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How to calculate a circuit breaker. Examples of calculating circuit breakers in an electrical circuit How to choose an input circuit breaker

Instructions

A properly selected circuit breaker should trip in the event of a short circuit in the wiring or when a load significantly exceeds the design load. At the same time, it should not turn off if, for example, you turned on the washing machine at the same time. That is why select a circuit breaker specifically for your wiring and load.

Buy circuit breakers only in specialized stores, this will allow you to buy a high-quality product with a high degree of probability. Remember that the rated current of the circuit breaker should not be higher than the maximum current load allowed for your network. In other words, the machine should work, and the wiring should not burn out.

The parameters of the circuit breaker are calculated as follows. Let's assume that you turn on a 2 kW electric kettle. Divide the power, in watts, by 220, we get a current of 9.1 A. This figure can be rounded to 10 so that there is some margin in the calculations. This means that the circuit breaker must withstand a current of 10 amperes. Now calculate the total power of all electrical appliances you turn on at the same time and calculate, using the diagram above, the current strength. Let’s say you get 30 amperes, which means the circuit breaker must be designed for this current.

Having carried out the previous calculations, you have calculated what current the circuit breaker should be designed for. But you also need to know how much current your network can handle, and that depends on the wires you use. For example, if the wiring is made with 2.5 mm aluminum wire (the most common option), it can withstand a current of 24 amperes and a load of 5.2 kW. This means that in your case the circuit breaker should be designed for a current of slightly less than 24 amperes. If you use copper wire of this section, it will withstand a current of 30 amperes and a load of 6.6 kW. If you are using a wire of a different cross-section, find current and load data for it on the Internet.

When installing wiring in your house, ensure in advance that it is divided into several isolated circuits. For example, make separate lighting circuits and wiring to outlets. This will allow you to install a separate circuit breaker on each circuit, which will significantly improve overall safety. Electrical appliances such as electric water heaters must also be connected through an RCD - a residual current device that can protect a person from electric shock. The RCD reacts to leakage, so if the phase wire is touched, it will immediately turn off the current.

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

Basic functions of machines

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

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

Machine calculation parameters

Each circuit breaker primarily protects the wiring connected downstream of it. Basic calculations of these devices are carried out based on the rated load current. Power calculations are carried out in the case when the entire length of the wire is designed to carry the load, in accordance with the rated current.

The final choice of rated current for the machine depends on the cross-section of the wire. Only after this can the load value be calculated. The maximum current allowed for a wire with a certain cross-section must be greater. Thus, when choosing a protective device, the minimum wire cross-section present in the electrical network is used.

When consumers have a question about which machine should be installed at 15 kW, the table also takes into account the three-phase electrical network. There is a methodology for such calculations. In these cases, the rated power of a three-phase circuit breaker is determined as the sum of the powers of all electrical appliances planned to be connected through the circuit breaker.

For example, if the load of each of the three phases is 5 kW, then the operating current is determined by multiplying the sum of the powers of all phases by a factor of 1.52. Thus, it turns out 5x3x1.52 = 22.8 amperes. The rated current of the machine must exceed the operating current. In this regard, the most suitable protective device would be rated 25 A. The most common ratings of circuit breakers are 6, 10, 16, 20, 25, 32, 40, 50, 63, 80 and 100 amperes. At the same time, the compliance of the cable cores with the declared loads is clarified.

This technique can be used only in cases where the load is the same on all three phases. If one of the phases consumes more power than all the others, then the rating of the circuit breaker is calculated based on the power of this particular phase. In this case, only the maximum power value is used, multiplied by a factor of 4.55. These calculations allow you to select a machine not only according to the table, but also according to the most accurate data obtained.

Calculation of the cross-section of cable and wire cores

Possible problems are easier to understand with a concrete example. Initial data:

  • standard power supply with alternating voltage U = 220 V;
  • the apartment has old aluminum wiring (section 2.5 mm square);
  • amperage of the machine – 30 A;
  • connect 6 convectors of 750 W and one iron of 850 W.
  • total power (P) of consumers – 5,350 W;
  • current (I) in the circuit is calculated by the formula I = P/U = 5,350 / 220 = 24.32 A).

The machine will not work in such a situation (30(amp)gt;24.32A). Such a current will greatly heat the aluminum wire and melt the insulation. A circuit destroyed by a short circuit will have to be restored, which is difficult when installing networks inside building structures. In the worst situation, significant material assets will be destroyed by fire.

Machine selection table by power

Individual work operations are simplified using specialized calculators. Such programs provide free information and help sites. But the selection of a machine based on power will have to be done on the basis of real equipment.

Typical algorithm:

  • clarify the initial consumption data of individual devices;
  • distribute into groups, clarify the total values;
  • The results obtained are used to select protective equipment.

This parameter indicates the preservation of functionality when current loads are exceeded multiple times (times):

  • B (3-5);
  • C (5-10);
  • D (40-50).

Tabular method

The reference materials indicate how much load power can be used if the machines are installed in different power networks. Example for 2 A model (values ​​in kW):

  • 220 V, 1 (2) poles, single-phase connection – 0.4;
  • 380 V, 3 poles, “triangle” – 2.3;
  • 380 V, 4 poles, star – 1.3.

The result must be increased to the closest value in the model range for reliability.

Graphic method

This technique uses similar principles. But the test parameters are presented in a clear graphical form.

Nuances of choice

In any case, the choice of circuit breaker based on current (power) is made with a reserve. Experts recommend using a multiplying factor of 1.4-1.6. At the same time, the ability of the wiring to withstand the maximum load is checked.

To calculate these parameters, the definitions of total (S), active (P) and reactive (Q) power are used. The following formulas are suitable for calculating single-phase 220 V networks:

  • S = U *I;
  • P = U * I * cos ϕ;
  • Q = U * I * sin ϕ.

The initial data for the calculation can be taken from reference books. Measurement results are also used.

Incandescent lamps and heaters are not reactive. Such loads do not shift the phases of currents and voltages. Power is consumed completely at twice the frequency.

Capacitive load

When a capacitor is connected to an AC network, energy is exchanged in both directions. This process is not accompanied by useful work.

Energy ratio

The explanations presented consider an ideal situation. However, in reality, each reactive element has a certain electrical resistance. One must not forget about the corresponding losses in connecting wires and other circuit components.

With significant values ​​of the capacitive (inductive) component, the noted problems must be taken into account. In some schemes, in addition to increasing the load capacity of the machines, additional compensation components are used.

The power of the protective device is selected based on the wiring current (calculated or tabulated value) taking into account the consumption of the connected load. The rating of the machine is chosen less in order to maintain the integrity of the power line during operation. At different sections of the network, conductors of the appropriate cross-section are installed, guided by the principles of a tree structure.

You can purchase AVs with short circuit ratings: 3,000, 4,500, 6,000, 10,000 Amperes. The choice of AV with the required rating depends on the length of the cable or overhead line from the transformer substation (TS) to your house, apartment or cottage.

If the transformer substation is located nearby, then the short-circuit currents are very high, so you need to purchase a circuit breaker with a cutoff of 10,000 A. In the private sector of households, there is a large length of overhead power lines, so you need to use a circuit breaker with a short-circuit current of 4,500 A. In other cases, the average value is - 6,000 A.

Electromagnetic release

B – the circuit opens when the rated current is exceeded by 3–5 times;

C – exceeded by 5–10 times;

D – exceeded by 10–20 times.

To select a circuit breaker based on power (P), you need to calculate the load current using the formula, then, based on the data obtained, select a circuit breaker of a larger value.

Example of selecting an automatic switch

I – current consumption;

P – total power of consumers;

U – network voltage.

I = 3,620/220 = 16.4A

As you can see, the consumed load current is 16.4 A. And based on this, you can select AB. You can take a 16 A automatic machine, but it will work at the very limit. Any machine is designed in such a way that the specified rated current is increased by 13% and if overloaded it will work for some time. Why take an AB that will work to the limit. You need to take it with a reserve. The next AB rating is 20 A.

Look at the power table to select an AB by rating.

Table 2.

Connection type Single phase 220 V, Three-phase (delta), 380 V Three-phase (star), 220 V
Machine rating, A
1 200 W 1 100 W 700 W
2 400 W 2,300 W 1,300 W
3 700 W 3,400 W 2,000 W
6 1,300 W 6,800 W 4 000W
10 2,200 W 11,400 W 6,600 W
16 3,500 W 18,200 W 10,600 W
20 4,400 W 22,800 W 13,200 W
25 5,500 W 28,500 W 16,500 W
32 7,000 W 36,500 W 21,100 W
40 8,800 W 45,600 W 26,400 W
50 11,000 W 57,000 W 33,000 W
63 13,900 W 71,800 W 41,600 W

Industry produces specific sections of wire or cable. Each conductor section has a certain current load. Using a certain cross-section, you can also select a circuit breaker (AB) according to its rating. If you are not sure about the cross-section of a particular wire or cable, then this matter can be calculated using a formula.

The easiest way is to use a table where you can immediately determine which AB you need. The table contains data without taking into account the length of the wire (cable).

Table 3.

Circuit breaker current, A Wire cross-section, mm² power, kWt
Copper Aluminum 220 V 380 V (cos φ = 0.8)
5 1 2,5 1,1 2,6
6 1 2,5 1,3 3,2
10 1,5 2,5 2,2 5,3
16 1,5 2,5 3,5 8,4
20 2,5 4 4,4 10,5
25 4 6 5,5 13,2
32 6 10 7 16,8
40 10 16 8,8 21,1
50 10 16 11 26,3
63 16 25 13,9 33,2

The main thing in selecting the AV and the cross-section of the wire (cable) is that the current of the automatic switch is less than the permissible current of the conductor.

Conclusion

You learned how to choose the right AB from this article. Before purchasing automatic switches, you should already know which manufacturers produce quality products. Choose only trusted companies.

The selection of circuit breakers is, first of all, based on the power that the home electrical network must withstand.

Why is it important to choose a machine based on load power:

  1. If there is a discrepancy This indicator gradually heats up the wiring.
  2. Constant heating causes the insulating layer to melt. This creates two problems at once: toxic smoke and the risk of fire.
  3. Against the background of melting insulation a short circuit appears. The AV finally works (which did not happen before, because the device was selected incorrectly), but fire, and even more so smoke, could already have spread in the apartment.

The first option is the most accessible. It is necessary to take into account the total power of the network, that is, the total power of simultaneously switched on electrical appliances. Even small light bulbs, underfloor heating if equipped, kitchen appliances and electrical entertainment devices are taken into account. The resulting figure should be expressed in kW.

An example of how to calculate power:

  • washing machine – 700 W;
  • electric stove – 2.5 kW;
  • Microwave – 1.8 kW;
  • 5 light bulbs – 600 W;
  • refrigerator – 400 W;
  • TV – 200 W;
  • PC – 550 W;
  • vacuum cleaner – 1 kW.

What are circuit breakers for and how do they work?

Circuit breakers from different manufacturers

Devices in this category are capable of detecting excessive electrical energy consumption. This occurs when there is a short circuit or when powerful or reactive loads are connected. In such situations, the circuit breaker turns off the 220 (380) V power source without user intervention.

To perform the noted functions, two technologies are used in the standard design. With a rapid increase in current above a calculated level, the solenoid creates a magnetic field that moves the rod. Through a mechanical drive, this unit opens the contact group. The node parameters are calculated taking into account starting loads in order to eliminate false alarms.

The second protection is organized using a well-known phenomenon - heating the conductor by passing current. The corresponding section of the chain is created from a bimetallic plate. As the temperature increases, it changes shape until the contact breaks. Some models of machines have special adjustments for adjusting the sensitivity level.

The main function of circuit breakers is to protect the insulation of wires and power cables from destruction under the influence of short circuit currents. These devices are not able to protect people from electric shock; they only protect the network and equipment. The operation of automatic switches ensures normal operation of the wiring, completely eliminating the threat of fire.

When choosing a machine, you must take into account that the overestimated characteristics of the device will facilitate the passage of currents that are critical for wiring. In this case, the protected area will not be disconnected, which will lead to melting or fire of the insulation. If the characteristics of the machine are underestimated, the line will constantly break when starting powerful equipment. Automatic machines fail very quickly due to contacts sticking under the influence of too high currents.

The main operating elements of the machines are releases that directly break the circuit 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 area 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 activates a spring associated with a release device.
  • Thermal bimetallic releases. Provide network overload protection. They ensure that the circuit breaks when a current passes that does not correspond to the maximum operating parameters of the cable. Under the influence of high current, the bimetallic strip bends and causes the release to trip.

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

What types of circuit breakers are there?

Each individual line must have its own circuit breaker

In addition to the cross-section, when choosing suitable cable products, pay attention to the actual operating conditions. Standardized values ​​are given for heating to a temperature not exceeding 60°C. When installing the line on a site near a country house, it is necessary to provide protection from humidity and other adverse external influences.

Carefully check all parts of the electrical network. The basic rule is reliable protection, taking into account the performance of the area with the worst parameters. It should be taken into account that copper is designed with the same cross-section for greater loads compared to aluminum. The purity of the metal is of certain importance. As impurities increase, conductivity deteriorates and losses due to useless and dangerous heating increase.

In such real estate objects, the following standard solutions are used to create a high-quality power supply system:

  • the introductory machine must be placed before the counter;
  • a general residual current device (RCD) is installed behind the control device;
  • Next, separate lines are equipped with automatic switches (AB).

The RCD prevents accidents that provoke leakage currents. In some situations, it prevents electric shock. However, complex protective measures are carried out using circuit breakers. Effective grounding must be used.

Ratings of automatic devices for kitchen wiring

As a rule, it is convenient to install several groups in the kitchen to evenly distribute the loads. It is recommended to carefully select the distribution of powerful consumers:

  • hobs;
  • ovens;
  • heating boilers, boilers, flow heaters;
  • electric convectors, heat guns;
  • air conditioners.

Let me give you an example:

  • Household electric stove for 220 volts. Power consumption 5000 watts (5 kWatt).
  • The load current can be calculated using Ohm's law.
  • Iload=5000W÷220 volts=22.7 Amperes.

Conclusion: A circuit breaker of at least 23 Amps must be installed on the power line for this electric stove. There are no such machines on sale, so we choose a machine with the highest closest rating of 25 Amperes.

To calculate the current load of a group of consumers, the so-called demand coefficient is introduced. The demand coefficient (Kc) determines the probability of simultaneous inclusion of all consumers in the group over a long period of time. Ks=1 corresponds to the simultaneous operation of all electrical appliances in the group.

It is clear that turning on and operating all electrical appliances in an apartment practically never happens. There are entire systems for calculating the demand coefficient for houses and entrances. For each apartment, the demand coefficient differs for individual rooms, individual consumers and even for different lifestyles of residents. For example, the demand coefficient for a TV is usually 1, and the demand coefficient for a vacuum cleaner is 0.1.

Therefore, to calculate the current load and select a circuit breaker in a wiring group, the demand factor influences the result. The estimated power of the electrical wiring group is calculated using the formula:

  • P(calculated)=K(demand)×P(installed power).
  • I (load current) = P (calculated power) ÷ 220 volts.
  • Estimated Power in the network is calculated as follows:
  • 480×0.7 75 160 150 380 1000 400 700×0.3=2711,W
  • K(demand) apartments=2711÷3345=0.8
  • Load current:
  • 3345÷220×0.8=12Amp.
  • Accordingly, we select a circuit breaker one step higher: 16 Ampere.

To protect conductors of a single-phase 220 V network, there are single-pole and double-pole disconnecting devices. To single-pole wires, only one conductor is connected - phase, to double-pole wires, both phase and neutral. Single-pole circuit breakers are installed on 220 V indoor lighting circuits, on socket groups in rooms with normal operating conditions. They are also installed on some types of load in three-phase networks, connecting one of the phases.

For three-phase networks (380 V) there are three and four poles. These circuit breakers (the correct name is a circuit breaker) are installed on a three-phase load (ovens, hobs and other equipment that operate on a 380 V network).

In rooms with high humidity (bathroom, bathhouse, swimming pool, etc.) two-pole circuit breakers are installed. They are also recommended for installation on powerful appliances - washing machines, dishwashers, boilers, ovens, etc.

It’s just that in emergency situations - in the event of a short circuit or insulation breakdown - phase voltage can reach the neutral wire. If a single-pole device is installed on the power line, it will disconnect the phase wire, and the zero with dangerous voltage will remain connected. This means there is still a possibility of electric shock when touched.


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


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

Selection of circuit breaker rating based on wire cross-section

The main function of the AB is to protect electrical wiring. For this reason, first ensure compliance with the rating of the switch in amperes, the cross-section and material (copper, aluminum) of the cable cores.

How much electricity is needed for the operation of lamps and other products is noted in the accompanying documentation. Power is indicated on the housing. This data can be obtained from the manufacturer's official website. However, simply adding up kilowatts is not enough.

cos(f) – parameter with which you can determine the total (nominal) power from the active (consumed)

The simple calculation algorithm shown in the example describes the situation with a resistive load. It is this component (active power - P) that is indicated in the technical data sheet of the corresponding product. It is determined by the meter for regular payments for consumed energy.

However, when connecting a machine or other electrically driven equipment, you will have to take into account the inductive component. They act in a similar way if there is a capacitor in the circuit.

Formulas and explanations:

  • P = S * cos ϕ;
  • Q = S * sin ϕ;
  • S = P/ cos ϕ;
  • ϕ – angle between vectors P and S (phase shift).

The reactive component (Q) denotes the cyclic exchange of energy between the power source and the load. The sum of the vectors P and Q will help determine the final apparent power (S).

Turning on a powerful pump (another reactive load) is accompanied by an inrush of current and a subsequent oscillatory process with a transition to normal operating mode. The pulse duration, as a rule, does not exceed 1.5-2 seconds. This duration is not sufficient to heat up the bimetallic plate. But this may be enough to move the solenoid rod.

The list shows typical over-rated levels that trigger tripping by the solenoid coil. The time delays before the bimetallic plate breaks the circuit (seconds) are given in parentheses:

  • A – 30% (20-30);
  • B – 200% (4-5);
  • C – 5 times (1.5);
  • D – 10 times (0.4).

The corresponding modes were taken into account when creating profile standards. To prevent erroneous shutdown, you need to choose the appropriate type of machine.

This correction factor (Ks) is used to take into account loads under real operating conditions: Design = S * Ks. Its value (interval from 0 to 1) indicates the number of connected consumers. This method is convenient to use when creating office and industrial projects, which involve the use of the same type of equipment: machines, computers, etc.

Measuring voltage with a multimeter

The given formulas with phase shift are used to correct inductive and capacitive loads. Resistive ones are taken into account according to passport data without recalculation. The cos ϕ value is taken from the accompanying documentation.

The current can be calculated as follows:

  • P/U – constant power supplies, resistive loads;
  • P/ (U * cos ϕ) = P/ (220 * cos ϕ) – one phase, ~220V, consumer reactive characteristics;
  • P/ (U * √3 * cos ϕ) = P/ (380 * 1.7321 * cos ϕ) – three-phase network ~380V, inductive (capacitive) technical parameters.

You can measure real voltages using a multimeter. The methodology for performing work operations is given in the manufacturer’s official instructions.

Selection of core cross-section

The necessary information about load capacities is contained in the official documentation of cable manufacturers. It is recommended to select a larger cross-section from the serial range to prevent overheating and damage during operation. According to current rules, conductors with an area of ​​1.5 mm or more are suitable for residential premises.

The limit value of the nominal value is determined by the formula Ir ≤ Ipr/1.45, where Ipr is the permissible current in long-term mode for a certain wiring. If you plan to install a network, proceed as follows:

  • clarify the consumer connection diagram;
  • collect passport data of equipment, measure voltage;
  • according to the presented diagram, they are calculated separately, the currents in individual circuits are summed up;
  • for each group it is necessary to select a machine that will withstand the appropriate load;
  • determine cable products with a suitable conductor cross-section.

If the networks are installed in grooves and covered with plaster, disassembly is too difficult. In this case, select the machine according to the cable cross-section. They start by assessing the load capacity of existing lines. The obtained result is used to evaluate suitable models of protective devices. Next, consumers are distributed into groups taking into account the total power (shared use).

An example of choosing the machine's nominal value for each line

For correct conclusions, it is necessary to take into account the characteristics of the connected equipment. If the total current is calculated to be 19 amperes, users prefer to buy a 25A device. This solution assumes the possibility of applying additional loads without significant restrictions.

However, in some situations it is better to choose a 20A circuit breaker. This ensures a relatively shorter time for power outages when the current increases (temperature increases) with a bimetallic disconnector. This precaution will help maintain the integrity of the electric motor windings when the rotor rotation is blocked by a jammed drive.

Different response times are useful to ensure selective operation of protective equipment. Devices with lower latency are installed on the lines. In an emergency, only the damaged part is disconnected from electricity. The input machine will not have time to turn off. Power supply through other circuits is useful for maintaining lighting, alarms, and other engineering systems in working order.

Actually, from the functions of the circuit breaker, the rule for determining the rating of the circuit breaker follows: it must operate until the current exceeds the capabilities of the wiring. This means that the current rating of the machine must be less than the maximum current that the wiring can withstand.


Based on this, the algorithm for selecting a circuit breaker is simple:

  • Calculate the wire cross-section for a specific area.
  • See what maximum current this cable can withstand (see the table).
  • Next, from all the ratings of the circuit breakers, we select the nearest smaller one. The ratings of the machines are tied to the permissible long-term load currents for a particular cable - they have a slightly lower rating (see the table). The list of denominations looks like this: 16 A, 25 A, 32 A, 40 A, 63 A. From this list you choose the appropriate one. There are even smaller ratings, but they are practically not used anymore - we have too many electrical appliances and they have considerable power.

Example

The algorithm is very simple, but it works flawlessly. To make it clearer, let's look at an example. Below is a table that shows the maximum permissible current for conductors that are used when laying wiring in a house and apartment. Recommendations regarding the use of machines are also given there.

Cross section of copper wires Permissible continuous load current Maximum load power for single-phase network 220 V Rated current of circuit breaker Circuit breaker current limit
1.5 sq. mm 19 A 4.1 kW 10 A 16 A lighting and alarm
2.5 sq. mm 27 A 5.9 kW 16 A 25 A socket groups and electric heated floor
4 sq.mm 38 A 8.3 kW 25 A 32 A air conditioners and water heaters
6 sq.mm 46 A 10.1 kW 32 A 40 A electric stoves and ovens
10 sq. mm 70 A 15.4 kW 50 A 63 A opening lines

In the table we find the selected wire cross-section for this line. Suppose we need to lay a cable with a cross-section of 2.5 mm2 (the most common when laying to medium-power devices). A conductor with this cross-section can withstand a current of 27 A, and the recommended rating of the machine is 16 A.

How will the circuit work then? As long as the current does not exceed 25 A, the machine does not turn off, everything works as normal - the conductor heats up, but not to critical values. When the load current begins to increase and exceeds 25 A, the machine does not turn off for some time - perhaps these are starting currents and they are short-lived.

Power calculation

Is it possible to choose a machine based on load power? If only one device is connected to the power line (usually large household appliances with high power consumption), then it is permissible to make a calculation based on the power of this equipment. You can also choose an introductory machine based on power, which is installed at the entrance to a house or apartment.

If we are looking for the rating of the input circuit breaker, we need to add up the power of all devices that will be connected to the home network. Then the found total power is substituted into the formula, and the operating current for this load is found.


After we have found the current, select the nominal value. It may be either slightly more or slightly less than the found value. The main thing is that its shutdown current does not exceed the maximum permissible current for this wiring.

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

1000 W / (220 V x 0.95) = 4.78 A

Example of circuit breaker selection

A modern apartment uses all of the above devices (with a total power of 7.75 kW) and additionally the following items (indicators are indicated in kW).

  • kettle – 1.2;
  • oven – 1.2;
  • heater – 1.4.

The total load on the electrical network is 11.55 kW. How to choose AB in this case:

  1. Calculate the denomination using Ohm's formula. 11500/220 = 52.5 A.
  2. Select a conductor that corresponds to 52.5 A or higher. Depending on the manufacturer, DDT with this rating can withstand an aluminum core of 10 mm or 16 mm.
  3. Since the electrical network is for domestic use, AB type C is selected.

The article is intended for those who have a high school knowledge of electrical engineering and want to become familiar with the application of electrical calculations in some cases of everyday life. Please write your feedback and suggestions for adding other calculations in the comments.

1. Calculation of the magnitude of alternating electric current with a single-phase load.

Let's assume that we have an ordinary house or apartment in which there is an alternating current electrical network with a voltage of 220 volts.

The house has electrical appliances:

1. To illuminate the house, 5 light bulbs of 100 watts each and 8 light bulbs of 60 watts each are installed. 2. Electric oven, power 2 kilowatts or 2000 watts. 3. TV with a power of 0.1 kilowatt or 100 watts. 4. Refrigerator with a capacity of 0.3 kilowatts or 300 watts. 5. Washing machine with a power of 0.6 kilowatts or 600 watts. We are interested in what current will flow at the input to our house or apartment when all of the above electrical appliances are operating simultaneously and whether our electric meter, designed for a current of 20 amperes, will be damaged?

Calculation: 1. Determine the total power of all devices: 500 + 480 + 2000 + 100 + 300 + 600 = 3980 watts 2. The current flowing in the wire at this power is determined by the formula:

Where: I - current in amperes (A) P - power in watts (W) U - voltage in volts (V) cos φ - power factor (for household electrical networks you can take 0.95) Substitute the numbers into the formula: I = 3980 / 220 * 0.95 = 19.04 A Conclusion: The meter will withstand, since the current in the circuit is less than 20 A. For the convenience of users, a current calculation form is given below.

You should enter in the appropriate fields of the form the total power value in watts of all your electrical appliances, voltage in volts, usually 220 and power factor, 0.95 for household loads, click the "Calculate" button and the current value in amperes will appear in the "Current" field. If you have a load in kilowatts, you should convert it to watts by multiplying by 1000. To clear the entered power value, click the "Clear" button. Clearing the default voltage and cosine values ​​should be done by pressing the delete key and moving the cursor to the appropriate cell (if necessary).

Calculation form for determining the current for a single-phase load.

The same calculation can be performed for a retail outlet, garage or any facility that has a single-phase input. But what if we know the current, which we determined using a current clamp or an ammeter, but we need to know the connected power?

Calculation form for determining power for a single-phase load.

What is the value of cos φ for other pantographs?(Attention! The values ​​of cosine phi for your equipment may differ from those indicated): Incandescent lamps and electric heating devices with resistance heating (cosφ ≈ 1.0) Asynchronous motors, at partial load (cosφ ≈ 0.5) Rectifier electrolysis units (cosφ ≈ 0 .6) Electric arc furnaces (cosφ ≈ 0.6) Induction furnaces (cosφ ≈ 0.2-0.6) Water pumps (cosφ ≈ 0.8) Compressors (cosφ ≈ 0.7) Machines, machine tools (cosφ ≈ 0, 5) Welding transformers (cosφ ≈ 0.4) Fluorescent lamps connected via an electromagnetic choke (cosφ ≈ 0.5-0.6)

2. Calculation of the magnitude of direct electric current.

Direct current for everyday life is used mainly in electronic devices, as well as in the on-board electrical network of a car. Let's say you decide to install an additional headlight in a car with a 60-watt lamp and connect it from the low beam headlight. And the question immediately arises - will the existing 10 amp fuse for the low beam headlight hold when connecting another headlight?

Calculation: Let's assume that the power of the low beam headlight bulb is 65 watts. Let's calculate the current using the formula:

where: I - current in amperes (A) P - power in watts (W) U - voltage in volts (V)

As we see, unlike the formula for alternating current - cos φ - is not here. Let's substitute the numbers into the formula: I = 65 /12 = 5.42 A 65 W - lamp power 12 V - voltage in the vehicle's on-board network 5.42 A - current in the lamp circuit. The power of two lamps in the main and additional headlights will be 60 + 65 = 125 W I = 125/12 = 10.42 A Conclusion: When connecting 2 headlights, a fuse rated at 10 A may not withstand it, so it is advisable to replace it with the nearest one with a high setting current. Before replacement, it is necessary to check the value of the continuous permissible current for the wire of this circuit, and the fuse tripping current must be less than the continuous permissible current of the wire.

For the convenience of users, a current calculation form is given below. You should enter in the appropriate fields of the form the total power value in watts of all your electrical appliances, the voltage in volts, click the "Calculate" button and the current value in amperes will appear in the "Current" field. To clean, click the "Clear" button. Calculation form for determining direct current.

3. Calculation of the magnitude of alternating electric current with a three-phase load.

Now let's assume that we have an ordinary house or apartment in which there is an alternating current electrical network with a voltage of 380/220 volts. Why are two voltages indicated - 380 V and 220 V? The fact is that when connected to a three-phase network, 4 wires enter your house - 3 phases and a neutral (in the old way - zero).

So, the voltage between the phase wires or otherwise - the linear voltage will be 380 V, and between any of the phases and the neutral or otherwise the phase voltage will be 220 V. Each of the three phases has its own designation in the Latin letters A, B, C. The neutral is designated by the Latin N .

Thus, between phases A and B, A and C, B and C - there will be a voltage of 380 V. Between A and N, B and N, C and N there will be 220 V and electrical appliances with a voltage of 220 V can be connected to these wires, which means the house can have both three-phase and single-phase loads.

Most often, there is both and it is called a mixed load.

First, let's calculate the current for a purely three-phase load.

The house has three-phase electrical appliances:

1. Electric motor with a power of 3 kilowatts or 3000 watts.

2. Electric water heater with a power of 15 kilowatts or 15,000 watts.

In fact, three-phase loads are usually counted in kilowatts, therefore, if they are written in watts, they should be divided by 1000. We are interested in what current will flow at the input to our house or apartment when all of the above electrical appliances are operating simultaneously and whether our electric meter will be damaged rated for 20 amperes?

Calculation: We determine the total power of all devices: 3 kW + 15 kW = 18 kW 2. The current flowing in the phase wire at this power is determined by the formula:

Where: I - current in amperes (A) P - power in kilowatts (kW) U - linear voltage, V cos φ - power factor (for household electrical networks you can take 0.95) Substitute the numbers into the formula: = 28.79 A

Conclusion: The meter will not withstand it, so it needs to be replaced with a current of at least 30 A. For the convenience of users, a current calculation form is given below.

In order not to use a calculator, simply enter your numbers in the form below and press the "Calculate" button.

Calculation form for determining the current for a three-phase load.

But what to do when we know the current of the three-phase load (the same for each phase), which we determined using a current clamp or an ammeter, but we need to know the connected power?

Let's transform the formula for calculating current into calculating power.

In order not to use a calculator, simply enter your numbers in the form below and press the "Calculate" button.

Calculation form for determining power for a three-phase load.

Now let's calculate the current for mixed three-phase and single-phase loads.

So, 3 phases are installed in the house and the electrician installing the electrical wiring must strive to ensure that the phases are loaded evenly, although this is not always the case.

In our house it turned out, for example, like this: - phase A and neutral with the voltage between them, as we already know - 220 V is supplied to the garage and well, as well as yard lighting, total load - 12 light bulbs of 100 watts, electric pump 0.7 kW or 700 watts. - phase B and neutral with a voltage between them - 220 V are brought into the house, the total load is 1800 watts. - phase C and neutral with a voltage between them of 220 V are brought into the summer kitchen, the total load of the electric stove and lamps is 2.2 kW.

We have single-phase loads: phase A load is 1900 watts, phase B - 1800 watts, phase C - 2200 watts, a total of three phases 5.9 kW. In addition, the diagram shows three-phase loads of 3 kW and 15 kW, which means the total power of the mixed load will be 23.9 kW.


We enter the values ​​of these powers one by one and calculate the currents.

For phase A it will be - 9.09 A, for B - 8.61 A, for C - 10.53 A. But we already have a three-phase load current passing through the wires of all three phases, therefore, in order to find out the total value of the current in each of phases, you just need to add the currents of three-phase and single-phase loads. Phase A 28.79 A + 9.09 A = 37.88 A Phase B 28.79 A + 8.61 = 37.40 A Phase C 28.79 A + 10.53 = 39.32 A. Highest mixed current load in phase C.

But what to do when we know the current of a mixed three-phase load (different for each phase), which we determined using a current clamp or an ammeter, and we need to know the connected power?

In this case, it is necessary to determine the power consumption of each of the three phases using the calculation form for determining the power for a single-phase load and then simply add these powers, which will give us the total power of the mixed three-phase load. Using the example for a mixed load, we see that the total current in phase A was 37.88 A, phase B - 37.40 A, phase C - 39.32 A.

7.2. Checking the selected section for voltage loss.

To begin with, from the known connected power P = 3980 W, phase voltage U f = 220 V and cosine phi 0.95, you need to determine the load current. I will not repeat myself, since we already covered this at the beginning of section 1. “Calculation of the magnitude of alternating electric current for a single-phase load.” In addition, to select the material and cross-section of the wire, it is necessary to add a safety factor of 30% to the load current or, which is the same thing, multiply by 1.3. In our case, the load current is 19.04 A. The safety factor is 30% of the load current 1.3 · I n = 1.3 · 19.04 = 24.76 A.

We select an aluminum wire and, according to Table 1.3.5 of the PUE, determine the nearest largest cross-section, which will be equal to 4 mm 2 for openly laid wires at a current of 32 A.

In order for the user to substitute their values, a calculation form consisting of two parts is given below.

Calculation form for determining voltage losses in a two-wire single-phase or two-phase network.

Part 1. Calculate the load current and current with a safety factor of 30% to select the wire cross-section.

Devices for shutting off electricity during overloads and short circuits are installed at the entrance to any home network. It is necessary to correctly calculate the current ratings of circuit breakers, otherwise their operation will be ineffective. Do you agree?

We will tell you how to calculate the parameters of the machine, according to which this protective device is selected. From our article you will learn how to choose the device required to protect the electrical network. Taking into account our advice, you will purchase an option that will clearly operate at a dangerous moment for wiring.

To ensure the correct selection of trip device ratings, an understanding of their operating principles, conditions and response times is necessary.

The operating parameters of circuit breakers are standardized by Russian and international regulatory documents.

Basic elements and markings

The design of the switch includes two elements that react when the current exceeds the established range of values:

  • The bimetallic plate, under the influence of the passing current, heats up and, bending, presses on the pusher, which disconnects the contacts. This is “thermal protection” against overload.
  • The solenoid, under the influence of a strong current in the winding, generates a magnetic field that presses on the core, which then acts on the pusher. This is a “current protection” against short circuit, which reacts to such an event much faster than the plate.

Types of electrical protection devices have markings that can be used to determine their main parameters.

Each circuit breaker is marked with its main characteristics. This allows you to avoid confusing devices when they are installed in the panel

The type of time-current characteristic depends on the setting range (the magnitude of the current at which operation occurs) of the solenoid. To protect wiring and devices in apartments, houses and offices, switches of type “C” or, much less common, “B” are used. There is no particular difference between them for everyday use.

Type “D” is used in utility rooms or carpentry in the presence of equipment with electric motors that have high starting power.

There are two standards for disconnect devices: residential (EN 60898-1 or GOST R 50345) and a more stringent industrial (EN 60947-2 or GOST R 50030.2). They differ slightly and machines of both standards can be used for residential premises.

In terms of rated current, the standard range of automatic machines for domestic use contains devices with the following values: 6, 8, 10, 13 (rare), 16, 20, 25, 32, 40, 50 and 63 A.

Time-current response characteristics

In order to determine the speed of operation of the machine during an overload, there are special tables depending on the shutdown time on the coefficient of excess of the nominal value, which is equal to the ratio of the existing current strength to the rated one:

K = I / I n.

A sharp drop down in the graph when the range coefficient value reaches from 5 to 10 units is due to the operation of the electromagnetic release. For type “B” switches this occurs at a value from 3 to 5 units, and for type “D” – from 10 to 20.

The graph shows the dependence of the response time range of type “C” circuit breakers on the ratio of the current strength to the value that is set for this switch

With K = 1.13, the machine is guaranteed not to disconnect the line within 1 hour, and with K = 1.45, it is guaranteed to disconnect within the same time. These values ​​are approved in clause 8.6.2. GOST R 50345-2010.

To understand how long it takes for the protection to operate, for example, at K = 2, you need to draw a vertical line from this value. As a result, we get that, according to the above graph, the shutdown will occur in the range from 12 to 100 seconds.

Such a large spread of time is due to the fact that heating of the plate depends not only on the power of the current passing through it, but also on the parameters of the external environment. The higher the temperature, the faster the machine operates.

Rules for choosing denomination

The geometry of intra-apartment and house electrical networks is individual, so there are no standard solutions for installing switches of a certain rating. The general rules for calculating the permissible parameters of machines are quite complex and depend on many factors. It is necessary to take them all into account, otherwise an emergency situation may be created.

The principle of indoor wiring

Internal electrical networks have a branched structure in the form of a “tree” – a graph without cycles. Compliance with this design principle is called, according to which all types of electrical circuits are equipped with protective devices.

This improves the stability of the system in the event of an emergency and simplifies the work to eliminate it. It is also much easier to distribute the load, connect energy-intensive devices and change the wiring configuration.

At the base of the graph there is an input machine, and immediately after the branching, group switches are placed for each individual electrical circuit. This is a standard scheme proven over the years

The functions of the input circuit breaker include monitoring the general overload - preventing the current from exceeding the permitted value for the object. If this happens, there is a risk of damage to the external wiring. In addition, it is likely that protective devices outside the apartment, which are already part of the common property or belong to the local power grid, will be triggered.

The functions of group machines include current control on individual lines. They protect the cable in a dedicated area and the group of electricity consumers connected to it from overload. If such a device does not operate during a short circuit, then it is insured by an input circuit breaker.

Even for apartments with a small number of electrical consumers, it is advisable to install a separate line for lighting. When you turn off the circuit breaker of another circuit, the light will not go out, which will allow you to eliminate the problem in more comfortable conditions. In almost every panel, the nominal value of the input machine is less than the amount on the group ones.

Total power of electrical appliances

The maximum load on the circuit occurs when all electrical appliances are turned on at the same time. Therefore, usually, the total power is calculated by simple addition. However, in some cases this figure will be less.

For some lines, the simultaneous operation of all electrical appliances connected to it is unlikely, and sometimes impossible. Homes sometimes specifically place restrictions on the operation of powerful devices. To do this, you need to remember not to turn them on at the same time or use a limited number of sockets.

The probability of simultaneous operation of all office equipment, lighting and auxiliary equipment (kettles, refrigerators, fans, heaters, etc.) is very low, therefore, when calculating the maximum power, a correction factor is used

When electrifying office buildings, the empirical simultaneity coefficient is often used for calculations, the value of which is taken in the range from 0.6 to 0.8. The maximum load is calculated by multiplying the sum of the powers of all electrical appliances by a factor.

There is one subtlety in the calculations - it is necessary to take into account the difference between the rated (total) power and consumed (active), which are related by the coefficient (cos ( f)).

This means that for the device to operate, a power current equal to the consumed divided by this coefficient is required:

Ip = I/cos(f)

  • I p – rated current strength, which is used in load calculations;
  • I is the current consumed by the device;
  • cos(f)<= 1.

Usually the rated current is indicated immediately or through the indication of the cos (f) value in the technical data sheet of the electrical device.

For example, the coefficient value for fluorescent light sources is 0.9; for LED lamps – about 0.6; for ordinary incandescent lamps - 1. If the documentation is lost, but the power consumption of household devices is known, then for guarantee take cos (f) = 0.75.

How to select a circuit breaker according to the load power is written in, the contents of which we advise you to familiarize yourself with.

Selection of core cross-section

Before laying a power cable from the distribution panel to a group of consumers, it is necessary to calculate the power of electrical appliances when they operate simultaneously. The cross-section of any branch is selected according to calculation tables depending on the type of wiring metal: copper or aluminum.

Wire manufacturers provide similar reference materials to their products. If they are missing, then they are guided by the data from the reference book “Rules for the Construction of Electrical Equipment” or produce.

However, consumers often play it safe and choose not the minimum acceptable cross-section, but one step larger. So, for example, when buying a copper cable for a 5 kW line, choose a core cross-section of 6 mm 2, when according to the table a value of 4 mm 2 is sufficient.

The reference table presented in the PUE allows you to select the required cross-section from the standard range for various operating conditions of the copper cable

This is justified for the following reasons:

  • Longer service life of a thick cable, which is rarely subjected to the maximum permissible load for its cross-section. Re-wiring is not an easy and expensive job, especially if the room has been renovated.
  • The bandwidth reserve allows you to seamlessly connect new electrical appliances to the network branch. So, you can add an additional freezer to the kitchen or move the washing machine there from the bathroom.
  • The start of operation of devices containing electric motors produces strong starting currents. In this case, a voltage drop is observed, which is expressed not only in the blinking of the lighting lamps, but can also lead to breakdown of the electronic part of the computer, air conditioner or washing machine. The thicker the cable, the smaller the voltage surge will be.

Unfortunately, there are many cables on the market that are not made according to GOST, but according to the requirements of various specifications.

Often the cross-section of their cores does not meet the requirements or they are made of conductive material with greater resistance than required. Therefore, the actual maximum power at which permissible heating of the cable occurs is less than in the standard tables.

This photo shows the differences between cables made according to GOST (left) and according to TU (right). There is an obvious difference in the cross-section of the conductors and the tightness of the insulating material.

Calculation of the circuit breaker rating for cable protection

The machine installed in the panel must ensure that the line is disconnected when the current power goes beyond the range permitted for the electric cable. Therefore, it is necessary to calculate the maximum permissible rating for the switch.

According to the PUE, the permissible long-term load of copper cables laid in boxes or in the air (for example, over a suspended ceiling) is taken from the table above. These values ​​are intended for emergency situations when there is a power overload.

Some problems begin when relating the rated power of the switch to the long-term permissible current, if this is done in accordance with the current GOST R 50571.4.43-2012.

A fragment of clause 433.1 of GOST R 50571.4.43-2012 is given. There is an inaccuracy in formula “2”, and for a correct understanding of the definition of the variable In, you need to take into account Appendix “1”

Firstly, deciphering the variable In as rated power is misleading, if you do not pay attention to Appendix “1” to this paragraph of GOST. Secondly, there is a typo in formula “2”: the coefficient of 1.45 was added incorrectly, and this fact is stated by many experts.

According to clause 8.6.2.1. GOST R 50345-2010 for household switches rated up to 63 A, the conditional time is 1 hour. The set tripping current is equal to the nominal value multiplied by a factor of 1.45.

Thus, according to both the first and modified second formulas, the rated current of the circuit breaker must be calculated using the following formula:

I n<= I Z / 1,45

  • I n – rated current of the machine;
  • I Z – long-term permissible cable current.

Let's calculate the ratings of switches for standard cable sections for a single-phase connection with two copper conductors (220 V). To do this, we divide the long-term permissible current (when laying through the air) by a tripping coefficient of 1.45.

Let's choose a machine so that its face value is less than this value:

  • Section 1.5 mm 2: 19 / 1.45 = 13.1. Rating: 13 A;
  • Section 2.5 mm 2: 27 / 1.45 = 18.6. Rating: 16 A;
  • Section 4.0 mm 2: 38 / 1.45 = 26.2. Rating: 25 A;
  • Section 6.0 mm 2: 50 / 1.45 = 34.5. Rating: 32 A;
  • Section 10.0 mm 2: 70 / 1.45 = 48.3. Rating: 40 A;
  • Section 16.0 mm 2: 90 / 1.45 = 62.1. Rating: 50 A;
  • Section 25.0 mm 2: 115 / 1.45 = 79.3. Denomination: 63 A.

13A circuit breakers are rarely on sale, so devices with a rated power of 10A are often used instead.

Cables based on aluminum cores are now rarely used when installing internal wiring. There is also a table for them that allows you to select a section based on load

In a similar way, for aluminum cables we calculate the ratings of the machines:

  • Section 2.5 mm 2: 21 / 1.45 = 14.5. Rating: 10 or 13 A;
  • Section 4.0 mm 2: 29 / 1.45 = 20.0. Rating: 16 or 20 A;
  • Section 6.0 mm 2: 38 / 1.45 = 26.2. Rating: 25 A;
  • Section 10.0 mm 2: 55 / 1.45 = 37.9. Rating: 32 A;
  • Section 16.0 mm 2: 70 / 1.45 = 48.3. Rating: 40 A;
  • Section 25.0 mm 2: 90 / 1.45 = 62.1. Rating: 50 A.
  • Section 35.0 mm 2: 105 / 1.45 = 72.4. Denomination: 63 A.

If the power cable manufacturer declares a different dependence of the permissible power on the cross-sectional area, then it is necessary to recalculate the value for the switches.

The formulas for the dependence of current on power for single-phase and three-phase networks are different. Many people who have devices designed for 380 Volts make a mistake at this stage

How to determine the technical parameters of a circuit breaker by marking, in detail. We recommend that you read the educational material.

Prevention of overload from consumer work

Sometimes a machine is installed on the line with a rated power significantly lower than what is necessary to ensure that the electrical cable remains operational.

It is advisable to reduce the rating of the switch if the total power of all devices in the circuit is significantly less than the cable can withstand. This happens if, for safety reasons, when after installation of the wiring some of the devices were removed from the line.

Then reducing the rated power of the machine is justified from the position of its faster response to emerging overloads.

For example, when an electric motor bearing jams, the current in the winding increases sharply, but not to short circuit values. If the machine reacts quickly, the winding will not have time to melt, which will save the engine from an expensive rewinding procedure.

They also use a value less than the calculated value due to strict restrictions on each circuit. For example, for a single-phase network, a 32 A switch is installed at the entrance to an apartment with an electric stove, which gives 32 * 1.13 * 220 = 8.0 kW of permissible power. Suppose that when wiring the apartment, 3 lines were organized with the installation of group circuit breakers with a nominal value of 25 A.

If the number of group circuit breakers installed in the distribution board is large, then they must be signed and numbered. Otherwise you might get confused

Let's assume that there is a slow increase in load on one of the lines. When the power consumption reaches a value equal to the guaranteed tripping of the group switch, only (32 – 25) * 1.45 * 220 = 2.2 kW will remain for the remaining two sections.

This is very little relative to total consumption. With such a distribution panel design, the input circuit breaker will turn off more often than devices on the lines.

Therefore, in order to maintain the principle of selectivity, it is necessary to install switches with a rating of 20 or 16 amperes in the areas. Then, with the same imbalance in power consumption, the other two links will account for a total of 3.8 or 5.1 kW, which is acceptable.

Let's consider the possibility with a rating of 20A using the example of a separate line dedicated to the kitchen.

The following electrical appliances are connected to it and can be turned on simultaneously:

  • Refrigerator with a rated power of 400 W and a starting current of 1.2 kW;
  • Two freezers, power 200 W;
  • Oven, power 3.5 kW;
  • When operating an electric oven, it is allowed to additionally turn on only one additional device, the most powerful of which is an electric kettle, consuming 2.0 kW.

A twenty-amp machine allows you to pass current for more than an hour with a power of 20 * 220 * 1.13 = 5.0 kW. A guaranteed shutdown in less than one hour will occur with a current flow of 20 * 220 * 1.45 = 6.4 kW.

In the kitchen, refrigeration equipment and the stove must have a permanent connection to electricity. If there is a risk of excess current, then the simultaneous operation of other devices can be eliminated by allocating only two sockets for them

When the oven and electric kettle are turned on simultaneously, the total power will be 5.5 kW or 1.25 parts of the machine’s nominal value. Since the kettle does not work for long, it will not turn off. If at this moment the refrigerator and both freezers turn on, the power will be 6.3 kW or 1.43 parts of the nominal value.

This value is already close to the guaranteed tripping parameter. However, the likelihood of such a situation occurring is extremely low and the duration of the period will be insignificant, since the operating time of the motors and the kettle is short.

The starting current that occurs when starting the refrigerator, even in the sum of all operating devices, will not be enough to trigger the electromagnetic release. Thus, under the given conditions, a 20 A circuit breaker can be used.

The only caveat is the possibility of increasing the voltage to 230 V, which is permitted by regulatory documents. In particular, GOST 29322-2014 (IEC 60038:2009) defines the standard voltage as 230 V with the possibility of using 220 V.

Now most networks supply electricity with a voltage of 220 V. If the current parameter is adjusted to the international standard of 230 V, then the ratings can be recalculated in accordance with this value.

Conclusions and useful video on the topic

Switch device. Selecting an input machine depending on the connected power. Power distribution rules:

Selecting a switch based on cable capacity:

Calculating the rated current of a circuit breaker is a complex task, for which many conditions must be taken into account. The ease of maintenance and safety of the local electrical network depends on the installed machine.

If you have doubts about the ability to make the right choice, you should contact experienced electricians.

Please write comments in the block below. Tell us about your own experience in selecting circuit breakers. Share useful information and photos on the topic of the article, ask questions.