Electricity. Permissible values \u200b\u200bof currents and stresses. Extremely permissible currents of IH MA and the tension of the UPR to the maximum allowable voltage value

To properly design methods and means of protecting people from electric shock, it is necessary to know the permissible levels of tensions and values \u200b\u200bof currents flowing through the human body.

The tension is called the voltage between the two points circuit points, which simultaneously concerns a person. The maximum permissible values \u200b\u200bof the voltage of the touch U PD and currents of the I PD, flowing through the human body along the path "hand - hand" or "hand - legs" with normal (non-accidental) mode of electrical installation, according to GOST 12.1.038-82 * are shown in Table. one.

In case of emergency mode of production and household appliances and electrical installations with a voltage to 1000 V with any neutral mode, the maximum permissible values \u200b\u200bof the PD and PD I PD should not exceed the values \u200b\u200bgiven in Table. 2. Emergency mode means that the electrical installation is faulty, and there may be dangerous situations leading to electricians.

With the duration of exposure more than 1 with the value of U PD and I PD correspond to the release values \u200b\u200bfor alternating and conditionally non-bore for constant currents.

Table 1

Maximum allowable values \u200b\u200bof tension and currents

in the normal mode of electrical installation

Note. Touch voltage and currents for persons performing in high temperatures (above 25 С) and humidity (relative humidity of more than 75%) should be reduced by 3 times.

table 2

Maximum allowable tension values

and currents in the emergency mode of electrical installation

4. Human body resistance

The value of the current through the human body strongly affects the severity of electricians. In turn, the current itself according to the law of Ohm is determined by the resistance of the human body and the voltage attached to it, i.e. tension touch.

The conductivity of living fabrics is due not only by physical properties, but also with the most complex biochemical and biophysical processes inherent in alive matter. Therefore, the resistance of the human body is a complex variable value having a nonlinear dependence on a plurality of factors, including from the state of the skin, the environment, the central nervous system, physiological factors. In practice, under the resistance of the body of a person, the module of its complex resistance is understood.

The electrical resistance of various tissues and liquids of the human body is not equally: leather, bones, adipose tissue, tendons have relatively large resistance, and muscle tissue, blood, lymph, nerve fibers, spinal and brain - low resistance.

Human body resistance, i.e. The resistance between the two electrodes imposed on the surface of the body is mainly determined by the skin resistance. The skin consists of two main layers: outdoor (epidermis) and internal (dermis).

The epidermis can be conventionally submitted to consisting of horny and spike layers. The horny layer consists of dead oroging cells, deprived of blood vessels and nerves and therefore is a layer of inanimate fabric. The thickness of this layer varies in the range of 0.05 - 0.2 mm. In a dry and unpolluted state, the horny layer can be considered as a porous dielectric, permeated with a set of ducts of the sebaceous and sweat glands and possessing high resistivity. The sprout layer is adjacent to the horn layer and consists mainly of living cells. The electrical resistance of this layer due to the presence of cells in it and at the stage of oroging the cells can several times higher than the resistance of the inner layer of the skin (dermis) and internal tissues of the body, although it is small in comparison with the resistance of the horn layer.

The dermis consists of fibers of the connective tissue forming a thick, durable, elastic mesh. In this layer there are blood and lymphatic vessels, nervous endings, hair roots, as well as sweat and sebaceous glands, the output flows of which come to the surface of the skin, penetrating the epidermis. The electrical resistance of the dermis, which is a lively cloth, is small.

The complete resistance of the human body is the sum of the resistance of the tissues located on the current flow path. The main physiological factor determining the amount of human body resistance is the condition of the skin in the current circuit. With a dry, clean and intact skin, the resistance of the human body, measured at a voltage of 15-20 V, fluctuates from units to dozens com. If on the skin area where electrodes are applied, scraping the horny layer, the resistance of the body will fall to 1 - 5 com, and when removing all the epidermis - up to 500 - 700 ohms. If under the electrodes completely remove the skin, the resistance of the internal tissues will be measured, which is 300 - 500 ohms.

For an approximate analysis of current flow processes along the path "hand - hand" through two identical electrodes, a simplified version of the equivalent circuit of the circuit of the electric current flow through the human body can be used (Fig. 1).

Fig. 1. Equivalent human body resistance scheme

In fig. 1 marked: 1 - electrodes; 2 - epidermis; 3 - internal fabrics and human body organs, including dermis; İ H - current flowing through the human body; Ů H is the voltage applied to the electrodes; R n - active resistance epidermis; C n - capacitance of the conditional capacitor, the plates of which are the electrode and well-conductive tissue of the human body tissue, located under the epidermis, and the dielectric itself is the epidermis itself; R VN is the active resistance of the inner tissues, including the dermis.

From the scheme Fig. 1 It follows that the complex resistance of the human body is determined by the relation

where z n \u003d (jc n) -1 \u003d -jh n is the complex resistance of the capacity with H;

X n - module z n; F, F is the frequency of alternating current.

In the future, under the resistance of the body of a person we will imply a module of its complex resistance:

. (1)

At high frequencies (more than 50 kHz) x H \u003d 1 / (C H)<< R ВН, и сопротивления R Н оказываются практически закороченными ма­лыми сопротивлениями емкостей C Н. Поэтому на высоких частотах со­противление тела человека z h в приближенно равно сопротивлению его внутренних тканей: R ВН z h в. (2)

With constant current in the steady mode, capacitive resistance are infinitely large (with 
0 X N.

). Therefore, human constant current resistance

R H \u003d 2R H + R VN. (3)

From expressions (2) and (3) you can determine

R n \u003d (R h -z H c) / 2. (four)

Based on expressions (1) - (4), it is possible to obtain a formula for calculating the value of the capacity C N:

, (5)

where Z hf is the complex body resistance module at frequency f;

C H has the dimension of the ICF; z hf, r h and r vn - com; F - kHz.

Expressions (2) - (5) allow you to determine the parameters of the equivalent circuit (Fig. 1) according to the results of experimental measurements.

The electrical resistance of the human body depends on a number of factors. Damage to the horn layer of the skin can reduce the resistance of the human body to its internal resistance. Moisturizing the skin can lower its resistance by 30 - 50%. The moisture that fell on the skin dissolves mineral substances and fatty acids on its surfaces, derived from the body along with later and fat discharges becomes more electrically conductive, improves contact between the skin and electrodes, penetrates into the withdrawal ducts of sweat and fat glands. With long-term moisturizing of the skin, its outer layer is breaking down, the moisture is saturated and its resistance can decrease to an even greater degree.

With short-term impact on the human heating or elevated ambient temperature, the human body resistance decreases due to the reflex expansion of blood vessels. With a longer exposure, sweating occurs, as a result of which the skin resistance decreases.

With an increase in the electrode area, the resistance of the outer layer of the skin R n decreases, the container with H increases, and the resistance of the body of the person decreases. At frequencies of more than 20 kHz, the specified effect of electrodes area is almost lost.

The resistance of the human body also depends on the place of the application of the electrodes, which is explained by the different thickness of the horny layer of the skin, the uneven distribution of the sweat glands on the body surface, the unequal degree of filling the blood vessels.

The passage of current through the human body is accompanied by local heating of the skin and irritating effect, which causes a reflex extension of the vessels of the skin and, accordingly, the reinforced supply of its blood and increased sweating, which, in turn, leads to a decrease in skin resistance in this place. For small stresses (20 -30 c) for 1 - 2 minutes, the skin resistance under the electrodes can be reduced by 10 - 40% (on average by 25%).

The increase in the voltage applied to the human body causes a decrease in its resistance. At stresses in tens of volts, this is due to the reflex reactions of the organism in response to the irritant effect of the current (enhancing the supply of blood vessels by blood, sweating). With increasing voltage up to 100 V and above, local, and then continuous electrical trifles of the horn layer of the skin under electrodes occur. For this reason, at stresses, about 200 V and above, the resistance of the human body is almost equal to the resistance of the inner tissues R HV.

In an indicative estimate of the danger of electric shock, the resistance of the human body is taken equal to 1 com (R h \u003d 1 com). The exact value of the calculated resistance in the development, calculation and verification of protective measures in electrical installations is selected according to GOST 12.038-82 *.

GOST 12.1.038-82 *

Group T58.

Interstate standard

Labor safety standards

ELECTRICAL SAFETY

Maximum allowable values \u200b\u200bof tension and currents

Occupational Safety Standards System. Electric Safety.
Maximum Permissible Valuies of Pickp Voltages and Currents

OKSTA 0012.

Date of introduction 1983-07-01

Information details

Enforced by Resolution of the USSR State Committee on Standards from 30.07.82 N 2987

Restriction of the validity of the Discontinued Protocol N 2-92 of the Interstate Council on Standardization, Metrology and Certification (IUS 2-93)

* Reprint (June 2001) with a change in N 1, approved in December 1987 (IUS 4-88)


This standard establishes the maximum permissible values \u200b\u200bof the touches and currents flowing through the human body, intended for the design of methods and means of protecting people, when they interact with electrical installations of the production and domestic purpose of direct and alternating current with a frequency of 50 and 400 Hz.

The terms used in the standard and their explanations are shown in the application.

1. Maximum allowable values \u200b\u200bof tension and currents

1. Maximum allowable voltage values
Topping and current

1.1. The maximum allowable values \u200b\u200bof the touch and current voltages are installed for the routes of current from one hand to the other and by hand to the legs.

(Modified edition, meas. N 1).

1.2. Touch voltages and currents flowing through the human body at normal (non-accidental) electrical installation mode should not exceed the values \u200b\u200bindicated in Table 1.

Table 1

Notes:

1. Touch voltages and currents are shown in the duration of exposure not more than 10 minutes per day and are established on the basis of the sensation reaction.

2. Touch voltages and currents for persons performing operation in high temperatures (above 25 ° C) and humidity (relative humidity of more than 75%) should be reduced three times.

1.3. The maximum allowable values \u200b\u200bof the tap and current voltages during emergency mode of industrial electrical installations to 1000 V with a deaf-free or isolated neutral and above 1000 V with an isolated neutral should not exceed the values \u200b\u200bindicated in Table 2.

table 2

Note. The maximum permissible values \u200b\u200bof the tensions and currents flowing through the human body with the duration of exposure more than 1 s, shown in Table 2, correspond to the release (variable) and non-library (constant) currents.

1.4. The maximum permissible values \u200b\u200bof the touch voltage during emergency mode of production electrical installations with a current frequency of 50 Hz, voltage above 1000 V, with a deaf grounding neutral should not exceed the values \u200b\u200bindicated in Table 3.

1.5. The maximum allowable values \u200b\u200bof the tap and current voltages during emergency mode of household electrical installations to 1000 V and a frequency of 50 Hz should not exceed the values \u200b\u200bindicated in Table 4.

Table 3.

Table 4.

Note. The values \u200b\u200bof the tensions and currents are installed for people with a body weight from 15 kg.

1.3-1.5. (Modified edition, meas. N 1).

1.6. Protection of a person from the effects of tensions and currents ensures the design of electrical installations, technical methods and protective equipment, organizational and technical activities according to GOST 12.1.019-79.

2. Control of tension and current voltages

2.1. To control the maximum permissible values \u200b\u200bof touches and currents, voltages and currents are measured in places where the electrical circuit can occur through the human body. The accuracy class of measuring instruments is not lower than 2.5.

2.2. When measuring the currents and stresses of touch, the resistance of the human body in the electrical circuit at a frequency of 50 Hz should be modeled by resistance resistor:

for table 1 - 6.7 com;

for table 2 at exposure time

up to 0.5 s - 0.85 com;

more than 0.5 C - resistance having a dependence on the voltage according to the drawing;

for table 3 - 1 com;

for table.4 for exposure time

up to 1 s - 1 com;

more than 1 s - 6 com.

The deviation from the indicated values \u200b\u200bis permitted within ± 10%.

2.1, 2.2. (Modified edition, meas. N 1).

2.3. When measuring the voltages of touch and currents, the resistance to spreading current with the legs of a person should be simulated using a square metal plate with a size of 25x25 cm, which is located on the surface of the Earth (floor) in places of possible person. The load on the metal plate should be created by a mass of at least 50 kg.

2.4. When measuring touches and currents in electrical installations, modes and conditions that create the greatest values \u200b\u200bof the tension and currents that affect the human body should be installed.

Appendix (Reference). Terms and their explanations

ATTACHMENT
Reference

(Modified edition, meas. N 1).

The text of the document is drilled by:
official edition
System of labor safety standards: Sat. Gostov. -
M.: IPK Publishing standards, 2001

GOST 12.1.038-82 *

Group T58.

Interstate standard

Labor safety standards

ELECTRICAL SAFETY

Maximum allowable values \u200b\u200bof tension and currents

Occupational Safety Standards System. Electric Safety.
Maximum Permissible Valuies of Pickp Voltages and Currents

Date of introduction 1983-07-01

Information details

Enforced by Resolution of the USSR State Committee on Standards from 30.07.82 N 2987

Restriction of the validity of the Discontinued Protocol N 2-92 of the Interstate Council on Standardization, Metrology and Certification (IUS 2-93)

* Reprint (June 2001) with a change in N 1, approved in December 1987 (IUS 4-88)

This standard establishes the maximum permissible values \u200b\u200bof the touches and currents flowing through the human body, intended for the design of methods and means of protecting people, when they interact with electrical installations of the production and domestic purpose of direct and alternating current with a frequency of 50 and 400 Hz.

The terms used in the standard and their explanations are shown in the application.

1. Maximum allowable voltage values
Topping and current

1.1. The maximum allowable values \u200b\u200bof the touch and current voltages are installed for the routes of current from one hand to the other and by hand to the legs.

(Modified edition, meas. N 1).

1.2. Touch voltages and currents flowing through the human body at normal (non-accidental) electrical installation mode should not exceed the values \u200b\u200bindicated in Table 1.

Table 1

Notes:

1. Touch voltages and currents are shown in the duration of exposure not more than 10 minutes per day and are established on the basis of the sensation reaction.

2. Touch voltages and currents for persons performing operation in high temperatures (above 25 ° C) and humidity (relative humidity of more than 75%) should be reduced three times.

1.3. The maximum allowable values \u200b\u200bof the tap and current voltages during emergency mode of industrial electrical installations to 1000 V with a deaf-free or isolated neutral and above 1000 V with an isolated neutral should not exceed the values \u200b\u200bindicated in Table 2.

table 2

Note. The maximum permissible values \u200b\u200bof the tensions and currents flowing through the human body with the duration of exposure more than 1 s, shown in Table 2, correspond to the release (variable) and non-library (constant) currents.

1.4. The maximum permissible values \u200b\u200bof the touch voltage during emergency mode of production electrical installations with a current frequency of 50 Hz, voltage above 1000 V, with a deaf grounding neutral should not exceed the values \u200b\u200bindicated in Table 3.

1.5. The maximum allowable values \u200b\u200bof the tap and current voltages during emergency mode of household electrical installations to 1000 V and a frequency of 50 Hz should not exceed the values \u200b\u200bindicated in Table 4.

Table 3.

Table 4.

Note. The values \u200b\u200bof the tensions and currents are installed for people with a body weight from 15 kg.

1.3-1.5. (Modified edition, meas. N 1).

1.6. Protection of a person from the effects of tensions and currents ensures the design of electrical installations, technical methods and protective equipment, organizational and technical activities according to GOST 12.1.019-79.

2. Control of tension and current voltages

2.1. To control the maximum permissible values \u200b\u200bof touches and currents, voltages and currents are measured in places where the electrical circuit can occur through the human body. The accuracy class of measuring instruments is not lower than 2.5.

2.2. When measuring the currents and stresses of touch, the resistance of the human body in the electrical circuit at a frequency of 50 Hz should be modeled by resistance resistor:

for table 1 - 6.7 com;

for table 2 at exposure time

up to 0.5 s - 0.85 com;

more than 0.5 C - resistance having a dependence on the voltage according to the drawing;

for table 3 - 1 com;

for table.4 for exposure time

up to 1 s - 1 com;

more than 1 s - 6 com.

The deviation from the indicated values \u200b\u200bis permitted within ± 10%.

2.1, 2.2. (Modified edition, meas. N 1).

2.3. When measuring the voltages of touch and currents, the resistance to spreading current with the legs of a person should be simulated using a square metal plate with a size of 25x25 cm, which is located on the surface of the Earth (floor) in places of possible person. The load on the metal plate should be created by a mass of at least 50 kg.

2.4. When measuring touches and currents in electrical installations, modes and conditions that create the greatest values \u200b\u200bof the tension and currents that affect the human body should be installed.

Appendix (Reference). Terms and their explanations

ATTACHMENT
Reference

(Modified edition, meas. N 1).

The text of the document is drilled by:
Official edition
System of labor safety standards: Sat. Gostov. -
M.: IPK Publishing standards, 2001

Permissible long-term currents for wires with rubber or polyvinyl chloride insulation, cords with rubber insulation and cables with rubber or plastic insulation in lead, polyvinyl chloride and rubber shells are shown in Table. 1.3.4-1.3.11. They are accepted for temperatures: lived +65, ambient air +25 and land + 15 ° C.

When determining the number of wires paved in one pipe (or lived a multicore conductor), the zero working conductor of the four-wire three-phase current system, as well as ground and zero protective conductors are not accepted into the calculation.

Permissible long-term currents for wires and cables laid in boxes, as well as in the trays with beams, must be accepted: for wires - by table. 1.3.4 and 1.3.5 as for wires laid in the pipes, for cables - in Table. 1.3.6-1.3.8 as for cables laid in the air. With the number of simultaneously loaded wires more than four, laid in pipes, boxes, as well as in trays, beams, currents for wires should be taken in Table. 1.3.4 and 1.3.5 as for wires laid open (in the air), with the introduction of decreasing coefficients 0.68 for 5 and 6; 0.63 for 7-9 and 0.6 for 10-12 conductors.

For wires of secondary circuits, reduction coefficients are not entered.

Table 1.3.4. Permissible long-term current for wires and cords with rubber and polyvinyl chloride insulation with copper conductors

Table 1.3.5. Permissible long-term current for wires with rubber and polyvinyl chloride insulation with aluminum residential

Table 1.3.6. Permissible long-term current for wires with copper veins with rubber insulation in metal protective shells and cables with copper veins with rubber insulation in lead, polyvinyl chloride, nimite or rubber sheath, armored and unarmented

Table 1.3.7. Permissible long-term current for cables with aluminum veins with rubber or plastic insulation in lead, polyvinyl chloride and rubber shells, armored and unarmented

Note. Permissible long-term currents for four-core cables with plastic insulation to voltage up to 1 kV can be selected in Table. 1.3.7, as for three-core cables, but with a coefficient of 0.92.

Table 1.3.8. Permissible long-term current for portable hose lungs and medium cords, portable hose heavy cables, mining flexible hose, floodlight cables and portable wires with copper conductors

________________

* Currents relate to cords, wires and cables with zero residential and without it.

Table 1.3.9. Permissible long-term current for portable hose-hose with copper veins with rubber insulation of cables for peat enterprises

__________________

Table 1.3.10. Permissible long-term current for hose with copper veins with rubber insulation cables for mobile electrical receivers

__________________

* Currents relate to cables with zero living and without it.

Table 1.3.11. Permissible long-term current for wires with copper veins with rubber insulation for electrified transport 1.3 and 4 kV

Table 1.3.12. Reduced coefficient for wires and cables laid in boxes

1.3.11

Permissible long-term currents for wires laid in trays, with a single-row laying (not in beams), be taken as for wires laid in the air.

Permissible long-term currents for wires and cables laid in boxes should be taken in Table. 1.3.4-1.3.7 As for single wires and cables, laid open (in the air), using reduction coefficients specified in Table. 1.3.12.

When choosing reduction coefficients, control and backup wires and cables are not taken into account.

Our modern life is full of diversity of household appliances and devices that greatly facilitate our life, make it more comfortable, but at the same time a whole complex of dangerous, harmful factors appear: electromagnetic fields of various frequencies, an increased level of radiation, noise, vibration, hazard of mechanical injury, presence Toxic substances, as well as the most important thing - electric current.

Electric current is called an ordered movement of electrical particles. For your security, it is necessary to know the effect of electric current to the human body, protection against damage to the current, assistance to the victim from the effects of electric shock.

Impact on the human body of electric current

The electric current has biological, thermal, electrolytic action.

Thermal: Heating tissues when electric current flows.

Electrolytic: Blood decomposition and other body fluids.

Biological: The excitation of living tissues of the body is accompanied by convulsions, muscle spasms, cardiac activity, respiratory stop.

When electric current acts on a person, bodily electricians arise: burns, electrical signs, leather metallization, mechanical damage, blinding electric arc light, or an electric blow can occur - this is a general defeat of the body that can be accompanied by convulsions, loss of consciousness, stopping the breath and heart , and even clinical death.

Electrical signs - It is the stains of gray and pale yellow, bruises, scratches on the skin of a person who were exposed to current. The sign of the sign corresponds to the strength of the current-carrying part, which the man touched. In most cases, the treatment of electrical signs ends safely, and the affected place is completely restored.

Mechanical damage There are under the action of an electric current when the muscles decrease involuntarily. Mechanical damage (bone fractures, blood vessels, leather breaks) are damage that require long treatment.

Electric shock. From time to time there are cases when children from curiosity shove their fingers into an electrical outlet or begin to pick it with nail, wire or other metal objects. Most often it happens to children under three years. There are cases when children get a blow to electric shock from fallen on earth and under wires. When exposed to electric current on the body, an involuntary convulsive contraction of the muscles may occur, which prevents the child to break away from the current source. In the place of contact with the current there is a wheelbarrief. In severe case, respiratory disorder appears and cardiac activity. The first thing to be done is to free the child from the effect of electric current. The safest is to quickly turn the plugs if the accident occurred in the house. If for any reason it is impossible to do this, then you need to throw a rubber mat, a board or thick fabric to your feet or put on rubber boots or galoshes on the feet; You can put on the hands of household rubber gloves. The victim drag off the wire, clutching with one hand for clothes. You can also try to move away the most victim from the source of the current or remove the source from it. It is necessary to do this with one hand so that even when you receive a shock, the current has not passed through the whole body of the one who assisted. The victim must be put, heat heat, free from the shocking clothes, if possible, give warm drinks. On the decented electric part of the body, you should impose a sterile bandage from a bandage or clean fabric, in a mixture of alcohol or vodka. If the child has lost consciousness, he is given to sniff out the ammonia alcohol and splash in the face of cold water. If the child lies unconscious and there is no breathing, but there is a pulse, it is necessary to immediately make it an artificial respiration by the "mouth in the mouth". For this, the baby's head will throw back and pushing the nostrils to him, blow in the mouth of the air portions, putting his lips to the lips of the child.

Electric burn different degrees - the result of short circuits in electrical installations and the finding of the body (hands) in the medium of the light and thermal effect of the electric arc; Burns of III and IV degree with severe outcome - when contacting a person with parts, which passes a current voltage over 1000 V.

Metalization of the skin These are the smallest metal particles penetrate the upper layers of the skin that melted under the action of an electric arc or dissolved in electrolytes electrolytes. In the affected place, the skin becomes a tight, rough and acquires that color which has a metal (for example, green - from copper with copper). The work associated with the probability of occurrence of an electric arc should be done in glasses, and the worker's clothes should be fastened to all buttons.

Electrophthalmia is an ultraviolet ray (the source of which is the Voltov arc, it is striking eyes). As a result of Electrophthalmia, an inflammatory process comes, and if the necessary treatment measures are taken, the pain passes.

Depending on the value of the current, its voltage, frequency, duration of exposure, the current path and the overall condition of the person depends on the outcome of the electrical current to the human body. It has been established that current by force of more than 0.05 A can be fatally injured for a person for 0.1 s. The largest number of lesions from the electric current (about 85%) falls on the settings of up to 1000 V. For the human body, variable and permanent current are dangerous. The most dangerous alternating current having a frequency of 20-100 Hz; And the frequency of 400 Hz is not so dangerous. Virtually safe for a person in raw materials can be considered voltage up to 12 V, in dry rooms - up to 36 V. The likelihood of human damage to electric current depends on the climatic conditions in the room (temperature, humidity), as well as conductive dust, metal structures connected to the ground , conductive floor, etc.

In accordance with the "rules of the device of electrical installations of consumers" (PUE), all rooms are divided into three classes:

without increased danger - non-suck (up to + 35 ° C), dry (up to 60%), non-chosen, with non-conductive floor, not cluttered with equipment;

with increased danger - at least one factor of increased danger, i.e. hot or wet (up to 75%), dusty, with conductive flooring, etc.;

particularly dangerous - have two or more factors of increased danger or at least one factor is special danger, i.e. Special damp (up to 100%) or the presence of a chemically active medium.

Possible values \u200b\u200bof currents and voltages of contact, depending on the timing of the protection, are indicated in GOST 12.1.038-88. Under this document, for a normal (non-accidental) mode of operation of industrial equipment, permissible touch voltages should not be greater than 2 V at a current frequency of 50 Hz, 3 V at 400 Hz and 8 V for DC, but the total duration of exposure should not exceed 10 minutes per day. In the normal mode of operation of household equipment, the presence of tensions is not allowed. In particularly dangerous (or with an increased danger), the premises are subject to grounding all equipment at a voltage of over 42V variable and DC. In normal rooms, all equipment at a voltage of 380 V and above alternating and 440 V and above DC. All equipment, regardless of the supply voltage, is grounded only in explosive rooms.

With an increase in the duration of the effect of electric current on a person, the threat of lesion increases. After 30 seconds. The resistance of the human body flow flows by about 25%, after 90 sec. by 70%. The resistance of the human body electric current fluctuates in a wide range. Dry, coarse corn leather, no fatigue and normal state of the nervous system increases the resistance of the human body. Nervous fibers and muscles have the smallest resistance. For the minimum estimated resistance of the human body, a value from 500 to 1000 ohms is taken.

At that moment, when a person closes his body with two phase wires of the current installation, it falls under the full linear network voltage. When taking into account that the calculated resistance of the human body is taken by 1000 ohms, then with a two-phase touch to the active parts of the installation, the voltage in which 100 V may be fatal, due to the fact that the current passing through the human body reaches the value of 0.1 A .

If a current of 0.06 A and more, electric shock occurs through the human body. Man's resistance by electrical current variable value. It depends on many factors, including from the psychological state and physical condition of man. Within 20-100 kΩ there is an average resistance value. It may decrease to 1 com at particularly unfavorable conditions. In this case, it will be dangerous for the life of a person's voltage 100 V and below.

The value of the current passing through the human body depends on its resistance. And the resistance depends mainly on the state of the human skin. The resistance of the human body depends on the frequency of the current. For the calculated amount of electrical resistance of the body, resistance is made equal to 1.0 com. At current frequencies of 6-15 kHz, it is the smallest.

Permanent current is less dangerous than variable. Permanent current up to 6 mA almost do not feel. With a current of 20 mA, convulsions appear in the muscles of the forearm. Alternating current begins to be felt at 0.8 mA. The current of 15 mA causes contraction of the muscles of the hands. Especially dangerous is the passage of current through the heart.

The danger of damage to constant and alternating current changes with an increase in voltage. At voltage up to 220, an alternating current is more dangerous, and at a voltage above 500 to a dangerous constant current. The more current flows, the less the resistance of the human body becomes. May come death if the effect of the electric current is not interrupted. If the current passes from the hands to the legs, then what kind of shoes on a person on a person, from which material it is, what quality it is. The degree of damage is also a significant impact of resistance in the place of contact of the person with the Earth. Electric current has difficult consequences, up to the stop of the heart and stopping breathing. Therefore, you need to be able to provide the first aid to the affected electric shock.

Static electricity - This is a potential supply of electrical energy generated on equipment as a result of friction, induction influence of strong electrical discharges. In the premises with a large amount of dust of organic origin, static discharges can be formed, and also accumulate in humans when using linen and clothing made of shoe, wool and artificial fibers, when moving on a toxconducting synthetic flooring, such as linoleum, cavuroline, etc.

The rationing of the electrostatic field is carried out in accordance with GOST 12.1.045-84 the electric field strength at workplaces should not exceed 60 kV / m for an hour. The time of staying in the electric field at 20 ≤ ≤ 60 (kV) is calculated by the formula T \u003d (60 / E) 2, where E is the actual value of the field strength. The resistance of grounding devices for protection against static electricity should not exceed 100 (OM).