3 phase circuit breaker 25 ampere. What kind of machine should I put into the house? Characteristics of double-pole switches
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.
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 it becomes important to correctly calculate the power of the machine for 380 volts, ensuring the reliability and durability of the use of the electrical network.
Purpose and work
The first automatic device designed to protect an electrical circuit from overcurrents was invented by the American scientist studying electromagnetism, 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 Corporation Brown, Boveri & Cie from Switzerland.
The innovation of the design is its reusability due to the ability to turn on the module when it is activated by pressing one button. The advantages over fuses were undeniable, and the accuracy of the machine was much better. When using the device in a network designed for 380 volts, all phases are switched off at once. This approach allows you to avoid skewed signal levels and the occurrence of overvoltages.
The direct purpose of a three-phase circuit breaker is to disconnect the line when a short circuit occurs in it or the power consumption of the devices is exceeded. Protection modules belong to the group of switching equipment and, due to their simple designs, ease of use and reliability, they are widely used in both domestic and industrial energy networks. Typically the device requires 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 the appearance of 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 its damage or even fire.
The choice of an automatic protection module is related to the ability of the electrical 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 that triggers the machine.
Design of the protective module
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 temperature-resistant dielectric and does not support combustion. On the front panel there is a manual control lever, and the main technical characteristics are also printed.
Structurally, the body consists of two halves, screwed together. In the middle of it are the following elements:
It is the design of the releases that ensures almost instantaneous operation of the circuit breaker. An electromechanical contact reacts to the occurrence of a current in the circuit it protects, the parameters of which exceed the nominal value. The design of the release includes an inductance coil with a core, the position of which is fixed by a spring, and it is already 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 conductivities (bimetallic plate).
Operating principle
After connecting the power and load electrical lines to the three-phase circuit breaker, it is turned on by moving the lever to the upper position. As a result, the lever engages through the latch with the switching contact. The formed connection is ensured by the displacement of the movable contact group relative to their holder.
In a normal situation, current passes through the contact between the power and moving contacts. Then it goes to the bimetallic plate and the solenoid winding, and from it it goes to the terminal and the load connected to the machine.
If a current begins to flow through the switch with a value exceeding the permissible value, then the bimetallic plate begins to heat up. Due to the different thermal expansion of the metals, it bends, eventually breaking the contact. The current strength 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 current value. Its setting is carried out at the factory by changing the distance between the plate and the moving contact. An adjusting screw is used for this.
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. When the signal value is abnormal, the magnetic field rapidly increases in the coil turns, the flows of which draw the core inward, overcoming the action of the spring, and this leads to a break in the circuit.
The operation of the electromagnetic release occurs in a fraction of a second, while it does not respond to currents slightly exceeding the rated ones. Simultaneously with the disconnection of the entire three-phase line, the lever is also lowered, which will again need to be moved to the upper position to connect the load to the network.
Device characteristics
The correct selection of a 3-phase machine consists not only of determining its operating conditions, but also the power and type of load that will be connected to it. Incorrectly selected module power leads to deterioration of electrical wire protection, and 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 design of the cut-off, and others.
Power selection
There are two ways to determine the required power for a 3-phase machine. Moreover, one complements the other, and does not exclude it. The first method is associated with finding the total value of energy consumption and load, and the second - with the cross-section of the electrical wiring.
Based on the definition that the machine protects not the equipment, but the electrical wiring, you need to select the power based 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 square meters. According to the technical characteristics, copper wiring of this diameter can withstand a long-term current of no more than 10 amperes. Accordingly, the largest simultaneous energy consumption by devices connected to the output of the machine should not exceed 3.8 kW. This value is obtained from a simple formula for finding power - P = U*I, where:
- P - maximum permissible power consumption, W;
- U - three-phase network voltage, 380 volts;
- I is the maximum current withstood by the wiring, 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 you turn on a 2 kW boiler, nothing bad will happen. But if you connect a 3 kW electric furnace to this line, the wiring will not withstand it and will catch fire, so to prevent an accident it is necessary to install a 10 A automatic machine, which allows you to load the line up to only 2.2 kW.
The advantage of using a three-phase machine is that three lines can be connected to it at the same time, and 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 if a delta load is connected - 11.4 kW. That is, for the example given, if it is not possible to route the line to different phase outputs of the protection device, you will need to purchase a 6 A machine.
If you plan to modernize 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% reserve (I = 4*3 = 12 A + reserve = 14 A), so the most suitable device in this case would be an automatic at 16 A.
Nuances when calculating
To simplify the calculation of power, it is customary to use not a percentage as a reserve, but multiplication by a coefficient. This additional number is generally considered to be 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 using tables.
Thus, when calculating power, the parameters of the electrical wiring are first taken into account, and then the energy consumed by the protected circuit breaker of electrical equipment. Here we also take into account the correct remark from the electrical installation rules (PUE), indicating that the installed circuit breaker must provide protection for the weakest section of the circuit.
The days when traditional ceramic plugs could be found on electrical panels of apartments or private houses are long gone. Nowadays, automatic switches of a new design - the so-called circuit breakers - are widely used.
What are these devices for? How to do it correctly in each specific case? Of course, the main function of these devices is to protect the electrical network from short circuits and overloads.
The machine must turn off when the load significantly exceeds the permissible limit or when a short circuit occurs when the electric current increases significantly. However, it must pass current and operate normally if, for example, you turn on the washing machine and electric iron at the same time.
What does a circuit breaker protect?
Before choosing a machine, it is worth understanding how it works and what it protects. Many people believe that the machine protects household appliances. However, this is absolutely not true. The machine does not care about the devices that you connect to the network - it protects the electrical wiring from overload.
Indeed, when the cable is overloaded or a short circuit occurs, the current increases, which leads to overheating of the cable and even fire of the wiring.
The current increases especially strongly during a short circuit. The magnitude of the current can increase to several thousand amperes. Of course, no cable can last long under such a load. Moreover, the cable has a cross-section of 2.5 square meters. mm, which is often used for laying electrical wiring in private households and apartments. It will simply light up like a sparkler. An open fire indoors can cause a fire.
Therefore correct plays a very important role. A similar situation occurs during overloads - the circuit breaker protects the electrical wiring.
When the load exceeds the permissible value, the current increases sharply, which leads to heating of the wire and melting of the insulation. In turn, this can lead to a short circuit. And the consequences of such a situation are predictable - open fire and fire!
What currents are used to calculate machines?
The function of a circuit breaker is to protect the electrical wiring connected downstream of it. The main parameter by which automatic machines are calculated is the rated current. But the rated current of what, the load or the wire?
Based on the requirements of PUE 3.1.4, the setting currents of circuit breakers that serve to protect individual sections of the network are selected as less as possible than the calculated currents of these sections or according to the rated current of the receiver.
The calculation of the machine based on power (based on the rated current of the electrical receiver) is carried out if the wires along the entire length in all sections of the electrical wiring are designed for such a load. That is, the permissible current of the electrical wiring is greater than the rating of the machine.
The time and current characteristics of the machine are also taken into account, but we will talk about that later.
For example, in an area where a wire with a cross-section of 1 square meter is used. mm, the load value is 10 kW. We select the machine according to the rated load current - set the machine to 40 A. What will happen in this case? The wire will begin to heat up and melt, since it is designed for a rated current of 10-12 amperes, and a current of 40 amperes passes through it. The machine will turn off only when a short circuit occurs. As a result, wiring may fail and even cause a fire.
Therefore, the determining value for choosing the rated current of the machine is the cross-section of the current-carrying wire. The load size is taken into account only after selecting the wire cross-section. The rated current indicated on the machine must be less than the maximum current permissible for a wire of a given cross-section.
Thus, the choice of machine is made based on the minimum cross-section of the wire used in the wiring.
For example, the permissible current for a copper wire with a cross-section of 1.5 kW. mm, is 19 amperes. This means that for this wire we select the closest value of the rated current of the machine to the smaller side, which is 16 amperes. If you choose a machine with a value of 25 amperes, the wiring will heat up, since the wire of this cross-section is not designed for such a current. To produce it correctly, it is necessary, first of all, to take into account the cross-section of the wire.
Calculation of the input circuit breaker
The electrical wiring system is divided into groups. Each group has its own cable with a certain cross-section and circuit breakers with a rated current that satisfies this cross-section.
To select the cable cross-section and rated current of the machine, you need to calculate the expected load. This calculation is made by summing up the power of the devices that will be connected to the site. The total power will determine the current flowing through the wiring.
The current value can be determined using the following formula:
- P - total power of all electrical appliances, W;
- U - network voltage, V (U=220 V).
Despite the fact that the formula is applied to active loads that are created by ordinary light bulbs or devices with a heating element (electric kettles, heaters), it will still help to approximately determine the amount of current in a given area. Now we need to select the conductive cable. Knowing the current value, we can use the table to select the cable cross-section for a given current.
After this you can produce for electrical wiring of this group. Remember that the machine must turn off before the cable overheats, so we select the rating of the machine that is closest to the lower value of the calculated current.
We look at the rated current on the machine and compare it with the maximum permissible current for a wire with a given cross-section. If the permissible current for the cable is less than the rated current indicated on the machine, select a cable with a larger cross-section.
Three-phase type circuit breakers are input switches. Devices are used in AC and DC circuits. consists of a set of expanders. The process of switching them is based on a change in frequency in the circuit. Modulators are integral elements of automatic machines. They consist of resistors as well as capacitors.
Wired modifications have a stabilizer. Triodes in the devices are designed to transmit a signal to the central unit. The modifications have regulators of single-channel and two-channel types. Insulators are used with covers to protect the system. To increase the power of the machine, converters are needed.
Purpose of the device
Three-phase automatic machines are specified for high-power drive devices. In AC circuits they are used in conjunction with rectifiers. Many modifications are able to work with controllers. If we consider powerful models, they are suitable for power plants.
How is the model connected?
A standard three-phase input circuit breaker is connected via a dinistor. The output contacts of the device are connected to the expander. A relay is needed to stabilize the input signal. as a rule, does not exceed 230 V. Connection to drive mechanisms is possible only through an adapter. Contactors in this case are used of the inverting type. When considering low power drive devices, relays are often used at 120 V.
Description of the device PL6-C10/3
This machine (three-phase, 25A) is suitable for AC circuits; the device is of a single-channel type. According to experts, the output voltage reaches a maximum of 300 A. The conductivity parameter of the resistor is no more than 3 microns. The power of three-phase machines of this series is 2 kW. The modification's capacitor is used with an adapter. It is also important to note that the machine has a varicap. The specified element is installed at the bottom of the structure, and it is responsible for frequency stabilization.
Characteristics of model PL6-C10/5
This machine is connected via a 200 V relay. According to experts, the expanders in the device are used with high-quality capacitive filters. The model has a two-channel regulator. The device is excellent for 3 A drive mechanisms.
The modification's tetrodes are of the low-resistance type. The resistance value on the plate is 30 ohms. The direct output voltage does not exceed 120 V. The model is not suitable for circuits with alternating current. The specified three-phase machine costs (market price) approximately 1,300 rubles.
Modification parameters PL6-C10/8
The three-phase circuit breaker of the specified series is connected via a 230 V relay. A linear stabilizer is used to protect the modification. According to experts, the model’s efficiency indicator is high. The power of this device is 2.3 kW. The modification's transceiver is used with two capacitors. The resistance parameter on the plate is 33 Ohms. This machine does not have a protection system against wave failures. The output voltage of the model in this series is 230 V.
Description of the VA47-29 device
The specified automatic machine (100A) of three-phase type is used for drive devices of low power. According to experts, its capacitors are installed with electrode filters. They protect the system well from wave failures. The main disadvantage of devices is considered to be a low conductivity threshold. The modification does not have a pulse rectifier. This machine is not suitable for low-power drive devices. The modification's regulator is of a two-channel type. The varicap itself is used with diode capacitors. The maximum frequency efficiency is 60%.
Characteristics of the model BA47-33
The specified input machine has a high input voltage parameter. The permissible relay overload level is 40 A. In this case, drive devices can only be connected with single adapters. Resistors for modifications are of low-resistance type. The resistance parameter on the expanders is 30 ohms.
If you believe the experts, then problems with frequency failures are not terrible for the machine. To protect the device there is a modulator. In total, it has three capacitors installed. The transceiver of the model is located in the upper part of the structure. The regulator of this machine is of a two-channel type. It is connected to the contacts via an adapter. The varicap in the device is responsible for receiving the signal. The maximum input voltage is 300 V.
There is no protection system against dinistor failures. If we consider contact drive mechanisms, then the machine can be connected via a 240 V relay. In this case, the frequency of the device is 55 Hz. When connecting, insulators are used with filters. Most often they are used of the electrode type.
VA47-35 modification parameters
The presented machine is suitable for 30 A drives. According to experts, the model uses two high-quality filters. The conductivity indicator on the expander is at least 3 microns. The input impedance of the machine of this type is 30 Ohms. The modulator in this case is used with two adapters. Resistors are used as operational type. The overload indicator of insulators does not exceed 23 A.
This machine does not have a pulse noise protection system. The triode in the device is installed at the bottom of the structure. The model's contacts are located under the closing mechanism. The position of the resistors is changed by a transistor. The conductivity of the varicap is at around 4 microns. The output voltage of the machine in this series is at least 300 A. The model is connected only through a 230 V relay. The machine does not have a phase distortion protection system.
Description of the Legrand 32 device
The automatic machine (three-phase) of the presented series is suitable for drives on an expander. The resistors in the modification are of the operational type. The output voltage of the machine does not exceed 230 V. At maximum load, the stabilizer comes into operation. In this case, the capacitors are installed behind the rectifier. The triode in the machine of the presented series is used of the broadband type. The converter is installed as standard at the bottom of the model, next to the triode. The device can be connected via a 230 V relay.
Characteristics of the Legrand 40 model
The specified machine (three-phase) is produced with two wire resistors. The model is doing well with voltage stabilization. The conductivity on the capacitor is no more than 3 microns. According to experts, the machine of this series is excellent for 40 A drives.
The varicap in the device is used with a line filter. It is also important to note that the machine only uses one converter. The maximum overload indicator of the expander is 3 A. The output voltage at the contacts does not exceed 250 V. This machine does not have a phase distortion protection system. 300V relays must not be used.
Legrand 45 modification parameters
The specified machine (three-phase) is necessary to turn off the drive devices. The model's regulator is of a single-channel type. According to experts, the modification’s stabilizer is used with a high-quality adapter. The resistors in the device are installed behind the contacts. In total, the model has three capacitors that have good conductivity.
It is also important to note that an expander is used to stabilize the output voltage. The filters in the machine of this series are of the linear type. The regulator is attached to the modulator via a dinistor. A 200 V relay can be used for connection. The modification's converter is designed for heavy overloads.
Description of the Legrand 50 device
The presented machine (three-phase) is suitable for drives of various powers. The conductivity of the device is 3 microns. Resistors in it are used with capacitive capacitors. It is also important to note that the model uses a diode expander. According to experts, the model is excellent for 30 A drives. The thyristor in the device is used with a line filter.
The contacts of the machine of the presented series are located behind the expander. This modification can be connected via a 200 V relay. The model’s rectifier is used with a dinistor. The regulator is of a single-channel type. This machine does not work in an alternating current circuit.
Characteristics of the ABB 30 model
The presented series are produced with three resistors. The output voltage on the capacitors is 230 A. The machine does not have a pulse noise protection system. It is also important to note that the model will stand out for its low resistance. The capacitors on the expander are of the capacitive type. The varicap in the device can solve problems with increased voltage.
Only 240 V relays are suitable for connecting the device. The modification's triode is of the operational type. In total, the model uses four linear filters. According to experts, the automatic machine is suitable for 43 A drives.
ABB 30 modification parameters
These three-phase ABB machines are suitable for 30 A drive mechanisms. They do not have an interference protection system. According to experts, the expander is used with high-quality linear filters. In total, the modification has three resistors. Their conductivity is at least 4 microns. The capacitors in this case are located behind the contacts. To increase the output voltage, only an operational expander is used.
The modulator in the device is used with two filters. The regulator is standardly installed as a single-channel type. It is connected to the modulator via a transceiver. The model's converter is not designed for heavy loads. It is also important to note that the machine of this series is not suitable for 35 A drive mechanisms. The modification’s tetrode is of the magnetic type. The dinistor is located at the bottom of the structure, and is connected to the modulator via a triode.
The choice of protective circuit breakers is made not only during the installation of a new electrical network, but also when upgrading the electrical panel, as well as when additional powerful devices are included in the circuit, increasing the load to a level that old emergency shutdown devices cannot cope with. And in this article we will talk about how to correctly select a machine based on power, what should be taken into account during this process and what are its features.
Failure to understand the importance of this task can lead to very serious problems. After all, users often do not bother themselves when choosing a circuit breaker based on power, and take the first device they come across in the store, using one of two principles - “cheaper” or “more powerful”. This approach, associated with the inability or unwillingness to calculate the total power of devices connected to the electrical network and select a circuit breaker in accordance with it, often becomes the reason for the failure of expensive equipment due to a short circuit or even a fire.
What are circuit breakers for and how do they work?
Modern AVs have two degrees of protection: thermal and electromagnetic. This allows you to protect the line from damage as a result of prolonged excess of the flowing current of the rated value, as well as a short circuit.
The main element of the thermal release is a plate made of two metals, which is called bimetallic. If it is exposed to a current of increased power for a sufficiently long time, it becomes flexible and, acting on the disconnecting element, causes the circuit breaker to operate.
The presence of an electromagnetic release determines the breaking capacity of the circuit breaker when the circuit is exposed to short-circuit overcurrents, which it cannot withstand.
An electromagnetic type release is a solenoid with a core, which, when a high power current passes through it, instantly moves towards the disconnecting element, turning off the protective device and de-energizing the network.
This makes it possible to protect the wire and devices from an electron flow, the value of which is much higher than that calculated for a cable of a particular cross-section.
What is the danger of a cable mismatch with the network load?
Selecting the correct power circuit breaker is a very important task. An incorrectly selected device will not protect the line from a sudden increase in current.
But it is equally important to choose the correct cross-section of the electrical cable. Otherwise, if the total power exceeds the rated value that the conductor can withstand, this will lead to a significant increase in the temperature of the latter. As a result, the insulating layer will begin to melt, which can lead to a fire.
To more clearly imagine the consequences of a mismatch between the wiring cross-section and the total power of the devices connected to the network, let’s consider this example.
New owners, having bought an apartment in an old house, install several modern household appliances in it, giving a total load on the circuit equal to 5 kW. The current equivalent in this case will be about 23 A. In accordance with this, a 25 A circuit breaker is included in the circuit. It would seem that the choice of the circuit breaker in terms of power was made correctly, and the network is ready for operation. But after some time after turning on the appliances, smoke appears in the house with a characteristic smell of burnt insulation, and after a while a flame appears. In this case, the circuit breaker will not disconnect the network from the power supply - after all, the current rating does not exceed the permissible one.
If the owner is not nearby at this moment, the melted insulation will cause a short circuit after some time, which will finally trigger the machine, but the flames from the wiring may already spread throughout the house.
The reason is that although the power calculation of the machine was done correctly, the wiring cable with a cross-section of 1.5 mm² was designed for 19 A and could not withstand the existing load.
So that you do not have to take out a calculator and independently calculate the cross-section of electrical wiring using formulas, we present a standard table in which it is easy to find the desired value.
Weak link protection
So, we are convinced that the calculation of the circuit breaker should be made based not only on the total power of the devices included in the circuit (regardless of their number), but also on the cross-section of the wires. If this indicator is not the same along the electrical line, then we select the section with the smallest cross-section and calculate the machine based on this value.
The PUE requirements state that the selected circuit breaker must provide protection for the weakest section of the electrical circuit, or have a current rating that will correspond to a similar parameter for the installations connected to the network. This also means that the connection must be made using wires with a cross-section that can withstand the total power of the connected devices.
How to select the wire cross-section and rating of the circuit breaker - in the following video:
If a careless owner ignores this rule, then in the event of an emergency that arises due to insufficient protection of the weakest section of the wiring, he should not blame the selected device and scold the manufacturer - only he himself will be to blame for the current situation.
How to calculate the rating of a circuit breaker?
Let's assume that we took into account all of the above and selected a new cable that meets modern requirements and has the required cross-section. Now the electrical wiring is guaranteed to withstand the load from switched on household appliances, even if there are quite a lot of them. Now we proceed directly to the selection of a circuit breaker based on current rating. Let's remember the school physics course and determine the calculated load current by substituting the corresponding values into the formula: I=P/U.
Here I is the value of the rated current, P is the total power of the installations included in the circuit (taking into account all consumers of electricity, including light bulbs), and U is the network voltage.
To simplify the selection of a circuit breaker and save you from the need to use a calculator, we present a table that shows the ratings of the circuit breakers that are included in single-phase and three-phase networks and the corresponding total load power.
This table will make it easy to determine how many kilowatts of load correspond to which rated current of the protective device. As we can see, a 25 Ampere circuit breaker in a network with a single-phase connection and a voltage of 220 V corresponds to a power of 5.5 kW, for a 32 Ampere circuit breaker in a similar network - 7.0 kW (this value is highlighted in red in the table). At the same time, for an electrical network with a three-phase delta connection and a rated voltage of 380 V, a 10 Amp circuit breaker corresponds to a total load power of 11.4 kW.
Visually about the selection of circuit breakers in the video:
Conclusion
In the presented material, we talked about why electrical circuit protection devices are needed and how they work. In addition, taking into account the information presented and the tabular data provided, you will not have any difficulty with the question of how to choose a circuit breaker.