Permissible currents and voltages. Maximum permissible currents Ih mA and touch voltage Upr V. Emergency mode of electrical installation

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 performing work in high temperatures(above 25°C) and humidity (relative humidity more than 75%) should 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

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 humans from the effects of touch voltages and currents is ensured by the design of electrical installations, technical methods and protective equipment, organizational and technical measures for

Depending on the duration of exposure to a person

Table 2

The permissible values ​​of touch voltage and current passing through the human body are used to develop a set of protective measures and determine the parameters of protective devices at which it is still possible to ensure safety. Sometimes the term “safe current” is used, which has no meaning, since a current of any magnitude has some effect on the human body. Yes, electric current 0.02 - 0.07mA, 50Hz causes pain in certain points on the human body. Therefore, it is legitimate to use the concept of “permissible current”. The permissible current value should be set based on those threshold current values ​​at which a real danger appears. Thus, in hazardous working conditions (altitude, near moving or rotating parts, etc.), when a person during work is forced to have constant contact with live parts, the long-term permissible current should be taken below the sensation threshold, no more 0.5mA. When working under normal (safe) conditions, the non-permissible current threshold should be taken as the long-term permissible current in case of accidental contact, 10mA, since exceeding this current value poses a real danger.

Current frequency

It has been established that the resistance of the human body also includes a capacitive component:

Therefore, an increase in the frequency of the applied voltage is accompanied by a decrease in the total resistance of the body and an increase in the current passing through the person. With an increase in the current passing through the human body, the danger of injury increases, which means that an increase in frequency should lead to an increase in such danger.

However, this assumption is valid only in the frequency range from 0 to 50 Hz. In the frequency range from 0 to 50 Hz with decreasing frequency, the value of the non-releasing current increases and at a frequency equal to zero ( D.C.), becomes approximately 3 times larger (see Fig. 2).

An increase in frequency above this range, despite an increase in the current passing through the human body, is accompanied by a decrease in the danger of injury, which completely disappears at a frequency 450-500 kHz, i.e. such currents cannot affect a person. However, in this case, the danger of burns remains when current passes through the human body and when an electric arc occurs.

The risk of injury is taken to be the reciprocal of the non-releasing current at a given frequency, expressed as a percentage. The danger at 50 Hz as the highest in the entire frequency scale.

Then the danger of injury at the desired frequency is determined from the expression

where, are non-releasing currents at 50 Hz and the desired frequency f, mA.

In a simplified way, the change in the danger of current with a change in frequency can be explained by the nature of the irritating effect of the current on the cells of living tissue.

If you apply to a living tissue cell constant voltage, then in the intracellular substance, which can be considered as an electrolyte, electrolytic dissociation occurs, as a result of which molecules will disintegrate into positive and negative ions. These ions will begin to move to the cell membrane, positive ions to the negative electrode, and negative ions to the positive electrode. This phenomenon will cause a disruption in the normal state of the cell and the natural biochemical processes occurring in it.

It can be assumed that in the frequency range from 0 to 50 Hz, a greater disruption of the natural state of the cell is caused by a current in which the ion makes from one to several “full” runs per unit of time inside the cell membrane. Presumably, either one “full” path of ions, or the maximum number of “full” paths that occur at a frequency 50 Hz. Since ions, as material particles, have a certain speed of movement in the electrolyte, then at a certain frequency (obviously 50 Hz) the ion will not have time to reach the cell membrane during the polarity change. This position will presumably correspond to less disruption of the normal state of the cell. With a further increase in frequency, the travel distance of the ions will decrease and a moment may come when the movement of the ions stops, and therefore there will be no dangerous disruption to the state of the cell. This situation occurs at frequencies higher 450-500 kHz.

Current paths

In the practice of operating electrical installations, when a person is connected to an electrical circuit, current flows through him, as a rule, along the “arm-to-leg” or “arm-to-arm” path. However, there are many possible current paths in the human body. The degree of damage in these cases depends on which vital organs (heart, lungs, brain) of a person are affected by the current, as well as on the magnitude of the current directly affecting these organs and in particular the heart.

Typical current paths (current loops) in the human body are shown in Fig. 3.

The current is distributed throughout the entire volume of the body, but most most it passes along the path of least resistance - along the blood and lymphatic vessels, nerve trunks and branches.

In this case, the path of least resistance does not have to be the shortest between the electrodes. Measurements have shown that the value of the human body’s resistance to electric current is different for different current loops:

- "hand - hand" – 1360 Ohm;

- "arm - legs" – 970 Ohm;

- "arms - legs" - 670 Ohm.

The danger of various current loops can be assessed using the data in Table 3.

The most dangerous loops are head - arms, head - legs, when the current can pass through the head and spinal cord. However, these loops occur relatively rarely. The next most dangerous path is the right arm - legs, when the greatest current flows through the heart along the longitudinal axis.

Despite the small amount of current flowing through human hearts during a leg-to-leg loop at a step voltage equal to 80-120 V, leg muscle spasms occur, the person falls and, touching the ground with his hand, falls under high voltage, since the current loop will now be “arms - legs” (“arm – leg”), which can lead to electric shock.

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 sheaths are given in Table. 1.3.4-1.3.11. They are accepted for temperatures: cores +65, ambient air +25 and ground + 15°C.

When determining the number of wires laid in one pipe (or cores of a stranded conductor), the neutral working conductor of a four-wire three-phase current system, as well as grounding and neutral protective conductors are not taken into account.

Permissible long-term currents for wires and cables laid in boxes, as well as in trays in bundles, must be accepted: for wires - according to table. 1.3.4 and 1.3.5 as for wires laid in pipes, for cables - according to table. 1.3.6-1.3.8 as for cables laid in the air. If the number of simultaneously loaded wires is more than four, laid in pipes, boxes, and also in trays in bundles, the currents for the wires should be taken according to the table. 1.3.4 and 1.3.5 as for wires laid openly (in the air), with the introduction of reduction factors of 0.68 for 5 and 6; 0.63 for 7-9 and 0.6 for 10-12 conductors.

For secondary circuit wires, reduction factors are not introduced.

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

Table 1.3.5. Permissible continuous current for rubber and polyvinyl chloride insulated wires with aluminum conductors

Table 1.3.6. Permissible continuous current for wires with copper conductors with rubber insulation in metal protective sheaths and cables with copper conductors with rubber insulation in lead, polyvinyl chloride, nayrite or rubber sheaths, armored and unarmored

Table 1.3.7. Permissible continuous current for cables with aluminum conductors with rubber or plastic insulation in lead, polyvinyl chloride and rubber sheaths, armored and unarmored

Note. Permissible continuous currents for four-core cables with plastic insulation for voltages up to 1 kV can be selected according to table. 1.3.7, as for three-core cables, but with a coefficient of 0.92.

Table 1.3.8. Permissible continuous current for portable light and medium hose cords, portable heavy duty hose cables, mine flexible hose cables, floodlight cables and portable wires with copper conductors

________________

* Currents refer to cords, wires and cables with and without a neutral core.

Table 1.3.9. Permissible continuous current for portable hose cables with copper conductors and rubber insulation for peat enterprises

__________________

Table 1.3.10. Permissible continuous current for hose cables with copper conductors and rubber insulation for mobile electrical receivers

__________________

* Currents refer to cables with and without a neutral core.

Table 1.3.11. Permissible continuous current for wires with copper conductors with rubber insulation for electrified transport 1.3 and 4 kV

Table 1.3.12. Reduction factor for wires and cables laid in boxes

1.3.11

Permissible long-term currents for wires laid in trays for single-row installation (not in bundles) should be taken as for wires laid in the air.

Permissible long-term currents for wires and cables laid in boxes should be taken according to table. 1.3.4-1.3.7 as for single wires and cables laid openly (in the air), using the reduction factors indicated in table. 1.3.12.

When choosing reduction factors, control and reserve wires and cables are not taken into account.

When using data below the maximum permissible values ​​of currents and touch voltages, the following considerations must be kept in mind.

1. The product of the threshold value of ventricular fibrillation current and the value of the resistance of the human body can give a threshold value of ventricular fibrillation voltage, but it must be borne in mind that these quantities are not independent. In reality, a relatively small proportion of people have high body resistance and low ventricular fibrillation current threshold, while a large proportion of people have low body resistance and high ventricular fibrillation current threshold.

Therefore, the product of the resistance values ​​of the human body and the threshold values ​​of the ventricular fibrillation current, which have the same probability, will give the threshold values ​​of the ventricular fibrillation voltages related to a non-existent person.

1. Even if the current threshold values ​​and the body resistance value were mutually independent, then simply multiplying their values, which have the same probability, would give a threshold voltage value that has a lower probability compared to the probability of each of the two values ​​being interchanged.
2. The threshold values ​​for ventricular fibrillation current given in Publication IEC-479 were derived from experiments in dogs. More recent studies indicate that the human heart has a higher threshold value for ventricular fibrillation current compared to the dog heart and, therefore, the published threshold values ​​can be considered as overestimated values.

Non-emergency mode of electrical installation

The maximum permissible values ​​of touch voltages and currents passing through the human body are used in the design of electrical installations of direct and AC frequency 50 and 400 Hz. The maximum permissible values ​​of touch voltages and currents are established for current paths from one hand to the other and from hands to feet.
Touch voltage and current passing through the human body, with a duration of exposure of no more than 10 minutes. per day should not exceed the values ​​​​given in the table. 1. Table data 1. apply to electrical installations of all voltage classes, both with insulated and grounded neutral.

Table 1. Maximum permissible values ​​of touch voltages and currents passing through the human body in non-emergency mode
electrical installations

Electrical installation emergency mode

Touch voltages and currents passing through a person during emergency operation of electrical installations with voltages up to 1 kV with a grounded or insulated neutral and above 1 kV with an insulated neutral should not exceed the values ​​​​given in table. 2.
Touch voltages and currents passing through a person during emergency operation of electrical installations with voltages above 1 kV with an effectively grounded neutral should not exceed the values ​​given in table. 3.
To control the normalized values ​​of touch voltages and currents, voltages and currents must be measured in places where they can be expected highest values controlled quantities.
When measuring touch voltages and currents, the resistance to current flow from a person's feet to the ground should be modeled by a metal flat plate with a contact surface area of ​​625 cm2. The pressure of the plate to the ground must be created by a mass of at least 50 kg.
Measurements should be made for conditions corresponding to the highest values ​​of touch voltages and currents passing through the human body.
* Touch voltages and currents for persons working in conditions of high temperatures (more than 25°C) and humidity (relative humidity more than 75%) must be reduced by 3 times.

Table 2. Normalized values ​​of touch voltage and currents passing through a person for electrical installations with voltages up to 1 kV with a grounded and insulated neutral and above 1 kV with an insulated neutral

Table 3. Normalized values ​​of touch voltage and currents passing through a person for electrical installations with voltages above 1 kV with a frequency of 50 Hz with an effectively grounded neutral

GOST 12.1.038-82*

Group T58

INTERSTATE STANDARD

Occupational Safety Standards System

ELECTRICAL SAFETY

Maximum permissible values ​​of touch voltages and currents

Occupational safety standards system. Electric safety.
Maximum permissible values ​​of pickp voltages and currents

Date of introduction 1983-07-01

INFORMATION DATA

ENTERED INTO EFFECT by Decree of the USSR State Committee on Standards dated July 30, 1982 N 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 Amendment 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.

1. 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

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.

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 3

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 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 a short circuit can occur electrical circuit through the human body. Accuracy class measuring instruments 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%.

2.1, 2.2. (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 25x25 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

APPLICATION
Information

(Changed edition, Amendment No. 1).

The text of the document is verified according to:
official publication
System of occupational safety standards: Sat. GOST. -
M.: IPK Standards Publishing House, 2001