Installation 

Protective shutdown of electrical installations. Scope, basic requirements for RCDs, their types. Protective automatic shutdown In what cases is protective shutdown used

Protective shutdown is a protection system that automatically turns off the electrical installation in the event of a danger of human injury. electric shock(in the event of a ground fault, reduced insulation resistance, grounding or zeroing fault). Protective shutdown is used when it is difficult to ground or neutralize, and also in addition to it in some cases.

Depending on what is the input value, to the change of which the protective shutdown reacts, circuits are distinguished protective shutdown: on case voltage relative to earth; for earth fault current; for zero sequence voltage or current; to the phase voltage relative to earth; for direct and alternating operating currents; combined.

One of the protective shutdown circuits for the case voltage relative to the ground is shown in fig. 13.2.

Rice. 13.2. Residual trip circuit for case voltage relative to ground

The main element of the circuit is a protective relay RZ. When one phase is shorted to the housing, the housing will be energized above the permissible voltage, the RZ relay core is drawn in and closes the power supply circuit of the AB circuit breaker coil, as a result of which the electrical installation is turned off.

The advantage of the scheme is its simplicity. Disadvantages: the need to have an auxiliary ground RB; non-selectivity of shutdown in case of connection of several cases to one grounding; setpoint variability with changes in resistance RВ. Residual current devices that respond to zero-sequence current are used for any voltage, both with grounded and isolated neutral.

Fires and explosions

Fires and explosions are the most common emergency events in modern industrial society.

Most often and, as a rule, with severe social and economic consequences, fires occur at fire and fire hazardous objects.

The objects at which explosions and fires are most likely include:

Enterprises of the chemical, oil refining and pulp and paper industries;

Enterprises using gas and oil products as raw materials for energy carriers;

Gas and oil pipelines;

All types of transport transporting explosive and flammable substances;

Fuel stations;

Food industry enterprises;

Companies using paints and varnishes and etc.

EXPLOSIVE AND FIRE HAZARDOUS substances and mixtures are;

Explosives and gunpowder used for military and industrial purposes, manufactured at industrial enterprises stored in warehouses separately and in products and transported various types transport;

Mixtures of gaseous and liquefied hydrocarbon products (methane, propane, butane, ethylene, propylene, etc.), as well as sugar, wood, flour, etc. dust with air;

Vapors of gasoline, kerosene, natural gas on various vehicles, fuel stations, etc.

Fires at enterprises can also occur due to damage to electrical wiring and energized machines, furnaces and heating systems, containers with flammable liquids, etc.

There are also cases of explosions and fires in residential premises due to malfunctions and violations of the rules for the operation of gas stoves.

Characteristics of combustible substances

Substances that can burn on their own after the ignition source is removed are called combustible, in contrast to substances that do not burn in air and are called non-combustible. An intermediate position is occupied by hardly combustible substances that ignite under the action of an ignition source, but stop burning after the latter is removed.

All combustible substances are divided into the following main groups.

1. COMBUSTIBLE GASES (GH) - substances capable of forming flammable and explosive mixtures with air at temperatures not exceeding 50 ° C. Combustible gases include individual substances: ammonia, acetylene, butadiene, butane, butyl acetate, hydrogen, vinyl chloride, isobutane, isobutylene , methane, carbon monoxide, propane, propylene, hydrogen sulfide, formaldehyde, and vapors of flammable and combustible liquids.

2. FLAMMABLE LIQUIDS (FLL) - substances that can burn independently after the ignition source is removed and have a flash point not higher than 61 ° C (in a closed crucible) or 66 ° (in an open one). Such liquids include individual substances: acetone, benzene, hexane, heptane, dimethylformamide, difluorodichloromethane, isopentane, isopropylbenzene, xylene, methyl alcohol, carbon disulfide, styrene, acetic acid, chlorobenzene, cyclohexane, ethyl acetate, ethylbenzene, ethyl alcohol, as well as mixtures and technical products gasoline, diesel fuel, kerosene, white spirit, solvents.

3. COMBUSTIBLE LIQUIDS (GZh) - substances that can burn independently after the ignition source is removed and have a flash point above 61 ° (in a closed crucible) or 66 ° C (in an open one). Flammable liquids include the following individual substances: aniline, hexadecane, hexyl alcohol, glycerin, ethylene glycol, as well as mixtures and technical products, for example, oils: transformer, vaseline, castor.

4. COMBUSTIBLE DUST (FP) - solid substances in a finely dispersed state. Combustible dust in the air (aerosol) is capable of forming explosive mixtures with it. Dust (airgel) deposited on the walls, ceiling, equipment surfaces is a fire hazard.

Combustible dusts are divided into four classes according to the degree of explosion and fire hazard.

1st class - the most explosive - aerosols with a lower concentration limit ignition (explosive) (NKPV) up to 15 g / m3 (sulfur, naphthalene, rosin, mill dust, peat, ebonite).

2nd class - explosive - aerosols having a LEL value from 15 to 65 g / m3 (aluminum powder, lignin, flour, hay, shale dust).

3rd class - the most flammable - aerogels with a LEL value greater than 65 g / m3 and a self-ignition temperature of up to 250 ° C (tobacco, elevator dust).

4th class - flammable - aerogels with a LEL value of more than 65 g / m3 and an autoignition temperature of more than 250 ° C (sawdust, zinc dust).

In accordance with NPB 105-03, buildings and structures that house production facilities are divided into five categories.

Room category Characteristics of substances and materials located (circulating) in the room
And explosive and flammable Combustible gases, flammable liquids with a flashpoint of not more than 28 ° C in such an amount that they can form explosive vapor-gas-air mixtures, upon ignition of which an estimated excess explosion pressure in the room develops in excess of 5 kPa. Substances and materials capable of exploding and burning when interacting with water, atmospheric oxygen or one with the other in such an amount that the calculated overpressure of the explosion in the room exceeds 5 kPa.
B explosive and flammable Flammable dusts or fibres, flammable liquids with a flash point of more than 28 ° C, flammable liquids in such an amount that they can form explosive dust or vapor-air mixtures, upon ignition of which an estimated overpressure of the explosion in the room develops in excess of 5 kPa.
B1 - B4 fire hazardous Combustible and slow-burning liquids, solid combustible and slow-burning substances and materials that can only burn when interacting with water, atmospheric oxygen or one with the other, provided that the premises in which they are available or circulated do not belong to categories A or B
G Non-combustible substances and materials in a hot, incandescent or molten state, the processing of which is accompanied by the release of radiant heat, sparks and flames, combustible gases, liquids and solids that are burned or disposed of as fuel
D Non-flammable substances and materials in a cold state

EXAMPLES of production facilities located in premises of categories A, B, C, D and D.

Category A: shops for the processing and use of metallic sodium and potassium, oil refining and chemical industries, warehouses for gasoline and cylinders for combustible gases, premises for stationary acid and alkaline battery installations, hydrogen stations, etc.

The nature of the development of a fire and the explosion that follows it largely depends on the fire resistance of structures - the properties of structures to maintain their bearing and enclosing capacity in a fire. In accordance with SNiP 2.01.02.85, five degrees of fire resistance of buildings and structures are distinguished: I, II, III, IV, V.

The fire resistance of building structures characterizes the following parameters:

1) the minimum fire resistance limit of a building structure - the time in hours from the beginning of the impact of fire on the structure until the formation of through cracks in it or reaching a temperature of 200 ° C on the surface opposite to the fire.

2) the maximum limit for the spread of fire along building structures visually determined size of damage in centimeters, which is considered to be charring or burnout of materials, as well as melting of thermoplastic materials outside the heating zone.

All Construction Materials according to flammability, they are divided into three groups: FIRE-RESISTANT, FIRE-RESISTANT and COMBUStable.

The non-combustible materials and structures include metals and inorganic mineral materials used in construction and products made from them: sand, clay, gravel, asbestos, brick, concrete, etc.

FIRM-RESISTANT materials include materials and products made from them, consisting of combustible and non-combustible components: adobe brick, gypsum dry plaster, fibrolite, lenolium, ebonite, etc.

COMBUSTIBLE materials include all materials of organic origin: cardboard, felt, asphalt, roofing material, roofing felt, etc.

Basic concepts of fires and explosions.

FIRE is an uncontrolled burning outside a special focus, causing material damage.

BURNING - a chemical oxidation reaction, accompanied by the release of a large amount of heat and usually glow. For combustion to occur, it is necessary to have a combustible substance, an oxidizing agent (usually atmospheric oxygen, as well as chlorine, fluorine, iodine, bromine, nitrogen oxides) and an ignition source. In addition, it is necessary that the combustible substance be heated to a certain temperature and be in a certain quantitative ratio with the oxidizing agent, and the ignition source would have sufficient energy.

EXPLOSION - an extremely rapid release of energy in a limited volume, associated with a sudden change in the state of matter and accompanied by the formation of a large amount of compressed gases capable of producing mechanical work.

An explosion is a special case of combustion. But in the usual sense, it has in common with combustion only that it is an oxidative reaction. An explosion is characterized by the following features:

High rate of chemical transformation;

A large number of gaseous products;

Powerful crushing (blasting) action;

Strong sound effect.

The duration of the explosion is about 10-5...10-6 s. Therefore, its power is very high, although the reserves of internal energy of explosives and mixtures are not higher than those of combustible substances that burn under their usual conditions.

When analyzing explosive phenomena, two types of explosions are considered: explosive combustion and detonation.

The first includes explosions of air-fuel mixtures (mixtures of hydrocarbons, vapors of petroleum products, as well as sugar, wood, flour and other dust with air). characteristic feature such an explosion is a burning velocity of the order of several hundred m/s.

DETONATING - a very rapid decomposition of an explosive (gas-air mixture). propagating along it at a speed of several km / s and characterized by features inherent in any explosion indicated above. Detonation is typical for military and industrial explosives, as well as for fuel-air mixtures in a closed volume.

The difference between explosive combustion and detonation lies in the rate of decomposition, in the latter it is an order of magnitude higher.

In conclusion, three types of decomposition should be compared: ordinary combustion, explosive and detonation.

NORMAL BURNING processes proceed relatively slowly and at a variable speed - usually from fractions of a centimeter to several meters per second. The burning rate essentially depends on many factors, but mainly on external pressure, increasing noticeably with an increase in the latter. In the open air, this process proceeds relatively sluggishly and is not accompanied by any significant sound effect. In a limited volume, the process proceeds much more energetically, is characterized by a more or less rapid increase in pressure and the ability of combustion gases to do work.

EXPLOSIVE COMBUSTION, in comparison with the usual one, is a qualitatively different form of the propagation of the process. Distinctive features explosive combustion are: a sharp jump in pressure at the site of the explosion, a variable speed of propagation of the process, measured in hundreds of meters per second and relatively little dependent on external conditions. The nature of the action of the explosion is a sharp blow of gases to environment, causing crushing and severe deformation of objects at relatively short distances from the explosion site.

DETONATION is an explosion propagating with the maximum possible speed for a given substance (mixture) and given conditions (for example, mixture concentration), exceeding the speed of sound in a given substance and measured in thousands of meters per second. Detonation does not differ in the nature and essence of the phenomenon from explosive combustion, but is its stationary form. The detonation velocity is a constant value for a given substance (a mixture of a certain concentration). Under detonation conditions, the maximum destructive effect of the explosion is achieved.

A protective shutdown is understood as a quick, within a time of not more than 200 ms, automatic disconnection from the power source of all phases of the consumer or part of the wiring in case the insulation is damaged or there is another emergency that threatens a person with electric shock.

Protective automatic power off- automatic opening of the circuit of one or more phase conductors (and, if required, the neutral working conductor), performed for electrical safety purposes.

Protective shutdown can be both the only and main measure of protection, and an additional measure for grounding and zeroing networks in relation to electrical installations with an operating voltage of up to 1000 volts.

Assignment of a protective shutdown- Ensuring electrical safety, which is achieved by limiting the time of exposure to dangerous current on a person.

Safety shutdown- high-speed protection that provides automatic shutdown of the electrical installation in the event of a danger of electric shock in it. This risk can arise when:

    phase short circuit on the body of electrical equipment;

    when the insulation resistance of the phases relative to the ground drops below a certain limit;

    the appearance of a higher voltage in the network;

    touching a person to a live part that is energized.

In these cases, some electrical parameters change in the network: for example, the case voltage relative to earth, phase voltage relative to earth, zero sequence voltage, etc. can change. Any of these parameters, or rather, changing it to a certain limit, at which danger arises electric shock to a person, can serve as an impulse that triggers a protective shutdown device, i.e., automatic shutdown of a dangerous section of the network.

Current devices protective shutdowns were usually used in electrical installations of four types:

    Mobile installations with an isolated neutral (in such conditions, in principle, the construction of a full-fledged grounding device is problematic). Protective disconnection is then applied either in conjunction with earthing or as an independent protective measure.

    Fixed installations with isolated neutral (where the protection of electrical machines that people work with is necessary).

    Mobile and fixed installations with any type of neutral where there is a high risk of electric shock or if the installation operates in explosive environments.

    Fixed installations with solidly earthed neutral on some high power consumers and on remote consumers where earthing is not enough for protection or where it is protective measure not quite effective, does not give a sufficient multiplicity of the phase-to-earth fault current.

To implement the protective shutdown function, special protective shutdown devices were used. Their schemes may differ, the designs depend on the features of the protected electrical installation, on the nature of the load, on the neutral grounding mode, etc.

Residual current device- a set of individual elements that respond to a change in any parameter of the electrical network and give a signal to turn off the circuit breaker. A residual current device, depending on the parameter to which it reacts, can be attributed to one or another type, including types of devices that respond to case voltage relative to earth, earth fault current, phase voltage to earth, zero sequence voltage, current zero sequence, operational current, etc.

Here, a specially installed protection relay can be used, which is arranged in the same way as highly sensitive voltage relays with breaking contacts, which are included in the power circuit of a magnetic starter, say, an electric motor.

The purpose of the protective shutdown is to implement a set of protection or some of the following types of it with one device:

    from single-phase short circuits to the ground or to electrical equipment normally isolated from voltage;

    from incomplete short circuits, when a decrease in the insulation of one of the phases creates a danger of human injury;

    from damage when a person touches one of the phases of electrical equipment, if the touch occurred in the coverage area of ​​\u200b\u200bthe protection of the device.


An example is a simple residual current device based on a voltage relay. The relay winding is connected between the body of the protected equipment and the ground electrode.

Under conditions when the relay winding has a resistance that is much higher than that of the auxiliary grounding switch, which is placed outside the protection grounding spreading zone, the K1 relay winding will be energized with respect to the ground.

Then, at the time of an emergency breakdown to the case, the voltage will be greater than the relay operation voltage and the relay will operate, closing the shutdown circuit of the Q1 circuit breaker or opening the power supply circuit of the Q2 magnetic starter winding by its operation.

Another variant simple device protective shutdown for electrical installations is (overcurrent relay). Its winding is included in the break of the ground wire, due to which the contacts open the power circuit of the magnetic starter winding in the same way if the power circuit of the winding of the circuit breaker is closed. Instead of the relay winding, by the way, it is sometimes possible to use the winding of the switch - release as an overcurrent relay.

When a residual current device is put into operation, it is mandatory to check it: scheduled full and partial checks are carried out to make sure that the device works reliably, that shutdowns occur when necessary.

Once every three years, a full scheduled inspection is carried out, often along with the repair of associated circuits of electrical installations. The inspection also includes insulation tests, verification of protection settings, tests of protection devices and a general inspection of the apparatus and all connections.

As for partial checks, they are carried out from time to time depending on particular conditions, but they include: insulation check, general inspection, protection tests in action. If the protective device does not work quite correctly, a deeper check is carried out using a special algorithm.

In our time, the protective shutdown is most widely used in electrical installations used in networks with voltages up to 1 kV with a grounded or isolated neutral.

Electrical installations with voltage up to 1 kV residential, public and industrial buildings and outdoor installations should, as a rule, be powered from a solidly earthed neutral source. To protect against electric shock from indirect contact in such electrical installations, automatic power off must be performed.

When performing automatic power off in electrical installations with voltages up to 1 kV, all exposed conductive parts must be connected to a solidly grounded neutral of the power source if the TN system is used, and grounded if the IT or TT systems are used. At the same time, the characteristics of protective devices and the parameters of protective conductors must be coordinated in order to ensure a normalized time for disconnecting a damaged circuit by a protective switching device in accordance with the rated phase voltage of the supply network.

Protection is carried out, which, working in standby mode, constantly monitors the conditions for electric shock to a person.


RCDs are used in electrical installations up to 1 kV:

    in mobile email installations with an isolated neutral (especially if it is difficult to create a grounding device. It can be used both as independent protection and in combination with grounding);

    in stationary electrical installations with isolated neutral for the protection of hand-held electrical machines as the only protection, and in addition to others;

    in conditions of increased danger of electric shock and explosion hazard in stationary and mobile electrical installations with different neutral modes;

    in stationary electrical installations with a dead-earthed neutral on separate remote consumers of electrical energy and a consumer of high rated power, on which zeroing protection is not effective enough.

The principle of operation of the RCD is that it constantly monitors the input signal and compares it with a predetermined value (setpoint). If the input signal exceeds the setting, the device operates and disconnects the protected electrical installation from the network. As input signals of residual current devices, various parameters of electrical networks are used, which carry information about the conditions of electric shock to a person.

Protective shutdown - a type of protection against electric shock in electrical installations, which provides automatic shutdown of all phases of the emergency section of the network. The duration of disconnection of the damaged section of the network should be no more than 0.2 s.

Areas of application for residual current: addition to protective earth or zeroing in an electrified tool; addition to zeroing to turn off electrical equipment remote from the power source; measure of protection in mobile electrical installations with voltage up to 1000 V.

The essence of the protective shutdown is that damage to the electrical installation leads to changes in the network. For example, when a phase is shorted to earth, the phase voltage changes relative to the earth - the value of the phase voltage will tend to the value of the linear voltage. This creates a voltage between the source neutral and earth, the so-called zero-sequence voltage. The total resistance of the network relative to the ground decreases when the insulation resistance changes in the direction of its decrease, etc.

The principle of constructing protective shutdown schemes is that the listed regime changes in the network are perceived by the sensitive element (sensor) of the automatic device as signal input values. The sensor acts as a current or voltage relay. At a certain value of the input value, the protective shutdown is activated and switches off the electrical installation. The value of the input variable is called the setpoint.

The block diagram of the residual current device (RCD) is shown in fig.

Rice. Structural diagram of the residual current device: D - sensor; P - converter; KPAS - emergency signal transmission channel; IO - executive body; MOP - a source of danger of defeat

The sensor D responds to a change in the input value B, amplifies it to the value KB (K is the transfer coefficient of the sensor) and sends it to the converter P.

The converter is used to convert the amplified input value into a KVA alarm. Further, the channel for transmitting the emergency signal of the KPAS transmits the AC signal from the converter to the executive body (EO). The executive body performs a protective function to eliminate the danger of damage - it turns off the electrical network.

The diagram shows areas of possible interference that affect the operation of the RCD.

On fig. given circuit diagram protective shutdown by means of the maximum current relay.

Rice. Residual current device diagram: 1 - maximum current relay; 2 - current transformer; 3 - ground wire; 4 - ground electrode; 5 - electric motor; 6 - starter contacts; 7 - block contact; 8 - starter core; 9 - working coil; 10 - testing button; 11 - auxiliary resistance; 12 and 13 - stop and turn buttons; 14 - starter

The coil of this relay with normally closed contacts is connected through a current transformer or directly into the cut of the conductor going to a separate auxiliary or common ground electrode.

The electric motor is switched on by pressing the "Start" button. In this case, voltage is applied to the coil, the starter core is retracted, the contacts close and the electric motor is connected to the network. At the same time, the auxiliary contact is closed, as a result of which the coil remains energized.

When one of the phases is shorted to the case, a current circuit is formed: the place of damage - the case - the ground wire - the current transformer - the earth - the capacitance and insulation resistance of the wires of undamaged phases - the power source - the place of damage. If the current value reaches the current relay operation setting, the relay will operate (i.e., its normally closed contact will open) and break the magnetic starter coil circuit. The core of this coil will be released and the starter will turn off.

To check the serviceability and reliability of the protective shutdown, a button is provided, when pressed, the device is triggered. The auxiliary resistance limits the earth fault current to the required value. Buttons are provided to enable and disable the starter.

The system of public catering enterprises includes a large complex of mobile (inventory) buildings made of metal or with a metal frame for street trade and service (snack bars, cafes, etc.). As technical means protection against electrical injuries and from a possible fire in electrical installations, the mandatory use of a residual current device at these facilities is prescribed in accordance with the requirements of GOST R50669-94 and GOST R50571.3-94.

Glavgosenergonadzor recommends using for this purpose an electromechanical device of the ASTRO-UZO type, the principle of which is based on the effect of possible leakage currents on a magnetoelectric latch, the winding of which is connected to the secondary winding of a leakage current transformer, with a core made of special material. The core in the normal mode of operation of the electrical network keeps the release mechanism in the on state. In the event of any malfunction in the secondary winding of the leakage current transformer, an EMF is induced, the core is retracted, and the magnetoelectric latch is activated, which is associated with the mechanism of free decoupling of contacts (the knife switch is turned off).

ASTRO-UZO has a Russian certificate of conformity. The device is included in the State Register.

A residual current device should be equipped not only with the above structures, but also with all premises with an increased or special risk of electric shock, including saunas, showers, electrically heated greenhouses, etc.

Protective shutdown is especially important when used in the house a large number of various electrical appliances. In this article, we will consider protective shutdown devices that are recommended and used in the construction of private houses. A diagram of the residual current device will be given. Let's analyze the question of what and when to use - RCD or difavtomat (differential automaton). In addition, we will find out the main differences between circuit breakers.

Types of circuit breakers

An important step in the organization of electrical safety are protective electrical apparatus or, as they are more commonly called, automatons. Conventionally, they can be divided into three types:

  • automatic switches (AB);
  • differential shutdown devices (RCD);
  • differential automatic switches (DAV).

Fig 1. Circuit breaker


Fig 2. Residual current device (RCD)


Fig 3. Differential circuit breaker (DAB)

The principle of operation of residual current devices

Automatic switches (AB), see Fig. 1, we install to protect electrical wiring from overcurrent, and electrical consumers from short circuits. Overcurrent leads to heating of the conductor, which leads to ignition of the wiring and its failure.

Residual current device (RCD) principle of operation(Fig. 2). We install to protect against electric shock, in the event of a breakdown of the insulation of equipment and wiring. The RCD will also protect us in case of touching open uninsulated sections of wiring or equipment that are energized with 220 V and will not allow a fire to occur if the wiring is faulty.

If there is a difference in currents, then the RCD turns off the voltage supply. It is necessary to choose an RCD according to two parameters: sensitivity and rated current. Usually for home purposes, an RCD with a sensitivity of 300 mA is chosen. The rated current is selected depending on the total power of electrical consumers and must be equal to or be an order of magnitude lower than the rated current of the introductory circuit breaker (AB), because the RCD does not protect against short circuits and overcurrents. An RCD residual current device is usually installed in the circuit after the meter to protect all wiring in the house, see fig. 4, 5. According to modern standards, the installation of an RCD is mandatory.


Rice. 4. RCD connection diagram


Rice. 5 Wiring diagram for power supply at home using RCD

1 - w distribution flow; 2- neutral; 3 - sh ina grounding; 4 - f aza; 5 - RCD; 6 - av tomatic switch; 7 - pconsumer nutrition.

Differential circuit breakers (DAB) combine the functions of RCD and AV. The scheme of the differential machine is based on the protection of circuits from short circuits and overloads, as well as the protection of people from electric shock when touching live parts, see fig. 6.


Rice. 6. Scheme of work of DAV

These devices are widely used in household electrical networks(220/380 V), in socket networks. The differential circuit breaker consists of a fast-acting circuit breaker and a residual current device that responds to the difference in currents in the forward and reverse directions.

The principle of operation of the differential machine. If the insulation of the electrical wiring is not damaged and there is no human contact with live parts, then there is no leakage current in the network. This means that the currents in the forward and reverse (phase-zero) load conductors are equal. These currents induce equal but oppositely directed magnetic fluxes in the magnetic core of the current transformer DAV. As a result, the current in the secondary winding is zero and does not trigger the sensitive element - the magnetoelectric latch.

If a leak occurs, for example: when a person touches a phase conductor, the balance of currents and magnetic fluxes is disturbed, an unbalance current appears in the secondary winding, which causes the magnetoelectric latch to operate, which in turn acts on the release mechanism of the machine with a contact system.

To carry out periodic monitoring of the performance of the RCD and DAV, a testing circuit is provided. By pressing the "Test" button, a differential trip current is artificially created. The operation of the protection devices means that it is generally in good order.

Choice of circuit breaker

Now, let's decide in which case and which circuit breaker we prefer:

  • To protect the wiring of the lighting network, from which all our lamps are powered, we choose circuit breakers (AB) with tripping currents 16 A.
  • The socket network in the house, which is used to turn on the irons, table lamps, TV, computer, etc., must protect circuit breakers with differential protection (DAV).
  • For the socket network, we choose DAV with a trip current of 25 A and differential current shutdown 30 mA.
  • To connect the air conditioner in the house, dishwasher, electric ovens, microwave ovens and other powerful devices that are so necessary for us in everyday life, we need our own individual socket and, therefore, our own circuit breaker with differential protection. For example, to connect an electric furnace with a power of 6 kW, a differential circuit breaker with tripping currents of 32 and 30 mA is required.

Paying attention, that the sockets must all be with a grounding contact. Power equipment, such as a grinder, I advise you to connect to a circuit breaker. Since the entire network in our house is for a voltage of 220 V, we also select the listed circuit breakers for the appropriate voltage.

Let's talk about the circuit breaker, which, for security reasons, needs to be put on the input. If we protected all the outlet lines with automatic switches with differential protection, then at the input we put an automatic switch (AB) with a rated current of certain technical conditions and a single-line diagram of the project "Electrical equipment of a residential building".

But it is possible to put a residual current device (RCD) with a differential protection current of 300 mA after the introductory circuit breaker (AB). See Fig. 5 for such a switching scheme. If we choose this protection option, then it does not oblige us to install differential circuit breakers for the outlet network, but simply install a circuit breaker (AB), see the same fig. 5. Such a scheme is acceptable if we have only one outlet line with a number of outlets. But it is absolutely not rational if we have a number of independent receivers included in individual sockets.

For example: You have current leakage to the case washing machine and you accidentally touch it. The differential protection will immediately work and the DAV of the washing machine will turn off. It will not be difficult for you to determine and eliminate the cause. And imagine how much work is needed to find the reason for the RCD shutdown at the input.

I want to say that in today's market circuit breakers and UZO a very large selection of devices, both domestic and foreign. It should be taken into account that domestic products are distinguished by large overall dimensions, the possibility of current regulation, lower price, and the service life in domestic conditions is almost the same.

Table 1. Cost comparison of circuit breakers

Conclusion

So, in the article we have considered the issues of electrical safety. They became especially relevant when a huge number of electrical appliances, consumer electronics and computers entered our home. The wiring carries a very high load and a protective shutdown is necessary. Modern technology is very expensive and demanding on the quality of networks. Therefore, you should not save on protection measures, because the cost of an RCD is not commensurate with the cost of equipment in your home, and even more so with the price of a human life.

Attention: Prices are valid for 2009.

Safety shutdown- high-speed protection that provides automatic shutdown of the electrical installation in the event of a danger of electric shock in it.

Such a danger may arise, in particular, when a phase is shorted to the electrical equipment case; when the insulation resistance of the phases relative to the ground drops below a certain limit; the appearance of a higher voltage in the network; touching a person to a live part that is energized. In these cases, some electrical parameters change in the network: for example, the case voltage relative to earth, phase voltage relative to earth, zero sequence voltage, etc. can change. Any of these parameters, or rather, changing it to a certain limit, at which danger arises electric shock to a person, can serve as an impulse that causes the operation of a protective shutdown device, i.e. automatic shutdown of a dangerous section of the network.

Residual current devices(RCD) must ensure the shutdown of a faulty electrical installation for a time not exceeding 0.2 s.

The main parts of the RCD are a residual current device and a circuit breaker.

Residual current device- a set of individual elements that respond to a change in any parameter of the electrical network and give a signal to turn off the circuit breaker.

Circuit breaker- a device used to turn on and off circuits under load and in case of short circuits.

RCD types.

RCD responding to case voltage relative to earth , are intended to eliminate the danger of electric shock in the event of an increased voltage on a grounded or grounded housing.

RCDs responding to operational direct current , are designed to continuously monitor the insulation of the network, as well as to protect a person who has touched the current-carrying part from electric shock.

Consider a circuit that provides protection when voltage appears on the case relative to ground.

Rice. Residual shutdown circuit at voltage on

hull relative to the ground.

The scheme works as follows. When the button P is turned on, the power circuit of the winding of the MP magnetic starter is closed, which turns on the electrical installation with its contacts and self-locks along the circuit composed of normally closed contacts of the “stop” button C, protection relay RZ and auxiliary contacts.

When a voltage appears relative to the ground on the case U z, equal in magnitude to the long-term permissible contact voltage, under the action of the RZ (KRP) coil, the protection relay is activated. RZ contacts break the MP winding circuit, and the faulty electrical installation is disconnected from the network. The artificial circuit circuit, activated by the K button, serves to monitor the health of the shutdown circuit.

It is advisable to use protective shutdown in mobile electrical installations and when using hand-held power tools, since their operating conditions do not allow ensuring safety by grounding or other protective measures.