What type of protective characteristics of machines have. Circuit breakers: selection, connection, maintenance

20.06.2020

Topic: what types of electric machines are divided into, their types and classification.

The circuit breaker is an electrical device, the main purpose of which is to switch its operating state when a certain situation occurs. Electric automata combine two devices, this is a conventional switch and a magnetic (or thermal) release, the task of which is to timely break the electrical circuit in case the threshold value of the current is exceeded. Circuit breakers, like all electrical devices, also have different varieties, which divides them into certain types. Let's get acquainted with the main classifications circuit breakers.

1 "Classification of machines by the number of poles:

A) single-pole machines

b) single-pole machines with neutral

c) bipolar machines

d) three-pole machines

e) three-pole circuit breakers with neutral

e) four-pole machines

2» Classification of automata according to the type of releases.

into construction various kinds circuit breakers, usually, there are 2 main types of releases (breakers) - electromagnetic and thermal. Magnetic ones are used for electrical protection against short circuits, and thermal breakers are mainly designed to protect electrical circuits for a certain overload current.

3 "Classification of automata by tripping current: B, C, D, (A, K, Z)

GOST R 50345-99, according to the instantaneous tripping current, the automata are divided into the following types:

A) type "B" - over 3 In to 5 In inclusive (In is the rated current)

b) type "C" - over 5 In to 10 In inclusive

C) type "D" - over 10 In to 20 In inclusive

Machine manufacturers in Europe have a slightly different classification. For example, they have an additional type "A" (over 2 In to 3 In). Some manufacturers of circuit breakers also have additional tripping curves (ABB has circuit breakers with K and Z curves).

4 "Classification of automata according to the type of current in the circuit: constant, variable, both.

Rated electric currents for the main circuits of the release are selected from: 6.3; 10; sixteen; twenty; 25; 32; 40; 63; one hundred; 160; 250; 400; 630; 1000; 1600; 2500; 4000; 6300 A. Also, automatic machines for the rated currents of the main electrical circuits of automatic machines are also produced: 1500; 3000; 3200 A.

5 "Classification by the presence of current limitation:

a) current limiting

b) non-limiting

6 "Classification of machines by types of releases:

A) with overcurrent release

b) with independent release

c) with minimum or zero voltage release

7 "Classification of machines according to the time delay characteristic:

A) no time delay

b) with a time delay independent of the current

c) with a time delay inversely dependent on current

d) with a combination of these characteristics

8" Classification by the presence of free contacts: with contacts and without contacts.

9 "Classification of machines according to the method of connecting external wires:

A) with rear connection

b) with front connection

c) with combined connection

d) with universal connection (both front and rear).

10" Classification by type of drive: with manual, with motor and with spring.

P.S. Everything has its varieties. After all, if there were only one thing in its single copy, it would be at least just boring and too limited! The diversity is good because you can choose exactly what best suits your needs.

A circuit breaker, or, more simply, an automaton, is an electrical device that is familiar to almost everyone. Everyone knows that the machine turns off the network when there are some problems in it. If not to be wiser, then these problems are too much electric current. Excessive electric current is dangerous for the failure of all conductors and household electrical equipment, possible overheating, ignition and, accordingly, fire. Therefore, high current protection is a classic electrical circuits, and it existed at the dawn of electrification.

Any overcurrent protection device has two important tasks:

1) timely and accurately recognize too high current;

2) break the circuit before this current can cause any damage.

In this case, high currents can be divided into two categories:

1) high currents caused by network overload (for example, switching on a large number household electrical appliances, or a malfunction of some of them);

2) when the neutral and phase conductors are directly connected to each other, bypassing the load.

It may seem strange to someone, but it is with short-circuit overcurrents that everything is extremely simple. Modern electromagnetic releases easily and completely accurately determine the short circuit and turn off the load in a fraction of a second, preventing even the slightest damage to conductors and equipment.

With overload currents, everything is more complicated. Such a current does not differ much from the nominal one, for some time it can flow through the circuit without any consequences. Therefore, there is no need to turn off such a current instantly, especially since it could occur for a very short time. The situation is aggravated by the fact that each network has its own limiting overload current. And not even one.

Circuit breaker device

There is whole line currents, for each of which it is theoretically possible to determine its maximum network outage time, which ranges from several seconds to tens of minutes. But false positives must also be excluded: if the current is harmless to the network, then the shutdown should not occur in a minute or an hour - never at all.

It turns out that the overload protection trip setting must be adjusted for a specific load, its ranges must be changed. And, of course, before installing the overload protection device, it must be loaded and checked.

So, in modern "automatic machines" there are three types of releases: mechanical - for manual switching on and off, electromagnetic (solenoid) - for switching off short-circuit currents, and the most difficult - thermal for protection against overloads. It is the characteristic of thermal and electromagnetic releases that is circuit breaker characteristic, which is indicated by a Latin letter on the body before the number indicating the current rating of the device.

This feature means:

a) the range of operation of the overload protection, due to the parameters of the built-in bimetallic plate, which bends and breaks the circuit when a large electric current flows through it. Fine tuning is achieved by adjusting the screw that presses this very plate;

b) the operating range of the overcurrent protection, determined by the parameters of the built-in solenoid.

Below we list characteristics of modular circuit breakers, we will talk about how they differ from each other and what the machines that have them are intended for. All characteristics represent the relationship between the load current and the tripping time at this current.

1) Characteristic MA - no thermal release. In fact, it really is not always needed. For example, protection of electric motors is often carried out using overcurrent relays, and in such a case, an automatic machine is needed only for protection against short-circuit currents.

2) Feature A. The thermal release of an automaton of this characteristic can already work at a current of 1.3 of the nominal. In this case, the shutdown time will be about an hour. At a current that is twice the rated current, an electromagnetic release can come into action, which operates in about 0.05 seconds. But if, when the current is doubled, the solenoid still does not work, then the thermal release still remains “in play”, disconnecting the load in about 20-30 seconds. At a current that is three times the rated current, the electromagnetic release is guaranteed to operate in hundredths of a second.

Circuit breakers of characteristic A are installed in those circuits where short-term overloads cannot occur in normal operating mode. An example would be circuits containing devices with semiconductor elements capable of failing at a slight excess of current.

3) Characteristic V. The characteristic of these automata differs from characteristic A in that the electromagnetic release can only operate at a current that exceeds the rated current not by two, but by three or more times. The solenoid response time is only 0.015 seconds. The thermal release with a threefold overload of the machine B will work in 4-5 seconds. Guaranteed operation of the machine occurs with a five-fold overload for alternating current and at a load exceeding the nominal by 7.5 times in DC circuits.

Circuit breakers characteristic B are used in lighting networks, as well as other networks in which the starting current increase is either small or absent at all.

4) Characteristic C. This is the most known characteristic for most electricians. Automata C are distinguished by an even greater overload capacity compared to automata B and A. Thus, the minimum operating current of the electromagnetic release of the automaton of characteristic C is five times the rated current. At the same current, the thermal release trips after 1.5 seconds, and the guaranteed operation of the electromagnetic release occurs at a tenfold overload for alternating current and at a 15-fold overload for DC circuits.

Characteristics of circuit breakers B, C and D

5) Characteristic D- has a very high load capacity. The minimum operating current of the electromagnetic solenoid of this machine is ten rated currents, and the thermal release can operate in 0.4 seconds. Guaranteed operation is provided with a twenty-fold current overload.

Circuit breakers characteristic D are intended, first of all, for connection of the electric motors having big starting currents.

6) K characteristic has a large spread between the maximum solenoid actuation current in AC and DC circuits. The minimum overload current at which the electromagnetic release can operate is eight rated currents for these machines, and the guaranteed operating current of the same protection is 12 rated currents in the AC circuit and 18 rated currents in the DC circuit. The operating time of the electromagnetic release is up to 0.02 seconds. The thermal release of the machine K can operate at a current exceeding the rated current by only 1.05 times.

Due to such features of the characteristic K, these machines are used to connect a purely inductive load.

7) Z characteristic also has differences in the currents of guaranteed operation of the electromagnetic release in AC and DC circuits. The minimum possible operating current of the solenoid for these machines is two rated, and the guaranteed operating current of the electromagnetic release is three rated currents for AC circuits and 4.5 rated currents for DC circuits. The thermal release of automata Z, like that of automata K, can operate at a current of 1.05 of the nominal.

Z machines are used only for connecting electronic devices.

Alexander Molokov

Electrical overloads are common. To protect appliances powered by electricity from such voltage drops, circuit breakers were invented. Their task is simple - to break the electrical circuit if the voltage exceeds the nominal limits.

The first such devices were plugs familiar to everyone, which are still in some apartments. As soon as the voltage jumps above 220 V, they are knocked out. Modern types of circuit breakers are not only plugs, but also many other varieties. Their remarkable feature is the possibility of repeated use.

Classification

Modern GOST 9098-78 distinguishes 12 classes of circuit breakers:

This classification of circuit breakers is very convenient. If you wish, you can figure out which of the devices to install in the apartment, and which for production.

Types (kinds)

GOST R 50345-2010 divides circuit breakers into the following types(the division occurs according to sensitivity to overloads), marked with letters of the Latin alphabet:

These are the main circuit breakers used in residential buildings and apartments. In Europe, the marking begins with the letter A - the most sensitive circuit breakers to overloads. They are not used for domestic needs, but are actively used to protect the power supply circuits of precision instruments.

There are also three more markings - L, Z, K.

Distinctive design features

Automatic devices consist of the following units:

main contact system;
arc chute;
the main drive of the release device;
various types of release;
other auxiliary contacts.

The contact system can be multistage (one-, two- and three-stage). It consists of arcing, main and intermediate contacts. Single-stage contact systems are mainly made from sintered metal.

In order to somehow protect parts and contacts from the destructive force of an electric arc, reaching 3,000 ° C, an arc chute is provided. It consists of several arc quenching grids. There are also combined devices that can extinguish a high current electric arc. They contain slit chambers along with a grille.

For any circuit breaker, there is a current limit. Due to the protection of the machine, it can not lead to breakage. With huge overloads of such a current, the contacts can either burn out or even weld to each other. For example, for the most common household appliances with a trip current from 6 A to 50 A, the current limit can be from 1000 A to 10,000 A.

Modular designs

Designed for small currents. Modular automatic switches consist of separate sections (modules). The whole structure is mounted on a DIN rail. Let's consider in more detail the device of the modular switch:

On / off is made by a lever.
The terminals to which the wires are connected are screw.
The device is fixed to the DIN rail with a special latch. This is very convenient, because such a switch can be easily dismantled at any time.
The connection of the entire electrical circuit is made due to the movable and fixed contacts.
Disconnection occurs with the help of some kind of release (thermal or electromagnetic).
Contacts are specially placed next to the arc chute. This is due to the occurrence of a powerful electric arc during the disconnection of the connection.

VA series - industrial switches

Representatives of these machines are primarily intended for use in AC circuits of 50-60 Hz, with an operating voltage of up to 690 V. They are also used for direct current of 450 V and current strength of up to 630 A. Such switches are designed for very rare operational use ( no more than 3 times per hour) and protection of lines from short circuit and electrical overload.

Important features of this series include:

high breaking capacity;
a wide range of electromagnetic releases;
button for testing the device with free tripping;
load break switches with special protection;
remote control through a closed door.

AP series

Automatic circuit breaker ap is able to protect electrical installations, motors from sudden voltage surges and short circuits within the network. The launches of such mechanisms are not intended to be very frequent (5-6 times per hour). Automatic switch ap can be two-pole and three-pole.

Everything structural elements located on a plastic base, which is closed from above with a lid. In case of large overloads, the free tripping mechanism is activated, and the contacts open automatically. At the same time, the thermal release withstands the operating time, and the electromagnetic release provides instantaneous disconnection in the event of a short circuit.

When operating the machine, it is desirable to adhere to the following conditions:

With air humidity of 90%, the temperature should not exceed 20 degrees.
The operating temperature ranges from -40 to +40 degrees.
Vibration at the attachment point should not exceed 25 Hz.

It is strictly forbidden to work in an explosive atmosphere containing gases that destroy metal and winding, near the pure energy of heating devices, water flows and splashes, in places with conductive dust.

The variety of circuit breakers allows you to easily choose a device for an apartment or house. It is best to invite a specialist to install it.

To ensure that all equipment in the house or at work is protected from voltage surges electric current you need to install special circuit breakers. They will be able to fix the jump and quickly respond to it by turning off the entire system from the electricity supply. A person cannot do this on his own, but a machine of a certain type can do it in a few seconds.

Device sensitivity

Before you get acquainted with the types of machines, you need to find out with what sensitivity the devices are suitable for home use, and which ones will be inappropriate. Such an indicator will indicate how quickly the device will respond to a power surge. It has several markings:

A- used for super sensitive types of machines. They instantly detect a jump in the network and also instantly respond to it. Most often they are used in production to protect expensive equipment. Practically not suitable for domestic purposes.

V- such marking is applied to those types of circuit breakers that react with a slight delay. Manufacturers of expensive household appliances install them to protect the device itself. If a small failure occurs, then the device reacts to it itself and at the same time does not turn off the entire network in the house.
WITH those machines that are able to turn off the household network with a significant increase or decrease in voltage have the marking. If the jump is small, then the device may turn off for a while, but then return to normal operation.
Marking machine D installed only in the shield that connects the house or apartment to common system. Its sensitivity to power surges is minimal, so it is only a fallback option. If the voltage drop is very large, then the entire house or apartment is disconnected from the electrical network.

Classification of automata

There are different types of automata in relation to the type of current, rated voltage or current indicator and others. technical specifications. Therefore, you need to specifically understand each item separately.

Current type

In relation to this characteristic, the machines are divided into:

For work in the alternating current network;
For work in a network of a direct current;
Universal models.

Everything is clear here and no further explanation is needed.

In terms of rated current

The value of this characteristic will depend on the network with what maximum value the circuit breaker can operate. There are devices that can operate from 1 A to 100 A and more. The minimum value with which machines can be found on sale is 0.5 A.

Rated voltage indicator

This characteristic indicates with what voltage this type of circuit breakers can operate. Some can work in a network with a voltage of 220 or 380 volts - these are the most common options for domestic use. But there are machines that will do just fine with higher rates.

The ability to limit the flow of electricity

According to this characteristic, there are:

Current limiting - immediately eliminate the access of electric current to the device. Therefore, during a short circuit, neither the device nor the electrical network wiring is damaged.
Non-limiting - work much slower.

Other characteristics

The number of poles can be from one to four. Accordingly, they are called single-pole, two-pole, and so on.

According to the structure, they distinguish:

Air;
Modular;
Molded case circuit breakers.

According to the drop rate, high-speed, normal and selective devices are produced. They can be set with a time delay function that can be inversely dependent on the current or independent of it. The time delay may or may not be set.

Automatic machines also have a drive, which can be manual, connected to an engine or a spring. The switches differ both in the presence of free contacts and in the method of connecting the conductors.

An important characteristic will be protection against impact environment. Here you can highlight:

IP protection;
From mechanical impact;
Current conduction of the material.

All characteristics can be combined in various combinations. It all depends on the model and manufacturer.

Switch types

The machine inside contains a release, which, with the help of a lever, latch, spring or rocker, is able to instantly disconnect the network from the supply of electricity. Types of circuit breakers and are distinguished by the type of release. There are:

Circuit breaker with magnetic release - responds to surges instantly. Well suited for networks where short circuits often occur. The release is a moving core solenoid. During the jump, the core is drawn in and the circuit is opened. Responds in a split second.
Thermal circuit breaker - protects the electrical network from excessive load. The release is represented by a bimetallic plate. Under the influence of a current with an increased value, the plate heats up and bends, thereby turning off the electricity supply. These types of machines are able to respond from a few seconds or up to 1 minute to overvoltage. It all depends on what indicators the device is designed for.

Circuit breakers are much more profitable than fuses. This is because after cooling, the machine can already be turned on, and it will work as it should if the cause of the overload is eliminated. The fuse needs to be replaced. It may not be available and replacement may take a long time.

infoelectric.ru

Topic: what types of electric machines are divided into, their types and classification.

The circuit breaker is an electrical device, the main purpose of which is to switch its operating state when a certain situation occurs.

electric tomatoes combine two devices, this is a conventional switch and a magnetic (or thermal) release, the task of which is to timely break the electrical circuit in case the threshold value of the current is exceeded. Circuit breakers, like all electrical devices, also have different varieties, which divides them into certain types. Let's get acquainted with the main classifications of circuit breakers.

1 "Classification of machines by the number of poles:

a) single-pole machines

b) single-pole machines with neutral

c) bipolar machines

d) three-pole machines

e) three-pole circuit breakers with neutral

e) four-pole machines

2» Classification of automata according to the type of releases.

The design of various types of circuit breakers usually includes 2 main types of releases (openers) - electromagnetic and thermal. Magnetic ones are used for electrical protection against short circuits, and thermal breakers are mainly designed to protect electrical circuits for a certain overload current.

3 "Classification of automata by tripping current: B, C, D, (A, K, Z)

GOST R 50345-99, according to the instantaneous tripping current, the automata are divided into the following types:

a) type "B" - over 3 In to 5 In inclusive (In is the rated current)

b) type "C" - over 5 In to 10 In inclusive

C) type "D" - over 10 In to 20 In inclusive

4 "Classification of automata according to the type of current in the circuit: constant, variable, both.

5 "Classification by the presence of current limitation:

a) current limiting

b) non-limiting

6 "Classification of machines by types of releases:

a) with overcurrent release

b) with independent release

c) with minimum or zero voltage release

7 "Classification of machines according to the time delay characteristic:

a) no time delay

b) with a time delay independent of the current

c) with a time delay inversely dependent on current

d) with a combination of these characteristics

8" Classification by the presence of free contacts: with contacts and without contacts.

9 "Classification of machines according to the method of connecting external wires:

a) with rear connection

b) with front connection

c) with combined connection

d) with universal connection (both front and rear).

10" Classification by type of drive: with manual, with motor and with spring.

electrohobby.ru

Automatic protective switches: classification and differences

In addition to residual current devices that are not used individually, there are 3 types of circuit breakers. They work with loads of different sizes and differ from each other in their design. These include:

Modular AV. These devices are mounted in household networks in which currents of insignificant magnitude flow. They usually have 1 or 2 poles and a width that is a multiple of 1.75 cm.

Cast switches. They are designed to work in industrial networks, with currents up to 1 kA. Made in a cast case, which is why they got their name.
Air electric machines. These devices are available with 3 or 4 poles and can withstand currents up to 6.3 kA. Used in electrical circuits with high power installations.

There is another type of circuit breaker - differential. We do not consider them separately, since such devices are ordinary circuit breakers, which include an RCD.

Release types

The releases are the main working components of the AB. Their task is to break the circuit when the permissible current value is exceeded, thereby stopping the supply of electricity to it. There are two main types of these devices, which differ from each other in the principle of decoupling:

Electromagnetic.
Thermal.

Electromagnetic type releases provide almost instantaneous operation of the circuit breaker and de-energize the circuit section when an overcurrent short circuit occurs in it.

They are a coil (solenoid) with a core drawn in under the influence of a large current and causing the tripping element to operate.

The main part of the thermal release is a bimetallic plate. When a current exceeding the rated value of the protective device passes through the machine, the plate begins to heat up and, bending to the side, touches the disconnecting element, which operates and de-energizes the circuit. The time for the thermal release to operate depends on the magnitude of the overload current passing through the plate.

Some modern devices are equipped as an option with minimum (zero) releases. They perform the function of turning off the AV when the voltage drops below the limit value corresponding to the technical data of the device. There are also remote releases, with which you can not only turn off, but also turn on the AB, without even approaching the switchboard.

The presence of these options significantly increases the cost of the device.

Number of poles

As already mentioned, the circuit breaker has poles - from one to four.

It’s not difficult to choose a device for a circuit according to their number, you just need to know where they are used different types AB:

Single terminals are installed to protect lines that include sockets and lighting fixtures. They are mounted on a phase wire without capturing zero.
The two-pole must be included in the circuit to which it is connected Appliances with sufficiently high power (boilers, washing machines, electric stoves).
Three-terminal networks are mounted in networks of a semi-industrial scale, to which devices such as borehole pumps or workshop equipment.
Four-pole ABs allow you to protect electrical wiring with four cables from short circuits and overloads.

The use of machines of different poles - in the following video:

Characteristics of circuit breakers

There is another classification of machines - according to their characteristics. This indicator indicates the degree of sensitivity of the protective device to the excess of the rated current. The corresponding marking will show how quickly the device will react in the event of an increase in current. Some types of ABs work instantly, while others take time.

There is the following marking of devices according to their sensitivity:

A. Breakers of this type are the most sensitive and respond instantly to an increase in load. They are practically not installed in household networks, protecting circuits with high-precision equipment with their help.
B. These circuit breakers operate with a slight delay when the current increases. Usually they are included in lines with expensive household appliances (LCD TVs, computers, and others).
C. Such devices are the most common in household networks. Their shutdown does not occur immediately after the increase in current strength, but after a while, which makes it possible to normalize it with a slight difference.
D. The sensitivity of these devices to the increase in current is the lowest of all the listed types. They are most often installed in shields on the approach line to the building. They provide insurance for apartment machines, and if for some reason they do not work, they turn off the general network.

Features of the selection of machines

Some people think that the most reliable circuit breaker is the one that can handle the most current, which means it can provide the most circuit protection. Based on this logic, an air-type machine can be connected to any network, and all problems will be solved. However, this is not at all the case.

To protect circuits with different parameters, it is necessary to install devices with appropriate capabilities.

Mistakes in the selection of AB are fraught with unpleasant consequences. If you connect a high-power protective device to a normal household circuit, it will not de-energize the circuit, even when the current value is much higher than that which the cable can withstand. The insulating layer will heat up, then start to melt, but no shutdown will occur. The fact is that the current strength, which is destructive for the cable, will not exceed the AB rating, and the device will “think” that emergency did not have. Only when the melted insulation causes a short circuit will the machine turn off, but by that time a fire may already have started.

Here is a table that shows the ratings of machines for various electrical networks.

If the device is designed for less power than that which the line can withstand and which the connected devices have, the circuit will not be able to work normally. When the equipment is turned on, the AB will constantly knock out, and eventually, under the influence of high currents, it will fail due to “sticky” contacts.

Clearly about the types of circuit breakers in the video:

Conclusion

The circuit breaker, the characteristics and types of which we examined in this article, is a very important device that protects the electrical line from damage by powerful currents. The operation of networks that are not protected by automatic machines is prohibited by the Electrical Installation Rules. The most important thing is to choose the right type of AB that is suitable for a particular network.

yaelectric.ru

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Release definition

circuit breakers;
releases performing auxiliary functions.

independent release (remote shutdown of the circuit breaker by a signal from the auxiliary circuit);
undervoltage release (turns off the machine when the voltage drops below the permissible level);
release zero voltage(causes disconnection of contacts with a significant voltage drop).

Definitions of terms found below

Types of releases used in circuit breakers

provide basic overcurrent protection, factory settings do not change during operation:
- thermal release or overload release;
- electromagnetic release or short circuit release;

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- semiconductor release;
- electronic release;

additional trip units for extending the functionality:
- independent release;
- undervoltage release;
- zero voltage release.

Thermal release

conditional non-trip current 1.05 In (time 1 hour for In ≤ 63A and 2 hours for In ≥ 80A);
conditional tripping current 1.3 In for AC and 1.35 In for DC.

no rubbing surfaces;
have good vibration resistance;
easily tolerate pollution;
simplicity of design → low price.

constantly consume electrical energy;
sensitive to changes in ambient temperature;
when heated from third party sources may cause false positives.

Electromagnetic release

3.5 In;
7 In;
10 In;
12 In;
other.

B(3-5);
C(5-10);
D(10-50).

simplicity of design;

creates a magnetic field;
works instantly, without time delay.

Thermal magnetic or combined release

Semiconductor release

adjustment of the rated current of the machine;
setting the exposure time in the short circuit zone, as well as overload;
operation setting in the event of a short circuit;
switches for protection against switching currents, from single-phase short circuit;
a switch that disables the time delay in case of short circuit (transition from the selectivity mode to the instantaneous mode).

a wide range of adjustments for the most complex schemes power supply;
ensuring selectivity (selectivity), relative to series-connected automata with lower amperages.

high price;
fragile controls.

Electronic release

a variety of settings for the user;
high accuracy of execution of a given program;
health indicators and causes of operation;
logic selectivity with upstream and downstream switches.

high price;
fragile control unit;
exposure to electromagnetic fields.

Shunt release

Undervoltage release

disconnects the switched on circuit breaker without time delay when the voltage drops from 0.7 to 0.35 from Un;
if the voltage is higher than 0.7 Un, no shutdown is performed;
prevents reclosing if the mains voltage is lower than 0.85 Un.

After the device has tripped, manual cocking of the free trip mechanism is required, unless a solenoid drive is installed.

Zero voltage release

causes disengagement of the main contacts at a voltage of 0.35 to 0.1 of the nominal;
does not turn off the switched on machine at a voltage of more than 0.55 Un;
allows re-closing when the voltage is restored more than 0.85 of the nominal.

As in the case of the undervoltage release, manual cocking of the machine is required, and then turning it on.

More about the device of an independent trip device, zero and undervoltage release С‡РёС‚Р°Р№ Р·РґРµСЃСЊ.

Phenomena caused by overcurrents

When a short circuit current occurs, the following phenomena occur:

electrodynamic forces;
a magnetic field;
thermal stress (overheating).

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Circuit breakers are not at all like the usual ones that are installed in every room to turn the light on and off (Fig. 1). Their task is somewhat different. Circuit breakers are installed in switchboards and serve to protect the circuit from power surges and non-periodic power outages in certain sections of the power grid.

Rice. one.

Automata, as they are often called, are installed at the entrance to a house or apartment and are located in special boxes, metal or plastic (Fig. 2).

Rice. 2. Distribution board with automatic machines

There are many types of circuit breakers. Some of them serve only as circuit breakers and protect the network from overload. Such are, for example, the old AE type circuit breakers in a black carbolite case (Fig. 3).

Rice. 3. AE series circuit breaker

In most of the old shields in the porches residential buildings they are worth it. However, they are quite reliable and are still in operation.
Modern variations allow additional functions, such as undercurrent protection.

According to the response time to an unacceptable voltage, the automata are divided into 3 types: selective, normal and high-speed. The response time of a normal machine ranges from 0.02 to 0.1 s. In selective circuit breakers, this time is the same. High-speed circuit breakers work faster - they have this value is only 0.005 s.

All circuit breakers are enclosed in a plastic unbreakable case with a special fastening (bar or rail) on the rear plane. Installing the machine on such a mount is very easy - just insert it on the rail until it clicks. You can remove it with a screwdriver by gently pulling on the special tab on top of the circuit breaker. This greatly simplifies the task of installing the machine in a cabinet (Fig. 4).

Rice. 4.

Inside the case is the "stuffing" of the machine, its main safety devices, which can be 2 (Fig. 5).

Rice. 5. Internal

We are talking about electromagnetic and thermal releases - peculiar mechanisms for automatically breaking the circuit. A bimetallic plate, when heated by an unacceptably high current passing through it, straightens and opens the contacts - this is a thermal release. In terms of response time, it is the slowest.

The electromagnetic release operates according to the rule " dead hand". The coil located in the center of the machine is continuously kept in place by a stable voltage. As soon as he jumps out of the nominal limits, the coil literally jumps out of its place, breaking the circuit. This way of breaking the chain is the fastest.
All circuit breakers have contacts for connecting incoming and outgoing wires (Fig. 6).

Rice. 6. Wires are connected to the contacts of the circuit breaker using screw terminals

Automata are distinguished by the degree of sensitivity to tripping. In the standard most common models, circuit breakers with a threshold value approximately equal to 140% of the nominal are most often used. With an increase in voltage by one and a half times, an electromagnetic (fast) release is triggered. With a slight excess of the rated voltage, the thermal release operates. The shutdown process can take hours, which is highly dependent on the ambient temperature. However, the machine will react to voltage changes in any case.

Circuit breakers are distinguished by the number of poles. What does it mean? In one machine there can be several independent from each other electrical lines, which are interconnected by a common shutdown mechanism (Fig. 7 and 8). Automatic machines are one-, two-, three- and four-pole (this applies to domestic use).

Rice. 7. in a plastic box in the off state

Rice. 8. : all lines are triggered at the same time when disconnected, they are connected together with one lever jumper

The circuit breaker has differences in other indicators. They differ in the threshold current strength that they pass through themselves. In order for the machine to work and turn off the power supply in an emergency, it must be set to a certain sensitivity threshold. This setting is made by the manufacturer, so they immediately write on the machine numerical value this threshold. For domestic needs, machines with indicators of 6.3, 10, 16, 25, 32, 40, 63, 100 and 160 A are used (Fig. 9). There are machines with values of both 1000 and 2600 A, but they are not used in everyday life. These figures mean the total power of all consumers of electric current that will be connected to the circuit "guarded" by the machine.
Machine sensitivity it is necessary to calculate not only by the total power of the proposed energy consumers, but also by wiring and electrical installation products - sockets and switches.
Table 1 shows the typology of automata.

Table 1. Types of machines

A type	Purpose
A	For opening circuits with a large length of electrical wiring and protecting semiconductor devices
B	For lighting networks of general purpose
C	For lighting circuits and electrical installations with moderate starting currents (motors and transformers)
D	For circuits with active-inductive loads, as well as protection of electric motors with high starting currents
K	For inductive loads
Z	For electronic devices

Table 2. Two-core copper cable laid in a conduit

Section, mm2		Cable current/1.45, A	Automatic, A	Excess current, %
1,5	19	13,1	13	—
2,5	27	18,62	16	—
4	38	26,2	25	—
6	50	34,48	32	—
10	70	48,27	40(50)	3,5
16	90	62,06	50(63)	1,5

Table 3. Two-core copper wire laid in a box

Section, mm2	Maximum continuous cable current, A	Cable current/1.45, A	Automatic, A	Excess current, %
1	15	10,34	10	—
1,5	18	12,41	10(13)	4,7
2	23	15,86	13(16)	0,87
2,5	25	17,24	16	—
4	32	22,06	20	—
6	40	27,58	25	—
10	48	33,1	32	—
16	55	37,93	32(40)	5,4

The maximum continuous current of the cable is assumed for core temperature +65 and air +25 °C. The number of simultaneously laid conductors is up to 4. A number of automatic machines: 0.5 A, 1 A, 2 A, 3 A, 4 A, 6 A, 10 A, 13 A, 16 A, 20 A, 25 A, 32 A, 40 A, 50 A and 63 A. Data in Table. 3 are also suitable for a three-core cable. In this case, the third core must be a wire protective earth or nulls.

Rice. 9. A row of 16 A single-pole automata. Let's say for a separate section in an apartment, for example, a kitchen, we have one 6.3 A automaton (it happens, too - the electricians were joking). According to the well-known formula Watt \u003d Volt x Ampere, we calculate how many devices (and which ones) can be powered from our network. It turns out that this value is equal to 1386 W, since the default voltage is 220 V. This means that even a powerful kettle cannot be turned on in such a kitchen, not to mention a refrigerator or electric stove - the machine will work instantly and will not allow unacceptable, in its opinion, current to pass through controlled territory. In this case, it is urgent to change the circuit breaker to 25 or even 32 A.