To properly design methods and means of protecting people from electric shock, it is necessary to know the permissible levels of touch voltages and the values of currents flowing through the human body.
Touch voltage is the voltage between two points in a current circuit that are simultaneously touched by a person. The maximum permissible values of touch voltages U PD and currents I PD flowing through the human body along the “arm-arm” or “arm-legs” path under normal (non-emergency) electrical installation mode, according to GOST 12.1.038-82* are given in table. 1.
In emergency mode of industrial and household appliances and electrical installations with voltage up to 1000 V with any neutral mode, the maximum permissible values of U PD and I PD should not exceed the values given in table. 2. Emergency mode means that the electrical installation is faulty and dangerous situations may occur, leading to electrical injuries.
When the duration of exposure is more than 1 s, the values of U PD and I PD correspond to releasing values for alternating current and conditionally non-painful values for direct current.
Table 1
Maximum permissible values of touch voltages and currents
in normal operation of the electrical installation
Note. Touch voltages and currents for persons working in conditions of high temperatures (above 25 °C) and humidity (relative humidity more than 75%) must be reduced by 3 times.
table 2
Maximum permissible values of touch voltage
and currents in emergency operation of an electrical installation
|
Duration of electric current, s |
Production electrical installations |
Appliances, electrical installations |
||
4. Electrical resistance of the human body
The value of current through the human body greatly influences the severity of electrical injuries. In turn, the current itself, according to Ohm’s law, is determined by the resistance of the human body and the voltage applied to it, i.e. tension of touch.
The conductivity of living tissues is determined not only by physical properties, but also by the most complex biochemical and biophysical processes inherent only to living matter. Therefore, the resistance of the human body is a complex variable that has a nonlinear dependence on many factors, including the condition of the skin, the environment, the central nervous system, and physiological factors. In practice, the resistance of the human body is understood as the modulus of its complex resistance.
The electrical resistance of various tissues and fluids of the human body is not the same: skin, bones, adipose tissue, tendons have a relatively high resistance, and muscle tissue, blood, lymph, nerve fibers, spinal cord and brain have low resistance.
The resistance of the human body, i.e. The resistance between two electrodes placed on the surface of the body is mainly determined by the resistance of the skin. The skin consists of two main layers: the outer (epidermis) and the inner (dermis).
The epidermis can be conventionally represented as consisting of a stratum corneum and a germinal layer. The stratum corneum is composed of dead keratinized cells, lacks blood vessels and nerves, and is therefore a layer of nonliving tissue. The thickness of this layer ranges from 0.05 – 0.2 mm. In a dry and uncontaminated state, the stratum corneum can be considered as a porous dielectric, penetrated by many ducts of the sebaceous and sweat glands and having a high resistivity. The germinal layer is adjacent to the stratum corneum and consists mainly of living cells. The electrical resistance of this layer, due to the presence of dying and keratinizing cells in it, can be several times higher than the resistance of the inner layer of the skin (dermis) and internal tissues of the body, although compared to the resistance of the stratum corneum it is small.
The dermis consists of connective tissue fibers that form a thick, strong, elastic mesh. This layer contains blood and lymphatic vessels, nerve endings, hair roots, as well as sweat and sebaceous glands, the excretory ducts of which extend to the surface of the skin, penetrating the epidermis. The electrical resistance of the dermis, which is living tissue, is low.
The total resistance of the human body is the sum of the resistances of the tissues located in the path of current flow. The main physiological factor that determines the value of the total resistance of the human body is the condition of the skin in the current circuit. With dry, clean and intact skin, the resistance of the human body, measured at a voltage of 15 - 20 V, ranges from units to tens of kOhms. If the stratum corneum is scraped off in the area of the skin where the electrodes are applied, the body resistance will drop to 1 - 5 kOhm, and when the entire epidermis is removed - to 500 - 700 Ohm. If the skin under the electrodes is completely removed, the resistance of the internal tissues will be measured, which is 300 - 500 Ohms.
For an approximate analysis of the processes of current flow along the “hand-to-hand” path through two identical electrodes, a simplified version of the equivalent circuit diagram of the flow of electric current through the human body can be used (Fig. 1).
Rice. 1. Human body resistance equivalent circuit
In Fig. 1 is indicated: 1 – electrodes; 2 – epidermis; 3 – internal tissues and organs of the human body, including the dermis; İ h – current flowing through the human body; Ů h – voltage applied to the electrodes; R Н – active resistance of the epidermis; C H is the capacity of a conventional capacitor, the plates of which are the electrode and the well-conducting tissues of the human body located under the epidermis, and the dielectric is the epidermis itself; R VN – active resistance of internal tissues, including the dermis.
From the diagram in Fig. 1 it follows that the complex resistance of the human body is determined by the relation
where Z Н = (jС Н) -1 = -jХ Н – complex resistance of capacitance С Н;
Х Н – module Z Н; f , f – frequency of alternating current.
In what follows, by the resistance of the human body we mean the module of its complex resistance:
.
(1)
At high frequencies (more than 50 kHz) Х Н =1/(C Н)<< 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 direct current in steady state, capacitances are infinitely large (at 
0 X N 
). Therefore, the resistance of the human body to direct current
R h = 2R H + R VN. (3)
From expressions (2) and (3) we can determine
R Н = (R h -z h в)/2. (4)
Based on expressions (1) – (4), you can obtain a formula for calculating the value of capacitance Cn:
,
(5)
where z hf is the modulus of complex resistance of the body at frequency f;
C H has the dimension μF; z hf , R h and R HV – kOhm; f - kHz.
Expressions (2) – (5) allow us to determine the parameters of the equivalent circuit (Fig. 1) based on the results of experimental measurements.
The electrical resistance of the human body depends on a number of factors. Damage to the stratum corneum of the skin can reduce the resistance of the human body to the value of its internal resistance. Moisturizing the skin can reduce its resistance by 30 – 50%. Moisture that gets on the skin dissolves minerals and fatty acids located on its surface, removed from the body along with sweat and fatty secretions, becomes more electrically conductive, improves contact between the skin and the electrodes, and penetrates the excretory ducts of the sweat and fat glands. When the skin is moisturized for a long time, its outer layer loosens, becomes saturated with moisture and its resistance can decrease even more.
When a person is briefly exposed to thermal radiation or elevated ambient temperature, the resistance of the human body decreases due to the reflex expansion of blood vessels. With longer exposure, sweating occurs, as a result of which the skin's resistance decreases.
With an increase in the area of the electrodes, the resistance of the outer layer of skin R H decreases, the capacitance C H increases, and the resistance of the human body decreases. At frequencies above 20 kHz, the indicated influence of the electrode area is practically lost.
The resistance of the human body also depends on the location of application of the electrodes, which is explained by the different thickness of the stratum corneum of the skin, the uneven distribution of sweat glands on the surface of the body, and the unequal degree of blood filling of the skin vessels.
The passage of current through the human body is accompanied by local heating of the skin and an irritating effect, which causes a reflex dilatation of skin vessels and, accordingly, increased blood supply and increased sweating, which, in turn, leads to a decrease in skin resistance in a given place. At low voltages (20 -30 V) in 1 - 2 minutes, the resistance of the skin under the electrodes can decrease by 10 - 40% (on average by 25%).
An increase in voltage applied to the human body causes a decrease in its resistance. At voltages of tens of volts, this occurs due to reflex reactions of the body in response to the irritating effect of the current (increased supply of blood vessels to the skin, sweating). When the voltage increases to 100 V and above, local and then continuous electrical breakdowns of the stratum corneum under the electrodes occur. For this reason, at voltages of about 200 V and higher, the resistance of the human body is almost equal to the resistance of the internal tissues R VN.
When making an approximate assessment of the risk of electric shock, the resistance of the human body is taken to be 1 kOhm (R h = 1 kOhm). The exact value of design resistances when developing, calculating and testing protective measures in electrical installations is selected in accordance with GOST 12.038-82*.
INTERSTATE STANDARD
Occupational Safety Standards System
ELECTRICAL SAFETY
Maximum permissible values of touch voltages and currents
Date of introduction 1983-07-01
APPROVED AND ENTERED INTO EFFECT by Resolution of the USSR State Committee on Standards dated June 30, 1982 No. 2987.
The validity period was lifted according to Protocol No. 2-92 of the Interstate Council for Standardization, Metrology and Certification (IUS 2-93)
REISSUE (June 2001) with Change No. 1 approved in December 1987 (IUS 4-88)
This standard establishes the maximum permissible values of touch voltages and currents flowing through the human body, intended for the design of methods and means of protecting people when they interact with industrial and household electrical installations of direct and alternating current with a frequency of 50 and 400 Hz.
The terms used in the standard and their explanations are given in the appendix.
- MAXIMUM ALLOWABLE VOLTAGE VALUES
TOUCH AND CURRENTS
1.1. Limits for touch voltages and currents are established for current paths from one hand to the other and from hand to feet.
(Changed edition, Amendment No. 1).
1.2. Touch voltages and currents flowing through the human body during normal (non-emergency) operation of an electrical installation should not exceed the values indicated in Table 1.
Table 1
Notes :
1 Touch voltages and currents are given for a duration of exposure of no more than 10 minutes per day and are set based on the reaction of the sensation.
2 Touch voltages and currents for persons working in conditions of high temperatures (above 25 ° C) and humidity (relative humidity more than 75%) must be reduced by three times.
1.3. The maximum permissible values of touch voltages and currents during emergency operation of industrial electrical installations with voltages up to 1000 V with a solidly grounded or insulated neutral and above 1000 V with an isolated neutral should not exceed the values specified in Table 2.
table 2
| Type of current | Normalized | Maximum permissible values, no more, for the duration of exposure to current t, With | |||||||||||
| magnitude | 0,01-0,08 | 0,1 | 0,2 | 0,3 | 0,4 | 0,5 | 0,6 | 0,7 | 0,8 | 0,9 | 1,0 | St.1.0 | |
| Variable 50 Hz | U,B | 550 | 340 | 160 | 135 | 120 | 105 | 95 | 85 | 75 | 70 | 60 | 20 |
| I, mA | 650 | 400 | 190 | 160 | 140 | 125 | 105 | 90 | 75 | 65 | 50 | 6 | |
| Variable 400 Hz | U,B | 650 | 500 | 500 | 330 | 250 | 200 | 170 | 140 | 130 | 110 | 100 | 36 |
| I, mA | 8 | ||||||||||||
| Constant | U,B | 650 | 500 | 400 | 350 | 300 | 250 | 240 | 230 | 220 | 210 | 200 | 40 |
| I, mA | 15 | ||||||||||||
| Rectified full wave | ,B | 650 | 500 | 400 | 300 | 270 | 230 | 220 | 210 | 200 | 190 | 180 | – |
| , mA | |||||||||||||
| Rectified half wave | ,B | 650 | 500 | 400 | 300 | 250 | 200 | 190 | 180 | 170 | 160 | 150 | – |
| , mA | |||||||||||||
Note . The maximum permissible values of touch voltages and currents flowing through the human body for a duration of exposure of more than 1 s, given in Table 2, correspond to releasing (alternating) and non-painful (direct) currents.
1.4. The maximum permissible values of touch voltages during emergency operation of industrial electrical installations with a current frequency of 50 Hz, voltage above 1000 V, with solid grounding of the neutral should not exceed the values specified in Table 3.
Table 3
1.5. The maximum permissible values of touch voltages and currents during emergency operation of household electrical installations with voltages up to 1000 V and a frequency of 50 Hz should not exceed the values specified in Table 4.
Table 4
| Duration | Standardized value | Duration | Standardized value | ||
| impact t, With | U,B | I, mA | impact t, With | U,B | I, mA |
| From 0.01 to 0.08 | 220 | 220 | 0,6 | 40 | 40 |
| 0,1 | 200 | 200 | 0,7 | 35 | 35 |
| 0,2 | 100 | 100 | 0,8 | 30 | 30 |
| 0,3 | 70 | 70 | 0,9 | 27 | 27 |
| 0,4 | 55 | 55 | 1,0 | 25 | 25 |
| 0,5 | 50 | 50 | St. 1.0 | 12 | 2 |
Note. The values of touch voltages and currents are established for people with a body weight of 15 kg.
1.3.-1.5. (Changed edition, Amendment No. 1).
1.6. Human protection from the effects of touch voltages and currents is ensured by the design of electrical installations, technical methods and means of protection, organizational and technical measures in accordance with GOST 12.1.019-79.
- CONTROL OF TOUCH VOLTAGES AND CURRENTS
2.1. To control the maximum permissible values of touch voltages and currents, voltages and currents are measured in places where an electrical circuit may close through the human body. The accuracy class of measuring instruments is not lower than 2.5.
2.2. When measuring touch currents and voltages, the resistance of the human body in an electrical circuit at a frequency of 50 Hz should be modeled by a resistance resistor:
for table 1 – 6.7 kOhm;
for table 2 at exposure time
up to 0.5 s -0.85 kOhm;
more than 0.5 s – resistance depending on voltage according to the drawing;
for table 3 – 1 kOhm;
for table 4 at exposure time
up to 1 s -1 kOhm;
more than 1 s – 6 kOhm.
Deviation from the specified values is allowed within ±10%.
(Changed edition, Amendment No. 1).
2.3. When measuring touch voltages and currents, the resistance to the spread of current from a person’s legs should be modeled using a square metal plate measuring 25 x 25 cm, which is located on the surface of the earth (floor) in places where the person may be located. The load on the metal plate must be created by a mass of at least 50 kg.
2.4. When measuring touch voltages and currents in electrical installations, modes and conditions must be established that create the highest values of touch voltages and currents affecting the human body.
APPLICATION
(informative)
TERMS AND THEIR EXPLANATIONS
| Term | Explanation |
| Touch voltage | According to GOST 12.1.009-76 |
| Electrical installation emergency mode | Operation of a faulty electrical installation, in which dangerous situations may arise leading to electrical injury to people interacting with the electrical installation |
| Household electrical installations | Electrical installations used in residential, municipal and public buildings of all types, for example, in cinemas, cinemas, clubs, schools, kindergartens, shops, hospitals, etc., with which both adults and children can interact |
| Release current | Electric current that does not cause irresistible convulsive contractions of the muscles of the hand in which the conductor is clamped when passing through the human body |
(Changed edition, Amendment No. 1).
1. Maximum permissible values of touch voltages and currents
1.1. Limits for touch voltages and currents are established for current paths from one hand to the other and from hand to feet.
(Changed edition, Amendment No. 1).
1.2. Touch voltages and currents flowing through the human body during normal (non-emergency) operation of an electrical installation should not exceed the values indicated in table. 1 .
Table 1
Notes:
1. Touch voltages and currents are given for a duration of exposure of no more than 10 minutes per day and are set based on the reaction of the sensation.
2. Touch voltages and currents for persons working in conditions of high temperatures (above 25°C) and humidity (relative humidity more than 75%) must be reduced by three times.
1.3. The maximum permissible values of touch voltages and currents during emergency operation of industrial electrical installations with voltages up to 1000 V with a solidly grounded or insulated neutral and above 1000 V with an isolated neutral should not exceed the values specified in table. 2.
table 2
| Type of current | Normalize May magnitude |
Maximum permissible values, no more, for the duration of exposure to current t, s |
|||||||||||
| 0,01- 0,08 |
0,1 | 0,2 | 0,3 | 0,4 | 0,5 | 0,6 | 0,7 | 0,8 | 0,9 | 1,0 | St. 1,0 |
||
| Variable 50 Hz | U, V I, mA |
550 650 |
340 400 |
160 190 |
135 160 |
120 140 |
105 125 |
95 105 |
85 90 |
75 75 |
70 65 |
60 50 |
20 6 |
| Variable 400 Hz |
U, V I, mA |
650 | 500 | 500 | 330 | 250 | 200 | 170 | 140 | 130 | 110 | 100 | 36 8 |
| Constant | U, V I, mA |
650 | 500 | 400 | 350 | 300 | 250 | 240 | 230 | 220 | 210 | 200 | 40 15 |
| Rectified full-wave |
U_ampl, V I_ampl, mA |
650 | 500 | 400 | 300 | 270 | 230 | 220 | 210 | 200 | 190 | 180 | - |
| Rectified half-wave |
U_ampl, V I_ampl, mA |
650 | 500 | 400 | 300 | 250 | 200 | 190 | 180 | 170 | 160 | 150 | - |
Note. The maximum permissible values of touch voltages and currents flowing through the human body with a duration of exposure of more than 1 s, given in table. 2 correspond to releasing (alternating) and non-painful (direct) currents.
1.4. The maximum permissible values of touch voltages during emergency operation of industrial electrical installations with a current frequency of 50 Hz, voltage above 1000 V, with solid grounding of the neutral should not exceed the values specified in table. 3.
Table 3
1.5. The maximum permissible values of touch voltages and currents during emergency operation of household electrical installations with voltages up to 1000 V and a frequency of 50 Hz should not exceed the values specified in table. 4 .
Table 4
Note. The values of touch voltages and currents are established for people with a body weight of 15 kg.
1.3-1.5. (Changed edition, Amendment No. 1).
1.6. Protection of a person from the effects of touch voltages and currents is ensured by the design of electrical installations, technical methods and means of protection, organizational and technical measures for
Occupational safety standards system. Electric safety.
Maximum permissible values of pick-up voltages and currents
OKSTU 0012
Date of introduction 1983-07-01
The validity period was lifted according to Protocol No. 2-92 of the Interstate Council for Standardization, Metrology and Certification (IUS 2-93)
REISSUE (June 2001) with Change No. 1 approved in December 1987 (IUS 4-88)
sets the maximum permissible values of currents flowing through the human body, intended for the design of methods and means of protecting people when they interact with electrical installations for industrial and household purposes of direct and alternating current with a frequency of 50 and 400 Hz.
The terms used in the standard and their explanations are given in the appendix.
1. MAXIMUM ALLOWABLE VALUES OF TOUCH VOLTAGES AND CURRENTS
1.1. Limits for touch voltages and currents are established for current paths from one hand to the other and from hand to feet.(Changed edition, Amendment No. 1).
1.2. Touch voltages and currents flowing through the human body during normal (non-emergency) operation of an electrical installation should not exceed the values indicated in Table 1.
Table 1
Notes:1.3. The maximum permissible values of touch voltages and currents during emergency operation of industrial electrical installations with voltages up to 1000 V with a solidly grounded or insulated neutral and above 1000 V with an isolated neutral should not exceed the values specified in Table 2.
1 Touch voltages and currents are given for a duration of exposure of no more than 10 minutes per day and are set based on the reaction of the sensation.
2 Touch voltages and currents for persons working in conditions of high temperatures (above 25 ° C) and humidity (relative humidity more than 75%) must be reduced by three times.
table 2
| Type of current | Standardized value | Maximum permissible values, no more, for duration of current exposure t, s |
|||||||||||
| 0,01-0,08
| 0,1
| 0,2
| 0,3
| 0,4
| 0,5
| 0,6
| 0,7
| 0,8
| 0,9
| 1,0
| St.1.0 |
||
| Variable 50 Hz | U, B | 550 | 340 | 160 | 135 | 120 | 105 | 95 | 85 | 75 | 70 | 60 | 20 |
| I, mA | 650 | 400 | 190 | 160 | 140 | 125 | 105 | 90 | 75 | 65 | 50 | 6 | |
| Variable 400 Hz | U, B | 650 | 500 | 500 | 330 | 250 | 200 | 170 | 140 | 130 | 110 | 100 | 36 |
| I, mA | 8 | ||||||||||||
| Constant | U, B | 650 | 500 | 400 | 350 | 300 | 250 | 240 | 230 | 220 | 210 | 200 | 40 |
| I, mA | 15 | ||||||||||||
| Rectified full wave | U, B | 650 | 500 | 400 | 300 | 270 | 230 | 220 | 210 | 200 | 190 | 180 | - |
| I, mA | |||||||||||||
| Rectified half wave | U, B | 650 | 500 | 400 | 300 | 250 | 200 | 190 | 180 | 170 | 160 | 150 | - |
| I, mA | |||||||||||||
Note. The maximum permissible values of touch voltages and currents flowing through the human body for a duration of exposure of more than 1 s, given in Table 2, correspond to releasing (alternating) and non-painful (direct) currents.1.4. The maximum permissible values of touch voltages during emergency operation of industrial electrical installations with a current frequency of 50 Hz, voltage above 1000 V, with a dead neutral should not exceed the values specified in Table 3.
Table 3
| | Maximum permissible value of touch voltage U, in |
| Up to 0.1 | 500 |
| 0,2 | 400 |
| 0,5 | 200 |
| 0,7 | 130 |
| 1,0 | 100 |
| St. 1.0 to 5.0 | 65 |
1.5. The maximum permissible values of touch voltages and currents during emergency operation of household electrical installations with voltages up to 1000 V and a frequency of 50 Hz should not exceed the values specified in Table 4.
Table 4
| Duration of exposure t, s | Standardized value | Duration of exposure t, s | Standardized value |
||
|
| U, B | I, mA |
| U, B | I, mA |
| From 0.01 to 0.08 | 220 | 220 | 0,6 | 40 | 40 |
| 0,1 | 200 | 200 | 0,7 | 35 | 35 |
| 0,2 | 100 | 100 | 0,8 | 30 | 30 |
| 0,3 | 70 | 70 | 0,9 | 27 | 27 |
| 0,4 | 55 | 55 | 1,0 | 25 | 25 |
| 0,5 | 50 | 50 | St. 1.0 | 12 | 2 |
Note. The values of touch voltages and currents are established for people with a body weight of 15 kg.1.3.-1.5. (Changed edition, Amendment No. 1).
1.6. Protection of a person from the effects of touch voltages and currents is ensured by the design of electrical installations, technical methods and means of protection, organizational and technical measures for.
2. CONTROL OF TOUCH VOLTAGES AND CURRENTS
2.1. To control the maximum permissible values of touch voltages and currents, voltages and currents are measured in places where an electrical circuit may close through the human body. The accuracy class of measuring instruments is not lower than 2.5.2.2. When measuring touch currents and voltages, the resistance of the human body in an electrical circuit at a frequency of 50 Hz should be modeled by a resistance resistor:
for table 1 - 6.7 kOhm;Deviation from the specified values is allowed within ±10%.
for table 2 at exposure time
up to 0.5 s -0.85 kOhm;
more than 0.5 s - resistance depending on voltage according to the drawing;
for table 3 - 1 kOhm;
for table 4 at exposure time
up to 1 s -1 kOhm;
more than 1 s - 6 kOhm.
(Changed edition, Amendment No. 1).
2.3. When measuring touch voltages and currents, the resistance to the spread of current from a person’s legs should be modeled using a square metal plate measuring 25 x 25 cm, which is located on the surface of the earth (floor) in places where the person may be located. The load on the metal plate must be created by a mass of at least 50 kg.
2.4. When measuring touch voltages and currents in electrical installations, modes and conditions must be established that create the highest values of touch voltages and currents affecting the human body.
APPENDIX (reference)
TERMS AND THEIR EXPLANATIONS
| Term | Explanation |
| Touch voltage | By |
| Electrical installation emergency mode | Operation of a faulty electrical installation, in which dangerous situations may arise leading to electrical injury to people interacting with the electrical installation |
| Household electrical installations | Electrical installations used in residential, municipal and public buildings of all types, for example, in cinemas, cinemas, clubs, schools, kindergartens, shops, hospitals, etc., with which both adults and children can interact |
| Release current | Electric current that does not cause irresistible convulsive contractions of the muscles of the hand in which the conductor is clamped when passing through the human body |
(Changed edition, Amendment No. 1).
Material presented on the page IS NOT AN OFFICIAL PUBLICATION
MAXIMUM ALLOWABLE VOLTAGE VALUES
TOUCH AND CURRENTS
1.1. Limits for touch voltages and currents are established for current paths from one hand to the other and from hand to feet.
(Changed edition, Amendment No. 1).
1.2. Touch voltages and currents flowing through the human body during normal (non-emergency) operation of an electrical installation should not exceed the values indicated in Table 1.
Table 1
|
Type of current |
U, IN |
I, mA |
|
No more |
||
|
Variable, 50 Hz |
||
|
Variable, 400 Hz |
||
|
Constant |
||
Notes :
1 Touch voltages and currents are given for a duration of exposure of no more than 10 minutes per day and are set based on the reaction of the sensation.
2 Touch voltages and currents for persons working in conditions of high temperatures (above 25 ° C) and humidity (relative humidity more than 75%) must be reduced by three times.
1.3. The maximum permissible values of touch voltages and currents during emergency operation of industrial electrical installations with voltages up to 1000 V with a solidly grounded or insulated neutral and above 1000 V with an isolated neutral should not exceed the values specified in Table 2.
table 2
|
Type of current |
Normalized |
Maximum permissible values, no more, for the duration of exposure to currentt, With |
|||||||||||
|
Magnitude |
0,01-0,08 |
St.1.0 |
|||||||||||
|
Variable 50 Hz |
U, B |
||||||||||||
|
I, mA |
|||||||||||||
|
Variable 400 Hz |
U, B |
||||||||||||
|
I, mA |
|||||||||||||
|
Constant |
U, B |
||||||||||||
|
I, mA |
|||||||||||||
|
Rectified full wave |
, B |
||||||||||||
|
, mA |
|||||||||||||
|
Rectified half wave |
, B |
||||||||||||
|
, mA |
|||||||||||||
Note . The maximum permissible values of touch voltages and currents flowing through the human body for a duration of exposure of more than 1 s, given in Table 2, correspond to releasing (alternating) and non-painful (direct) currents.
1.4. The maximum permissible values of touch voltages during emergency operation of industrial electrical installations with a current frequency of 50 Hz, voltage above 1000 V, with solid grounding of the neutral should not exceed the values specified in Table 3.
Table 3
|
Duration of exposuret, With |
Maximum permissible touch voltage valueU, V |
|
Up to 0.1 |
|
|
St. 1.0 to 5.0 |
1.5. The maximum permissible values of touch voltages and currents during emergency operation of household electrical installations with voltages up to 1000 V and a frequency of 50 Hz should not exceed the values specified in Table 4.
Table 4
|
Duration |
Standardized value |
Duration |
Standardized value |
||
|
Impacts t , With |
U, B |
I, mA |
Impacts t , With |
U, B |
I, mA |
|
From 0.01 to 0.08 |
|||||
|
St. 1.0 |
|||||
Note. The values of touch voltages and currents are established for people with a body weight of 15 kg.
1.6. Human protection from the effects of touch voltages and currents is ensured by the design of electrical installations, technical methods and means of protection, organizational and technical measures in accordance with GOST 12.1.019-79.
2. CONTROL OF TOUCH VOLTAGES AND CURRENTS
2.1. To control the maximum permissible values of touch voltages and currents, voltages and currents are measured in places where an electrical circuit may close through the human body. The accuracy class of measuring instruments is not lower than 2.5.
2.2. When measuring touch currents and voltages, the resistance of the human body in an electrical circuit at a frequency of 50 Hz should be modeled by a resistance resistor:
For Table 1 - 6.7 kOhm;
For Table 2 at exposure time
Up to 0.5 s -0.85 kOhm;
More than 0.5 s - resistance depending on voltage according to the drawing;
For table 3 - 1 kOhm;
For Table 4 at exposure time
Up to 1 s -1 kOhm;
More than 1 s - 6 kOhm.
Deviation from the specified values is allowed within± 10%.