Danger of including a person in an electrical circuit. Schemes for connecting a person to an electrical current circuit. Scheme of single-phase connection of a person to a three-phase current network with a grounded neutral

9.2. Schemes of possible inclusion of a person in an electric current circuit.

During the operation of electrical installations, the possibility of accidental human contact with live parts that are energized cannot be excluded. A touch will be most dangerous if a person is standing on the ground or a conductive base (floor, platform) and his shoes have some electrical conductivity.

Human contact with live parts can be single-phase (single-pole in DC circuits) or two-phase (double-pole). In both cases, an electrical circuit is formed, one of the sections of which will be the human body. In the first case, the current path through a person can be “arm - legs”. In the second case - “hand - hand”. Other schemes for connecting a person to an electrical circuit are possible, for example, when touching live parts with the face, neck, back, etc., or “leg-to-leg” switching.

With a two-phase (two-pole) connection, a person is under the full operating voltage of the electrical installation and the current passing through him will be equal to

I person = U l /R person, (9.1)

where U l - linear voltage; R person - resistance of the human body.

With a single-pole (single-phase) touch, which is more common, the current flowing through a person will depend not only on the voltage of the electrical installation and the resistance of the human body, but also on other factors: the neutral mode of the power source, the state of the network insulation, the state (electrical conductivity) of the floor, human footwear, air humidity, etc.

Such diseases that aggravate the outcome of electrical injury include: increased function of the thyroid gland, many diseases of the nervous system, angina pectoris. Particularly noteworthy is the influence of alcohol intoxication. In addition to the fact that a person in a state of alcoholic intoxication more often makes mistakes and receives electrical injury, due to alcohol intoxication, his central nervous system loses its regulatory role in controlling breathing and blood circulation, which significantly aggravates the outcome of the injury.

Inclusion of a person in an electric current circuit

Reasons for inclusion. A person is included in an electric current circuit through direct contact of the body with a live part of an electrical installation that is energized. This usually occurs due to negligence or as a result of erroneous human actions, as well as due to malfunction of electrical installations and technical protective equipment. Such cases, for example, include the following:

Touching live parts under voltage, assuming that they are de-energized;

During repair, cleaning or inspection, touching previously de-energized live parts, but to which voltage was mistakenly applied by an unauthorized person or a faulty starting device spontaneously turned on;

Touching metal parts of electrical installations that are not usually energized, but become energized relative to the ground due to damage to the electrical insulation or other reasons (short circuit to the frame);

The appearance of step voltage on the surface of a conductive base (floor) along which a person walks; and etc.

Switching schemes. A person can become involved in an electric current circuit by touching one phase of an electrical installation that is energized, two phases at the same time, or the neutral protective conductor and a phase. Contact with the neutral protective conductor is safe (Fig. 2, a, I), other cases entail serious consequences.

Rice. 2. Diagrams of the paths of electric current passing through the human body: a – touching the wires; b – occurrence of touch voltage; c – Occurrence of step voltage; I-touch the neutral wire; II – touching the phase wire; III – touching the phase and neutral wires; IV – touching phase wires; 0 – neutral wire; 1, 2, 3 – phase wires; 4 – neutral point; 5- single grounding conductor (electrode); A, B, C - electrical installations

Single-phase (single-pole) touch (Fig. 2, a, II and III) occurs most often when replacing lamps and maintaining lamps, changing fuses and servicing electrical installations, etc. In a neutrally grounded system, a person will be exposed to phase voltage Uph (in V), which is less than linear Ul:

Accordingly, the magnitude of the phase current passing through the human body will be less. If a person is reliably isolated from the ground (shod in dielectric galoshes, the floor is dry and non-conductive), then single-phase contact does not pose a danger.

Biphasic (two-pole) touch is more dangerous because a person comes under linear voltage (Fig. 2, a, IV). Even with a voltage of 127 V and an estimated human body resistance of 1000 Ohms, the current in the circuit will be lethal (127 mA). With a two-phase touch, the danger of injury will not decrease even if the person is reliably isolated from the ground (floor).

Two-phase contact occurs rarely, usually when performing work under voltage, which is strictly prohibited.

If the insulation of live parts is damaged and shorted to the body of electrical equipment, a significant potential can arise. A person who in this case touches the body of the electrical installation (Fig. 2, b) will be under touch voltage Uп (in V)

where Ich is the magnitude of the current passing through a person along the “arm-leg” path, A; Rch – human body resistance, Ohm.

Touch voltage is the potential difference between two points of an electrical circuit that are simultaneously touched by a person, or the voltage drop in the resistance of the human body.

The touch voltage will increase as the distance between the electrical installation and the ground electrode increases, reaching a maximum at a distance of 20 m or more. When a phase wire falls on the surface of the earth, a zone of current spreading appears (Fig. 2, c).

A person passing through this zone will be under step voltage (potential difference) between two points of the current circuit, located one step apart (0.8 m). The highest step voltage will be near the closing point and, gradually decreasing, will drop to zero at a distance of 20 m.

You should not approach a fallen wire closer than 6-8 m. If you need to approach, you should turn off the power to the wire or wear dielectric galoshes (boots).

Psycho-emotional alertness - “attention factor” when working with electric current

The formation of psycho-emotional alertness among workers, the “attention factor” when working with electric current, is the most important condition for personal prevention of electrical injuries. This factor is based on knowledge of the physiological effect of electric current on the body when the victim enters an electrical circuit.

In particular, the “attention factor” plays a decisive role in many cases of lesions, i.e., essentially, the severity of the outcome of the lesion is determined to a large extent by the state of the person’s nervous system at the time of the lesion.

It is necessary that a person be “collected”, which allows him to expect some event during work that requires attention.

Such a statement is valid mainly in case of electric shock with a voltage of 220-300 V. At high voltages, a severe outcome most often occurs from arc burns. There is already reason to believe that the risk of burns increases almost linearly depending on the voltage value.

The attention factor undoubtedly causes the mobilization of the body's defense systems, enhances the blood circulation of the heart muscle and cerebral blood flow through the pituitary-adrenal system and makes them more resistant to external stimuli (electrical trauma).

With the attention factor, it is much more difficult to upset the biosystem of automatic regulation of the most important systems of the body (central nervous system, blood circulation, respiration).

However, it should be noted that the role of the attention factor is not yet sufficiently reflected in protective measures for electrical safety.

But there is confidence that new views on the electrical safety of living tissue, further study of the nature of the electrical activity of the human body will reveal the biophysics of the mechanism of human injury, which will be taken into account in the development of measures to protect against the effects of electric current.

Measures to ensure safe operation of electrical equipment

Technical methods and means of protection that ensure electrical safety are indicated taking into account: the electrical power source of rated voltage, type and frequency of current; neutral mode, type of execution; environmental conditions; possibility of relieving voltage from live parts; the nature of possible human contact with the elements of the current circuit.

All cases of electric shock to a person are a consequence of touching at least two points of an electrical circuit, between which there is a potential difference. The danger of such contact largely depends on the characteristics of the electrical network and the way a person is connected to it. By determining the current per hour passing through a person, taking these factors into account, appropriate protective measures can be selected to reduce the risk of injury.

Two-phase inclusion of a person in a current circuit (Fig. 8.1, a). It occurs quite rarely, but is more dangerous compared to single-phase, since the highest voltage in a given network is applied to the body - linear, and the strength of the current, A, passing through a person does not depend on the network diagram, the mode of its neutral and other factors, i.e. .e.

I = Ul/Rch = √ 3Uph/Rch,

where Uл and Uф are linear and phase voltage, V; Rch is the resistance of the human body, Ohm (according to the Electrical Installation Rules, in calculations Rch is taken equal to 1000 Ohms).

Cases of two-phase contact can occur when working with electrical equipment without removing the voltage, for example, when replacing a blown fuse at the entrance to a building, using dielectric gloves with rubber breaks, connecting a cable to unprotected terminals of a welding transformer, etc.

Single-phase switching. The current passing through a person is influenced by various factors, which reduces the risk of injury compared to two-phase touch.

Rice. 8.1. Schemes for possible connection of a person to a three-phase current network:

a - two-phase touch; b—single-phase contact in a network with a grounded neutral; c - single-phase touch in a network with an isolated neutral

In a single-phase two-wire network, isolated from the ground, the current strength, A, passing through a person, with equal insulation resistance of the wires relative to the ground r1 = r2 = r, is determined by the formula

Ich = U/(2Rch + r),

where U is the network voltage, V; r — insulation resistance, Ohm.

In a three-wire network with an insulated neutral, with r1 = r2 = r3 = r, the current will flow from the point of contact through the human body, shoes, floor and imperfect insulation to other phases (Fig. 8.1, b). Then

Ich = Uph/(Ro + r/3),

where Ro is the total resistance, Ohm; RO = Rch + Rop + Rp; Rob - shoe resistance, cm: for rubber shoes Rob ≥ 50,000 Ohm; Rn - floor resistance, Ohm: for a dry wooden floor, Rп = 60,000 Ohm; g - wire insulation resistance, Ohm (according to the Electrical Regulations, it must be at least 0.5 MOhm per phase of a network section with voltage up to 1000 V).

In three-phase four-wire networks, the current will flow through a person, his shoes, the floor, the grounding of the source neutral and the neutral wire (Fig. 8.1, c). Current strength, A, passing through a person,

Ich=Uf(Ro + Rn),

where RH is the neutral grounding resistance, Ohm. Neglecting resistance RH, we get:

Agricultural enterprises mainly use four-wire electrical networks with a solidly grounded neutral with a voltage of up to 1000 V. Their advantage is that they can be used to obtain two operating voltages: linear Ul = 380 V and phase Uph = 220 V. Such networks do not require high requirements for the quality of wire insulation and are used when the network is highly branched. A three-wire network with an insulated neutral at voltages up to 1000V is used somewhat less frequently; it is safer if the insulation resistance of the wires is maintained at a high level.

Touch tension. It occurs as a result of touching live electrical installations or metal parts of equipment.

If an electric current flows through a grounding rod immersed in the ground so that its upper end is located at ground level, then the touch voltage, V,

where I3 is the ground fault current, A; ρ is the resistivity of the base (soil, floor, etc.) on which the person is located, Ohm*m; l and d—length and diameter of the ground electrode, m; x is the distance from a person to the center of the ground electrode, m; a is the touch voltage coefficient.

α = Rch/(Rch + Rob + Rn) = Rch/Ro.

Neglecting the resistance of the shoes (when it is wet or in the absence of it), we can write for the following cases:

the soles of the feet are removed from one another at a distance of a step

α=1/(1 + 1.5ρ/Rh);

feet are close

α=1/(1 + 2ρ/Rch).

Step voltage. This is the voltage Ush on the human body when the legs are positioned at points in the field of current spreading from the ground electrode or from a wire that has fallen to the ground, where the feet are located, when a person walks in the direction of the ground electrode (wire) or away from it (Fig. 8.2).

If one leg is at a distance x from the center of the ground electrode, then the other is at a distance x + a, where a is the step length. Usually in calculations we take a = 0.8 m.

The maximum voltage in this case occurs at the point where the current closes to the ground, and as it moves away from it it decreases according to the hyperbola law. It is assumed that at a distance of 20 m from the fault point the earth potential is zero.

The connection of a person to the electrical network can be single-phase or two-phase. Single-phase connection is a human connection between one of the network phases and the ground. The strength of the damaging current in this case depends on the neutral mode of the network, human resistance, shoes, floor, and phase insulation relative to the ground. Single-phase switching occurs much more often and often causes electrical injuries in networks of any voltage. With a two-phase connection, a person touches two phases of the electrical network. With a two-phase switching on, the strength of the current flowing through the body (striking current) depends only on the network voltage and the resistance of the human body and does not depend on the neutral mode of the network supply transformer. Electrical networks are divided into single-phase and three-phase. A single-phase network can be isolated from the ground or have a grounded wire. In Fig. 1 shows possible options for connecting a person to single-phase networks.

Thus, if a person touches one of the phases of a three-phase four-wire network with a solidly grounded neutral, then he will be practically under phase voltage (R3≤ RF) and the current passing through the person during normal operation of the network will practically not change with changes in insulation resistance and capacitance wires relative to ground.

The effect of electric current on the human body

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

The thermal effect manifests itself in burns of the skin or internal organs.

During electrolytic action, due to the passage of current, decomposition (electrolysis) of blood and other organic liquid occurs, accompanied by the destruction of red blood cells and metabolic disorders.

The biological effect is expressed in irritation and excitation of living tissues of the body, which is accompanied by spontaneous convulsive contraction of muscles, including the heart and lungs.

There are two main types of electric shock:

§ electrical injuries,

§ electric shocks.

Electric shocks can be divided into four degrees:

1. convulsive muscle contractions without loss of consciousness;

2. with loss of consciousness, but with preservation of breathing and heart function;

3. loss of consciousness and disturbance of cardiac activity or breathing (or both);

4. clinical death, i.e. lack of breathing and blood circulation.

Clinical death is a transition period between life and death, begins from the moment the activity of the heart and lungs stops. A person in a state of clinical death does not show any signs of life: she has no breathing, no heartbeat, no reaction to pain; The pupils of the eyes are dilated and do not react to light. However, it should be remembered that in this case the body can still be revived if help is given to it correctly and in a timely manner. The duration of clinical death can be 5-8 minutes. If help is not provided in a timely manner, biological (true) death occurs.

The result of electric shock to a person depends on many factors. The most important of them are the magnitude and duration of the current, the type and frequency of the current and the individual properties of the organism.

Determination of the current spreading resistance of single grounding conductors and the procedure for calculating the protective grounding loop for stationary process equipment (GOST 12.1.030-81. CCBT. Protective grounding, grounding)

Implementation of grounding devices. A distinction is made between artificial grounding devices, intended exclusively for grounding purposes, and natural ones - third-party conductive parts that are in electrical contact with the ground directly or through an intermediate conducting medium, used for grounding purposes.

For artificial grounding electrodes, vertical and horizontal electrodes are usually used.

The following can be used as natural grounding conductors: water supply and other metal pipes laid in the ground (with the exception of pipelines of flammable liquids, flammable or explosive gases); casing pipes of artesian wells, wells, pits, etc.; metal and reinforced concrete structures of buildings and structures that have connections to the ground; lead sheaths of cables laid in the ground; metal sheet piles for hydraulic structures, etc.

The calculation of protective grounding aims to determine the basic parameters of grounding - the number, dimensions and order of placement of single grounding conductors and grounding conductors, at which the touch and step voltages during the phase closure to the grounded body do not exceed permissible values.

To calculate grounding, the following information is required:

1) characteristics of the electrical installation - type of installation, types of main equipment, operating voltages, methods of grounding neutrals of transformers and generators, etc.;

2) electrical installation plan indicating the main dimensions and placement of equipment;

3) the shapes and sizes of the electrodes from which it is planned to construct the designed group grounding system, as well as the expected depth of their immersion into the ground;

4) data from measurements of soil resistivity in the area where the ground electrode is to be constructed, and information about the weather (climatic) conditions under which these measurements were made, as well as characteristics of the climatic zone. If the earth is assumed to be two-layer, then it is necessary to have measurement data on the resistivity of both layers of the earth and the thickness of the top layer;

5) data on natural grounding conductors: what structures can be used for this purpose and their resistance to current spreading, obtained by direct measurement. If for some reason it is impossible to measure the resistance of the natural ground electrode, then information must be provided that allows this resistance to be determined by calculation;

6) calculated ground fault current. If the current is unknown, then it is calculated using the usual methods;

7) calculated values ​​of permissible touch (and step) voltages and protection duration, if the calculation is made based on touch (and step) voltages.

Grounding calculations are usually made for cases where the ground electrode is placed in homogeneous ground. In recent years, engineering methods for calculating grounding systems in multilayer soil have been developed and began to be used.

When calculating grounding conductors in homogeneous soil, the resistance of the upper layer of the earth (layer of seasonal changes), caused by freezing or drying out of the soil, is taken into account. The calculation is made using a method based on the use of grounding conductivity utilization factors and is therefore called the utilization factor method. It is performed with both simple and complex designs of group grounding conductors.

When calculating grounding systems in a multilayer earth, a two-layer earth model is usually adopted with the resistivities of the upper and lower layers r1 and r2, respectively, and the thickness (thickness) of the upper layer h1. The calculation is made by a method based on taking into account the potentials induced on the electrodes that are part of the group grounding system, and is therefore called the method of induced potentials. Calculation of grounding conductors in multi-layer earth is more labor-intensive. At the same time, it gives more accurate results. It is advisable to use it in complex designs of group grounding conductors, which usually take place in electrical installations with an effectively grounded neutral, i.e. in installations with voltages of 110 kV and higher.

When calculating a grounding device by any method, it is necessary to determine the required resistance for it.

The required resistance of the grounding device is determined in accordance with the PUE.

For installations with voltages up to 1 kV, the resistance of the grounding device used for protective grounding of exposed conductive parts in an IT system must meet the following conditions:

where Rз is the resistance of the grounding device, ohm; Upred.add – touch voltage, the value of which is assumed to be 50 V; Iз – total ground fault current, A.

As a rule, it is not necessary to accept a grounding device resistance value of less than 4 ohms. A grounding device resistance of up to 10 ohms is allowed if the above condition is met, and the power of transformers and generators supplying the network does not exceed 100 kVA, including the total power of transformers and (or) generators operating in parallel.

For installations with voltages above 1 kV above 1 kV, the resistance of the grounding device must correspond to:

0.5 Ohm with an effectively grounded neutral (i.e. with large earth fault currents);

250/Iz, but not more than 10 Ohms with an isolated neutral (i.e. with low ground fault currents) and the condition that the ground electrode is used only for electrical installations with voltages above 1000 V.

In these expressions, Iз is the calculated ground fault current.

During operation, there may be an increase in the resistance to the spreading of the ground electrode current above the calculated value, therefore it is necessary to periodically monitor the value of the ground electrode resistance.

Ground loop

The ground loop is classically a group of vertical electrodes of small depth connected by a horizontal conductor, mounted near an object at a relatively small mutual distance from each other.

Traditionally, a steel corner or reinforcement 3 meters long, which was driven into the ground using a sledgehammer, was used as grounding electrodes in such a grounding device.

A 4x40 mm steel strip was used as a connecting conductor, which was laid in a pre-prepared ditch 0.5 - 0.7 meters deep. The conductor was connected to the mounted grounding conductors by electric or gas welding.

To save space, the ground loop is usually “rolled” around the building along the walls (perimeter). If you look at this ground electrode from above, you can say that the electrodes are mounted along the contour of the building (hence the name).

Thus, a ground loop is a ground electrode consisting of several electrodes (groups of electrodes) connected to each other and mounted around the building along its contour.

The severity of electric shock is largely determined by the way a person is connected to the circuit. The patterns of circuits formed when a person comes into contact with a conductor depend on the type of power supply system used.

The most widely used are four-wire networks with a voltage of 380/220 V. What is it? Four wires go from the source of electrical energy to consumers, three of which are called phase, and one is called neutral. The voltage between two phase wires is 380V (this voltage is called linear), and between the neutral wire and any of the phase wires is 220V (this voltage is called phase voltage).

To power lighting installations, televisions, and refrigerators, a single-phase network is used - one phase wire and a neutral wire (that is, 220 V). The most common electrical networks are those in which the neutral wire is grounded. Touching the neutral wire poses virtually no danger to humans; Only the phase wire is dangerous. However, it is difficult to figure out which of the two wires is neutral - they look the same. This is done using a special device - a phase detector.

Let's consider possible schemes for connecting a person to an electrical circuit when touching the current conductors of a single-phase (two-wire) network. The rarest, but also the most dangerous, is a person touching two wires or current conductors connected to them.

Suppose you decide to repair the electrical wiring - insulate the wires, repair or install a new socket and switch, but you forgot to turn off the power. While performing installation work, you touched the phase wire with one hand and the neutral wire with the other. Current will flow through you along the “hand-to-hand” path, that is, the resistance of the circuit will only include the resistance of the body. If we take the body resistance to be 1 kOhm (this figure is usually accepted in calculations), then according to Ohm’s law a current will flow through you:

I (current) = 220 V: 1000 Ohm = 0.22 A = 220 mA.

This is a deadly current. The severity of the electrical injury, and even your life, will depend, first of all, on how quickly you free yourself from contact with the current conductor (break the electrical circuit), because the time of exposure in this case is decisive.

When working with electrical wiring, be sure to turn off the power supply, and hang a warning sign on the switch: “Do not turn it on - people are working,” or better yet, place an observer.

Electric shock can occur when repairing household electrical appliances (vacuum cleaner, coffee maker, washing machine), television and radio equipment. You know well that you cannot work under voltage, and you turned off the power supply with the switch on the electrical appliance. However, the voltage will be at the input contacts of the switch. During operation, you may forget about this and touch them, or accidentally press the switch and turn on the electric current. The voltage on some elements of household equipment can reach very high values. For example, the voltage supplied to the cathode ray tube of a TV or PC monitor reaches 15000-18000 V.

Repairs to electrical appliances, television and radio equipment, and electrical equipment can only be performed when the electrical plug of the device is unplugged from the socket.

Much more often there are cases when a person with one hand comes into contact with a phase wire or part of a device, a device that is electrically connected to it.

You decide to drill a hole using an electric drill. You hadn’t used the drill for a long time, but it was in good working order. Your work can be completed either successfully or end in electric shock of varying severity - from a mild shock to death. Why might this happen? Insulation ages over time, and its insulating properties deteriorate (electrical resistance decreases). Insulation deteriorates especially quickly when left in a damp room or in an aggressive environment for a long time (for example, in an environment of sulfuric acid vapors). Conductive dust or water that gets into the drill can short-circuit the phase conductor to the body (handle) of the drill. The insulation of the supply wires can be chewed by a mouse. If the body of the electric drill is metal, you are actually in contact with the phase wire; if it is plastic, electrical contact may occur if the integrity of the body is broken (cracked) or the body is wet.

How will the current flow through a person, and what kind of electrical circuit will be formed? If the second hand also rests on the body of the drill or does not touch any other conductive objects, the current will flow along the hand-to-foot path. The current through a person, shoes, base (floor), reinforced concrete structures of the building will flow into the ground and through it to the neutral wire (after all, the neutral wire is grounded). A closed electrical circuit is formed, the magnitude of the current in which will be determined by its total electrical resistance. If you are wearing insulating dry shoes (leather, rubber) standing on a dry wooden floor, the circuit resistance will be large, and the current strength according to Ohm's law will be small.

For example, floor resistance is 30 kOhm, leather shoes are 100 kOhm, human resistance is 1 kOhm. The current that will flow through a person:

I (current) = 220 V: (30000 + 100000 + 1000) Ohm = 0.00168 A = 1.68 mA.

This current is close to the threshold perceptible current. You will feel the flow of current, stop working, eliminate the fault.

If you stand barefoot on wet ground, a current will flow through your body:

I(current) = 220 V: (3000 + 1000) Ohm = 0.055 A = 55 mA.

This current can cause damage to the lungs and heart, and with prolonged exposure, death. If you stand on wet ground with dry and intact rubber boots, a current will flow through your body:

I(current) = 220 V: (500000 + 1000) Ohm = = 0.0004 A = 0.4 mA.

You may not feel the flow of such current. But a small crack or puncture in the sole of a boot can dramatically reduce the resistance of the rubber sole and make work dangerous.

Before you start working with electrical devices (especially those that have not been in use for a long time), they must be carefully inspected for damage to the insulation. Electrical devices must be wiped from dust and, if they are wet, dried. Wet electrical devices must not be used! It is better to store electric tools, instruments, and equipment in plastic bags to prevent dust or moisture from getting into them. You must work in dry shoes. If the reliability of an electrical device is in doubt, you need to play it safe - place a dry wooden floor or rubber mat under your feet. You can use rubber gloves.

Another current flow pattern occurs when your other hand touches a highly conductive object that is electrically connected to ground. This could be a water pipe, a heating radiator, a metal garage wall, etc. Current flows along the path of least electrical resistance. These objects are practically short-circuited to the ground, their electrical resistance is very small. The path of current flow through the body in this case is “hand-to-hand”, that is, it practically coincides with the case of simultaneous hands touching two wires - phase and neutral. As was shown earlier, the current can reach a value of 220 mA, i.e. deadly. In a damp room, even wooden structures become good conductors of electricity.

Working in damp rooms, in the presence of highly conductive objects connected to the ground near a person, poses an extremely high danger and requires compliance with increased electrical safety measures. Often in such rooms they use reduced voltages - 36 and 12 volts.

When working with electrical devices, do not touch objects that may be electrically connected to ground.

We have not considered all possible electrical network diagrams and touch options. In production, you may be dealing with more complex electrical circuits that carry much higher voltages and are therefore more dangerous. However, the main conclusions and recommendations for ensuring safety are almost the same.

Issues of final control.

1. Which touch to live conductors is most dangerous for a person?

2. Why does touching objects connected to the ground (such as a water pipe) with your hand when working with electrical devices dramatically increase the risk of electric shock?

3. Why do you need to remove the electrical plug from the socket when repairing electrical equipment?

4. Why do you need to wear shoes when working with electrical devices?

5.How can you reduce the risk of electric shock?

6. What electrical safety rules must be observed when operating electrical devices?

7. A man, while in a bathtub filled with water, decided to shave with an electric razor. What can happen and what is the risk of electrocution for a man?

8. The girl took a bath and, standing barefoot on the wet tiled floor, decided to dry her hair with a hairdryer. Assess the danger and possible consequences.

9. Tell about cases of electric shock that happened to you or other people. What was the cause of the damage and what electrical safety rules were violated?

10. Based on the instructions of the teacher, who sets the network parameters and the pattern of human contact with live wires or objects, assess the danger of electric shock.

I. Cars use a direct electric current of 12V. The negative pole of the car is connected to the car body, the positive pole is connected to the insulated electrical wiring. Assess the danger of such current to humans.