safetylife Trauma Talk Fire

The greatest use was currently obtained three-phase three-wire networks with deaf-free neutral and three-phase four-wire networks with an isolated transformer or generator neutral.

Plug-free neutral is a transformer or generator neutral attached directly to a grounding device.

Isolated neutral - neutral of a transformer or generator, not attached to a grounding device.

To ensure safety, there is a division of the operation of electrical installations (electrical networks) into two modes:

• - normal mode when the specified values \u200b\u200bof the parameters of its operation are ensured (there is no closure on Earth);
• - emergency mode with single-phase closure on Earth.

In the normal mode of operation, the least dangerous person is a network with an isolated neutral, but it becomes the most dangerous in emergency mode. Therefore, from the point of view of electrical safety, the network with an isolated neutral is preferable, provided that the high level of phase isolation is maintained and alarms in emergency mode.

In a low-winded neutral network, it is not necessary to maintain a high level of insulation phases. In emergency mode, such a network is less dangerous than the network with an isolated neutral. The network with a deaf-earth neutral is preferable to a technological point of view, since it allows you to simultaneously receive two voltages: a phase, for example, 220 V, and a linear, for example, 380 V. On a network with an isolated neutral, you can only get a single voltage - linear. In this regard, at stresses up to 1000, networks with a deaf-free neutral are used.

A number of the main causes of accidents that occurred from the effects of electric current can be distinguished:

• - a random touch or approximation on a dangerous distance to the current-carrying parts under voltage;
• - the appearance of voltage on the metal structural parts of electrical equipment (housings, casing, etc.), including as a result of insulation damage;
• - the appearance of voltage on disconnected current-carrying parts on which people work, due to the erroneous installation of the installation;
• - The occurrence of step tension on the ground surface as a result of the closure of the wire to the ground.

The main measures of protection against lesion are the following:

• - ensuring the inaccessibility of current-carrying parts under stress;
• - Electrical network separation;
• - elimination of the danger of damage when the tension appears on the housings, casing and other parts of electrical equipment, which is achieved by using low stresses, using double insulation, potential leveling, protective grounding, reducing, protective disconnection, etc.;
• - the use of special electric equipment - portable devices and devices;
• - Organization of safe operation of electrical installations.

Double isolation - This is an electrical insulation consisting of working and additional isolation. Working isolation is intended for insulation of current-carrying parts of the electrical installation and provides its normal operation and protection against shock. Additional insulation is provided additionally to the working to protect against damage to the current in the event of damage to the working isolation. Double isolation is widely used when creating manual electrical machines. In this grounding or changer is not required.

Protective grounding - This is a deliberate electrical connection with the Earth or its equivalent of open conductive parts (available to the touch of conductive parts of the electrical installation, which in normal operation are not under voltage, but may be under it during insulation damage) to protect against indirect touch, from static electricity, accumulating With friction of dielectrics, from electromagnetic emissions, etc. The equivalent of the earth can be the water of the river or the sea, the stone coal in the career of the location, etc.

With a protective earth, the grounding conductor connects the open conductive part of the electrical installation, for example, a housing, with a grounding. The earthing is a conductive part in electrical contact with the ground.

Since the current goes along the path of least resistance, it is necessary to ensure small compared to the resistance of the human body (1000 Ohm) resistance of the grounding device (earthing and ground conductors). In networks with voltage up to 1000 V it should not exceed 4 ohms. Thus, in the case of breakdown, the potential of grounded equipment decreases. The potentials of the base on which the person and grounded equipment are standing (the rise in the potential of the base on which a person stands is to a value close to the value of the potential of an open conductive part). Due to this, the tension of the touch and the person step is reduced to a permissible level.

As the main means of protection, grounding is used at a voltage of up to 1000 V in networks with an isolated neutral; At voltages above 1000 V - in networks with any neutral mode.

Stage - a deliberate electrical connection with a zero protective conductor of metal inadequate parts, which may be energized, for example, due to a closure on the body. It is necessary to ensure protection against electric shock with an indirect touch by reducing the voltage of the body relative to the Earth and restricting the current time through the human body due to the rapid shutdown of the electrical installation from the network.

The principle of the reasancement is that when the phase wire is closed on the underlined electromotor body (electrical installation), a chain of a single-phase short circuit current is formed (that is, closures between phase and zero protective conductors). A single-phase short circuit current causes the maximum current protection. For this, fuses can be used, circuit breakers. As a result, it turns off the damaged electrical installation from the supply network. In addition, before responding to the maximum current protection, there is a decrease in the voltage of the damaged housing relative to the Earth, due to the action of the re-ground of the zero protective conductor and the redistribution of the voltage in the network when the short circuit current flows.

The reinforcement is used in electrical installations by voltage up to 1000 V in three-phase AC networks with a grounded neutral.

Protective shutdown - This is a high-speed protection that ensures automatic shutdown of the electrical installation in it occurs in the danger of human damage to electric. Such a danger may occur, in particular, when the phase is closed on the body, reducing the insulation resistance is lower than a certain limit, as well as in the case of a person's touch directly to the current-carrying parts under voltage.

The main elements of the protective shutdown device (UZO) are the device of a protective disconnection and executive body.

The protective shutdown device is a set of individual elements that perceive the input value react to its changes and at a given value give a signal to turn off the switch.

The executive body is a circuit breaker, which ensures the disablement of the corresponding section of the electrical installation (electrical network) upon receipt of the signal from the instrument of the protective shutdown.

The basis of the action of the protective shutdown as an electric power facility is the principle of restriction (due to the rapid shutdown) of the current flow through the human body with an unintentional touching it to the electrical installation elements under voltage.

Of all the well-known electric protection products, the UDO is the only one that protects a person from electric shock with direct touch to one of the current-carrying parts.

Another important property of the UZO is its ability to protect against fires and fires arising from objects due to possible damage to the isolation, electrical wiring and electrical equipment faults.

Scope of the Uzo - Network of any voltage with any neutral mode. But they received the greatest distribution in networks voltage up to 1000 V.

Electroplature -these are portable and transported products that serve to protect people working with electrical installations from electric shock, from exposure to an electrical arc and an electromagnetic field.

In the appointment, the electric power facilities (EES) are conditionally divided into insulating, enclosing and auxiliary.

Insulating EZS serve to isolation of a person from parts of electrical equipment under stress, as well as from the ground. For example, insulating sticks of a montercene tool, dielectric gloves, bots and galoishes, rubber mats, tracks; Stands; insulating caps and lining; insulating stairs; Insulating stands.

Fencing ESS are designed to temporarily fencing the current parts of electrical installations under voltage. These include portable fences (shirms, barriers, shields and cells), as well as temporary portable grounding. Warning posters can be attributed to them conditionally.

Auxiliary protective equipment serve to protect staff from falling from height (safety belts and insisting ropes), for safe lifting to height (stairs, claws), as well as to protect against light, heat, mechanical and chemical influences (safety glasses, gas masks, mittens , overalls, etc.).

The voltage between the two points of the circuit of the current, which simultaneously concerns a person called the tension of the touch. The danger of such a touch, estimated by the value of the current passing through the human body, or the tension of the touch depends on the number of factors: the circuit circuit circuit circuit through the human body, the network voltage, the network diagram, the mode of its neutral (i.e., grounded or isolated neutral ), degrees of insulation of current parts from Earth, as well as on the value of the capacity of the current-carrying parts relative to the Earth, etc.

The most typical two cases of circuit circuit through the body of a person: when a person concerns two wires at the same time and when it concerns only one wire. With regard to alternating current networks, the first scheme is usually called a two-phase touch, and the second one is single-phase.

Two-phase touch is more dangerous, because the largest voltage in this network is applied in this network - linear, and therefore a larger current will go through a person.

Single-phase touch occurs many times more often than two-phase, but it is less dangerous, because the voltage under which the person turns out, does not exceed the phase, i.e. Less linear 1.73 times.

The main causes of electric shock:

1) a random touch to the current-carrying parts under voltage as a result: erroneous actions during work; The defective faults that the victims affected the current parts and others concerned.

2) the appearance of voltage at the metal structural parts of electrical equipment as a result: damage to the insulation of the current-carrying parts; closure of the network phase to the Earth; Falls of the wire (under stress) on the structural parts of electrical equipment, etc.

3) the appearance of voltage on the disconnected current parts as a result: the erroneous turn on the disabled installation; closures between disconnected and stressed currents; discharge of lightning in electrical installation and others.

4) the emergence of the stress of the step on the land plot where the person is, as a result: the closure of the phase to the Earth; potential takeaway with a long conductive subject (pipeline, railway rails); Faults in the protective grounding device, etc.

The voltage of the step is called the voltage between the points of the Earth, due to the spreading of the closure current on the ground while touching their feet of the person.

If a person is in the zone of current spreading, for example, during damage to the power line of the power line, or the insulation disorder of the power cable, laid in the ground, or when flowing the current through the ground and stand on the surface of the Earth, having different potentials in places where the feet are located legs, then at the length of the step occurs the voltage uhes \u003d φ x ─ φ x + 8, where φ x and φ x + 8 - the potentials of the location of the points of the legs; S \u003d 0.8 m - step length.

The electric current flowing through the human body in this case depends on the value of the closure current to the ground, the resistance of the base of the floor and shoes, as well as from the location of the feet feet.

Step voltage can be zero if both legs of a person are on an equipotential line, i.e. Electric field lines with the same potential. Step voltage can be reduced to a minimum if you bring down the legs of the legs together. The largest electric potential will be in the place of contact of the conductor with the ground. As it removed from this site, the potential of the surface of the soil decreases, and at a distance of approximately 20 m, it can be accepted with zero.

Step voltage is always less tension. In addition, the flow of current on the bottom loop "foot - leg" is less dangerous than along the path "Hand - Leg". However, in practice there are many cases of lesion of people when exposed to the tension of the step. The defeat at the stress of the step is exacerbated by the fact that due to convulsive cuts of the muscles of the legs, a person may fall, after which the current chain closes on the body through vital organs. In addition, human growth determines a greater difference in potentials attached to his body.

Characterization of human lesions with electric shock. Electrical resistance of the human body. 2.

The main causes of electric shock. 3.

Methods and means used. four

to protect against electric shock. four

when touched to metal inactive parts, 4

it turned out to be energized. four

Organizational activities ensuring the safety of work in electrical installations. four

Technical activities ensuring safe performance of work in current electrical installations. four

Characterization of human lesions with electric shock. Electrical resistance of the human body

Electric current, passing through the human body, has a biological, electrochemical, thermal and mechanical action.

The biological effect of the current is manifested in irritation and excitation of tissues and organs. As a result, skeletal muscle convulsions are observed, which can lead to a stopping of breathing, disruptive fractures and dislocation of the limbs, spasm of voice ligaments.

The electrolytic effect of the current is manifested in electrolysis (decomposition) of fluids, including blood, and also significantly changes the functional state of the cells.

The thermal effect of electric current leads to the burns of the skin, as well as the death of the fattened tissues, up to charred.

The mechanical effect of the current is manifested in the bundle of tissues and even the tears of body parts.

Electricalravum can be divided into local, common (electric shocks) and mixed (local electric shocks and electrical shocks at the same time). Local electricians make up 20% of the electric shocks taken into account, electrical shocks - 25% and mixed - 55%.

Local electricians - clearly pronounced local disorders of the body tissue, most often these are superficial damage, i.e., damage to the skin, sometimes soft tissues, as well as articular bags and bones. Local electricians are cured, and human performance is restored in whole or in part.

Characteristic types of local electricians - Electric burns, electrical signs, leather metallization, electrophthalmia and mechanical damage.

The most common electric shocks are electric burns. They make up 60 - 65%, and about 1/3 of them are accompanied by other electricians.

Distinguish burns: current (contact) and arc.

Contact electricity, i.e., tissue lesions in the entrance places, the exit and on the way of movement of electrotock arise as a result of the contact of a person with a current-carrying part. These burns occur during the operation of electrical installations of relatively small voltage (not higher than 1-2 kV), they are relatively lungs.

Arc burn due to the effect of an electric arc that creates a high temperature of the arc burn occurs when operating in electrical installations of different stresses, is often a consequence of random short circuits in the installations above 1000 V and up to 10 kV or erroneous personnel operations. The defeat arises from the flame of an electric arc or a clothes tavering from it.

Combined lesions (contact electrogy and thermal burns from the flame of an electric arc or tanned clothing, the electricity in combination with various mechanical damage, the electricity simultaneously with thermal burns and mechanical injury) is also.

In the depth of the defeat, all burns are divided into four degrees: the first is redness and swelling of the skin; Second - water bubbles; The third is a measuring of surface and deep layers of the skin; Fourth - charred skin, muscle defeat, tendons and bones.

Electrical signs They are clearly defined stains of gray or pale yellow on the surface of the skin of a person who has exploited the current. Signs have a round or oval shape with a deepening in the center. They are in the form of scratches, small wounds or bruises, warts, hemorrhages in the skin and corns. Sometimes their form corresponds to the shape of the current-supported part, to which the victim touched, and also resembles a lightning form. In most cases, electrical signs are painless and their treatment ends safely. Signs arise about 20% of current victims.

Metatallization of skin - penetration into its upper layers of metal particles that melted under the action of an electric arc. This is possible with short circuits, disconnects of disconnectors and switches under load, etc.

The affected area of \u200b\u200bleather has a rough surface, color
which is determined by the color of the compounds of the metal that has fallen into the skin:
green - when contact with copper, gray - with aluminum, blue

green - with brass, yellow-gray - with lead.

Skin metallization is observed about 10% of victims.

Ethekrophthalmia - Inflammation of the outer shells of the eyes as a result of the impact of a powerful stream of ultraviolet rays. Such irradiation is possible in the presence of an electrical arc (for example, with a short circuit), which is a source of intensive radiation of not only visible light, but also ultraviolet and infrared rays. Electrophthalmia arises relatively rarely (in 1-2% of victims), most often when conducting electric welding work.

Mechanical damage arise as a result of sharp, involuntary, convulsive cuts of muscles under the action of the current passing through the human body. At the same time, skin breaks, blood vessels and nervous tissue, as well as dislocations of the joints and bone fractures are possible. Mechanical damage - serious injuries; Treat them long. They occur relatively rarely.

Electric strike - This is the excitation of the body tissues passing through it by electric shock, accompanied by a reduction in muscles.

Distinguish four degrees of electric shock:

I - a convulsive cut of the muscles without losing consciousness;

II - a convulse reduction of muscles with a loss of consciousness, but with the preserved breath and heart work;

III - loss of consciousness and violation of cardiac activity or breathing
(either the other together)

IV - clinical death, i.e., the absence of breathing and blood circulation,
The danger of exposure to electric current on a person depends on

the resistance of the human body and the voltage attached to it, the strength of the current, the duration of its exposure, the path of passage, genus and frequency of the current, the individual properties of the victim and other factors.

The electrical conductivity of various tissues of the organism is not the same. The greatest electrical conductivity has a spinal fluid, blood serum and lymph, then one-piece blood and muscle tissue. Poorly conduct electric current internal organs having a dense protein base, brain substance and adipose tissue. Leather has the greatest resistance and, mainly its top layer (epidermis).

The electrical resistance of the human body with dry, clean and intact skin at a voltage of 15-20 V is ranging from 3,000 to 100,000 ohms, and sometimes more. When removing the top layer of skin, the resistance decreases to 500 to 700 ohms. With full removal of the skin, the resistance of the internal tissues of the body is only 300 - 500 ohms. The calculations are taken by the resistance of the human body equal to 1000 ohms.

The resistance of the human body depends on the floor and age of people: in women it resistance is less than that of men, children are less than in adults, young people are less, CHS in the elderly: this is explained by the thickness and degree of degradation of the top layer of the skin.

The electricity and frequency of it also affect electrical resistance. At frequencies of 10 - 20 kHz, the top layer of the skin almost loses its electrical strength resistance.

The main causes of electric shock

1. Random touch to the current-carrying parts under voltage as a result: erroneous actions during work;

faults of protective tools that the victims concerned the current parts and others.

2. The appearance of voltage on metal structural parts
Electrical equipment as a result:

damage to the insulation of the current parts; closure of the network phase to the Earth;

drops of wire under voltage, on the structural parts of electrical equipment, etc.

3. The appearance of the voltage on the disconnected current parts in re
Cause:

erroneous turning on the disabled installation;

closures between disconnected and stressed currents;

discharge of lightning in electrical installation and others.

4. Appearance schedule voltageon the plot of land where is located
Man, as a result:

closure phase to the ground;

potential takeaway with a long conductive subject (pipeline, railway rails);

faults in the protective grounding device, etc.

Step voltage - the voltage between the two points of the circuit of the current, located one of the other at a distance of the step, on which the person is simultaneously.

The greatest value of the step voltage near the place of closure, and the smallest - at a distance of more than 20 m.

At a distance of 1 m from the earthinger, the step voltage drop is 68% of the total voltage, at a distance of 10 m - 92%, at a distance of 20 m - almost equal to zero.

The danger of the tension of the step increases, if the person who has exposed to its effect falls: the tension of the step increases, since the current passes no longer through the legs, but through the whole body of man.

Methods and means applied

to protect against electric shock

when touched to metal inadvertent parts,

it turned out under stress

To protect against electric shock when touched with metallic inadperture parts, the following methods and tools are used:

protective grounding, reinforcement, potential leveling, system of protective conductors, protective shutdown, insulation of inadvertent parts, Electrical separation of the network, small voltage, insulation control, compensation of ground closure currents, personal protective equipment.

Technical methods and means are used separately or in combination to ensure optimal protection.

Organizational activities that ensure the safety of work in electrical installations

Organizational activities that ensure the safety of work in electrical installations are:

registration of the work of the outfit and admission, the order or list of works performed in the order of current operation;

tolerance;

supervision during operation;

registration of a break in the work, translations to another workplace, the end of work.

Technical measures ensuring safe performance of work in current electrical installations

In accordance with the requirements of safety regulations during the operation of electrical installations of consumers, the following technical measures should be made in the specified procedure for the operation with the removal of voltage;

the necessary shutdowns are made and measures are taken that prevent voltage supply to work due to the erroneous or spontaneous switching on switching equipment;

on the drives of manual and on the remote control keys, prohibitive posters are suspended;

checked the absence of voltage on the current-carrying parts, on which grounding should be imposed to protect people from electric shock;

there is grounded (ground knives are included, and where they are missing, portable groundings are installed);

1. Random touch to the current-carrying parts under the voltage as a result:

erroneous actions during work;

faults of protective tools that the victims concerned the current parts and others.

2. The appearance of voltage on the metal structural parts of electrical equipment as a result:

damage to the insulation of the current parts; closure of the network phase to the Earth;

drops of wire under voltage, on the structural parts of electrical equipment, etc.

3. The appearance of voltage on the disconnected current parts as a result: the erroneous turn on the shut off installation;

closures between disconnected and stressed currents;

discharge of lightning in electrical installation and others.

4. The emergence of the tension of the step on the plot of land where the person is, as a result:

closure phase to the ground;

potential takeaway with a long conductive subject (pipeline, railway rails);

faults in the protective grounding device, etc.

Step voltage - the voltage between the two points of the circuit of the current circuit, located one of the other at a distance of the step, on which the person is at the same time.

The greatest value of the step voltage near the place of closure, and the smallest - at a distance of more than 20 m.

At a distance of 1 m from the earthinger, the step voltage drop is 68% of the total voltage, at a distance of 10 m - 92%, at a distance of 20 m - almost equal to zero.

The danger of the tension of the step increases, if the person who has exposed to its effect falls: the tension of the step increases, since the current passes no longer through the legs, but through the whole body of man.

42. The most important factors affecting the outcome of electric shock are:

the value of the current flowing through the human body; current exposure time; current frequency;

passage of current; Individual properties of the human body. Current value. Under normal conditions, the smallest current of industrial frequency, which causes physiological sensations in humans, is on average 1 millia minute (MA); For DC current, this value is 5 mA. Duration of current exposure. The prolonged effect of electrical current with parameters that did not seek initially danger to the body can lead to death as a result of a decrease in human body resistance. It has already been noted above that when exposed to electric current on the human body, the activity of sweat glands increases, as a result of which the humidity of the skin increases, and the electrical resistance decreases sharply. As the experiments showed, the initially measured ohmic resistance of the human body, which make up tens of thousands of orals, decreased under the influence of electric current to several hundred ohms. Current and frequency. Currents of various kinds (with other things being equal) represent a different degree of danger to the body. The nature of their impact is also unequal. Permanent current produces thermal and electrolytic effect in the body, and the variable is predominantly cutting muscles, vessels, voice ligaments, etc. It has been established that the alternating current of the voltage is below 500 in a more dangerous to it by direct current voltage, and with an increase in voltage over 500 V Increases the danger from the effects of DC. The role of the Tok path. The path of the current in the human body is essential for the outcome of the defeat. The passing current is distributed in the body throughout its volume, but it passes the largest part along the path of the smallest resistance, mainly along the flows of tissue liquids, blood and lymphatic vessels and shells of the nerve trunks. Features of individual properties of a person. The physical and mental state of a person at the time of exposure to its electric current is of great importance. The dangers of lesion of the current are more susceptible to persons suffering from heart diseases, lungs, nervous diseases, etc. Therefore, labor legislation has been established by the professional selection of workers serving electrical installations, depending on the state of health.

43. Basic measures to protect against elimination EL. Current are:

Ensuring the inaccessibility of current-carrying parts that are under voltage for random touch, eliminating the risk of lesion when stresses on the housings, casing; - protective grounding, reinforcement, protective shutdown; - the use of low voltages; - The use of double isolation. Analysis of the causes of electrical exchanging detects the following main conditions for the occurrence of human lesion by electric shock: 1. Contact with current-carrying parts under voltage. 2. Damage to the insulation of electrical equipment and wiring, creating the ability to transition voltage on their structural parts. Touching the structural parts of it substantiated, can cause an electrician. 3. High voltage transition to low voltage system.

The main causes of accidents from the effect of electric current are the following.

1. Random touch or approximation on a dangerous distance to the current-carrying parts under voltage.

2. The appearance of voltage at the metal structural parts of electrical equipment - housings, casing, etc. - as a result of damage to isolation and other reasons.

3. The appearance of voltage on the disconnected current parts on which people operate, due to the erroneous installation of the installation.

4. The occurrence of step tension on the surface of the Earth as a result of the closure of the wire to the ground.

The main measures of protection against lesion are: ensuring the inaccessibility of the current-carrying parts under voltage, for random touch; protective network separation; elimination of the danger of damage when the tension appears on the housings, casing and other parts of the electrical equipment, which is achieved by the use of low stresses, using double insulation, equalizing the potential, protective grounding, reducing, protective disconnection, etc.; the use of special protective equipment - portable devices and devices; Organization of safe operation of electrical installations.

Classification of premises for the danger of damage to the current. The environment and the surrounding environment enhance or weaken the danger of damage to the current. Taking into account this "rules of electrical installations", all rooms are divided by the degree of danger of lesion of people with electric shock to three classes: 1 - without increased danger; 2 - with increased danger and 3 - especially dangerous.

Premises without increased danger are dry, damage with normal air temperature and with insulating (for example, wooden) floors, i.e., in which there are no conditions for the premises with increased danger and especially dangerous.

An example of premises without increased danger can be the usual office premises, instrumental, laboratories, as well as some industrial premises, including the sets of instrument plants, placed in dry, damages with insulating floors and normal temperature.

Premises with increased hazard are characterized by the presence of one of the following five conditions that create increased danger:

damp, when the relative humidity of the air is longer than 75%; Such rooms are called raw;

high temperatures when the temperature of the air is long exceeded + 30 ° C; Such rooms are called hot;

conductive dust, when conductive technological dust (for example, coal, metallic, etc.) is released under the conditions of production in the premises, in such a quantity that it settles on the wires, penetrates the inside of machines, devices, etc.; Such rooms are called dust with conductive dust;

conductive floors - metal, earth, reinforced concrete, brick, etc.;

the possibilities of simultaneously touching a person to having a connection with the ground metal structures of buildings, technological apparatus, mechanisms, etc., on the one hand, and to the metal housings of electrical equipment - on the other.

An example of room with increased danger can serve as stairwells of various buildings with conductive floors, warehouse unheated rooms (even if they are placed in buildings with insulating floors and wooden racks), etc.

The premises are particularly dangerous are characterized by the presence of one of the following three conditions that create a special danger:

special damp, when the relative air humidity is close to 100% (walls, gender and objects located in the room are covered with moisture); Such rooms are called especially raw;

chemically active medium, i.e., premises in which, under the terms of production, there are pairs or deposits that are destroying for insulation and current parts of electrical equipment are formed; Such rooms are called premises with a chemically active medium:

the simultaneous presence of two or more conditions inherent in premises with increased danger.

Particularly dangerous premises are most of the industrial premises, including all the sets of engineering plants, test stations, electroplating shops, workshops, etc. To the same premises include sections of work on the Earth under the open sky or under a canopy.

The inaccessibility of the current-carrying parts of electrical installations for random touch can be provided by a number of ways: insulation of current-carrying parts, placement of them in an inaccessible height, fencing, etc.

Protective network separation. In an extensive electrical network, i.e. with a large length, quite a good insulation may have a small resistance, and the wire capacity relative to the Earth is a greater value. These circumstances are extremely undesirable under security conditions, since in such networks voltage up to 1000 V with an isolated neutral, the protective role of the insulation of the wires is lost and the threat of human lesion is increasing in case of contact with the network (or to any object that produced it under phase voltage).

This significant drawback can be eliminated by the so-called protective separation of the network, i.e., the separation of an extensive (extended) network into separate small lengths and electrically unnecessary sites.

The separation is carried out with the help of special separation transformers. Insulated areas of the network have a large insulation resistance and low wire capacity relative to the Earth, thereby significantly improving security conditions.

Apply reduced voltage. When working with portable manual power tools - a drill, a wrench, an electric chub, etc., and also a manual portable lamp man has a long contact with the enclosures of this equipment. As a result, it dramatically increases the danger of damage to the current in case of damage to the isolation and the appearance of voltage on the case, especially if the work is carried out in a room with increased danger, especially dangerous or outdoors.

To eliminate this danger, it is necessary to feed the hand tool and portable lamps with a reduced voltage not higher than 36 V.

In addition, in particularly dangerous premises under particularly unfavorable conditions (for example, work in a metal tank, work sitting or lying on a conductive floor, etc.) To power the hand portable lamps, even lower voltage is required - 12 V.