This material will focus on how NOT to choose a cable cross-section.

I often see that the required cable cross-section is chosen according to the number of kilowatts that can be “loaded” on this cable.

Usually the argument sounds like this: "A cable with a cross section of 2.5 mm2 can withstand a current of 27 amperes (sometimes 29 amperes), so we put the machine on 25 A."

And in practice, sometimes you come across outlet groups protected by a 25A machine, and lighting by a 16A machine.

This approach to the selection of circuit breakers leads to overheating, melting and damage to the insulation, and as a result - to a short circuit and fire.

Let's turn to table 1.3.4. from PUE.

The permissible continuous current for copper wires laid hidden is 25 A. It seems that everything is correct, is it so?

If you install the machine at 25A, which is called "on the forehead", and from we remember that the thermal protection of the machine a can be triggered when the rated current is exceeded by 13%, which in our case will be 25x1.13 = 28.25A. And the response time will be over an hour.

And with an overload of 45%, the thermal release will trip in less than 1 hour, i.e. 25Ax1.45 = 36.25 A. But it can work in an hour.

It is clear that at such currents, the cable will simply burn out.

If the 16A machine is installed on the lighting, the result will be the same, you can calculate it yourself.

In addition, sockets are available for a maximum current of 16A, and switches - 10A. If you install oversized circuit breakers on sockets and lighting, this will lead to their melting, destruction of contacts and potentially a fire. I think you have seen fused sockets - the result of connecting a very powerful load, for which the sockets are not designed.

REMEMBER! In our apartments and houses, socket groups are made with a 2.5 mm2 cable with the installation of a 16A circuit breaker, lighting groups are made with a 1.5 mm2 cable with a 10A circuit breaker installed. A smaller denomination is possible, a larger one is not allowed!

A variation of this approach: knocks out the machine, especially for the outlet group of the kitchen, where powerful appliances are connected. In reserve, so that a 32A and even 40A machine is installed. And this is when the wiring is done with a 2.5 mm2 cable !!! The consequences are obvious and discussed above.

There are still situations when a cable of a larger cross-section (for example 4 mm2) is laid before the branch box, and then the lines are laid out at 2.5 mm2 and the machine is installed at 25A or 32A.

The circuit breaker current must be selected based on the weakest point in the line, in our example, this is a 2.5 mm2 cable. Therefore, such a group still needs to be protected with a 16A machine gun.

If you install the circuit breaker for 25A, then when you turn on a load close to 25A to one of the outlets, the cable to the branch box will burn out, and for a cable with a cross section of 4 mm2 from the branch box to the circuit breaker, this will be a normal mode.

All these points must be taken into account when calculating the cable cross-section.

Watch a detailed video:

Calculation of the cable cross-section. Errors

No, dear reader, today we will not be talking about choosing a manufacturer, although, I will not deny, I am not indifferent to this trinity in the photo. Today I will try to tell you how to choose the parameters of machines based on the conditions of their use. The choice of circuit breakers must be approached as responsibly as possible, since it is these modest workers in the power grids that take the brunt of the brunt in most emergencies.

Any serious manufacturer (well, or someone who wants to seem serious) indicates on the front side of the machine body some obscure, but very important designations. Let's look at the pictures:

Numbers 1, 2, 3 mark the same type of designation on machines from different manufacturers. What are they talking about? Let's sort it out in order. If you don't understand any words or abbreviations, take a look at. And be patient, dear reader, the article will be long. So:

DIGIT 1

In the photographs, the number 1 indicates the rated current of the machine, measured in amperes. This is the most important parameter of the circuit breaker. We do not pay attention to the letter to the left of the rated current, more on it later.

What exactly is a circuit breaker for? That's right, to protect, but to protect what? Maybe home appliances? No. He is not obliged to protect household appliances. The machine protects the wiring. And it is the section of the wiring that is connected AFTER the machine, and not BEFORE it. The wiring can be made with cables of different cross-sections, respectively, and the long-term current can withstand different ones. The task of the machine is to prevent a prolonged flow of current exceeding the value permissible for a given cable. What do the PUEs say about this?

Table 1.3.4. Permissible continuous current for wires and cords with rubber and PVC insulation with copper conductors

Conductor cross-section, mm 2	Current, A, for wires laid
	open	in one pipe
		two single core	three one vein	four one vein	one two vein	one three vein
1,5	23	19	17	16	18	15
2,5	30	27	25	25	25	21
4	41	38	35	30	32	27
6	50	46	42	40	40	34
10	80	70	60	50	55	50
16	100	85	80	75	80	70

I edited the table, removing from it sections that are not used in everyday life. Cooling conditions for a cable laid in a gate are practically the same as for a cable laid in a pipe. A three-core cable with a protective PE conductor should be considered here as a two-core cable, since no current flows through the protective conductor in normal operation. Therefore, we are interested in the penultimate column of the table (highlighted in red), which indicates the permissible continuous currents for a two-core cable laid in a pipe. Everything seems to be clear; a cable with a cross-section of 1.5 squares is protected with a 16A machine (the closest downward standard rating from 18A), 2.5 squares - 25A and so on ...

But it was not there! It was in the USSR that you could buy a cable with a 2.5 squares cross-section declared by the manufacturer and be 100% sure that it is. Now "effective managers" are ready to do anything in order to extract additional benefits. And the overwhelming majority of cable products come with an underestimated cross-section of conductors. Let's say you bought a cable with a cross-section of 2.5 squares, measured the diameter of the core with a micrometer, calculated the area of ​​the circle and realized that, to put it mildly, you were deceived. The real cross-section of the vein turned out to be, for example, 2.1 squares.

But that is not all. Was the cable sold to you as a copper one? Electrical copper should be reddish, easy to bend and not springy. Now look at what you have in your hands. Are the veins yellowish, bent with effort and clearly springy? Congratulations . The manufacturer also saved on the chemical composition of the veins. This is no longer copper, but rather brass. And the electrical conductivity of brass is lower than that of copper.

What to do? Well, first of all, not all manufacturers cheat. There is, for example, Rybinskelektrokabel or Kolchuginsky Elektrokabel, which produce honest GOST products. True, it will be more expensive. And you won't be able to buy it in Yaroslavl on a swoop, you have to order it. If necessary, we will do it, I have a discount. If you need cheaper, you can buy in specialized stores, the cable there is also of quite acceptable quality, there is no frank leftist. The main thing is not to buy the cable at the grocery store, shops that sell everything from flower pots to cars.

But back to the topic of our conversation. Let's say the cable you purchased is, so to speak, not entirely honest. Nothing wrong with that. You just need to reduce the value of the machine by one step. For example, if according to table 1.3.4 for a cable with a cross-section of 2.5 squares the permissible current is 25A, then we will supply an automatic machine with a rating of 16A. For a cable with 6 squares conductors, the table allows 40A, but we will install a 32A machine. In short, it's better to play it safe a little. But the point is not only about reinsurance. There is one more good reason to reduce the value of the machine by one step from the table value. About her later.

Let's briefly summarize this part of the article, adjusting the cross-section of the cable cores and the rating of the circuit breaker, taking into account reasonable reinsurance and the scope of application:

We continue talking about the number 1 in the pictures. Now let's talk about the letter to the left of the designation of the rated current of the machine:

This letter indicates the characteristic of the electromagnetic (instantaneous) release. Anyone who is not familiar with the circuit breaker device and does not know what an electromagnetic release (EMR) is, please. EMR is triggered when a short-circuit current (TKZ) occurs. But the machine must be able to distinguish between short and overload. For example, a current of 25A went through an automatic machine with a nominal value of 16A. This is an overload, but not a short-circuit current. The bimetallic plate of the thermal release (TP) heats up and forces the circuit breaker to shut down. But this takes time, TP does not know how to work instantly. And if the current is not 25, but 200A? Now this already looks like a shorty. While the TR goes off, the fire may start! Here the EMR comes into play, which will force the machine to shut down immediately.

Where is the border beyond which the EMR should regard the overload as a short circuit and instantly turn off the machine? This border is indicated by the letter to the left of the designation of the rated current of the machine. It is called the characteristic of the electromagnetic release. This letter denotes the multiplicity of the cut-off current EMR (Iotc) in relation to the rated current of the machine (Iн). That is, the ratio Iotc / In. These letters may be different, but there are three most common:

The letter "B". Iotc = 3 ... 5Iн

The letter "C". Iotc = 5 ... 10Iн

The letter "D". Iots = 10 ... 20Iн

Let's look at two examples:

First example. A circuit breaker with a rated current of 16A and characteristic "C" (C16) has a current of 100A. Will the cutoff (EMR) work or will the machine take time to trigger the TR? We multiply the rated current of the machine by the multiplicity factor corresponding to the characteristic "C" (in the calculations for reliability, you should use the greatest value the multiplicity factor from the range for the corresponding characteristic; if for characteristic "C" the range is 5 ... 10, in the calculations we take the value of the coefficient equal to 10):

16x10 = 160A

The electromagnetic (instantaneous) release of the C16 machine will trip at a current not less than 160A. But our current through the machine is 100A. Means what? That's right, EMR in this example will not work and you can only hope for TR.

Example two. The conditions are the same as in the previous example, but the EMR characteristic is no longer "C", but "B" (automaton B16):

16x5 = 80A

The minimum operating current of the EMR in this case is 80A. And we have 100A. Therefore, we have a reserve of 20A and the cutoff will work confidently; the machine will turn off instantly.

For clarity, I stole the following picture on the Internet:

The picture is called "Time-current characteristic of the circuit breaker". Knowing how many times the current through the machine is greater than its nominal value, it can be used to determine the response time. In the picture, light gray indicates the operation area of ​​the electromagnetic release, and above it - the thermal one, in a darker color. Again, a few examples:

1. The current through the machine is twice its nominal value. It follows from the picture that an automaton with any characteristic will turn off in the time interval from 10 to 50 seconds.

2. The current through the machine is eight times the nominal. Automatic machine with characteristic "B" will turn off in 0.01 seconds, EMR will work. And the automatic machine with the characteristic "C" will work in the time interval 0.01 ... 3 seconds. Remember the interval of the cut-off current multiplicity 5 ... 10Iн for the "C" characteristic? In our example, we have an eight-fold overload that lies within this interval. Therefore, the response time will depend on the specific instance of the machine. For one machine, the EMR will work (0.01 seconds), for the other it will not, and the machine will have to turn off the thermal release in 3 seconds.

3. The current through the machine is 15 times higher than the rated one. Here automatic machines with characteristics "B" and "C" will work instantly, and an automatic machine with characteristic "D" (interval of cut-off current multiplicity 10 ... Again, this will depend on the specific instance.

4. Thirty times the rated current. A specific shorty! In this case, all three machines ("B", "C" and "D") "click" immediately.

But this is not all the "interestingness" of this picture. Do you see in the upper left corner two lines going up and next to them two numbers - 1.13 and 1.45? These are very interesting numbers. These are the overload multiplicity factors at which the machine is triggered for more than an hour (1.13) and less than an hour (1.45). In other words, if the overload is less than 1.13, then the machine will not work at all. If in the range from 1.13 to 1.45, then it will work in more than an hour. And if the overload ratio is more than 1.45, for example, 1.6, then the machine will work in less than an hour.

Let's go back a little to the choice of the rated current of the machine. Remember table 1.3.4? Let's calculate what will happen if you blindly use this table and do not think with your head. For a cable with 2.5 kV conductors, when laid in a gate, the table allows a continuous current of 25A. We turn off the brains and stupidly put a 25A machine on this line. And then we arrange an overload; let's say 1.4 times. 25x1.4 = 35A! And the time-current characteristic tells us that it will take more than an hour for the machine to operate with such an overload. That is, for more than an hour, a current will flow through the cable almost one and a half times higher than the maximum permissible! And if, in addition, the cable is laid so that the cooling conditions are unimportant, for example, in a corrugation or in a layer of insulation, or both at the same time? We do not forget about the fact that the cable, possibly with a lowered cross-section of the conductors, is also not forgotten. What will happen in the end? Let us fry the cable! A fire will most likely not happen, but insulation degradation will inevitably occur, which will make itself felt in a few years. And if such overloads occur regularly, then much earlier. This is another reason for reducing the value of the machine by one step from the table value. Greetings to you, jamshuts, molding machines 25A on outlet lines! Especially for you I repeat:

1.5 sq. Mm. - 10A. Lighting lines.

2.5 sq. Mm. - 16A. Outlet lines.

4 mm2 - 25A. Lines of flowing water heaters of moderate (up to 5 kW) power.

6 sq. Mm. - 32А Lines of electric stoves or instantaneous water heaters of high power; entrance to apartments with gas stoves.

10 sq. Mm. - 50A. Entering into apartments with electric stoves.

By the way, there is one more nuance. Most common household outlets are designed to accommodate 2.5 squares of conductors. But the permissible current indicated on the outlet is 16A. Therefore, the machine must have a rating of no more than 16A, despite the fact that table 1.3.4 allows a continuous current of 25A for a cable with 2.5 squares conductors. Household appliances that have a regular plug designed to be plugged into a regular outlet never have a power more than 3.5 kW, which means they easily fit into the 16A limit.

But back to the characteristics of the electromagnetic release. How to choose the right letter to the left of the rated current of the machine? It is clear that it is necessary to strive to ensure that the EMR of the machine is confidently triggered when the TKZ occurs. In other words, the product of the rated current of the machine and the multiplicity factor must certainly be less than the TKZ, which can occur in the protected section of the network. And the higher the TKZ is, the more confidently the machine will work. But what does the expected TKZ depend on? From just three factors:

1. The length of the network. The greater the distance from the transformer substation to your house, the further your entrance is from the house ASU and the higher your floor, the less the expected TKZ will be.

2. Cross-section of conductors. If the risers of your house are laid with aluminum wires with a cross section of only 6 squares, and in the apartment the APPV noodles with a cross section of 2.5 squares, you should not count on a large TKZ.

3. The state of the connections. A bunch of "snotty" twists in the floorboards will also reduce the expected TKZ.

There are special instruments for measuring the expected TKZ. Their price tag is inhumane, so they are not available to most home craftsmen. But when choosing the characteristic of an electromagnetic release, you can be guided by several simple rules:

Characteristic "B". It is preferable in the old housing stock, where there has been no reconstruction of the intra-house electric networks. Also, in rural and country houses, powered by long-distance overhead lines. It should be noted here that the price of machines with characteristic "B" is slightly higher than with characteristic "C" and they are not available on free sale, ordered position. But again, dear reader, if necessary, we will do it.

Characteristic "C". Slot machines with this characteristic are the most widespread and available for sale. They can be used in power grids that are in satisfactory condition.

Characteristic "D". Due to the large multiplicity of the cut-off current (10 ... 20In), such machines are used in industry to protect lines with high starting currents, arising, for example, when starting powerful electric motors. And in everyday life they have no place! This is what GOST 32395-2013 "Distribution Boards for Residential Buildings" says:

"6.6.5 Circuit breakers ... .. must have short-circuit current releases (electromagnetic, types B, C)"

As you can see, the characteristic "D" in residential buildings is unacceptable.

Well, dear reader, we figured out the rated current of the circuit breaker and the characteristic of the electromagnetic release. Now let's move on to the number 2 in the pictures.

DIGIT 2

In the photographs, the number 2 indicates the breaking capacity of the machine (OS), measured in amperes. This is the maximum short-circuit current that the machine is able to turn off, while maintaining its operability. Above, I said that in the old housing stock, in rural areas and in summer cottages, the expected TKZ does not reach large values ​​and to ensure protection it is necessary to use automatic machines with the characteristic "B", that is, with more sensitive EMRs capable of responding to relatively low short-circuit current.

But the situation can be just the opposite. If you have a newly-built apartment, risers at the entrance of a large section, and the substation is located right in the yard, the expected TKZ can reach very large values, up to 2000 ... 3000A! The machine will, of course, work, but when its contacts disperse, a powerful arc will arise between them, which must be extinguished immediately. Here is the ability of the machine to extinguish the arc caused by a short circuit and indicates its breaking capacity.

The breaking capacity can be 3000, 4500, 6000 and 10000A. By the way, machines with OS 3000 and 4500A are prohibited for use in the EU countries. European firms no longer produce automatic machines with OS 3000A; 4500-amperes are produced, but sold only in the vastness of the CIS. Actually, there is no crime in this; an automatic machine with a breaking capacity of 4500A is suitable for use in residential buildings. Here is a machine from ABB model SH201L with OS 4500A:

This series is called “Compact Home” by ABB, which means that it is intended for use in residential construction.

But I still prefer to use machines with a breaking capacity of 6000A. The fact is that the higher the breaking capacity of the machine, the greater its resource. And given that the difference in the price of machines with OS 4500 and 6000A is only about 20 rubles, the scanty savings on their own safety are inappropriate.

And finally, dear reader, we got to the number 3 in the pictures.

DIGIT 3

The number 3 in the pictures indicates the class of current limitation. What is it?

Let's imagine how the machine works when a short circuit occurs:

1. The short-circuit current causes an increase in the magnetic flux in the coil of the electromagnetic release.

2. The core of the coil moves under the influence of its magnetic field and strains (provokes) the contact group disengagement mechanism.

3. The tripping mechanism is triggered and opens the contacts.

4. The arc formed between the contacts is extinguished by the arc chute.

It is clear that each of these four steps takes some time. But we have a short man and a huge current flows in the emergency line! This means that the response time of the machine should be as short as possible; the less this time is, the less troubles the shorty's current will have time to do. And it is very desirable that the automatic device works before the short-circuit current reaches its maximum value.

An automatic device with a current limiting class 2 is triggered in a time no more than 1/2 half-period. And an automaton with a class 3 works faster, in no more than 1/3 of a half-period and, of course, is more preferable. Note that in the second case (class 3), the machine will operate before the short-circuit current reaches its maximum.

Content:

The action of short circuits has a detrimental effect on electrical wiring, leads to its destruction and serves common reason fires. In order to prevent such situations, various means of protection are installed. Circuit breakers are now widely used to replace porcelain fused plugs. These devices are more reliable and sophisticated. In this regard, the question often arises of how to choose the right machine for power and load.

The principle of operation of the circuit breaker

The main function of the circuit breakers is to protect the insulation of wires and power cables from damage caused by short-circuit currents. These devices are not able to protect people from electric shock, they only protect the network and equipment. The action of the circuit breakers ensures the normal operation of the wiring, completely eliminating the threat of fire.

When choosing an automatic machine, it is imperative to take into account that the overestimated characteristics of the device will contribute to the passage of currents that are critical for wiring. In this case, shutdown of the protected area will not occur, which will lead to melting or ignition of the insulation. In the case of underestimated characteristics of the machine, the line will constantly break when starting powerful equipment. The machines fail very quickly due to sticking contacts under the influence of too high currents.

The main working elements of the machines are those that directly break the chain in critical situations. They are divided into the following types:

• Electromagnetic releases. They react almost instantly to short-circuit currents and cut off the desired section within 0.01 or 001 seconds. The design includes a coil with a spring and a core that retracts under the influence of high currents. During retraction, the core actuates a spring associated with the trip device.
• Thermal bimetallic releases. Provide network overload protection. They provide an open circuit when a current is passed that does not meet the operating limits of the cable. Under the influence of high current, the bimetallic plate bends and triggers the release.

Most machines used in everyday life use an electromagnetic and thermal release. A well-coordinated combination of these two elements ensures reliable operation of protective equipment.

Current circuit breaker ratings table

The need to select circuit breakers arises during the design of electrical networks in new homes, as well as when connecting devices and equipment with a higher power. Thus, in the process of further operation, reliable electrical safety of objects is ensured.

A negligent attitude towards the choice of a device with the necessary parameters leads to serious negative consequences. Therefore, before choosing an automatic protective device, it is imperative to make sure that the installed wiring can withstand the planned load. In accordance with the PUE, the circuit breaker must provide overload protection for the weakest section of the circuit. Its rated current must match the current of the connected device. Accordingly, the conductors are selected with the required one.

To calculate the power of the machine by current, you must use the formula: I = P / U, where P is the total power of all electrical appliances available in the apartment. Having calculated the required current, you can choose the most suitable machine. The table, with which you can select a circuit breaker, depending on specific operating conditions, greatly simplifies the calculations. The calculation of the automatic machine according to the current power is carried out mainly for electrical installations - electric motors, transformers and other devices with a reactive load.

Table of the dependence of the power of the machine on the cross-section of the wire

Each electrical wiring is divided into certain groups. Accordingly, each group uses an electric wire or cable with a certain section, and protection is provided by an automatic machine with the most suitable rating.

The table will help you choose a circuit breaker and cable cross-section, depending on the expected load of the electrical network, calculated in advance. The table helps to make the right choice of the machine according to the load power. When calculating current loads, it should be remembered that the calculations of the load of one consumer and a group of household appliances differ from each other. When calculating, it is necessary to take into account the difference between single-phase and three-phase power supply.

Circuit breakers are designed to protect electrical wiring from overloads and short circuits. It is a mistake to believe that when choosing an electrical appliance, one should be guided by the indicators of the load on the network. The machine protects cables and wires, not connected household appliances.

With an increase in the load on electrical network the current strength increases, due to which the wires begin to warm up, and the insulation melts. At this moment, the circuit breaker trips. The current ceases to flow to this section of the circuit, because the electrical appliance opens it. Automatic switches are placed at the input.

Types of machines

The types of circuit breakers are distinguished by releases. A release is a structural element of the machine, which is entrusted with the main function of breaking the power grid in the event of an increase in voltage.

• Electromagnetic releases - instant response and tripping of the machine. Principle of operation: as the current strength increases, the core retracts in hundredths of a second, thereby tensioning the spring, which forces the releases
• Thermal bimetallic releases - a network break occurs only if the limit values ​​of the cable parameters are violated. The principle of operation is to bend the plate when it is heated. She pushes the lever in the machine and it shuts down
• Semiconductor releases - used on AC / DC mains at the input. The line break is carried out by the transformer relay unit

Overload sensitivity characteristics

First, you need to pay attention to the main characteristics of the response:

• Characteristic A - for wiring with particularly sensitive equipment. Calculation for the instantaneous response of the machine to overload
• Characteristic B - to protect electrical wiring (sockets and lighting) from the load in residential buildings. A small delay in the operation of the machine when the current increases 3-5 times from the nominal value
• Characteristic C - to protect electrical wiring from the load in residential buildings and for networks with a large inrush current. The most common characteristic. The automatic machine does not respond to small voltage surges, but only triggers in case of serious overloads - an increase in current strength by 5-10 times of the nominal value
• Characteristic D - to protect electrical wiring from a load with a high inrush current. Installed at the input to control the electrical network of the entire building. Disconnects the network when the current increases 10-50 times from the nominal value

Selection of the machine by the number of poles

Depending on the purpose of using the machine, the number of poles of the machine is selected:

• Single pole - to protect lighting and sockets
• Two-pole - to protect powerful household appliances (washing machine, electric stove, etc.)
• Three-pole - to protect generators, borehole pumps, etc.
• Four-pole - to protect a four-wire network

Selecting an automatic machine by power

The selection of the circuit breaker is based on the rated current. To calculate it, you need to use the generally accepted formula:

Where: I is the magnitude of the current

P is the power of all electrical appliances in W

U - voltage in the network in V (usually 220V)

In addition to choosing a circuit breaker for power, it is necessary to take into account the calculation of the maximum operating current. The rated current must be greater than or equal to the maximum. For the calculation, you need to sum up the power of all devices and divide it by the voltage in the network, multiplied by the reduction factor.

Calculation of limit values ​​depending on the type of wiring:

• For aluminum wires - up to 6A per 1 square millimeter
• For copper wires - up to 10A per 1 square millimeter

When installing a circuit breaker, multiplying factors must also be taken into account. They are calculated from the number of electricity consumers:

• Number of consumers 2 -0.8
• Number of consumers 3 - 0.75
• More than 5 consumers - 0.7

In addition to the increasing ones, decreasing coefficients are also used for the calculation: the difference between the total and consumed power. A value of 1 is for the simultaneous connection of several household appliances and 0.75 - if there are household appliances, but due to the lack of sockets, they cannot be turned on at the same time.

After calculation, you need to check the table as much as possible permissible value current for the conductor:

Basic rules for choosing machines

• You need to buy a machine in specialized stores
• When choosing a manufacturer, give preference to the most famous and reliable
• You cannot buy machines with a damaged case.
• The choice of the machine must correspond to the parameters of the wiring after calculating the power
• For old electrical wiring, in which aluminum wires were used, you can use an automatic machine no more than 16A, or two 16A each if there are two outgoing wires. It is impossible to turn on several types of household appliances at the same time.

When designing an electrical network at an enterprise or in an apartment, you cannot do without installing circuit breakers. They protect consumer property and human lives from unforeseen situations. A professional electrician should know well how to choose the right circuit breakers for reliable and safe operation of the power grid, how to select the machines according to the power of the load used and other parameters.

What is the circuit breaker used for?

A circuit breaker or, in a simple way, an automatic machine is necessary to prevent overheating of the insulation of wires and to protect the electrical circuit from short-circuit current. In addition, in the presence of a circuit breaker, the maintenance of electrical lines becomes more convenient, since at any time you can de-energize the circuit in the required area.

To perform these tasks, the machine has a thermal and electromagnetic release in its design. Each circuit breaker is designed for a specific rated current and time-current characteristic. The maximum operating current of the line depends on these parameters.

When electric current passes through the wires, the wire heats up and the more, the greater its value. If an automatic machine is not installed in the circuit, then at a certain value of the current, the insulation may begin to melt, which can lead to a fire.

What are the automatic circuit breakers

Apartment circuit breakers are modular devices. This means that they can be installed in residential distribution boards on a special DIN rail, while their overall dimensions are the same for different manufacturers and the same number of poles.

In electrical cabinets at the enterprise or transformer substations, there are also non-modular circuit breakers. They are distinguished by their large dimensions and rated current. They look like the picture below.

By the number of poles, machines are divided into single-pole, two-pole, three-pole and four-pole. Most often, a single-phase electrical network is designed so that a single-pole machine breaks the phase in a certain area, and zero is taken from a special zero bus. But if the space in the dashboard allows, you can put a two-pole machine on the network section for zero and phase. In this case, they will be torn together. Three-pole and four-pole circuit breakers are used for a 380 V network.

Also two, three and four-pole circuit breakers are used as.

Rest specifications refer to workers and are selected based on the parameters of the network, the power of consumers and the characteristics of the cable.

Selection of the rating of the machine according to the load power

When choosing the rating of the circuit breaker, it is necessary to correctly calculate the maximum load of the electrical section of the network.

The table of the ratio of the cable cross-section and the rating of the circuit breaker to the power consumption is shown below:

Copper section	Permissible load current	Power in the network 220 V	Rated current	Limiting current
1.5 mm²	19 A	4.1 kW	10 A	16 A
2.5 mm²	27 A	5.9 kW	16 A	25 A
4.0 mm²	38 A	8.3 kW	25 A	32 A
6.0 mm²	46 A	10.1 kW	32 A	40 A
10.0 mm²	70 A	15.4 kW	50 A	63 A

For example, for sockets in an apartment, the cross-section of a copper wire of 2.5 mm² is most often used. According to the table above, such a wire can withstand a current of up to 27 A, but the machine is selected for 16 A. Similarly, a 1.5 mm² copper cable and a circuit breaker rating of 10 A are used for lighting.

Breaking capacity

The breaking capacity of a circuit breaker is the ability of the circuit breaker to turn off at extremely high short-circuit currents. On the machine given characteristic indicated in amperes: 4500 A, 6000 A, 10000 A. That is, with a large instantaneous short-circuit current, but not reaching 4500 amperes, the machine is able to work and open the electrical circuit.

In apartments, you can most often find machines with a breaking capacity of 4500 A or 6000 A.

Time-current characteristic

If the current passing through the circuit breaker exceeds the nominal value, logically, the machine should work. So it will happen, but with some delay. The time after which the machine turns off depends on the magnitude and duration of this excess of the rated current. The greater the difference, the faster the machine turns off.

In the documentation for the circuit breaker, you can see a special graph of the dependence of the value of the ratio of the current to the rated current, from the time when this happens. The lower the current, the longer the time.

Before the rating of the machine, a Latin letter is indicated, which is responsible for the maximum value of the current. The most common values ​​are:

• V- exceeding the rated current by 3-5 times;
• WITH- 5-10 times excess ( most often this type is installed in apartments);
• D- 10-20 times ( used for equipment with high starting current).

Which manufacturers should you trust

The choice of the machine is made taking into account the manufacturer. Popular and quality brands include: ABB, Schneider Electric, Legrand and some others. Affordable products with budget prices are produced by firms EKF, IEK, TDM other. In operation, many products behave almost the same, so you should not always pay extra money for a brand with the same product quality. Schneider Electric products can cost 3-5 times more than IEK.

TDM - the product is manufactured in China in two series: VA 47-29 and VA 47-63. VA 47-29 has notches on the body for passive cooling. You can seal the device with special plugs sold separately. VA 47-63 are produced without cooling notches. The price of all products is within 130 rubles.

The Chinese firm Energia produces the same series as the TDM, but with lateral recesses and an on indicator. Series 47-63 without indicator and recesses on the body.

IEK (China) products have won great popularity among buyers, as well as DEKraft and EKF products.

KEAZ is a plant in Kursk that manufactures products of the VM63 and VA 47-29 series. The set of switches includes seals, there is an indication of the on state.

Hungarian GE products have significant weight and great popularity.

Moellers are manufactured in Serbia and Austria, are analogous to Chinese automatic circuit breakers, but have a higher build quality.

Schneider Electric has several product lines. The cost is in the range of 150-180 rubles. An alternative is Legrand TX products.

In Russia, many electricians love ABB products ( Germany), which is of high quality and reliability. Available in two series: S ( industrial series) and SH ( household series). Products cost 250-300 rubles.

A circuit breaker is required in the electrical circuit of any network. For the right choice, you need to calculate the total load and get the limit current. Check the table and make sure that the cross-section of the wire and the rating of the machine match each other. A correctly selected circuit breaker eliminates the possibility of a fire due to melted wires or a short circuit in the network.