Types of circuit breakers - what are the machines. Electric machines

23.06.2020

Hello friends. Post topic - types and types circuit breakers(automatic, AB). I also want the results of the crossword puzzle tournament.

Types of machines:

Can be divided into switches alternating current, 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 the 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 blog news so as not to miss it.

Rated voltage, another difference. In most cases, ABs operate in networks with a voltage of 220 or 380 volts.

There are current-limiting and non-current-limiting.

All models of switches are classified according to the number of poles. They are divided into single-pole, two-pole, three-pole and four-pole machines.

Types of releases - overcurrent release, shunt release, undercurrent or zero release voltage.

The speed of operation of automatic switches. Allocate high-speed, normal and selective automata. There are with or without a time delay, independent or inversely dependent on the current, the operating time delay. Features can be combined.

They differ in terms of protection from environment– IP, mechanical impacts, material conductance. By type of drive - manual, motor, spring.

By the presence of free contacts and the method of connecting conductors.

Machine types:

What does type AB mean?

Circuit breakers contain two types of circuit breakers - thermal and magnetic.

The magnetic quick release is designed for short circuit protection. The tripping of the circuit breaker can take place from 0.005 to several seconds.

The thermal circuit breaker is much slower, designed for overload protection. Works with the help of a bimetallic plate that heats up when the circuit is overloaded. Response time from a few seconds to minutes.

The combined tripping characteristic depends on the type of connected load.

There are several types of AV shutdown. They are also called - types of time-current characteristics of the trip.

A, B, C, D, K, Z.

A- used to open circuits with a large long electrical wiring, serves as a good protection for semiconductor devices. They work at 2-3 rated currents.

B– for the lighting network general purpose. They operate at 3-5 rated currents.

C– lighting circuits, electrical installations with moderate starting currents. It can be motors, transformers. The overload capacity of the magnetic circuit breaker is higher than that of type B circuit breakers. They operate at 5-10 rated currents.

D- used in circuits with active-inductive load. For motors with high starting currents, e.g. 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.

It seems everything, if there is something to add, leave a comment.

At the same time, for a long time, the automatic transmission was installed on cars of the middle class and the premium segment, but later the unit became massive.

Due to the huge popularity, as well as taking into account the constant tightening of norms and standards regarding fuel efficiency and environmental friendliness, manufacturers are constantly improving automatic transmission, offering innovative solutions, etc.

As a result, today it is possible to distinguish at least three main types of "automatic machines", which differ greatly from each other in design and operating principles, but each of them is called automatic transmission. Next, we will talk about what automatic boxes are, as well as what features this or that unit has.

If we talk about the advantages, the hydraulic machine has a fairly large resource (in some cases up to 500 thousand km.), And also provides a good level of driving comfort.

As for the main disadvantages, such a box is expensive to repair, requires regular maintenance, is demanding on the quality of gear oil, is afraid of prolonged loads and harsh operating conditions, is not very economical,. We also note that losses in the gas turbine engine lead to the fact that the efficiency of hydromechanical automata decreases compared to analogues. As a result, acceleration dynamics suffer.

(variable transmission CVT) is a separate type of automatic transmission, which for a number of reasons is not as widespread as a hydromechanical automatic transmission.

Such a transmission, like an automatic transmission, has a torque converter to transmit torque from the internal combustion engine, but the box itself is very different. In short, there are two pulleys mounted on the variator shafts. These pulleys are interconnected by a belt or chain. Depending on the load and speed, the driving and driven pulleys change their diameter, as a result of which the torque on the wheels also changes. And it happens extremely smoothly.

Given the fact that there are no usual fixed speeds (steps), thanks to this feature, the CVT variator is called a continuously variable transmission (flexible change in gear ratio). This type of automatic machine differs from analogues in maximum smoothness, since the gear change does not actually occur. The engine speed is also kept at the same level, without a sharp increase and decrease.

As in the case of automatic transmission, additional modes can be implemented (winter, economical, sports, as well as Tiptronic with imitation of manual gear shifting). When driving a car with a CVT, drivers note the complete absence of tangible shocks, vibrations, etc. You should also highlight the good acceleration dynamics and fuel efficiency.

However, there are also disadvantages. First of all, it does not have a large resource, it is extremely difficult and expensive to repair, demanding on the quality and level of oil. This means that such a box is not installed in tandem with powerful engines during operation, it is highly recommended not to load the transmission.

(robot box or robot automatic transmission) is another type of automatic transmission, which for a number of reasons became really massive about 20 years ago.

It is noteworthy that this unit was developed a long time ago and is actually a manual gearbox with one clutch, in which the control of the clutch operation is automated, as well as the selection and engagement / disengagement of the desired gear.

In simple words, automatic transmission robot is an automated (robotic) mechanics. Such a box is distinguished by low production costs (which significantly reduces the cost of the entire machine), allows you to achieve significant fuel savings (similar to mechanics), as well as dynamic acceleration.

If we consider the disadvantages, then, first of all, we should highlight a noticeable decrease in comfort compared to automatic transmissions and CVTs. In simple words, the clutch remains exactly the same as in the manual transmission, while the robot does not always select the right gear quickly and accurately, cannot smoothly control the clutch, etc.

As a result, at the moment of switching, shocks, jerks, etc. are felt, the robot delays gear changes, does not always accurately select gears in accordance with constantly changing conditions while driving.

Also, actuators (servomechanisms, actuators) on robotic gearboxes quickly fail, quality repair often impossible, that is, a complete replacement is needed. It is important to understand that such mechanisms are quite expensive.

(for example, DSG or Powershift) can be considered a more technologically advanced and advanced version of a conventional box - a robot. At the same time, units of this type are devoid of many of the shortcomings of their predecessors.

On the one hand, the design remained similar to the mechanics, however, the engineers conditionally placed two such mechanical boxes at once in one case. One box has even gears, the other odd, and each has a separate clutch.

In short, while the car is moving, for example, in one gear, the next one is already selected and engaged, but not engaged, since the clutch is disengaged. At the moment of gear shifting, the working clutch is quickly disengaged, then the second one is instantly connected. The gear change is so fast that the driver almost does not feel it.

At the same time, the control of such a robot is more like an automatic transmission control scheme (there is a valve body called Mechatronic, more gear oil is needed, etc.). At the same time, there is also a large number of servomechanisms (by analogy with a single-disk robot that has one clutch).

Among the advantages, one can single out high fuel efficiency and excellent acceleration dynamics, a high level of comfort, as well as the best ability of the box to cope with high loads compared to automatic transmissions and CVTs.

At the same time, the preselective box is complex and expensive to manufacture, has a noticeably shorter resource, and in practice requires intervention earlier than an automatic transmission or a variator. As for repairs, robots of this type require only qualified maintenance, often sets of expensive special equipment are also required for many procedures (for example,).

How to distinguish a robot from an automatic machine or a variator

The fact is that manufacturers strive to simplify the entire process of interaction between the driver and the box as much as possible. For this reason, for example, a robot can have the same selector and modes (P-R-N-D) as a CVT or automatic transmission.

As for the driving experience (provided that the transmission and the car itself are in perfect working order), you can pay attention to the following:

AT - often denotes a hydromechanical machine;
CVT - CVT;
AMT - robotic box with one clutch;

You can also ask a question at specialized auto forums, study technical literature separately, etc.

Summing up

As you can see, each automatic transmission has both strong and weaknesses. Also, taking into account the diversity, you may be faced with the fact that it is difficult to immediately determine which automatic transmission is on a particular car.

Finally, we note that during operation it is important to separately take into account certain features of a particular machine, depending on the type of transmission and type of automatic transmission. You also need to strictly follow the rules for servicing an automatic transmission, which allows you to increase the resource of the unit.

Design and principle of operation

Understanding the circuit breaker's automatic tripping mechanism will help you select the right model. Structurally, the machine includes the following key elements:

terminals;
toggle switch;
electromagnetic release;
bimetallic plate.

Depending on the type of overload, one of two mechanisms is triggered.

When an overload of the circuit occurs with a current that exceeds the nominal value by several times, the bimetallic plate is triggered. It heats up within a few seconds, resulting in its thermal expansion. When a certain size is reached, its significant bending is carried out and the chain opens. The setting of the plate parameters is carried out by the manufacturer. For switches used in everyday life, the operating time takes 5–20 s. They are usually marked with the letters: B, C, D.

The short circuit mode (SC) is characterized by an avalanche-like increase in current, which exceeds not only the nominal value, but also its maximum permissible loads. There is no time left to heat the plate during the jump, otherwise the wiring may melt. In such a situation, an electromagnetic release is triggered. The magnetic field drives the core, which opens the circuit. Instant operation allows you to protect the premises from the consequences of a short circuit.

Classification

Electric machines differ in the following key characteristics:

number of poles;
time current characteristic;
operating current;
breaking capacity.

Number of poles

This characteristic corresponds to the number of electrical wiring lines that can be directly connected to the machine. All output wires will be disconnected at the same time when the machine is triggered.

Single pole machine. This is the simplest type of circuit protection devices. Only 2 wires are connected to it: one goes to the load, the second is power. It mounts on a standard 18mm din rail. The power wire is fed from above, and the load to the bottom terminal. It can work in single, two or three phase power lines. In addition to the power and load wires, it has a neutral and ground, which are connected to the corresponding busbars. Such machines are not installed at the input, since the circuit will open only along the phase line. The zero wiring remains closed and, in case of failures, potential may remain on it.

A two-pole machine, its difference from a single-pole one. This type of circuit breakers allows you to completely de-energize the electrical wiring of the room. It allows you to synchronize the moment of turning off two of its output lines. The latter leads to more high level safety during electrical work. It can be used as a separate toggle switch for appliances such as a water heater or a washing machine. The connection is made using 4 cables: a pair at the input and output.

A simple question is logical: is it possible to connect two single-pole machines instead of one two-pole one? Of course no. After all, when the shutdown is automatically triggered, all output lines are turned off at the two-terminal network. For a pair of independent automata, overload may not occur on one of the lines and the de-energization will be partial. In ordinary apartments, you can connect a phase and neutral line to this machine. When opened, a complete deenergization of the entire group of devices that are powered from it will occur.

Three and four-pole machines. All three or four phase conductors are connected to the poles of the corresponding circuit breaker. They are used when connected by a star, when the phase wires are protected from overloads, and the middle wire remains switched all the time, or by a triangle, when there is no middle central cable, and the phase wires are protected.

If an overload occurs on one of the lines, a shutdown occurs immediately on all the others. 6 (three-phase machine) or 8 wires are connected to these machines. 3-4 at the output and the same number of lines at the output. They are mounted on din rails with a length of 54 (three-phase machine) and 72 mm, respectively. They are used most often in industrial installations, when connecting powerful electric motors.

Time current parameter

The nature of food consumption various devices varies even when power values match. Uneven dynamics of consumption during correct operation, a surge in load during turn-on - all these phenomena lead to significant changes in such a parameter as current consumption. Power dissipation can lead to false tripping of the circuit breaker.

To exclude such situations, dynamic operation parameters are introduced, called time-current characteristics of circuit breakers. Automata according to this parameter are divided into several types. Each group has its own response time. The front panel of the switch is marked with the corresponding letter from the list: A, B, C, D, K, Z.

Rated current

The differences of automata depending on the nominal values of the current are divided into several groups (12 current levels). It is directly related to the response time when the power consumption is exceeded. The operating value can be determined purely theoretically by adding up the sums of the currents consumed by each of the devices separately. In this case, a small margin should be taken. Also, do not forget about the possibilities of electrical wiring.

Machines are designed primarily to prevent damage to it. Depending on the metal of the wires and their cross section, the maximum load is calculated. The ratings of the circuit breakers for current allow such a separation.

Breaking capacity

This parameter depends on the maximum current in the event of a short circuit, provided that the machine performs a network shutdown. According to the magnitude of the short-circuit current, all automata are divided into three groups.

The first includes devices with a nominal value of 4.5 kA. They are used in private houses intended for human habitation. The current limit is approximately 5 kA. This is due to the fact that the resistance of the system of conductive cables leading to the house from the substation is 0.05 ohms.
The second group has rated 6 kA. This level is already used in residential apartment buildings and public places. The current limit can reach 5.5 kA (wiring resistance 0.04 Ohm). In this case, models of types are used: B, C, D.
In industrial plants the nominal value is 10 kA. The limit value of the current that can occur in the circuit near the substation has the same value.

How to choose the right machine

Until recently, porcelain fuses with fusible elements were widely used. They were well suited for the same type of load of Soviet apartments. Now the number of household appliances has become much larger, as a result of which the probability of getting a fire with old fuses has increased. To prevent this, it is necessary to carefully approach the choice of a machine with the correct characteristics. Excess power reserves should be avoided. The final choice is made after a few simple steps.

Determining the number of poles

When determining given parameter switch should be guided simple rule. If you plan to secure sections of the circuit with devices that have low power consumption (for example, lighting devices), then it is better to leave your choice on a single-pole machine (usually class B or C). If you plan to connect a complex household device with significant power consumption (washing machine, refrigerator), then you should install a two-pole machine (class C, D). If a small production workshop or a garage with multi-phase propulsion systems is being equipped, then it is worth choosing a three-pole option (class D).

Power consumption calculation

As a rule, by the time it is planned to connect the machine, the wiring to the room has already been connected. Based on the cross section of the cores and the type of metal (copper or aluminum), it is possible to determine maximum power. For example, for copper core in 2.5 mm 2 this value is 4–4.5 kW. But the wiring is often summed up with a large margin. Yes, and the calculation should be done before the start of all installation work.

In this case, you will need a value about what the total power will be used by all devices. It is always possible to turn them on at the same time. So, in an ordinary kitchen, the following appliances are often used:

refrigerator- 500 W;
Electric kettle- 1700 W;
microwave– 1800 W

The total load is 4 kW and a 25 A machine is enough for it. But there are always consumers who turn on sporadically and can create factors that contribute to the operation of the circuit breaker. Such devices can be a combine or a mixer. Therefore, you should take the machine with a margin of 500-1200 watts.

Rated current calculation

Since the power in single-phase networks is equal to the product of voltage and current, it is easy to determine the current as a quotient of power and voltage. For the above example, this value is easy to calculate, knowing that the mains voltage is 220 V. The current consumption is 18.8 A. With a margin of 500-1200 V, it will be 20.4-23.6 A.

In order for the work not to stop even with such short-term excess loads, the rated current for the machine can be taken equal to 25 A. Approximately the same value corresponds to the rating, based on a copper cable with a cross section of 2.5 mm 2, which is enough with a margin for such loads. A machine with a rated current of 25 A will work before it starts to heat up.

Determination of the current characteristic time

This parameter is determined by a special table that lists the starting currents and their flow time. For example, for a household refrigerator, the starting current ratio is 5. With a power of 500 W, the operating current is 2.2 A. The starting current will be 2.2 * 7 \u003d 15.4 A. Data on the frequency is also taken from a special table.

Table No. 1. Starting currents and pulse durations for household appliances

For the selected device, this characteristic does not exceed 3 s. The choice becomes obvious: for such a consumer, it is necessary to take a type B circuit breaker. It is permissible to make a choice of the machine according to the load power. You can skip the last step by opting for a class B switch. For domestic needs, the characteristics of class B and C electrical switches are most often sufficient.

Installation protective equipment- an important stage in the construction of electrical networks. In the event of the occurrence of large currents, heating occurs, causing the melting of the insulating layer of the conductor. This situation leads to a fire. A sharp increase in the magnitude of the current is associated with a short circuit that occurs during the operation of faulty equipment.

In order to avoid the threat of fire and damage to wires, various types of electric machines are used, depending on the parameters used in conjunction with electrical devices.

Principle of operation and varieties

The principle of operation of electrical switches is to break the electrical circuit when a short circuit occurs. Or exceeding the permissible power for which the electrical network is designed. Electric circuit breakers are always located at the beginning of the protected section of the circuit. In this case, the type of connected load does not matter.

According to their form and parametric values, automata are divided into:

by the number of poles;
according to the time-current characteristic;
by rated current.

It is also necessary to note the current limiting class. This value is characterized by the speed of the device's response to an emergency situation. The division is into three classes. For domestic use, the third class is used.

Regardless of their characteristics, the principle of operation for all switches is identical. To connect the machine to the electrical network, it is necessary to set the control switch to the "on" position. The current flowing to the switch is fed through the input terminal to the solenoid coil, and from it to the bimetallic plate. The plate is a strip of two pressed metals with different coefficients of thermal linear expansion. The current from the plate comes to the output terminal and then enters the electrical circuit. The plate and solenoid are called releases.

Current release - important element designs, it can be:

electromagnetic (solenoid);
thermal (bimetallic plate);
combined (combination of thermal and electromagnetic);
independent (remotely acting on the switch, it turns off).

There are two conditions under which the electrical switch will trip to open the line: overload mode and short circuit mode.

The principle of operation in overload mode is based on the ability of a bimetallic strip to bend under the influence of heat. With an increase in power to the line, the current flowing through the electric machine increases, exceeding the working value switch. As a result, the release heats up, its plate bends, and the contact breaks. Accordingly, the electrical circuit is broken. The current supply is stopped. The amount of current at which the plate breaks the contact is set at the factory with an adjustment screw. After the plate has cooled, it returns to its previous shape, and the contact appears again.

In the short circuit mode, the current increases very quickly, the magnetic field formed by it in the solenoid sets the core in motion. The core acts on the release, and the electrical circuit breaks, and an arc appears. The appearance of an arc negatively affects internal parts automatic machine, therefore, a device for extinguishing it is used. The arc chute is made of plates parallel to each other, passing through which the arc dissipates.

Thus, the main structural parts can be noted:

current terminals;
release:
control lever;
release adjusting screw;
arc chamber.

Number of poles

The number of poles indicates how many wires can be passed through the switch at the same time. There are devices with the number of outputs from one to four. The device of a single-pole switch is no different from a multi-pole one, only in the second case, when passing electric current several chains are broken at the same time.

Single-pole devices are more often used in domestic conditions and are placed in a break in the phase wire, the zero one is connected directly through the block, as an introductory machine, its use is not recommended. For installation at the entrance, two-pole circuit breakers are used, the phase and neutral wires are connected to them at the same time. For use in a three-phase network, a three-pole machine is already used as an input. To protect a four-phase electrical network, for example, a star-connected motor, a four-phase automatic machine is used. In this case, three phase and one neutral wire are connected.

The usual scheme for building protection on electrical switches comes down to installing an input automaton of the required number of poles. After it, single-pole ones are installed - one for each group. In this case, the value of the rated current of a single-pole machine is already calculated based on the parameters of the group to which it is connected. Its value is chosen less than the input value.

Time-current characteristic

This parameter indicates the ratio of the actual current flowing through the machine to the nominal value. Depending on the value of the ratio, the sensitivity of the automaton is determined, which is characterized by the number of false positives. There are machines various kinds. They are marked with letters of the Latin alphabet. The most common switches are labeled B, C and D.

Electric machines with characteristic B are switched off within 5-20 seconds. In this case, the current value can exceed the nominal value by five times. These models are widely used in household premises. Marking C means switching off interval 1-10 seconds, while the load is ten times the value. Class D circuit breakers are used to protect engines. The operating current exceeds the nominal by 14−20 times.

Rated current

Indicates the amount of current that can pass through an electric machine without it tripping. Strictly defined values \u200b\u200bare produced from 1 to 63 amperes. There are 12 values in total: 1A, 2A, 3A, 6A, 10A, 16A, 20A, 25A, 32A, 40A, 50A, 63A.

The choice of rated current depends on the power value that the wiring can withstand without damage. This value is determined by the cross section of the wire and the material of its manufacture. In homes, the most popular machines for use are 6A, 10A and 16A. Automatic machines with a nominal value of 20A, 25A, 32A are used in apartments as introductory, i.e., two-pole.

Location and accommodation

The method of placement (whether it is a single-phase electric machine or another type) is strictly vertical. The fixed part of the control lever must be on top, i.e. the device is switched on by switching from bottom to top. Devices are placed in accessible places, and the possibility of their mechanical damage is excluded.

DIN rail mounting is the most popular. Usually such a rail is installed in the shield. Electrical switches structurally have special grooves into which the rail is inserted.

What are the machines, how are they marked - you need to know this information in order to choose the right device. Regardless of the manufacturer and type of electric machines, they are always marked on front side. Marking is carried out according to a single scheme. It includes an indication of all the main parameters:

On the control lever, inscriptions are made indicating the set position - “on.” and "off" or "1" and "0".

Leading brands and manufacturers

The leaders in the production of circuit breakers are the following brands:

This famous brands, producing any kind of automatic machines. They are characterized by high quality housing, long service life and high mechanical strength. Often, protective covers are additionally installed on them. These manufacturers produce their devices from solid materials. Their quality is confirmed by certificates and a warranty period given by manufacturers for their products.

When assembling an electrical panel or connecting a new large household appliance, home master will definitely face such a problem as the need to select circuit breakers. They provide electrical and fire safety, because right choice machine is a guarantee of the safety of you, family and property.

What is the machine for?

In the power supply circuit, an automatic machine is installed to prevent overheating of the wiring. Any wiring is designed for the passage of a certain current. If the passed current exceeds this value, the conductor starts to heat up too much. If this situation persists for a sufficient period of time, the wiring begins to melt, which leads to 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 closing, the currents in the circuit increase many times and can reach thousands of amperes. So that they do not destroy the wiring and do not damage the equipment included in the line, the circuit breaker must turn off the power as soon as possible - as soon as the current exceeds a certain limit.

In order for the protective circuit breaker to perform its functions properly, it is necessary to correctly select the machine in all respects. There are not so many of them - only three, but each one must be dealt with.

What are automatic protection

To protect the conductors of a single-phase 220 V network, there are single-pole and two-pole disconnecting devices. Only one conductor is connected to single-pole - phase, to two-pole and phase and zero. Single-pole machines are placed on 220 V circuits for internal lighting, on socket groups in rooms with normal conditions operation. They are also put 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 put on a three-phase load (ovens, hobs and other equipment that runs on a 380 V network).

In rooms with high humidity(bathroom, sauna, swimming pool, etc.) put two-pole circuit breakers. They are also recommended to be installed on powerful equipment - on washing and dishwashers, boilers, ovens etc.

Just in emergency situations- in case of a short circuit or breakdown of insulation - phase voltage can get to the neutral wire. If a single-pole device is installed on the power line, it will disconnect the phase wire, and zero with a dangerous voltage will remain connected. So, there is a possibility of electric shock when touched. That is, the choice of the machine is simple - single-pole switches are placed on some of the lines, and two-pole switches on some. The exact amount depends on the network condition.

For a three-phase network, there are three-pole circuit breakers. Such an automatic machine is placed at the entrance and at consumers, to which all three phases are supplied - an electric stove, three-phase hob, oven, etc. The remaining consumers are equipped with bipolar circuit breakers. They must necessarily disconnect both phase and neutral.

An example of a three-phase network wiring - types of circuit breakers

The choice of the circuit breaker rating does not depend on the number of wires connected to it.

Deciding on a 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 wiring capabilities. And 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 choosing a circuit breaker is simple:

for a specific area.
See what maximum current this cable can withstand (there is in the table).
Further, from all the denominations of circuit breakers, we select the nearest smaller one. The ratings of the machines are tied to the permissible continuous load currents for a particular cable - they have a slightly lower rating (there is in the table). The list of ratings looks like this: 16 A, 25 A, 32 A, 40 A, 63 A. From this list, choose the right one. There are denominations and less, 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 indicates the maximum allowable current for conductors that are used for. There are also recommendations regarding the use of machines. They are given in the column "Rated current of the circuit breaker". It is there that we are looking for denominations - it is slightly less than the maximum allowable, so that the wiring works in normal mode.

Cross section of copper wires	Permissible continuous load current	Maximum load power for a single-phase network 220 V	Rated current of the circuit breaker	Circuit breaker current limit
1.5 sq. mm	19 A	4.1 kW	10 A	16 A	lighting and signaling
2.5 sq. mm	27 A	5.9 kW	16 A	25 A	socket groups and electric underfloor heating
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	introductory lines

In the table we find the selected wire section for this line. Let us 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 such a cross section can withstand a current of 27 A, and the recommended rating of the machine is 16 A.

How will the chain work then? As long as the current does not exceed 25 A, the machine does not turn off, everything works in the normal mode - 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 enough long time the current will exceed 25 A by 13%. In this case, if it reaches 28.25 A. Then the electric bag will work, de-energize the branch, since this current already poses a threat to the conductor and its insulation.

Power calculation

Is it possible to choose an automatic machine according to the load power? If only one device will be connected to the power line (usually a large Appliances with a large power consumption), it is permissible to make a calculation according to the power of this equipment. Also in terms of power, you can choose an introductory machine, which is installed at the entrance to a house or apartment.

If we are looking for the value of the introductory machine, it is necessary 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, the operating current for this load is found.

After you have found the current, select the value. It can be either a little more or a little less than the found value. The main thing is that its tripping current does not exceed the maximum allowable current for this wiring.

When can this method be used? If the wiring is laid with a large margin (this is not bad, by the way). Then, in order to save money, you can install automatic switches corresponding to the load, and not to the cross section of the conductors. But once again we pay attention that the long-term permissible current for the load must be greater than the limiting current of the circuit breaker. Only then will the choice of circuit breaker be correct.

Choosing a breaking capacity

The selection of a packet box for the maximum allowable load current is described above. But the circuit breaker should also turn off when a short circuit (short circuit) occurs from the network. This characteristic is called the breaking capacity. It is displayed in thousands of amperes - this order can be reached by currents during a short circuit. The choice of a machine for breaking capacity is not very difficult.

This characteristic shows at what maximum value of the short circuit current the machine remains operational, that is, it can not only 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 made very rarely, but are guided by the distance from the transformer substation.

If the substation is located near the entrance to your house / apartment, they take a machine with a breaking capacity of 10,000 A, for all other city apartments, 6,000 A is enough. If the house is located in countryside go, you choose an automatic circuit breaker for a summer cottage, a breaking capacity of 4,500 A may well be enough. The networks here are usually old and short-circuit currents are not large. And since the price increases significantly with increasing breaking capacity, the principle of reasonable economy 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 inoperable at the same time. In the worst case, 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 should operate when the current rises above a certain mark. But the network periodically experiences short-term congestion. They are usually associated with inrush currents. For example, such overloads can be observed when the refrigerator compressor, motor washing machine etc. The circuit breaker should not trip during such temporary and short-term overloads, because they have a certain delay in 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 “waits”, its contacts will melt. That's why there is an electromagnetic automatic release. It works at a certain current value, which can no longer be an overload. This indicator is also called the cut-off current, since in this case the circuit breaker cuts off the line from the power supply. The magnitude of the tripping current can be different and is displayed by the letters that precede the numbers indicating the rating of the machine.

There are three most common types:

With what characteristic to choose a package? In this case, the choice of a circuit breaker is also based on the remoteness of your household from the substation and the state of the power grid, the choice of a circuit breaker is carried out using simple rules:

With the letter "B" on the case, they are suitable for summer cottages, houses in villages and towns that receive power through air ducts. They can also be installed in apartments of old houses in which the reconstruction of the house electrical network has not been carried out. These circuit breakers are not always on sale, they cost a little more than category C, but they can be delivered to order.
Bags with a "C" on the body are the most widely used variant. They are installed in networks with a normal state, suitable for apartments in new buildings or after major repairs, in private houses near the substation.
Class D is put in enterprises, in workshops with equipment that has high starting currents.

That is, in fact, 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 manufacturers. The choice of a machine cannot be considered complete if you have not thought about what brand of circuit breakers you will buy. You definitely shouldn’t take unknown firms - an electrician is not an area where you can experiment. Details about choosing a manufacturer in the video.