The main causes of electric shock. The main causes and conditions of electric shock. What is electric current

Due to the widespread use of electricity, both in production processes and for solving household problems, a significant threat of damage is created. electric shock. To prevent such situations, there are a number of rules that allow you to protect personnel and ordinary people from the deplorable consequences of illiterate handling of electricity. To do this, it is important to understand the causes of electric shock and the measures necessary in certain situations to prevent electric shock.

The concept of electric shock

An electric shock should be understood as such a situation when an electric charge from a current source uses the human body as one of the flow paths or the only path. In this case, the directed movement of particles creates a spontaneous contraction of the muscles that fall under its influence on the flow path, the current destroys tissues and causes other damage.

Electric shock can occur both during normal operation of electrical installations and in emergency situations (damage to wire insulation, breakdown of dielectrics, destruction of insulators, when an electric arc burns, etc.). In addition to interaction with current in everyday life, there is the possibility of being struck by lightning. But whatever the current flow, it can cause a number of adverse consequences for the human body.

How does electricity affect the human body?

If we do not consider planned electric shocks, during medical or cosmetic procedures with devices whose action is aimed at passing electric current through the tissues of the body, then in all cases of electrical injuries, the body receives three main current effects:

• thermal- lead to burns at the points of electric current. Unlike the usual one, an electric burn is further complicated by tissue damage by small particles of hot metal. Which after the impact remain in the skin, respectively, and the healing of such wounds takes longer and requires additional effort. Light, medium, or severe burns may occur, depending on the conditions under which the shock occurs.
• dynamic- causes contraction and subsequent damage to muscles and ligaments. Since all the muscles in the body are controlled by electrical impulses, when current flows, their spontaneous contraction occurs. Because of this, mechanical damage to tissues can occur - ruptures. As well as convulsive compression of the limbs, in which a person cannot unclench his fingers on his own and free himself from the action of the current. The same effect occurs with the heart, which can cause a fatal shock.
• electrolytic- when current flows, blood vessels have the lowest resistance, which are the conductors in the body. When an electric current passes through the vessels, the blood acts as a conductor, which, with prolonged exposure, decomposes into plasma and blood cells.

Depending on the situation, damage may also result in electrical shock. The condition of the victim is characterized by the lack of an adequate response to the events and dilated pupils. In this state, it is difficult to judge the damage done to the body, due to the fact that a person cannot report his own well-being. Therefore, his condition is determined by indirect factors (pulse, respiration, etc.).

The main causes of electric shock

The reasons may be due to various factors and situations. Because of these differences in situations, the rules regulate the use of certain remedies or impose obligations on the implementation of certain measures. In this connection, the causes of the defeat are divided into those that can occur in living conditions, and those that may occur in production.

At home

The most common causes of damage in the domestic environment are any malfunctions or careless handling of the operated devices by the person himself. The strength of the current acting on a person depends on the resistance of the electrical circuit, which includes the resistance of the skin, shoes, current spreading in the floor or some other point. The lowest resistance value is obtained in the case of wounds on the skin, a wet surface of the hands, or when a person touches grounded elements.

Special attention should pay attention to the following reasons for the defeat:

• Insulation failure inside appliances- for the most part, all home vacuum cleaners, kettles, microwaves, washing machines and other helpers are equipped with reliable insulation at the factory. However, due to natural aging or damage, the insulation resistance may deteriorate, resulting in electric shock. This problem is characterized by a potential transfer to the case or metal parts of electrical appliances and causes the occurrence.
• Damage to the insulating sheath of wires- applies to both wiring and all kinds of power cords and extension cords. There is a possibility of electric shock from places where kinks, blows or chafing occurred, especially if water gets on them.
• Contact with improvised devices and exposed live parts. Both do not guarantee a person any compliance with the standards. Therefore, interaction with questionable devices or bare wires can lead to severe electric shock.
• Spontaneous repair attempts- when people without the necessary skills and knowledge try to repair some appliances or electrical wiring. At the same time, they expose themselves to the danger of accidentally touching the elements under voltage, which is the cause of the defeat. For example, when replacing an electric lamp in a lamp, when the voltage is not removed from the cartridge.
• Using switches or sockets with a damaged casing. The case of these devices acts as a natural barrier, which, if damaged, opens access to current-carrying elements and there is a threat of electric shock.
• Attempts to replace lamps in the presence of voltage in the cartridge– due to negligence, a person may touch the internal components, which will lead to electric shock. It is also possible that a burnt-out lamp is destroyed and disintegrates in the hands, and some parts can become conductors of electric current. In this case, the disconnected switch is not a guarantee of the absence of voltage due to the fact that it may not break the phase.
• Operation of electrical appliances in conjunction with water– attempts to dry your head with a hairdryer and use an electric shaver while in the bathroom, adding water to the switched on electric kettle and other options when the device comes into contact with water can cause electric shock.
• Temporary wiring on twists- often in everyday life, in order to speed up the supply of voltage and not spend a lot of time on a full-fledged laying in the wall, or at least a channel, make a connection open way. It is these "snot" hung in the context of all norms around the house, barn or garage that can cause electric shock.

In production

The vast majority of work that is performed in production provides for a number of measures aimed at preventing electric shock. But, due to the violation of these measures and rules, personnel in contact with electrical installations or simply performing work in the immediate vicinity may be exposed to voltage.

Consider the most common causes electric shock at work:

• • Absence protective equipment or use of unsuitable. This is especially true in situations where any devices remain energized while working on them.
  • Insulation failure and lack of grounding- in power circuits, this is damage to insulators, cable insulation and other severe damage to equipment. They determine the presence of potential on the body, load-bearing structures, which can lead to fatal injury in case of contact. Initially, grounding is provided as insurance in case of damage to the insulation, so electric shock is possible only if there is no or faulty grounding.
  • Electric arc burning- can occur as an integral part of the operation of the same switches, welding machines or short circuits, and an emergency. An arc strike can cause burns, characterized by the transfer of part of the charge and the subsequent passage of current through a person.
  • Falling wires to the ground- creates a danger zone, which is 10 m for open areas and 8 m for indoors. In this space, currents spread if the protection does not turn off the line. Due to the spreading of currents on the ground surface, a potential is formed, which decreases in proportion to the distance from the point of incidence. In such a zone, the cause of the lesion is formed by the potential difference between the feet of a person.
    
  • Violation of safety signs– most of the dangerous places at the enterprise are fenced off. On the fence itself or in places where voltage is possible, temporary or permanent signs or posters are installed. In the event that a person intentionally or negligently violates the requirements of the signs, an electric shock may occur.
  • If switching or operation has not taken place or is not completely. Since most high-voltage equipment is remotely controlled, and the electrical contact nodes in switches and disconnectors are quite difficult to control, information about the absence of voltage is obtained through pointers or signaling devices. In the case when, for mechanical reasons, the switch or disconnector did not turn off at least one of the phases, there is a threat of electric shock in some section of the network, so it is imperative to use the pointer.
  • Wrong voltage supply- when performing work with the removal of voltage, a potential can be accidentally applied to the line or to the electrical installation both by employees and as a result of an emergency. If the personnel goes beyond the protective zone, fenced with grounding, or does not install them at all, then there is a danger of electric shock for them.
  • Induced voltage- is the most dangerous factor in de-energized wires and neutral elements (sections of the conductor enclosed by two insulators). In production, the most dangerous is the defeat of direct current. Because the frequency of the alternating current drops to zero on its own and rises again, due to which its effect is inconsistent.
    
  • Violation of the procedure for removing or hanging grounding- according to the requirements of the rules, when installing the ground, it is first connected to the ground, and then hung on the conductor. Otherwise, if there is a potential in the line, the worker will first bring the ground to the line potential, and when he tries to connect it to the ground loop, he himself will become an element in the current flow circuit. Grounding is removed in the reverse order - first it is removed from the current-carrying elements, and then disconnected from the circuit. When removed, there is also a similar threat.

What to do in case of electric shock?

If you witness someone being electrocuted and still under its influence, you need to get them free as soon as possible. Since the outcome of an electrical injury directly depends on the duration of contact, the response speed should be maximum.

First, it is necessary to de-energize the electrical installation or its parts with which a person interacts. The best for this are automatic switches, switches or fuses located in the immediate vicinity. For high-voltage networks, their analogues are switches and disconnectors. If these are not available, other measures may be used to reduce the duration of exposure.

by the most important rule upon release, it is the observance of the safety rules by the rescuer himself, so that he does not get struck by the current. Otherwise, to prevent death, any means will do.

Release up to 1000 V

For lines up to 1 kV, any dry clothing wrapped around the hand can be suitable, ideally these should be dielectric gloves. They can pull off the victim by the lagging ends of just dry clothes. Use a tool with insulated handles to cut through the wire. It is also possible to break the electrical circuit by placing a dielectric sheet between the victim and the ground.

In devices above 1 kV, it is dangerous to approach the victim already because the rescuer himself can fall under step voltage. But, at the same time, you can make a sketch of any uninsulated wire between the source and the victim. Try to pull the wire with an insulating rod, but with dielectric gloves. The cable, also with gloves, is allowed to cut phase by phase with an ax.

Measures for protection against electric shock

To avoid electric shock and minimize the causes that can cause it, it is enough to follow a number of simple rules:

• Don't touch electrical appliances, switches, plugs, sockets with wet hands;
• Do not allow faulty devices or devices that do not have case grounding to be connected to the network (absence is allowed only for devices designed for very low voltage);
• Do not violate the instructions prescribed by electrical signs that regulate certain actions;
• Do not leave appliances turned on when leaving the house, do not allow the plug to be pulled out by the cord;
• When working in electrical installations, it is imperative to comply with the requirements of the rules, instructions, the order of technological processes;
• Work in electrical installations should only be carried out using the necessary protective equipment.

Video in the development of the topic

An electric shock occurs when an electrical circuit is closed through the human body. The most common cases of electric shock in cases where a person touches two or one wire, while having contact with the ground. In the first case, the touch is called two-phase, in the second - single-phase.

With a two-phase touch (Fig. 10-1), a person is exposed to line voltage, so a large current flows through him

where is the line voltage and the average (with good contacts) resistance of the human body. The current in this case is deadly, although a person can be well isolated from the ground.

In the case of a single-phase touch in a network with a grounded neutral wire (Fig. 10-2), a series circuit is formed from the resistances of the human body, shoes, floor and neutral ground ( neutral wire) current source. A phase (and not linear, as in the previous case) voltage is applied to this circuit. However, if a person in wet or nailed shoes stands on damp ground or on a conductive floor, then these resistances, like the resistance (10 ohms), are negligible compared to the resistance of the human body. Current will flow in this circuit:

This current is deadly.

However, if a person is wearing special rubber shoes and is on a dry wooden floor, then, assuming the resistance of the shoes is 45,000 ohms and the floor is 100,000 ohms, in the circuit under consideration we get the current value:

i.e. harmless to humans. The last case shows how important it is for safety reasons to use non-conductive shoes and especially an insulating floor.

In the case of a single-phase contact with a network with an isolated neutral, the circuit closes through the human body and through the imperfect insulation of the network wires (Fig. 10-3). In good condition, the insulation has a very high resistance, so such a touch should not be dangerous. This is true only for normal (fail-safe) networks. In networks with a voltage of 1000 V or more, the capacitance between phases and ground can create a large capacitive current that is dangerous to humans.

Statistics show that electric shocks are commonly found in the home and at work. How to protect yourself and what to do in case of exposure to current?

What is an electrical injury?

Cases of electric shock are rare, but at the same time they are among the most dangerous injuries. With such a lesion, a fatal outcome is possible - statistics show that it occurs on average in 10% of injuries. This phenomenon is associated with the effect of electric current on the body. Therefore, representatives of professions related to electricians can be attributed to the risk group, but they are not excluded among people who accidentally encountered the action of current in everyday life or on sections of power lines. As a rule, the cause of such damage is technical difficulites or non-compliance with safety regulations.

Types of electric shock

The nature of the impact on the body and its degree can be different. The classification of the lesion is based precisely on these features.

Electrical burn

Electric shock is one of the most common injuries. There are several variants of such an injury. First of all, it should be noted the contact form, when an electric current passes through the body upon contact with a source. An arc lesion is also distinguished, in which the current itself does not pass directly through the body. The pathological effect is associated with an electric arc. If there is a combination of the forms described above, such a lesion is called mixed.

Electrophthalmia

An electric arc leads not only to a burn, but also to irradiation of the eyes (it is a source of UV rays). As a result of such exposure, inflammation of the conjunctiva occurs, the treatment of which can take a long time. In order to avoid such a phenomenon, special protection against electric shock and compliance with the rules for working with its sources are necessary.

Metallization

Among the types of skin lesions, metallization of the skin stands out with its clinical features, which occurs due to the penetration of metal particles melted under the action of an electric current. They are the smallest in size, penetrate into the surface layers of the epithelium of open areas. Pathology is not fatal. Clinical manifestations soon disappear, the skin acquires a physiological color, and pain stop.

electrical signs

Thermal and chemical action leads to the formation of specific signs. They have sharp contours and color from gray to yellowish. The shape of the signs can be oval or round, as well as resemble lines and dots. The skin in this area is characterized by the occurrence of necrosis. It becomes hardened due to the necrosis of the surface layers. Due to cell death in the post-traumatic period, there are no complaints among complaints. The lesions disappear after some time due to regeneration processes, while the skin acquires a natural color and elasticity. This type of injury is very common and usually non-fatal.

Mechanical damage

They occur with prolonged exposure to current. Mechanical injuries are characterized by ruptures of muscles and ligaments, which occurs due to muscle tension. In addition, the neurovascular bundle is additionally damaged, and such severe injuries as fractures and complete dislocations are also possible. More serious and highly qualified assistance is required in case of electric shock with such a clinic. In case of untimely assistance or too long exposure, a fatal outcome is possible.

As a rule, these types do not occur separately, but are combined. This factor makes it difficult to provide first aid and further treatment.

What determines the degree of electric shock?

This indicator depends not only on the strength, duration of action and the nature of the current, but also on the resistance of the body. The skin and bones have a high resistance index, while the liver and spleen, on the contrary, have a low resistance index. Fatigue contributes to a decrease in resistance, and therefore, in such cases, a fatal outcome is most likely. Wet skin also contributes to this. Clothes and shoes made of leather, silk, wool and rubber will help protect the body from harmful effects, as they will act as an insulator. It is these factors that affect the risk of electric shock.

Effects

Electrical current causes multiple damage. First of all, it acts on the nervous system, due to which motor activity and sensitivity worsen. In addition, there are, for example, severe convulsions and loss of consciousness can cause death due to respiratory arrest. After rescuing the victim, deep lesions of the central nervous system. The main ones lead to this.

Impact on the heart can also lead to death, as the current leads to impaired contractility and causes fibrillation. Cardiomyocytes begin to work inconsistently, as a result of which the pumping function is lost, and the tissues do not receive required amount oxygen with blood. This leads to the development of hypoxia. Another formidable complication is rupture of blood vessels, which can lead to death from blood loss.

Muscle contraction often reaches such a force that a fracture of the spine is possible, and, consequently, damage to the spinal cord. On the part of the sense organs, there is a violation of tactile sensitivity, tinnitus, hearing loss, damage to the eardrum and elements of the middle ear.

Complications do not always appear immediately. Even with a short exposure, electrical injury can make itself felt in the future. Long-term effects - arrhythmias, endarteritis, atherosclerosis. From the side of the nervous system, neuritis, vegetative pathologies and encephalopathy can occur. In addition, contractures are possible. That is why means of protection against electric shock are important.

The reasons

The main etiological factor is the action of the current. Additional conditions are the state of the body and the presence or absence of any protection. Electrical shock is usually caused by improper use or lack of protection when working with wiring. The risk group includes professions related to working with current. However, electrical injury can happen to anyone. Cases of defeat in everyday life are not uncommon, but they mostly end favorably. In addition, episodes of contact with such lesions are frequent. Attention and knowledge of safety precautions will protect against such phenomena.

Clinical manifestations of electrical injury

Symptoms depend on the type of lesion, while their complex is based on a combination of manifestations of the described types of injuries. Also, the clinic depends on the severity. It should be noted that the most dangerous functional deviations of the respiratory, nervous and cardiovascular systems. The victim is in severe pain. A characteristic suffering expression appears on the face, and the skin becomes pale. Under the action of current, muscle contraction occurs, the duration of which depends on the preservation of their integrity. All this can cause loss of consciousness, and in a more severe case - death. Protecting against electric shock will help prevent this condition.

The effect of current on the body

The changes that occur in the body under the influence of current are associated with the versatility of its effects. It has a thermal effect by converting electrical energy into thermal energy due to tissue resistance. This is due to the formation of burns and marks. Thermal action adversely affects the body, as it inevitably leads to the destruction of tissues.

Electrochemical action mainly affects the circulatory system. This leads to a change in the charge of many molecules, and also sticks together blood cells, thickening the blood and promoting the formation of blood clots.

The biological effect is associated with a violation of organs and systems - the effect on muscle tissue, the respiratory system, and nerve cells.

The multiple effect of the current on the body aggravates the condition of the victim, increasing the risk of death. The combined factors of electric shock can lead to a different outcome. Even the action of 220 volts on the body will cause irreversible damage.

First aid

All types of electric shock require otherwise a fatal outcome is possible. First of all, it is necessary to stop the effect of current on the victim, that is, turn it off from the circuit. To do this, the rescuer should definitely protect himself with insulating materials and only after that pull the victim away from the source. After you need to call an ambulance team and start providing first aid. These activities are carried out before the arrival of specialists. A person exposed to current does not tolerate cold, so it must be transferred to a warm, dry surface. First aid is aimed at restoring vital functions - breathing and blood circulation. This requires cardiopulmonary resuscitation. Every person should be trained in it or have at least the slightest idea. Resuscitation is carried out on a hard surface. The rescuer combines artificial respiration and cardiac massage. It is required to observe the ratio - 2 breaths and 30 clicks. Salvation begins with a massage, since the restoration of blood circulation is a priority. It is performed with straight arms, placing the palms on top of each other (pressure is applied to the area of ​​the wrist on the lower part of the sternum). The recommended frequency is 100 compressions per minute (the chest should move 5 cm). After the oral cavity is cleaned of secretions and artificial respiration is carried out. To protect the rescuer, it is recommended to manipulate through a handkerchief. Resuscitation can be carried out by two rescuers, while maintaining the ratio of 2 breaths and 15 clicks. When one person takes a breath, the second is contraindicated to touch the chest. When inhaling, the chest of the victim must necessarily rise - this indicates the correctness of the procedure.

Treatment

Electric shock requires prompt resuscitation and subsequent treatment. The therapy is carried out in a hospital. Even if the victim feels satisfactory, and the damage is minor, preventive monitoring is required to help avoid complications.

Treatment is aimed at the speedy healing of skin lesions, as well as the elimination of other disorders associated with the harmful effects of current. Observation in the hospital is carried out until complete recovery.

Prevention

To prevent all types of electric shock will help compliance with safety regulations. Do not use electrical appliances that are defective. It is also contraindicated to touch them with wet hands, as this will improve the conduction of current. Working with electrical appliances and wiring requires the use of protective equipment against electric shock. These include gloves, special pads. Tools must have an insulated handle. Also, for prevention, the public should be informed about the possibility of such an injury. A special role is played by informing in the media, as well as conducting conversations with schoolchildren. This will reduce the risk of electric shock.

Electrical injuries are very dangerous, and their outcome depends on many factors. It is influenced not only by current indicators (voltage, duration), but also by the body's defenses. For example, a current of 220 volts, depending on the conditions of exposure, can lead to both non-fatal injuries and death. It is very important to observe safety precautions - this will help to avoid such defeats.

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 Dishwasher), and the other - building structural elements 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 TN-S systems or TN-C-S, will prevent an accident.

Proper ground connection of all enclosures 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 homemade machine, heating, welding... 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 upon commissioning electrical circuit inlet 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 - important element 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

Main technical means protection of a person from electric shock, used separately or in combination with each other, are (PUE): protective grounding, protective grounding, protective shutdown, electrical network separation, low voltage, electrical protective equipment, potential equalization, double insulation, warning signaling, blocking, safety 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.

The dotted lines in the figure show the equivalent resistance Z of /3, which replaces the complex resistances of the phase insulations in case of their equality, but is connected to the neutral N of the electrical network.

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.

When one of the phases is closed to the zeroed body of the electrical installation, a short circuit occurs, formed by a phase voltage source and complex resistances of the phase (Ż f) and zero protective (Ż nzp) conductors, the current value in which guarantees the rapid operation of the protection element closest to the electrical installation (Pr2) . In order to further increase the level of electrical safety, for example, when the NZP is broken, it is re-grounded (in Fig. 4.7 R p- resistance of the repeated ground electrode). With absence R p the voltage on the case of a damaged installation may exceed 0.5U f, and in the case of using a repeated ground electrode, it may be somewhat reduced.

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).

Sensor D responds to changes in one or more parameters Ue, characterizing electrical safety. Its output signal U d is proportional to the RCD input signal used, to which it responds. In the FAS alarm generator, the sensor signal U d is compared with the set response level Up. If U d > Up, then the signal U ac through the matching element (in terms of power, voltage) of the ES leads to the opening of the contacts of the tripping device of the OS.

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.

Application of low voltages . A significant increase in the level of electrical safety can be achieved by reducing the operating voltages of electrical installations. If the rated voltage of the electrical installation does not exceed the long-term permissible value of the contact voltage, then even simultaneous contact of a person with current-carrying parts of different phases or poles can be considered relatively safe.

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 grounded or neutralized and therefore do not have the appropriate connection. 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