Electrical circuit breakers perform the function of protecting wiring from overloads, short circuits, and accidents that may occur during voltage surges. To avoid an emergency, it is necessary to install electrical circuit breakers in apartments, private houses, garages, cottages and outbuildings. When overloads or surges occur, the device reacts and operates differently. In one situation or another, individual parts of the device are triggered, while other parts continue to work, ensuring the safety of the home.
Operating principle of the circuit breaker
The switch has compact, small sizes, the device is placed in plastic made of heat-resistant materials. On one side - the front - there is a handle that allows you to turn the device on and off, on the other - at the back - there is a latch, which is attached to a special DIN rail. Screw terminals are located at the bottom and top.
The operating principle of the switches depends on the state of the network and the flow of current through the wiring. When the electrical switch device is in normal mode, a current flows through the circuit breaker, the indicators of which may be equal to or less than the set nominal value. The voltage from the external network goes to the upper terminal with a fixed contact. From here the current flows to a closed moving contact, and then passes to the solenoid coil, which is flexible copper conductor. From here the current goes to the thermal release, from which it flows to the lower terminal. It is she who is connected to the network.
Table of current circuit breaker ratings
The standard current that passes through the wiring may be more or less than the established values. Based on them, a classification of time-current characteristics for releases in devices has been compiled. Each type in state standard marked with a Latin letter, and the permissible excess should be sought using the coefficient formula - k=I/In.
Table 1 shows the norms for each type of time-current indicators.
Table 1
Table 2 shows the time-current characteristics of automatic current switching devices.
Table 2
| Type | Characteristic | Types of chains |
| A | Protection on the AB segment is activated when the coefficient is equal to 1.3. The current is turned off within 60 minutes. If the current continues to increase, the shutdown time is reduced by exactly half. Electromagnetic protection at a speed of 0.05 sec. will work if the nominal value exceeds 2 times. | Not subject to short-term overloads, used in industrial scale, and not everyday life. |
| IN | The standard nominal value can be exceeded by 3-5 times. The solenoid is activated if the overload increases by 5 times. Then de-energization will occur within 0.015 seconds. The thermocouple will turn off within 4 seconds. already at three times the excess. | Characteristic for circuits without high inrush currents. |
| WITH | Overload occurs more often than with other types, the permissible indicators are 5 times higher than the norm. As soon as the standard mode is exceeded, the thermoelement will automatically turn off. | In household networks, where there is often a load of different types. |
| D | Exceeding the standard norm occurs 10 times, after which the thermoelement is turned off, and 20 times for the solenoid. | Used to protect starting devices carrying high current. |
| TO | The solenoid will turn off if the current exceeds 8 times. | Such devices must be installed on circuits that have an inductive load. |
| Z | A slight excess is typical - from 2 to 4 times. | Used to connect electronic devices. |
| M.A. | The thermocouple is not used to disconnect the load. | Installed on devices with electric motors. |
Selection of circuit breaker by power
One of the main indicators by which the choice is made circuit breaker, is the load power. This allows you to calculate the required current value for the device and its protection against voltage surges. The calculation is carried out based on the rated current, so it is recommended to select according to the power of individual sections. It is worth taking into account lower or nominal values of calculated currents. The permissible current of the electrical wiring will be greater than the rated power of the circuit breaker.
It is also necessary to take into account such an indicator as the time-current characteristic of the device. The main parameter for determining the rated power is the cross-section of the wire. The permissible current value, which is indicated on the circuit breaker, should be slightly less than the maximum current for the wire cross-section. Select a device based on the smallest cross-section of the wire that is laid in the wiring.
The dangers of a cable mismatch with the network load
If the circuit breaker does not match the network power and load, then it will not protect the wiring from the fact that the current strength and voltage sharply increases or decreases.
The cable cross-section for the network load must exactly match the power of the device. If the total power in different areas is greater than the nominal value, then the temperature will increase. This may cause the cable insulating layer to melt. As a result, the electrical wiring will start to catch fire. Also, if the cable cross-section does not correspond to the load, the following phenomena will be observed:
- Smoke.
- Smell of burnt insulation.
- A flame appears.
- The switch will not be disconnected from the network, since the rated current through the wiring will not exceed permissible limits.
The process of melting the insulating layer will cause a short circuit over time. Next, the circuit breaker will turn off; at this time, the fire can engulf the entire house.
Weak link protection
The rules for electrical installations state that the switch for the electrical network must protect the weakest section as much as possible or contain a current rating that will fully correspond to the parameters of the installations that are included in the network. To connect wires to the network, it is necessary that their cross-sections have the total power of all connected devices.
Compliance with such rules can protect an apartment or house from an accident due to a weak section of electrical wiring. The described requirements cannot be ignored, since the home owner is capable of losing not only the automatic power switch device, but also the apartment.
How to calculate the rating of a circuit breaker
- I - indicator/value of rated current.
- P is the total power of all installations that are included in the circuit. Light bulbs and other devices that consume electricity are taken into account.
- U is the current voltage in the network.
To calculate the denomination, you can use Table 3:
| Connection type | Single phase in kilowatts | Three-phase (delta) in kilowatts | Three-phase (star) in kilowatts |
| U, B Automatic, in amperes |
220 | 380 | 220 |
| 1 Ampere | 0,2 | 1,1 | 0,7 |
| 2 | 0,4 | 2,3 | 1,3 |
| 3 | 0,7 | 3,4 | 2 |
| 6 | 1,3 | 6,8 | 4 |
| 10 | 2,2 | 11,4 | 6,6 |
| 16 | 3,5 | 18,2 | 10,6 |
| 20 | 4,4 | 22,8 | 13,2 |
| 25 | 5,5 | 28,5 | 16,5 |
| 32 | 7,0 | 36,5 | 21,1 |
| 40 | 8,8 | 45,6 | 26,4 |
| 50 | 11 | 57 | 33 |
| 63 | 13,9 | 71,8 | 41,6 |
Using Table 3, you can easily calculate how many kilowatts of load a particular type of rated current can withstand. You must select clearly according to the specified values so that the voltage and type of connection exactly match and correspond to each other. This will help avoid excess load and possible accidents.
Unacceptable mistakes when purchasing
Buying a circuit breaker is not something you do every day. Therefore, you need to be careful when choosing a device so as not to cause a fire at home or short circuit the wiring. The following types of mistakes should not be made during purchase:
- Choose the right machine according to the power of electrical wiring in an apartment or private building. Many consumers do exactly the opposite - they focus on the power of the electrical appliances they operate. This is wrong, since the electrical wiring may not withstand it and begin to melt.
- Calculation of the nominal current of the current must be done based on average indicators. This way the wiring will definitely withstand the current load.
- For a dacha or garage, the AB rating should be more powerful, since the equipment used in such places has more power than in an apartment.
- Devices should be purchased only from trusted manufacturers, so that everything technical specifications were accurate and of high quality, did not threaten the safety of housing and residents.
- You should purchase circuit breakers only in specialized stores, do not use the services of intermediaries. This eliminates the risk of purchasing counterfeits and low-quality products.
Buying electric machines is not a very difficult task. You should adhere to the above recommendations to avoid mistakes in choosing such a device for your home. It is recommended to purchase a circuit breaker with a person who understands electricity, special equipment, types of cross-sections, device power, network voltages and phases.
The main difference between these switching devices from all other similar devices consists of a complex combination of abilities:
1. maintain rated loads in the system for a long time by reliably passing powerful flows of electricity through its contacts;
2. protect operating equipment from accidental malfunctions electrical diagram due to the rapid removal of power from it.
Under normal equipment operating conditions, the operator can manually switch loads with circuit breakers, providing:
different power plans;
changing the network configuration;
removal of equipment from operation.
Emergency situations in electrical systems ah arise instantly and spontaneously. A person is not able to quickly react to their appearance and take measures to eliminate them. This function is assigned to automatic devices, built into the switch.
In the energy sector, it is common practice to divide electrical systems by type of current:
constant;
variable sinusoidal.
In addition, there is a classification of equipment according to voltage:
low voltage - less than a thousand volts;
high voltage - everything else.
For all types of these systems, their own circuit breakers are created, designed for repeated operation.
AC circuits
Based on the power of transmitted electricity, circuit breakers in alternating current circuits are conventionally divided into:
1. modular;
2. in a molded case;
3. power air.
Modular designs
The specific design in the form of small standard modules with a width that is a multiple of 17.5 mm determines their name and design with the possibility of installation on a Din rail.
The internal structure of one of these circuit breakers is shown in the picture. Its body is entirely made of durable dielectric material, eliminating .
The supply and output wires are connected to the upper and lower terminals, respectively. To manually control the state of the switch, a lever with two fixed positions is installed:
the top one is designed to supply current through a closed power contact;
the lower one ensures a break in the power supply circuit.
Each of these machines is designed for long work at a certain value (In). If the load becomes greater, then the power contact breaks. For this purpose, two types of protection are placed inside the case:
1. thermal release;
2. current cut-off.
The principle of their operation makes it possible to explain the time-current characteristic, which expresses the dependence of the response time of the protection on the load current passing through it or an accident.
The graph presented in the picture is shown for one specific circuit breaker, when the cutoff operating zone is selected at 5÷10 times the rated current.
During the initial overload, a thermal release made of , which, with increased current, gradually heats up, bends and acts on the tripping mechanism not immediately, but with a certain time delay.
In this way, it allows small overloads associated with short-term connection of consumers to resolve themselves and eliminate unnecessary shutdowns. If the load provides critical heating of the wiring and insulation, then the power contact breaks.
When an emergency current occurs in the protected circuit, capable of burning the equipment with its energy, the electromagnetic coil comes into operation. With an impulse, due to the surge of the load that has arisen, it throws the core onto the disconnecting mechanism in order to instantly stop the over-the-top mode.
The graph shows that the higher the short circuit currents, the faster they are switched off by the electromagnetic release.
The household automatic PAR fuse works on the same principles.
When large currents break, an electric arc is created, the energy of which can burn out the contacts. To eliminate its effect, circuit breakers use an arc suppression chamber, which divides the arc discharge into small streams and extinguishes them due to cooling.
Cut-off ratio of modular structures
Electromagnetic releases are configured and selected to work with certain loads because when started they create different transient processes. For example, when turning on various lamps, a short-term surge of current due to the changing resistance of the filament can approach three times the nominal value.
Therefore, for the socket group of apartments and lighting circuits, it is customary to choose automatic switches with a time-current characteristic of type “B”. It is 3÷5 In.
Asynchronous motors, when spinning a rotor with a drive, cause large overload currents. For them, machines with characteristic “C” are selected, or - 5÷10 In. Due to the created reserve of time and current, they allow the engine to spin up and be guaranteed to reach operating mode without unnecessary shutdowns.
IN industrial production On machines and mechanisms there are loaded drives connected to motors, which create more increased overloads. For such purposes, automatic circuit breakers of characteristic “D” with a rating of 10÷20 In are used. They have proven themselves well when working in circuits with active-inductive loads.
In addition, machines have three more types of standard time-current characteristics that are used for special purposes:
1. “A” - for long wiring with an active load or protection of semiconductor devices with a value of 2÷3 In;
2. “K” - for pronounced inductive loads;
3. “Z” - for electronic devices.
IN technical documentation at different manufacturers The cut-off ratio for the last two types may be slightly different.
This class of devices is capable of switching higher currents than modular designs. Their load can reach values up to 3.2 kiloamperes.
They are manufactured according to the same principles as modular designs, but, taking into account the increased requirements for carrying increased loads, they are made to have relatively small dimensions and high technical quality.
These machines are designed for safe operation in industrial facilities. Based on the rated current, they are conventionally divided into three groups with the ability to switch loads up to 250, 1000 and 3200 amperes.
Design of their housing: three- or four-pole models.
Power air circuit breakers
They work in industrial installations and operate with very high load currents up to 6.3 kiloamperes.
These are the most complex devices for switching devices of low-voltage equipment. They are used to operate and protect electrical systems as input and output devices of high-power distribution installations and for connecting generators, transformers, capacitors or powerful electric motors.
Schematic representation of them internal structure shown in the picture.
Here, a double break of the power contact is used and arc-extinguishing chambers with grilles are installed on each side of the shutdown.
The operating algorithm involves a switching coil, a closing spring, a spring charging motor drive and automatic elements. To control the flowing loads, a current transformer with a protective and measuring winding is built in.
Automatic switches for high-voltage equipment are very complex technical devices and are manufactured strictly individually for each voltage class. They are usually used.
They are subject to the following requirements:
high reliability;
security;
speed;
ease of use;
relative noiselessness during operation;
optimal cost.
Loads that break during an emergency shutdown are accompanied by a very strong arc. To extinguish it they use various ways, including breaking the circuit in a special environment.
This switch includes:
contact system;
arc extinguishing device;
live parts;
insulated housing;
drive mechanism.
One of these switching devices is shown in the photograph.
For quality work circuits in such designs, in addition to the operating voltage, take into account:
the rated value of the load current for its reliable transmission in the on state;
maximum current short circuit according to the effective value that the disconnecting mechanism can withstand;
permissible component of the aperiodic current at the moment of circuit break;
automatic reclosure capabilities and provision of two automatic reclosure cycles.
According to the methods of extinguishing the arc during shutdown, switches are classified into:
oil;
vacuum;
air;
SF6;
autogas;
electromagnetic;
autopneumatic.
For reliable and comfortable work they are equipped with a drive mechanism that can use one or more types of energy or combinations thereof:
charged spring;
lifted load;
compressed air pressure;
electromagnetic pulse from the solenoid.
Depending on the conditions of use, they can be created with the ability to operate under voltage from one to 750 kilovolts inclusive. Naturally they have different designs. dimensions, automatic and remote control, setting up protections for safe operation.
Auxiliary systems of such circuit breakers can have a very complex branched structure and are located on additional panels in special technical buildings.
DC circuits
These networks also operate a huge number of circuit breakers with different capabilities.
Electrical equipment up to 1000 volts
Modern technologies are being introduced here on a massive scale modular devices, having the ability to be mounted on a Din rail.
They successfully complement the classes of old machine guns such as , AE and other similar ones, which were fixed to the walls of shields with screw connections.
Modular DC designs have the same structure and operating principle as their AC counterparts. They can be performed in one or several blocks and are selected according to the load.
Electrical equipment above 1000 volts
High-voltage circuit breakers for direct current operate in electrolysis production plants, metallurgical industrial facilities, railway and urban electrified transport, and energy enterprises.
Basic technical requirements the operation of such devices corresponds to their alternating current counterparts.
Hybrid switch
Scientists from the Swedish-Swiss company ABB managed to develop a high-voltage DC switch that combines two power structures:
1. SF6;
2. vacuum.
It is called hybrid (HVDC) and uses the technology of sequential arc extinguishing in two environments at once: sulfur hexafluoride and vacuum. For this purpose, the following device has been assembled.
Voltage is supplied to the upper busbar of the hybrid vacuum circuit breaker, and voltage is removed from the lower busbar of the SF6 circuit breaker.
The power parts of both switching devices are connected in series and controlled by their own individual drives. In order for them to work simultaneously, a control device for synchronized coordinate operations was created, which transmits commands to the control mechanism with independent power supply via a fiber optic channel.
Through the use of high-precision technologies, the design developers were able to achieve consistency in the actions of the actuators of both drives, which fits into a time period of less than one microsecond.
The switch is controlled by a relay protection unit built into the power line through a repeater.
The hybrid circuit breaker has significantly improved the efficiency of composite gas and vacuum structures by using their joint characteristics. At the same time, it was possible to realize advantages over other analogues:
1. the ability to reliably turn off short-circuit currents at high voltage;
2. the possibility of little effort for switching power elements, which made it possible to significantly reduce the dimensions and. accordingly, the cost of equipment;
3. availability of compliance with various standards for the creation of structures operating as part of a separate circuit breaker or compact devices at one substation;
4. the ability to eliminate the consequences of rapidly increasing recovering stress;
5. the ability to form a base module to work with voltages up to 145 kilovolts and higher.
A distinctive feature of the design is the ability to break an electrical circuit in 5 milliseconds, which is almost impossible to achieve with power devices of other designs.
The hybrid switch device was named one of the top ten developments of the year by MIT (Massachusetts Institute of Technology) Technology Review.
Other manufacturers of electrical equipment are also engaged in similar research. They also achieved certain results. But ABB is ahead of them in this matter. Its management believes that large losses occur during the transmission of alternating current electricity. They can be significantly reduced by using high-voltage direct voltage circuits.
In practical application, it is important not only to know the characteristics of circuit breakers, but also to understand what they mean. Thanks to this approach, most technical issues can be resolved. Let's look at what is meant by certain parameters indicated on the label.
Abbreviation used.
Device markings contain all necessary information, describing the main characteristics of circuit breakers (hereinafter referred to as AB). What they mean will be discussed below.
Time-current characteristic (VTC)
Using this graphical display, you can get a visual representation of the conditions under which the circuit power-off mechanism will be activated (see Fig. 2). On the graph, the time required to activate the AB is displayed as a vertical scale. The horizontal scale shows the I/In ratio.
Rice. 2. Graphic display of time and current characteristics of the most common types of machinesThe permissible excess of the standard current determines the type of time-current characteristics for releases in devices that perform automatic shutdown. In accordance with current regulations (GOST P 50345-99), each type is assigned a specific designation (from Latin letters). The permissible excess is determined by the coefficient k=I/In; for each type, the values established by the standard are provided (see Fig. 3):
- “A” – maximum – three times excess;
- “B” - from 3 to 5;
- “C” - 5-10 times more than standard;
- “D” - 10-20 times excess;
- "K" - from 8 to 14;
- "Z" - 2-4 more than standard.
Figure 3. Basic activation parameters for various types
Note that this schedule fully describes the conditions for activation of the solenoid and thermoelement (see Fig. 4).
Taking into account all of the above, we can summarize that the main protective characteristic of an AV is due to the time-current dependence.
List of typical time-current characteristics.
Having decided on the labeling, let’s move on to considering the various types of devices that meet a certain class depending on the characteristics.
Characteristic type "A"
AB thermal protection of this category is activated when the ratio of the circuit current to the rated current (I/I n) exceeds 1.3. Under these conditions, shutdown will occur after 60 minutes. As the rated current is further exceeded, the tripping time becomes shorter. Activation of electromagnetic protection occurs when the nominal value is doubled, the response speed is 0.05 seconds.
This type is installed in circuits not subject to short-term overloads. As an example, we can cite circuits based on semiconductor elements, when they fail, the excess current is insignificant. This type is not used in everyday life.
Characteristic "B"
The difference between this type and the previous one is the operating current; it can exceed the standard one from three to five times. In this case, the solenoid mechanism is guaranteed to be activated at a five-fold load (de-energization time - 0.015 seconds), the thermoelement - three times (it will take no more than 4-5 seconds to turn off).
These types of devices have found application in networks that are not characterized by high inrush currents, for example, lighting circuits.
Characteristic "C"
This is the most common type, its permissible overload is higher than that of the two previous types. When the normal operating mode is exceeded five times, the thermocouple is triggered; this is a circuit that turns off the power supply within one and a half seconds. The solenoid mechanism is activated when the overload exceeds the norm by ten times.
These AVs are designed to protect an electrical circuit in which a moderate inrush current may occur, which is typical for a household network, which is characterized by a mixed load. When buying a device for your home, it is recommended to choose this type.
Legrand three-pole circuit breaker Characteristic "D"
ABs of this type are characterized by high overload characteristics. Namely, ten times the norm for the thermoelement and twenty times for the solenoid.
Such devices are used in circuits with high inrush currents. For example, to protect starting devices asynchronous electric motors. Figure 9 shows two devices in this group (a and b).
Figure 9. a) VA51-35; b) BA57-35; c) BA88-35 Characteristic "K"
For such AVs, activation of the solenoid mechanism is possible when the current load is 8 times higher, and is guaranteed to occur when there is a twelve-fold overload of the normal mode (eighteen-fold for constant voltage). Load disconnection time is no more than 0.02 seconds. As for the thermoelement, its activation is possible when it exceeds 1.05 from the standard mode.
Scope of application: circuits with inductive loads.
Characteristic "Z"
This type is distinguished by a small permissible excess of the standard current, the minimum limit is two times the standard current, the maximum is four times. The thermoelement response parameters are the same as those of AB with characteristic K.
This subtype is used for connecting electronic devices.
Characteristics "MA"
A distinctive feature of this group is that a thermoelement is not used to disconnect the load. That is, the device only protects against short circuits, this is quite enough to connect electric motor. Figure 9 shows such a device (c).
Normal operation current
This parameter describes the maximum permissible value for normal operation; if it is exceeded, the load shedding system will be activated. Figure 1 shows where this value is displayed (using IEK products as an example).
Thermal parameters
This term refers to the operating conditions of the thermoelement. This data can be obtained from the corresponding time-current graph.
Ultimate breaking capacity (UCC).
This term refers to the maximum permissible load value at which the device can open the circuit without loss of functionality. In Figure 5, this marking is indicated by a red oval.
Rice. 5. Device from Schneider Electric Current limiting categories
This term is used to describe the ability of an AV to trip a circuit before the short-circuit current in it reaches its maximum. The devices are produced with current limiting of three categories, depending on the load disconnection time:
- 10 ms. and more;
- from 6 to 10 ms;
- 2.5-6 ms.
Note that ABs belonging to the first category may not have appropriate markings.
A small life hack on how to choose the right switch for your home
From the very beginning of the emergence of electricity, engineers began to think about the safety of electrical networks and devices from current overloads. As a result, many different devices have been designed that are distinguished by reliable and high-quality protection. One of the latest developments is electric automatic machines.
This device is called automatic because it is equipped with a function to turn off the power in automatic mode in the event of short circuits or overloads. Conventional fuses must be replaced with new ones after tripping, and the circuit breakers can be turned on again after eliminating the causes of the accident.
Such a protective device is necessary in any electrical network circuit. A circuit breaker will protect a building or premises from various emergency situations:
- Fires.
- Electric shocks to a person.
- Electrical wiring faults.
Types and design features
Need to know information about existing types circuit breakers in order to correctly select the appropriate device during purchase. There is a classification of electric machines according to several parameters.
Breaking capacity
This property determines the short circuit current at which the machine will open the circuit, thereby turning off the network and devices that were connected to the network. Based on this property, machines are divided into:
- 4500 ampere circuit breakers are used to prevent faults in the power lines of older residential buildings.
- At 6000 amperes, they are used to prevent accidents during short circuits in the network of houses in new buildings.
- At 10,000 amperes, used in industry for protection electrical installations. A current of this magnitude can occur in the immediate vicinity of a substation.
The circuit breaker trips when a short circuit occurs, accompanied by the occurrence of a certain amount of current.
The machine protects electrical wiring from damage to insulation by high current.
Number of poles
This property tells us about the largest number of wires that can be connected to the machine to provide protection. In the event of an accident, the voltage at these poles is switched off.
Features of machines with one pole
Such electrical circuit breakers are the simplest in design and serve to protect individual sections of the network. Two wires can be connected to such a circuit breaker: input and output.
The purpose of such devices is to protect electrical wiring from overloads and short circuits of wires. The neutral wire is connected to the neutral bus, bypassing the machine. Grounding is connected separately.
Electrical machines with one pole are not input, since when it is disconnected, the phase is broken, and the neutral wire still remains connected to the power supply. This does not provide 100% protection.
Properties of machines with two poles
In cases where an emergency requires complete disconnection from the electrical network, circuit breakers with two poles are used. They are used as introductory ones. In emergency cases, or in the event of a short circuit, all electrical wiring turns off at the same time. This makes it possible to carry out repair and maintenance work, as well as work on connecting equipment, since complete safety is guaranteed.
Two-pole electrical circuit breakers are used when it is necessary to have a separate switch for a device operating on a 220-volt network.
A machine with two poles is connected to the device using four wires. Of these, two come from the power supply, and the other two come from it.
Three-pole electrical circuit breakers
In an electrical network that has three phases, 3-pole circuit breakers are used. The grounding is left unprotected, and the phase conductors are connected to the poles.
The three-pole circuit breaker serves as an input device for any three-phase load consumers. Most often, this version of the machine is used in industrial conditions for powering electric motors.
You can connect 6 conductors to the machine, three of which are phases of the electrical network, and the remaining three coming from the machine and provided with protection.
Using a four-pole circuit breaker
To provide protection for a three-phase network with a four-wire system of conductors (for example, an electric motor connected in a star circuit), a 4-pole circuit breaker is used. It plays the role of an input device for a four-wire network.
It is possible to connect eight conductors to the device. On the one hand - three phases and zero, on the other hand - the output of three phases with zero.
Time-current characteristic
When devices that consume electricity and electrical network operate in normal mode, then normal current flow occurs. This phenomenon also applies to electric machines. But, if the current increases for various reasons above the rated value, the circuit breaker is triggered and the circuit is broken.
The parameter of this operation is called the time-current characteristic of the electrical machine. It is a dependence of the operating time of the machine and the relationship between the actual current passing through the machine and the rated current value.
The importance of this characteristic lies in the fact that it ensures smallest number false alarms on the one hand, and current protection on the other hand.
In the energy industry, there are situations where a short-term increase in current is not associated with an accident, and the protection should not operate. The same thing happens with electric machines.
The time-current characteristics determine after what time the protection will operate and what current parameters will arise. The greater the overload, the faster the machine will operate.
Electric machines marked “B”
Automatic switches of category “B” are capable of switching off in 5 - 20 s. In this case, the current value ranges from 3 to 5 rated current values ≅0.02 s. Such machines are used to protect household devices, as well as all electrical wiring of apartments and houses.
Properties of machines marked “C”
Electrical circuit breakers of this category can turn off in 1 - 10 s, at 5 - 10 times the current load ≅0.02 s. These are used in many areas, most popular for houses, apartments and other premises.
The meaning of the marking "D" on automatic
Automatic machines with this class are used in industry and are made in the form of 3-pole and 4-pole versions. They are used to protect powerful electric motors and various three-phase devices. Their operation time is up to 10 seconds, while the operation current can exceed the rated value by 14 times. This makes it possible to use it with the necessary effect to protect various circuits.
Electric motors with significant power are most often connected through electrical machines with characteristic “D”, because starting current is high.
Rated current
There are 12 versions of the machines, which differ in the characteristics of the rated operating current, from 1 to 63 amperes. This parameter determines the speed at which the machine turns off when the current limit value is reached.
Based on this property, the machine is selected taking into account the cross-section of the wire cores and the permissible current.
Operating principle of electric machines
Normal mode
During normal operation of the machine, the control lever is cocked, current flows through the power wire at the top terminal. Next, the current flows to the fixed contact, through it to the moving contact and along flexible wire to the solenoid coil. After it, the current flows through the wire to the bimetallic plate of the release. From it, the current passes to the lower terminal and further to the load.
Overload mode
This mode occurs when the rated current of the machine is exceeded. The bimetallic plate is heated by a high current, bends and opens the circuit. The action of the plate requires time, which depends on the value of the passing current.
The circuit breaker is an analog device. There are certain difficulties in setting it up. The tripping current of the release is adjusted at the factory using a special adjusting screw. After the plate has cooled, the machine can function again. The temperature of the bimetallic strip depends on the environment.
The release does not act immediately, allowing the current to return to its nominal value. If the current does not decrease, the release trips. Overload can occur due to powerful devices on the line, or the connection of several devices at once.
Short circuit mode
In this mode, the current increases very quickly. The magnetic field in the solenoid coil moves the core that activates the release and disconnects the power supply contacts, thereby removing the emergency load of the circuit and protecting the network from possible fire and destruction.
An electromagnetic release acts instantly, which is different from a thermal release. When the contacts of the operating circuit open, an electric arc appears, the magnitude of which depends on the current in the circuit. It causes destruction of contacts. To prevent this negative effect, an arc chute is made, which consists of parallel plates. In it, the arc fades and disappears. The resulting gases are discharged into a special hole.
The development of power grid security tools has become relevant since their inception. Various overloads led not only to cable damage, but also to fires.
Today the most popular devices of this type steel circuit breakers.
They help prevent events such as fires and damage to electrical wiring. Since they are automatic, operation occurs without human intervention. Choice the correct switch will help protect the premises from accidents.
Design and principle of operation
Understanding the automatic switch operation mechanism will help you select the right model. Structurally, the machine includes the following key elements:
- terminals;
- toggle switch;
- electromagnetic release;
- bimetallic plate.
Depending on the type of overload, one of two mechanisms is triggered.
If a circuit overload occurs with a current that exceeds the nominal value by several times, the bimetallic plate is triggered. It heats up within a few seconds, causing it to expand thermally. When it reaches a certain size, it bends significantly and the chain opens. The plate parameters are adjusted by the manufacturer. For switches used in everyday life, the response time takes 5–20 s. They are usually marked with the letters: B, C, D.
The short circuit (SC) mode is characterized by an avalanche-like increase in current, exceeding not only the nominal value, but also its maximum permissible load. There is no time left for heating the plate during the jump, otherwise the wiring may melt. In such a situation, an electromagnetic release is triggered. The magnetic field sets the core in motion, which opens the circuit. Instant operation allows you to protect the premises from the consequences of a short circuit.
Classification
Electric machines differ in the following key characteristics:
- number of poles;
- time current characteristic;
- operating current value;
- breaking capacity.
Number of poles
This characteristic corresponds to the number of electrical wiring lines that can be directly connected to the machine. All output wires will be disconnected simultaneously when the machine is triggered.
Single-pole circuit breaker. This is the simplest type of circuit protection devices. Only 2 wires are connected to it: one goes to the load, the second is power. It is placed on a standard 18 mm din strip. The power wire is supplied from the top, and the load is connected to the bottom terminal. It can work in electrical wiring lines with one, two or three phases. In addition to the power and load wires, it has a neutral and ground, which are connected to the corresponding buses. Such machines are not installed at the entrance, since the circuit will only open along the phase line. The neutral wiring remains closed and in the event of a failure, potential may remain on it.
A two-pole machine, its difference from a single-pole one. This type of circuit breaker allows you to completely cut off the electrical wiring in the room. It allows you to synchronize the moment when you turn off your two output lines. The latter leads to more high level safety during electrical installation work. It can be used as a separate toggle switch for appliances such as a water heater or washing machine. The connection is made using 4 cables: a pair at the input and output.
A simple question is logical: is it possible to connect two single-pole circuit breakers instead of one double-pole one? Of course not. After all, when a two-terminal switch is automatically triggered, all output lines are switched off. For a pair of independent machines, an overload may not occur on one of the lines and the blackout will be partial. IN ordinary apartments You can connect a phase and neutral line to this machine. When opened, there will be a complete blackout of the entire group of devices that are powered from it.
Three and four pole machines. All three or four phase wires are connected to the poles of the corresponding circuit breaker. They are used when connected by a star, when phase wires are protected from overloads, and the middle wire remains switched all the time, or a triangle when there is no middle central cable, and the phase wires are protected.
If an overload occurs on one of the lines, a shutdown occurs immediately on all the others. These machines are connected to 6 (three-phase machine) or 8 wires. 3-4 at the output and the same number of lines at the output. They are mounted on DIN rails with a length of 54 (three-phase automatic) and 72 mm, respectively. They are used most often in industrial installations, when connecting powerful electric motors.
Time current parameter
Nutritional consumption patterns various devices varies even when the power values are the same. Uneven consumption dynamics at correct operation, a load surge during switching on - all these phenomena lead to significant changes in such a parameter as current consumption. Power dispersion can lead to false tripping of the circuit breaker.
To eliminate such situations, dynamic operating parameters are introduced, called time-current characteristics of circuit breakers. Based on this parameter, machines are divided into several types. The triggering time of the machine is different for each group. The front panel of the switch is marked with the corresponding letter from the list: A, B, C, D, K, Z.
Rated current
The differences in automatic machines depending on the rated current values are divided into several groups (12 current levels). It is directly related to the response time when power consumption is exceeded. The operating value can be determined purely theoretically by adding up the sums of currents consumed by each device separately. In this case, you should take a small reserve. You should also not forget about the electrical wiring options.
The machines are designed primarily to prevent damage. Depending on the metal of the wires and their cross-section, the maximum load is calculated. The current ratings of circuit breakers allow this division to be made.
Breaking capacity
This parameter depends on the maximum current value when a short circuit occurs, provided that the machine disconnects the network. Based on the magnitude of the short-circuit current, all circuit breakers are divided into three groups.
- The first includes devices with a rating of 4.5 kA. They are used in private houses intended for human habitation. The current limit is approximately 5 kA. This is due to the fact that the resistance of the conductive cable system leading to the house from the substation is 0.05 Ohm.
- The second group has rated 6 kA. This level is already used in residential apartment buildings and public places. The maximum current can reach 5.5 kA (wiring resistance 0.04 Ohm). Models of the following types are used: B, C, D.
- In industrial installations the rating is 10 kA. The maximum current value that can occur in the circuit near the substation has the same value.
How to choose the right machine
Until recently, porcelain fuses with fusible elements were widely used. They were well suited for the same type of load in Soviet apartments. Now the number household appliances became much larger, as a result of which the likelihood of a fire with old fuses increased. To prevent this, you need to carefully select a machine with the right characteristics. Excessive power reserves should be avoided. The final choice is made after completing a few simple steps.
Determination of the number of poles
When determining this switch parameter, you should follow a simple rule. If you plan to secure sections of the circuit with devices that have low power consumption (for example, lighting devices), then it is better to leave your choice on a single-pole circuit breaker (usually class B or C). If you plan to connect a complex household device with significant power consumption (washing machine, refrigerator), then you should install a two-pole circuit breaker (class C, D). If you are equipping a small production workshop or garage with multiphase motor systems, then you should choose a three-pole option (class D).
Power consumption calculation
As a rule, by the time it is planned to connect the machine, the wiring to the room has already been installed. Based on the cross-section of the conductors and the type of metal (copper or aluminum), it is possible to determine maximum power. For example, for a 2.5 mm 2 copper core this value is 4–4.5 kW. But the wiring is often supplied with a large margin. Yes, and the calculation should be done before all installation work begins.
In this case, you will need a value about how much total power will be used by all devices. It is always possible to turn them on simultaneously. So, in an ordinary kitchen, the following appliances are often used:
- fridge– 500 W;
- electric kettle– 1700 W;
- microwave oven– 1800 W
The total load is 4 kW and a 25 A circuit breaker is enough for it. But there are always consumers who turn on sporadically and can create factors that contribute to the circuit breaker tripping. Such devices can be a combine or a mixer. Therefore, you should take a machine with a reserve of 500–1200 W.
Rated current calculation
Since power in single-phase networks is equal to the product of voltage and current, the current can easily be determined as the quotient of power and voltage. For the above example, this value is easy to calculate, knowing that the mains voltage is 220 V. The current consumed is 18.8 A. Taking into account a reserve of 500–1200 V, it will be 20.4–23.6 A.
In order for the work not to stop even with such short-term excess loads, the rated current for the machine can be taken equal to 25 A. The nominal value corresponds to approximately the same value, based on a copper cable with a cross-section of 2.5 mm 2, which is sufficient with a margin for such loads. A circuit breaker with a rated current of 25 A will work before it starts to heat up.
Determination of time current characteristic
This parameter is determined using a special table that lists the starting currents and their flow time. For example, for a household refrigerator, the starting current multiplicity is 5. With a power of 500 W, the operating current is 2.2 A. The starting current value will be 2.2 * 7 = 15.4 A. Periodicity data is also taken from a special table.
Table No. 1. Starting currents and pulse duration for household appliances
For the selected device, this characteristic does not exceed 3 s. The choice becomes obvious: for such a consumer it is necessary to take a type B circuit breaker. It is permissible to select a circuit breaker based on load power. You can skip the last step and opt for a class B circuit breaker. For household needs most often the characteristics are sufficient electrical switches class B and C.
