What kind of machine is needed for the power of the electric motor. Calculation of circuit breakers

It is impossible to imagine the modern world without electricity. Various devices work in every house, and sometimes people don’t even think about how much power all devices and devices connected to the power grid consume.

Household appliances have become so much a part of people's lives that as soon as some device fails, a person begins to get nervous, and some even panic.

Since many different devices usually work in an apartment or house, the uninterrupted operation of a computer, refrigerator or TV and other devices often leads to exceeding the permissible limits in electrical networks, and as a result, a short circuit occurs.

Purpose of circuit breakers

In order to prevent such a situation, there are automatic switches. The most common and well-established are ABB switches. Indoors, they usually put a 16 amp machine. Such switches are produced in the form of modules, due to which they can be freely mounted in the required quantity and in the right place.

It is best to use special DIN rails designed to mount switches on them. Any person, even not very versed in electrics, will be able to install such switches. The only thing you need is to choose the right value of the device used.

Among other things, if necessary, it can be supplemented with various remote shutdown sensors, operation indicators, etc., which will ultimately make the use of the electrical installation more comfortable and durable.

When the electricity suddenly turns off in a house or apartment, they begin to look for the cause. And it often lies in exceeding the permissible load on the network. In other words, much more electrical appliances are included in the sockets than were calculated during construction, or than were allocated to a particular consumer.

So how can you determine what load the machine can withstand at the entrance to a house or apartment, or at a particular consumption group? There are a few simple rules, and if you follow them, there should be no problems with power outages. And it doesn't matter which machine is used - 16 amps or 25, etc.

How the machines are mistakenly chosen

In practice, they usually choose an automatic machine, especially without hesitation. Many start from the necessary load, namely, they try to install such an automatic machine so that it simply does not turn off under heavy load. So, for example, if 5 kW is required, then they put the machine on 25A, if there is a 3 kW load, the machine is 16 amperes, and so on. But this approach is not thought out at all, since it will only lead to equipment breakdown or, even worse, to electrical wiring or even a fire.

That's why it was invented to protect against overload. This is for protection, not decoration of the electrical panel.

The principle of operation of the circuit breaker

AB is designed to protect against overload all devices connected in the electrical circuit immediately after itself.

If it is chosen incorrectly, then it will not work properly. So, for example, if you use an electric cable that is designed for 4-5 amperes and run 20-30 amperes through it, then such an automatic machine will not turn off immediately, but will wait until the insulation melts and a short circuit occurs. Then it will turn off. But this is not what the correct operation of the circuit breaker should lead to. Therefore, it is important to take into account in advance, setting the machine to 16 amperes, how many kW it will withstand if there are wires of a certain section and a maximum workload.

Ideally, it should turn off as soon as it senses an overload. Then the wires will remain in order, and the connected equipment will not burn out.

Choosing the right machine

How to understand how many kilowatts a 16 amp machine can withstand in practice?

The most common correct way to select a circuit breaker is as follows:

determine the cross section of the wire
according to the rules of electrical installations, find the current that is permissible for such a wire section
choose the appropriate machine for these parameters

For example, there is a copper wire with a cross section of 1.5 sq. mm. The current for it is allowed a maximum of 18-19 amperes. Accordingly, according to the rules, you need to choose a suitable machine, but with a downward shift according to the table. And it turns out 16 amperes. That is, you can put a 16 amp machine.

If the wire is copper, and its cross section is 2.5 sq. mm., then only current up to 26-27 amperes is permissible. Therefore, it is possible to use a 25 ampere automatic machine as much as possible. Although, for reasons of reliability, it is better to install an automatic machine for 20 amperes.

Thus, the parameters of the required machine for the remaining wire sections are calculated.

When using, you can select machines in the same way, only increase the cross section not down, but up.

Example: for an aluminum wire with a cross section of 4 sq. mm, the permissible current is the same as for a copper wire with a cross section of 2.5 sq. mm. And for the same wire, but made of aluminum, - as for 10 mm square. copper. At 6 mm - the same as at 4 mm from copper. Further - similarly.

Types of machines

When choosing a circuit breaker, it is very important to study all the characteristics of the device. It is also necessary to carefully calculate the total power of all devices that are supposed to be connected to each group of machines. Not only the speed of operation of the switch, but also the quality of its operation will depend on these factors.

Most often, both in everyday life and in production, there are 16A automatic machines. Usually they are installed in electrical panels. Therefore, the question of how much a 16 amp machine can withstand is always relevant.

Features of switches

Circuit breakers are made of materials that are completely harmless to human health. A self-extinguishing thermoplastic is used in the manufacture of the instrument housing. It is able to withstand very high temperatures. Its contacts are made of copper plates silver plated for better contact and durability.

In the design of the circuit breaker there is a special thermal relay, which is triggered when the norm of the passing current is exceeded, and the electrical circuit opens without leading to a short circuit. The higher the current indicator, the faster the response speed of the machine. The account goes on fractions of a second.

The scope of use of circuit breakers is very extensive and extends from installing them in introductory electrical panels to distribution panels of apartments or houses. To use circuit breakers, special ones are produced with already installed DIN rails for the required number of circuit breakers. The buyer only needs to choose the one that meets his wishes and install the shield in the apartment or in the house.

Despite all the seeming ease of use of circuit breakers, it is better to entrust the connection of a 16 amp machine to a specialist.

In terms of rated current, circuit breakers differ both in current strength (nominal from 1A to 6300A) and in circuit load (220V, 380 and 400V). In addition, switches are usually distinguished by the speed of operation.

To organize a trouble-free in-house power supply, it is necessary to allocate separate branches. Each line must be equipped with its own protection device that protects the cable insulation from melting. However, not everyone knows which device to purchase. Do you agree?

You will learn everything about the choice of automatic machines according to the load power from the article presented by us. We will tell you how to determine the rating to find the switch of the required class. Taking into account our recommendations guarantees the purchase of the required devices that can eliminate threatening situations during the operation of the wiring.

Power supply organizations carry out the connection of houses and apartments, performing work on bringing the cable to the switchboard. All activities for the installation of wiring in the room are carried out by its owners or hired specialists.

To choose an automatic machine to protect each individual circuit, you need to know its rating, class and some other characteristics.

Basic parameters and classification

Household machines are installed at the entrance to a low-voltage electrical circuit and they are designed to solve the following tasks:

manual or electronic switching on or de-energization of the electrical circuit;
circuit protection: current cut-off at a slight long-term overload;
circuit protection: instantaneous current cut-off in case of short circuit.

Each switch has a characteristic, expressed in amperes, which is called ( I n) or “nominal”.

The essence of this value is easier to understand using the overrating factor:

K = I / In,

where I is the real current strength.

K< 1.13: отключение (расцепление) не произойдет в течение 1 часа;
K > 1.45: Shutdown will occur within 1 hour.

These parameters are fixed in clause 8.6.2. GOST R 50345-2010. To find out how long it will take to turn off at K> 1.45, you need to use a graph that reflects the time-current characteristic of a particular model of the machine.

If the current exceeds the nominal value of the circuit breaker by 2 times for a long time, the opening will occur within a period of 8 seconds to 4 minutes. Response speed depends on model setting and ambient temperature

Also, each type of circuit breaker has a current range ( I a), at which the instantaneous release mechanism is triggered:

class “B”: I a = (3 * I n .. 5 * I n ];
class “C”: I a = (5 * I n .. 10 * I n ];
class “D”: I a = (10 * I n .. 20 * I n ].

Type “B” devices are mainly used for lines that are of considerable length. In residential and office premises, class “C” machines are used, and devices marked “D” protect circuits where there is equipment with a large starting current coefficient.

The standard line of household machines includes devices with ratings of 6, 8, 10, 16, 20, 25, 32, 40, 50 and 63 A.

Structural arrangement of releases

In modern there are two types of releases: thermal and electromagnetic.

The bimetallic release has the form of a plate made of two conductive metals with different thermal expansion. Such a design, when the nominal value is exceeded for a long time, leads to heating of the part, its bending and the operation of the circuit opening mechanism.

For some machines, using the adjusting screw, you can change the parameters of the current at which the trip occurs. In the past, this technique was often used to “fine” tune the device, but this procedure requires in-depth specialized knowledge and several tests.

By turning the adjusting screw (highlighted with a red rectangle) counterclockwise, you can achieve a longer response time of the thermal release

Now on the market you can find many models of standard ratings from different manufacturers, in which the time-current characteristics are slightly different (but still comply with regulatory requirements). Therefore, it is possible to choose a machine with the necessary “factory” settings, which eliminates the risk of incorrect calibration.

An electromagnetic release prevents the line from overheating due to a short circuit. It reacts almost instantly, but at the same time, the value of the current strength must be several times higher than the nominal value. Structurally, this part is a solenoid. The overcurrent generates a magnetic field that moves the core, opening the circuit.

Compliance with the principles of selectivity

In the presence of an extensive electrical circuit, protection can be organized in such a way that, in the event of a short circuit, only the branch on which the emergency occurs is disconnected. To do this, apply the principle of selectivity switches.

A visual diagram showing the principle of operation of the system of automatic switches with the implemented function of selectivity (selectivity) of operation in the event of a short circuit

To ensure selective shutdown, instantaneous cut-off machines are installed on the lower stages, opening the circuit in 0.02 - 0.2 seconds. The circuit breaker located on the higher stage either has a trip delay of 0.25 - 0.6 s or is made according to a special “selective” scheme in accordance with DIN VDE 0641-21.

For guaranteed security, it is better to use machines from one manufacturer. For circuit breakers of the same model range there are selectivity tables which indicate the possible combinations.

The simplest installation rules

The section of the circuit that needs to be protected by the switch can be single- or three-phase, have a neutral, as well as a PE (“ground”) wire. Therefore, automata have from 1 to 4 poles, to which a conductive core is connected. When conditions for tripping are created, all contacts are disconnected simultaneously.

The machines in the shield are mounted on a specially designated DIN rail. It provides a compact and secure connection, as well as convenient access to the switch.

The machines are installed as follows:

single-pole per phase;
bipolar for phase and neutral;
three-pole for 3 phases;
four-pole for 3 phases and neutral.

It is prohibited to do the following:

install single-pole machines to neutral;
put the PE wire into the machine;
install three single-pole circuit breakers instead of one three-pole one, if at least one three-phase consumer is connected to the circuit.

All these requirements are spelled out in the PUE and must be observed.

In each house or room to which electricity is supplied, an introductory machine is installed. Its denomination is determined by the supplier and this value is specified in the contract for connecting electricity. The purpose of such a switch is to protect the site from the transformer to the consumer.

After the introductory machine, a counter (single- or three-phase) and is connected to the line, the functions of which differ from the operation of the automatic and differential switch.

If the room is wired into several circuits, then each of them is protected by a separate machine, the power of which is . Their ratings and classes are determined by the owner of the premises, taking into account the existing wiring or the power of the connected devices.

The electricity meter and circuit breakers are installed in a switchboard that meets all safety requirements and can easily fit into the interior of the room

When choosing a location for placement, it must be remembered that the properties of the thermal release are affected by air temperature. Therefore, it is desirable to have a rail with machine guns inside the room itself.

Calculation of the required denomination

The main protective function of the circuit breaker extends to the wiring, so the selection of the rating is carried out according to the cable cross section. In this case, the entire circuit must ensure the normal operation of the devices connected to it. The calculation of system parameters is not difficult, but many nuances must be taken into account in order to avoid errors and problems.

Determination of the total power of consumers

One of the main parameters of the electrical circuit is the maximum possible power of the consumers of electricity connected to it. When calculating this indicator, you cannot simply summarize the passport data of devices.

Active and nominal component

For any device powered by electricity, the manufacturer must indicate the active power ( P). This value determines the amount of energy that will be irretrievably converted as a result of the operation of the device and for which the user will pay according to the meter.

But for devices with the presence of capacitors or an inductor, there is another power with a non-zero value, which is called reactive ( Q). It reaches the device and returns almost instantly.

The reactive component does not participate in the calculation of the used electricity, but together with the active component forms the so-called “full” or “rated” power ( S), which gives a load on the chain.

cos(f) - a parameter with which you can determine the total (rated power) from the active (consumed). If it is not equal to one, then it is indicated in the technical documentation for the electrical appliance

Increased starting currents

The next feature of some types of household appliances is the presence of transformers, electric motors or compressors. Such devices consume starting (starting) current at the start of operation.

Its value can be several times higher than the standard values, but the time of operation at increased power is small and usually ranges from 0.1 to 3 seconds. Such a short-term surge will not lead to the operation of the thermal release, but the electromagnetic component of the switch, which is responsible for the short-circuit overcurrent, may react.

This situation is especially relevant for leased lines, to which equipment such as woodworking machines is connected. In this case, you need to calculate the amperage and, perhaps, it makes sense to use a “D” class machine.

Accounting for the demand factor

For circuits to which a large number of equipment is connected and there is no device that consumes the largest part of the current, use the demand factor ( ks). The meaning of its use is that all devices will not work at the same time, so the summation of the rated powers will lead to an overestimated figure.

The demand coefficient for groups of electricity consumers is set in clause 7 of SP 256.1325800.2016. These indicators can also be based on an independent calculation of the maximum power.

This coefficient can take a value equal to or less than one. Estimated power calculations ( P r) of each device occurs according to the formula:

P r = ks * S

The total rated power of all devices is used to calculate the circuit parameters. The use of the demand coefficient is advisable for office and small retail premises with a large number of computers, office equipment and other equipment powered from one circuit.

For lines with a small number of consumers, this coefficient is not used in its pure form. Those devices are removed from the power calculation, whose inclusion at the same time as more energy-consuming devices is unlikely.

So, for example, there is little chance of a one-time work in a living room with an iron and a vacuum cleaner. And for workshops with a small number of staff, only 2-4 of the most powerful power tools are taken into account.

Current Calculation

The choice of the machine is made according to the maximum value of the current strength allowed in the circuit section. It is necessary to obtain this indicator, knowing the total power of electrical consumers and the voltage in the network.

According to GOST 29322-2014, from October 2015, the voltage value should be equal to 230 V for an ordinary network and 400 V for a three-phase one. However, in most cases, the old parameters are still valid: 220 and 380 V, respectively. Therefore, for the accuracy of the calculations, it is necessary to take measurements using a voltmeter.

Another problem, especially relevant for, is the provision of power supply with insufficient voltage. Measurements on such problematic objects may show values that go beyond the range defined by GOST.

Moreover, depending on the level of consumption of electricity by neighbors, the voltage value can vary greatly in a short time.

This creates a problem not only for the functioning of devices, but also for. When the voltage drops, some devices simply lose power, and some that have an input regulator increase electricity consumption.

It is difficult to qualitatively calculate the necessary circuit parameters under such conditions. Therefore, either you will have to lay cables with a deliberately large cross section (which is expensive), or solve the problem by installing an input stabilizer or connecting the house to another line.

The stabilizer is installed next to the switchboard. It often happens that this is the only way to get the standard voltage values in the house.

After the total power of electrical appliances was found ( S) and the value of the voltage ( U), current strength calculation ( I) is carried out according to formulas that are a consequence of Ohm's law:

I f = S / U f for a single-phase network

I l \u003d S / (1.73 * U l) for a three-phase network

Here the index " f” means phase parameters, and “ l” are linear.

Most three-phase devices use the star connection type, and it is also according to this scheme that the transformer operates, which produces current for the consumer. With a symmetrical load, the linear and phase forces will be identical ( l = I f), and the voltage is calculated by the formula:

U l \u003d 1.73 * U f

The nuances of selecting the cable section

The quality and parameters of wires and cables are regulated by GOST 31996-2012. According to this document, specifications are developed for manufactured products, where a certain range of values of basic characteristics is allowed. The manufacturer is obliged to provide a table of correspondence between the cross section of the conductors and the maximum safe current.

The maximum allowable current depends on the cross-section of the conductors of the wires and the method of installation. They can be laid in a hidden (in a wall) or open (in a pipe or box) way.

It is necessary to choose a cable in such a way as to ensure the safe flow of current corresponding to the calculated total power of electrical appliances. According to the PUE (Electrical Installation Rules), the minimum used in residential premises must be at least 1.5 mm 2.

Standard sizes have the following values: 1.5; 2.5; 4; 6 and 10 mm 2 .

Sometimes there is a reason to use wires with a cross section one step larger than the minimum allowable. In this case, it is possible to connect additional devices or replace existing ones with more powerful ones without costly and time-consuming work on laying new cables.

Calculation of machine parameters

For any circuit, the following inequality must be satisfied:

I n<= I p / 1.45

Here I n is the rated current of the machine, and Ip- admissible current for wiring. This rule provides guaranteed tripping when the permissible load is exceeded for a long time.

The inequality “In<= Ip / 1.45” является основным условием при комплектовании пары “автомат – кабель”. Пренебрежение этим правилом может привести к возгоранию проводки

In this case, the sequence of actions is as follows:

Calculation of the total current strength of electrical appliances connected to the network.
The choice of an automaton with a nominal value not less than the calculated value.
Selection of the cable section according to the nominal value of the machine.

S = 4 kW; I = 4000 / 220 = 18 A;
I n = 20 A;
I p >= I n * 1.45 = 29 A; D \u003d 4 mm 2.

If the wiring has already been laid, then the sequence of actions is different:

Determination of the permissible current with a known cross section and the method of wiring according to the table provided by the manufacturer.
Selection of a circuit breaker.
Calculation of the power of connected devices. Completing a group of devices in such a way that the total load on the circuit is less than the nominal value.

Example. Let two single-core cables be laid in an open way, D = 6 mm 2, then:

I p = 46 A;
I n<= I p / 1.45 = 32 A;
S \u003d I n * 220 \u003d 7.0 kW.

In point 2 of the last example, there is a slight allowable approximation. The exact value of I n = I p / 1.45 = 31.7 A is rounded up to a value of 32 A.

Choice between multiple denominations

Sometimes a situation arises when you can select several machines with different ratings to protect the circuit. For example, with a total power of electrical appliances of 4 kW (18 A), wiring with a cross section of copper conductors of 4 mm 2 was chosen with a margin. For this combination it is possible to supply switches for 20 and 25 A.

If the electrical wiring diagram assumes the presence of multi-level protection, then you need to choose the machines so that the nominal value of the higher one (in the figure on the right is 25 A) is greater than that of the switches of lower levels

The advantage of choosing a switch with the highest rating is the ability to connect additional devices without changing the circuit elements. Most often, they do so.

In favor of choosing an automaton with a lower rating is the fact that its thermal release will respond faster to an increased current strength. The fact is that some devices may experience a malfunction, which will lead to an increase in energy consumption, but not to the value of a short circuit.

For example, a failure of a washing machine motor bearing will lead to a sharp increase in current in the winding. If the machine quickly reacts to exceeding the permitted values and turns off, then the motor will not burn out.

Conclusions and useful video on the topic

The design of the circuit breaker and its classification. The concept of the time-current characteristic and the selection of the nominal value according to the cable cross-section:

Calculation of the power of devices and the choice of the machine using the provisions of the PUE:

The choice of a circuit breaker must be taken responsibly, since the safety of the electrical system at home depends on it. With all the many input parameters and calculation nuances, it must be remembered that the main protective function of the machine extends to wiring.

Please write comments, ask questions, post photos on the topic of the article in the block below. Share useful information that may be useful to site visitors. Tell us about your own experience in choosing circuit breakers to protect country or home electrical wiring.

Any electrical circuit in an apartment and a house must be protected by an overload and overcurrent short circuit circuit breaker. This simple truth can be clearly demonstrated in any electrical panel of an apartment, a floor panel, an input distribution panel at a house, etc. electrical cabinets and boxes.

The question is not whether to install a circuit breaker or not, the question is how to calculate the circuit breaker so that it performs its tasks correctly, works when necessary and does not interfere with the stable operation of electrical appliances.

Examples of calculation of circuit breakers

You can read the theory of calculations of circuit breakers in the article:. Here are some practical examples of calculating circuit breakers in the electrical circuit of a house and apartment.

Example 1. Calculation of the introductory machine at home

Let's start with examples of calculating circuit breakers from a private house, namely, we will calculate the introductory machine. Initial data:

Mains voltage Un = 0.4 kV;
Estimated power Рр = 80 kW;
Power factor COSφ = 0.84;

1st calculation:

To select the rating of the circuit breaker, we consider the rating of the load current of this electrical network:

Ip = Рр / (√3 × Un × COSφ) Iр = 80 / (√3 × 0.4 × 0.84) = 137 A

2nd calculation

To avoid false tripping of the circuit breaker, the rated current of the circuit breaker (thermal release current) should be selected 10% more than the planned load current:

Icurrent release = Ip × 1.1
It.r \u003d 137 × 1.1 \u003d 150 A

The result of the calculation: According to the calculation made, we select the circuit breaker (according to PUE-85, clause 3.1.10) with the release current closest to the calculated value:

I nom.av \u003d 150 Amperes (150 A).

Such a choice of a circuit breaker will allow the electrical circuit of the house to work stably in operating mode and operate only in emergency situations.

Example 2. Calculation of a kitchen group circuit breaker

In the second example, we will calculate which circuit breaker should be selected for the kitchen electrical wiring, which is correctly called the kitchen electrical wiring socket. It can be the kitchen of an apartment or a house, there is no difference.

Similarly to the first example, the calculation consists of two calculations: the calculation of the load current of the electric circuit of the kitchen and the calculation of the thermal release current.

Load current calculation

Initial data:

Mains voltage Un = 220 V;
Estimated power Рр = 6 kW;
Power factor COSφ = 1;

1. Estimated power we consider it as the sum of the capacities of all household appliances in the kitchen, multiplied by the utilization factor, which is also the utilization rate of household appliances. 1. Utilization factor household appliances is a correction factor that reduces the estimated (total) power consumption of the electrical circuit and takes into account the number of simultaneously operating electrical appliances.

That is, if the kitchen has 10 sockets for 10 household appliances (stationary and portable), you need to consider that all 10 appliances will not work at the same time.

Utilization factor

Write down the planned household appliances on a piece of paper.
Next to the device, put its power according to the passport.
Sum up all the power of the devices according to the passport. This Calculation.
Think about what appliances can work at the same time: kettle + toaster, microwave + blender, kettle + microwave + toaster, etc.
Calculate the total powers of these groups. Calculate the average total power of groups of simultaneously turned on devices. It will be Pnominal(rated power).
Divide Calculation on Pnominal, get the utilization rate of the kitchen.

In fact, in the theory of calculations, the utilization factor inside the house (without utility networks) and the apartment is taken equal to one if the number of outlets is not more than 10. This is true, but in practice, it is the utilization factor that allows modern kitchen appliances to work on old electrical wiring.

Note:

In the theory of calculations, 1 household outlet is planned for 6 square meters. meters of the apartment (house). Wherein:

utilization factor = 0.7 - for sockets from 50 pcs.;
utilization factor = 0.8 - sockets 20-49 pcs.;
utilization factor = 0.9 - sockets from 9 to 19 pieces;
utilization factor=1.0 – sockets ≤10pcs.

Let's go back to the kitchen circuit breaker. We consider the load current rating of the kitchen:

Ip = Pp / 220V;
Ir \u003d 6000 / 220 \u003d 27.3 A.

Release current:

Icalc.= Ip×1.1=27.3×1.1=30A

According to the calculation made, we choose for the kitchen at 32 Amperes.

Conclusion

The given example of calculating the kitchen turned out to be somewhat overestimated, usually 16 amperes are enough for, given that the stove, washing machine, dishwasher are put into separate groups.

These examples of calculating circuit breakers for group circuits only show the general principle of calculations, and do not include the calculation of engineering circuits, including the operation of pumps, machines and other engines of a private house.

Photo gallery of automatic protection devices

Modern systems for protecting electrical wiring from burnout and ignition involve the use of circuit breakers and are divided according to the type of network into single-phase and three-phase. In the private sector, in most cases, devices of the second type are used, so the correct calculation of the machine for power for 380 volts becomes relevant, which ensures the reliability and durability of the use of the electrical network.

Appointment and work

The first automatic device designed to protect an electrical circuit from overcurrent was invented by the American electromagnetist Charles Grafton Page in 1836. But only 40 years later, a similar design was described by Edison. . The modern type of protective devices was patented in 1924. Brown, Boveri & Cie Corporation of Switzerland.

The innovation of the design was the reusability of use due to the ability to turn on the module when it is triggered by pressing one button. The advantages over fuses were undeniable, while the accuracy of the machine was much better. When using the device in a network designed for 380 volts, all phases are turned off at once. This approach avoids the distortion of signal levels and the occurrence of overvoltages.

The direct purpose of a three-phase circuit breaker is to turn off the line when a short circuit occurs in it or when the power consumption of the devices is exceeded. Protection modules belong to the group of switching equipment and due to their simple design, ease of use and reliability, they are widely used in both domestic and industrial power networks. Usually the device assumes manual control, but some types are equipped with an electromagnetic or electric motor drive, which makes it possible to control them remotely.

Some users mistakenly assume that the machine protects the devices connected to it, but in fact this is not the case. It does not react in any way to the types and types of devices connected to it, and the only reason for its operation is overload and overcurrent. At the same time, if the machine does not turn off the line, the electrical wiring will begin to heat up, which will lead to damage or even ignition.

The choice of an automatic protection module is associated with the ability of an electric line to withstand a current of a certain value, which is directly related to the cable material and its cross section. In other words, when choosing a module, the main parameter is the power or maximum current, which leads to the operation of the machine.

Protection module design

Despite the wide range of products offered by various manufacturers, the designs of circuit breakers are similar to each other. The body of the device is made of a dielectric that is resistant to temperatures and does not support combustion. On the front panel there is a manual control lever, and the main technical characteristics are also applied.

Structurally, the body consists of two halves, twisted together by bolts. In the middle of it are the following elements:

It is the designs of the releases that provide almost instantaneous operation of the circuit breaker. An electromechanical contact reacts to the occurrence in the circuit it protects of a current whose parameters exceed the nominal value. The design of the release includes an inductor with a core, the position of which is fixed by a spring, and already it is connected to a movable power contact. The solenoid windings are connected in series with the load. The thermal release is a compressed strip of two metals with different thermal conductivity (bimetallic plate).

Operating principle

After connecting the power and load electric lines to the three-phase machine, it is turned on by moving the lever to the upper position. As a result, the lever engages through the latch with the closing contact. The formed connection is provided due to the displacement of the movable contact group relative to their holder.

Under normal circumstances, the current flows through the contact between the power contact and the moving contact. Then it enters the bimetallic plate and the solenoid winding, and from it it already gets to the terminal and the load connected to the machine.

If a current with a value exceeding the allowable value begins to flow through the switch, then the bimetallic plate begins to heat up. Due to the different thermal expansion of the metals, it bends, eventually breaking the contact. The strength of the current at which the connection breaks depends on the thickness of the plate. The thermomagnetic release is characterized by slow operation, although it can detect even small changes in the magnitude of the current. Its setting is carried out at the factory by changing the distance between the plate and the moving contact. For this, an adjusting screw is used.

But for a current that instantly increases its value, the reaction rate of the bimetallic plate will be extremely low, so a solenoid is used along with it. In the normal state, the core is pushed out by the spring and closes the contact of the machine. With an abnormal value of the signal in the turns of the coil, the magnetic field rapidly increases, the flows of which draw the core inward, overcoming the action of the spring, and this leads to a circuit break.

The operation of the electromagnetic release occurs in a fraction of a second, while it does not react to currents slightly exceeding the rated ones. Simultaneously with the disconnection of the entire three-phase line, the lever also drops, which again needs to be moved to the upper position to connect the load to the network.

Device specifications

The correct selection of a 3-phase machine is not only in determining the conditions for its operation, but also in terms of power and type of load that will be connected to it. Incorrectly selected power of the module leads to a deterioration in the protection of the electrical wire, while such a device itself can become a source of an emergency.

But still, no matter how important it is to choose the right power, automatic devices are also characterized by other technical parameters that affect their operation. The main ones include:

In addition to technical parameters, automatic devices are also characterized by quality indicators. The most common ones include the type of drive, the method of connecting external conductors, the cut-off design, and others.

Power selection

There are two ways to determine the required power for a 3-phase machine. At the same time, one complements the other, and does not exclude it. The first method is associated with finding the total value of the energy consumed and the load, and the second - with the cross section of the electrical wiring.

Based on the definition that the machine does not protect the equipment, but the electrical wiring, it is necessary to select the power, focusing on the parameters of the latter. This is true, but only until the network upgrade is planned. For example, the existing wiring in the house is designed for 1.5 squares. According to the technical specifications, copper wiring of this diameter can withstand a long-term current of not more than 10 amperes. Accordingly, the maximum simultaneous energy consumption of devices connected to the machine output should not exceed 3.8 kW. This value is obtained from a simple formula for finding power - P \u003d U * I, where:

P - the highest allowable power consumption, W;
U - voltage of a three-phase network, 380 volts;
I is the maximum current that the wiring can withstand, A.

The resulting number indicates that the total load connected to the line at the same time should not exceed this value, i.e. when the 2 kW boiler is turned on, nothing bad will happen. But if you connect a 3 kW electric furnace to this line, then the wiring will not stand it and catch fire, therefore, to prevent an accident, you must install a 10 A automatic machine, which allows you to load the line up to 2.2 kW.

The advantage of using a three-phase machine is that three lines can be connected to it at the same time, while the value of the rated current will be determined by summing the powers of all phases. Thus, for a 380 volt machine, it will be 6.6 kW, and in the case of connecting a triangle-type load, it will be 11.4 kW. That is, for the given example, if it is not possible to separate the line to different phase outputs of the protection device, you will need to purchase a 6 A machine.

If it is planned to upgrade the wiring or use a thick cable, then the calculation can be made based on the power consumption of the load. For example, if the load of each phase does not exceed 4 kW, then the rated current is calculated as the sum of the powers plus 15–20% of the margin (I \u003d 4 * 3 \u003d 12 A + margin \u003d 14 A), so the most suitable device in this case will be an automatic at 16 A.

Nuances in the calculation

To simplify the determination of power as a margin, it is customary to use not a percentage, but a multiplication by a coefficient. This additional number is considered to be equal to 1.52.

In practice, it is rarely possible to load all three phases equally, therefore, when one of the lines consumes a lot of energy, the circuit breaker rating is calculated based on the power of this particular phase. In this case, the largest value of energy consumed is taken into account and multiplied by a factor of 4.55, and then it will be possible to do without the use of tables.

Thus, when calculating the power, first of all, the parameters of the electrical wiring are taken into account, and then the energy consumed by the protected automatic machine of the electrical equipment. Here, the correct remark from the rules for the installation of electrical installations (PUE) is taken into account, indicating that the installed circuit breaker must protect the weakest section of the circuit.

When conducting electrical work, safety should always be the main criterion. After all, a lot depends on this, up to the life and health of a person. And the reason for such an event does not matter at all. In any case, it is necessary to choose the right protective devices. It is in connection with this that it will be necessary to calculate the machine in terms of power, taking into account some important nuances.

Anyone who has dealt with electrical wiring has heard of circuit breakers or circuit breakers. First of all, a competent electrician will always advise you to treat the choice of such an important part of the electrical network with particular scrupulousness. Since later it is this simple device that can save you from many troubles.

It doesn’t matter at all what kind of electrical work is being carried out - whether new wiring is laid in a newly built house, the old one is being replaced, the shield is being modernized, or a separate branch is being laid for too energy-intensive devices - in any case, special attention must be paid to the selection of the machine in terms of power and other parameters.

Any modern machine has two degrees of protection. It means that he can help in two, the most common situations.

Thus, the machine is able to protect not only personal property, but in some cases life. Although for this it is necessary to carry out a competent calculation of the circuit breaker in terms of power and a number of other parameters. And also, you should not take the machine “with a margin”, since at critical values \u200b\u200bof the currents in the network it may simply not work, which is equivalent to its absence.

As for protecting a person from electric shock as a result of touching live parts, it is preferable to use an RCD.

Principle of operation

The main task of the protective switch is to cut off the supply of electric current from the supply cable to the consumer's network. This happens due to the releases located in the body of the machine. And there are two types of such parts:

Electromagnetic, which is a coil, a spring and a core, which, when the rated currents are exceeded, is drawn in and disconnects the contacts through the spring. This happens almost instantly - from 0.01 to 0.001 seconds, which can provide reliable protection.
Bimetallic thermal - are triggered by the passage of currents that exceed the limit values. In this case, the bimetallic plate, which is the basis of such a release, bends and breaks the contacts.

For a more reliable shutdown, in most modern models of machines, they try to use both types of releases.

Considering the variety of electrical networks and certain situations, vending machines can be of different types. The principle of their operation is no different - the same releases work, but depending on the situation and a number of other nuances, they use different variations.

So, for a standard single-phase network with a voltage of 220 volts, single-pole and two-pole AB are produced. The former are able to break only one wire - the phase. The latter can work with both phase and zero. Of course, it is preferable to use the second option. Especially when it comes to rooms with high humidity. Of course, a single-pole machine will do its job quite well, but situations may arise when the burnt wires are closed to each other. In this case, of course, the phase will be cut off, but the neutral wire will be energized, which can be extremely dangerous.

For three-phase networks with a voltage of 380 volts, three- or four-pole machines are used. They must be installed both at the entrance and directly in front of the consumer. As is clear, such machines cut off all three phases connected to them. In rare cases, it is possible to use one- or two-pole protective devices to cut off, respectively, one or two phases.

Of course, any automatic machine will perfectly cope with the tasks assigned to it - this is beyond doubt if it is in good condition. But the fact is that it is necessary to select AB taking into account several parameters.

If the selected automaton is too "weak", then constant false positives will occur. Conversely, a model that is too “strong” will be of rather dubious utility.

Load power

One of the possibilities to choose a protective device is the choice of the machine according to the load power. To do this, you need to know the value of the load current. And from these data, choose the appropriate denomination. Easiest (and more accurate) This can be done using Ohm's law according to the formula:

where P is the power of the consumer (refrigerator, microwave oven, washing machine, etc.), and U is the mains voltage.

For example, the consumer will be taken 1.5 kW, and the mains voltage is the usual 220 V. Having these data, substituting them into the formula, you get:

I \u003d 1500/220 \u003d 6.8 A.

In the case of a three-phase network of 380 volts, the voltage will be 380 V.

Based on Ohm's law, you can easily calculate the load power, from which to select the required value of the machine. However, one should not forget that, choosing AB in this way, it is necessary to add the load of all consumers.

There is another formula for choosing a circuit breaker by current, but it is a little more complicated, but the end result will be much more accurate. In practice, this is not important, but for informational purposes it is still worth quoting it:

The values of I, P, U will be the same as in Ohm's law, but cos φ is the power factor that takes into account the reactive component in the load. This value helps to determine table 6.12 of the normative document SP 31−110−2003 "Design and installation of electrical installations of residential and public buildings."

For example, the same data will be used, that is, the consumer is 1.5 kW, and the voltage is still the same 220 V. According to the table, cos φ will be equal to 0.65, as for computers. Hence:

I \u003d 1500 W / 220 V * 0.65 \u003d 4.43 A.

Choosing an automatic machine only by load power will be an unforgivable mistake, which can be expensive. After all, if you do not take into account the cable cross-section, then all meaning in the selection of the machine is lost. However, the obtained load values \u200b\u200band the AB rating can help in selecting the required cable.

To do this, you do not need to do any calculations, since it is enough to use table No. 1.3.6 and 1.3.7 of the PUE, where the concept of long-term permissible current means a voltage passing through the conductor for a long time that does not cause excessive heating. Simply put, this value can be taken as the calculated load power. And get the required cross section of copper or aluminum wire.

By short circuit current

Although some calculations were required to select a circuit breaker for power, they were extremely simple. This cannot be said at all about the calculations when choosing an automatic machine for short-circuit currents.

But when choosing the value of AB for a house, cottage, apartment or office, such calculations will be redundant, since the main indicator that especially affects the data is the length of the conductor. But in such situations, it is extremely small to significantly affect the result. Therefore, such calculations are carried out only when designing substations and other similar structures, where the length of the cables is significant.

Therefore, when choosing a circuit breaker, models with the designation “C” are usually purchased, which take into account the values of starting currents.

Denomination selection

The choice of circuit breaker rating must meet certain requirements. More specifically, the machine must work before the currents can exceed the allowable wiring values. It follows from this that the nominal value of the machine should be slightly less than the current strength that the wiring can withstand.

Selecting the right AB is quite simple. Moreover, there is a table of current ratings of automata, and this greatly simplifies the task.

From all this, you can create an algorithm, according to which it is easiest to choose the machine of the desired denomination:

For a single section, the cross section and material of the wire are calculated.
From the table, the value of the maximum current that the cable can withstand is taken.
It remains only to select an automaton with a value slightly less than the long-term permissible current using the table.

The table contains five ratings AB 16 A, 25 A, 32 A, 40 A, 63 A, from which the protective device will be selected. Automata of smaller values are practically not used, since the loads of modern consumers simply will not allow this. Thus, having the necessary values, it is very easy to choose an automaton corresponding to a particular case.

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