Installation of circuit breakers

Automatic circuit breakers in electrical circuits are devices that automatically turn off the power supply by opening contacts. The contacts open when short circuit, exceeding the current load in excess of the calculated one and when non-standardized leakage currents appear in the network. Circuit breakers also serve as a switch for manually opening the network.
In turn, automatic protection devices are divided into the following groups:

• modular fuses (single use);

• electromechanical devices (reusable) that respond to currents above the tripping current and to heating of the wires due to exceeding rated currents loads that have replaced fuses.

• relatively recent devices protective shutdown(RCD) that respond to the appearance of a leakage current, which should not be in a normal network. Used to protect people who are at risk of injury electric shock, as well as to protect against the risk of fire in case of violation of the insulation of wires and contacts;

Recently, combined devices have also appeared that combine a circuit breaker and an RCD, the so-called differential automata.

diffavtomat - protection device

In this article we will consider circuit breakers, features of their device, selection and installation.

The device of automatic protection

• 1. A modern circuit breaker consists of one (one phase) to four (three phases with a neutral wire) pairs of spring-loaded contacts enclosed in a plastic case. Contacts in the closed state are held by a latch. To close the contacts, a lever is brought out to the outside. By pressing the lever, overcoming the resistance of the opening spring, we close the contacts, and they are fixed in the closed state by a latch.

• 2. To open the contacts, simply move the latch and the opening spring attached to the break contact(s) will open the circuit. The electric arc that occurs when the contacts open is extinguished by a special extinguishing device. The latch is pushed back to open, firstly, by a solenoid connected in series in the circuit at a certain

the value of the current flowing through it, and, secondly, a bimetallic plate, also connected in series, bending when heated and shifting the latch to open. You can also open the contacts manually by pressing the button, which is mechanically connected to the latch. Contacts (terminals) for connecting to wires are located above and below. The device is fastened by snapping onto the so-called DIN - rail (DIN - Deutsche Industri Normen - German industry standards) DIN - rail is equipped with power input shields, these shields are also equipped with electricity meters. The machine is mounted on a DIN rail by simple snapping, and to remove it, you need to move a special fixation frame with a screwdriver.

Automatic circuit breaker protects the power grid and devices connected after it.
In the event of a short circuit, the current flowing through the solenoid increases many times, the solenoid retracts the core connected to the latch and the circuit opens. If the current load increases (before the solenoid is triggered) and this causes excess heating of the wires, the bimetallic plate is triggered. Moreover, if the response time of the solenoid is about 0.2 seconds, then the response time of the bimetallic plate is about 4 seconds.

Rated current and instantaneous tripping current of the machine. Circuit breaker selection

The main characteristic when choosing a machine is rated current, which is indicated on the marking of the machines. To understand its meaning, you need to know that any electrical network consists of so-called groups, each group forms an independent "loop", all loops are connected to the input wires in parallel, that is, independently. This is done, firstly, to increase the reliability of the electrical network and reduce the possibility of overloads, and secondly, with the help of groups, all current loads are equalized and reduced to some standard values, which allows you to save on wires - for each group, its own wire section is selected.
As a rule, one group consists of lighting devices, another - sockets, the third - energy-consuming electric stoves, washing machines, etc. For each group, when designing a power supply network, the rated current is determined, based on which the cross section of the wires is calculated. It should be noted that the rated current of a group of consumers is calculated not by simply summing up the powers of consumers, but taking into account the probability of simultaneous inclusion of several consumers in the network. For this, the so-called probability coefficient is introduced, calculated by a special method.

Based on the calculated rated currents of each consumer group, the required wire cross-section is calculated, and circuit breakers are selected (each group has its own circuit breaker). The automata are selected in such a way that, according to the known rated current of the group, the automaton with the nearest higher value of the rated current is selected. For example, with a rated current of a group of 15A, we select an automaton with a rated current value of 16A.

It must be understood that the circuit breaker does not operate when the rated current is slightly exceeded, but when the current in the network is several times higher than the rated current. This current is called the instantaneous trip current (as opposed to the bimetallic plate operation current) of the circuit breaker. This is the second parameter to consider when choosing a machine. By the magnitude of the instantaneous trip current, or rather, by its relation to the rated current, the automata are divided into three groups, denoted by the Latin letters B; FROM; and D. (In the European Union, class A machines are also produced.) What do these letters mean?

Class B circuit breakers are designed for instantaneous tripping at currents above 3 and up to 5 rated currents.
Class C, respectively, above 5 and up to 10 rated currents.
Class D - above 10 and up to 20 rated currents.

What are these classes for?

The fact is that there is such a thing as the starting load current, which for some consumers can exceed the rated operating current several times. For example, any electric motors at the time of starting (while the motor rotor is stationary) operate practically in short circuit mode, that is, they load the network only with the active resistance of copper windings, which is small. And only when the motor rotor is gaining momentum, reactance appears, reducing the current. The starting currents of electric motors are 4-5 times higher than the nominal (working currents). (True, the duration of the flow of starting currents is small, the bimetallic plate of the circuit breaker will not have time to work).

If we use class B automata to protect motors, we will get a false operation of the automaton at the starting current every time the engine is started. And we may not be able to start the engine at all. That is why class D circuit breakers must be used to protect engines.

protection of the machine from starting currents - electric motor

Class B - for the protection of lighting networks, heating devices, where starting currents are minimal or absent. Accordingly, class C is for devices with average starting currents.

average starting currents - lighting lamps

Naturally, to select a circuit breaker, you need to take into account the voltage, type of current, working environment, etc., but all this does not need special comments.

Installation and installation of circuit breakers

We note right away that the work on the installation and installation of circuit breakers must be carried out by qualified personnel who have received appropriate training and have permission to carry out such work. This is a safety requirement set out in the PUE.

Installation and installation of machines are made on the basis of a circuit diagram, which must be attached in a conspicuous place inside the power supply input panel. circuit diagram specific installation is developed on the basis of typical schemes. As a rule, the following equipment is located in the input shield:

1. A switch is installed at the entrance - a knife switch, a batch switch or a general circuit breaker (circuit breakers are installed in modern shields). This is done in order to be able to carry out electrical work inside the shield, simply by disconnecting the entire shield from the power supply.
2. Next, an electric meter is connected, which is sealed to protect against all kinds of "craftsmen" to "save" electricity.
3. After the meter, the supply wires branch into groups, and at the input of each group, its own circuit breaker is placed, and after it, an RCD (residual current device). RCDs are selected so that their rated current exceeds the rated current of the circuit breaker. Further, the wires go out of the shield to the groups of consumers, to each group with its own separate cable.

Circuit breakers and RCDs are mounted on a DIN rail. The installation itself is not difficult, you just need to note that to facilitate installation, there are ready-made jumper strips or jumpers - this is for supplying, for example, to all machines phase voltage, the input wire is connected to the first machine, and to the rest - using jumpers. Also in the shield are installed common clamping strips for neutral wires and for ground wires. All this greatly simplifies installation.

In the electrical wiring of an apartment or house, there is always an element called a circuit breaker, or, more often, a machine.

This device is intended for automatic protection electrical network from troubles that may occur during overload or short circuit. In addition, it can be used to manually turn on and off the electrical circuit.

There are many different designs of machines that are designed to protect the electrical networks of both individual apartments or houses, as well as industrial enterprises or trading floors.

Circuit breakers are defined by rated current and group. Depending on these characteristics, circuit breakers are divided into 3 groups - B, C and D. In household electrical networks, type C devices are usually used, in which the instantaneous off current lies in the range from 5 to 10 values ​​​​of the rated current. Next, automata of type C of modular form will be considered.

The structure of the circuit breaker also includes the following blocks:

• frame;
• control mechanism;
• switching device;
• releases;
• arc chamber.

The body of the device is a plastic box, the dimensions of which are standardized. On the front side there is a lever for turning the machine on and off, on the back there is a latch for fastening on a DIN-rail, and at the top and bottom there are terminals for connecting wires.

One of the distinguishing characteristics of an electric machine is a control mechanism that is designed to be manually turned on and off. It consists of a handle or buttons.

The switching device is a set of power and auxiliary contacts. These contacts may be movable or fixed.

Releases are devices designed to open the electrical circuit if the current in the circuit exceeds the specified values. The machine has electromagnetic and thermal releases. Electromagnetic is an inductor with a metal core connected by a system of levers with a movable power contact of the machine. In thermal - a bimetallic plate is used, which, under the influence of the current flowing through it, bends and acts through the levers on the movable contact of the machine.

Before using the device, it is necessary to check the operation of the releases of the circuit breakers.

To weaken the impact of the arc that occurs when the power contacts open, the machine has a special chamber consisting of metal plates. The electric arc entering this chamber is broken by plates into several parts and extinguished.

The principle of operation of the machine during overload

When too many consumers of electricity are connected to the power circuit, a current may appear in the circuit, the value of which may exceed the maximum value for this electrical network. In practice, this may occur, for example, when the apartment turns on washing machine, iron, kettle, boiler, and other powerful consumers of electricity.

In the case when the actual circuit current exceeds the nominal one of the machine, the thermal release is activated in the latter.

A bimetallic plate consisting of two layers of metals heats up when current passes through it. Under the action of heat, this plate bends, acts on the movable contact of the machine and opens the circuit.

Before that, it is necessary to determine the load and the type of wiring for which protection is being installed. As a result of this, the required pole of the machine is indicated.

The correct installation of the circuit breaker must be done according to the relevant wiring diagrams. You can read about the nuances of this process.

The magnitude of the operating current of the thermal release is usually greater than the rated current of the circuit breaker by 13-45%. This value can be changed with the help of an adjusting screw during factory adjustment within a fairly wide range. The time delay for turning off the machine during overload is necessary so that there are no unnecessary trips with a short increase in current, which, for example, happens during start-up.

Action of the device in case of a short circuit

When a short circuit appears in the circuit, a rapid and sharp increase in current occurs in the entire network, including in the coil of the electromagnetic release. Under the action of a sharply increased electromagnetic field, the core is drawn into the coil. The lever located on the core acts on the movable power contact, disconnects it from the fixed contact and opens the electrical circuit.

Exposure to short circuit currents can adversely affect the condition of connected appliances, wiring, and even cause a fire. To reduce the impact of such currents, the tripping time of the release should be as short as possible. Modern automatic machines, when exposed to short-circuit currents, operate in no more than 0.02 seconds.

Restarting the machine - what needs to be done?

When the machine is triggered due to overload, the circuit can be switched on again only after the bimetallic plate has cooled down. In this case, before turning on the circuit breaker again, it is necessary to analyze the load of the circuit and try to reduce it by disconnecting unnecessary devices. A 12-volt power supply, which you can buy or assemble yourself. How to decorate your car with LED lighting.

Conclusions:

1. For guard electrical circuit from overload and short circuit, a circuit breaker is used.
2. In the machine, the opening of the circuit during overload by the thermal release is carried out with a time delay, and in the event of a short circuit - by the electromagnetic release instantly.
3. Before restarting after the overload circuit breaker trips, the number of consumers must be reduced.
4. Before switching on again after the machine has tripped due to a short circuit, it is necessary to first eliminate the cause of the short circuit.

The principle of operation of an electric machine on video

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, which are distinguished by reliable and high-quality protection. One of the latest developments has become electric machines.

This device is called automatic due to the fact that it is equipped with the function of turning off the power in automatic mode, in the event of short circuits, overloads. Conventional fuses after operation must be replaced with new ones, and the machines can be turned on again after the causes of the accident have been eliminated.

Such a protective device is necessary in any electrical network scheme. The circuit breaker will protect the building or premises from various emergencies:

• Fires.
• Electric shocks to a person.
• Electrical faults.

Types and design features

It is necessary to know information about the existing types of circuit breakers in order to choose the right one at the time of purchase suitable device. 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 the devices that were connected to the network. According to this property, automata are divided into:

• Automatic machines for 4500 amperes are used to prevent malfunctions in the power lines of old 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 amps, used in industry for protection electrical installations. A current of this magnitude can be formed in the immediate vicinity of the substation.

The operation of the circuit breaker occurs during short circuits, accompanied by the occurrence of a certain amount of current.

The machine protects the wiring from damage to the 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 turned off.

Features of machines with one pole

Such electric machines are the simplest in design, and serve to protect individual sections of the network. Two wires can be connected to such a circuit breaker: an input and an output.

The task 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.

Electric machines with one pole are not introductory, since when it is turned off, the phase breaks, and the neutral wire still remains connected to the power supply. It does not provide 100% protection.

Properties of automata with two poles

In cases where an accident requires a complete disconnection from the electrical network, use circuit breakers with two poles. They are used as input. In emergency cases, or in case of a short circuit, all electrical wiring is turned 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 electric machines are used when it is necessary to have a separate switch for a device powered by a 220 volt network.

An automatic 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 out of it.

Three-pole electric machines

In an electrical network with three phases, 3-pole machines are used. Grounding is left unprotected, and the phase conductors are connected to the poles.

A three-pole machine serves as an input device for any three-phase load consumers. Most often, this version of the machine is used in industrial conditions to supply electricity to electric motors.

6 conductors can be connected to the machine, three of which are the phases of the electrical network, and the remaining three are coming from the machine and provided with protection.

Using a four-pole machine

To provide protection three-phase network with a four-wire system of conductors (for example, an electric motor connected according to the "star" scheme), a 4-pole circuit breaker is used. It plays the role of an introductory device of 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 normally, normal current flows. This phenomenon also applies to the electric machine. But, in the case of an increase in current strength for various reasons, higher nominal value, the automatic release trips and the circuit breaks.

The parameter of this operation is called the time-current characteristic of the electric machine. It is the dependence of the time of operation of the machine and the ratio between the real strength of the current passing through the machine and the nominal value of the current.

The importance of this characteristic lies in the fact that the least number of false positives is provided on the one hand, and current protection is carried out, on the other hand.

In the energy industry, there are situations when a short-term increase in current is not associated with an accident, and the protection should not work. It also happens with electric machines.

Time-current characteristics determine how long the protection will operate, and what current strength parameters will occur.

Electric machines marked "B"

Circuit breakers with a property marked with the letter "B" are capable of tripping in 5 to 20 s. In this case, the current value is up to 5 nominal current values. Such models of machines are used to protect household appliances, as well as all electrical wiring in apartments and houses.

Properties of machines marked "C"

Electric machines with this marking can turn off in a time interval of 1 - 10 s, at 10 times the current load. Such models are used in many areas, most popular for houses, apartments and other premises.

The meaning of the marking "D" on the machine

With this class, automata 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 nominal 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 electric machines with characteristic "D".

Rated current

There are 12 versions of automatic 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 switches off when the current limit is reached.

The machine for this property is selected taking into account the cross-section of the conductors of the wires, the allowable current.

The principle of operation 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 goes to the fixed contact, through it to the moving contact and through flexible wire to the solenoid coil. After it, the current goes through the wire to the bimetallic release plate. 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 large 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 with a special adjusting screw. After the plate has cooled down, the machine can function again. The temperature of the bimetal 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 connecting 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, which activates the release, and disconnects the contacts of the power supply, thereby removing the emergency load of the circuit and protecting the network from possible fire and destruction.

The electromagnetic release operates instantly, which is different from the thermal release. When the contacts of the working circuit are opened, 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.

A circuit breaker (it is also sometimes called a "circuit breaker") is designed to turn off an electrical circuit equipped with it in the event of a short circuit or current exceeding a certain value.

The operation of the circuit breaker can be based on thermal or electromagnetic principles. It is worth noting that most modern switches simultaneously use both of these principles. Figure 1 illustrates how this works.

The current flowing between the connection points of the machine (A-B) passes through the electromagnet coil L and the bimetallic plate 2. When the maximum permissible current value is exceeded, the bimetallic plate is heated (thermal principle), it is deformed, activating the release S - a device that opens electrical circuit. However, here there is a rather high inertia, which determines the long response time of the thermal release.

The electromagnetic release is activated by a significant excess of current through the coil L, which causes the core 1 to move, which also acts on the contact S, causing the circuit breaker to trip, and this happens very quickly.

Thus, the combination of the above principles of operation of the circuit breaker makes it possible to monitor sufficiently long, but not instantaneous current excesses (thermal) and a sharp significant increase in current, for example, during a short circuit (electromagnetic).

CIRCUIT BREAKER SELECTION

Before choosing a circuit breaker, you should familiarize yourself with its main technical characteristics. I propose to do this on a specific example (Figure 2).

If you look at the switch, you can see a number of markings on its body.

1. Trademark (manufacturer), catalog or serial number below. The manufacturer may be of interest to us in terms of reputation, respectively quality.

   The serial number indicates a number of such specifications circuit breaker as the number of operating cycles, protection class, resistance to vibration loads, etc., that is, quite specific reference information. However, it also characterizes the breaking capacity of the circuit breaker, which should be taken into account in a good way.



2. The alphanumeric index at the top defines the rated current (In) - here 10 Amperes and the type (class) that defines the instantaneous trip (off) current (Ic):
   • B (Ic=over 3*In to 5*In) - used for sufficiently long lines of force, whose own resistance can significantly limit the short-circuit current,
   • C (Ic=over 5*In to 10*In) - the most common type, suitable for household lines with low inductive load,
   • D (Ic=over 10*In to 20*In) - recommended for protection of power supply circuits of powerful electric motors, other devices with high starting currents (inductive load).
   Under it are the limits of operating voltages, their type is variable (~) or constant (-).


3. This is the switch circuit, it is similar to the one I gave above. It shows that this switch has electromagnetic (a) and thermal (b) automatic releases.

Thus, the choice of a circuit breaker should be made taking into account the current load, which is determined by the power of electricity consumers (you can see about this) and the conditions of its operation described above.

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Automatic circuit breakers (automatic devices) are designed for operational switching on and off of low-voltage electrical circuits and protecting them from short-circuit currents and overloads, as well as from the disappearance or reduction of mains voltage.
The role of protective elements that respond to the deviation of one or another controlled value from its normal value is performed by releases. The following releases can be installed in automatic machines:
maximum current, triggered instantly at a short circuit current in the circuit;
minimum voltage, triggered in the event of a decrease or loss of voltage;
reverse current, which are triggered when the direction of the current in the circuit changes direct current;
independent (from any parameters of the electrical circuit), which serve to remotely turn off the machines;
thermal, used for protection against overloads (by type of thermal relays of starters);
combined, including electromagnetic and thermal releases simultaneously.
Circuit breakers are equipped with a free trip mechanism (MCP), which allows you to ensure that the machine is turned off during or after switching on.
On fig. schematically shows the design of the circuit breaker having arcing 1 and main 2 contacts. The main contacts, made of copper, have a low contact resistance and can pass through for a long time. high current. Arcing contacts made of cermet are connected in parallel with the main ones.
The machine is turned on manually when the handle 7 is turned clockwise around the axis 03 or remotely by an electromagnetic drive 8. In this case, the levers 5 of the mechanism: ma free disengagement move the contact lever 3 to the right, overcoming the force of the opening spring 4. Ex: turning the lever 3 around the axis O, the arcing contacts 7 are closed, compressing their shock-absorbing spring, then the main ones 2: The switched on automatic machine becomes latch when the swivel joint Og is moved down.

Basic design of the circuit breaker
The machine is switched off manually by turning the handle counterclockwise or automatically and remotely when current flows through the winding of the opening electromagnet of the release 6. Its core moves the Og hinge upward and the rigid system of levers 5 "breaks" along the hinge. Trip spring 4 trips the circuit breaker. The arc arising between the contacts 1 is extinguished in the arc chamber by dividing into a number of arcs by metal plates 9.
A threaded automatic device with a combined release is shown in fig. 2. Turning on the machine manually by pressing button 1, turning off - button 2. When the machine is turned on, the current flows from the central contact 10 through fixed contacts 6 and 11 connected by a contact bridge 5, a bimetallic plate 13, a flexible connection 14, the winding of the electromagnetic release 15 to the threaded sleeve 7.
In the event of a short circuit, the core 16 of the electromagnet is pulled down, the latch lever 3 rotates around the axis O, releasing the lever 4. The movable system of the switch moves upward under the action of the compressed spring 9, the pusher 8 opens the contacts.
During prolonged overload, the bimetallic plate 12 heats up and bends, the latch pin 13 moves to the left, releasing the lever 4, and the machine turns off.
The appearance of the circuit breaker is shown in fig. 2, a. It is assembled in a plastic case, has a metal base with a thread, with which it is screwed into the threaded sleeve of the cork fuse base.


Rice. 2. Threaded circuit breaker: a - appearance; b - the principle of the device
Circuit breakers are widely used, in which manual control is carried out using Handle 8 (Fig. 3). , the thermal relay regulator 9. The control handle 8 is at the same time an indicator of the switch position: the upper position - the switch is on, the lower one - is off.

Rice. 3. Circuit breaker with control handle
Thus, circuit breakers are both switching and protective devices for low-voltage electrical circuits.