The conditions and the main causes of electric shock. The main causes of human lesion by electric shock. The concept of stepping voltage and tension

Due to the widespread use of electricity, both in manufacturing processes and for solving household problems, a significant threat to electric shock is created. To prevent such situations, there are a number of rules to protect the staff and simple alternates from the deposits of illiterate circulation of electricity. To do this, it is important to understand the causes of electric shock and the measures necessary in various situations to eliminate the lesion of the current.

The concept of electric

Under an electric strike, it should be understood such a situation where the electrical charge from the current source as one of the paths or the only path uses the human body. At the same time, the directional movement of particles creates a spontaneous contraction of the muscles falling under its impact on the course of the flow, the current destroys the tissue and causes other damage.

Heavyweight can occur both in the normal operation of electrical installations and emergency situations (damage to the insulation of wires, sample of dielectrics, destruction of insulators, during the combustion of the electrical arc, etc.). In addition to interaction with current in everyday life, there is a possibility of lightning damage. But whatever current flow, it can cause a number of adverse consequences for the human body.

How does electricity act on the human body?

If you do not consider the planned exposure to the current, with medical or cosmetic procedures, the effects of which are directed to transmitting an electric current through the body tissues, then with all cases of electrical injury, the body receives three main current effects:

Thermal - lead to burns at the exposure points of the electric flow. In contrast to the usual, electric burn is further complicated by the damage to the tissues with small particles of the hot metal. Which after impact remain in the skin, respectively, the expansion of such wounds occurs longer and requires additional effort. Depending on the conditions of the electric shock, light, medium or heavy burns can be formed.
Dynamic - causes reduction and subsequent damage to muscles and ligaments. Since all the muscles in the body are controlled by electrical pulses, then when the current flows, their reduction is occurring. Because of which mechanical damage to tissues - ruptures. As well as the convulsive compression of the limbs, in which a person cannot independently dismiss the fingers and free himself from the current action. The same effect occurs with the heart, which can cause deadly shock.
Electrolytic - When current leaks, blood vessels have the lowest resistance, which are conductors in the body. When the electric flow through the vessels, the blood acts as a conductor, which, with long-term exposure, decomposes on plasma and blood taurus.

Depending on the situation, damage may also lead to electrical shock. The condition of the victim is characterized by the absence of an adequate response to occurring events and extended pupils. In such a state, it is difficult to judge the damage caused by damage, due to the fact that a person cannot report on his own well-being. Therefore, its condition is determined by indirect factors (pulse, breathing, etc.).

The main causes of electric shock

Causes can be caused by various factors and situations. Because of these differences in situations, the rules regulate the use of certain means of protection or impart into obligations to fulfill certain measures. In this connection, the causes of the defeat are divided into such that may be happening in living conditions, and those that may occur in production.

At home

The most frequent causes of damage in household conditions are any malfunction or careless appeal of the person itself with the operating devices. The strength of the current affecting a person depends on the resistance of the electrical circuit, which includes skin resistance, shoes, spreading current in the floor or any other point. The smallest amount of resistance is obtained in the case of a wound on the skin, the wet surface of the hands or when a person concerns grounded elements.

Special attention should be paid to such reasons for lesions:

Insulation disorders inside - For the most part, all homemade vacuum cleaners, teapots, microwaves, washing and other helpers are equipped with reliable insulation on the factory. But, due to natural aging or due to damage, the insulation resistance can be disturbed, which causes electric shock. This problem is characterized by the transition of the potential on the body or metal parts of electrical devices and causes the occurrence.
Damage to the insulating sheath of wires - refers to both the wiring and all sorts of feeding cords and extension cords. From the places where the bears occurred, blows or mistresses, there is the possibility of electric shock, especially when water hits them.
Contact with homemade devices and bare current-friendly parts. Both do not guarantee a person no compliance with standards. Therefore, interaction with dubious devices or bare wires can lead to severe shock.
Spontaneous attempts of repair - When people without the presence of the necessary skills and knowledge are trying to repair some devices or wiring. At the same time, they expose themselves dangers to randomly touch the elements that are under voltage, which is the cause of the defeat. For example, when replacing the electrical lamp in the lamp when the voltage is not removed from the cartridge.
Using switches or sockets with damaged housing. The case of these devices performs the function of a natural barrier, which during damage opens access to current elements and arises the threat of lesion to the current.
Attempts to replace lamps in the presence of voltage in the cartridge - due to negligence, a person may touch the internal elements, which will lead to electric shock. The situation is also possible when the blur lamp is destroyed, and disintegrates in their hands, and some parts can become electrotocker conductors. In this case, the disconnected switch is not a guarantee of the lack of voltage due to the fact that it may not break the phase.
Operation of electrical appliances together with water - Attempts to dry the head with a hairdryer and use the electric shaver, while in the bathroom, the water tank into the included electric kettle and other options for contacting the device with water can cause damage to the current.
Temporary wiring on twists - It is often in everyday life to speed up the supply of voltage and not spend a lot of time on a full-fledged laying into the wall or at least the channel make an open method. It is these "snot" that rave into incision all the standards around the house, a shed or a garage can cause damage to the current.

In production

The predominant majority of work that are performed in production provide a number of measures aimed at preventing electrical damage. But, due to the violation of these events and the rules, the staff contacting electrical installations or simply performing work in the immediate vicinity can be affected by stress.

Consider the most frequent causes of damage to the current in production:

- Lack of protective equipment or using unsuitable. Especially relevant in those situations where any devices remain under voltage while working on them.
- Insulation disorder and no grounding - In the power chains these are damage to insulators, cable insulation and other heavy damage to the equipment. They determine the presence of potential on the housing, carrying structures that can lead to death in case of contact. Initially, the grounding is provided for as insurance in case of insulation damage, so the lesion is possible only in the absence or malfunction of grounding.
- The burning of an electric arc - It can occur as an integral part of the work of the same switches, welding machines or short-circuit, and an emergency. The lesion of the arc can cause burns, characterized by the transition to the part of the charge and the subsequent passage of the current through the person.
- Falling Wires to Earth - Creates a dangerous zone, which is 10 m for an open area and 8 m for premises. In this space, there is spreading of currents if the protection does not turn off the line. Due to the spreading of currents on the surface of the soil, the potential is formed, which decreases in proportion to the removal from the point of the fall. In such a zone, the cause of the damage becomes, the resulting potential difference between the footsteps of a person.
- Violation of safety signs - Most dangerous places in the enterprise are protected. At the fencing itself or in places, there are time or regular signs or posters are postponed. In the case when a person deliberately or by negligence violates the demand of the signs, lesion can occur.
- If the switching or triggering did not occur or are not fulfilled. Since most of the high-voltage equipment is remotely controlled, and the electrical contact nodes in the switches and disconnectors are quite difficult to monitor, the absence of voltage is obtained by means of pointers or alarms. In the case when for mechanical reasons, the switch or disconnector did not turn off at least one of the phases, there is a threat of lesion to the current on some kind of network, so it is necessary to use the pointer.
- Error voltage supply - When performing work with the removal of voltage, in line or electrical installation, it is randomly informed by the potential of both employees and as a result of an emergency. If the staff goes beyond the protective zone, fenced by grounding, or it will not install them at all, then for them there is a threat of lesion.
- Induced tension - It is the most dangerous factor in de-energized wires and neutral elements (sections of the conductor fencing with two insulators). At the production of the most dangerous is the damage to constant current. Because the frequency of alternating current itself falls to zero and rises again, due to which its impact is non-permanent.
- Violation of the procedure for removing or hiding grounding - According to the requirements of the rules when installing a ground, it first connects it from the ground, and then wrapped onto the conductor. Otherwise, in the presence of potential in the line, the employee will first be grounded under the potential of the line, and when it will try to connect it to a grounding circuit, it will be the element in the current flow chain. Removing the ground is made in the reverse order - first removed from the current-handing elements, and then turns off from the contour. When removing, there is also a threat.

What to do in case of lesion?

If you witness that someone is affected by electricity and is still under its impact, you need to free it as soon as possible. Since the outcome of the electrician directly depends on the duration of the contact, the response rate must be maximum.

First, it is necessary to de-energize the electrical installation or its parts with which the person interacts. It is best for this machine guns, switches or fuses located in the immediate vicinity. For high-voltage networks, their analogue are switches and disconnectors. If there are no other measures at hand to reduce the duration of exposure.

The most important rules for release is compliance with the saving security rules themselves, so that it is not affected by the current. Otherwise, in order to prevent the deadly outcome, any funds will be suitable.

Overcoming up to 1000 in

For lines of up to 1 kV, any dry clothes wound on hand can be suitable, ideally there should be dielectric gloves. They can be touched by the victim for the lagging ends of the dry clothes. Use the handle tool to eat the wire. You can also break the electrical chain through the room between the victim and the earth of the dielectric sheet.

In devices above 1 kV approach the victim, it is also dangerous that the saving and himself can get under step tension. But, at the same time, it is possible to draw any uninsulated wire between the source and the victims. Try to drag the wire with an insulating barbell, but in dielectric gloves. The cable, also in gloves, is allowed to cut the ax in the ax.

Electric shock protection measures

To avoid damage to the current and minimize the reasons that can determine how to adhere to a number of simple rules:

Do not touch electrical devices, switches, forks, rosettes with wet hands;
Preventing inclusion in the network of faulty devices or devices that have no grounding of the housing (the absence is allowed only in devices designed for very low voltage);
Do not violate instructions prescribed by electrical signs that regulate certain actions;
Do not throw the devices on, leaving the house, prevent pulling the plug for the cord;
When working in electrical installations, be sure to comply with the requirements of the rules, instructions, the order of technological processes;
Work in electrical installations is performed only with the use of the necessary means of protection.

Video in the development of the topic

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.

Rod and current frequency also affect the degree of defeat. The most dangerous is the variable current with a frequency of 20 to 1000 Hz. AC is more dangerous than constant, but it is characteristic only for stresses up to 250-300 V; At high stresses, the constant current becomes more dangerous. With an increase in the frequency of alternating current passing through the human body, the full resistance of the body decreases, and the current current increases. However, the decrease in resistance is possible only within the frequencies from 0 to 50-60 Hz. The further increase in current frequency is accompanied by a decrease in the danger of the lesion, which completely disappears at a frequency of 450-500 kHz. But these currents can cause burns both in the occurrence of an electric arc and during passing them directly through the human body. Reducing the risk of lesion with an increase in frequency is almost noticeable at a frequency of 1000-2000 Hz.

Individual properties of a person and the state of the environment also have a noticeable effect on the severity of the lesion.

Conditions and causes of electric shock

Human damage by electric flow or electric arc can occur in the following cases:

· With a single-phase (single) touch isolated from human Earth to uninsulated current-generating parts of electrical installations under voltage;

· With the simultaneous touch of a person to two uninsulated parts of electrical installations under voltage;

· When a person is approaching, not isolated from the Earth, for a dangerous distance to the current-carrying, non-protected insulation parts of electrical installations under voltage;

· With a touch of a person who is not isolated from the ground, to the inactive metal parts (housings) of electrical installations that are under voltage due to the closure on the case;

· Under the action of atmospheric electricity during the discharge of lightning;

· As a result of an electrical arc;

· When freeing another person under voltage.

You can allocate the following reasons for electricians:

Technical reasons are the inconsistency of electrical installations, protection and equipment for safety requirements and conditions of application related to defects of design documentation, manufacturing, installation and repair; Faults of installations, protective equipment and devices occurring during operation.

Organizational and technical reasons - non-compliance with safety measures at the stage of operation (maintenance) of electrical installations; The late replacement of faulty or outdated equipment and the use of installations not commissioned in the desired order (including self-made).

Organizational reasons - non-fulfillment or incorrect implementation of organizational security measures, inconsistency of the work performed by the task.

Organizational and social reasons:

· Work in overtime (including work to eliminate the consequences of accidents);

· Missing the work of the specialty;

· Violation of work discipline;

· Admission to work on electrical installations of persons under 18 years of age;

· Attracting the work of persons unformed orders for employment to the organization;

· Admission to the work of persons with medical contraindications.

When considering the reasons, it is necessary to take into account the so-called human factors. These include both psychophysiological, personal factors (the absence of individual qualities necessary for this work, violation of his psychological state, etc.) and socio-psychological (unsatisfactory psychological climate in the team, living conditions, etc.).

Electric shock protection measures

According to the requirements of regulatory documents, the safety of electrical installations is ensured by the following major measures:

1) inaccessibility of current parts;

2) proper, and in some cases of increased (double) isolation;

3) grounding or reducing electrical equipment and elements of electrical installations that can be under voltage;

4) reliable and high-speed automatic protective shutdown;

5) the use of reduced stresses (42 V and below) to power portable current collectors;

6) protective separation of chains;

7) locking, warning alarms, inscriptions and posters;

8) the use of protective equipment and devices;

9) carrying out planned-warning repairs and preventive tests of electrical equipment, apparatus and networks in operation;

10) carrying out a number of organizational events (special training, certification and re-certification of persons electrical personnel, instructions, etc.).

To ensure electrical safety at the meat and dairy industries, the following technical methods and protection means are used: protective grounding, reinforcement, low voltage use, winding isolation control, personal protective equipment and safety devices, protective disconnecting devices.

Protective grounding is a deliberate electrical connection with a severity or its equivalent of metal inadequate parts that may be energized. It protects against electric shock when touched by metal hardware, metal structures of electrical installations, which, due to disruption of electrical insulation, are substituted.

The essence of protection lies in the fact that when closing the current passes on both parallel branches and is distributed in between them inversely proportionate to their resistance. Since the resistance of the "Land" chain is many times the resistance of the chain "Corps-Earth", the current passing through a person is reduced.

Depending on the placement of the grounding agent relative to grounded equipment, remote and contour grounding devices are distinguished.

Remote earthingers are located at some distance from the equipment, while the grounded electrical installation housings are located on Earth with zero potential, and a person touching the housing is under full earthing voltage.

Contour earthingers are located along the contour around the equipment in close proximity, so the equipment is located in the zone of current spreading. In this case, when you closure to the body, the soil potential on the territory of the electrical installation (for example, substation) acquires values \u200b\u200bclose to the grounding potential and grounded electrical equipment, and the touch voltage is reduced.

A reinforcement is a deliberate electrical connection with a zero protective conductor of metal inadvertent parts, which may be under voltage. With such an electrical connection, if it is reliably performed, any closure on the body turns into a single-phase short circuit (i.e., the closure between the phases and zero wire). At the same time, there is a current of such a force at which the protection of protection (fuse or machine) is ensured and the automatic shutdown of the damaged installation from the supply network.

Electrical safety.

The main reasons for human lesion by electric shock:

Disruption of isolation or loss of insulating properties;
Direct touch or dangerous approximation to the current-carrying parts under voltage;
Inconsistency of actions.

The effect of electric current on the living fabric wears a versatile and peculiar character, there are several of them:

Thermal action: There are burns of individual parts of the body, heating to high temperatures of blood vessels, nerves, hearts, brain and other organs, which causes serious functional changes. According to the Joule-Lenza law, the amount of heat distinguished heat is directly proportional to the square of the current force, the resistance of the human body and the exposure time.
The electrolytic effect is expressed in the decay of blood molecules and lymphs per ions. The physicochemical composition of these fluids changes, which leads to a violation of the life process.
The mechanical action of the current leads to a bundle, rupture of body tissues as a result of an electrodynamic effect, as well as instantaneous explosion-like formation of steam from tissue fluid and blood.
The biological effect is the excitation of living fabrics, causing a convulse reduction and disruption of internal bioelectric processes.

Distinguish two types of lesions:

Local electricians causing local damage to the body.

Electric burn - the most common electric shock:

Two types - a current (or pin) arising when the current pass through the human body as a result of contact with current-time parts, the contact burns most often occurs at a voltage of no more than 2000 volts;

- Arc burn is possible with different voltages. As a result of an electric arc lesion when passing through the human body, a fatal outcome is possible.

Electrical signs - sharply outlined stains of gray or pale yellow on the surface of a human body that has exploited an electric current.
Metalization of the skin occurs in the case of penetration into the upper layers of the skin of the smallest particles of metal, which melted under the action of an electric arc.
Mechanical damage - a consequence of sharp involuntary cuts of muscles under the action of current (rupture of tendons, skin, vessels, sometimes dislocations and fractures are possible).
Electrophthalmia - inflammation of the cornea and the conjunctivities of the eye under the action of ultraviolet rays from the electric arc.

General electricians lead to the defeat of the whole organism, they are divided into four degrees:

I - convulsive cuts of muscles;

II - convulsive muscle contraction with loss of consciousness;

Iii - loss of consciousness with impaired respiratory and cardiac functions;

IV - clinical death (time segment from the moment of stopping the heart and breathing before the death of the brain cells of about 4 - 6 minutes, during this period a person can assist)

Factors affecting the danger of damage to the current:

The main affixing factor is the current of the current, the larger the current, the more dangerous its impact.

Three threshold values \u200b\u200bare installed for the impact characteristics:

Threshold tangible current 0.5 - 1.5 mA for alternating current 50 Hz and 5 - 7 mA for permanent - minimum current causing pain (itching, tingling).
The threshold is not released 8 - 16 mA 50 Hz and 50 - 70 mA 0 Hz - the minimum value of the current in which the convulsive cut of the arm muscles does not allow a person to free themselves from the current-carrying parts.
The threshold fibrillation 100 mA 50 Hz and 300 mA 0 Hz - causes heart fibrillation - chaotic high-end reductions in the heart muscle, in which blood circulation is stopped.

The resistance of the body of a person is made of skin resistance and internal organs, at what:

Ringly \u003d 3000 - 20 000 Ohm,

Internal organs RVN \u003d 500 - 700 ohms,

RF \u003d 2RN + RV

Skin resistance depends on its condition: dry - wet, there is no damage, contamination, time and density of contact.

Duration of exposure.
Path, genus and current frequency.
Individual features of a person (age, psychological, physical).
Environmental conditions.

Classification of premises by the degree of danger of electroporations.

The safety of electrical equipment depends on the factors of its environment. Taking into account these factors, all the premises are divided into three classes:

The first - without increased danger (dry, without dust, with normal temperature, with insulating floors, humidity up to 70%).
The second - premises with increased danger are characterized by one of the following signs: relative humidity\u003e 75%, the presence of conductive dust, the presence of conductive floors, high air temperature (\u003e 30, periodically\u003e 35 and briefly\u003e 40), the ability to simultaneously touch the person to metal parts of electrical installations and to metal structures connected to the Earth.
The third - premises are especially dangerous: the presence of humidity is close to 100%, the presence of a chemical aggressive environment, the presence of two or more signs of premises with increased danger.

Electrical installations are classified by voltage into two groups:

Electrical installations with rated voltage up to 1000 V.
Electrical installations with voltage over 1000 V.

Electrical products according to the method of protecting a person from electric shock is divided into five classes: 0; 01; I; II, III.

Class 0 - Products with a rated voltage of more than 42 V with working insulation and not having tools for grounding or reassembly (household appliances).

Class 01 - Products with working insulation and element of grounding (reinforcement).

Class I - Products with working isolation, ground element and power wire with grounding (reducing) bus.

Class II - Products having all available contacts double or enhanced insulation.

Class III - products without internal and external electrical circuits with voltage above 42 V.

The lesion of the current is a consequence of the simultaneous touch of a person to two points of the electrical circuit, between which there is a potential difference. The danger of such a touch depends on the characteristics of the chain and the scheme for the inclusion of a person in it, determining the current strength, taking into account these factors, it is possible to choose protective measures with a large degree of accuracy.

Possible human inclusion schemes in electrical chain:

Two-phase inclusion - more dangerous than single-phase, because The largest voltage is applied to the body - linear: J \u003d Ul / RF,

where Ul is a linear voltage (B);

RF - the resistance of the human body (OM), with calculations take 1000 ohms.

Single-phase inclusion - on the current passing through a person affects various factors, which reduces the danger of lesion: JCh \u003d U / (2rch + R),

where U is the voltage in the network (B);

R is insulation resistance (OM).

Or: jch \u003d u / r0; R0 - shoes resistance; Paul resistance; Wire insulation resistance; Resistance to human body.

Touch voltage - occurs as a result of touches of electrical installations.

UPR \u003d * (ln - ln) * α,

where is the strength of the current closure on the ground (a);

ρ is the specific resistance of the base of the floor (OM * M);

L and D - length and diameter of the grounding (M);

X is the distance from the person to the grounding point (M);

α - Touch voltage coefficient.

Stepper voltage - voltage on the human body at the position of the legs at the points of the field of expansion of the current with the earthing or from the wires fallen on Earth.

When a person moves to the source of the electric field or from it, the length of the step is taken in the calculations of 0.8 m.

The maximum voltage value at the point of circuit of the electric current to the ground and as it removes it from it. It is believed that at a distance of 20 m from the location of the closure, the potential is zero.

X is the distance of a person from the point of closure;

A - foot length;

ρ is the resistivity of the soil.

Consequently, it is necessary to leave the voltage zone as shorter steps as possible.

Protective measures from electric shock:

Organizational events

Recruitment;
Training of electrical safety rules, certification;
Appointment of responsible persons;
Conduct periodic inspections, measurements and testing electrical equipment.

Application of individual protective

Basic insulating protective equipment (dielectric gloves, insulated tool);
Additional protective equipment (dielectric mats and stands);
Auxiliary devices (screens, monterskie, etc.).

Technical events

Protective grounding is a deliberate electrical connection with the Earth or its equivalent of metal inadvertising parts of electrical installations, which may be under voltage.

According to the rules, all electrical installations operating at the rated voltage of AC are more than 50 V and permanent more than 120 V (except lamps suspended in a room without increased danger at an altitude of at least 2 m).

As artificial entrancers, steel pipes, corners, pins are used in the ground. The water and sewer pipes laid in the ground can be attributed to the ground, cables with a metal shell.

The principle of grounding is reduced to safe values \u200b\u200bof touches or steps in the event of a circuit of the current on the metal housings of electrical equipment.

Considering that the resistance of the human body is much more resistance to the grounding device, the main current in the event of a closure will be held through the earthing.

There are shortcomings:

Part of the current will pass through the human body.
In case of violation in the circuit of the grounding device, the danger of damage to the current increases sharply. According to the standards, the resistance of the grounding device is checked at least 1 time per year, in particularly dangerous rooms - at least 1 time per quarter.

The reinforcement is a deliberate compound with a zero protective conductor of metal inactive parts of electrical equipment that may be energized.

The principle of the protection of the protective reinforcement is to turn a closure on the body into a single-phase closure (between the phase and zero protective conductor) in order to create a large current capable of ensuring the triggering of a protective disconnecting device (fuses, magnetic starters with thermal protection, etc.).

To ensure automatic shutdown of the emergency equipment, the resistance of the short circuit network must be small (about 2 ohms).

Disadvantages - depriving the protection of electrotransmitters when the zero wire break.

Protective shutdown is a high-speed shutdown of electrical installations (up to 1000 V) when it occurs in hazardous electric shock.

The response time of the UZO does not exceed 0.03 ... 0.04 s.

With a decrease in the flow of current flow through a person, the danger is reduced.

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.