Selecting a machine based on load power and cable cross-section

Today we will tell you how to select a machine based on load power. You will also find out how dependent the power indicators, the rated current of the device and the cross-section of the electrical wiring are on each other. Let's start with brief definitions of the main concepts:

• power is the rate at which electricity is transmitted or converted;
• rated current of the circuit breaker - the maximum transmitted current to which the thermal release does not respond;
• The wire cross-section is the cut area of ​​the current-carrying core.

An adequate selection of circuit breakers is made taking into account the cable cross-section, since the wiring must be able to pass the required load and not overheat. And the issue of power depends on peak loads on the line, that is, you need to know how much the amount of power in the network will increase when all consumers simultaneously require power.

When choosing a circuit breaker, pay attention to the current rating, which you need to select as accurately as possible. It’s not worth taking with a large margin, because the wiring melts when the permissible power consumption is exceeded, and the machine itself is in no hurry to disconnect the circuit, because for it the power is quite normal. As a result, a fire or burning of sockets may occur if the owner of the apartment/house does not notice something is wrong and does not smell the characteristic smell. Again, from a rational point of view, spending money on an expensive AV with a high rating is not profitable if the real requirements for protecting your home network are modest or standard.

If you choose a machine in favor of a small nominal value (less than required), you will end up with “knocking out” the light at peak loads. Limitations on electricity consumption will force you to either calculate the total power before each connection of devices to the network, or even abandon the use of powerful equipment.

Differences between protective devices

It is necessary to distinguish between a device in the form of a difavtomat and a residual current device.
At first glance, there is no particular visible difference, but this is not so. The RCD is used to de-energize the network when the slightest leak in the circuit is detected. For example, if an electrical cable is damaged, in order not to injure a person, the circuit will be turned off.

https://www.youtube.com/watch?v=YK6f4Imfh0E

The difavtomat, in addition to the RCD, is equipped with a built-in automatic type switch. It serves to de-energize the system, prevent short circuits, overload the circuit, in general. In a word, it's two in one.

A conventional circuit breaker (circuit breaker) protects the circuit from overload, but it cannot create a safe environment for humans. Therefore, in modern buildings either difautomatic devices are installed, or RCDs and automatic devices are installed together.

The selection of any protective device depends on the characteristics of the network. Primarily from the load connected to it. Therefore, it is important to know how to calculate the power of the machine based on the load.

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.

Advantages and disadvantages

The advantage of the difavtomat is its compactness, versatility, 100% protection of the circuit from sudden overloads or other dangers. Well, the main “trump card” is the cost, which is lower than the total cost of the RCD and automatic type switch.

If you take into account a single case, the difference is not very noticeable, but when buying for the whole house, the benefit is significant. However, a lot depends on the brand of the product. Installation takes little time; the difavtomat also fits quite compactly on the rail.

Automats also have their drawbacks. If it fails, you will have to purchase the product as a set, and not separately.

The occurrence of a short circuit will lead to difficulties in finding its cause. With a divided installation, identification is much simpler: the RCD is turned off - leakage, the circuit breaker - short circuit.

Which type of protective device to choose is not an easy question. As many electricians do: if we are talking about a small apartment, then use a difavtomat.

When you are going to install complex structures, it is best to install separate RCD units and automatic type switches in a group. Moreover, each group must have its own separate switch.

The dangers of a cable mismatch with the network load

To select a circuit breaker based on load power, it is necessary to calculate the load current and select the rating of the circuit breaker greater than or equal to the obtained value. The current value expressed in amperes in a single-phase 220 V network usually exceeds the load power value expressed in kilowatts by 5 times, i.e.

You can calculate more accurately and calculate the current according to Ohm's law I=P/U - I=1200 W/220V =5.45A. For three phases the voltage will be 380V. You can

Which manufacturers should you trust?

And finally, let’s pay attention to the manufacturers. The choice of a circuit breaker cannot be considered complete if you have not thought about which brand of circuit breakers you will buy. You definitely shouldn’t take on unknown companies - electrical engineering is not a field where you can conduct experiments. Learn more about choosing a manufacturer in the video.

Sources

• https://220.guru/elektrooborudovanie/avtomaty-uzo/nominaly-avtomatov.html
• https://sovet-ingenera.com/elektrika/uzo-schet/vybor-avtomata-po-moshhnosti-nagruzki.html
• https://sovet-ingenera.com/elektrika/uzo-schet/nominaly-avtomaticheskix-vyklyuchatelej-po-toku.html
• https://rusenergetics.ru/oborudovanie/nominaly-avtomaticheskikh-vyklyuchateley-po-toku
• https://www.calc.ru/Tablitsa-Dlya-Vybora-Avtomaticheskikh-Vyklyuchateley.html
• https://stroychik.ru/elektrika/vybor-avtomata

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Weak link protection

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.

How many kilowatts do you need to heat a house?

The main consumers of electric current in homes are lighting, cooking, heating and hot water.

During the cold season, it is important to pay attention to the heating of the house. Electric heating in a house can be of several types:

• water (batteries and boiler);
• purely electric (convector, heated floor);
• combined (warm floor, radiators and boiler).

Let's look at electric heating options and energy consumption.

1. Heating using a boiler. If you plan to install an electric boiler, then the choice should fall on a three-phase boiler. The boiler system equally divides the electrical load into phases. Manufacturers produce boilers with different capacities. To choose the right one, you can make a simplified calculation by dividing the area of ​​the house by 10. For example, if the house has an area of ​​120 m2, then for heating you will need a 12 kW boiler. To save on electricity, you need to install a two-tariff mode for using electricity. Then at night the boiler will operate at an economical rate. Also, in addition to the electric boiler, you need to install a buffer tank, which will accumulate warm water at night and distribute it to heating devices during the day.
2. Convector heating. As a rule, convectors are installed under windows and connected directly to an outlet. Their number should correspond to the presence of windows in the room. Experts recommend calculating the total amount for the power consumption of all heating devices and equally distributing it across all three phases. For example, the heating of one floor can be connected to the first one. To another phase, the entire second floor. To the third phase, add a kitchen and a bathroom. Today, convectors have improved functions. This way you can set the desired temperature and choose the heating time. To save money, you can set the time and date of operation of the convector. The device has a “multi-tariff” option, which turns on the heater at the required power or at a reduced rate (after 23-00 and before 8-00). Energy calculations for convectors are similar to the boiler in the previous paragraph.
3. Heating using underfloor heating. A very convenient heating option, as you can set the desired temperature for each room. It is not recommended to install heated floors in the place where furniture, refrigerators, and bathrooms are installed. Calculations show that a house of 90 m2 with an installed convector and heated floor on one floor consumes from 5.5 to 9 kW of electricity.

Selecting a circuit breaker based on short-circuit current

The selection of a circuit breaker for protection against short circuit (short circuit) is carried out based on the calculated value of the short circuit current at the end of the line. The calculation is relatively complicated, the value depends on the power of the transformer substation, the cross-section of the conductor and the length of the conductor, etc.

From the experience of carrying out calculations and designing electrical networks, the most influential parameter is the length of the line, in our case the length of the cable from the panel to the outlet or chandelier.

Because in apartments and private houses this length is minimal, then such calculations are usually neglected and circuit breakers with characteristic “C” are selected; you can, of course, use “B”, but only for lighting inside an apartment or house, because such low-power lamps do not cause a high inrush current, and already in the network for kitchen appliances with electric motors, the use of machines with characteristic B is not recommended, because the machine may be triggered when the refrigerator or blender is turned on due to a jump in the starting current.

We invite you to familiarize yourself with: Do-it-yourself chimney for a stove

Nuances

In general, readers should not have any questions regarding the selection of packages according to the cable cross-section, but there are some subtleties that we did not mention above.

1. A machine with which type of electromagnetic release to choose. In everyday life, machines of categories “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 important when using appliances such as electric kettles, toasters and irons. Depending on the type of equipment used, you should choose a specific category; it is advisable to give preference to category “B” switches.
2. A machine with a maximum switching capacity to choose. Depends on the location of the electricity input from the substation to the apartment, if in close proximity, then you should choose one with a switching capacity of 10,000 amperes, otherwise for city apartments there are enough devices for 5,000–6,000 amperes. You can play it safe and choose the option of 10,000 amperes; ultimately, this indicator only affects whether the machine will be operational after a short circuit.
3. What type of wire to choose: aluminum or copper We strongly do not recommend purchasing aluminum conductors. Copper wiring is more durable and can handle higher currents.

How to calculate the rating of a circuit breaker

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.

How many kilowatts do you need for your home? Electricity consumption table

Our modern society cannot imagine its life without electricity. It is firmly rooted in the daily and industrial life of a person in the twenty-first century.

Electricity is used not only to illuminate streets, residential buildings and other premises. Today, electricity is needed to power the telephone, computer, TV and many other household appliances in our homes, which make the life of a modern person much easier.

Many home owners use electricity for heating, although this is not the cheapest type of heating, it is quite reliable and easy to use.

Like people in the past, modern society cannot exist without electricity. Every year, scientists are developing new technologies that require power. Of course, today electric current is used more widely than before. But after several decades, its consumption will increase several times. So, for example, if 10 years ago 1.5 - 2 kW of electricity was enough for a house or apartment, today this figure has increased to 15 kW, almost 10 times.

Let's try to figure out how many kilowatts a home currently needs.

Selecting a machine based on the long-term permissible current (LTC) of the conductor.

The selection of a circuit breaker for protection against overload or overheating of a conductor is carried out based on the DDT value for the protected section of the wire or cable. The rating of the machine must be less than or equal to the DDT value of the conductor indicated in the table above. This ensures automatic shutdown of the machine when the DDT in the network is exceeded, i.e. part of the wiring from the machine to the last electrical receiver is protected from overheating, and as a result, from fire.

Selecting the breaking capacity

The protection device disconnects the line in some cases. This characteristic is called breaking capacity. For individual apartments no calculations are made; more often the distance to the substation is simply taken into account.

For electrical wiring in a building located near the substation, a device with a breaking capacity of about 10,000 A is required. For other houses, it is enough to select a 6,000 A circuit breaker. In a country or village house, an electrical circuit breaker with a breaking capacity of 4,500 A is used; it must provide network protection.

Selection of machine by power

As you can see, all three indicators (power, current and wire cross-section) are interconnected, so the rating of the machine can, in principle, be selected according to any of them. At the same time, it is necessary to make sure that all parameters fit together and, if necessary, make appropriate adjustments.

In any case, remember the following:

1. Installing an overly powerful circuit breaker can lead to the fact that before it operates, electrical equipment that is not protected by its own fuse will fail.
2. A machine with a low number of amperes can become a source of nervous stress, cutting off power to the house or individual rooms when the electric kettle, iron or vacuum cleaner is turned on.

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.

What is important to know when connecting electrical appliances in an apartment

So, having calculated the approximate rating of the required machine, you need to give an explanation regarding the power. Many people wonder whether it is possible to plug in very powerful electrical appliances into a regular outlet, such as an electric boiler, for example.

According to the rules of the PUE, connecting an electric boiler with a power of more than 3 kW to a regular outlet is unacceptable. And each outlet has its own specific characteristics. Most often, home sockets are rated at 16 amperes, and, therefore, electrical appliances with a power of no more than 3.5 kW can be connected to them.

Therefore, any more or less powerful electrical appliance must be connected only through a separate circuit breaker. Moreover, it is the phase wire that is supplied to the circuit breaker, and not the working zero. Thus, knowing the approximate power of the equipment, you can easily calculate the rating of the circuit breaker.

Example of circuit breaker selection

We have a group from the panel to which we plan to connect a dishwasher -1.2 kW, a coffee maker - 0.6 kW and an electric kettle - 2.0 kW.

We count the total load and calculate the current.

Load = 0.6 1.6 2.0 = 4.2 kW. Current = 4.2*5=21A.

We suggest you familiarize yourself with: Calculation of wire cross-section based on current load

We look at the table above; all conductor cross-sections except 1.5 mm2 for copper and 1.5 and 2.5 for aluminum are suitable for the current we have calculated.

We choose a copper cable with cores with a cross section of 2.5 mm2, because... It makes no sense to buy a cable with a larger cross-section for copper, and aluminum conductors are not recommended for use, and may already be prohibited.

We look at the scale of denominations of the machines produced - 0.5; 1.6; 2.5; 1; 2; 3; 4; 5; 6; 8; 10; 13; 16; 20; 25; 32; 40; 50; 63.

The circuit breaker for our network is suitable for 25A, since it is not suitable for 16A because the calculated current (21A) exceeds the rating of the 16A circuit breaker, which will cause it to trip when all three power receivers are turned on at once. A 32A machine is not suitable because it exceeds the DDT of the 25A cable we selected, which can cause overheating of the conductor and, as a result, a fire.

Cost of 1 kilowatt of electricity according to the meter for Russian cities for 2021

As for other cities, the tariffs there will be different. Let's consider them further. You can find out how much one kilowatt of electricity costs for large Russian cities in 2021 in the table below.

* electricity tariffs within the social norm of consumption.

The following average rates apply for the supply of electricity in Russian cities:

• The cost of 1 kW with electric stoves in Russian cities ranges from 1 rub. up to 4 rubles.
• The cost of 1 kW with gas stoves ranges from 1 rub. up to 5.5 rubles.

The information above allows us to conclude that citizens of the Russian Federation will still have to pay more for electricity, but the largest increase in tariffs by 2.4% occurred only from 07/01/2019.

Social norm for electricity consumption and current tariffs

Please note that electricity rates will become even more confusing in the coming period. The reason for this will be the introduction of a social norm for electricity consumption

The point here is that a household has the opportunity to receive a predetermined amount of electrical energy at a social (“reduced”) tariff, and everything that will be consumed in excess of the established norm. It will be necessary to pay at a rate that is 30% higher.

This means that there will be a doubling of the gradation of tariffs, namely: if at the moment there is a single one-rate tariff for electricity for the population of rural areas, then after the innovation of the social norm there will already be 2 such tariffs (within the limit of the social norm and exceeding it).

It is also important that the social norm has a clear link to the number of residents who are officially registered and live in a given living space. Now subscribers will have to not only calculate the amount of payment for electricity by multiplying the consumed kWh. at the current tariff, but also to calculate, based on the number of registered residents, which part of the electricity is included in the social norm, and which already exceeds it.

Calculation of consumer power

Each electrical network in an apartment or house can be divided into sections (rooms). Depending on what devices are planned to be used in a particular area, electrical wiring calculations are made. Typically, the electrical wiring zones for each machine are divided among themselves into each room of the apartment or house.

One section of wiring for one room, the second for another, and the third for the kitchen and bathroom. In this situation, such powerful consumers as electric stoves, ovens, water heaters, and heating boilers stand apart. This technique requires a dedicated power line, so in modern homes designed for use with electric stoves, a separate circuit breaker is installed to provide power to the device.

Calculating the required current for a particular section of wiring is quite simple. To do this, use the formula I=P/U, 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 network voltage (the standard is 220 volts). To calculate, you need to add up the power of those electrical appliances that you plan to use on the line, and then divide the resulting sum by 220. From here we get the current strength, according to which you will need to select a cable of a certain cross-section.

As an example, let’s take an area (room) and calculate for it a machine and a cable of the required cross-section. The following will work simultaneously in the room:

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

Let's add these indicators (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 the optimal cable cross-section for this based on the table, take a copper cable with a cross-section of 2.5 mm or 4 mm square (be sure to take it with a reserve) and a circuit breaker 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-permissible current for a particular wire), the wiring will start to catch fire. The rating of the machine must correspond to the value of the continuous-permissible current of the conductor or be less.

Experienced electricians repeatedly say that you should not install cables with a small cross-section because they are cheap; you should choose a cable with a reserve to avoid overloading the electrical section and causing a fire in the wiring. But choosing a powerful machine gun is contraindicated!

The wiring is installed once, it is difficult to replace it, but replacing the switch in the event of a significantly increased load is much easier.

At the moment, more and more powerful electrical appliances are appearing, so it’s worth taking care in advance in case you decide to use a more powerful vacuum cleaner or add some additional device to the room.

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.

Active load

Active load

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.

Summary table for selecting a circuit breaker for a three-phase 380 V network.

* - double cable, two cables connected in parallel, for example 2 cables VVGng 5x120

Tags: machine, power, calculation, table

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