed to reach operating mode without unnecessary shutdowns.
IN industrial production On machines and mechanisms there are loaded drives connected to motors, which create more increased overloads. For such purposes, automatic circuit breakers of characteristic “D” with a rating of 10÷20 In are used. They have proven themselves well when working in circuits with active-inductive loads.
In addition, machines have three more types of standard time-current characteristics that are used for special purposes:
1. “A” - for long wiring with an active load or protection of semiconductor devices with a value of 2÷3 In;
2. “K” - for pronounced inductive loads;
3. “Z” - for electronic devices.
In the technical documentation different manufacturers The cut-off ratio for the last two types may be slightly different.
This class of devices is capable of switching higher currents than modular designs. Their load can reach values up to 3.2 kiloamperes.
They are manufactured according to the same principles as modular designs, but, taking into account the increased requirements for carrying increased loads, they are made to have relatively small dimensions and high technical quality.
These machines are designed for safe work at industrial facilities. Based on the rated current, they are conventionally divided into three groups with the ability to switch loads up to 250, 1000 and 3200 amperes.
Design of their housing: three- or four-pole models.
Power air circuit breakers
They work in industrial installations and operate with very high load currents up to 6.3 kiloamperes.
These are the most complex devices for switching devices of low-voltage equipment. They are used to operate and protect electrical systems as input and output devices of distribution installations increased capacity and for connecting generators, transformers, capacitors or powerful electric motors.
Schematic representation of them internal structure shown in the picture.
Here, a double break of the power contact is used and arc-extinguishing chambers with grilles are installed on each side of the shutdown.
The operating algorithm involves a switching coil, a closing spring, a spring charging motor drive and automatic elements. To control the flowing loads, a current transformer with a protective and measuring winding is built in.
Circuit breakers of high-voltage equipment are very complex technical devices and are manufactured strictly individually for each voltage class. They are usually used.
They are subject to the following requirements:
high reliability;
security;
speed;
ease of use;
relative noiselessness during operation;
optimal cost.
Loads that break during an emergency shutdown are accompanied by a very strong arc. To extinguish it they use various ways, including breaking the circuit in a special environment.
This switch includes:
contact system;
arc extinguishing device;
live parts;
insulated housing;
drive mechanism.
One of these switching devices is shown in the photograph.
For high-quality operation of the circuit in such designs, in addition to the operating voltage, the following are taken into account:
the rated value of the load current for its reliable transmission in the on state;
maximum short-circuit current based on the effective value that the disconnecting mechanism can withstand;
permissible component of the aperiodic current at the moment of circuit break;
automatic reclosure capabilities and provision of two automatic reclosure cycles.
According to the methods of extinguishing the arc during shutdown, switches are classified into:
oil;
vacuum;
air;
SF6;
autogas;
electromagnetic;
autopneumatic.
For reliable and comfortable work they are equipped with a drive mechanism that can use one or more types of energy or combinations thereof:
charged spring;
lifted load;
pressure compressed air;
electromagnetic pulse from the solenoid.
Depending on the conditions of use, they can be created with the ability to operate under voltage from one to 750 kilovolts inclusive. Naturally they have different designs. dimensions, automatic and remote control, setting up protections for safe operation.
Auxiliary systems of such circuit breakers can have a very complex branched structure and are located on additional panels in special technical buildings.
DC circuits
These networks also operate a huge number of circuit breakers with different capabilities.
Electrical equipment up to 1000 volts
Here, modern modular devices that can be mounted on a Din rail are being introduced en masse.
They successfully complement the classes of old machine guns such as , AE and other similar ones, which were fixed to the walls of shields with screw connections.
Modular DC designs have the same structure and operating principle as their AC counterparts. They can be performed in one or several blocks and are selected according to the load.
Electrical equipment above 1000 volts
High-voltage circuit breakers for direct current operate in electrolysis production plants, metallurgical industrial facilities, railway and urban electrified transport, and energy enterprises.
Basic technical requirements the operation of such devices corresponds to their alternating current counterparts.
Hybrid switch
Scientists from the Swedish-Swiss company ABB managed to develop a high-voltage DC switch that combines two power structures:
1. SF6;
2. vacuum.
It is called hybrid (HVDC) and uses the technology of sequential arc extinguishing in two environments at once: sulfur hexafluoride and vacuum. For this purpose, the following device has been assembled.
Voltage is supplied to the upper busbar of the hybrid vacuum circuit breaker, and voltage is removed from the lower busbar of the SF6 circuit breaker.
The power parts of both switching devices are connected in series and controlled by their own individual drives. In order for them to work simultaneously, a control device for synchronized coordinate operations was created, which transmits commands to the control mechanism with independent power supply via a fiber optic channel.
Through the use of high-precision technologies, the design developers were able to achieve consistency in the actions of the actuators of both drives, which fits into a time period of less than one microsecond.
The switch is controlled by a relay protection unit built into the power line through a repeater.
The hybrid circuit breaker has significantly improved the efficiency of composite SF6 and vacuum designs by exploiting their combined characteristics. At the same time, it was possible to realize advantages over other analogues:
1. the ability to reliably turn off short-circuit currents at high voltage;
2. possibility of small effort for switching power elements, which made it possible to significantly reduce the dimensions and. accordingly, the cost of equipment;
3. availability of compliance with various standards for the creation of structures operating as part of a separate circuit breaker or compact devices at one substation;
4. the ability to eliminate the consequences of rapidly increasing recovering stress;
5. Possibility of formation base module for working with voltages up to 145 kilovolts and higher.
A distinctive feature of the design is the ability to tear electrical circuit in 5 milliseconds, which is almost impossible to perform with power devices of other designs.
The hybrid switch device was named one of the ten best developments of the year according to technology review MIT (Massachusetts Institute of Technology).
Other manufacturers of electrical equipment are also engaged in similar research. They also achieved certain results. But ABB is ahead of them in this matter. Its management believes that when transmitting alternating current electricity, large losses occur. They can be significantly reduced by using high-voltage direct voltage circuits.
When assembling an electrical panel or connecting new large household appliances, House master will definitely encounter such a problem as the need to select circuit breakers. They provide electrical and fire safety, That's why right choice machine is a guarantee of the safety of you, family and property.
What is the machine used for?
A machine is installed in the power supply circuit to prevent overheating of the wiring. Any wiring is designed to carry a certain current. If the current passed exceeds this value, the conductor begins to heat up too much. If this situation persists for a sufficient period of time, the wiring begins to melt, resulting in a short circuit. A circuit breaker is installed to prevent this situation.
The second task of the circuit breaker is to turn off the power when a short circuit current (SC) occurs. When a short circuit occurs, the currents in the circuit increase many times over and can reach thousands of amperes. To prevent them from destroying the wiring and damaging the equipment included in the line, the circuit breaker must turn off the power as quickly as possible - as soon as the current exceeds a certain limit.
In order for the protective circuit breaker to properly perform its functions, it is necessary to correctly select the machine according to all parameters. There are not many of them - only three, but you need to deal with each one.
What types of circuit breakers are there?
To protect conductors single-phase network 220 V there are single-pole and double-pole disconnecting devices. To single-pole wires, only one conductor is connected - phase, to double-pole wires, both phase and neutral. Single-pole circuit breakers are installed on 220 V indoor lighting circuits, on socket groups in rooms with normal operating conditions. They are also installed on some types of load in three-phase networks, connecting one of the phases.
For three-phase networks (380 V) there are three and four poles. These circuit breakers (the correct name is a circuit breaker) are installed on a three-phase load (ovens, hobs and other equipment that operate on a 380 V network).
In rooms with high humidity(bathroom, bathhouse, swimming pool, etc.) install two-pole circuit breakers. They are also recommended to be installed on powerful equipment - washing and dishwashers, boilers, ovens etc.
Just in emergency situations- in the event of a short circuit or insulation breakdown, phase voltage may reach the neutral wire. If a single-pole device is installed on the power line, it will disconnect the phase wire, and the zero will dangerous voltage it will remain connected. This means there is still a possibility of electric shock when touched. That is, the choice of machine is simple - single-pole switches are installed on some lines, and double-pole switches on others. The specific amount depends on the network condition.
For a three-phase network, there are three-pole circuit breakers. Such a machine is installed at the entrance and at consumers, to which all three phases are supplied - electric stove, three-phase hob, oven, etc. The remaining consumers are equipped with two-pole circuit breakers. They must disconnect both phase and neutral.
Example of three-phase network wiring - types of circuit breakers
The choice of circuit breaker rating does not depend on the number of wires connected to it.
Deciding on the denomination
Actually, from the functions of the circuit breaker, the rule for determining the rating of the circuit breaker follows: it must operate until the current exceeds the capabilities of the wiring. This means that the current rating of the machine must be less than the maximum current that the wiring can withstand.
Based on this, the algorithm for selecting a circuit breaker is simple:
- for a specific area.
- See what maximum current this cable can withstand (see the table).
- Next, from all the ratings of the circuit breakers, we select the nearest smaller one. The ratings of the machines are tied to the permissible long-term load currents for a particular cable - they have a slightly lower rating (see the table). The list of denominations looks like this: 16 A, 25 A, 32 A, 40 A, 63 A. From this list you choose the appropriate one. There are smaller values, but they are practically not used anymore - we have too many electrical appliances and they have considerable power.
Example
The algorithm is very simple, but it works flawlessly. To make it clearer, let's look at an example. Below is a table that shows the maximum permissible current for conductors that are used at. Recommendations regarding the use of machines are also given there. They are given in the column “Nominal current of the circuit breaker”. This is where we look for the ratings - it is slightly less than the maximum permissible for the wiring to work normally.
| Cross section of copper wires | Permissible continuous load current | Maximum load power for single-phase network 220 V | Rated current of circuit breaker | Circuit breaker current limit | |
|---|---|---|---|---|---|
| 1.5 sq. mm | 19 A | 4.1 kW | 10 A | 16 A | lighting and alarm |
| 2.5 sq. mm | 27 A | 5.9 kW | 16 A | 25 A | socket groups and electric heated floor |
| 4 sq.mm | 38 A | 8.3 kW | 25 A | 32 A | air conditioners and water heaters |
| 6 sq.mm | 46 A | 10.1 kW | 32 A | 40 A | electric stoves and ovens |
| 10 sq. mm | 70 A | 15.4 kW | 50 A | 63 A | opening lines |
In the table we find the selected wire cross-section for this line. Suppose we need to lay a cable with a cross-section of 2.5 mm 2 (the most common when laying to medium-power devices). A conductor with this cross-section can withstand a current of 27 A, and the recommended rating of the machine is 16 A.
How will the circuit work then? As long as the current does not exceed 25 A, the machine does not turn off, everything works as normal - the conductor heats up, but not to critical values. When the load current begins to increase and exceeds 25 A, the machine does not turn off for some time - perhaps these are starting currents and they are short-lived. It turns off if the current exceeds 25 A by 13% for a sufficiently long time. In this case, if it reaches 28.25 A. Then the power supply will work and de-energize the branch, since this current already poses a threat to the conductor and its insulation.
Power calculation
Is it possible to choose a machine based on load power? If only one device (usually a large device) will be connected to the power line, Appliances with high power consumption), then it is permissible to make a calculation based on the power of this equipment. You can also choose an introductory machine based on power, which is installed at the entrance to a house or apartment.
If we are looking for the rating of the input circuit breaker, we need to add up the power of all devices that will be connected to the home network. Then the found total power is substituted into the formula, and the operating current for this load is found.
After we have found the current, select the nominal value. It may be either slightly more or slightly less than the found value. The main thing is that its shutdown current does not exceed the maximum permissible current for this wiring.
When can you use this method? If the wiring is laid with a large margin (this is not bad, by the way). Then, in order to save money, you can automatically install switches that correspond to the load, and not the cross-section of the conductors. But once again we draw attention to the fact that the long-term permissible current for the load must be greater than the maximum current of the circuit breaker. Only then will the choice of circuit breaker be correct.
Selecting the breaking capacity
The selection of a packager based on the maximum permissible load current is described above. But the network circuit breaker must also turn off when a short circuit (short circuit) occurs in the network. This characteristic is called breaking capacity. It is displayed in thousands of amperes - this is the order currents can reach during a short circuit. Selecting a machine based on its breaking capacity is not very difficult.
This characteristic shows at what maximum value of the short-circuit current the circuit breaker remains operational, that is, it will not only be able to turn off, but will also work after being turned on again. This characteristic depends on many factors and for accurate selection it is necessary to determine the short-circuit currents. But for wiring in a house or apartment, such calculations are done very rarely, and are based on the distance from the transformer substation.
If the substation is located close to the entrance to your house/apartment, take a circuit breaker with a breaking capacity of 10,000 A; for all other city apartments, 6,000 A is sufficient. If the house is located in rural areas Whether you are choosing an electrical circuit breaker for your dacha, a breaking capacity of 4,500 A may well be enough. The networks here are usually old and the short-circuit currents are not large. And since the price increases significantly with increasing breaking capacity, the principle of reasonable savings can be applied.
Is it possible to install bags with a lower breaking capacity in city apartments? In principle, it is possible, but no one guarantees that after the first short circuit you will not have to change it. He may have time to turn off the network, but will be inoperative. In the worst case scenario, the contacts will melt and the machine will not have time to turn off. Then the wiring will melt and a fire may occur.
Type of electromagnetic release
The machine must operate when the current rises above a certain level. But short-term overloads periodically occur in the network. They are usually associated with inrush currents. For example, such overloads can be observed when turning on the refrigerator compressor, motor washing machine etc. The circuit breaker should not turn off during such temporary and short-term overloads, because they have a certain delay for operation.
But if the current has increased not because of an overload but because of a short circuit, then during the time that the circuit breaker “wait”, its contacts will melt. This is what an electromagnetic automatic release is for. It operates at a certain current value, which can no longer be an overload. This indicator is also called cut-off current, since in this case the circuit breaker cuts off the line from the power supply. The magnitude of the operating current can be different and is displayed by letters that appear in front of the numbers indicating the rating of the machine.
There are three most popular types:
What characteristics should you choose? In this case, the choice of a circuit breaker is also based on the distance of your household from the substation and the state of the electrical networks; the choice of a circuit breaker is carried out using simple rules:
- With the letter “B” on the body they are suitable for dachas, houses in villages and towns that receive power supply through air ducts. They can also be installed in apartments of old houses in which the internal electrical network has not been reconstructed. These circuit breakers are not always on sale; they cost a little more than category C, but can be delivered to order.
- Bags with a “C” on the body are the most widely used option. They are installed in networks with normal condition, suitable for apartments in new buildings or after major renovations, in private houses near the substation.
- Class D is installed in enterprises and workshops with equipment with high starting currents.
That is, in essence, the choice of a circuit breaker in this case is simple - type C is suitable for most cases. It is available in stores in a large assortment.
Which manufacturers should you trust?
And finally, let’s pay attention to the manufacturers. The choice of a circuit breaker cannot be considered complete if you have not thought about which brand of circuit breakers you will buy. You definitely shouldn’t take on unknown companies - electrical engineering is not a field where you can conduct experiments. Learn more about choosing a manufacturer in the video.
