In the event of an emergency in the electrical network - a short circuit, fire or electric shock to a person, it must be immediately de-energized. Previously, this function was performed by fuses. Their main disadvantage is that they turn off only one, and most often only the phase, line.
And according to today's rules for the operation of electrical installations, a complete break is required. In addition, they do not act quickly enough and after operation they must be replaced. These shortcomings are deprived of automatic fuses and switches.
The family of electrical devices, which in everyday use is often called an "electric machine", is very diverse. If such a comparison is allowed, it consists of several clans, differing in the type of influence to which they respond, as well as in design.
Depending on this, they are used to protect the entire electrical network as a whole, individual circuits and devices, or a person. There is also an intra-clan division. For example, in terms of speed.
Types of circuit breakers by type of impact:
- Operation from overcurrents (short circuit) and heating. The most common type. They are used to protect the entire power supply circuit (introductory machines) or individual devices.
- Response to differential current. These are the so-called RCDs - residual current devices that are used to prevent electric shock to a person.
- Thermal relays. Used in electric drives to protect electric motors from overloads.
Design differences:
- AP series. The so-called apeshki are large black boxes made of electrical plastic with two buttons: ON (white) and OFF (red). They react to heat and overcurrents. Usually used in three-phase networks to protect individual devices. Reliable massive design, considered obsolete.
- Series VA. A modern small-sized device with an on-off lever located horizontally.
- Automatic fuses. Replaced the so-called plugs with Edison E14 threaded base. Also outdated, but still widely used in household electrical networks design.
Depending on the number of connection points, which are called poles, switches are one-, two-, three- and four-pole.
Single-pole switches only one line, usually a phase line. They are used in low-load electrical circuits. For example, lighting. Their second name is “modular circuit breakers”, since they are usually assembled in a package (several on one DIN rail) and placed in a switchboard, next to a common zero bus. They also include automatic fuses, the input of which is the central contact, and the output is a threaded ring.
Bipolar are used in single-phase networks to protect the entire electrical circuit, then they are called introductory, or one device.
Three- and four-pole devices are used to work in three-phase networks, in which there can be three (in the case of a solidly grounded neutral) or four conductors.
Device of automatic switches
The principle of the design of switches that respond to overcurrents and overheating is the same as for devices such as AP, VA or automatic fuses. Type BA switches have screw terminals. A movable contact is connected to the input, which is connected to the control lever by a system of levers and springs.
In the on state, it has electrical contact with an electromagnetic release - a solenoid with a movable core-rod. The conductor at its output is connected to another control element - a bimetallic plate resting against the stem. An additional element of the device is an arc chute - a package of plates made of electrical fiberboard.
The release is designed to operate when a current of a certain rating passes through its coil. When this value is reached, the solenoid pushes the stem and opens the contact. Please note that the bimetal is connected to the output terminal. Therefore, there is a significant difference in how to put the circuit breaker. Flipped upside down, it stops responding to a short due to the additional plate resistance.
Residual current circuit breakers
They are called RCDs - residual current devices. Outwardly, they are very similar to VA machines, differing only in the "Test" button. Fundamental differences in the device of the electromagnetic release. It is based on a differential transformer.
Its primary winding is made up of two coils, to which the phase and neutral wires are connected. The secondary winding is connected by a solenoid. In the normal state, the currents in the phase and neutral conductors are equal in magnitude, but opposite in phase. They cancel each other out and no electromagnetic field is induced in the primary winding.
With a partial breakdown of the insulation and the connection of the phase line to the ground loop, the balance is disturbed, a magnetic flux occurs in the primary winding, which generates an electric current in the secondary. The solenoid activates and opens the contact.
This happens if, for example, a person takes an electrical appliance with his hand, the case of which is shorted to a phase. These devices do not protect either from a short circuit or from overheating, so they are placed in series with VA circuit breakers. And definitely after them. Read about the correct connection.
Differential switches
They are also called automatic differential current switches - the abbreviation of RCBO. They combine the automatic VA and RCD. Their use simplifies the electrical circuit and its installation - instead of two devices, you can put one.
It is possible to distinguish an RCBO from an RCD by a schematic representation on the front panel, which is not always possible due to insufficient technical literacy, or by a letter in front of the denomination number and its value. More about it.
The residual current device can be written, for example, I n 16A and I ∆n 10 mA. The first value is the rated current of the circuit in which the device can operate. Note that there is no letter before it. The second is the trip current, it never exceeds a few amperes. RCBO is marked differently: C16 10 mA. The letter C is the time-current characteristic.
Time-current characteristics of circuit breakers
Depending on the design of the electromagnetic release solenoid, the circuit breaker can operate at different speeds. This is called the time characteristic. The main ones are:
- A - the fastest possible response. It is necessary to protect semiconductor circuits sensitive to the quality of electricity. The device can only work in tandem with a compensation type stabilizer. It is better not to use it at home, since the quality standards for household networks are low, it will constantly work.
- B - increased sensitivity, but the response time is reduced. Can be used to protect power supply circuits of local area networks.
- C is the most common type of appliance used in everyday life. Satisfactory sensitivity and average response speed.
- B - industrial version with reduced sensitivity. It is used in networks with large amplitudes of voltage drops. For example, connected to traction substations of electric transport.
Circuit breakers are an important element of the electrical circuit. The operation of electrical installations without them can lead to a man-made disaster of a local nature and endanger the life of the operating personnel.
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 (division occurs according to sensitivity to overloads), marked with Latin letters:
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.
All structural elements are located on a plastic base, which is closed with a lid on top. 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.
Production automation- this is a process in the development of machine production, in which the functions of control and control, previously performed by a person, are transferred to instruments and automatic devices. The introduction of automation in production can significantly increase labor productivity and product quality, reduce the proportion of workers employed in various areas of production.
Before the introduction of automation tools, the replacement of physical labor took place through the mechanization of the main and auxiliary operations of the production process. Intellectual labor for a long time remained non-mechanized (manual). Currently, operations of physical and intellectual labor, amenable to formalization, are becoming the object of mechanization and automation.
Modern manufacturing systems that provide flexibility in automated manufacturing include:
CNC machines first appeared on the market in 1955. Mass distribution began only with the use of microprocessors.
Industrial robots first appeared in 1962. Mass distribution is associated with the development of microelectronics.
· Robotized technological complex (RTC), first appeared on the market in 1970-80s. Mass distribution began with the use of programmable control systems.
· Flexible production systems, characterized by a combination of technological units and computer-controlled robots, with equipment for moving workpieces and changing tools.
Automated warehouse systems Automated Storage and Retrieval Systems, AS/RS). Provide for the use of computer-controlled lifting and transport devices that lay products in the warehouse and remove them from there on command.
computer-based quality control systems Computer-aided Quality Control, CAQ) - a technical application of computers and computer-controlled machines for checking the quality of products.
· Computer-aided design system Computer-aided Design, CAD) is used by designers in the development of new products and technical and economic documentation.
Planning and linking individual elements of the plan using a computer (eng. Computer-aided Planning, CAP). SAR- is divided according to various characteristics and purposes, according to the state of approximately the same elements.
COMPUTER (electronic computer)
Outline the main provisions of the technology of cleaning and washing operations. Compare cleaning and washing equipment and justify its choice. Evaluate the possibilities of designing a cleaning and washing station.
Washing work is often carried out manually using a hose with a gun and a pump of low (0.3-0.4 MPa) or high (1.5-2.0 MPa) pressure or mechanized using washing installations. A progressive way is mechanized and automatic washing of cars, automotive components and parts, which allows you to replace manual labor as much as possible and increase labor productivity with high-quality washing.
So, consider the main existing types of car washes:
A hand wash is a traditional car wash performed by humans. The car is washed with water and car shampoo using sponges, brushes, rags, etc., that is, contact washing.
The advantage of a manual car wash is that a person in the process of work sees which areas are more polluted and need more thorough cleaning.
Cons: with such a wash, there is a high risk of damaging the paintwork on the car body; and hand washing the car will take the most time.
A brush car wash is a contact wash, in which people do not participate, it is carried out using special automatic installations. The process consists of several stages: first, the machine is washed with water under pressure, then with hot foam, then quickly rotating brushes are taken to clean the machine of dirt. The last step is to apply protective wax and dry the car.
A brush washer is suitable for tough dirt that a touchless washer might not be able to handle. Brushes are made of synthetic threads, rounded at the ends. High-quality brushes should not scratch the paintwork.
Touchless car wash is a wash with active foams. This technology is used in conventional non-contact car washes, where washing is carried out by people using special devices, as well as in conveyor and portal car washes. During such a wash, the main layer of dirt is washed off with a high-pressure water jet, then active foam is applied with special equipment, under the action of which the remaining dirt lags behind the body, and after a while the foam is also washed off with a stream of water under pressure. As a rule, such a wash ends with the application of a protective polish, which will give an attractive shine and protect against rapid pollution and the harmful effects of the environment.
A touchless car wash or pressure washer causes the least damage to the body paintwork.
Dry washing is washing with a special shampoo-polish. Motorists carry out such a wash with their own hands. This wash does not require water. Dry shampoo manufacturers claim that the silicone oil and surfactants (surfactants) in the shampoo soften, soak and coat dirt particles, ensuring the integrity of the paintwork in this type of washing. Dry washing for a while will provide shine and protection of the body from the effects of negative environmental factors.
The disadvantage of such a wash is the impossibility or inconvenience of processing hard-to-reach places in the car. Therefore, this type of washing is recommended to be used in between water washes to keep the car clean and tidy.
There are two types of automatic car washes:
Conveyor type (or tunnel). This is when the vehicle is slowly conveyed through several archways with various cleaning and rinsing functions (for example: pre-wash, wheel wash, underbody wash, high pressure wash, dryer).
The biggest plus of such car washes is the speed of work and high productivity. All arches work simultaneously, so the driver does not have to wait for the previous car to go through all the procedures.
portal type. With such a wash, the car is stationary, and the portal (washing arch) moves relative to it.
The disadvantage compared to the conveyor car wash is that the portal car wash is not able to quickly take such a number of cars.
Outline the main provisions of the technology of diagnostic work. Compare diagnostic equipment and justify its choice. Evaluate the possibilities of designing a post of diagnostic work
1.1. The Manual sets out the main provisions for organizing the diagnostics of the technical condition of the rolling stock of road transport in passenger cars, trucks, buses and mixed motor transport enterprises (ATP) of various capacities.
1.2. Technical diagnostics is part of the technological process of maintenance (TO) and repair (R) of vehicles, the main method for conducting control and control and adjustment work. In the ATP technical service management system, diagnostics is a subsystem of information.
1.3. The organization of vehicle diagnostics is based on the planned preventive maintenance and repair system in force in the USSR, set out in the "Regulations on the maintenance and repair of rolling stock of road transport."
1.4. In the conditions of ATP, technical diagnostics should solve the following tasks:
Refinement of failures and malfunctions identified during operation;
Identification of cars, the technical condition of which does not meet the requirements of traffic safety and environmental protection;
Identification of malfunctions before maintenance, the elimination of which requires labor-intensive repair or adjustment work in the current repair zone (TR);
Clarification of the nature and causes of failures or malfunctions identified in the process of maintenance and repair;
Forecasting the failure-free operation of units, systems and the car as a whole within the inter-inspection run;
Issuance of information on the technical condition of the rolling stock for planning, preparation and management of the production of maintenance and repair;
Quality control of the performed maintenance and repair work.
Vehicle diagnostic technology contains: list and sequence of operations, repeatability coefficients, labor intensity, category of work, tools and equipment used, technical conditions for the performance of work.
3.2. Depending on the shift program and the type of rolling stock, diagnostic work is carried out at separate posts (dead-end or through) or posts located in a line.
3.3. The technology is compiled separately for the types of diagnostics D-1, D-2 and others.
3.4. For specialized repair, adjustment and diagnostic posts, Dr technology is compiled for individual diagnosed units, systems and types of work (brake system, steering, wheel alignment, wheel balancing, headlight installation, etc.).
3.5. When developing a diagnostic technology, one should be guided by the established lists of diagnostic operations by types of diagnostics (Appendices 1, 2), which are part of the control work given in the current Regulations on the maintenance and repair of rolling stock of road transport, as well as a list of diagnostic features (parameters) and their limit values (Appendix 5).
3.6. A typical diagnostic technology should contain preparatory work performed before diagnosing, proper diagnosing, adjustment and final work performed based on the results of diagnosing.
3.7. The diagnostic technology D-1 and D-2 is compiled taking into account the specific conditions of the ATP.
3.8. Diagnostics at the posts (lines) in the scope of D-1 and D-2 are performed by diagnostic operators or diagnostic mechanics. Drivers are attached to them to help them, who, in addition to driving cars in the process of diagnosing, are engaged in placing cars at diagnostic posts, removing them, distilling to the appropriate zone (storage, waiting, MOT and TR), as well as preparatory and some adjustment work . In the ATP, where there are no full-time ferry drivers, this work is assigned to the drivers of the vehicles being diagnosed or column mechanics who have the right to drive.
Control and diagnostic (Dr) and adjustment operations at the posts of maintenance and repair are carried out by repair workers.
3.9. At posts (lines) D-1 and D-2, repair work related to the elimination of identified malfunctions, as a rule, is not performed. The exception is adjustment work, the implementation of which is provided for by the technological process in the process of diagnosing.
3.10. Performing diagnostic operations before maintenance and current repairs is mandatory, regardless of the availability of diagnostic tools. In the absence of the latter in the ATP, the control and diagnostic operations provided for by this "Manual ..." are performed subjectively by a diagnostician in order to identify the necessary volumes of current repairs performed before maintenance.
Circuit breakers are called devices that are responsible for protecting the electrical circuit from damage associated with exposure to a large current. Too strong a flow of electrons can damage household appliances, as well as cause overheating of the cable, followed by melting and ignition of the insulation. If the line is not de-energized in time, this can lead to a fire. Therefore, in accordance with the requirements of the PUE (Electrical Installation Rules), the operation of a network in which electric circuit breakers are not installed is prohibited. AB have several parameters, one of which is the time-current characteristic of the automatic protective switch. In this article we will tell you how circuit breakers of categories A, B, C, D differ and which networks they are used to protect.
Features of the operation of circuit breakers
Whatever class the circuit breaker belongs to, its main task is always the same - to quickly determine the occurrence of excessive current, and de-energize the network before the cable and devices connected to the line are damaged.
Currents that can be dangerous to the network are divided into two types:
- overload currents. Their appearance most often occurs due to the inclusion of devices in the network, the total power of which exceeds that which the line can withstand. Another cause of overload is a malfunction of one or more devices.
- Overcurrents caused by short circuit. A short circuit occurs when the phase and neutral conductors are connected to each other. In the normal state, they are connected to the load separately.
The device and principle of operation of the circuit breaker - in the video:
Overload currents
Their value most often slightly exceeds the nominal value of the machine, so the passage of such an electric current through the circuit, if it does not drag on for too long, does not cause damage to the line. In this regard, in this case, an instantaneous de-energization is not required; moreover, the magnitude of the electron flow often quickly returns to normal. Each AB is designed for a certain excess of electric current at which it works.
The operating time of the protective circuit breaker depends on the magnitude of the overload: with a slight excess of the norm, it can take an hour or more, and with a significant one - a few seconds.
The thermal release, which is based on a bimetallic plate, is responsible for turning off the power under the influence of a powerful load.
This element is heated under the influence of a powerful current, becomes plastic, bends and triggers the machine.
Short circuit currents
The flow of electrons caused by a short circuit greatly exceeds the rating of the protection device, as a result of which the latter immediately operates, turning off the power. An electromagnetic release, which is a solenoid with a core, is responsible for detecting a short circuit and the immediate reaction of the device. The latter, under the influence of overcurrent, instantly acts on the circuit breaker, causing it to trip. This process takes a fraction of a second.
However, there is one nuance. Sometimes the overload current can also be very high, but not caused by a short circuit. How is the machine supposed to tell the difference between them?
On the video about the selectivity of circuit breakers:
Here we smoothly move on to the main issue to which our material is devoted. There are, as we have already said, several AB classes that differ in their time-current characteristics. The most common of these, which are used in household electrical networks, are devices of classes B, C and D. Circuit breakers belonging to category A are much less common. They are the most sensitive and are used to protect high-precision devices.
Between themselves, these devices differ in instantaneous trip current. Its value is determined by the multiplicity of the current passing through the circuit to the nominal value of the machine.
Tripping characteristics of protective circuit breakers
Class AB, determined by this parameter, is indicated by a Latin letter and is affixed on the body of the machine in front of the number corresponding to the rated current.
In accordance with the classification established by the PUE, circuit breakers are divided into several categories.
Machine type MA
A distinctive feature of such devices is the absence of a thermal release in them. Devices of this class are installed in the connection circuits of electric motors and other powerful units.
Overload protection in such lines is provided by an overcurrent relay, the circuit breaker only protects the network from damage as a result of exposure to overcurrent short circuits.
Class A appliances
Automata type A, as was said, have the highest sensitivity. The thermal release in devices with a time-current characteristic A most often trips when the current exceeds the nominal value AB by 30%.
The electromagnetic trip coil de-energizes the network for approximately 0.05 seconds if the electric current in the circuit exceeds the rated current by 100%. If, for any reason, after doubling the strength of the electron flow, the electromagnetic solenoid does not work, the bimetallic release cuts off the power within 20 - 30 seconds.
Automatic machines with a time-current characteristic A are included in the lines, during which even short-term overloads are unacceptable. These include circuits with semiconductor elements included in them.
Class B protective devices
Devices of category B are less sensitive than those of type A. The electromagnetic release in them is triggered when the rated current is exceeded by 200%, and the response time is 0.015 seconds. The operation of a bimetallic plate in a circuit breaker with characteristic B, with a similar excess of the AB rating, takes 4-5 seconds.
Equipment of this type is intended for installation in lines that include sockets, lighting devices and in other circuits where there is no starting increase in electric current or has a minimum value.
Automatic machines of category C
Type C devices are most common in household networks. Their overload capacity is even higher than those previously described. In order for the electromagnetic trip solenoid installed in such a device to operate, it is necessary that the flow of electrons passing through it exceeds the nominal value by 5 times. The operation of the thermal release when the rating of the protection device is exceeded five times occurs after 1.5 seconds.
The installation of circuit breakers with a time-current characteristic C, as we said, is usually carried out in domestic networks. They perfectly cope with the role of input devices for protecting the general network, while category B devices are well suited for individual branches to which groups of outlets and lighting devices are connected.
This will ensure the selectivity of the circuit breakers (selectivity), and in the event of a short circuit in one of the branches, the entire house will not be de-energized.
Category D circuit breakers
These devices have the highest overload capacity. For the operation of an electromagnetic coil installed in an apparatus of this type, it is necessary that the current rating of the circuit breaker be exceeded by at least 10 times.
The operation of the thermal release in this case occurs after 0.4 sec.
Devices with characteristic D are most often used in general networks of buildings and structures, where they play a safety net. Their operation occurs if there is no timely power outage by circuit breakers in separate rooms. They are also installed in circuits with a large amount of starting currents, to which, for example, electric motors are connected.
Protective devices of category K and Z
Automata of these types are much less common than those described above. Type K devices have a large variation in the current required for electromagnetic tripping. So, for an alternating current circuit, this indicator should exceed the nominal value by 12 times, and for a constant current - by 18 times. The electromagnetic solenoid is activated in no more than 0.02 seconds. The operation of the thermal release in such equipment can occur when the rated current is exceeded by only 5%.
These features determine the use of type K devices in circuits with an exclusively inductive load.
Type Z devices also have different actuation currents of the electromagnetic trip solenoid, but the spread is not as large as in category K AB. 4.5 times more than the nominal.
Devices with characteristic Z are used only in lines to which electronic devices are connected.
Conclusion
In this article, we examined the time and current characteristics of circuit breakers, the classification of these devices in accordance with the PUE, and also figured out in which circuits devices of various categories are installed. This information will help you determine what security equipment to use on your network based on the devices connected to it.
An electric machine, or circuit breaker, is a mechanical switching device, by means of which it is possible to manually achieve a de-energization of the entire electrical network or a specific section of it. This can be done in a house, apartment, country house, garage, etc. Moreover, such a device is equipped with the function of automatically turning off the electric cable in case of emergency: for example, in the event of a short circuit or overload. The difference between such circuit breakers and conventional fuses is that after operation they can be turned on again with the button.
Automata (automatic switches) are what came to replace conventional traffic jams, i.e. fuses in a ceramic case, where the overcurrent protection was a blown nichrome wire.
Unlike cork, machine - reusable device, and its protection functions are separated. Firstly, protection against overcurrents (short circuit currents or short circuits), and secondly, protection against overload, i.e. the mechanism of the machine breaks the load circuit when the operating current of the machine is slightly exceeded.
According to these functions, the circuit breaker contains two types of breakers. Magnetic quick release short circuit protection with arc quenching system (response time in milliseconds) and slow thermal disconnect with a bimetallic plate (its reaction time is from several seconds to several minutes, depending on the load current).
Classification of electric machines
There are several typical circuit breakers: A, B, C, D, E, K, L, Z
- BUT– for breaking long circuits and for protecting electronic devices.
- B- for lighting networks.
- With- for lighting networks and electrical installations with moderate currents (current overload capacity is twice that of B).
- D– for circuits with inductive loads and electric motors.
- K– for inductive loads.
- Z– for electronic devices.
Main criteria for choosing a circuit breaker
Limiting short-circuit current
This indicator must be taken into account immediately. It means the maximum current value at which the electric machine will work and open the circuit. Here the choice is not great, since there are only three options: 4.5 kA; 6 kA; 10kA.
When choosing, one should be guided by the theoretical probability of a high short-circuit current. If there is no such probability, then it will be enough to purchase a 4.5 kA automatic machine.
Machine current
Accounting for this indicator is the next step. We are talking about the required nominal value of the operating current of the electric machine. To determine the operating current, you need to be guided by the power that is supposed to be connected to the wiring, or by the value of the allowable current (the level that will be maintained in normal mode).
What do you need to know when determining the parameter in question? It is not recommended to use machines with an overestimated operating current. Just in this case, the machine will not turn off the power during overload, and this can cause thermal destruction of the wiring insulation.
The pole of the machine
This is perhaps the simplest indicator. To choose the number of poles for a switch, you need to proceed from how it will be used.
So, a single-pole machine is your choice if you need to protect the wiring that goes from the electrical panel to sockets and lighting circuits. A bipolar switch is used when it is necessary to protect all wiring in an apartment or house with single-phase power. Protection of three-phase wiring and load is provided by a three-pole circuit breaker, and four-pole ones are used to protect four-wire power.
Characteristics of the machine
This is the last indicator that you need to pay attention to. The time-current characteristic of the circuit breaker is determined by the loads that are connected to the protected line. When choosing a characteristic, the following are taken into account: the operating current of the circuit, the rated current of the machine, the cable capacity, the operating current of the switch.
In the event that it is necessary to connect small starting currents to the power supply line, i.e. electrical appliances, characterized by a small difference between the operating current and the current that occurs when turned on, preference should be given to the tripping characteristic B. For more serious loads, characteristic C is chosen. Finally, there is one more characteristic - D. if you intend to connect powerful devices with high starting points. What devices are we talking about? For example, about the electric motor.
RCD classification
The RCD responds to differential current, i.e. the difference between the currents flowing in the forward and reverse wires. A differential current appears when a person touches a protected circuit and a grounded object. RCDs to protect people are selected for current 10-30 mA , fire RCDs - for a current of 300 mA. The latter protects the entire wiring system, and in case of fire, leakage currents usually occur earlier than short-circuit currents.
Residual current devices protect people from electric shock.
The choice of RCD is difficult because it is a more complex device than an automatic machine. For example, there is difavtomatami- devices that combine an automatic machine and an RCD. RCDs are also subdivided according to the type of execution into electronic and electromechanical. Experience has shown that it is better to use electromechanical RCDs. They are better protected from false positives and from breakdowns.
By number of poles RCDs are divided into:
- bipolar for 220 V circuits;
- four-pole for 380 V circuits.
According to the terms of operation on the:
- AC- responding only to alternating sinusoidal differential current.
- BUT- responding both to alternating sinusoidal differential current and to direct pulsating differential current.
- AT- reacting to alternating sinusoidal differential current, to direct pulsating differential current and to direct differential current.
By the presence of a delay on RCDs without delay for general use and with a time delay of type S. According to the current characteristic (difavtomatov) for B, C, D. And, finally, according to the rated current.
You should be aware that if the conventional Residual Current Device and the machine are in series in the same circuit, then the machine must be at a lower current than the RCD. Otherwise, the RCD may be damaged, because. the machine breaks the load circuit with a delay.
In conclusion, it must be said that you should choose devices from well-known companies: ABB abb, GE POWER, siemens siemens, LEGRAND and others at least certified in Russia. It is better to choose electromechanical RCDs, because. they are much more reliable than electronic ones. Instead of a tandem of an RCD and an automatic machine, it is better to choose a difavtomat, this will make the design of the shield more compact and reliable. The current characteristics must be selected depending on the wiring used. The operation current of automata and difavtomatov must be less than the maximum allowable cable currents.
For copper three-wire cables, you can give the following data on the correspondence of the cross section of the cable conductors in square millimeters and the currents of the machines:
- 3 x 1.5mm 2 - 16 Amps;
- 3 x 2.5 mm 2 - 25 A;
- 3 x 4 mm 2 - 32 Amps;
- 3 x 6mm 2 - 40 A;
- 3 x 10 mm 2 - 50 Amps;
- 3 x 16 mm 2 - 63 A.
We hope that after reading all the material it will be easier for you to understand the design and construction of electrical wiring.
The history of the creation of the RCD
The first residual current device (RCD) was patented by the German company RWE in 1928, when the principle of current differential protection, previously used to protect generators, lines and transformers, was applied to protect a person from electric shock.
In 1937 Schutzapparategesellschaft Paris & Co. manufactured the first operating device based on a differential transformer and a polarized relay, which had a sensitivity of 0.01 A and a speed of 0.1 s. In the same year, with the help of a volunteer (an employee of the company), an RCD was tested. The experiment ended successfully, the device worked well, the volunteer experienced only a mild electric shock, although he refused to participate in further experiments.
All subsequent years, with the exception of the war and the first post-war years, intensive work was carried out to study the effect of electric current on the human body, the development of electrical protective equipment and the improvement and implementation of protective shutdown devices.
In our country, the problem of using residual current devices first arose in connection with the electrical and fire safety of schoolchildren about 20 years ago. It was during this period that they developed and put into production UZOSH (UZO school) for the equipment of school buildings. Interestingly, RCDs of this type are still installed in school buildings, although due to outdated technologies, these devices no longer fully meet modern electrical and fire safety requirements.
Another event that exacerbated the problem of installing an RCD was the reconstruction of the Rossiya Hotel in Moscow after the infamous fire, which was caused by the most ordinary short circuit. The fact is that the principles of power supply were violated during the construction of this hotel complex. Several tragic incidents that led to the death of service personnel forced the hotel management to schedule the installation of residual current devices in order to ensure electrical and fire safety.
At that time, such installations were produced only for industrial use. One of the defense enterprises was entrusted with developing a protective shutdown installation for domestic purposes. But they did not have time to prevent the tragedy, and the fire that arose as a result of a short circuit in the Rossiya Hotel led to numerous victims. After the fire, during the restoration of the building, work was carried out to install an RCD in each room. Since domestic RCDs were manufactured in a very short time and had flaws, they gradually began to be replaced by devices from SIEMENS (Germany).
By this time, our electrical engineering enterprises also began to think about the problem of producing household protective shutdown devices. So, the Gomel plant "Electroapparatura" and the Stavropol electrical plant "Signal" developed and began to produce household protective shutdown devices. And since 1991-1992, the mass introduction of protective shutdown devices in housing construction began, at least in Moscow.
In 1994, the standard “Power supply and electrical safety of mobile (inventory) buildings made of metal or with a metal frame for street trading and consumer services was adopted. Technical requirements". In the same year, a decree of the Moscow government was issued on the introduction of an RCD, which prescribed the mandatory equipping of new buildings in Moscow with protective shutdown devices.
In 1996 came out Letter of the Main Directorate of Civil Service of the Ministry of Internal Affairs of Russia dated 05.03.96 No. 20 / 2.1 / 516 « On the use of residual current devices (RCD)". And the Moscow government made another decision to improve the reliability of power supply to the entire housing stock, regardless of the year of construction. We can say that from that moment the legalized mass introduction of RCDs in housing construction began.
At present, the areas of application of RCDs are already clearly defined, a number of regulatory documents are in force that regulate the technical parameters and requirements for the use of RCDs in electrical installations of buildings. Today, the RCD is an indispensable element of any switchboard, all mobile objects are equipped with these devices without fail (residential trailer houses on camping sites, shopping vans, catering vans, small temporary outdoor electrical installations, arranged on the squares during the festive festivities), hangars , garages.
An RCD connection option that provides the safest operation of electrical wiring. In addition, RCDs are built into socket blocks or plugs through which power tools or household electrical appliances are connected, operated in especially dangerous, humid, dusty, with conductive floors, etc., rooms.
When assessing the risk that determines the sum insured, insurance companies must take into account the presence of RCDs on the insurance object and their technical condition.
Currently, there are an average of two RCDs for every inhabitant of developed countries. Nevertheless, for many years, dozens of companies have consistently produced these devices of various modifications in significant quantities, constantly improving their technical parameters.
These are the main indicators should be considered when choosing a circuit breaker. Accordingly, if you know all the necessary data, then the choice will not be difficult. It remains only to take into account the latest criterion - the manufacturer of the machine. What does it affect? It is obvious that on price.
Indeed, there is a difference. Thus, well-known European brands offer their circuit breakers at a price that is twice the cost of domestic counterparts and three times the price of devices from the South-Eastern countries. Also, the presence or absence of a switch with clearly defined indicators in the warehouse depends on the choice of a particular manufacturer.
