Which machine to put on 6 kW single-phase. Calculation of the cable cross-section, circuit breakers

The circuit breaker is a serious piece of equipment, the choice of which should be taken with great responsibility. This is due to the fact that a short circuit or a strong power surge leads to fire, failure of household and other appliances. In addition, the ignition of the wiring is the cause of a fire in the house.

The working mechanism is usually hidden in a plastic case. This case material was chosen due to its good dielectric properties. The internal mechanism in the open state carries with it a danger, as electricity passes through it.

The circuit breaker is designed to perform the following functions:

To de-energize the network by manually pressing the switch.
For automatic de-energization rooms in the event of a short circuit or power surge.

It is worth noting that such a device has a fairly simple design, and it does not filter the supplied voltage to detect an incorrect frequency or low voltage indicator. Operation occurs only with a short circuit and a jump in the higher side of the voltage.

How to choose?

Having determined the important indicators, it is possible to make an informed choice of circuit breakers.

The choice can be made according to the following indicators:

By wire section. A certain wire section determines the possible load and current indicators. In this case, you should choose an automatic machine that turns off the network when a current occurs that does not exceed the maximum current in the wire. An example is a wire with a cross section of 1 sq. mm. The load value can be 10 kW. If the maximum force that will pass through the wire is 10 A, then the machine should be designed to turn off when a current of about 9.5 A occurs. If you do not make a choice based on such information, the machine will only work in case of a short circuit. However, the value of the current, during a short circuit, significantly exceeds the allowable indicator with an increase in load. An increase in load will cause a fire in the wiring.
For short circuit current. Even professionals in the field do not always select a circuit breaker based on its short circuit current rating. As a rule, such a value is indicated in the technical documentation or on the marking in the form of a number. Short circuit current limit - the maximum value at which an automatic circuit break will be carried out. It is important to note that this indicator is often used as a choice when installing in industrial premises, since a short circuit can occur in close proximity to a substation. In residential buildings, the value of the short circuit current is relatively small, which greatly facilitates the choice.
Power selection. In order to make a choice by power, you should use special tables. A similar table allows you to make a choice based on the following data: voltage value and number of phases, number of poles, load power. At the intersection of the above indicators, you can find the value that the circuit breaker should break. As noted earlier, the total power can be calculated by taking into account the consumer power of all connected electrical appliances.

All information about circuit breakers is contained in the specification or marking.

Kinds

Circuit breakers allow you to protect both equipment and end-user wiring from short circuits and high voltages.

The main classification is the purpose of the equipment in question:

Class "B" often used in the home. This version is not designed for high currents, when a minimum short circuit occurs, the circuit is opened. The high sensitivity means that class "B" models are not used in industry where a power surge can occur due to switching on or off equipment of high power. High sensitivity allows you to protect household appliances and electronics, for example, computers from burnout.
Class "C" considered a general industrial version, used in networks where it is also necessary to control the voltage in the network within a small range.
Class "D" used in a network to which an electric motor with a high starting power is connected. This class is also used in industry and has a small range of possible deviation from the normal value.

According to the type of current supplied Three categories of the considered switch can be distinguished:

For AC mains.
For DC network.
Universal version.

According to the number of poles, we can distinguish:

single-pole;
bipolar;
tripolar;
four-pole;

Also, the classification is by release type:

Maximum release.
Independent release.
Minimum or zero trip.

Depending on the situation, it may take a period of time to wait after a change in the indicators of the supplied electricity before it is turned off.

According to this indicator, the following classification can be made:

Without endurance.
With exposure regardless of the applied voltage.
With exposure, which is the reciprocal of the electricity supplied.

The above types of circuit breakers are widely used in everyday life and industry, but there are several nuances that should be considered when choosing them.

release

In addition, attention should be paid to type of breaker installed. It is the main working body, it opens the circuit at certain values.

This structural element differs in action specification and current range, the following classification can be made:

electromagnetic type is very popular, as it disconnects the circuit in a matter of seconds. The design includes a coil and a core, as well as a spring. The core is retracted under certain conditions, and the spring acts on the release device.
Bimetal thermal version- often installed for machines that respond to current, the magnitude of which can lead to the destruction of the cable. It also responds to a short circuit. However, the accuracy of the operation of such a circuit breaker is small. An example is the case when a current of 20 A passes through a cable that has a cross section for 16 A - the shutdown will occur after a few tens of minutes. If the current is 35 A, then the shutdown will occur instantly.
semiconductor It is used extremely rarely in the manufacture of household switches. Disengagement occurs during the operation of a special block of semiconductor relays.

It is worth noting that when marking, there is rarely an indication of which type of circuit breaker was used in production. To do this, enter the model number and study the specification.

Criterias of choice

As previously noted, it is important to make the right choice of switch. This is due to the fact that with the wrong choice, it may either not work at the right time, or it may constantly work from overload.

Also, there is a possibility of its failure.

You can select a circuit breaker according to the following indicators:

Number of poles. An important indicator can be called how many poles there are. Their number depends on what type of network you are connecting to. One- and two-pole versions are used exclusively in a single-phase network. Three- and four-pole must be used in a three-phase network. Often, they are connected to a system with neutral grounding. For domestic use, machines with 1 or 2 poles are also suitable.
Rated voltage machine. It determines what voltage the equipment in question is designed for. Regardless of where the machine is installed and for what tasks it is installed, it should be borne in mind that the minimum voltage of the machine must be equal to or greater than the mains voltage.
Maximum operating current. Another important indicator that should be considered is the maximum current. The choice on it is carried out taking into account the following nuance: the nominal indicator must be greater than the maximum value of the current strength that can pass through one of the protected sections of the network for a long or short period of time. In order to determine the maximum current that can occur in the network, you should calculate the maximum power. To do this, the summation of all power indicators of devices that are connected to the site is carried out. According to the accepted calculations, with a 220 V network, a load of 1 kW determines the maximum current strength of 5 A. In a three-phase network with a voltage of 380 V at the same load, the power is 3 A. Using these data, you can make an approximate calculation of what maximum current can appear in the chain.
Breaking capacity is another parameter to choose from. In order to make a choice according to this indicator, it is worth calculating the rated current. The machine must be able to turn off the power supply, the strength of which exceeds the strength of the short circuit at the point of the installed device.

The above selection criteria refer to domestic versions.

For industrial, the following data is additionally calculated:

Thermal resistance.
electrodynamic stability.

These calculations are carried out due to the fact that a heavy load with prolonged exposure can lead to heating of the elements of the machine. Most often, they manufacture switches with nominal current values: from 4 to 100 or 160 A. Household switches are produced with a rating of 16 to 25 A and the ability to turn off electricity with a power value of up to 3 kA.

Switch marking

Regardless of who is the manufacturer, a certain marking is applied to the case.

Such marking is as follows:

From 16. The standard to which the installation is carried out. The letter means the multiplicity of the maximum current. The digital value in this case means the nominal value of the current, the unit of measurement is Ampere. In this case, 16 amps can pass through the device in operation.
Number "3" stands for speed class. The higher the score, the better.
"4500"- a number that must be in the marking. This indicator is measured in amperes, indicates the maximum current value at which the circuit breaker operates.
A series of module is applied so that you can find out all the features of the device.
Specified Rated voltage.
A symbol is applied The that is used when creating the schema.

All models must have a similar designation, which is applied to the body. Often, the manufacturer also applies his brand.

When designing electrical wiring in a room, you need to start by calculating the current strength in the circuits. An error in this calculation can then be costly. An electrical outlet may melt if the current is too strong for it. If the current in the cable is greater than that calculated for a given material and cross-section of the core, the wiring will overheat, which can lead to melting of the wire, breakage or short circuit in the network with unpleasant consequences, among which the need for a complete replacement of electrical wiring is not the worst.

Knowing the strength of the current in the circuit is also necessary for the selection of circuit breakers, which should provide adequate protection against network overload. If the machine is standing with a large margin at face value, by the time it is triggered, the equipment may already be out of order. But if the rated current of the circuit breaker is less than the current that occurs in the network at peak loads, the machine will drive you crazy, constantly de-energizing the room when you turn on the iron or kettle.

The formula for calculating the power of an electric current

According to Ohm's law, current (I) is proportional to voltage (U) and inversely proportional to resistance (R), and power (P) is calculated as the product of voltage and current. Based on this, the current in the network section is calculated: I = P / U.

In real conditions, one more component is added to the formula and the formula for a single-phase network takes the form:

and for a three-phase network: I \u003d P / (1.73 * U * cos φ),

where U for a three-phase network is assumed to be 380 V, cos φ is the power factor, reflecting the ratio of the active and reactive components of the load resistance.

For modern power supplies, the reactive component is insignificant, the value of cos φ can be taken equal to 0.95. The exceptions are powerful transformers (for example, welding machines) and electric motors, they have a large inductive resistance. In networks where it is planned to connect such devices, the maximum current strength should be calculated using a cos φ factor of 0.8 or the current strength should be calculated using the standard method, and then a multiplying factor of 0.95 / 0.8 = 1.19 should be applied.

Substituting the effective voltage values of 220 V / 380 V and a power factor of 0.95, we obtain I \u003d P / 209 for a single-phase network and I \u003d P / 624 for a three-phase network, that is, in a three-phase network with the same load, the current is three times less. There is no paradox here, since three-phase wiring provides for three phase wires, and with a uniform load on each of the phases, it is divided into three. Since the voltage between each phase and working neutral wires is 220 V, the formula can also be rewritten in a different form, so it is clearer: I \u003d P / (3 * 220 * cos φ).

We select the rating of the circuit breaker

Applying the formula I \u003d P / 209, we get that with a load with a power of 1 kW, the current in a single-phase network will be 4.78 A. The voltage in our networks is not always exactly 220 V, so it will not be a big mistake to calculate the current strength with a small margin as 5 A for each kilowatt of load. It is immediately clear that it is not recommended to turn on an iron with a power of 1.5 kW in an extension cord marked “5 A”, since the current will be one and a half times higher than the passport value. And you can immediately “calibrate” the standard ratings of the machines and determine what load they are designed for:

6 A - 1.2 kW;
8 A - 1.6 kW;
10 A - 2 kW;
16 A - 3.2 kW;
20 A - 4 kW;
25 A - 5 kW;
32 A - 6.4 kW;
40 A - 8 kW;
50 A - 10 kW;
63 A - 12.6 kW;
80 A - 16 kW;
100 A - 20 kW.

Using the "5 amperes per kilowatt" technique, you can estimate the current strength that occurs in the network when connecting household devices. We are interested in peak loads on the network, so for the calculation you should use the maximum power consumption, and not the average. This information is contained in the product documentation. It is hardly worthwhile to calculate this indicator yourself, summing up the nameplate capacities of compressors, electric motors and heating elements included in the device, since there is also such an indicator as efficiency, which will have to be estimated speculatively with the risk of making a big mistake.

When designing electrical wiring in an apartment or a country house, the composition and passport data of the electrical equipment that will be connected are not always known for certain, but you can use the indicative data of electrical appliances common to our everyday life:

electric sauna (12 kW) - 60 A;
electric stove (10 kW) - 50 A;
hob (8 kW) - 40 A;
instantaneous electric water heater (6 kW) - 30 A;
dishwasher (2.5 kW) - 12.5 A;
washing machine (2.5 kW) - 12.5 A;
jacuzzi (2.5 kW) - 12.5 A;
air conditioning (2.4 kW) - 12 A;
microwave oven (2.2 kW) - 11 A;
storage electric water heater (2 kW) - 10 A;
electric kettle (1.8 kW) - 9 A;
iron (1.6 kW) - 8 A;
solarium (1.5 kW) - 7.5 A;
vacuum cleaner (1.4 kW) - 7 A;
meat grinder (1.1 kW) - 5.5 A;
toaster (1 kW) - 5 A;
coffee maker (1 kW) - 5 A;
hair dryer (1 kW) - 5 A;
desktop computer (0.5 kW) - 2.5 A;
refrigerator (0.4 kW) - 2 A.

The power consumption of lighting fixtures and consumer electronics is small, in general, the total power of lighting fixtures can be estimated at 1.5 kW and a 10 A machine per lighting group is enough. Consumer electronics are connected to the same outlets as irons, it is not advisable to reserve additional power for it.

If you sum up all these currents, the figure is impressive. In practice, the ability to connect the load is limited by the amount of allocated electrical power, for apartments with an electric stove in modern houses it is 10-12 kW and there is an automatic machine with a nominal value of 50 A at the apartment input. And these 12 kW must be distributed, given that the most powerful consumers concentrated in the kitchen and bathroom. The wiring will be less of a concern if it is broken down into enough groups, each with its own machine. For an electric stove (hob), a separate input is made with a 40 A automatic machine and a power outlet with a rated current of 40 A is installed, nothing else needs to be connected there. For a washing machine and other bathroom equipment, a separate group is made, with an automatic machine of the appropriate rating. This group is usually protected by an RCD with a rated current 15% greater than the rating of the circuit breaker. Separate groups are allocated for lighting and for wall sockets in each room.

It will take some time to calculate the powers and currents, but you can be sure that the work will not be in vain. Properly designed and well-installed electrical wiring is the key to the comfort and safety of your home.

The selection of a circuit breaker is a very important parameter, which often determines the quality of operation of specific electrical appliances and the network as a whole. To choose the right circuit breaker, you should be guided by certain rules that you need to know.

The choice of the machine according to the load power must be done correctly, otherwise problems may arise.

Circuit breakers are one of the elements of protecting the electrical network from overloads, and they must be of high quality. The power consumption of electricity should not exceed the power of the machine itself, therefore, before buying it, you need to carefully calculate your real needs.

Learn more about selection methods

There are several ways to ensure that the choice of circuit breakers is successful and of the highest quality. To choose the right option, it is worth correctly determining the indicator of the rated load in the electrical network.

The more equipment works, the more powerful the machine is needed.

Table Selection

The easiest way to choose the desired machine using a special table, which is quite voluminous. Having learned the total power indicator of all devices, you can easily select a single-phase, two-phase or three-phase switch.

The selection can be done in a matter of minutes, if the total power of the devices is slightly lower than in the table, then it is worth choosing approximately the same option, but it is better that its power is even slightly higher.

Graphical selection

You can select the circuit breaker according to your needs using a special graphic diagram. This scheme can be found on the Internet without any problems, it indicates the rated current of the machine and its power in kilowatts.

Specific current ratings correspond to certain power indicators, due to which you can determine the desired option. This method is almost as convenient as a table, so many consumers actively use it.

If you look at the indicators of the graph, which are located horizontally, you can find indicators of the current load, and the data on the power of a particular section of the network used is indicated vertically. You need to calculate the power yourself, and then, using this indicator, you can determine which switch is required.

Special nuances of choice

When choosing a machine, you need to take into account the fact that the number of household appliances can increase significantly in the house. Given this factor, it is worth taking an automatic machine that has a slightly higher power than is currently needed. If the number of appliances in the house increases, and it is actively used, accordingly, the load on the electrical network becomes higher.

Advice! If the machine is already installed, and there are more appliances in the house, then you just need to buy a new one and install it. Only in this case, you need to take care of the new wiring, because. The old one may not be able to handle the load.

Having calculated the amount of voltage in a particular segment, when buying a machine, it is worth adding another 50% to this number so that, if necessary, you do not have to urgently run for a new switch. The calculation of the required power is easy to carry out. Even a schoolboy can cope with such a banal task.

Using a multiplier, you can safely insure yourself against unforeseen situations. But there are also cases when it is advised to use not an increasing, but a decreasing coefficient, but they are quite rare.

It is important! If the network has an increased load, due to the inclusion of many powerful electrical appliances, then you need to not only change the switch, but also check whether the wiring can withstand such loads.

How to choose a three-phase machine?

Three-phase machines are just perfect for a 380 volt network, they are considered the most powerful.
To decide on the choice of this device, you should follow these rules:

determine the total power of all used devices;
calculate the power connected to the power supply system of lighting devices;
multiply the result by a coefficient whose value reaches 1.52;
choose a circuit breaker for the house according to the table.

Knowing how to choose a machine for a 220 or 380 volt network, you can safely buy a machine for your home, having confidence that it is of high quality. In this case, it is worth considering the fact that the rated current strength should be 15% more than the result obtained earlier in the calculations.

The principle of choosing single-phase and two-phase machines is approximately the same as for three-phase.

conclusions

Absolutely every adult should learn how to choose a circuit breaker, since it is impossible to do without it in a house. To choose the right machine, you need to calculate the total power of all functioning devices, making a small addition of power for the future.

Additionally, you need to see if the wiring can withstand a specific load value.

A high-quality machine should be bought in a specialized store, determining its power and model using a special table or diagram. When choosing a machine, you need to take into account your real needs and then it will be really good.

The main thing is to correctly determine the power of all electrical appliances in the house. This can be easily done if you look at the case of a device, where literally all the technical characteristics are written. Given all the nuances of choice, you can find and buy a machine for your home that will withstand the load of electrical appliances used.

It is very simple to carry out the necessary calculations, therefore it is simply impossible to cope with such an easy task, which many users have already proven by choosing this item for the home for the first time, without experience.

The table shows that at currents up to 1.13 * In, the machine will not work. If an overload of the circuit occurs by 13% more than the rated current (1.13 * In), the circuit breaker will turn off no earlier than in an hour, and if the overload is up to 45% (1.45 In), the thermal release of the machine must operate within one hour ( i.e. it can work in an hour). Thus, in the current range of 1.13-1.45 from the rated current In, the thermal release of the machine will operate in a time from several minutes to several hours. From all this it follows that when choosing a circuit breaker, it is worth considering not only its rated current, but also the setting value of the thermal release, which should not exceed the long-term permissible current for the protected line.

What will happen if you do not take into account the setting of the thermal release when choosing an automatic machine? For convenience, consider an example:

Let's take the most common rating of the machine - 16 A, the overload current at which the machine will work for an hour will be equal to 16 * 1.45 = 23.2 A (a table was presented above, from which it can be seen that the setting value of the thermal release is 1.45 rated current). Accordingly, it is for this current that the cable section should be selected. From table 1.3.4. we select a suitable section: for hidden electrical wiring made of copper - this is a minimum of 2.5 mm 2 (maximum overload current 27 A).

In a similar way, calculations can be made for a 10 A machine. The current at which the machine turns off within an hour will be 10 1.45 = 14.5 A. According to the table, this current corresponds to a cable with a cross section of 1.5 mm 2.

Very often, installers neglect this rule and, to protect the line with a cross section of 2.5 mm 2, they install a circuit breaker with a nominal value of 25A (after all, the line can withstand a current of 25 A for a long time). But at the same time, they forget that the non-switchable current of such an automaton is 25 * 1.13 = 28.25 A, and this is already more than the long-term permissible overload current. The current at which the machine will turn off within an hour will be 25 * 1.45 = 36.25 A !!! With such a current and for such a time, the cable will overheat and burn out.

Also, do not forget that the cable products market is dominated by cables produced not according to GOST, but according to TU. It follows from this that their actual cross section will be underestimated. Buying a cable produced according to specifications, instead of a cable with a core cross section of 2.5 mm 2, you can get a cable with an actual core cross section of less than 2.0 mm 2!
Here is an example of what can happen if the rule for choosing the cable section and the machine is neglected:

electrotech.by

Table for selecting machines by power

An extended table for selecting automatic circuit breakers by power, including a three-phase connection with a star and a delta, allows you to select a circuit breaker that matches the power consumption. To work with the table, that is, to select the machine corresponding to the power, it is enough knowing this power, select a value in the table greater than or equal to this power value.
in the leftmost column you will see the rated current of the machine corresponding to the selected power. At the top, above the selected power, you will see the type of connection of the machine, the number of poles and the voltage used. If the selected power corresponds to several power values in the table for example, a power of 6.5 kW can be obtained by connecting a single-phase 32A circuit breaker, connecting a 6A three-pole circuit breaker with a three-phase trio and connecting a 10A four-pole circuit breaker with a three-phase star, you should select the connection method available to you. That is, when choosing a machine for a power of 6.5 kW in the absence of a three-phase power supply, you need to choose only from a single-phase connection, where a single-pole and two-pole machine 32A will be available. The transition from the link in the table for a certain power corresponding to the connection possibilities is carried out to a circuit breaker corresponding to the rated current and the number of poles with a time current characteristic C. on the page of each machine.

The choice of machines for power and connection

single phase

Connection type =>	single phase introductory	Three-phase triangle	Three-phase star
The pole of the machine =>	single pole machine	Bipolar machine	Three-pole machine	four-pole machine
Supply voltage =>	220 volt	220 volt	380 Volt	220 volt
	V	V	V	V
Automatic 1A >	0.2 kW	0.2 kW	1.1 kW	0.7 kW
	0.4 kW	0.4 kW	2.3 kW	1.3 kW
Automatic 3A >	0.7 kW	0.7 kW	3.4 kW	2.0 kW
Automatic 6A >	1.3 kW	1.3 kW	6.8 kW	4.0 kW
Automatic 10A >	2.2 kW	2.2 kW	11.4 kW	6.6 kW
Automatic 16A >	3.5 kW	3.5 kW	18.2 kW	10.6 kW
Automatic 20A >	4.4 kW	4.4 kW	22.8 kW	13.2 kW
Automatic 25A >	5.5 kW	5.5 kW	28.5 kW	16.5 kW
Automatic 32A >	7.0 kW	7.0 kW	36.5 kW	21.1 kW
Automatic 40A >	8.8 kW	8.8 kW	45.6 kW	26.4 kW
Automatic 50A >	11 kW	11 kW	57 kW	33 kW
Automatic 63A >	13.9 kW	13.9 kW	71.8 kW	41.6 kW

An example of selecting an automatic machine by power

One of the ways to select a circuit breaker is to select the circuit breaker according to the load power. The first step, when choice of machine by power, the total power of the loads connected on a permanent basis to the wiring / network protected by the machine is determined. The resulting total power is increased by the consumption factor, which determines the possible temporary excess of power consumption due to the connection of other, initially unaccounted for electrical appliances.
An example is kitchen wiring, designed to connect an electric kettle (1.5 kW), microwave oven (1 kW), refrigerator (500 watts) and hood (100 watts). The total power consumption will be 3.1 kW. To protect such a circuit, you can use a 16A circuit breaker with a rated power of 3.5 kW. Now imagine that a coffee machine (1.5 kW) was placed in the kitchen and connected to the same electrical wiring.
The mmar power removed from the wiring when connecting all of the indicated electrical appliances in this case will be 4.6 kW, which is more than the power of the 16 Amp auto switch, which, when all appliances are turned on, will simply turn off due to excess power and leave all appliances without power, including the refrigerator. To reduce the likelihood of such situations, an increasing consumption factor is applied. In our case, when connecting the coffee machine, the power increased by 1.5 kW, and the consumption coefficient became 1.48 (round up to 1.5). That is, in order to be able to connect an additional device with a power of 1.5 kW, the calculated power of the network must be multiplied by a factor of 1.5, obtaining 4.65 kW of power that can be obtained from the wiring.
At choice of machine by power it is also possible to use a reduction factor of consumption. This coefficient determines the difference in power consumption, in the direction of reduction, from the total calculated due to the non-use of all electrical appliances included in the calculation at the same time. In the previously discussed example of 3.1 kW kitchen wiring, the reduction factor will be 1, since the kettle, microwave, refrigerator and extractor fan can be turned on at the same time, and in the case of 4.6 kW wiring (including a coffee machine), the reduction factor can be be equal to 0.67 if it is impossible to turn on the electric kettle and the coffee machine at the same time (for example, there is only one socket for both devices and there are no tees in the house)
Thus, at the first step, the estimated power of the protected wiring is determined, and the increasing (increasing power when connecting new electrical appliances) and decreasing (the impossibility of simultaneously connecting some electrical appliances) coefficients are determined.
When choosing a machine, it is preferable to use the power obtained by multiplying the multiplying factor by the rated power, while naturally taking into account the possibilities of electrical wiring (the cross section of the wire must be sufficient to transmit such power).

Rated power of the machine

The rated power of the machine, that is, the power, the consumption of which in the wiring protected by the circuit breaker will not lead to the shutdown of the machine, is calculated in the general case by the formula, which can be described by the phrase \u003d \u003d\u003e “Power \u003d Voltage multiplied by the Current strength multiplied by the cosine Phi”, where the voltage is the alternating voltage of the mains in Volts, the current strength is the current flowing through the machine in Amperes and cosine phi is the value of the trigonometric function Cosine for the angle phi (angle phi is the angle of shift between the voltage and current phases). Since in most cases the choice of automatic power is made for domestic use, where there is practically no shift between the phases of current and voltage caused by reactive loads such as electric motors, the cosine is close to 1 and the power can be approximately calculated as voltage multiplied by current.
Since the power has already been determined, then from the formula we get the current, namely the current that corresponds to the calculated power by dividing the power in watts by the mains voltage, that is, by 220 volts.
in our example with a power of 3.1 kW (3100 watts), a current equal to 14 amperes is obtained (3100 watts / 220 volts = 14.09 amperes). This means that when all these devices are connected with a total power of 3.1 kW, a current approximately equal to 14 Amperes will flow through the circuit breaker.
After determining the current strength by power consumption, the next step in choosing a circuit breaker is choosing a current circuit breaker
To select the machine for the power of a three-phase load, the same formula is used, taking into account the fact that the shift between the voltage and current phases in a three-phase load can reach large values and, accordingly, the cosine value must be taken into account. In a large number of cases, a three-phase load is marked indicating the value of the cosine of the phase shift, for example, on the label of an electric motor, one can see that this is exactly the cosine of the phase shift angle involved in the calculation. Accordingly, when calculating a three-phase load, the power, let's say the power indicated on the nameplate of the connected three-phase, at 380 Volts, electric motor is 7 kW, the current is calculated as 7000/380/0.6 = 30.07
The resulting current is the sum of the currents in all three phases, that is, one phase (one pole of the machine) accounts for 30.07 / 3~10 Amperes, which corresponds to the choice of a three-pole machine D10 3P. Characteristic D in this example was chosen due to the fact that when starting the motor, while the motor rotor is spinning, the currents significantly exceed the rated values, which can lead to switching off the circuit breaker with characteristic B and characteristic C.

Maximum circuit breaker power

The maximum power of the machine, that is, the power and, accordingly, the current that the machine can pass through itself and not turn off, depends on the ratio of the current flowing through the machine and the rated current of the machine specified in the technical data of the circuit breaker. This ratio can be called the reduced current, which is a dimensionless coefficient, no longer related to the rated current of the machine. The maximum power of the machine depends on the time-current characteristics, the reduced current and the duration of the flow of the reduced current through the machine, which is described in the section Time-current characteristics of circuit breakers.

Maximum short-term power of the machine

The maximum short-term power of the machine can be several times higher than the rated power, but only for a short time. The value of the excess and the time that the machine does not turn off the load in case of such an excess is described by the characteristics (operating curves) indicated by a Latin letter, or indicated in the marking of the machine before the number indicating the rated current of the circuit breaker.

No electrical device, no electrical appliance, should be used without protective automatics. The circuit breaker (AB) is installed for a specific device, or for a group of consumers connected to one line. In order to correctly answer the question of what power corresponds, for example, to a machine with a nominal value of 25A, you should first get acquainted with the device of the circuit breaker and the types of protective devices.

Structurally, AB combines mechanical, thermal and electromagnetic releases that operate independently of each other.

Mechanical release

Designed to turn the machine on/off manually. Allows you to use it as a switching device. It is used during repair work to de-energize the network.

Thermal release (TR)

This part of the circuit breaker protects the circuit from overload. The current passes through the bimetallic plate, heating it. Thermal protection is inertial, and can pass currents for a short time exceeding the trip threshold (In). If the current exceeds the rated current for a long time, the plate heats up so much that it deforms and turns off the AB. After the bimetallic plate has cooled down (and the cause of the overload has been eliminated), the machine is turned on manually. In a 25A machine, the number 25 indicates the TR threshold.

Electromagnetic release (ER)

Breaks the electrical circuit in the event of a short circuit. The overcurrents generated during a short circuit require an instant response of the protective device, therefore, unlike a thermal one, the electromagnetic release is triggered instantly, in a fraction of a second. Shutdown occurs due to the passage of current through the winding of the solenoid with a movable steel core. The solenoid, acting, overcomes the resistance of the spring and turns off the moving contact of the circuit breaker. For short circuit tripping, currents exceeding In from three to fifty times are required, depending on the type of AB.

AB types by current-time characteristic

Let's ignore the protection devices for industrial electronics and motors with built-in thermal relays, and consider the most common types of machines:

Characteristic B - with a threefold excess of In, the TR is triggered after 4-5s. ER operation when In is exceeded three to five times. They are used in lighting networks or when connecting a large number of low-power consumers.
Characteristic C is the most common type of AB. TP is triggered in 1.5 s when In is exceeded five times, ER is triggered when In is exceeded 5-10 times. They are used for mixed networks, including devices of various types, including those with small starting currents. The main type of circuit breakers for residential and office buildings.
Characteristic D - machines with the highest overload capacity. They are used to protect electric motors, energy consumers with high starting currents.

Ratio of AB ratings and consumer capacities

To determine how many kilowatts can be connected through a circuit breaker of a certain power, use the table:

automatic 220v, A	power, kWt
automatic 220v, A	single-phase	three-phase
2	0,4	1,3
6	1,3	3,9
10	2,2	6,6
16	3,5	10,5
20	4,4	13,2
25	5,5	16,4
32	7,0	21,1
40	8,8	26,3
50	11,0	32,9
63	13,9	41,4

To calculate the power of an introductory machine at home, use a factor of 0.7 of the total power of consumers.

When determining the load capacity of a circuit breaker, it is important to consider not only its rating, but also its overload characteristic. This will help to avoid false positives during the start-up of powerful electrical appliances.

When designing the electrical network of a new house, in order to connect new powerful devices, in the process of upgrading the electrical panel, it is necessary to choose a circuit breaker for reliable electrical safety.

Some users are careless about this task, and may not hesitate to connect any existing machine, just to work, or when choosing, they are guided by the following criteria: cheaper, so that it doesn’t hit too hard, or more powerful, so that it doesn’t knock out once again.

Very often, such negligence and ignorance of the elementary rules for choosing the rating of a safety device leads to fatal consequences. This article will introduce the main criteria for protecting electrical wiring from overload and short circuit, in order to be able to choose the right circuit breaker according to the power consumption of electricity.

Briefly the principle of operation and purpose of circuit breakers

The circuit breaker in the event of a short circuit is activated almost instantly thanks to the electromagnetic splitter. With a certain excess of the rated current value, the heating bimetallic plate will turn off the voltage after a certain time, which can be found from the current characteristic time graph.

This safety device protects the wiring from short circuits and overcurrents exceeding the calculated value for a given wire section, which can heat up the conductive wires to the temperature of melting and ignition of the insulation. To prevent this from happening, it is necessary not only to choose the right protective switch that matches the power of the connected devices, but also to check whether the existing network can withstand such loads.

Appearance of a three-pole circuit breaker

Wires must match the load

It often happens that a new electric meter, automatic devices, RCDs are installed in an old house, but the wiring remains old. A lot of household appliances are bought, the power is summed up and an automatic machine is selected for it, which regularly holds the load of all the included electrical appliances.

Everything seems to be correct, but suddenly the insulation of the wires begins to emit a characteristic smell and smoke, a flame appears, and the protection does not work. This can happen if the wiring parameters are not designed for.

Let's say the cross section of the core of the old cable is 1.5mm², with a maximum allowable current limit of 19A. We accept that at the same time several electrical appliances were connected to it, making up a total load of 5 kW, which in current equivalent is approximately 22.7A, it corresponds to a 25A automatic machine.

The wire will heat up, but this machine will remain on all the time until the insulation melts, which will cause a short circuit, and the fire can already flare up in full swing.

Protect the weakest link in the wiring

Therefore, before making a choice of the machine according to the protected load, you need to make sure that the wiring will withstand this load.

According to PUE 3.1.4, the machine must protect the weakest section of the electrical circuit from overloads, or be selected with a rated current corresponding to the currents of the connected electrical installations, which again implies their connection with conductors with the required cross section.

If you ignore this rule, you should not blame the incorrectly calculated machine and curse its manufacturer if a weak link in the wiring causes a fire.

Molten wire insulation

Calculation of the nominal value of the machine

We assume that the wiring is new, reliable, correctly calculated, and meets all the requirements. In this case, the choice of the circuit breaker comes down to determining the appropriate rating from a typical range of values, based on the rated load current, which is calculated by the formula:

where P is the total power of electrical appliances.

An active load is implied (lighting, electric heating elements, household appliances). Such a calculation is fully suitable for a home electrical network in an apartment.

Let's say the power calculation is made: P \u003d 7.2 kW. I \u003d P / U \u003d 7200 / 220 \u003d 32.72 A. We select a suitable machine for 32A from a number of values: 1, 2, 3, 6, 10, 16, 20, 25, 32, 40, 63, 80, 100.

This denomination is slightly less than the calculated one, but there is practically no simultaneous inclusion of all electrical appliances in the apartment. It is also worth considering that in practice the operation of the machine starts from a value 1.13 times more than the nominal value, due to its time-current characteristic, that is, 32 * 1.13 = 36.16A.

To simplify the choice of a circuit breaker, there is a table where the ratings of the machines correspond to the power of a single-phase and three-phase load:

Current machine selection table

The value found by the formula in the above example is the closest in terms of power value, which is indicated in the highlighted red cell. Also, if you want to calculate the current for a three-phase network, when choosing a machine, check out the article about

The selection of circuit breakers for electrical installations (electric motors, transformers) with a reactive load, as a rule, is not made by power. The rating and type are selected according to the operating and starting current indicated in the passport of this device.

The time of ceramic plugs that were screwed into household electrical panels has long passed. Currently, various types of circuit breakers that perform protective functions are widely used. These devices are very effective at short circuits and overloads. A lot of consumers have not yet fully mastered these devices, so the question often arises, which machine should be installed at 15 kW. Reliable and durable operation of electrical networks, appliances and equipment in a house or apartment completely depends on the choice of the machine.

The main functions of machines

Before choosing an automatic protective device, it is necessary to understand the principles of its operation and capabilities. Many consider the protection of household appliances to be the main function of the machine. However, this judgment is absolutely wrong. The machine does not react in any way to devices connected to the network, it only works in case of short circuits or overloads. These critical conditions lead to a sharp increase in current strength, causing overheating and even ignition of cables.

A special increase in current strength is observed during a short circuit. At this moment, its value increases to several thousand and the cables are simply not able to withstand such a load, especially if its cross section is 2.5 mm2. With such a cross section, an instantaneous ignition of the wire occurs.

Therefore, a lot depends on the correct choice of the machine. Accurate calculations, including software, make it possible to reliably protect the electrical network.

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Types of machines

Classification of circuit breakers occurs according to the following parameters:

number of poles;
rated and limiting currents;
applied type of electromagnetic release;
maximum breaking capacity.

Let's consider in order.

Number of poles

The number of poles is the number of phases that the machine is able to protect. By the number of poles, automata can be:

Rated and limit currents

Everything is simple here - such a current strength at which the machine will open the circuit. At the rated current and even a little more than the declared one, work will be carried out, however, only if the current limit is exceeded by 10–15%, a shutdown will occur. This is due to the fact that quite often the starting currents exceed the maximum possible currents for a short period of time, therefore, the machine has a certain margin of time, after which the circuit will open.

Type of electromagnetic release

This part of the machine, which allows you to open the circuit in case of a short circuit, as well as in the event of an increase in current (overload) by a certain number of times. Releasers are divided into several categories, consider the most popular:

B - opening when the rated current is exceeded by 3–5 times;
C - when exceeded by 5–10 times;
D - when exceeded by 10–20 times.

The maximum power of the switched off ability. This value of the short circuit current (defined in thousands of amperes) at which the machine will remain operational after opening the circuit due to a short circuit.

Selection of the optimal cable section

Each cable, like the machine, has a certain permitted load current. Depending on the section and material of the cable, the load current also varies. To select the machine according to the cable section, use the table.

It should be noted that it is allowed to choose a cable with a small margin, but not a package switch! The machine must correspond to the planned load! In accordance with the rules of electrical installations 3.1.4 - the currents of the settings of the automata should be chosen such that they will be less than the rated currents of the selected zones.

Consider an example, in a certain area, the wiring is laid with a cable with a cross section of 2.5 mm square, and the load is 12 kW, in this case, when installing the machine (at the minimum current) at 50 A, the wiring will ignite, since the wire with this cross section is designed for the allowed current in 27 A, and much more passes through it. In this case, there is no break in the circuit, since the machine is adapted to these currents, but the wire is not, the automation will turn off the machine only in the event of a short circuit.

Failure to follow this rule has serious consequences!

Important! First, you should calculate the power of consumers, and then choose a conductor of the appropriate section, and only after that choose an automatic machine (bag). The rated current of the bag must be less than the maximum current allowed for the wire of this section.

It is thanks to this principle that the wiring will never overheat and, therefore, there will be no fire.

Consumer power calculation

Each electrical network in an apartment or house can be divided into sections (premises). Depending on what devices are planned to be used in a particular area, electrical wiring is calculated. Usually, the wiring zones for each machine are divided among themselves for each room of an apartment or house. One section of wiring for one room, the second for another, and the third for the kitchen and bathroom. Standing apart in this situation are such powerful consumers as electric stoves, ovens, water heaters, heating boilers. This technique requires a dedicated power line, so modern homes designed for use with electric stoves have a separate circuit breaker to power the appliance.

Calculating the required current for a particular section of the wiring is quite simple. For this, the formula I \u003d P / U is used, according to which I is the current strength, P is the power (in watts) of all operating electrical appliances on this line, U is the mains voltage (it is standard - 220 volts). To calculate, it is necessary to add the power of those electrical appliances that are planned to be used on the line, and then divide the resulting amount by 220. From here we get the current strength, according to which it will be necessary to choose a cable of a certain section.

As an example, let's take a plot (room) and calculate for it an automaton and a cable of the required section. In the room will work simultaneously:

vacuum cleaner (1300 W);
electric iron (1000 W);
air conditioning (1300 W);
computer (300 W).

Let's add these figures (1300+1000+1300+300 = 3900 W) and divide them by 220 (3900/220 = 17.72). It turns out that the current strength is 17.72, we select for this the optimal cable cross-section based on the table, we take a copper cable with a cross section of 2.5 mm or 4 mm square (we definitely take it with a margin) and an automatic machine with a rated protection current of 20 amperes.

It is worth mentioning that you should not choose a circuit breaker with an overestimated rated current, since if the electrical network is overloaded (exceeding the continuous current for a certain wire), the wiring will start to ignite. The nominal value of the machine must correspond to the value of the continuous current of the conductor or be less.

Experienced electricians repeatedly say that you should not install cables of small cross section because of their cheapness, you should choose a cable with a margin in order to avoid overloading the electrical section and igniting the wiring. But choosing a powerful machine is contraindicated!

The wiring is mounted once, it is difficult to replace it, and it is much easier to replace the switch in case of a significantly increased load.

At the moment, there are more and more powerful electrical appliances, so you should take care in advance if you suddenly decide to use a more powerful vacuum cleaner or add some additional device to the room.

Nuances

Basically, readers should not have questions with the selection of a cable cross-section of a bag, but there are some subtleties that we did not mention above.

Machine with which type of electromagnetic release to choose
In everyday life, automatic machines of category "B" and "C" are most often used.
This is due to the fastest possible operation of package switches when the rated current is exceeded. This is extremely true when using appliances such as electric kettles, toasters and irons. Depending on the type of equipment used, a certain category should be selected, it is advisable to give preference to category “B” switches.
Automatic machine with what maximum power of the switched off ability to choose
It depends on the location of the input of electricity from the substation to the apartment, if in the immediate vicinity, then it is worth choosing with a switchable capacity of 10,000 amperes, otherwise for city apartments there are enough devices for 5000–6000 amperes. You can play it safe and choose the option of 10,000 amperes, in the end, this indicator only affects whether the machine will work after a short circuit.
Which type of wire to choose: aluminum or copper
We strongly do not recommend purchasing aluminum conductors. Copper wiring is more reliable and can handle higher currents.

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What are circuit breakers and how do they work?

Modern AB have two degrees of protection: thermal and electromagnetic. This allows you to protect the line from damage as a result of a long excess of the flowing current of the rated value, as well as a short circuit.

The main element of the thermal release is a plate of two metals, which is called bimetallic. If it is exposed to a current of increased power for a sufficiently long time, it becomes flexible and, acting on the disconnecting element, causes the machine to operate.

The presence of an electromagnetic release is due to the breaking capacity of the circuit breaker when the circuit is exposed to short-circuit overcurrents, which it cannot withstand.

The electromagnetic type release is a solenoid with a core, which, when a high power current passes through it, instantly shifts towards the disconnecting element, turning off the protective device and de-energizing the network.

This makes it possible to protect the wire and devices from an electron flow, the value of which is much higher than that calculated for a cable of a specific section.

Why is cable mismatch with network load dangerous?

The correct selection of the circuit breaker by power is a very important task. An incorrectly selected device will not protect the line from a sudden increase in current.

But it is equally important to choose the right electrical cable according to the cross section. Otherwise, if the total power exceeds the nominal value that the conductor can withstand, this will lead to a significant increase in the temperature of the latter. As a result, the insulating layer will begin to melt, which can lead to a fire.

In order to more clearly imagine what the mismatch between the wiring cross-section of the total power of devices connected to the network threatens, consider the following example.

The new owners, having bought an apartment in an old house, install several modern household appliances in it, giving a total load on the circuit equal to 5 kW. The current equivalent in this case will be about 23 A. In accordance with this, a 25 A circuit breaker is included in the circuit. It would seem that the choice of the machine in terms of power was made correctly, and the network is ready for operation. But some time after turning on the appliances, smoke appears in the house with a characteristic smell of burnt insulation, and after a while a flame appears. At the same time, the circuit breaker will not disconnect the network from the power supply - after all, the current rating does not exceed the allowable one.

If the owner is not nearby at this moment, the molten insulation will cause a short circuit after a while, which will finally trigger the machine, but the flame from the wiring may already spread throughout the house.

The reason is that although the power calculation of the machine was done correctly, the wiring cable with a cross section of 1.5 mm² was rated for 19 A and could not withstand the existing load.

So that you do not have to take up a calculator and independently calculate the cross section of the electrical wiring using formulas, we present a typical table in which it is easy to find the desired value.

Weak link protection

So, we made sure that the calculation of the circuit breaker should be made based not only on the total power of the devices included in the circuit (regardless of their number), but also on the cross section of the wires. If this indicator is not the same along the electric line, then we select the section with the smallest cross section and calculate the machine based on this value.

The requirements of the PUE state that the selected circuit breaker must provide protection for the weakest section of the electrical circuit, or have a current rating that will correspond to a similar parameter of the installations connected to the network. This also means that wires must be used for the connection, the cross section of which will be able to withstand the total power of the connected devices.

How to select the wire cross section and circuit breaker rating - in the following video:

If the negligent owner ignores this rule, then in the event of an emergency due to insufficient protection of the weakest section of the wiring, he should not blame the selected device and scold the manufacturer - only he will be responsible for the situation.

How to calculate the circuit breaker rating?

Let's assume that we have taken into account all of the above and selected a new cable that meets modern requirements and has the desired cross section. Now the electrical wiring is guaranteed to withstand the load from the included household appliances, even if there are a lot of them. Now we proceed directly to the choice of the circuit breaker according to the current rating. We recall the school physics course and determine the calculated load current by substituting the appropriate values into the formula: I = P / U.

Here I is the value of the rated current, P is the total power of the installations included in the circuit (taking into account all consumers of electricity, including light bulbs), and U is the mains voltage.

To simplify the choice of a circuit breaker and save you from having to take on a calculator, we present a table that shows the ratings of AB, which are included in single-phase and three-phase networks, and the corresponding total load powers.

This table will make it easy to determine how many kilowatts of load correspond to which rated current of the protective device. As we can see, a 25 Amp machine in a network with a single-phase connection and a voltage of 220 V corresponds to a power of 5.5 kW, for a 32 Amp AB in a similar network - 7.0 kW (in the table this value is highlighted in red). At the same time, for an electrical network with a three-phase delta connection and a rated voltage of 380 V, a 10 Amp machine corresponds to a total load power of 11.4 kW.

Clearly about the selection of circuit breakers on the video:

Conclusion

In the presented material, we talked about why electric circuit protection devices are needed and how they work. In addition, given the information provided and the tabular data given, you will not have any difficulty with the question of how to choose a circuit breaker.

Those times when traditional ceramic plugs could be found on the electrical panels of apartments or private houses are long gone. Now circuit breakers of a new design are widely used - the so-called circuit breakers.

What are these devices for? How to do it right in each case? Of course, the main function of these devices is to protect the electrical network from short circuits and overloads.

The machine should turn off when the load significantly exceeds the allowable rate or when a short circuit occurs, when the electric current increases significantly. However, it must pass current and work in normal mode if, for example, you turned on the washing machine and electric iron at the same time.

What does the circuit breaker protect?

Before choosing a machine, it is worth understanding how it works and what it protects. Many people believe that the machine protects household appliances. However, this is absolutely not the case. The machine does not care about the devices that you connect to the network - it protects the wiring from overload.

Indeed, when the cable is overloaded or a short circuit occurs, the current increases, which leads to overheating of the cable and even ignition of the wiring.

The current strength increases especially strongly during a short circuit. The magnitude of the current can increase to several thousand amperes. Of course, no cable is able to hold out for a long time under such a load. Moreover, a cable with a cross section of 2.5 square meters. mm, which is often used for wiring in private households and apartments. It will simply light up like a Bengal fire. An open flame indoors can lead to a fire.

Therefore correct plays a very important role. A similar situation occurs during overloads - the circuit breaker protects the electrical wiring.

When the load exceeds the allowable value, the current increases sharply, which leads to heating of the wire and melting of the insulation. In turn, this can lead to a short circuit. And the consequences of such a situation are predictable - open fire and fire!

What currents are used to calculate machines

The function of the circuit breaker is to protect the wiring connected after it. The main parameter by which the automatic machines are calculated is the rated current. But the rated current of what, load or wire?

Based on the requirements of PUE 3.1.4, the setting currents of circuit breakers that serve to protect individual sections of the network are selected as much as possible less than the rated currents of these sections or according to the rated current of the receiver.

The calculation of the machine in terms of power (according to the rated current of the electrical receiver) is carried out if the wires along the entire length in all sections of the wiring are designed for such a load. That is, the permissible current of the wiring is greater than the nominal value of the machine.

The time current characteristic of the machine is also taken into account, but we will talk about it later.

For example, in a section where a wire with a cross section of 1 sq. mm, the load value is 10 kW. We select the machine for the rated load current - we set the machine to 40 A. What will happen in this case? The wire will begin to heat up and melt, since it is rated for a rated current of 10-12 amperes, and a current of 40 amperes passes through it. The machine will turn off only when a short circuit occurs. As a result, wiring can fail and even a fire occurs.

Therefore, the determining value for choosing the rated current of the machine is the cross section of the conductive wire. The load value is taken into account only after selecting the wire section. The rated current indicated on the machine must be less than the maximum current allowed for a wire of a given section.

Thus, the choice of the machine is made according to the minimum cross-section of the wire that is used in the wiring.

For example, the permissible current for a copper wire with a cross section of 1.5 square meters. mm, is 19 amperes. This means that for this wire we select the nearest value of the rated current of the machine to the lower side, which is 16 amperes. If you select an automatic machine with a value of 25 amperes, then the wiring will heat up, since the wire of this section is not intended for such a current. In order to correctly produce, it is necessary, first of all, to take into account the cross section of the wire.

Calculation of the introductory circuit breaker

The wiring system is divided into groups. Each group has its own cable with a certain section and circuit breakers with a rated current that satisfies this section.

To select the cable section and the rated current of the machine, you need to calculate the expected load. This calculation is made by summing up the power of the devices that will be connected to the site. The total power will determine the current flowing through the wiring.

The current value can be determined using the following formula:

P is the total power of all electrical appliances, W;
U - mains voltage, V (U=220 V).

Despite the fact that the formula is used for active loads that are created by ordinary light bulbs or devices with a heating element (electric kettles, heaters), it will still help to approximately determine the amount of current in this area. Now we need to choose a conductive cable. Knowing the magnitude of the current, we can select the cable cross-section for a given current from the table.

After that, you can make for the wiring of this group. Remember that the machine must turn off before the cable overheats, so we choose the value of the machine to the nearest lower value from the rated current.

We look at the value of the rated current on the machine and compare it with the maximum allowable current for a wire with a given section. If the allowable current for the cable is less than the rated current indicated on the machine, choose a cable with a larger cross section.