Characteristics of electric shock to a person. Electrical resistance of the human body. 2

The main causes of electric shock. 3

Methods and means used. four

for protection against electric shock. four

when touching metal non-current-carrying parts, 4

under tension. four

Organizational measures to ensure the safety of work in electrical installations. four

Technical measures to ensure the safe performance of work in existing electrical installations. four

Characteristics of electric shock to a person. Electrical resistance of the human body

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

The biological effect of current is manifested in irritation and excitation of tissues and organs. As a result, skeletal muscle spasms are observed, which can lead to respiratory arrest, avulsion fractures and dislocations of the limbs, and spasm of the vocal cords.

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

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

The mechanical action of the current is manifested in the stratification of tissues and even the separation of body parts.

Electrical injuries can be conditionally divided into local, general (electric shocks) and mixed (local electrical injuries and electrical shocks at the same time). Local electric shocks make up 20% of the considered electric injuries, electric shocks - 25% and mixed - 55%.

Local electrical injuries- clearly expressed local disorders of body tissues, most often these are superficial injuries, i.e. damage to the skin, sometimes soft tissues, as well as articular bags and bones. Local electrical injuries are cured, and a person's working capacity is restored completely or partially.

Typical types of local electrical injuries- electrical burns, electrical signs, skin plating, electrophthalmia and mechanical damage.

The most common electrical injury is electrical burns. They make up 60 - 65%, and about 1/3 of them are accompanied by other electrical injuries.

There are burns: current (contact) and arc.

Contact electrical burns, i.e., tissue damage at the points of entry, exit and on the path of electric current flow occurs as a result of human contact with the current-carrying part. These burns occur during the operation of electrical installations of relatively low voltage (not higher than 1-2 kV), they are relatively light.

arc burn caused by exposure to an electric arc that creates a high temperature Arc burn occurs when working in electrical installations of various voltages, often the result of accidental short circuits in installations above 1000 V and up to 10 kV or erroneous operations of personnel. The defeat occurs from the flame of an electric arc or clothing caught fire from it.

There may also be combined lesions (contact electric burn and thermal burn from the flame of an electric arc or ignited clothing, electric burn in combination with various mechanical damage, electric burn simultaneously with thermal burn and mechanical injury).

According to the depth of the lesion, all burns are divided into four degrees: the first - redness and swelling of the skin; the second - water bubbles; the third is the necrosis of the superficial and deep layers of the skin; the fourth - charring of the skin, damage to muscles, tendons and bones.

electrical signs are clearly defined spots of gray or pale yellow color on the surface of the skin of a person who has been exposed to current. Signs are round or oval with a depression in the center. They come in the form of scratches, small wounds or bruises, warts, skin hemorrhages, and calluses. Sometimes their shape corresponds to the shape of the current-carrying part that the victim touched, and also resembles the shape of lightning. In most cases, electrical signs are painless and their treatment ends well. Signs occur in about 20% of those affected by the current.

Skin metallization- penetration into its upper layers of particles of metal melted under the action of an electric arc. This is possible in case of short circuits, trips of disconnectors and knife switches under load, etc.

The affected area of ​​the skin has a rough surface, color
which is determined by the color of the metal compounds on the skin:
green - in contact with copper, gray - with aluminum, blue -

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

Metallization of the skin is observed in approximately 10% of the victims.

Etectroophthalmia- inflammation of the outer membranes of the eyes as a result of exposure to a powerful stream of ultraviolet rays. Such exposure is possible in the presence of an electric arc (for example, during a short circuit), which is a source of intense radiation not only of visible light, but also of ultraviolet and infrared rays. Electrophthalmia occurs relatively rarely (in 1-2% of victims), most often during electric welding.

Mechanical damage occurs as a result of sharp, involuntary, convulsive muscle contractions under the influence of current passing through the human body. In this case, ruptures of the skin, blood vessels and nervous tissue are possible, as well as dislocations of the joints and bone fractures. Mechanical damage - serious injuries; their treatment is long. They occur relatively rarely.

electric shock- this is the excitation of body tissues by an electric current passing through it, accompanied by muscle contraction.

Distinguish four degrees of electric shock:

I - convulsive muscle contraction without loss of consciousness;

II - convulsive muscle contraction with loss of consciousness, but with preserved breathing and heart function;

III - loss of consciousness and impaired cardiac activity or breathing
niya (or both together)

IV - clinical death, i.e. lack 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 applied to it, the strength of the current, the duration of its impact, the path of passage, the type and frequency of the current, the individual properties of the victim and other factors.

The electrical conductivity of various tissues of the body is not the same. Cerebrospinal fluid, blood serum and lymph have the highest electrical conductivity, followed by whole blood and muscle tissue. The internal organs, which have a dense protein base, brain substance and adipose tissue, conduct electrical current poorly. The skin and, mainly, its upper layer (epidermis) has the greatest resistance.

The electrical resistance of the human body with dry, clean and intact skin at a voltage of 15 - 20 V is in the range from 3000 to 100,000 ohms, and sometimes more. When the top layer of the skin is removed, the resistance decreases to 500 - 700 ohms. With complete removal of the skin, the resistance of the internal tissues of the body is only 300 - 500 ohms. When calculating, the resistance of the human body is taken equal to 1000 ohms.

The resistance of the human body depends on the sex and age of people: in women, this resistance is less than in men, in children it is less than in adults, in young people it is less, NR IN THE ELDERLY: THIS is due to the thickness and degree of coarsening of the upper layer of the skin.

The electrical resistance is also affected by the type of current and its frequency. At frequencies of 10 - 20 kHz, the upper layer of the skin practically loses resistance to electric current.

The main causes of electric shock

1. Accidental contact with live parts under voltage as a result of: erroneous actions during work;

malfunctions of protective equipment with which the victim touched current-carrying parts, etc.

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

damage to the insulation of current-carrying parts; network phase closure to ground;

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

3. The appearance of voltage on disconnected current-carrying parts in re
Result:

erroneous inclusion of a disabled installation;

short circuits between disconnected and energized live parts;

lightning discharge into an electrical installation, etc.

4. Emergence step voltage on the land where
person as a result:

phase-to-earth short circuit;

removal of the potential by an extended conductive object (pipeline, railway rails);

malfunctions in the protective earthing device, etc.

Step Voltage - voltage between two points in a current circuit that are a step apart from one another and where a person is standing at the same time.

The highest step voltage is near the fault, and the lowest is at a distance of more than 20 m.

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

The danger of step voltage increases if the person who has been exposed to it falls: the step voltage increases, since the current no longer passes through the legs, but through the entire body of a person.

Methods and means used

for protection against electric shock

when touching metal non-current-carrying parts,

under tension

To protect against electric shock when touching metal non-current-carrying parts that are energized, the following methods and means are used:

protective earthing, grounding, potential equalization, system of protective conductors, protective shutdown, isolation of non-current-carrying parts, electrical separation of the network, low voltage, insulation control, compensation of earth fault currents, personal protective equipment.

Technical methods and means are used separately or in combination so as to provide optimal protection.

Organizational measures to ensure the safety of work in electrical installations

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

registration of work with a work permit, order or list of works performed in the order of current operation;

work permit;

supervision during work;

registration of a break in work, transfers to another workplace, completion of work.

Technical measures to ensure the safe performance of work in existing electrical installations

In accordance with the requirements of the Safety Rules for the operation of consumer electrical installations, to prepare the workplace during work with stress relief, the following technical measures must be performed in the specified order;

the necessary shutdowns have been made and measures have been taken to prevent the supply of voltage to the place of work due to erroneous or spontaneous switching on of the switching equipment;

prohibitory posters are posted on the manual drives and on the remote control keys of the switching equipment;

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

grounding is applied (grounding knives are turned on, and where they are absent, portable grounding devices are installed);

The most frequent cases:

• accidental contact with live parts under voltage (bare wires, contacts of electrical equipment, tires, etc.);
• the sudden appearance of voltage where, under normal conditions, it should not be;
• the appearance of voltage on disconnected parts of electrical equipment (due to erroneous switching on, voltage induction by neighboring installations, etc.);
• the occurrence of voltage on the surface of the earth as a result of a short circuit of the wire with the earth, a malfunction of grounding devices, etc.
• electric shock to a person who accidentally found himself under voltage. Currents through the human body of the order of 0.05-0.1 A are dangerous, large values ​​​​can be fatal;
• overheating of wires or an electric arc between them during short circuits, which leads to human burns or fires;
• overheating of damaged areas of insulation between wires by currents, leakage through the insulation, which can lead to spontaneous combustion of the insulation;
• overheating of electrical equipment cases due to their overload.

To ensure security, you must:

eliminate the possibility of a person touching live parts, which is achieved by placing electrical equipment in closed cases and turning it off during repairs;

if possible, use safe low voltages up to 36 V when using portable electrical equipment;

maintain a high level of isolation relative to earth;

reduce the effect of wire capacitance;

use protective earth (ground wire);

use network-wide leakage protection devices in networks with deaf neutral grounding.

In a network with grounding, the connection of electrical equipment cases to separate grounding conductors that are not connected to the neutral wire is prohibited.

The effect of electric current on the human body

The action of electric current on the human body is manifested in the following forms: thermal, electrolytic, mechanical, biological.

Thermal impact manifests itself in the form of current and arc burns.

Degrees of burn: redness, blistering, tissue necrosis, charring. In this case, the area of ​​damage should be taken into account.

In case of electric shock, a person may receive local electrical injury or electric shock.

Local electrical injuries: burns, metallization of the skin, electrical signs, electrophthalmia.

The electrolytic effect is manifested in the form of damage to internal organs due to electrochemical reactions in the human body.

Mechanical action can be direct or indirect. Direct mechanical action manifests itself in the form of a rupture of muscle tissues and walls of blood vessels due to the transformation of lymph or blood into steam. Indirect mechanical impact is manifested in the form of bruises, dislocations, fractures with sharp involuntary convulsive muscle contractions.

The biological effect is manifested in the form of an electric shock - the impact of an electric current on the central nervous system.

Electric shock has several degrees:

slight trembling in the joints, mild pain,

severe pain in the joints,

loss of consciousness and disturbance of cardiac activity or breathing,

loss of consciousness and cardiac arrest or respiratory arrest,

loss of consciousness, cardiac arrest, respiratory arrest, i.e. state of clinical death.

The degree of electric shock to a person is significantly affected by: the magnitude of the current, the duration of the current flow through the human body, the flow path, and the condition of the skin.

According to the magnitude and effect of the current on the human body, a tangible current and a non-releasing current are distinguished, in which the victim cannot unclench his hand on his own. Perceptible current - constant about 5 - 8 mA, variable - about 1 mA.

The value of the non-releasing current is about 15 - 30 mA. Currents greater than 30 mA are considered dangerous.

The value of the resistance of the human body, depending on external conditions, can vary over a wide range - from several hundred ohms to tens of kilohms. A particularly sharp drop in resistance is observed at voltages up to 40-50 V, when the resistance of the human body decreases tenfold. However, when carrying out calculations for electrical safety in networks with voltages above 50 V, it is customary to consider the resistance of the human body to be 1000 ohms.

The duration of the current flow and the magnitude of the allowable current are related by the empirical formula

The shorter the duration of current flow, the greater the value of the allowable current. If At \u003d 16 ms, then the value of the permissible current is 30 mA.

This current value determines the insulation requirements. So, for example, for a network with a phase voltage of 220 V, the insulation resistance must be at least

What is the general characteristic of the distribution of electrical injuries in railway transport?

On railways, more than 70% of cases of electrical injury occur in the power supply and locomotive facilities. It is necessary to pay maximum attention to the prevention of electrical injuries here, since electrical installations and power lines are the main object of service and the subject of labor.

More than 8% of cases of electrical injury occur in places with increased danger and especially dangerous (contact network, overhead power lines, etc.).

An analysis of the distribution of electrical injuries depending on the month, day of the week, decade and time of the incident during the day shows the following trend. The main share of electrical injuries falls on the period from June to September, when the largest amount of work is planned for all the facilities of the Ministry of Railways. On the days of the week, electrical injuries are distributed almost evenly, with the exception of Saturday and Sunday, when the amount of work is significantly reduced and mainly troubleshooting is carried out in emergency cases. The most unfavorable is the second decade. It accounts for 44 to 52% of all injuries. In terms of work completion time from their start, the largest number of cases occurs at the approaching lunch break (after 3-4 hours from the start of work). A large percentage of electrical injuries occur at the end of the working day due to fatigue, as well as haste at the end of work.

The largest number of accidents occurs during repair work - about 50%. The number of accidents during installation work is increasing. This indicates the insufficient use of existing protective equipment by maintenance personnel.

What are the causes of electric shock?

The main causes of accidents in the economy of electrification and power supply are non-shutdown of electrical installations, non-use of portable grounding and protective helmets, violation by workers of the dimensions of zones that are dangerous in relation to approaching live or grounded parts when working with de-energized or energized, lack of supervision on the part of work managers for performing operations in high-risk areas. Due to gross violations of safety regulations, when work is carried out without removing the voltage on live parts and near them, more than 88% of all accidents occur.

The cause of electrical injuries is often the inconsistency of work with the task, specialty and qualification group of the employee. Their share is more than 9%. The number of cases of electrical injuries occurring due to the supply of voltage to the work area without warning is from 22 to 32%. Electrical injuries also occur when wires sag or are very close together - up to 10-15% of cases, which indicates poor-quality maintenance of this line.

Accidents mainly occur along the external current circuit along the “phase-ground” path, therefore it is necessary to use protective grounding of electrical installations, follow the requirements of the instructions for grounding power supply devices on electrified railways.

The most frequent cases of current flow through the human body along the path "arm - arm" and "arm - legs". To prevent this, it is imperative to use special work shoes.

What organizational measures are required to be taken to prevent electrical injuries?

To prevent electrical injury, you must:

• improve the system of training in safe work practices;
• improve the quality of the briefing before starting work;
• improve the system of legal education;
• improve the qualifications of personnel in order to master safe labor practices;
• strengthen control over the implementation of fundamental standards;
• systematically conduct certification and certification of workplaces.

The education system should be improved by using a variety of visual aids and technical means in the educational process: photo showcases, operating layouts, control and teaching machines. movies, video recorders. The acquisition of safe work skills is facilitated by the creation and use of training grounds equipped with operating models of structures that imitate electrical equipment.

To increase the responsibility of personnel in terms of the unconditional implementation of safety regulations in accordance with the briefing, it is advisable to issue warning cards. In case of violation of safety regulations, it is necessary to withdraw coupons and assign violators a re-examination in safety regulations.

The improvement of legal education is facilitated by the quarterly holding of the day of labor law, when consultations are given on issues of labor legislation.

Improving the quality of vocational training, reducing the number of errors in the execution of orders, reducing the time for their execution is also facilitated by the widespread introduction of technological cards for the maintenance and repair of power supply devices and the introduction of training cards and knowledge testing.

What technical means increase the safety of maintenance of power supply devices?

To prevent injuries when working in KSO-type chambers, a blocking lock is installed on the drives of the grounding knives, as a result of which access to the chamber with disconnected grounding knives is impossible.

A special device has been created to monitor the insulation and condition of AC and DC operational circuits without disconnecting their power source.

A device for monitoring the serviceability of 110 kV bushings has been developed and is being used to detect partial breakdowns, moisture and complete overlaps in the main insulation of power transformer bushings.

Hazardous voltage signaling device type SOPN-1 allows you to remotely and directionally control the presence of voltage (working or induced) in electrical installations of alternating current and contact network from the ground

direct current.

A device for signaling the danger of approaching high-voltage installations has been developed and is being used.

These and some other tools have been developed by scientists and specialists from the electrical laboratory of the Moscow Institute of Railway Engineers.

The Department of Power Supply of Electric Railways of the Rostov Institute of Railway Engineers, in collaboration with specialists from the research and production laboratory of the North Caucasus Road, developed and introduced into trial operation a non-contact voltage indicator BIN-BU (universal). It is designed to remotely detect the presence of voltage on the current-carrying parts of AC and DC electrical installations with voltages from 3.3 to 110 kV. The objects of indication can be a contact network, traction substations, as well as power lines.

When preparing a workplace with de-energizing the contact network, there are cases when it remains energized due to the rotation of the shaft of the mast disconnector, shunting of the air gap and false tele-alarm. The Zlatoust power supply distance of the South Ural Road has created an RKN voltage control relay, which is installed at a substation or at a stage at the points of parallel connection of the contact network with the output of the RKN contacts to the TU-TS rack for remote signaling to the energy dispatcher about the presence or absence of voltage in the contact network.

Polymer insulating elements are widely used in contact network devices, on overhead lines and other electrical installations. The service life and reliability of their operation depend on the influence of ultraviolet rays, dust, snow, ambient temperature, relative humidity, contact with water and mechanical stress. By analogy with porcelain insulators, it is possible to overlap them in cases of contamination, and when the protective cover (coating) is depressurized and moisture gets on the supporting fiberglass rod, small currents can flow through it. This can lead to a deterioration in the electrical insulating properties and a decrease in mechanical strength. To control the tick along the entire insulating element, especially on sectional and mortise insulators (without their dismantling), a device for monitoring the insulating properties of polymer insulating elements (UCIP) has been developed.

For grounding wires of both the contact network and overhead lines (with a cross section of 6 to 18 mm2), a clamp was developed by rationalizers of the Petropavlovsk power supply section. The clamp allows you to hang the grounding rod also on the strip clamp. The principle of attaching the rod clamp to the wires is self-tightening. The clamp is removed from the wire by a sharp upward movement of the rod. The design of the clamp is convenient to use and ensures reliable contact with the wire.

A device for ensuring electrical safety during track work during the overhaul of one of the tracks of a multi-track section of a seamless track, electrified by an alternating current system. when trains continue to run on the existing tracks, it allows to ensure the safety of workers involved in the repair of the track.

In parentheses after the question are the numbers of regulatory documents on labor protection used in the formation of the answer -

Useful information:

1. Accidental contact with live parts under voltage as a result of: * erroneous actions during work; * malfunctions of protective equipment with which the victim touched current-carrying parts, etc. 2. The appearance of voltage on the metal structural parts of electrical equipment as a result of: * damage to the insulation of current-carrying parts, short circuit of the network phase to the ground; * falling wire under voltage on the structural parts of electrical equipment, etc. 3. The appearance of voltage on disconnected current-carrying parts as a result of: * erroneous switching on of a disconnected installation; * short circuits between disconnected and energized current-carrying parts; * lightning discharge into electrical installation, etc. 4. The occurrence of step voltage on the plot of land where the person is located, as a result of: * phase short circuit to the ground; * removal of potential by an extended conductive object (pipeline, railway rails); *faults in the protective earthing device, etc. Step Voltage- the voltage between two points of the current circuit, located one from the other at a step distance, at which a person is simultaneously standing. The highest step voltage is near the fault, and the lowest is at a distance of more than 20 m.

146. The concept of step voltage and touch voltage

In any electrical networks, a person in the current spreading zone may be under step voltage and touch voltage. Step voltage(step voltage) is the voltage between two points of the current circuit, located one from the other at a step distance (0.8 m) and on which a person is simultaneously standing. The danger of step voltage increases if the person who has been exposed to it falls: the step voltage increases, since the current no longer passes through the legs, but through the entire body of a person. The touch voltage is the voltage between two points of the current circuit, which are simultaneously touched by a person. The danger of such a touch is estimated by the value of the current passing through the human body, or by the voltage of the touch, and depends on a number of factors: the circuit for closing the current circuit through the human body, the network voltage, the circuit of the network itself, the mode of its neutral.

Passing through the body, the electric current causes thermal, electrolytic and biological effects.

thermal action It is expressed in burns of certain parts of the body, heating of blood vessels and nerve fibers.

Electrolytic action expressed in the decomposition of blood and other organic fluids, causing significant violations of their physico-chemical compositions.

Biological action manifests itself in irritation and excitation of living tissue of the body, which may be accompanied by involuntary convulsive contraction of muscles, including the muscles of the heart and lungs. As a result, various disorders in the body may occur, including a violation and even a complete cessation of the activity of the respiratory and circulatory organs.

The irritating effect of current on tissues can be direct, when the current passes directly through these tissues, and reflex, that is, through the central nervous system, when the current path lies outside these organs.

All the variety of action of electric current leads to two types of damage: electrical injuries and electric shocks.

electrical injury- these are clearly defined local damage to body tissues caused by exposure to electric current or an electric arc (electric burns, electrical signs, skin plating, mechanical damage).

electric shock- this is the excitation of the living tissues of the body by an electric current passing through it, accompanied by an involuntary convulsive contraction of the muscles.

Distinguish four degrees of electric shocks:

I degree - convulsive muscle contraction without loss of consciousness;

II degree - convulsive muscle contraction with loss of consciousness, but with preserved breathing and heart function;

III degree - loss of consciousness and impaired cardiac activity or respiration (or both);

Grade IV - clinical death, that is, the absence of breathing and blood circulation.

Clinical ("imaginary") death It is a transitional process from life to death that occurs from the moment the activity of the heart and lungs ceases. The duration of clinical death is determined by the time from the moment of cessation of cardiac activity and respiration until the onset of death of cells of the cerebral cortex (4-5 minutes, and in the case of death of a healthy person from random causes - 7-8 minutes). Biological (true) death- this is an irreversible phenomenon, characterized by the cessation of biological processes in the cells and tissues of the body and the breakdown of protein structures. Biological death occurs after the period of clinical death.

In this way, causes of death from electric shock there may be a cessation of the heart, cessation of breathing and electric shock.

Cardiac arrest or fibrillation, that is, chaotic rapid and multi-temporal contractions of the fibers (fibrils) of the heart muscle, in which the heart stops working as a pump, as a result of which blood circulation in the body stops, can occur with the direct or reflex action of an electric current.

Cessation of breathing as the root cause of death from electric current is caused by a direct or reflex effect of current on the chest muscles involved in the breathing process (as a result - asphyxia or suffocation due to lack of oxygen and excess carbon dioxide in the body).

Types of electrical injuries:

- electrical burns –

Skin electroplating

electrical signs

Electric shocks

Electrophthalmia

Mechanical damage

Electrical burn and arise under the thermal action of an electric current. The most dangerous are burns resulting from exposure to an electric arc, since its temperature can exceed 3000 ° C.

Skin electroplating- penetration into the skin under the action of an electric current of the smallest particles of metal. As a result, the skin becomes electrically conductive, i.e., its resistance drops sharply.

electrical signs- spots of gray or pale yellow color, arising from close contact with a current-carrying part (ps of which an electric current flows in working condition). The nature of electrical signs has not yet been sufficiently studied.

Electrophthalmia- damage to the outer shells of the eyes due to exposure to ultraviolet radiation from an electric arc.

Electric shocks - a common lesion of the human body, characterized by convulsive contractions muscles, disorders of the human nervous and cardiovascular systems. Often, electrical shocks are fatal.

Mechanical damage(tissue tears, fractures) occur with convulsive muscle contraction, as well as as a result of falls when exposed to electric current.

The nature of electric shock and its consequences depend on the value and type of current, the path of its passage, the duration of exposure, the individual physiological characteristics of a person and his condition at the time of the defeat.

electric shock- this is a severe neuro-reflex reaction of the body in response to strong electrical stimulation, accompanied by dangerous disorders of blood circulation, respiration, metabolism, etc. This state can last from several minutes to a day.

43. The impact of electric current on the human body. General and local injuries

Passing through the human body, the electric current has a thermal, electrolytic, mechanical and biological effect on it.

The causes of electrical accidents are many and varied. The main ones are:

1) accidental contact with open live parts under voltage. This can occur, for example, during the production of any work near or directly on live parts: in the event of a malfunction of protective equipment, through which the victim touched live parts; when carrying long metal objects on the shoulder, which can accidentally touch uninsulated electrical wires located at an accessible height in this case;

2) the appearance of voltage on the metal parts of electrical equipment (housings, casings, fences, etc.), which are not energized under normal conditions. Most often, this can occur due to damage to the insulation of cables, wires or windings of electrical machines and apparatus, which, as a rule, leads to a short circuit to the case;

3) the appearance of voltage on the disconnected current-carrying parts as a result of the erroneous switching on of the disconnected installation; short circuits between disconnected and energized live parts; lightning discharge into the electrical installation and other reasons

4) an electric arc that can form in electrical installations with a voltage of over 1000 V between a live part and a person, provided that the person is in close proximity to the live parts;

5) the occurrence of a step voltage on the earth's surface when the wire is shorted to the ground or when current drains from the ground electrode into the ground (in the event of a breakdown on the body of grounded electrical equipment);

6) other reasons, which include such as: uncoordinated and erroneous actions of personnel, leaving electrical installations energized without supervision, admission to repair work on disconnected equipment without first checking for a lack of voltage and a malfunction of the grounding device, etc.

All cases of electric shock to a person as a result of an electric shock are possible only when the electrical circuit is closed through the human body, that is, when a person touches at least two points of the circuit between which there is some voltage.

The voltage between two points in the current circuit, which are simultaneously touched by a person, is called the touch voltage.

A touch voltage of 20 V is considered safe in dry rooms, because the current passing through the human body will be below the threshold non-letting one and the person who received an electric shock will immediately tear his hands off the metal parts of the equipment.

In damp rooms, a voltage of 12 V is considered safe.

The step voltage is the voltage between the points of the earth, due to the spreading of the fault current to the ground while simultaneously touching the person's legs. The greatest electrical potential will be at the point of contact of the conductor with the ground. As we move away from this place, the potential of the ground surface decreases and at a distance of approximately 20 m, it can be taken equal to zero. Damage during step voltage is aggravated by the fact that due to convulsive contractions of the muscles of the legs, a person can fall, after which the current circuit closes on the body through the vital organs.