The main causes of electric shock in everyday life. What are the causes of electric shock? The main causes of electric shock at work

safety vital activity injury current fire

The most widely used at the moment are three-phase three-wire networks with a solidly grounded neutral and three-phase four-wire networks with an isolated neutral of a transformer or generator.

Solidly grounded neutral - the neutral of a transformer or generator, connected directly to the grounding device.

Isolated neutral - the neutral of a transformer or generator that is not connected to an earthing 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 ​​of the parameters of its operation are provided (there are no short circuits to the ground);
• - emergency mode in case of a single-phase earth fault.

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

In a network with a solidly grounded neutral, it is not required to maintain a high level of phase isolation. In emergency mode, such a network is less dangerous than a network with an isolated neutral. A network with a solidly grounded neutral is preferable from a technological point of view, as it allows you to simultaneously receive two voltages: phase, for example, 220 V, and linear, for example, 380 V. In a network with an isolated neutral, you can get only one voltage - linear. In this regard, at voltages up to 1000 V, networks with a dead-earthed neutral are more often used.

There are a number of main causes of accidents caused by exposure to electric current:

• - accidentally touching or approaching a dangerous distance to live parts under voltage;
• - the appearance of voltage on the metal structural parts of electrical equipment (casings, casings, etc.), including as a result of damage to the insulation;
• - the appearance of voltage on disconnected current-carrying parts on which people work, due to the erroneous switching on of the installation;
• - the occurrence of a step voltage on the earth's surface as a result of a wire shorting to the ground.

The main measures of protection against electric shock are the following:

• - ensuring the inaccessibility of live parts under voltage;
• - electrical separation of the network;
• - elimination of the danger of damage when voltage appears on cases, casings and other parts of electrical equipment, which is achieved by using low voltages, using double insulation, potential equalization, protective grounding, grounding, protective shutdown, etc.;
• - the use of special electrical protective equipment - portable devices and devices;
• - organization of safe operation of electrical installations.

double insulation- this is electrical insulation, consisting of working and additional insulation. Working insulation is designed to isolate the current-carrying parts of the electrical installation and ensures its normal operation and protection against electric shock. Additional insulation is provided in addition to the working insulation to protect against electric shock in case of damage to the working insulation. Double insulation is widely used in the creation of manual electric machines. In this case, grounding or zeroing of the cases is not required.

Protective earth- this is an intentional electrical connection to earth or its equivalent of exposed conductive parts (accessible to the touch conductive parts of an electrical installation that are not energized in normal operation, but may be energized if the insulation is damaged) to protect against indirect contact, from static electricity accumulating during friction of dielectrics, from electromagnetic radiation, etc. The equivalent of land can be river or sea water, quarry coal, etc.

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

Since the current follows the path of least resistance, it is necessary to provide a small resistance of the grounding device (grounding conductor and grounding conductors) compared to the resistance of the human body (1000 Ohm). In networks with voltage up to 1000 V, it should not exceed 4 ohms. Thus, in the event of a breakdown, the potential of the grounded equipment decreases. The potentials of the base on which the person stands and the grounded equipment are also equalized (by raising the potential of the base on which the person stands to a value close to the value of the potential of the open conductive part). Due to this, the values ​​of the touch and step voltages of a person are reduced to an acceptable level.

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

Zeroing- intentional electrical connection with a neutral protective conductor of metal non-current-carrying parts that may become energized, for example, due to a short to the housing. It is necessary to provide protection against electric shock in case of indirect contact by reducing the voltage of the case relative to the ground and limiting the time for the passage of current through the human body by quickly disconnecting the electrical installation from the network.

The principle of zeroing is that when the phase wire is closed to the zeroed housing of the electrical consumer (electrical installation), a single-phase short-circuit current circuit is formed (that is, a short circuit between the phase and neutral protective conductors). The single-phase short-circuit current causes the overcurrent protection to operate. Fuses, circuit breakers can be used for this. As a result, the damaged electrical installation is disconnected from the mains. In addition, before the operation of the overcurrent protection, the voltage of the damaged case decreases relative to the ground due to the action of re-grounding the zero protective conductor and the redistribution of voltage in the network during the flow of a short circuit current.

Zeroing is used in electrical installations with voltages up to 1000 V in three-phase AC networks with a grounded neutral.

Safety shutdown- this is a high-speed protection that provides automatic shutdown of an electrical installation when there is a danger of electric shock to a person in it. Such a danger may arise, in particular, when a phase is shorted to the case, the insulation resistance drops below a certain limit, and also if a person touches directly live parts that are energized.

The main elements of the residual current device (RCD) are the residual current device and the executive body.

Residual shutdown device - 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 an automatic switch that ensures the shutdown of the corresponding section of the electrical installation (electrical network) upon receipt of a signal from the residual current device.

The action of the protective shutdown as an electrical protective agent is based on the principle of limiting (due to quick shutdown) the duration of the current flow through the human body when it inadvertently touches the electrical installation elements under voltage.

Of all the known electrical protective equipment, the RCD is the only one that provides protection for a person from electric shock by direct contact with one of the live parts.

Another important property of the RCD is its ability to protect against fires and fires that occur at facilities due to possible damage to the insulation, faulty electrical wiring and electrical equipment.

Scope of RCD - networks of any voltage with any neutral mode. But they are most widely used in networks with voltages up to 1000 V.

Electrical protective equipment - these are portable and transportable products that serve to protect people working with electrical installations from electric shock, from the effects of an electric arc and electromagnetic field.

By appointment, electrical protective equipment (EPS) is conditionally divided into insulating, enclosing and auxiliary.

Insulating EZS serve to isolate a person from parts of electrical equipment under voltage, as well as from the ground. For example, insulating handles of a fitter's tool, dielectric gloves, boots and galoshes, rubber mats, tracks; stands; insulating caps and linings; insulating stairs; insulating pads.

Enclosing EZS are designed for temporary fencing of current-carrying parts of electrical installations under voltage. These include portable fences (screens, barriers, shields and cages), as well as temporary portable grounding. Conditionally, warning posters can also be attributed to them.

Auxiliary protective equipment is used to protect personnel from falling from a height (safety belts and safety ropes), to safely climb to a height (ladders, claws), as well as to protect against light, thermal, mechanical and chemical influences (goggles, gas masks, gloves , overalls, etc.).

Working with electric current requires special care: electric current strikes suddenly when a person is included in the current flow circuit.

• touching live parts, bare wires, contacts of electrical appliances, knife switches, lamp sockets, live fuses;
• touching parts of electrical equipment, metal structures of structures, etc., which are not in their normal state, but which are under voltage as a result of damage (breakdown) of insulation:
• being near the junction with the ground of a broken wire of the mains;
• being in close proximity to live parts that are energized above 1000 V;
• touching a live part and a wet wall or metal structure connected to the ground;
• simultaneous contact with two wires or other live parts that are energized;
• inconsistent and erroneous actions of the personnel (power supply to the installation where people work; leaving the installation energized without supervision; admission to work on disconnected electrical equipment without checking the absence of voltage, etc.).

The danger of electric shock differs from other industrial hazards in that a person is not able to detect it at a distance without special devices. Often this danger is discovered too late, when the person is already under stress.

The damaging effect of electric current

On living tissue is versatile. Passing through the human body, the electric current produces thermal, electrolytic, mechanical and biological effects.

thermal the action of the current is manifested in burns of certain parts of the body, heating and damage to blood vessels; electrolytic- in the decomposition of an organic fluid, including blood, which causes a violation of its composition, as well as the tissue as a whole; mechanical - in stratification, rupture of body tissues: biological - in irritation and excitation of living tissues of the body, as well as in violation of internal biological processes. For example, interacting with the body's biocurrents, an external current can disrupt the normal nature of their effect on tissues and cause involuntary muscle contractions.

Rice. Classification and types of electrical injuries

There are three main types of electric shock:

• electrical injury;
• electric shocks;
• electric shock.

electrical injury

Electrical injury - local damage to tissues and organs by electric current: burns, electrical signs, electroplating of the skin, damage to the eyes by exposure to an electric arc (electrophthalmia), mechanical damage.

Electrical burn- this is damage to the surface of the body or internal organs under the influence of an electric arc or high currents passing through the human body.

There are two types of burns: current (or contact) and arc.

current burn due to the passage of current directly through the human body as a result of touching the current-carrying part. Current burn - a consequence of the conversion of electrical energy into heat; as a rule, this is a skin burn, since human skin has many times greater electrical resistance than other body tissues.

Current burns occur when working on electrical installations of relatively low voltage (not higher than 1-2 kV) and in most cases are burns of I or II degree; however, sometimes severe burns occur.

At higher voltages between the current-carrying part and the human body or between the current-carrying parts, an electric arc is formed, which causes the occurrence of a burn of another type - arc.

arc burn due to the action of an electric arc on the body, which has a high temperature (over 3500ºC) and high energy. Such a burn usually occurs at high voltage electrical installations and is severe - III or IV degree.

The condition of the victim depends not so much on the degree of the burn, but on the surface area of ​​the body affected by the burn.

electrical signs- these are skin lesions in places of contact with electrodes of a round or elliptical shape, gray or white-yellow in color with sharply defined edges with a diameter of 5-10 mm. They are caused by the mechanical and chemical actions of the current. Sometimes they appear some time after the passage of an electric current. The signs are painless, there are no inflammatory processes around them. Swelling appears at the site of the lesion. Small signs heal safely, with large signs, necrosis of the body often occurs (usually hands).

Skin electroplating- this is the impregnation of the skin with the smallest particles of metal due to its splashing and evaporation under the influence of current, for example, when an arc is burning. The damaged area of ​​the skin acquires a hard, rough surface, and the victim feels the presence of a foreign body at the site of the lesion. The outcome of the lesion, as with a burn, depends on the area of ​​the affected body. In most cases, the metallized skin comes off, the affected area becomes normal and no traces remain.

Electroplating can occur during short circuits, trips of disconnectors and circuit breakers under load.

Electrophthalmia- this is an inflammation of the outer membranes of the eyes, which occurs under the influence of a powerful stream of ultraviolet rays. Such irradiation is possible when an electric arc (short circuit) is formed, which intensively emits not only visible light, but also ultraviolet and infrared rays.

Electrophthalmia is detected 2-6 hours after ultraviolet irradiation. In this case, redness and inflammation of the mucous membranes of the eyelids, lacrimation, purulent discharge from the eyes, eyelid spasms and partial blindness are observed. The victim experiences a severe headache and a sharp pain in the eyes, aggravated by the light, he develops the so-called photophobia.

In severe cases, the cornea of ​​​​the eye becomes inflamed and its transparency is disturbed, the vessels of the cornea and mucous membranes expand, and the pupil narrows. The illness usually lasts for several days.

The prevention of electrophthalmia during the maintenance of electrical installations is ensured by the use of safety glasses with ordinary glasses, which poorly transmit ultraviolet rays and protect the eyes from splashes of molten metal.

Mechanical damage arise as a result of sharp involuntary convulsive muscle contractions under the influence of current passing through the human body. As a result, ruptures of the skin, blood vessels and nervous tissue can occur, as well as dislocations of the joints and even bone fractures.

electric shock

electric shock- this is the excitation of living tissues of the body by an electric current passing through them, accompanied by involuntary convulsive muscle contractions.

The degree of negative impact of these phenomena on the body can be different. Small currents cause only discomfort. At currents exceeding 10-15 mA, a person is not able to independently get rid of current-carrying parts and the action of the current becomes prolonged (non-release current). At a current of 20-25 mA (50 Hz), a person begins to experience difficulty in breathing, which increases with increasing current. Under the action of such a current, suffocation occurs for several minutes. With prolonged exposure to currents of several tens of milliamps and an action time of 15-20 s, respiratory paralysis and death can occur. Currents of 50-80 mA lead to cardiac fibrillation, i.e. random contraction and relaxation of the muscle fibers of the heart, as a result of which blood circulation stops and the heart stops. The action of a current of 100 mA for 2-3 s leads to death (lethal current).

At low voltages (up to 100 V), direct current is approximately 3-4 times less dangerous than alternating current with a frequency of 50 Hz; at voltages of 400-500 V, their danger is compared, and at higher voltages, direct current is even more dangerous than alternating current.

The most dangerous current is industrial frequency (20-100 Hz). Reducing the danger of the action of current on a living organism is noticeably affected at a frequency of 1000 Hz and higher. High-frequency currents, starting from hundreds of kilohertz, cause only burns, without affecting the internal organs. This is due to the fact that such currents are not capable of causing excitation of nerve and muscle tissues.

Depending on the outcome of the lesion, electric shocks can be conditionally divided into four degrees:

• 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 (or both);
• IV - clinical death, i.e. lack of respiration and circulation.

Clinical death - it is a transitional period from life to death, occurring at the moment of cessation of the activity of the heart and lungs. A person in a state of clinical death lacks all signs of life: he does not breathe, his heart does not work, pain stimuli do not cause any reactions, the pupils of the eyes are dilated and do not react to light.

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 the cells of the cerebral cortex. In most cases, it is 4-5 minutes, and when a healthy person dies from an accidental cause, in particular from an electric current. - 7-8 min.

Causes of electrocution death include cardiac arrest, respiratory arrest, and electrical shock.

The work of the heart can stop as a result of either direct action of the current on the muscle of the heart, or a reflex action when the heart is not subject to direct action of the current. In both cases, cardiac arrest or fibrillation may occur.

Currents that cause cardiac fibrillation are called fibrillation, and the smallest one is

Fibrillation usually does not last long and is replaced by a complete cardiac arrest.

The cessation of breathing is caused by the direct, and sometimes reflex, action of the current on the muscles of the chest involved in the breathing process.

As with paralysis of breathing, and with paralysis of the heart, the functions of the organs are not restored on their own, first aid is necessary (artificial respiration and heart massage). The short-term action of large currents does not cause either respiratory paralysis or cardiac fibrillation. At the same time, the heart muscle contracts sharply and remains in this state until the current is turned off, after which it continues to work.

electric shock

electric shock- a kind of reaction of the nervous system of the body in response to strong irritation with an electric current: circulatory and respiratory disorders, increased blood pressure.

The shock has two phases:

• I - excitation phase;
• II - phase of inhibition and exhaustion of the nervous system.

In the second phase, the pulse quickens, breathing weakens, a depressed state and complete indifference to the environment occur, while consciousness is preserved. A state of shock can last from several tens of minutes to a day, after which a legal outcome occurs.

Parameters that determine the severity of electric shock

The main factors that determine the degree of electric shock are: the strength of the current flowing through a person, the frequency of the current, the time of exposure and the path of current flow through the human body.

Current strength

The flow through the body of an alternating current of industrial frequency (50 Hz), widely used in industry and in everyday life, a person begins to feel at a current strength of 0.6 ... 1.5 mA (mA - a milliamp is equal to 0.001 A). This current is called threshold sensible current.

Large currents cause pain in a person, which increases with increasing current. For example, at a current of 3 ... 5 mA, the irritating effect of the current is felt by the entire hand, at 8 ... 10 mA - a sharp pain covers the entire arm and is accompanied by convulsive contractions of the mouse of the hand and forearm.

At 10 ... 15 mA, arm muscle spasms become so strong that a person cannot overcome them and free himself from the current conductor. This current is called threshold non-release current.

At a current of 25 ... 50 mA, disturbances in the functioning of the lungs and heart occur, with prolonged exposure to such a current, cardiac arrest and cessation of breathing can occur.

Starting from the value 100 mA the flow of current through a person causes fibrillation hearts - convulsive non-rhythmic contractions of the heart; the heart stops working like a pump that pumps blood. This current is called threshold fibrillation current. A current of more than 5 A causes immediate cardiac arrest, bypassing the state of fibrillation.

The amount of current flowing through the human body (I h) depends on the contact voltage U pr and the resistance of the human body

R h: I h \u003d U pr / R h

The resistance of the human body is a non-linear value, depending on many factors: skin resistance (dry, wet, clean, damaged, etc.): current and applied voltage; duration of current flow.

The upper horny layer of the skin has the greatest resistance:

• with the stratum corneum removed R h = 600-800 Ohm;
• with dry intact skin R h \u003d 10-100 kOhm;
• with moistened skin R h \u003d 1000 Ohm.

The resistance of the human body (R 4) in practical calculations is assumed to be 1000 ohms. In real conditions, the resistance of the human body is a variable value and depends on a number of factors.

With an increase in the current passing through a person, its resistance decreases, as this increases the heating of the skin and sweating. For the same reason, R 4 decreases with increasing duration of current flow. The higher the applied voltage, the greater the current passing through the human body I h, the faster the skin resistance decreases.

With an increase in tension, the resistance of the skin decreases tenfold, therefore, the resistance of the body as a whole also decreases; it approaches the resistance of the internal tissues of the body, i.e. to its smallest value (300-500 ohms). This can be explained by electrical breakdown of the skin layer, which occurs at a voltage of 50-200 V.

Pollution of the skin with various substances, especially those that conduct electricity well (metal or coal dust, oka-chin, etc.), reduces its resistance.

The resistance of different parts of the human body is not the same. This is explained by the different thickness of the stratum corneum of the skin, the uneven distribution of the sweat glands on the surface of the body, and the uneven degree of filling of the skin vessels with blood. Therefore, the value of the resistance of the body depends on the place of application of the electrodes. The effect of the current on the body is enhanced by closing contacts in acupuncture points (zones).

Environmental conditions (temperature, humidity) also influence the outcome of electrical injuries. Elevated temperature, humidity increase the risk of electric shock. The lower the atmospheric pressure, the higher the risk of injury.

The mental and physical state of a person also affects the severity of electric shock. With diseases of the heart, thyroid gland, etc. a person is subjected to a stronger defeat at lower current values, since in this case the electrical resistance of the human body and the overall resistance of the body to external stimuli decrease. It was noted, for example, that in women the threshold values ​​of currents are approximately 1.5 times lower than in men. This is due to the weaker physical development of women. When using alcoholic beverages, the resistance of the human body decreases in the same way as the resistance of his body and attention.

Current frequency

The most dangerous industrial frequency current is 50 Hz. Direct current and current of high frequencies are less dangerous, and the threshold values ​​for it are greater. So, for direct current:

• threshold perceptible current — 3...7 mA;
• threshold non-release current — 50...80 mA;
• fibrillation current - 300 mA.

current flow path

The path of electric current through the human body is important. It has been established that the tissues of different parts of the human body have different specific resistances. When current passes through the human body, most of the current travels along the path of least resistance, mainly along the blood and lymphatic vessels. There are 15 current paths in the human body. The most frequent: hand - hand; right hand - legs; left hand - legs; leg - leg; head - legs: head - hands.

The most dangerous is the current path along the body, for example, from the arm to the leg or through the heart, head, spinal cord of a person. However, fatal defeats are known when the current passed along the path "leg - leg" or "arm - arm".

Contrary to the established opinion, the largest current through the heart is not along the path "left arm - legs", but along the path "right arm - legs". This is due to the fact that most of the current enters the heart along its longitudinal axis, which lies along the path "right arm - legs."

Rice. Characteristic current paths in the human body

Time of exposure to electric current

The longer the current flows through a person, the more dangerous it is. When an electric current flows through a person at the point of contact with the conductor, the upper layer of the skin (epidermis) is quickly destroyed, the electrical resistance of the body decreases, the current increases, and the negative effect of the electric current is aggravated. In addition, over time, the negative effects of the current on the body grow (accumulate).

The decisive role in the damaging effect of the current is played by the magnitude of the electric current flowing through the human body. An electric current occurs when a closed electrical circuit is created, in which a person is included. According to Ohm's law, the strength of the electric current / is equal to the electric voltage (/ divided by the resistance of the electrical circuit R:

Thus, the greater the voltage, the greater and more dangerous the electric current. The greater the electrical resistance of the circuit, the lower the current and the danger of human injury.

Circuit resistance equal to the sum of the resistances of all sections that make up the circuit (conductors, floor, shoes, etc.). The total electrical resistance necessarily includes the resistance of the human body.

Electrical resistance of the human body with dry, clean and undamaged skin, it can vary over a fairly wide range - from 3 to 100 kOhm (1 kOhm = 1000 Ohm), and sometimes more. The main contribution to the electrical resistance of a person is made by the outer layer of the skin - the epidermis, consisting of keratinized cells. The resistance of the internal tissues of the body is small - only 300 ... 500 ohms. Therefore, with delicate, moist and sweaty skin or damage to the epidermis (abrasions, wounds), the electrical resistance of the body can be very small. A person with such skin is most vulnerable to electric current. Girls have more delicate skin and a thin layer of the epidermis than boys; in men with calloused hands, the electrical resistance of the body can reach very high values, and the danger of their electric shock is reduced. In calculations for electrical safety, the resistance of the human body is usually taken to be 1000 ohms.

Electrical insulation resistance current conductors, if it is not damaged, is, as a rule, 100 or more kilo-ohms.

Electrical resistance of shoes and base (floor) depends on the material from which the base and sole of the shoe are made, and their condition - dry or wet (wet). For example, a dry sole made of leather has a resistance of about 100 kOhm, a wet sole - 0.5 kOhm; from rubber, respectively, 500 and 1.5 kOhm. A dry asphalt floor has a resistance of about 2000 kOhm, a wet one - 0.8 kOhm; concrete, respectively, 2000 and 0.1 kOhm; wooden - 30 and 0.3 kOhm; earth - 20 and 0.3 kOhm; from ceramic tiles - 25 and 0.3 kOhm. As you can see, with wet or wet grounds and shoes, the electrical hazard increases significantly.

Therefore, when using electricity in wet weather, especially on water, special care must be taken and increased electrical safety measures must be taken.

For lighting, household electrical appliances, a large number of devices and equipment in production, as a rule, a voltage of 220 V is used. There are electrical networks for 380, 660 and more volts; Many technical devices use voltages of tens and hundreds of thousands of volts. Such technical devices pose an exceptionally high danger. But even much lower voltages (220, 36 and even 12 V) can be dangerous depending on the conditions and electrical resistance of the circuit. R.

In the late 70s of the century before last, the first death of a person from electricity was recorded. A lot of time has passed since then, but the number of people affected by the same cause is only increasing. In connection with these events, people were forced to create a list of rules for dealing with electricity. For many years, future electricians have been trained in specialized educational institutions and immediately after which they undergo an “internship” in production and, of course, pass the final test exam, after which they receive a license and can independently work with electric current. What is most amazing is that no one in this world is immune from mistakes. Even a highly qualified specialist can easily get injured due to inattention. Can you say with confidence that for any problem related to electricity, you will solve it with ease and accuracy? If not, then this article is for you! Next, we will talk about what are the causes of electric shock and the main protective measures in everyday life.

What is electric current?

The concentrated movement of charged particles in space under the action of an electric field. This is how the term electric current is explained. What about particles? So they can be absolutely anything, for example: electrons, ions, etc. It all depends only on the object in which this very particle is located (electrodes / cathodes / anodes, etc.). If we explain according to the theory of electrical circuits, then the cause of the occurrence of an electric current is the “purposeful” course of charge holders in a conductive environment when exposed to an electric field.

How does electricity affect the human body?

A strong electric current that is passed through a living organism (human, animal) may cause a burn, or may cause an electrical injury by fibrillation (when the ventricles of the heart do not contract synchronously, but each “by itself”) and eventually this will lead to to lethal outcome.

But if you look at the other side of the coin, electric current is used in therapy, for resuscitation of patients (during ventricular fibrillation, a defibrillator is used, a device that, by means of electricity, simultaneously contracts the muscles of the heart, and thereby causing the heart to beat in its “familiar” rhythm), etc. etc., but that's not all. Every day, since our birth, electricity “flows” in us. It is used by our body in the nervous system to transmit impulses from one neuron to another.

Rules for handling electrical appliances

In fact, we will offer you a list of rules of what cannot be and what must be done when children interact with electrical appliances, BUT this does not mean that as an adult you can neglect these rules! So, let's begin!

When interacting with electrical appliances IT IS FORBIDDEN:

1. Touch exposed wires.
2. Activate broken electrical appliances, because in which case they can cause a fire or shock you.
3. Touch the wires with wet hands (especially if they are bare).

NECESSARY:

1. Remember that in no case should you pull on the wire in order to pull it out of the socket.
2. When leaving home, check to see if any electrical appliance has been left on.
3. If you are a child, then be sure to call an adult if, while plugging in an electrical appliance, you saw that the wire or the electrical appliance itself began to smoke.

The main causes of electric shock

An electric shock can occur while a person is near the place where the current-carrying parts included in the network are located. It can be described as irritation or interaction of body tissues with electricity. In the end, this will lead to absolutely involuntary (convulsive) contractions of the human muscles.

There are a number of reasons for electric shocks to a person, such as: the possibility of damage when replacing a light bulb in a lamp connected to the network, the interaction of the human body with equipment that is connected to the network, long (continuous) operation of electrical appliances, and of course people who repair everything themselves do not depending on whether it is successful or not (in other words, "Homemade"). Let's start by listing the main causes of electric shock, and then we'll figure out in order what the essence of these problems is.

The main causes of electric shock are:

1. Human interaction with faulty household electrical appliances.
2. Touching bare parts of the electrical installation.
   
3. Wrong voltage supply to the place of work. That is why in production you need to hang out a special one, as in the picture below:
   
4. The appearance of voltage on the body of equipment, which, under normal conditions, should not be energized.
5. Electric shock due to a faulty power line.
6. Replacing a light bulb in a luminaire connected to the network. People can be injured due to the fact that during the banal replacement of a light bulb, they simply forget to turn off the lights. It must be remembered that before changing the light bulb, the first thing to do is turn off the light.
7. The interaction of the human body with equipment that is connected to the network. There were cases when people were injured from this option. Everything is simple here. When interacting with an electrical appliance (for example, a washing machine), you hold on to a fragment of the house that is grounded (for example, a pipe) with your other hand. Thus, a current will pass through your body, which will cause damage. To prevent this from happening, it is recommended.
   
8. Long (continuous) operation of electrical appliances. In fact, the cases of damage in this way are minimal. The problem is this: appliances such as a washing machine can break down from long work and, in the case of a washing machine, at least leak. To avoid such incidents, simply check to see if the instruments are working properly more frequently. About that, we talked about in the corresponding article.
9. People who do everything themselves. This is considered the most common problem of all, because today with the help of the Internet you can find a lot of instructions like "How to do ...", even on our website in the section. However, the majority of people who start designing something do not have the proper knowledge and, due to ordinary carelessness, are injured or even maimed.
10. can be very dangerous for you or your equipment, after all, power surges can cause a fire or, worse, cause an electric shock. So how do you deal with it? To date, there are three main ways to reduce the effects of power surges, namely:, well, and. These three things in everyday life will serve as protection for you and your equipment from power surges.

Since 1879, the safety of people working with electricity has been a hot topic. It was then that the first case of death of a person from exposure to electric current was registered.

Since then, the number of victims has been increasing all the time. On the basis of sad statistics, safety rules have been created, each item in which is based on someone's tragedy.

Electricians of various professions are trained for several years by schools, technical schools, institutes and specialized courses. After that, graduates of institutions undergo internships at energy enterprises, pass numerous exams and tests. Only after that they are allowed to work independently.

However, even electricians who have worked for many years with higher fifth safety group due to mistakes and inattention, sometimes they get serious electrical injuries.

Unfortunately, an ordinary person does not have such theoretical training and practice of working with electricity. And he does not need to know all the intricacies of our profession. But, to follow the elementary rules, which, by the way, everyone is told from school and kindergarten, is simply necessary.

I would like the readers of the articles of this site to become active preachers of the safe handling of electrical installations, not only in production, but also in everyday life, among their loved ones. The word of a specialist, backed up by life facts, is always well imprinted in the memory and perceived with more confidence than ordinary text. It can never be redundant.

Human psychology quickly adapts to everything familiar: electricity surrounds us everywhere, making life easier, and malfunctions in it rarely occur, and usually cause little harm. But until a certain point...

Therefore, tell your surroundings once again the main causes of electric shock in everyday life. Be sure: your words will save loved ones from an accident.

What is forbidden to do with electrical appliances in the home

Damaged appliances

Any electrical receiver has a layer of insulation. It covers the most critical places of the wire even with several layers in order to exclude contact of human skin with the potential of the mains. But, careless handling of electrical wiring, mechanical impact on it, overheating from incorrect loads or loose contacts violate its dielectric properties.

Do not touch the bare metal of a wire that is energized or use switches, sockets and plugs with broken cases. This is a direct prerequisite for electrical injury.

To exclude such cases, conduct periodic inspections of the condition of all devices and electrical wiring. Better yet, check the condition of its insulation by measurements. But this is a rather dangerous event and can only be entrusted to specialists.

Repair work

All faulty electrical equipment must be taken out of service to eliminate breakdowns. And only a trained person can do it. Otherwise, the consequences of unskilled repairs can be unpredictable.

Careful handling of equipment

Electrical appliances connected to the network must not be disassembled. Be especially careful with the power cord. It is unacceptable to pull on it in order to move the electric stove, iron or pull the plug out of the socket.

In this way, you can easily arrange a short circuit. Power cords are often subjected to twisting, kinking, and stress. heating. Breaks and breaks can occur inside them. They can break good contact, cause sparks, leading to fire.

You must use your electrical appliances with care.

Replacing light bulbs in fixtures

Every adult, not to mention children, should know that it is forbidden to repair live electrical equipment. Any operation on electrical receivers must be performed with the power off.

Often people get injured when they screw in / turn out ordinary incandescent bulbs. The light switch must always be switched off.

The metal thread of the base can jam in the cartridge, and its fastening with the bulb can loosen. As a result, the glass part will turn, the internal voltage supply threads, made of open metal, will touch each other, creating a short circuit.

Contact with the body of devices connected to voltage

In a two-wire network (phase, zero) operated, when the insulation breaks down on the case, a life-threatening potential appears. If a person touches such a device with one part of the body (the figure shows a dishwasher), and the other part touches the structural elements of the building connected to the ground (in the picture - a pipeline), then a current will flow through his body along this path.

To prevent such injuries, there are protections that respond to the appearance of leakage currents. in such wiring it will reduce the damaging effect of the current, and in a circuit equipped with a protective PE conductor according to the TN-S or TN-C-S systems, it will prevent an accident.

Proper connection to the ground loop of all cases of household appliances, the use of a potential equalization system is the key to preventing electric shock to residents.

Long-term operation of electrical appliances

Modern refrigerators, freezers and some household appliances are designed to perform a continuous technological cycle. They are equipped with automatic control systems for this.

Even such devices can break down and need periodic monitoring by the owner. Burnt out electric motors, floors flooded with water, or cases of flooding of neighbors from below are clear evidence of this.

For working machinery and electrical equipment, inspection by a person is still required.

Homemade

We love to make things with our own hands. Now it is very easy to find a lot of tips on how to make a home-made machine, heating, welding ... But are we qualified to do all this not only working, but also safe for operation? Certainly not always.

The designs of many homemade heaters are not only fire hazardous, but can create electrical injury.

In any case, before putting home-made electrical appliances into operation, it is important not only to measure the resistance of electrical insulation, but also to test it. This is done by specialized electrical laboratories.

Maintaining electrical wiring protection

In all residential premises, when commissioning the electrical circuit, introductory shields are installed. They, as a rule, have a built-in electric meter and circuit breakers or fuses.

They must be kept in working order. This requirement is especially relevant for old houses in rural areas, where you can still find working, but obsolete electrical panels with an induction meter and two cork fuses. In them, instead of industrial fuse-links, the owners install home-made "bugs" - pieces of randomly selected wires.

Often their denominations are overstated: so as not to change once again in case of burnout. It is for this reason that they do not always quickly turn off the resulting short circuit, and in some cases do not work at all.

The same requirement applies to the settings of circuit breakers. Their selection, configuration and performance testing is an important element of electrical safety.

Children

They are always inquisitive, mobile, actively climb into all accessible and even forbidden places. In this way they learn about the world around them, master it. But is it always possible for an adult to keep track of the behavior of the baby, to protect him from falling under the action of the current? How to avoid accidents?

Parents need to take into account the age of the child and his development. Children under three years old should be excluded from access to electrical appliances by furniture elements, partitions, fences. Be sure to indicate the restricted areas and suggest that they should not be included there.

All contacts of electrical outlets must be closed with dielectric plugs. After all, kids can stick a nail, pin or other piece of metal there.

Children of all ages need to be persistently explained the rules for the safe handling of electricity in everyday life and on the street. To this end, a lot of books have been written for them and many educational cartoons have been shot. For example, "Advice from Aunt Owl."

Such video tutorials are created by specialists taking into account the specifics of child psychology. They are informative and memorable. Especially when parents give incidental explanations, and after watching it together, they share comments and ask leading questions.

In conclusion of the article, I would like to once again turn to electricians: for sure, based on your own experience, you also know the causes of electric shock in everyday life. Share them with your loved ones! Your advice will always be taken. They will help protect a person from getting electrical injuries.

The main causes of accidents due to electric shock are:

Accidental contact or approaching a dangerous distance to live parts under voltage;

The appearance of voltage on the structural metal parts of electrical equipment (housings, casings, etc.) as a result of damage to the insulation and other causes (the so-called electrical short circuit to the housing);

The appearance of voltage on disconnected current-carrying parts on which people work, due to erroneous inclusion;

The entry of a person into the zone of current spreading.

Classification of premises according to the danger of damage

human shock

Environmental conditions, on which the state of insulation depends, as well as the electrical resistance of the human body, have a significant impact on the safety of electrical installations. In this regard, with regard to the danger of electric shock to a person, the Electrical Installation Rules (PUE) distinguish between:

1) premises without increased danger, in which there are no conditions that create an increased or special danger;

2) high-risk areas, characterized by the presence of one of the following conditions that create an increased danger:

Relative humidity exceeds 75%;

Dust that can settle on live parts, penetrate into the equipment;

Conductive floors (metal, earthen, reinforced concrete, brick, etc.);

The temperature constantly or periodically (over a day) exceeds +35 °C;

The possibility of simultaneous contact of a person with the metal structures of buildings that are connected to the ground, on the one hand, and to the metal cases of electrical equipment, on the other;

3)especially dangerous premises, characterized by the presence of one of the following conditions that create a particular hazard:

Relative humidity is close to 100% (ceiling, walls, floor and objects in the room are covered with moisture);

Chemically active or organic environment that destroys insulation and current-carrying parts of electrical equipment;

Two or more high-risk conditions at the same time.

Rationing of touch voltages and currents

Through the human body

Maximum permissible values ​​of contact voltage U pd and currents I pd, flowing through the human body, are set for the current path "arm - arm" or "arm - legs" (GOST 12.1.038-82*). The indicated values ​​\u200b\u200bfor the normal (non-emergency) mode of the electrical installation are given in table. 4.2.

Table 4.2

Note. Contact voltages and currents for persons performing work in conditions of high temperatures (above 25 ° C) and humidity (relative humidity over 75%) should be reduced by 3 times.

In emergency mode of industrial and household appliances and electrical installations with voltage up to 1000 V in networks with any neutral mode, the maximum permissible values U pd And I pd should not exceed the values ​​given in GOST 12.1.038-82*. For a rough estimate U pd And I pd You can use the data in Table. 4.3. Emergency mode means that the electrical installation is out of order and dangerous situations may arise, leading to electrical injury. With an exposure duration of more than 1 s, the values ​​of U pd and I pd correspond to the releasing values ​​for alternating and non-painful for direct currents.

Table 4.3

Technical means of human protection

From electric shock

The main technical means of protecting a person from electric shock, used alone or in combination with each other, are (PUE): protective grounding, protective earthing, protective shutdown, electrical separation of the network, low voltage, electrical protective equipment, potential equalization, double insulation, preventive alarm, blocking, security signs.

Protective earth- this is a deliberate electrical connection with the ground of the Earth of metal non-current-carrying elements of electrical installations, which in emergency situations may be energized. The scope of protective grounding is electrical installations with voltages up to 1000 V, powered by SIN. At the same time, in rooms without increased danger, protective grounding is mandatory at a rated voltage of electrical installations of 380 V and above AC and 440 V and above DC, and in rooms with increased danger and especially dangerous, as well as in outdoor installations - at voltages above 50 V AC and above 120 V DC.

Protective earthing is specifically designed to ensure electrical safety and allows you to reduce the voltage applied to the human body to a long-term permissible value. Metal non-current-carrying elements of electrical installations accessible to human touch, which may be energized, for example, due to damage to the insulation of the phase conductor of the network, are subject to protective grounding. The protective grounding scheme is shown in fig. 4.6.

In the event of a phase breakdown to the case, the fault current is determined by the formula

in which the influence of parallel connection R And R h can be neglected ( R s ||R h<< Z из /3 ), because R<< Z из . As a result, the earth-fault current in LSS with voltage up to 1000 V practically does not exceed 5 A, and in most cases it is many times less.

To ensure acceptable safety of touching a damaged electrical installation in the LSS (phase-to-case short circuit), it is necessary to ensure a sufficiently small value of ground resistance at any time of the year.

Protective grounding is carried out using grounding device, which is a combination of grounding conductors (natural or artificial) and grounding conductors.

Natural grounding- these are electrically conductive elements of communications, buildings and structures that are directly in contact with the ground, used for grounding purposes. These include, for example, reinforcement of reinforced concrete foundations, metal water pipes laid in the ground, casing pipes of wells. It is forbidden to use pipelines of flammable liquids, explosive or combustible gases and mixtures as natural grounding conductors. According to the PUE, it is recommended to use natural ground electrodes for grounding in the first place.

Artificial grounding- these are steel electrodes (pipes, corners) specially designed for the grounding device, which have direct contact with the ground. They are used if there are no natural grounding conductors or their resistance to current spreading does not meet the requirements.

Grounding conductors- these are electrical conductors connecting the ground electrodes with the grounded elements of the installations.

PUE and GOST 12.1.030-81 * establish, in particular, that in networks with U f = 220 V the resistance of the grounding device must not exceed 4ohm ( R≤ 4 ohm). If the power of the network or autonomous source of electricity (transformers, generators) does not exceed 100 kVA, then R≤ 10 ohm. Thus, the voltage on the case of the emergency industrial electrical installation is provided, not exceeding 20 V, which is considered acceptable.

Protective zeroing- this is a deliberate electrical connection of non-current-carrying parts of electrical installations, which in emergency situations may be energized, with a solidly grounded neutral of the electrical network using a zero protective conductor (NZP). The scope of protective grounding is electrical installations with voltages up to 1000 V, powered by SZN. At the same time, in rooms without increased danger, protective grounding is mandatory at a rated voltage of electrical installations of 380 V and above AC and 440 V and above DC, and in rooms with increased danger and especially dangerous, as well as in outdoor installations - at voltages above 50 V AC and above 120 V DC.

The scheme of the protective neutralization option in the SZN is shown in fig. 4.7, where Pr1 and Pr2 are the fuses of the power line and electrical installation. The zero protective conductor must be distinguished from the zero working conductor N. The zero working conductor, if necessary, can be used to power electrical installations. In a real network, it can be combined with WIP, except for the case of powering portable power receivers, if it meets the additional requirements for WIP. Guaranteed continuity of the WIP must be ensured throughout the entire length from the element to be nulled to the neutral of the power source. This is ensured by the absence of protection elements (fuses and circuit breakers), as well as various kinds of disconnectors. All WIP connections must be welded or threaded. The total conductivity of the NZP should be at least 50% of the conductivity of the phase conductor.

Thus, with protective grounding, the safety of a person touching the body of a damaged installation is ensured by reducing the time of exposure to dangerous voltage, which is valid until the protection element is triggered.

In SZN with protective grounding, it is impossible to ground the body of the installation without first connecting it to the NZP.

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

Protective automatic power off is used as additional protection in electrical installations with voltage up to 1000 V in the presence of other protection measures in accordance with the Electrical Installation Rules (PUE) and is implemented using residual current devices (RCD).

The practical variety of RCDs is determined by the input signals used and the selected structural elements.

Electrical separation of the network. Real electrical networks can have a solidly grounded neutral, be extended and branched, which dramatically increases the danger of a single-phase human touch. On fig. 4.9 shows an example of an extensive single-phase network with connected electrical installations, containing N branches with corresponding insulation resistances. The resulting insulation resistance Z from the network is determined as the result of the parallel connection of the insulation resistances N of individual sections and the insulation resistances Z of the ED of electrical installations. It may be insufficient to ensure safety with a single-phase contact and may be, for example, tens of kOhm.

In order to increase safety in such cases, electrical separation of the network into a number of sections is used with the help of special isolating transformers RT (Fig. 4.10). The section of the network connected to the secondary winding of the RT has a small length and branching. Therefore, a large insulation resistance of the power conductors relative to the ground is easily ensured. Isolating transformers can be part of, for example, power supplies (voltage converters) of electronic devices. It should be borne in mind that the outputs of the secondary winding of the RT must be isolated from the ground.

Small is a voltage of not more than 50 V AC and not more than 120 V DC, used to reduce the risk of electric shock. The greatest degree of safety is achieved at voltages up to 12 V, since at such voltages the resistance of the human body is usually at least 6 kOhm and, therefore, the current passing through the human body will not exceed 2 mA. Such a current can be considered conditionally safe. In production conditions, to improve the safety of portable electrical installations, voltages of 36 V (in rooms with increased danger) and 12 V (in especially dangerous rooms) are used. However, in any case, low voltages are only relatively safe, because. in the worst case, the current through the human body can exceed the value of the threshold non-release.

Low voltage sources are isolation transformers. Receiving low voltages using autotransformers is not allowed, since the current-carrying elements of the low voltage network in this case are galvanically connected to the main electrical network.

The wide distribution of low voltage alternating current is hindered by the difficulty of implementing an extended low voltage network due to large energy losses and the presence of a step-down transformer. Therefore, their scope is limited mainly to hand-held electrified tools, portable lamps, local lighting fixtures in both high-risk and especially dangerous rooms.

Electrical protective equipment- this is personal protective equipment that serves to protect people from electric shock, from the effects of an electric arc and an electromagnetic field.

According to their purpose, protective equipment is conditionally divided into insulating, enclosing and protective.

Insulating protective equipment designed to isolate a person from parts of electrical installations under voltage and from the ground. Distinguish between basic and additional insulating means. Basic insulating means have insulation capable of withstanding the operating voltage of the electrical installation for a long time, and, therefore, with their help it is possible to touch live parts under voltage. The main insulating means for electrical installations with voltages up to 1000 V are insulating rods, insulating and electrical pliers, dielectric gloves, metalwork and assembly tools with insulating handles, and voltage indicators. Additional insulating means are used to ensure greater electrical safety only in conjunction with basic means to ensure greater safety. Additional insulating means include, for example, dielectric boots and galoshes, insulating stands and rugs. All insulating means must be tested after manufacture and periodically during operation, for which a corresponding mark is made on them.

Enclosing protective equipment designed for temporary fencing of live parts under voltage (insulating pads, shields, barriers), as well as to prevent the appearance of dangerous voltage on disconnected live parts (portable grounding devices).

Safety protective equipment serve to protect personnel from factors associated with their work with electrical installations. These include means of protection against falling from a height (safety belts), when climbing to a height (fitter's claws, ladders), from light, thermal, mechanical, chemical influences (goggles, shields, gloves) and electromagnetic fields (shielding helmets, suits ).

Potential equalization used in rooms with grounded or grounded electrical installations to increase the level of safety. At the same time, metal pipes of communications included in the building (hot and cold water supply, sewerage, heating, gas supply, etc.), metal parts of the building frame, centralized ventilation systems, metal sheaths of telecommunication cables, all simultaneously accessible exposed conductive parts of stationary electrical equipment.

double insulation is a combination of working and protective (additional) insulation, in which the metal parts of the electrical installation accessible to touch do not acquire dangerous voltage if only the working or only the protective insulation is damaged. According to the requirements of GOST 12.2.006-87, devices for household or similar general use must have double insulation. Double insulated installations should not be earthed or neutralized and therefore do not have suitable connections. As additional insulation, plastic cases, handles, bushings are used. If a double insulated device has a metal case, it must be isolated from structural parts of the installation that may be energized (chassis, regulator shafts, motor stators) by insulating elements.

Warning signal serves to issue a danger signal when approaching parts under high voltage.

Locks prevent access to non-disconnected current-carrying parts of the electrical installation, for example, during repairs. Electrical interlocks they break the circuit with contacts that open when the hardware door is opened, or do not allow it to be opened if the high voltage is not removed from the current-carrying parts. Mechanical interlocks have structural elements that do not allow you to turn on the device when the lid is open or open the device when it is turned on.

Safety signs and posters are designed to draw the attention of workers to the danger of electric shock, prescriptions, permissions for certain actions and instructions in order to ensure safety. They are forbidding, warning, prescriptive and indicative.

electromagnetic fields