1.7.1. This chapter of the Rules applies to all electrical installations of alternating and direct current voltage up to 1 kV and above and contains general requirements for their grounding and protection of people and animals from damage electric shock both in normal operation of the electrical installation and in the event of insulation damage.

Additional requirements are given in the relevant chapters of the EMP.

1.7.2. Electrical installations in relation to electrical safety measures are divided into:

electrical installations with voltages above 1 kV in networks with solidly grounded or effectively grounded neutral (see 1.2.16);

electrical installations with voltages above 1 kV in networks with isolated or grounded neutral through an arcing reactor or resistor;

electrical installations with voltage up to 1 kV in networks with dead-earthed neutral;

electrical installations with voltage up to 1 kV in networks with isolated neutral.

1.7.3. For electrical installations with voltage up to 1 kV, the following designations are accepted:

system TN- a system in which the neutral of the power source is solidly grounded, and the exposed conductive parts of the electrical installation are connected to the solidly grounded neutral of the source through zero protective conductors;

a b

Rice. 1.7.1. System TN-C variable ( a) and constant ( b) current. Zero protective and zero working conductors are combined in one conductor:

1 - grounding conductor of the neutral (middle point) of the power supply;
2 - exposed conductive parts;
3 - DC power supply

system TN-C- system TN, in which the zero protective and zero working conductors are combined in one conductor along its entire length (Fig. 1.7.1);

system TN-S- system TN, in which the zero protective and zero working conductors are separated along its entire length (Fig. 1.7.2);

system TN-C-S- system TN, in which the functions of the zero protective and zero working conductors are combined in one conductor in some part of it, starting from the power source (Fig. 1.7.3);

system IT- a system in which the neutral of the power source is isolated from the ground or grounded through devices or devices with high resistance, and the open conductive parts of the electrical installation are grounded (Fig. 1.7.4);

system TT- a system in which the neutral of the power source is solidly grounded, and the open conductive parts of the electrical installation are grounded using a grounding device that is electrically independent of the solidly grounded neutral of the source (Fig. 1.7.5).

The first letter is the state of the neutral of the power supply relative to earth:

T- grounded neutral;
I- isolated neutral.

Rice. 1.7.2. System TN-S variable ( a) and constant ( b) current. Zero protective and zero working conductors are separated:

1 1-1 1-2 2 - exposed conductive parts; 3 - source of power

The second letter is the state of open conductive parts relative to ground:

T- exposed conductive parts are earthed, regardless of the relation to earth of the neutral of the power supply or any point of the supply network;

N- exposed conductive parts are connected to a dead-earthed neutral of the power source.

Subsequent (after N) letters - combination in one conductor or separation of the functions of the zero working and zero protective conductors:

S- zero worker ( N) and zero protective ( RE) conductors are separated;

Rice. 1.7.3. System TN-C-S variable ( a) and constant ( b) current. Zero protective and zero working conductors are combined in one conductor in part of the system:

1 - source neutral earthing alternating current; 1-1 - ground electrode of the output of the direct current source; 1-2 - grounding conductor of the middle point of the direct current source; 2 - exposed conductive parts, 3 - source of power

FROM- the functions of the zero protective and zero working conductors are combined in one conductor ( PEN-conductor);

N- - zero working (neutral) conductor;

RE- - protective conductor (grounding conductor, zero protective conductor, protective conductor of the potential equalization system);

PEN- - combined zero protective and zero working conductors.

Rice. 1.7.4. System IT variable ( a) and constant ( b) current. Exposed conductive parts of the electrical installation are earthed. The neutral of the power supply is isolated from earth or grounded through a high resistance:

1 - earthing resistance of the neutral of the power supply (if any);
2 - ground electrode;
3 - exposed conductive parts;
4 - grounding device of the electrical installation;
5 - source of power

1.7.4. An electrical network with an effectively grounded neutral is a three-phase electrical network with a voltage above 1 kV, in which the earth fault factor does not exceed 1.4.

The earth fault ratio in a three-phase electrical network is the ratio of the potential difference between an intact phase and earth at the earth fault point of another or two other phases to the potential difference between the phase and earth at that point before the fault.

Rice. 1.7.5. System TT variable ( a) and constant ( b) current. Exposed conductive parts of the electrical installation are grounded using grounding, electrically independent of the neutral grounding conductor:

1 - grounding conductor of the neutral of the alternating current source;
1-1 - ground electrode of the output of the direct current source;
1-2 - grounding conductor of the middle point of the direct current source;
2 - exposed conductive parts;
3 - grounding switch of open conductive parts of the electrical installation;
4 - source of power

1.7.5. Solidly grounded neutral - the neutral of a transformer or generator, connected directly to the grounding device. The output of a single-phase alternating current source or the pole of a direct current source in two-wire networks, as well as the midpoint in three-wire DC networks.

1.7.6. Isolated neutral - the neutral of a transformer or generator that is not connected to a grounding device or connected to it through a high resistance of signaling, measuring, protection devices and other similar devices.

1.7.7. A conductive part is a part that can conduct an electric current.

1.7.8. Current-carrying part - a conductive part of an electrical installation that is under operating voltage during its operation, including a zero working conductor (but not PEN-conductor).

1.7.9. Open conductive part - a conductive part of an electrical installation that is accessible to the touch and is not normally energized, but which may become energized if the main insulation is damaged.

1.7.10. Third-party conductive part - a conductive part that is not part of the electrical installation.

1.7.11. Direct contact - electrical contact of people or animals with current-carrying parts that are energized.

1.7.12. Indirect touch - electrical contact of people or animals with open conductive parts that are energized when the insulation is damaged.

1.7.13. Protection against direct contact - protection to prevent contact with live parts under voltage.

1.7.14. Indirect contact protection - protection against electric shock when touching open conductive parts that are energized when the insulation is damaged.

The term insulation failure should be understood as a single insulation failure.

1.7.15. Grounding conductor - a conductive part or a set of interconnected conductive parts that are in electrical contact with the ground directly or through an intermediate conductive medium.

1.7.16. Artificial ground electrode - a ground conductor specially made for grounding purposes.

1.7.17. Natural ground conductor - a third-party conductive part that is in electrical contact with the ground directly or through an intermediate conductive medium used for grounding purposes.

1.7.18. Grounding conductor - a conductor connecting the grounded part (point) with the ground electrode.

1.7.19. Grounding device - a combination of grounding and grounding conductors.

1.7.20. Zero potential zone (relative earth) - a part of the earth that is outside the zone of influence of any grounding conductor, the electric potential of which is assumed to be zero.

1.7.21. Spreading zone (local earth) - the earth zone between the ground electrode and the zone of zero potential.

The term earth used in the chapter should be understood as earth in the spreading zone.

1.7.22. An earth fault is an accidental electrical contact between energized live parts and earth.

1.7.23. The voltage on the grounding device is the voltage that occurs when current drains from the ground electrode into the ground between the point of current input into the ground electrode and the zone of zero potential.

1.7.24. Touch voltage - the voltage between two conductive parts or between a conductive part and the ground when a person or animal touches them at the same time.

Expected touch voltage - the voltage between conductive parts that are simultaneously accessible to touch when a person or animal does not touch them.

1.7.25. Step voltage - the voltage between two points on the earth's surface, at a distance of 1 m from one another, which is taken equal to the length man's steps.

1.7.26. The resistance of the grounding device is the ratio of the voltage on the grounding device to the current flowing from the grounding conductor into the ground.

1.7.27. Equivalent resistivity of the earth with a heterogeneous structure - specific electrical resistance earth with a homogeneous structure, in which the resistance of the grounding device has the same value as in the earth with a heterogeneous structure.

The term resistivity used in the chapter for non-homogeneous earth should be understood as equivalent resistivity.

1.7.28. Grounding - Intentional electrical connection any point of the network, electrical installation or equipment with a grounding device.

1.7.29. Protective grounding - grounding performed for electrical safety purposes.

1.7.30. Working (functional) grounding - grounding of a point or points of current-carrying parts of an electrical installation, performed to ensure the operation of an electrical installation (not for electrical safety purposes).

1.7.31. Protective grounding in electrical installations with voltage up to 1 kV - deliberate connection of open conductive parts with a dead-earthed neutral of a generator or transformer in networks three-phase current, with solidly grounded source output single-phase current, with a grounded source point in DC networks, performed for electrical safety purposes.

1.7.32. Potential equalization - electrical connection of conductive parts to achieve equality of their potentials.

Protective equalization of potentials - equalization of potentials, performed for the purpose of electrical safety.

The term potential equalization used in the chapter should be understood as protective potential equalization.

1.7.33. Potential equalization - reducing the potential difference (step voltage) on the surface of the earth or floor with the help of protective conductors laid in the ground, in the floor or on their surface and connected to a grounding device, or by using special earth coatings.

1.7.34. Protective ( RE) conductor - a conductor intended for electrical safety purposes.

Protective earth conductor - a protective conductor intended for protective earth.

Potential equalization protective conductor - a protective conductor designed for protective potential equalization.

Zero protective conductor - a protective conductor in electrical installations up to 1 kV, designed to connect open conductive parts to a solidly grounded neutral of a power source.

1.7.35. Zero working (neutral) conductor ( N) - a conductor in electrical installations up to 1 kV, designed to power electrical receivers and connected to a dead-earthed neutral of a generator or transformer in three-phase current networks, with a dead-earthed output of a single-phase current source, with a dead-earthed source point in DC networks.

1.7.36. Combined zero protective and zero working ( PEN) conductors - conductors in electrical installations with voltage up to 1 kV, combining the functions of zero protective and zero working conductors.

1.7.37. The main ground bus is a bus that is part of the grounding device of an electrical installation up to 1 kV and is designed to connect several conductors for the purpose of grounding and potential equalization.

1.7.38. Protective automatic power off - automatic opening of the circuit of one or more phase conductors (and, if required, the zero working conductor), performed for electrical safety purposes.

The term auto power off as used in the chapter should be understood as protective auto power off.

1.7.39. Basic insulation - insulation of current-carrying parts, providing, among other things, protection against direct contact.

1.7.40. Additional insulation - independent insulation in electrical installations with voltage up to 1 kV, performed in addition to the main insulation for protection against indirect contact.

1.7.41. Double insulation - insulation in electrical installations with voltage up to 1 kV, consisting of basic and additional insulation.

1.7.42. Reinforced insulation - insulation in electrical installations with voltage up to 1 kV, providing a degree of protection against electric shock equivalent to double insulation.

1.7.43. Extra low (low) voltage (SLV) - voltage not exceeding 50 V AC and 120 V DC.

1.7.44. Isolating transformer - transformer, primary winding which is separated from the secondary windings by protective electrical separation of circuits.

1.7.45. Safety isolating transformer is an isolating transformer designed to supply extra-low voltage circuits.

1.7.46. Protective screen - a conductive screen designed to separate electrical circuit and/or conductors from live parts of other circuits.

1.7.47. Protective electrical separation of circuits - separation of one electrical circuit from other circuits in electrical installations with voltage up to 1 kV using:

• double insulation;
• basic insulation and protective screen;
• reinforced insulation.

1.7.48. Non-conductive (insulating) premises, zones, sites - premises, zones, sites in which (on which) protection in case of indirect contact is provided by high resistance of the floor and walls and in which there are no grounded conductive parts.

General requirements

1.7.49. The current-carrying parts of the electrical installation should not be accessible for accidental contact, and the open and third-party conductive parts accessible to touch should not be energized, which poses a risk of electric shock both in the normal operation of the electrical installation and in case of damage to the insulation.

1.7.50. To protect against electric shock in normal operation, the following protective measures against direct contact must be applied individually or in combination:

• basic insulation of current-carrying parts;
• enclosures and shells;
• setting up barriers;
• placement out of reach;
• the use of ultra-low (small) voltage.

For additional protection against direct contact in electrical installations with voltage up to 1 kV, if there are requirements of other chapters of the PUE, devices should be used protective shutdown(RCD) with a rated breaking differential current of not more than 30 mA.

1.7.51. In order to protect against electric shock in the event of insulation failure, the following protective measures against indirect contact must be applied individually or in combination:

• protective grounding;
• automatic power off;
• equalization of potentials;
• potential equalization;
• double or reinforced insulation;
• ultra-low (small) voltage;
• protective electrical separation of circuits;
• insulating (non-conductive) rooms, zones, sites.

1.7.52. Measures of protection against electric shock must be provided in the electrical installation or part of it, or applied to individual electrical receivers and can be implemented in the manufacture of electrical equipment, or during installation of the electrical installation, or in both cases.

The use of two or more protective measures in an electrical installation should not have a mutual influence that reduces the effectiveness of each of them.

1.7.53. Protection against indirect contact must be carried out in all cases if the voltage in the electrical installation exceeds 50 V AC and 120 V DC.

In rooms with heightened danger, especially dangerous and in outdoor installations, protection against indirect contact may be required at lower voltages, for example, 25 V AC and 60 V DC or 12 V AC and 30 V DC, subject to the requirements of the relevant chapters of the PUE.

Protection against direct contact is not required if the electrical equipment is located in the area of ​​the potential equalization system, and the highest operating voltage does not exceed 25 V AC or 60 V DC in rooms without increased danger and 6 V AC or 15 V DC - in all cases.

Note. Here and throughout the chapter, AC voltage refers to the rms value of AC voltage; DC voltage - DC or rectified current voltage with a ripple content of not more than 10% of the rms value.

1.7.54. For grounding electrical installations, artificial and natural grounding conductors can be used. If, when using natural grounding conductors, the resistance of the grounding devices or the contact voltage has an acceptable value, and the normalized values ​​​​of the voltage on the grounding device and the permissible current densities in natural grounding conductors are provided, the implementation of artificial grounding conductors in electrical installations up to 1 kV is not necessary. The use of natural grounding conductors as elements of grounding devices should not lead to their damage when short-circuit currents flow through them or to disruption of the operation of the devices with which they are connected.

1.7.55. For grounding in electrical installations of different purposes and voltages, geographically close, as a rule, one common grounding device should be used.

A grounding device used for grounding electrical installations of the same or different purposes and voltages must meet all the requirements for grounding these electrical installations: protecting people from electric shock if the insulation is damaged, operating conditions of networks, protecting electrical equipment from overvoltage, etc. in throughout the entire period of operation.

First of all, the requirements for protective earthing must be observed.

Grounding devices for protective grounding of electrical installations of buildings and structures and lightning protection of the 2nd and 3rd categories of these buildings and structures, as a rule, should be common.

When making a separate (independent) grounding conductor for working grounding, under the conditions of operation of information or other equipment sensitive to interference, special measures must be taken to protect against electric shock, excluding simultaneous contact with parts that may be under a dangerous potential difference if the insulation is damaged.

To combine grounding devices of different electrical installations into one common grounding device, natural and artificial grounding conductors can be used. Their number must be at least two.

1.7.56. The required values ​​of contact voltage and resistance of grounding devices when ground fault currents and leakage currents flow from them must be provided under the most unfavorable conditions at any time of the year.

When determining the resistance of grounding devices, artificial and natural grounding conductors should be taken into account.

When determining the resistivity of the earth, its seasonal value corresponding to the most unfavorable conditions should be taken as the calculated one.

Grounding devices must be mechanically strong, thermally and dynamically resistant to earth fault currents.

1.7.57. Electrical installations up to 1 kV in residential, public and industrial buildings and outdoor installations should, as a rule, be powered from a source with a solidly grounded neutral using a system TN.

To protect against electric shock in case of indirect contact in such electrical installations, automatic power off must be performed in accordance with 1.7.78-1.7.79.

System selection requirements TN-C, TN-S, TN-C-S for specific electrical installations are given in the relevant chapters of the Rules.

1.7.58. Power supply of electrical installations with voltage up to 1 kV AC from a source with isolated neutral using the system IT should be carried out, as a rule, if a power interruption is unacceptable at the first short circuit to the ground or to open conductive parts connected to the potential equalization system. In such electrical installations, for protection against indirect contact during the first earth fault, protective grounding must be performed in combination with network insulation monitoring or RCDs with a rated differential breaking current of not more than 30 mA should be used. In the event of a double earth fault, automatic power off shall be performed in accordance with 1.7.81.

1.7.59. Power supply of electrical installations with voltage up to 1 kV from a source with a dead-earthed neutral and with grounding of open conductive parts using a grounding conductor not connected to the neutral (system TT), is allowed only in cases where the electrical safety conditions in the system TN cannot be provided. To protect against indirect contact in such electrical installations, automatic power off with mandatory application RCD. In this case, the following condition must be met:

R a I a £ 50 V,

where I a - tripping current of the protective device;

R a - the total resistance of the grounding conductor and the grounding conductor, when using RCD to protect several electrical receivers - the grounding conductor of the most distant electrical receiver.

1.7.60. When using a protective automatic power off, the main potential equalization system must be made in accordance with 1.7.82, and, if necessary, an additional potential equalization system in accordance with 1.7.83.

1.7.61. When using the system TN re-grounding is recommended RE- and РEN- conductors at the input to the electrical installations of buildings, as well as in other accessible places. For re-grounding, natural grounding should be used first. The resistance of the re-grounding earth electrode is not standardized.

Inside large and multi-storey buildings, a similar function is performed by potential equalization by connecting a zero protective conductor to the main ground bus.

Re-grounding of electrical installations with voltage up to 1 kV, powered by overhead lines, must be carried out in accordance with 1.7.102-1.7.103.

1.7.62. If the automatic power off time does not meet the conditions 1.7.78-1.7.79 for the system TN and 1.7.81 for the system IT, then indirect contact protection for individual parts of the electrical installation or individual electrical receivers can be performed using double or reinforced insulation (class II electrical equipment), extra low voltage (class III electrical equipment), electrical separation of circuits of insulating (non-conductive) rooms, zones, sites.

1.7.63. System IT voltage up to 1 kV, connected through a transformer to a network with a voltage above 1 kV, must be protected by a breakdown fuse from the danger arising from damage to the insulation between the windings of the higher and lower voltages of the transformer. A blowout fuse must be installed in the neutral or phase on the low voltage side of each transformer.

1.7.64. In electrical installations with a voltage above 1 kV with an isolated neutral, to protect against electric shock, protective grounding of exposed conductive parts must be made.

In such electrical installations, it should be possible to quickly detect ground faults. Earth fault protection should be installed with a tripping action throughout the electrically connected network in cases where it is necessary for safety reasons (for lines supplying mobile substations and mechanisms, peat mines, etc.).

1.7.65. In electrical installations with voltages above 1 kV with an effectively grounded neutral, protective grounding of open conductive parts must be made to protect against electric shock.

1.7.66. Protective zeroing in the system TN and protective earth in the system IT electrical equipment installed on overhead lines (power and instrument transformers, disconnectors, fuses, capacitors and other devices) must be carried out in compliance with the requirements given in the relevant chapters of the PUE, as well as in this chapter.

The resistance of the grounding device of the overhead line support on which the electrical equipment is installed must comply with the requirements of Ch. 2.4 and 2.5.

Protective measures against direct contact

1.7.67. The basic insulation of live parts must cover the live parts and withstand all possible influences to which it may be subjected during its operation. Removal of the insulation should only be possible by destroying it. Coatings are not insulating against electric shock, unless otherwise noted. specifications for specific products. When performing insulation during installation, it must be tested in accordance with the requirements of Ch. 1.8.

In cases where the main insulation is provided by an air gap, protection against direct contact with current-carrying parts or approaching them at a dangerous distance, including in electrical installations with voltages above 1 kV, must be carried out by means of shells, fences, barriers or placement out of reach.

1.7.68. Fencing and enclosures in electrical installations with voltage up to 1 kV must have a degree of protection of at least IP 2X, except in cases where large gaps are necessary for normal operation electrical equipment.

Enclosures and enclosures must be securely fastened and have sufficient mechanical strength.

Entry beyond the fence or opening the shell should be possible only with the help of a special key or tool, or after removing the voltage from the current-carrying parts. If these conditions cannot be met, intermediate guards with a degree of protection of at least IP 2X should be installed, the removal of which should also be possible only with the help of a special key or tool.

1.7.69. Barriers are designed to protect against accidental contact with current-carrying parts in electrical installations with voltage up to 1 kV or approaching them at a dangerous distance in electrical installations with voltage above 1 kV, but do not exclude deliberate contact and approaching live parts when bypassing the barrier. Barriers do not require a wrench or tool to be removed, but they must be secured so that they cannot be removed unintentionally. Barriers must be of insulating material.

1.7.70. Placement out of reach to protect against direct contact with live parts in electrical installations with voltage up to 1 kV or approaching them at a dangerous distance in electrical installations with voltage above 1 kV can be applied if it is impossible to fulfill the measures specified in 1.7.68-1.7.69, or their insufficiency. In this case, the distance between conductive parts accessible to simultaneous contact in electrical installations with voltage up to 1 kV must be at least 2.5 m. There should not be parts within the reach area that have different potentials and are accessible to simultaneous contact.

In the vertical direction, the reach zone in electrical installations with voltage up to 1 kV should be 2.5 m from the surface on which people are located (Fig. 1.7.6).

The indicated dimensions do not include the use of aids (eg tools, ladders, long objects).

1.7.71. Installation of barriers and placement out of reach is allowed only in areas accessible to qualified personnel.

1.7.72. In electrical rooms of electrical installations with voltages up to 1 kV, protection against direct contact is not required if the following conditions are simultaneously met:

these rooms are clearly marked and can only be accessed with a key;

the possibility of free exit from the premises without a key is provided, even if it is locked from the outside;

the minimum dimensions of service passages correspond to Ch. 4.1.

Rice. 1.7.6. Reach zone in electrical installations up to 1 kV:

S- the surface on which a person can be;

AT- base surface S;

The boundary of the reach zone of current-carrying parts by the hand of a person located on the surface S;

0.75; 1.25; 2.50 m - distance from the edge of the surface S to the edge of reach

Protective measures against direct and indirect contact

1.7.73. Extra low (low) voltage (SLV) in electrical installations with voltage up to 1 kV can be used to protect against electric shock from direct and / or indirect contact in combination with protective electrical circuit separation or in combination with automatic power off.

In both cases, a safety isolating transformer in accordance with GOST 30030 “Isolating transformers and safety isolating transformers” or another source of SLV that provides an equivalent degree of safety should be used as a power source for SLV circuits in both cases.

The live parts of the HV circuits must be electrically separated from other circuits so that an electrical separation equivalent to that between the primary and secondary windings of an isolating transformer is ensured.

The conductors of the ELV circuits, as a rule, must be laid separately from the conductors of more than high voltage and protective conductors, either separated from them by a grounded metal screen (sheath), or enclosed in a non-metallic sheath in addition to the main insulation.

Plugs and sockets of plug connectors in ELV circuits must not allow connection to sockets and plugs of other voltages.

Plug sockets must be without protective contact.

For VLV values ​​above 25 V a.c. or 60 V d.c., protection against direct contact shall also be provided by guards or enclosures or insulation suitable for a test voltage of 500 V a.c. for 1 min.

1.7.74. When using SLV in combination with electrical separation of circuits, exposed conductive parts must not be intentionally connected to the earth electrode, protective conductors or exposed conductive parts of other circuits and to third-party conductive parts, unless the connection of third-party conductive parts to electrical equipment is necessary, and the voltage on these parts cannot exceed the CNN value.

SLV in combination with electrical separation of circuits should be used when using SLV it is necessary to provide protection against electric shock if the insulation is damaged not only in the SLV circuit, but also if the insulation is damaged in other circuits, for example, in the circuit supplying the source.

When using SLV in combination with automatic power off, one of the outputs of the SLV source and its case must be connected to the protective conductor of the circuit supplying the source.

1.7.75. In cases where the electrical installation uses electrical equipment with the highest operating (functional) voltage not exceeding 50 V AC or 120 V DC, such voltage can be used as a measure of protection against direct and indirect contact, if the requirements of 1.7.73 are met. -1.7.74.

Protective measures for indirect contact

1.7.76. Protection requirements for indirect contact apply to:

1) body electrical machines, transformers, devices, lamps, etc.;

2) drives of electrical apparatus;

3) frames of switchboards, control panels, shields and cabinets, as well as removable or opening parts, if the latter are equipped with electrical equipment with a voltage above 50 V AC or 120 V DC (in cases provided for by the relevant chapters of the PUE - above 25 V AC or 60 V DC);

4) metal structures of switchgears, cable structures, cable boxes, sheaths and armor of control and power cables, sheaths of wires, sleeves and pipes of electrical wiring, sheaths and supporting structures of busbars (busbars), trays, boxes, strings, cables and strips on which reinforced cables and wires (except for strings, cables and strips along which cables with grounded or grounded metal sheath or armor are laid), as well as other metal structures on which electrical equipment is installed;

5) metal sheaths and armor of control and power cables and wires for voltages not exceeding those specified in 1.7.53, laid on common metal structures, including common pipes, boxes, trays, etc., with cables and wires on higher voltages;

6) metal cases of mobile and portable power receivers;

7) electrical equipment installed on moving parts of machine tools, machines and mechanisms.

When used as a protective measure for automatic power off, these exposed conductive parts must be connected to a solidly earthed neutral of the power supply in the system. TN and grounded in systems IT and TT.

1.7.77. No need to intentionally connect to source neutral in the system TN and ground in systems IT and TT:

1) cases of electrical equipment and apparatus installed on metal bases: structures, switchgear, switchboards, cabinets, machine beds, machines and mechanisms connected to the neutral of the power source or grounded, while ensuring reliable electrical contact of these cases with the bases;

2) the structures listed in 1.7.76, while ensuring reliable electrical contact between these structures and the electrical equipment installed on them, connected to the protective conductor;

3) Removable or opening parts metal frames switchgear chambers, cabinets, fences, etc., if no electrical equipment is installed on the removable (opening) parts or if the voltage of the installed electrical equipment does not exceed the values ​​specified in 1.7.53;

4) fittings of insulators overhead lines power lines and fasteners attached to it;

5) open conductive parts of electrical equipment with double insulation;

6) metal brackets, fasteners, sections of pipes for mechanical protection of cables in places where they pass through walls and ceilings and other similar parts of electrical wiring with an area of ​​up to 100 cm 2, including pull-in and branch boxes of hidden electrical wiring.

1.7.78. When performing automatic power off in electrical installations with voltage up to 1 kV, all exposed conductive parts must be connected to a solidly grounded neutral of the power source, if the system is used TN, and grounded if systems are applied IT or TT. At the same time, the characteristics of the protective devices and the parameters of the protective conductors must be coordinated in order to ensure the normalized time for disconnecting the damaged circuit by the protective switching device in accordance with the rated phase voltage of the supply network.

In electrical installations in which automatic power off is applied as a protective measure, potential equalization must be carried out.

For automatic power off, protective switching devices that respond to overcurrents or differential currents can be used.

1.7.79. In system TN the time of automatic power off should not exceed the values ​​specified in Table. 1.7.1.

Table 1.7.1

TN

The given disconnection times are considered sufficient to ensure electrical safety, including in group circuits supplying mobile and portable electrical receivers and handheld power tools of class 1.

In circuits supplying distribution, group, floor and other boards and boards, the shutdown time should not exceed 5 s.

Off-time values ​​are allowed more than those indicated in Table. 1.7.1, but not more than 5 s in circuits supplying only stationary electrical receivers from switchboards or shields when one of the following conditions is met:

1) the total resistance of the protective conductor between the main ground bus and the switchboard or shield does not exceed the value, Ohm:

50× Z c / U 0 ,

where Z c - total resistance of the "phase-zero" circuit, Ohm;

U 0 - nominal phase voltage of the circuit, V;

50 - voltage drop in the section of the protective conductor between the main ground bus and the switchboard or shield, V;

2) to the bus RE switchboard or shield, an additional potential equalization system is connected, covering the same third-party conductive parts as the main potential equalization system.

It is allowed to use RCDs that respond to differential current.

1.7.80. It is not allowed to use RCDs that respond to differential current in four-wire three-phase circuits(system TN-C). If it is necessary to use RCDs to protect individual electrical receivers powered by the system TN-C, protective RE- the conductor of the electrical receiver must be connected to PEN- the conductor of the circuit supplying the electrical receiver to the protective switching device.

1.7.81. In system IT the time of automatic power off in case of a double circuit to open conductive parts must comply with Table. 1.7.2.

Table 1.7.2

The longest allowable protective shutdown time for the system IT

1.7.82. The main potential equalization system in electrical installations up to 1 kV must interconnect the following conductive parts (Fig. 1.7.7):

1) zero protective RE- or REN- the conductor of the supply line in the system TN;

2) a ground conductor connected to the grounding device of the electrical installation, in systems IT and TT;

3) a grounding conductor connected to the re-grounding conductor at the entrance to the building (if there is a grounding conductor);

4) metal pipes communications included in the building: hot and cold water supply, sewerage, heating, gas supply, etc.

If the gas supply pipeline has an insulating insert at the entrance to the building, only that part of the pipeline that is relative to the insulating insert from the side of the building is connected to the main potential equalization system;

5) metal parts of the building frame;

6) metal parts of centralized ventilation and air conditioning systems. In the presence of decentralized ventilation and air conditioning systems, metal air ducts should be connected to the bus RE power supply panels for fans and air conditioners;

Rice. 1.7.7. Potential equalization system in the building:

M- open conductive part; C1- metal water pipes entering the building; C2- metal sewer pipes entering the building; C3- metal gas supply pipes with an insulating insert at the inlet, entering the building; C4- ventilation and air conditioning ducts; C5- heating system; C6- metal water pipes in the bathroom; C7- metal bath; C8- third-party conductive part within reach of exposed conductive parts; C9- reinforcement of reinforced concrete structures; GZSH - main ground bus; T1- natural grounding; T2- lightning protection ground electrode (if any); 1 - zero protective conductor; 2 - conductor of the main potential equalization system; 3 - conductor of an additional potential equalization system; 4 - down conductor of the lightning protection system; 5 - contour (main) of working grounding in the room of information computing equipment; 6 - conductor of working (functional) grounding; 7 - potential equalization conductor in the working (functional) grounding system; 8 - ground conductor

7) grounding device of the lightning protection system of the 2nd and 3rd categories;

8) a grounding conductor of functional (working) grounding, if there is one and there are no restrictions on connecting the working grounding network to a protective grounding grounding device;

9) metal sheaths of telecommunication cables.

Conductive parts entering the building from the outside should be connected as close as possible to their point of entry into the building.

To connect to the main potential equalization system, all of these parts must be connected to the main ground bus (1.7.119-1.7.120) using the conductors of the potential equalization system.

1.7.83. The system of additional potential equalization must interconnect all open conductive parts of stationary electrical equipment that are simultaneously accessible to the touch and third-party conductive parts, including metal parts of the building structures accessible to touch, as well as zero protective conductors in the system TN and protective earth conductors in systems IT and TT, including protective conductors of socket outlets.

For potential equalization, specially provided conductors or open and third-party conductive parts can be used if they meet the requirements of 1.7.122 for protective conductors with respect to conductivity and continuity of the electrical circuit.

1.7.84. Protection by means of double or reinforced insulation may be provided by the use of class II electrical equipment or by enclosing electrical equipment having only basic insulation of live parts in an insulating sheath.

Conductive parts of equipment with double insulation must not be connected to the protective conductor and to the potential equalization system.

1.7.85. Protective electrical separation of circuits should be used, as a rule, for one circuit.

The highest operating voltage of the separated circuit must not exceed 500 V.

The circuit to be separated must be powered from an isolating transformer complying with GOST 30030 "Isolating transformers and safety isolating transformers", or from another source that provides an equivalent degree of safety.

Current-carrying parts of a circuit powered by an isolating transformer must not be connected to grounded parts and protective conductors of other circuits.

Conductors of circuits powered by an isolating transformer are recommended to be laid separately from other circuits. If this is not possible, then for such circuits it is necessary to use cables without a metal sheath, armor, screen or insulated wires, laid in insulating pipes, ducts and channels, provided that the rated voltage of these cables and wires corresponds to the highest voltage of the jointly laid circuits, and each circuit is protected from overcurrents.

If only one electrical receiver is supplied from an isolating transformer, then its exposed conductive parts must not be connected either to the protective conductor or to the open conductive parts of other circuits.

It is allowed to supply several electrical receivers from one isolation transformer, provided that the following conditions are met simultaneously:

1) exposed conductive parts of the circuit to be separated must not have electrical connection with the metal case of the power source;

2) the open conductive parts of the circuit to be separated must be interconnected by insulated ungrounded conductors of the local potential equalization system that does not have connections with protective conductors and open conductive parts of other circuits;

3) all socket outlets must have a protective contact connected to a local ungrounded potential equalization system;

4) all flexible cables, with the exception of those supplying class II equipment, must have a protective conductor used as a potential equalization conductor;

5) the shutdown time of the protective device in case of a two-phase short circuit to open conductive parts should not exceed the time specified in Table. 1.7.2.

1.7.86. Insulating (non-conductive) rooms, zones and sites can be used in electrical installations with voltage up to 1 kV, when the requirements for automatic power off cannot be met, and the use of other protective measures is impossible or impractical.

The resistance relative to the local ground of the insulating floor and walls of such premises, zones and sites at any point must be at least:

50 kOhm at a rated voltage of the electrical installation up to 500 V inclusive, measured with a megohmmeter for a voltage of 500 V;

100 kOhm at a rated voltage of the electrical installation of more than 500 V, measured with a megaohmmeter for a voltage of 1000 V.

If the resistance at any point is less than specified, such rooms, areas, areas should not be considered as a measure of protection against electric shock.

For insulating (non-conductive) rooms, zones, sites, it is allowed to use electrical equipment of class 0, subject to at least one of the following three conditions:

1) open conductive parts are removed from one another and from third-party conductive parts by at least 2 m. It is allowed to reduce this distance out of reach to 1.25 m;

2) exposed conductive parts are separated from external conductive parts by barriers of insulating material. At the same time, distances not less than those specified in paragraphs. 1, must be secured on one side of the barrier;

3) third-party conductive parts are covered with insulation that can withstand a test voltage of at least 2 kV for 1 min.

No protective conductor shall be provided in insulating rooms (zones).

Measures must be taken to prevent potential drift to third-party conductive parts of the room from the outside.

The floor and walls of such rooms should not be exposed to moisture.

1.7.87. When performing protection measures in electrical installations with voltage up to 1 kV, the classes of electrical equipment used according to the method of protecting a person from electric shock in accordance with GOST 12.2.007.0 “SSBT. Electrical products. General requirements safety" should be taken in accordance with Table. 1.7.3.

Table 1.7.3

The use of electrical equipment in electrical installations with voltage up to 1 kV

Class according to GOST 12.2.007.0 R IEC536	Marking	Purpose of protection	Conditions for the use of electrical equipment in an electrical installation
		On indirect contact	1. Application in non-conductive rooms. 2. Power supply from the secondary winding of an isolation transformer of only one electrical receiver
	Safety clip - sign or letters RE, or yellow-green stripes	On indirect contact	Connecting the grounding clamp of electrical equipment to the protective conductor of the electrical installation
		On indirect contact	Regardless of the protective measures taken in the electrical installation
		From direct and indirect contact	Powered by a safety isolating transformer

Grounding devices for electrical installations with voltages above 1 kV in networks with effectively grounded neutral

1.7.88. Grounding devices of electrical installations with voltages above 1 kV in networks with an effectively grounded neutral should be made in compliance with the requirements either for their resistance (1.7.90) or for touch voltage (1.7.91), as well as in compliance with the design requirements (1.7.92 -1.7.93) and to limit the voltage on the grounding device (1.7.89). Requirements 1.7.89-1.7.93 do not apply to grounding devices of overhead lines.

1.7.89. The voltage on the grounding device when the earth fault current drains from it should, as a rule, not exceed 10 kV. Voltage above 10 kV is allowed on grounding devices, from which the removal of potentials outside buildings and external fences of electrical installations is excluded. When the voltage on the grounding device is more than 5 kV, measures must be taken to protect the insulation of the outgoing communication and telemechanics cables and to prevent the removal of dangerous potentials outside the electrical installation.

1.7.90. The grounding device, which is carried out in compliance with the requirements for its resistance, must have a resistance of no more than 0.5 Ohm at any time of the year, taking into account the resistance of natural and artificial grounding conductors.

In order to equalize the electrical potential and ensure the connection of electrical equipment to the ground electrode system in the territory occupied by the equipment, longitudinal and transverse horizontal earth conductors should be laid and combined into a ground grid.

Longitudinal grounding conductors should be laid along the axes of electrical equipment from the service side at a depth of 0.5-0.7 m from the ground surface and at a distance of 0.8-1.0 m from foundations or equipment foundations. It is allowed to increase the distances from the foundations or bases of the equipment up to 1.5 m with the laying of one ground electrode for two rows of equipment, if the service sides face each other, and the distance between the bases or foundations of the two rows does not exceed 3.0 m.

Transverse ground electrodes should be laid in convenient places between equipment at a depth of 0.5-0.7 m from the ground. The distance between them is recommended to be taken as increasing from the periphery to the center of the grounding grid. In this case, the first and subsequent distances, starting from the periphery, should not exceed 4.0, respectively; 5.0; 6.0; 7.5; 9.0; 11.0; 13.5; 16.0; 20.0 m power transformers and short circuits to the grounding device should not exceed 6 x 6 m.

Horizontal grounding conductors should be laid along the edge of the territory occupied by the grounding device so that they together form a closed loop.

If the circuit of the grounding device is located within the external fence of the electrical installation, then at the entrances and entrances to its territory, the potential should be equalized by installing two vertical ground electrodes connected to an external horizontal ground electrode opposite the entrances and entrances. Vertical earthing should be 3-5 m long, and the distance between them should be equal to the width of the entrance or entrance.

1.7.91. The grounding device, which is carried out in compliance with the requirements for the contact voltage, must provide at any time of the year when the earth fault current drains from it, the contact voltage values ​​\u200b\u200bthat do not exceed the rated ones (see GOST 12.1.038). In this case, the resistance of the grounding device is determined by the allowable voltage on the grounding device and the ground fault current.

When determining the value of the allowable contact voltage, the sum of the protection action time and the total switch off time should be taken as the estimated exposure time. When determining the permissible values ​​​​of contact voltage at workplaces where, during the production of operational switching, short circuits may occur on structures that are accessible to touch by the personnel performing the switching, the duration of the backup protection should be taken, and for the rest of the territory - the main protection.

Note. Workplace should be understood as a place for operational maintenance of electrical apparatus.

The placement of longitudinal and transverse horizontal grounding conductors should be determined by the requirements for limiting contact voltages to normalized values ​​and the convenience of connecting grounded equipment. The distance between longitudinal and transverse horizontal artificial ground electrodes should not exceed 30 m, and the depth of their laying in the ground should be at least 0.3 m. 0.2 m

In the case of combining grounding devices of different voltages into one common grounding device, the contact voltage must be determined by the highest short-circuit current to earth of the combined outdoor switchgear.

1.7.92. When making a grounding device in compliance with the requirements for its resistance or contact voltage, in addition to the requirements of 1.7.90-1.7.91, you should:

lay grounding conductors connecting equipment or structures to the ground electrode in the ground at a depth of at least 0.3 m;

lay longitudinal and transverse horizontal grounding conductors (in four directions) near the locations of grounded neutrals of power transformers, short circuiters.

When the grounding device goes beyond the fence of the electrical installation, horizontal ground electrodes located outside the territory of the electrical installation should be laid at a depth of at least 1 m. In this case, the external contour of the grounding device is recommended to be made in the form of a polygon with obtuse or rounded corners.

1.7.93. It is not recommended to connect the external fence of electrical installations to a grounding device.

If 110 kV and higher overhead lines depart from the electrical installation, then the fence should be grounded using vertical ground electrodes 2-3 m long installed at the fence posts along its entire perimeter after 20-50 m. Installation of such ground electrodes is not required for a fence with metal posts and with those racks made of reinforced concrete, the reinforcement of which is electrically connected to the metal links of the fence.

To exclude the electrical connection of the external fence with the grounding device, the distance from the fence to the elements of the grounding device located along it from the inside, outside or on both sides must be at least 2 m. Horizontal ground electrodes, pipes and cables with a metal sheath or armor and other metal communications should be laid in the middle between the posts of the fence at a depth of at least 0.5 m. not less than 1 m.

The power supply of electrical receivers installed on the outer fence should be carried out from isolation transformers. These transformers are not allowed to be installed on the fence. The line connecting the secondary winding of the isolating transformer with the power receiver located on the fence must be isolated from the ground by the calculated voltage value at the grounding device.

If it is not possible to perform at least one of the above measures, then the metal parts of the fence should be connected to a grounding device and potential equalization should be performed so that the contact voltage from the external and inner sides fences did not exceed the permissible values. When performing a grounding device according to the permissible resistance, for this purpose a horizontal grounding conductor must be laid on the outer side of the fence at a distance of 1 m from it and at a depth of 1 m. This grounding conductor should be connected to the grounding device at least at four points.

1.7.94. If the grounding device of an electrical installation with a voltage above 1 kV of a network with an effectively grounded neutral is connected to the grounding device of another electrical installation using a cable with a metal sheath or armor or other metal ties, then in order to equalize the potentials around the specified other electrical installation or the building in which it is located, one of the following conditions must be met:

1) laying in the ground at a depth of 1 m and at a distance of 1 m from the foundation of the building or from the perimeter of the territory occupied by the equipment, a ground electrode connected to the potential equalization system of this building or this territory, and at the entrances and entrances to the building - laying conductors on a distance of 1 and 2 m from the ground electrode at a depth of 1 and 1.5 m, respectively, and the connection of these conductors to the ground electrode;

2) the use of reinforced concrete foundations as grounding conductors in accordance with 1.7.109, if this ensures an acceptable level of potential equalization. Providing conditions for equalizing potentials by means of reinforced concrete foundations used as grounding conductors is determined in accordance with GOST 12.1.030 “Electrical safety. Protective grounding, zeroing.

It is not necessary to fulfill the conditions specified in paragraphs. 1 and 2, if there are asphalt pavements around the buildings, including at the entrances and at the entrances. If there is no blind area at any entrance (entrance), potential equalization must be performed at this entrance (entrance) by laying two conductors, as indicated in paragraphs. 1, or the condition according to paragraphs. 2. In this case, the requirements of 1.7.95 must be met in all cases.

1.7.95. In order to avoid potential carryover, it is not allowed to supply electrical receivers located outside the grounding devices of electrical installations with a voltage above 1 kV of a network with an effectively grounded neutral, from windings up to 1 kV with a grounded neutral of transformers located within the circuit of the grounding device of an electrical installation with a voltage above 1 kV.

If necessary, such electrical receivers can be powered from a transformer with an isolated neutral on the side with a voltage of up to 1 kV along cable line, made with a cable without a metal sheath and without armor, or along an overhead line.

In this case, the voltage on the grounding device must not exceed the operating voltage of the breakdown fuse installed on the low voltage side of the transformer with isolated neutral.

The power supply of such electrical receivers can also be carried out from an isolating transformer. The isolation transformer and the line from its secondary winding to the power receiver, if it passes through the territory occupied by the grounding device of an electrical installation with a voltage above 1 kV, must be insulated from the ground by the calculated value of the voltage at the grounding device.

Grounding devices for electrical installations with voltages above 1 kV in networks with isolated neutral

1.7.96. In electrical installations with a voltage above 1 kV of a network with an isolated neutral, the resistance of the grounding device during the passage of the rated earth fault current at any time of the year, taking into account the resistance of natural grounding conductors, should be

R£250/ I,

but not more than 10 ohms, where I- rated earth fault current, A.

The following is taken as the rated current:

1) in networks without compensation capacitive currents- earth fault current;

2) in networks with compensation of capacitive currents:

for grounding devices to which compensating devices are connected, a current equal to 125% of the rated current of the most powerful of these devices;

for grounding devices to which compensating devices are not connected, the earth fault current passing in this network when the most powerful of the compensating devices is turned off.

The rated earth fault current must be determined for that of the network schemes possible in operation, in which this current has the greatest value.

1.7.97. When using a grounding device simultaneously for electrical installations with voltage up to 1 kV with isolated neutral, the conditions of 1.7.104 must be met.

When using a grounding device simultaneously for electrical installations with a voltage of up to 1 kV with a solidly grounded neutral, the resistance of the grounding device must not exceed that specified in 1.7.101, or sheaths and armor of at least two cables for voltages up to or above 1 kV or both voltages must be attached to the grounding device , with a total length of these cables of at least 1 km.

1.7.98. For substations with a voltage of 6-10 / 0.4 kV, one common grounding device must be made, to which must be connected:

1) transformer neutral on the side with voltage up to 1 kV;

2) transformer housing;

3) metal sheaths and armor of cables with voltage up to 1 kV and above;

4) open conductive parts of electrical installations with voltage up to 1 kV and above;

5) third-party conductive parts.

Around the area occupied by the substation, at a depth of at least 0.5 m and at a distance of not more than 1 m from the edge of the foundation of the substation building or from the edge of the foundations of openly installed equipment, a closed horizontal grounding conductor (circuit) connected to the grounding device must be laid.

1.7.99. A grounding device of a network with a voltage above 1 kV with an isolated neutral, combined with a grounding device of a network with a voltage above 1 kV with an effectively grounded neutral into one common grounding device, must also meet the requirements of 1.7.89-1.7.90.

Grounding devices of electrical installations with voltage up to 1 kV in networks with dead-earthed neutral

1.7.100. In electrical installations with a solidly grounded neutral, the neutral of a three-phase alternating current generator or transformer, the midpoint of a direct current source, one of the terminals of a single-phase current source must be connected to the ground electrode using a ground conductor.

An artificial earth conductor intended for neutral earthing should, as a rule, be located near the generator or transformer. For intrashop substations, it is allowed to place the ground electrode near the wall of the building.

If the foundation of the building in which the substation is located is used as natural grounding conductors, the neutral of the transformer should be grounded by attaching at least two metal columns or to embedded parts welded to the reinforcement of at least two reinforced concrete foundations.

When the built-in substations are located on different floors of a multi-storey building, the neutral grounding of the transformers of such substations must be carried out using a specially laid grounding conductor. In this case, the grounding conductor must be additionally connected to the building column closest to the transformer, and its resistance is taken into account when determining the spreading resistance of the grounding device to which the transformer neutral is connected.

In all cases, measures must be taken to ensure the continuity of the ground circuit and to protect the ground conductor from mechanical damage.

If in PEN- the conductor connecting the neutral of the transformer or generator with the bus PEN switchgear with voltage up to 1 kV, a current transformer is installed, then the grounding conductor must not be connected directly to the neutral of the transformer or generator, but to PEN conductor, if possible immediately after the current transformer. In that case, the separation PEN- conductor on RE- and N- conductors in the system TN-S must also be carried out behind the current transformer. The current transformer should be placed as close as possible to the neutral terminal of the generator or transformer.

1.7.101. The resistance of the grounding device to which the neutrals of the generator or transformer or the leads of a single-phase current source are connected, at any time of the year should be no more than 2, 4 and 8 ohms, respectively, at line voltages of 660, 380 and 220 V of a three-phase current source or 380, 220 and 127 In a single-phase current source. This resistance must be provided taking into account the use of natural grounding conductors, as well as grounding conductors for repeated grounding. PEN- or PE- an overhead line conductor with a voltage of up to 1 kV with a number of outgoing lines of at least two. The resistance of the ground electrode located in close proximity to the neutral of the generator or transformer or the output of a single-phase current source should be no more than 15, 30 and 60 Ohms, respectively, at line voltages of 660, 380 and 220 V of a three-phase current source or 380, 220 and 127 V of a single-phase current source current.

With earth resistivity r >

1.7.102. At the ends of overhead lines or branches from them longer than 200 m, as well as at the inputs of overhead lines to electrical installations in which automatic power off is applied as a protective measure in case of indirect contact, re-grounding must be performed PEN-conductor. In this case, first of all, natural grounding should be used, for example, underground parts of supports, as well as grounding devices designed for lightning surges (see Chap. 2.4).

The indicated repeated groundings are performed if more frequent groundings are not required under the conditions of lightning surge protection.

Re-grounding PEN-conductor in DC networks must be made using separate artificial grounding conductors, which should not have metal connections with underground pipelines.

Grounding conductors for repeated groundings PEN-conductor must have dimensions not less than those given in Table. 1.7.4.

Table 1.7.4

The smallest dimensions of grounding conductors and grounding conductors laid in the ground

Material	Section profile	Diameter, mm	Cross-sectional area, mm	Wall thickness, mm
	Rectangular
galvanized	for vertical grounding;
	for horizontal earthing
	Rectangular
	Rectangular
	Multiwire rope

* Diameter of each wire.

1.7.103. The total spreading resistance of grounding conductors (including natural ones) of all repeated groundings PEN- the conductor of each overhead line at any time of the year should be no more than 5, 10 and 20 Ohms, respectively, at line voltages of 660, 380 and 220 V of a three-phase current source or 380, 220 and 127 V of a single-phase current source. In this case, the spreading resistance of the grounding conductor of each of the repeated groundings should be no more than 15, 30 and 60 ohms, respectively, at the same voltages.

With the specific earth resistance r > 100 Ohm×m, it is allowed to increase the indicated norms by 0.01r times, but not more than tenfold.

Grounding devices of electrical installations with voltage up to 1 kV in networks with isolated neutral

1.7.104. Resistance of the earthing device used for protective earthing of exposed conductive parts in the system IT must meet the condition:

R £ U etc / I,

where R- grounding device resistance, Ohm;

U pr - touch voltage, the value of which is assumed to be 50 V (see also 1.7.53);

I - full current earth fault, a.

As a rule, it is not required to accept the resistance value of the grounding device as less than 4 ohms. Grounding device resistance up to 10 Ohm is allowed if the above condition is met, and the power of generators or transformers does not exceed 100 kV × A, including the total power of generators or transformers operating in parallel.

Grounding devices in areas with high earth resistivity

1.7.105. Grounding devices of electrical installations with voltages above 1 kV with an effectively grounded neutral in areas with high earth resistivity, including permafrost areas, are recommended to be performed in compliance with the requirements for touch voltage (1.7.91).

In rocky structures, it is allowed to lay horizontal ground electrodes at a shallower depth than required by 1.7.91-1.7.93, but not less than 0.15 m. In addition, it is allowed not to carry out the vertical ground electrodes required by 1.7.90 at the entrances and at the entrances.

1.7.106. When constructing artificial ground electrodes in areas with high earth resistivity, the following measures are recommended:

1) the installation of vertical ground electrodes of increased length, if the resistivity of the earth decreases with depth, and there are no natural recessed ground conductors (for example, wells with metal casing pipes);

2) the installation of remote ground electrode systems, if there are places with a lower earth resistivity near (up to 2 km) from the electrical installation;

3) laying in trenches around horizontal ground electrodes in rocky structures of wet clay soil, followed by tamping and backfilling with crushed stone to the top of the trench;

4) the use of artificial soil treatment in order to reduce its resistivity, if other methods cannot be applied or do not give the desired effect.

1.7.107. In areas of permafrost, in addition to the recommendations given in 1.7.106, one should:

1) place ground electrodes in non-freezing water bodies and thawed zones;

2) use well casing pipes;

3) in addition to deep earthing, use extended earthing at a depth of about 0.5 m, designed to work in summer time during thawing of the surface layer of the earth;

4) create artificial thawed zones.

1.7.108. In electrical installations with voltages above 1 kV, as well as up to 1 kV with an isolated neutral for earth with a resistivity of more than 500 Ohm × m, if the measures provided for in 1.7.105-1.7.107 do not allow obtaining earthing conductors acceptable for economic reasons, it is allowed to increase the required this chapter, the values ​​of the resistance of grounding devices by a factor of 0.002r, where r is the equivalent resistivity of the earth, Ohm × m. In this case, the increase in the resistance of grounding devices required by this chapter should not be more than tenfold.

Earthing switches

1.7.109. As natural grounding can be used:

1) metal and reinforced concrete structures of buildings and structures in contact with the ground, including reinforced concrete foundations of buildings and structures with protective waterproofing coatings in non-aggressive, slightly aggressive and medium-aggressive environments;

2) metal water pipes laid in the ground;

3) casing pipes of boreholes;

4) metal sheet piles of hydraulic structures, conduits, embedded parts of gates, etc.;

5) rail tracks of main non-electrified railways and access roads in the presence of a deliberate arrangement of jumpers between the rails;

6) other metal structures and structures located in the ground;

7) metal sheaths of armored cables laid in the ground. Cable sheaths can serve as the only grounding conductors when the number of cables is at least two. Aluminum cable sheaths are not allowed to be used as grounding conductors.

1.7.110. It is not allowed to use pipelines of flammable liquids, flammable or explosive gases and mixtures and sewerage and central heating pipelines as ground electrodes. These restrictions do not exclude the need to connect such pipelines to a grounding device in order to equalize potentials in accordance with 1.7.82.

Reinforced concrete structures of buildings and structures with prestressed reinforcement should not be used as grounding conductors, however, this restriction does not apply to overhead lines and support structures of outdoor switchgear.

The possibility of using natural grounding conductors according to the condition of the density of the currents flowing through them, the need for welding reinforcing bars of reinforced concrete foundations and structures, welding anchor bolts of steel columns to reinforcing bars of reinforced concrete foundations, as well as the possibility of using foundations in highly aggressive environments should be determined by calculation.

1.7.111. Artificial ground electrodes can be made of black or galvanized steel or copper.

Artificial ground electrodes should not be colored.

The material and smallest dimensions of the ground electrodes must correspond to those given in Table. 1.7.4.

1.7.112. The cross section of horizontal grounding conductors for electrical installations with voltages above 1 kV should be selected according to the condition of thermal resistance at an allowable heating temperature of 400 ° C (short-term heating corresponding to the time of protection and switch off).

If there is a risk of corrosion of the grounding devices, one of the following measures should be taken:

to increase the cross-sections of grounding conductors and grounding conductors, taking into account their estimated service life;

use earthing switches and earthing conductors with galvanized coating or copper.

In this case, one should take into account the possible increase in the resistance of grounding devices due to corrosion.

The trenches for horizontal grounding conductors must be filled with homogeneous soil that does not contain crushed stone and construction debris.

Earthing conductors should not be located (used) in places where the earth dries out under the influence of heat from pipelines, etc.

Grounding conductors

1.7.113. Cross-sections of grounding conductors in electrical installations with voltage up to 1 kV must comply with the requirements of 1.7.126 for protective conductors.

The smallest sections of grounding conductors laid in the ground must correspond to those given in Table. 1.7.4.

Laying aluminum bare conductors in the ground is not allowed.

1.7.114. In electrical installations with voltages above 1 kV, the cross-sections of the grounding conductors must be chosen so that when flowing through them maximum current single-phase short circuit in electrical installations with an effectively grounded neutral or two-phase short circuit current in electrical installations with isolated neutral, the temperature of the grounding conductors did not exceed 400 ° C (short-term heating corresponding to the total time of the protection and tripping of the circuit breaker).

1.7.115. In electrical installations with voltages above 1 kV with an insulated neutral, the conductivity of grounding conductors with a cross section of up to 25 mm 2 for copper or equivalent from other materials must be at least 1/3 of the conductivity of phase conductors. As a rule, the use of copper conductors with a cross section of more than 25 mm 2, aluminum - 35 mm 2, steel - 120 mm 2 is not required.

1.7.116. In order to carry out measurements of the resistance of the earthing device, it should be possible to disconnect the earthing conductor in a convenient place. In electrical installations with voltages up to 1 kV, this place, as a rule, is the main ground bus. Disconnecting the earth conductor must only be possible with a tool.

1.7.117. The grounding conductor connecting the working (functional) grounding conductor to the main grounding bus in electrical installations with voltage up to 1 kV must have a cross section of at least: copper - 10 mm 2, aluminum - 16 mm 2, steel - 75 mm 2.

1.7.118. An identification mark must be provided at the places where grounding conductors enter buildings.

Main ground bus

1.7.119. The main ground bus can be made inside the input device of the electrical installation with voltage up to 1 kV or separately from it.

Inside the input device, a bus should be used as the main ground bus. RE.

When installed separately, the main ground bus must be located in an accessible, convenient place for maintenance near the input device.

The cross section of a separately installed main ground bus must be at least RE (pen)-conductor of the supply line.

The main ground bus should usually be copper. It is allowed to use the main earthing bar made of steel. The use of aluminum tires is not allowed.

The busbar design shall provide for the possibility of individual disconnection of the conductors attached to it. Disconnection must only be possible with the use of a tool.

In places accessible only to qualified personnel (for example, switchboard rooms of residential buildings), the main earth bus should be installed openly. In places accessible to unauthorized persons (for example, entrances or basements of houses), it must have a protective shell - a cabinet or box with a key-lockable door. A sign must be placed on the door or on the wall above the tire.

1.7.120. If the building has several separate inputs, the main ground bus must be made for each input device. If there are built-in transformer substations, the main ground bus must be installed near each of them. These tires must be connected by a potential equalization conductor, the cross section of which must be at least half the cross section RE (pen)-conductor of that line among the substations outgoing from the low-voltage shields, which has the largest cross section. Third-party conductive parts may be used to connect several main earth busbars if they comply with the requirements of 1.7.122 for the continuity and conductivity of the electrical circuit.

Protective conductors ( pe- conductors)

1.7.121. As RE- conductors in electrical installations with voltage up to 1 kV can be used:

1) specially provided conductors:

veins multicore cables;

insulated or uninsulated wires in a common sheath with phase wires;

permanently laid insulated or bare conductors;

2) open conductive parts of electrical installations:

aluminum cable sheaths;

steel pipes for electrical wiring;

metal sheaths and supporting structures of busbars and complete devices factory made.

Metal boxes and trays of electrical wiring can be used as protective conductors, provided that the design of the boxes and trays provides for such use, as indicated in the manufacturer's documentation, and their location excludes the possibility of mechanical damage;

3) some third party conductive parts:

metal building structures of buildings and structures (trusses, columns, etc.);

reinforcement of reinforced concrete building structures of buildings, subject to the requirements of 1.7.122;

metal structures for industrial purposes (crane rails, galleries, platforms, elevator shafts, elevators, elevators, channel framing, etc.).

1.7.122. Use of exposed and third-party conductive parts as pe- conductors are allowed if they meet the requirements of this chapter for the conductivity and continuity of the electrical circuit.

Third party conductive parts can be used as RE- conductors, if they, in addition, simultaneously meet the following requirements:

1) the continuity of the electrical circuit is ensured either by their design or by appropriate connections protected from mechanical, chemical and other damage;

2) their dismantling is impossible unless measures are provided to preserve the continuity of the circuit and its conductivity.

1.7.123. Not allowed to be used as RE- conductors:

metal shells insulating tubes and tubular wires, carrying cables for cable wiring, metal hoses, as well as lead sheaths of wires and cables;

gas supply pipelines and other pipelines of combustible and explosive substances and mixtures, sewerage and central heating pipes;

water pipes with insulating inserts in them.

1.7.124. Zero protective conductors of circuits are not allowed to be used as zero protective conductors of electrical equipment powered by other circuits, as well as to use open conductive parts of electrical equipment as zero protective conductors for other electrical equipment, with the exception of shells and supporting structures of busbars and factory-made complete devices that provide the ability to connecting protective conductors to them in the right place.

1.7.125. The use of specially provided protective conductors for other purposes is not permitted.

1.7.126. The smallest cross-sectional areas of protective conductors must comply with Table. 1.7.5.

The cross-sectional areas are given for the case when the protective conductors are made of the same material as the phase conductors. The cross sections of protective conductors made of other materials must be equivalent in conductivity to those given.

Table 1.7.5

The smallest sections of protective conductors

It is allowed, if necessary, to take the cross-section of the protective conductor less than required, if it is calculated according to the formula (only for an opening time £ 5 s):

S ³ I /k,

where S- cross-sectional area of ​​​​the protective conductor, mm 2;

I- short-circuit current, providing the time of disconnection of the damaged circuit by the protective device in accordance with Table. 1.7.1 and 1.7.2 or for a time not exceeding 5 s in accordance with 1.7.79, A;

t- response time of the protective device, s;

k- coefficient, the value of which depends on the material of the protective conductor, its insulation, initial and final temperatures. Meaning k for protective conductors in various conditions are given in table. 1.7.6-1.7.9.

If the calculation results in a cross section that is different from that given in Table. 1.7.5, then the nearest larger value should be chosen, and when obtaining a non-standard section, conductors of the nearest larger standard section should be used.

The values ​​of the maximum temperature when determining the cross section of the protective conductor must not exceed the maximum permissible heating temperatures of the conductors during short circuit in accordance with Ch. 1.4, and for electrical installations in hazardous areas must comply with GOST 22782.0 “Explosion-proof electrical equipment. General technical requirements and test methods".

1.7.127. In all cases, the cross section of copper protective conductors that are not part of the cable or are not laid in a common sheath (pipe, box, on the same tray) with phase conductors must be at least:

• 2.5 mm 2 - in the presence of mechanical protection;
• 4 mm 2 - in the absence of mechanical protection.

The cross section of separately laid protective aluminum conductors must be at least 16 mm 2.

1.7.128. In system TN to meet the requirements of 1.7.88, it is recommended to lay zero protective conductors together with or in close proximity to phase conductors.

Table 1.7.6

Coefficient value k for insulated protective conductors not included in the cable, and for bare conductors touching the cable sheath (the initial temperature of the conductor is assumed to be 30 °C)

Parameter	Insulation material
	Polyvinyl chloride (PVC)	Polyvinyl chloride (PVC)	Butyl rubber
Final temperature, °C
k conductor:
copper
aluminum
steel

Table 1.7.7

Coefficient value k for the protective conductor included in the stranded cable

Parameter	Insulation material
	Polyvinyl chloride (PVC)	Cross-linked polyethylene, ethylene propylene rubber	Butyl rubber
Initial temperature, °С
Final temperature, °C
Aluminum	Maximum temperature, °С
	Maximum temperature, °С

* The specified temperatures are allowed if they do not impair the quality of the joints.

1.7.129. In places where damage to the insulation of phase conductors is possible as a result of sparking between an uninsulated zero protective conductor and a metal sheath or structure (for example, when laying wires in pipes, boxes, trays), zero protective conductors must have insulation equivalent to the insulation of phase conductors.

1.7.130. Non-isolated RE- conductors must be protected from corrosion. At the intersections RE- conductors with cables, pipelines, railway tracks, at the points of their entry into buildings and in other places where mechanical damage is possible RE- conductors, these conductors must be protected.

At the intersection of expansion joints and settlement joints, length compensation should be provided. RE- conductors.

Combined zero protective and zero working conductors ( pen- conductors)

1.7.131. In multi-phase circuits in the system TN for permanently laid cables, the cores of which have a cross-sectional area of ​​at least 10 mm 2 for copper or 16 mm 2 for aluminum, the functions of zero protective ( RE) and zero worker ( N) conductors can be combined in one conductor ( pen-conductor).

1.7.132. It is not allowed to combine the functions of the zero protective and zero working conductors in single-phase and direct current circuits. A separate third conductor must be provided as a zero protective conductor in such circuits. This requirement does not apply to branches from overhead lines with voltage up to 1 kV to single-phase consumers of electricity.

1.7.133. It is not allowed to use third-party conductive parts as the only pen-conductor.

This requirement does not preclude the use of exposed and third-party conductive parts as an additional pen-conductor when connecting them to the potential equalization system.

1.7.134. Specially provided pen- conductors must comply with the requirements of 1.7.126 for the cross section of protective conductors, as well as the requirements of Ch. 2.1 to the zero working conductor.

Insulation pen- conductors must be equivalent to the insulation of the phase conductors. No need to insulate the bus PEN busbars of low-voltage complete devices.

1.7.135. When the zero working and zero protective conductors are separated starting from any point of the electrical installation, it is not allowed to combine them beyond this point along the course of energy distribution. At the place of separation pen- conductor on the zero protective and zero working conductors, it is necessary to provide separate clamps or busbars for conductors interconnected. pen- the conductor of the supply line must be connected to the terminal or busbar of the zero protective RE-conductor.

Conductors of the potential equalization system

1.7.136. As conductors of the potential equalization system, open and third-party conductive parts specified in 1.7.121, or specially laid conductors, or a combination of them can be used.

1.7.137. The cross section of the conductors of the main potential equalization system must be at least half the largest cross section of the protective conductor of the electrical installation, if the cross section of the potential equalization conductor does not exceed 25 mm 2 for copper or equivalent from other materials. Larger conductors are generally not required. The cross section of the conductors of the main potential equalization system in any case should be at least: copper - 6 mm 2, aluminum - 16 mm 2, steel - 50 mm 2.

1.7.138. The cross section of the conductors of the additional potential equalization system must be at least:

when connecting two open conductive parts - the section of the smaller of the protective conductors connected to these parts;

when connecting an open conductive part and a third-party conductive part - half the cross section of the protective conductor connected to the open conductive part.

Cross-sections of additional potential equalization conductors that are not part of the cable must comply with the requirements of 1.7.127.

Connections and connections of grounding, protective conductors and conductors of the potential equalization and equalization system

1.7.139. Connections and connections of grounding, protective conductors and conductors of the potential equalization and equalization system must be reliable and ensure the continuity of the electrical circuit. Connections of steel conductors are recommended to be made by welding. It is allowed indoors and in outdoor installations without aggressive media to connect grounding and neutral protective conductors in other ways that ensure the requirements of GOST 10434 “Electrical contact connections. General technical requirements” for the 2nd class of connections.

Connections must be protected from corrosion and mechanical damage.

For bolted connections, measures must be taken to prevent contact loosening.

1.7.140. Connections must be accessible for inspection and testing, with the exception of joints filled with compound or sealed, as well as welded, soldered and pressed connections to heating elements in heating systems and their connections located in floors, walls, ceilings and in the ground.

1.7.141. When using devices for monitoring the continuity of the ground circuit, it is not allowed to connect their coils in series (in a cut) with protective conductors.

1.7.142. Connections of grounding and neutral protective conductors and potential equalization conductors to open conductive parts must be made using bolted connections or welding.

Connections of equipment subject to frequent dismantling or installed on moving parts or parts subject to shock and vibration must be made using flexible conductors.

Connections of protective conductors of electrical wiring and overhead lines should be carried out by the same methods as the connections of phase conductors.

When using natural ground electrodes for grounding electrical installations and third-party conductive parts as protective conductors and potential equalization conductors, contact connections should be made using the methods provided for by GOST 12.1.030 “SSBT. Electrical safety. Protective grounding, zeroing.

1.7.143. The places and methods of connecting grounding conductors to extended natural grounding conductors (for example, to pipelines) should be chosen so that when the grounding conductors are disconnected for repair work, the expected contact voltages and the calculated values ​​​​of the resistance of the grounding device do not exceed safe values.

Shunting of water meters, valves, etc. should be carried out using a conductor of the appropriate cross section, depending on whether it is used as a protective conductor of the potential equalization system, a neutral protective conductor or a protective earth conductor.

1.7.144. The connection of each open conductive part of the electrical installation to the zero protective or protective earth conductor must be carried out using a separate branch. Sequential connection of open conductive parts into the protective conductor is not allowed.

The connection of conductive parts to the main potential equalization system must also be carried out using separate branches.

The connection of conductive parts to an additional potential equalization system can be performed using both separate branches and connection to one common permanent conductor.

1.7.145. It is not allowed to include switching devices in the circuit RE- and pen- conductors, with the exception of cases of supplying electrical receivers with the help of plug connectors.

It is also allowed to simultaneously disconnect all conductors at the input to electrical installations of individual residential, country and garden houses and similar objects powered by single-phase branches from overhead lines. At the same time, the separation pen- conductor on RE- and n- conductors must be made before the introductory protective switching device.

1.7.146. If the protective conductors and/or potential equalization conductors can be disconnected using the same plug connector as the corresponding phase conductors, the socket and plug of the plug connector must have special protective contacts for connecting protective conductors or potential equalization conductors to them.

If the body of the socket outlet is made of metal, it must be connected to the protective contact of this socket.

Portable electrical receivers

1.7.147. Portable power receivers in the Rules include power receivers that can be in the hands of a person during their operation (hand-held power tools, portable household electrical appliances, portable electronic equipment, etc.).

1.7.148. Portable AC power receivers should be powered from a mains voltage not exceeding 380/220 V.

Depending on the category of the premises according to the level of danger of electric shock to people (see Chap. 1.1), for protection against indirect contact in circuits supplying portable electrical receivers, automatic power off, protective electrical separation of circuits, extra low voltage, double insulation can be used.

1.7.149. When using automatic power off, metal cases of portable electrical receivers, with the exception of double-insulated electrical receivers, must be connected to the neutral protective conductor in the system TN or grounded in the system IT, for which a special protective ( RE) a conductor located in the same sheath with phase conductors (the third core of a cable or wire - for single-phase and direct current electrical receivers, the fourth or fifth core - for three-phase current electrical receivers), attached to the body of the electrical receiver and to the protective contact of the plug connector. RE- the conductor must be copper, flexible, its cross section must be equal to the cross section of the phase conductors. The use of a zero worker for this purpose ( N) conductor, including those located in a common sheath with phase conductors, is not allowed.

1.7.150. It is allowed to use stationary and separate portable protective conductors and potential equalization conductors for portable electrical receivers of testing laboratories and experimental installations, the movement of which is not provided for during their operation. In this case, stationary conductors must meet the requirements of 1.7.121-1.7.130, and portable conductors must be copper, flexible and have a cross section not less than that of phase conductors. When laying such conductors not as part of a cable common with phase conductors, their cross-sections must be at least those specified in 1.7.127.

1.7.151. For additional protection against direct contact and indirect contact, sockets with rated current no more than 20 A outdoor installation, as well as indoor installation, but to which portable electrical receivers used outside buildings or in rooms with increased danger and especially dangerous can be connected, must be protected by residual current devices with a rated breaking differential current of not more than 30 mA. It is allowed to use hand-held power tools equipped with RCD plugs.

When using protective electrical separation of circuits in cramped rooms with conductive floors, walls and ceilings, as well as in the presence of requirements in the relevant chapters of the PUE in other rooms with special danger, each outlet must be powered by an individual isolating transformer or from its separate winding.

When using extra-low voltage, portable electrical receivers with voltage up to 50 V must be supplied from a safety isolating transformer.

1.7.152. To connect portable power receivers to the mains, plug connectors that comply with the requirements of 1.7.146 should be used.

In plug connectors of portable electrical receivers, extension wires and cables, the conductor on the side of the power source must be connected to the socket, and on the side of the electrical receiver - to the plug.

1.7.154. Protective conductors of portable wires and cables must be marked with yellow-green stripes.

Mobile electrical installations

1.7.155. Requirements for mobile electrical installations do not apply to:

• ship electrical installations;
• electrical equipment placed on moving parts of machine tools, machines and mechanisms;
• electrified transport;
• residential vans.

For testing laboratories, the requirements of other relevant regulations must also be met.

1.7.156. An autonomous mobile power source is a source that allows consumers to be powered independently of stationary sources of electricity (power systems).

1.7.157. Mobile electrical installations can be powered by stationary or autonomous mobile power sources.

Power supply from a stationary electrical network should, as a rule, be carried out from a source with a solidly grounded neutral using systems TN-S or TN-C-S. Combining the functions of a zero protective conductor RE and zero working conductor N in one common conductor PEN inside a mobile electrical installation is not allowed. Separation pen- supply line conductor on RE- and n- conductors must be carried out at the point of connection of the installation to the power supply.

When powered from an autonomous mobile source, its neutral, as a rule, must be isolated.

1.7.158. When powering stationary electrical receivers from autonomous mobile power sources, the neutral mode of the power source and protection measures must correspond to the neutral mode and protection measures adopted for stationary electrical receivers.

1.7.159. In the case of a mobile electrical installation being powered from a stationary power source, for protection against indirect contact, automatic power off must be performed in accordance with 1.7.79 using an overcurrent protection device. In this case, the shutdown time given in Table. 1.7.1, must be halved or, in addition to the overcurrent protection device, a residual current residual current device must be used.

In special electrical installations, the use of RCDs that respond to the potential of the housing relative to the ground is allowed.

When using an RCD that responds to the potential of the case relative to the ground, the setting for the value of the tripping voltage should be equal to 25 V with a trip time of not more than 5 s.

1.7.160. At the point of connection of the mobile electrical installation to the power source, an overcurrent protection device and RCD should be installed that responds to differential current, the rated differential breaking current of which must be 1-2 steps higher than the corresponding RCD current installed at the input to the mobile electrical installation.

If necessary, at the input to the mobile electrical installation, protective electrical separation of circuits can be applied in accordance with 1.7.85. At the same time, the isolation transformer, as well as the introductory protective device must be enclosed in an insulating sheath.

The device for connecting the power input to a mobile electrical installation must be double insulated.

1.7.161. When applying automatic power off in the system IT for protection against indirect contact, the following must be met:

protective earth in combination with continuous insulation monitoring acting on the signal;

automatic power off, providing a shutdown time in case of a two-phase short circuit to exposed conductive parts in accordance with Table. 1.7.10.

Table 1.7.10

The longest allowable protective shutdown time for the system IT in mobile electrical installations powered by an autonomous mobile source

To ensure automatic disconnection of the supply, an overcurrent protective device must be used in combination with an RCD reacting to differential current or a continuous insulation monitoring device acting to trip, or, in accordance with 1.7.159, an RCD reacting to the case potential relative to earth .

1.7.162. At the input to the mobile electrical installation, a main potential equalization bus must be provided that meets the requirements of 1.7.119 to the main ground bus, to which the following must be connected:

zero protective conductor RE or protective conductor RE supply line;

protective conductor of a mobile electrical installation with protective conductors of exposed conductive parts attached to it;

potential equalization conductors of the housing and other third-party conductive parts of a mobile electrical installation;

grounding conductor connected to the local grounding conductor of the mobile electrical installation (if any).

If necessary, open and third-party conductive parts must be interconnected by means of additional potential equalization conductors.

1.7.163. Protective earthing of a mobile electrical installation in the system IT must be performed in compliance with the requirements either for its resistance or for the contact voltage in case of a single-phase short circuit to open conductive parts.

When making a grounding device in compliance with the requirements for its resistance, the value of its resistance should not exceed 25 ohms. It is allowed to increase the specified resistance in accordance with 1.7.108.

When the grounding device is made in compliance with the requirements for the contact voltage, the resistance of the grounding device is not standardized. In this case, the following condition must be met:

R s £25/ I h,

where R h - resistance of the grounding device of a mobile electrical installation, Ohm;

I h - full current of a single-phase short circuit to open conductive parts of a mobile electrical installation, A.

1.7.164. It is allowed not to carry out a local ground electrode system for protective grounding of a mobile electrical installation powered by an autonomous mobile power source with an isolated neutral in the following cases:

1) an autonomous power source and electrical receivers are located directly on the mobile electrical installation, their cases are interconnected by means of a protective conductor, and other electrical installations are not powered from the source;

2) an autonomous mobile power source has its own grounding device for protective grounding, all open conductive parts of a mobile electrical installation, its body and other third-party conductive parts are securely connected to the body of an autonomous mobile power source using a protective conductor, and in case of a two-phase short circuit to different cases of electrical equipment in a mobile the electrical installation is provided with an automatic power off time in accordance with Table. 1.7.10.

1.7.165. Autonomous mobile power sources with isolated neutral must have a device for continuous monitoring of insulation resistance relative to the housing (ground) with light and sound signals. It shall be possible to check the integrity of the insulation monitoring device and to switch it off.

It is allowed not to install a continuous insulation monitoring device with an action on a signal on a mobile electrical installation powered by such an autonomous mobile source, if the condition 1.7.164, paragraphs 2.

1.7.166. Protection against direct contact in mobile electrical installations must be ensured by the use of insulation of live parts, fences and shells with a degree of protection of at least IP 2X. The use of barriers and placement out of reach is not allowed.

In circuits supplying socket outlets for connecting electrical equipment used outside the premises of a mobile installation, additional protection in accordance with 1.7.151.

1.7.167. Protective and grounding conductors and potential equalization conductors must be copper, flexible, as a rule, be in a common sheath with phase conductors. The cross section of the conductors must meet the requirements:

• protective - 1.7.126-1.7.127;
• grounding - 1.7.113;
• potential equalization - 1.7.136-1.7.138.

When using the system IT it is allowed to lay protective and grounding conductors and potential equalization conductors separately from phase conductors.

1.7.168. It is allowed to simultaneously disconnect all conductors of the line supplying the mobile electrical installation, including the protective conductor, using one switching device (connector).

1.7.169. If the mobile installation is powered by plug-in connectors, the plug of the plug-in connector must be connected on the side of the mobile installation and sheathed with insulating material.

Electrical installations of premises for keeping animals

1.7.170. The power supply of electrical installations of livestock buildings should, as a rule, be carried out from a mains voltage of 380/220 V AC.

1.7.171. In order to protect people and animals from indirect contact, an automatic power-off must be performed using a system TN-C-S. Separation PEN-conductor to zero protective ( RE) and zero worker ( N) conductors should be carried out on the inlet plate. When supplying such electrical installations from built-in and attached substations, a system should be applied TN-S, while the zero working conductor must have insulation equivalent to the insulation of the phase conductors throughout its entire length.

The time of protective automatic power off in the premises for keeping animals, as well as in the premises connected with them with the help of third-party conductive parts, must comply with Table. 1.7.11.

Table 1.7.11

The longest allowable protective shutdown time for the system TN in animal rooms

If the specified tripping time cannot be guaranteed, additional protective measures are required, such as additional potential equalization.

1.7.172. pen- the conductor at the entrance to the room must be re-grounded. The value of the re-grounding resistance must comply with 1.7.103.

1.7.173. In premises for keeping animals, it is necessary to provide protection not only for people, but also for animals, for which an additional potential equalization system must be made, connecting all open and third-party conductive parts accessible to simultaneous contact (water pipes, vacuum pipes, metal fences of stalls, metal ties and etc.).

1.7.174. Potential equalization must be carried out in the area where animals are placed in the floor using a metal mesh or other device, which must be connected to an additional potential equalization system.

1.7.175. The device for equalizing and equalizing electrical potentials must provide a contact voltage of not more than 0.2 V in the normal mode of operation of the electrical equipment, and in emergency mode with a shutdown time greater than that indicated in Table. 1.7.11 for electrical installations in rooms with increased danger, especially dangerous and in outdoor installations - no more than 12 V.

1.7.176. For all group circuits supplying socket outlets, there must be additional protection against direct contact using an RCD with a rated residual breaking current of not more than 30 mA.

1.7.177. In livestock buildings, in which there are no conditions that require potential equalization, protection must be performed using an RCD with a rated differential breaking current of at least 100 mA, installed on the input shield.

The lack of grounding of electrical equipment or its incorrect implementation can lead to industrial injuries, failure of automation devices or their incorrect operation, errors in the readings of measuring equipment. This occurs as a result of insulation breakdown between current-carrying parts and the equipment case. As a result, voltage appears on the case and electric current flows, which can cause injury to a person and lead to malfunction of electrical devices. To avoid this, the part of the installation that is not in normal condition energized, connected to a grounding device. This process is called grounding.

Grounding device - a system consisting of a ground loop and conductors that ensure the safe passage of current through the ground. Based on the Rules for the Construction of Electrical Installations, natural grounding conductors can be:

1. Building frames (reinforced concrete or metal) that are connected to the ground.
2. Protective metal braid of cables laid in the ground (except aluminum)
3. Pipes of wells, water pipes laid in the ground (except for pipelines with flammable liquids, gases, mixtures)
4. supports high voltage lines power lines
5. Non-electrified railway tracks (provided that the rails are welded)

For artificial grounding, according to the rules, unpainted steel bars (with a diameter of more than 10 mm), a corner (with a shelf thickness of more than 4 mm), sheets (with a thickness of more than 4 mm and a sectional section of more than 48 mm2) are used. To create a system with artificial grounding, metal rods, a corner or sheets with the above thickness and cross section, but not less than 2.5 m long, are dug or driven into the ground near the structure. Then they are welded together using bar or sheet steel. This structure must be more than 0.5 m from the ground surface. According to the requirements, the building's ground loop must have at least two connections to the ground electrode.
Depending on the purpose, equipment grounding is divided into two types: protective and working. Protective grounding serves for the safety of personnel and prevents the possibility of electric shock to a person due to accidental contact with the body of the electrical installation. Housings of electrical installations and electrical machines that are not fixed on "dead-earthed" supports, electrical cabinets, metal boxes of switchboards, metal hose and pipes with power cables, metal braids of power cables are subject to protective grounding.
Working grounding is used when, for production needs, in the event of damage to the insulation and breakdown to the case, continued operation of the equipment in emergency mode is required. Thus, for example, the neutrals of transformers and generators are grounded. Also, working grounding includes connection to a common grounding network of lightning rods that protect electrical installations from direct lightning strikes.

According to the Rules for the Installation of Electrical Installations, electrical networks with a rated voltage of over 42 V at alternating current and over 110 V at direct current must be grounded.

Classification of grounding systems

There are the following grounding systems:

• The TN system (which in turn is divided into subspecies TN-C, TN-S, TN-C-S)
• TT system
• IT system

The letters in the names of the systems are taken from the Latin alphabet and are deciphered as follows:
T - (from terre) earth
N - (from neuter) neutral
C - (from combine) combine
S - (from separate) to separate
I - (from isole) isolated
By the letters in the names of grounding systems, you can find out how the power source is arranged and grounded, as well as the principle of consumer grounding.

TN system

This is the most famous and popular grounding system. Its main difference is the presence of a "dead-earthed" neutral of the power source. Those. the neutral wire of the supply substation is directly connected to the ground.
TN-C is a subspecies of the grounding system, which is characterized by a combined ground and neutral neutral conductor. Those. they go with one wire from the supply transformer to the consumer. The absence of a separate PE (protective neutral) conductor in this system is clearly a disadvantage. The TN-C system was widely used in Soviet buildings and is unsuitable for modern new buildings, because. it does not have the possibility of equipotential bonding in the bathroom.
TN-S is a system in which the protective conductor of the potential equalization system and the working neutral conductors go through separate wires from the power source to the electrical installation. This system is only gaining widespread use when connecting buildings to the power supply. Is the safest. The disadvantages include its high cost, tk. additional wiring required.
TN-C-S - a system in which the neutral protective conductor and the neutral worker are combined with a wire, and are separated at the entrance to switchboard. According to the requirements of the Electrical Installation Rules, this system requires additional grounding.

TT system

This is a system in which the supply substation and the consumer's electrical installation have different, independent of each other earthing switches. The scope of the TT system is mobile objects with consumer electrical installations. These include mobile containers, stalls, wagons, etc. In most cases, a module-pin grounding is used for the consumer in the TT system.

IT system

A system in which the power supply is separated from ground through air or connected through high resistance, i.e. isolated. The neutral in this system is connected to earth through a large resistance. The IT system is used in laboratories and medical institutions that operate high-precision and sensitive equipment.

Motor grounding requirements

According to the requirements and regulations, the installed electric motor must be grounded before starting. The exception is those cases in which the motor housing is mounted on metal support, connected to the ground through the metal structure of the building or through the conductor of the ground electrode. In other cases, the motor housing must be connected by a wire to the ground loop of the building, made of a strip of metal by welding.



This is the working ground. Otherwise, if the insulation between the motor winding or current conductor and the motor housing is broken, the protective device will not work and will not turn off the power. And the engine will keep running.
Each electrical machine must have an individual connection to the ground. serial connection electric motors with a ground loop is prohibited, because if one of the connections to the ground conductor is broken, the entire circuit will be isolated from the ground. To install a protective earth, it is necessary to have an additional earth conductor in power cable, one end of which is connected to terminal box motor, and the other to the motor control cabinet. The electrical cabinet must first be connected to earth. In the event of a breakdown between the current conductor and this grounding conductor, a short-circuit current is formed, which will open the protective or switching device (thermal or current relay, circuit breaker).
The cross section of the grounding conductor that meets the requirements of the Electrical Installation Rules is given in table 1:

Table 1

Section of phase conductors, mm 2	The smallest section of protective conductors, mm 2
S≤16	S
16 < S≤35	16
S>35	S/2

The cross section of the phase conductors is calculated according to the current load of the consumer.

Requirements for grounding welding machines

As with any technological equipment that consumes electric current, for welding machines there are ground connection rules. In addition to the need to ground the body of the welding electrical installation with the ground loop of the building, one output of the secondary winding of the apparatus is grounded, and the electrode holder is connected to the second, respectively. At the same time, the output of the secondary winding requiring grounding must be indicated graphically and have a stationary output mount for convenient connection to the ground electrode. The transition resistance of the ground loop should not exceed 10 ohms. If it is necessary to increase the electrical conductivity of the ground loop, increase the contact area of ​​the connection.



Serial connection of welding machines with a ground electrode is also prohibited. Each apparatus must have a separate connection to the grounded main of the building.
Grounding consumer electrical installations is not a formality, but a necessary technical safety measure that will not only stabilize the operation of the equipment, but also save the lives of the personnel servicing and contacting it.

Introduction

Description, characteristics of the enterprise

a brief description of workshops

Characteristics of the work performed

Grounding and grounding of electrical equipment. Zeroing executions. Installation of protective earthing devices

1 General information

2 External ground loop and its installation

3 Measuring the resistance of earthing devices

4 Installation of the internal grounding network

5 PUE requirements for grounding electrical installations

Safety

1 Organization of the electrician's workplace

2 Safety requirements before starting work

3 Safety requirements during work

4 Safety requirements in emergency situations

5 Safety requirements at the end of work

Bibliography

Introduction

The electrical industry plays an important role in solving the problems of electrification, technical re-equipment of all branches of the national economy, mechanization, automation and identification of production processes.

The volume of electricity production in Russia by 2005 exceeds 1 trillion. kV/h Installed electric power individual enterprises reaches 3 million kW, and the number of electric machines on them - 100 thousand pieces. annual electricity consumption at a number of enterprises already today exceeds 5 billion kW/h. For every 10 years, the production and consumption of electricity in the world approximately doubles. The growth of labor productivity, the development of electrically intensive electrical processes, the implementation of security measures environment, the introduction of advanced technologies will lead in the period 1999-2010. to a further increase in the electric power of enterprises.

An important role in the development of domestic electrical engineering was played by the works of Russian scientists and inventors P.N. Yablochkova, A.N. Lodygina, M.O. Dolivo-Dobrovolsky and others. The priority in the creation and application of a three-phase AC system belongs to M.O. Dolivo-Dobrovolsky, who in 1891 carried out the transfer electrical energy with a power of about 150 kW at a voltage of 15 kV at a distance of 175 km. They also created synchronous generator, three-phase transformer and asynchronous motor.

In 1920, the All-Russian Congress of Soviets approved the State Plan for the Electrification of Russia (GOELRO), which provided for the construction of thirty new regional power plants with an energy production of up to 8.8 billion kWh per year within 10-15 years. This plan was completed in 10 years. Since 1930, large urban district thermal power plants have been gradually integrated into electrical systems, which to this day remain the main producers of electricity for the vast majority of enterprises.

Until 1960, the capacity of large generators of thermal power plants was 100 MW. Six to eight generators were installed at one power plant. Therefore, the capacity of large thermal power plants was 600-800 MW. After the development of blocks of 150-200 MW, the capacity of large power plants increased to 1200 MW, and after the development of blocks of 300 MW - to 2400 MW. Currently, thermal power plants with a capacity of 6000 MW with units of 500-800 MW are being introduced.

Efficiency of interconnection of power systems by saving the total installed capacity of generators due to the combination of load peaks of power systems shifted in time.

During the period of market reforms in Russia, the electric power industry, as before, is the most important life-supporting industry of the country. It includes over 700 power plants with a total capacity of 215.6 million kW.

The Unified Energy System of Russia is one of the world's largest highly automated electric power complexes that provides the production, transmission and distribution of electricity and centralized operational dispatch control of these processes. As part of the UES of Russia, about 450 large power plants of various departmental affiliations operate in parallel, with a total capacity of more than 200 million kW, and there are also over 2.5 million km of power transmission lines of various voltages, including 30 thousand km of backbone transmission lines with a voltage of 500, 750, 1150 kV.

Maintenance of electrical installations of industrial enterprises is carried out by hundreds of thousands of electricians, on whose qualifications the reliable and uninterrupted operation of electrical installations largely depends. The personnel must know the basic requirements of the Rules for the technical operation of electrical installations of consumers, GOSTs and other directive materials, as well as the design of electrical machines, transformers and devices, skillfully use the materials, tools, fixtures and equipment used in the operation of electrical installations.

1. Description, characteristics of the enterprise

"Omskshina" plant is one of the leading enterprises chemical industry Omsk region. The plant became part of the SIBUR holding - Russian Tires on January 1, 2006, which also includes almost all Russian tire industry enterprises. The finished products of the plant are automobile and aircraft tires of various assortments.

The company is located near the city center in industrial area of the city at 2 Buderkina Street. In fact, the main construction of the plant began in the autumn of 1941. The Yaroslavl and Leningrad tire plants were evacuated to Omsk. On February 24, 1942, the first tire in size 6.50-20 (for a lorry) rolled off the assembly line of the plant. This day is considered to be the birthday of the Omsk Tire Plant. In 1944, the plant was twice awarded the Red Banner of the USSR State Defense Committee.

Today, Omskshina is the second largest tire manufacturer in Russia. Three stages can be clearly traced in the history of the Omsk tire industry:

From 1942 to 1964 - the period of formation and development in the war and post-war years;

From 1964 to 1993 - the time of expansion of production, achievement of high economic indicators and development of the social sphere, ending with a period of decline in production;

From 1993 to the present - a period of privatization and restructuring of production, gaining new market positions.

2. Brief description of the shop

The finished products of the autotube workshop are various types of autotubes, as well as commercial rubber.

The equipment with which the autochamber shop is equipped and its quantity is presented in table 1.

Table 1. - List of equipment installed in the autocamera

Item No. Name of equipment Quantity 1 RS 270 rubber mixer ×30 32Rubber mixer RS ​​270 ×40 33 -grain of MCH 380/450 34 Drum Drum for granules 35valists individual SM 2100 660/66046 VALIARY DEMIRED SM 2130 660/66027 VALIALYS PD 800 550/55018 VALSTS INSTALLY PD 630 315/31519 Simplifier 60/160110 SimbaM/PECTIONAL DR 800/611111111111111111111111111111111111111111111111AROTHS IN 660312Турбовоздуходувка ТВ - 80 - 1,6813Агрегат измельчения резиновых отходов АПР 420/400114Машина одночервячная МЧТ - 250 315Машина одночервячная МЧТ - 200116Агрегат камерный317Агрегат флепповый118Станок стыковочный для ездовых камер ВМИ ЕПЕ1319Станок стыковочный для ездовых камер МИНЛАНД520Станок стыковочный для ездовых камер РОССИЯ221Индивидуальный вулканизатор камер ИВК - 458122Индивидуальный вулканизатор камер ИВК - 552723Individual vulcanizer of IVK chambers - 75924Individual vulcanizer of IVK chambers - 85225Vulcanizer of rim tapes VOL4926Hydraulic vulcanization press1427Buffing machine 828Valve bending machine929Chamber sleeve trimming machine230Stan ok for punching holes in flepps431Machine for punching valve heels132Device for screwing spools433Pneumatic knife for cutting rubber334Installation for checking auto-chambers for tightness2

3. Characteristics of the work performed

During my internship, I worked various works related directly to my specialty - electrician. Each working day began with a tour of the equipment and inspection of electrical installations. Also, in turn, the means were checked personal protection: mats, boots, gloves. After inspecting the equipment, an entry was made in the "Shift (operational) journal for duty personnel to record work Maintenance and repair of electrical equipment. The list of work, the assignment for the shift was also recorded in the journal. In addition to a certain task, I had to perform troubleshooting work that interfered with the productivity of the main production, i.e. replacement of a burned-out light bulb above the vulcanizer of the chambers or replacement of a burned-out engine on the punch of the second syringe of the machine. Shutdown and start-up of equipment (after a holiday) is logged.

I had to engage in locksmith work, the manufacture of fasteners for temporary wiring. I also had to perform rigging work not directly related to installation or maintenance, to take away the burned-out electric motor for rewinding.

Maintenance was carried out at transformer substation No. 26, maintenance of electrical machines (electric motor), as well as at switchgear 10 kW. Maintenance consisted of cleaning the installation from dirt and dust, drawing bolted connections.

4. Grounding and grounding of electrical equipment. Versions

zeroing. Installation of protective earthing devices

.1 General

If the insulation of electrical equipment is damaged, its various metal non-current-carrying parts may accidentally become energized, creating a danger of electric shock to a person. Touching equipment with damaged insulation, a person becomes a conductor for current to the ground. Currents from 0.05 A are dangerous for humans, and currents of 0.1 A are deadly.

The value of the current passing into the ground depends on the electrical resistance of the human body and the voltage of the damaged installation. The resistance of the human body varies widely: from several hundred to thousands of ohms, therefore, installations with relatively small voltage in relation to the earth.

The voltage relative to the ground in case of a short circuit to the case is the voltage between this case and ground points that are outside the zone of current spreading in the ground, but not closer than 20 meters from this zone.

One of the main measures to protect people from electric shock when touching installations that accidentally become energized is a protective earthing device.

Grounding is the intentional electrical connection of some part of an installation to earth, performed using earthing switches and earthing conductors.

A grounding conductor is a metal conductor or a group of conductors embedded in the ground.

A grounding conductor is a metal conductor connecting the grounded parts of an electrical installation with grounding conductors.

A grounding device is a combination of grounding conductors and grounding conductors. The safety of people is achieved only if the grounding device will have many times less resistance than the lowest resistance of the human body.

The resistance of the grounding device is the sum of the resistances of the grounding conductor relative to the earth and the grounding conductors, and it must be within the limits determined by the preliminary calculation. The maximum allowable resistance of grounding devices is determined by the voltage of the installation, the values ​​​​of earth fault currents, the presence of a neutral and some other conditions and are established by the current PUE (rules for electrical installations). Earth fault current - the current passing through the earth at the location of the fault.

To protect people from electric shock in case of damage to the insulation, metal non-current-carrying parts of electrical equipment are grounded. A set of measures and technical devices designed for this purpose is called protective grounding. Protective grounding is a deliberate connection to the ground under the means of grounding conductors and grounding conductors of non-current-carrying metal parts of electrical installations (disconnector drive handles, transformer casings, flanges of support insulators, transformer substation casings, etc.).

The task of protective grounding is to create a sufficiently low resistance between metal structures or the body of the protected device and the ground; in case of single-phase short circuits to the ground or to the case of conductive damaged parts of electrical installations, such a connection provides a decrease in current to a value that does not threaten human life and health, since the electrical resistance of his body is many times higher than the resistance metal conductor connected to earth. An earth fault is an accidental electrical connection of energized parts of an electrical installation directly to the earth or to its structural parts, not isolated from the earth.

Protective grounding is accepted in all networks with an isolated neutral and in networks with voltages above 1000 V with a grounded neutral. In the latter, single-phase fault points flow through the ground and cause the emergency section to shut down.

Figure 1. Scheme three-phase network with isolated neutral (a) and

modes of its operation when a person touches a linear wire

(b); grounding of one line wire and a person touching

to another (in); touching a person on a line wire in a system with

grounded neutral (g) and in a system with grounded neutral and

other line wires (d)

In a network with a solidly grounded neutral, power receivers are powered by the windings of the current source, connected to a star, the zero point of which is reliably connected to the ground. A dead-earthed neutral is a transformer or generator neutral connected to a grounding device directly or through low resistance.

Neutral grounding. The PUE states that urban electrical networks over 1000 V should be three-phase with an isolated neutral, and distribution networks in new cities should be three-phase four-wire with a tightly grounded neutral at a voltage of 380/220 V. However, networks with a voltage of 220/127 V with an isolated neutral are also common that use blowout fuses.

The windings of power transformers of domestic production with a voltage of 110 kV and above are also designed to work with a grounded neutral, since they have incomplete insulation of zero terminals.

On fig. 1 shown secondary windings transformer Tr, supplying a four-wire network with a voltage of 380/220 V, the neutral of which is isolated. Let the insulation be perfectly serviceable at the moment under consideration. Nevertheless, the three resistances R, connected in a star, the neutral of which is the earth, conditionally show the imperfection of the insulation of the wires, which to some extent still conducts current. Three capacitors C, connected in a star, the neutral of which is also the earth, are conventionally depicted electrical capacitance wires relative to the ground, which is very important in AC electrical installations, since the capacitance conducts alternating current.

What voltages operate in the considered electrical installation? The voltage between the linear wires is 380 V, and between each linear wire and the neutral of the transformer - 220 V, since the earth turned out to be the neutral of the star connections of three equal resistances R and three equal capacitances C. If the linear wire relative to the neutral of the transformer has the same voltage as and relative to earth, then the voltage between the neutral of the transformer and earth is zero, but, of course, only if the network is not loaded or the load of all phases is the same.

Figure 2. − Operation of a three-phase network with a solidly grounded

neutral when a person touches a conductive wire

(a), grounding (b) and grounding (c) of the electric motor

Touching a person standing on the ground to one of the line wires is unsafe, since current will pass through the imperfect insulation of the wire and the human body (Fig. 2). The strength of this current, and therefore the degree of danger, is determined by the values ​​of resistances, capacitances of capacitors and phase voltage. In this case, the person is under voltage of 220 V.

But what happens if one of the line wires is grounded and a person standing on the ground touches the other line wire? From fig. 3 it is clear that the person will now be not under phase, but under line voltage 380 V, which is much more dangerous.

In networks with a grounded neutral, a person standing on the ground and touching the line wire is exposed to phase voltage. If at the same time another linear wire is grounded, the fuse will blow, but the voltage will not increase from phase to linear.

Touching a conductive element in a network with a solidly grounded neutral is very dangerous, since this forms a closed circuit, through which, under the influence of voltage from phase A, a striking current flows through the human body, shoes, floor, ground and neutral ground. It is also dangerous to touch the electrical receiver, in which a short circuit to a grounded case has occurred.

In addition to ensuring the minimum resistance of the grounding device, it is also important to ensure uniform distribution of voltage around the protected device and over the entire area of ​​the electrical installation. Maximum potential (U 3) have a grounding conductor connected to the body of the damaged apparatus, and soil in contact with the grounding conductor. As you move away from the ground electrode, the potential on the earth's surface drops, gradually reaching zero. The soil resistance at this distance is called spreading resistance.

A person touching the body of the device with damaged insulation is under voltage, the value of which is determined by the potential drop in the area between the point of contact with the device and the point where the feet touch the ground. This voltage is called the touch voltage (U prik ). There will also be a potential difference between the feet of a person approaching a damaged apparatus, called the step voltage (U step ), the value of which depends on the step width and the distance to the damage site.

Figure 3. Scheme of the occurrence of step voltage

Step and touch voltages occur when a single-phase earth fault occurs in a grounded network. Let a single-phase fault current flow to the ground through a vertical grounding switch Z (Fig. 3.), located at point 0. As you move away from the ground electrode, the current density and the voltage drop caused by it continuously decrease, i.e. if the maximum potential is at point 0, then the potential at the point of the ground, located further than 20 m from the ground electrode, is practically equal to zero. The change in the soil potential depending on the distance from point 0 is characterized by the AM curve. By dividing the distance 0M into segments 0.8 m long (the average width of a person's step), it is easy to find out from this curve what voltage a person who is at a certain distance from the ground electrode is under. For example, if the legs of a walking person are at a distance of 1.6 and 2.4 m from the earth electrode, then the ground potentials are characterized by points C and D of the AM curve, and the VZ segment on a certain scale determines the potential difference, i.e. voltage.

The voltage under which a person may be walking in the area of ​​\u200b\u200bspreading a single-phase short circuit current on the ground is called the step voltage. This voltage decreases with distance from the ground electrode (VZh<БЕ<АД) и на расстоянии более 20 м от заземлителя оно практически исчезает.

Personal injury due to the appearance of a step voltage in the case of a single-phase earth fault is very rare due to the low values ​​of this voltage. But if this voltage occurs when a broken wire of an overhead line falls to the ground, it can reach large values. In such cases, one should leave the zone of action of the step voltage using dry boards, plastic sheets and other insulating materials, and in their absence, in small steps.

Also dangerous is the voltage that has arisen during the operation of protective grounding in the single-phase ground fault mode. If current I flows through the grounding conductor to the ground 3, then the resistance of the grounding device R 3it creates voltage drops I 3R 3, i.e. touch voltage. In this case, touching the body of the device with damaged insulation, a person can either get under full voltage I 3R 3, or under part of it. The most dangerous cases are when the receiver with damaged insulation and the person who touched it are at distances of more than 20 m from the ground electrode, and if the person is standing directly on the ground in damp shoes lined with nails.

4.2 External ground loop and its installation

To ensure the safety of people, protective grounding of electrical installations is carried out. Grounding is subject to:

metal casings and cases of electrical installations, various units and drives for them, lamps, metal frames of switchboards, control panels, shields and cabinets;

metal structures and metal cases of cable joints, metal sheaths of cables and wires, steel pipes for electrical wiring;

secondary windings of measuring transformers.

Grounding is not subject to:

fittings of suspension and pins of support insulators, equipment installed on grounded metal structures, since their supporting surfaces must be provided with cleaned unpainted places to ensure electrical contact;

cases of electrical measuring instruments and relays installed on shields, shields, cabinets, as well as on the walls of switchgear chambers;

metal sheaths of control cables in cases that are specifically specified in the project.

Protective grounding consists of an external device, which is artificial or natural grounding conductors laid in the ground and interconnected into a common circuit, and an internal network consisting of grounding conductors laid along the walls of the room in which the installation is located and connected to the external circuit.

Metal ground electrodes embedded in the ground, having a large area of ​​contact with the ground, provide a low electrical resistance of the circuit.

To ground electrical installations, first of all, natural grounding conductors should be used - metal pipelines laid in the ground (except for pipelines with combustible, flammable and explosive liquids or gases); casing; metal and reinforced concrete structures of buildings and structures, securely connected to the ground; lead sheaths of cables laid in the ground, and zero working wires with repeated grounding conductors of overhead lines with voltage up to 1000 V. Natural grounding conductors must be connected to the grounding line of the electrical installation in at least two places.

The connection of the grounding conductors to the grounding conductors, as well as the connection of the grounding conductors to each other, is carried out by welding, and the length of the overlap must be equal to twice the width of the conductor with a rectangular section and six diameters - with a round one. With a T-shaped overlap of two strips, the length of the overlap is determined by their width.

The connection of grounding conductors to pipelines is carried out by welding (Fig. 4.) or, if this is not possible, by clamps from the side of pipeline entry into the building. Welding seams located in the ground, after installation, are covered with bitumen to protect against corrosion.

Figure 4. - Connection to the pipeline by welding the grounding

conductor with a rectangular (a) and round (b) section and a clamp

If there are no natural grounding conductors or they do not meet the design requirements, an external grounding loop is mounted from artificial grounding conductors, which can be vertical, horizontal and in-depth.

Vertical grounding conductors are steel pipes or angle steel driven into the ground, as well as steel rods screwed into the ground. Steel strips laid in the ground with a thickness of at least 4 mm or round steel with a diameter of at least 10 mm are horizontal artificial grounding conductors that play the role of independent grounding elements or serve to connect vertical grounding conductors with each other.

A variety of horizontal grounding conductors are recessed grounding conductors laid at the bottom of pits during the construction of foundations for overhead line supports and buildings under construction. They are made in the workshops of the assembly organization after preliminary measurement from strip steel with a cross section of 30 ×4 mm or circular steel with a diameter of 12 mm. The shape of the grounding conductors, their number, section and placement is determined by the project.

As grounding conductors can be used:

natural conductors, i.e. metal structures of buildings;

metal structures for industrial purposes (crane tracks, switchgear frames, galleries, platforms, elevator shafts, lifts);

steel pipes for electrical wiring;

metal sheaths of cables (but not armor).

For zeroing, in all cases, the aluminum sheath of the cables is sufficient, and lead, as a rule, is not enough.

In hazardous areas, specially laid grounding conductors are used, and natural ones are considered as an additional measure of protection. When the neutral is grounded (networks 380/220 or 220/127 V), the grounding of electrical receivers of explosive installations must be carried out separately by dedicated conductors of wiring and cables; with an isolated neutral, steel conductors can be used for grounding.

The use of bare aluminum conductors as grounding conductors is prohibited due to their rapid destruction due to corrosion.

The installation of the external ground loop and the laying of the internal ground network are carried out according to the working drawings of the electrical installation project.

Punch work, installation of embedded parts, preparation of free holes, furrows and other openings, laying passageways in walls and foundations, digging earthen trenches for laying an external ground loop is carried out at the first stage of preparation for elementary work.

The external ground loop is laid in earthen trenches with a depth of 0.7 m. Artificial ground electrodes in the form of segments of steel pipes, round rods and angles 3 ... earth. Recessed grounding conductors are connected to each other with steel strips with a cross section of 40 ×4 mm by welding. The places where the strip is welded to the ground electrodes are covered with heated bitumen to protect against corrosion. Grounding conductors and grounding conductors located in the ground should not be painted. Trenches with grounding conductors and grounding conductors laid in them are covered with earth that does not contain stones and construction debris.

Natural grounding conductors are connected to the grounding lines of the electrical installation by at least two conductors connected in different places. The connection of grounding conductors with extended grounding conductors (pipelines) is carried out near their inputs into buildings using welding or clamps, the contact surface of which is serviced. The pipes in the places where the clamps are laid are cleaned. Places and methods of connection of current receivers are selected in such a way that when the pipeline is disconnected for repair work, the grounding device is continuously operated. Water meters and valves are equipped with bypass connections.

The internal grounding network is carried out by open laying indoors along the building surfaces of bare steel conductors with rectangular and round sections. Figure 5 shows examples of laying, fixing and connecting PE conductors.

Figure 5. - Options for laying (a) and fixing flat and round

tires with clips (b), electric welding (c) and built-in dowels (d),

overlap welding (d) and welding to the electrode (e)

Openly laid bare earth conductors are located vertically, horizontally or parallel to sloping building structures. Conductors with a rectangular cross section are installed with a large plane to the surface of the base. On rectangular sections of the gasket, the conductors should not have irregularities and bends that are noticeable to the eye. Grounding conductors laid on concrete or brick in dry rooms that do not contain caustic vapors and gases are fixed directly on the walls, and in damp, especially damp rooms with caustic vapors and gases - on supports at a distance of at least 10 mm from the wall surfaces. In the channels, grounding conductors are located at a distance of at least 50 mm from the lower surface of the removable floor. The distance between supports for fixing grounding conductors on straight sections is 600…1000 mm.

Grounding conductors in places where they cross with cables and pipelines, as well as in other places where mechanical damage is possible, are protected by pipes or other means.

In the premises, grounding conductors must be available for inspection, but this requirement does not apply to neutral conductors and metal sheaths of cables, hidden wiring pipelines and metal structures located in the ground. Through the walls, grounding conductors are laid in open openings, pipes or other rigid frames. Each grounded element of the electrical installation must be connected to the grounding line using a separate branch. Serial connection to the grounding conductor of several grounded elements is prohibited.

Neutrals of transformers, grounded tightly or through devices that compensate for capacitive current, are connected to the ground electrode system or to prefabricated grounding buses using separate grounding conductors. The grounded terminals of the secondary windings of instrument transformers are connected to their casings with grounding bolts.

Flexible jumpers that serve to ground metal sheaths and cable armor are attached to them with a wire bandage and soldered, and then connected by bolted contacts to the cable termination (sleeve) and the grounding structure. The cross section of flexible jumpers must correspond to the cross sections of the grounding conductors adopted for this electrical installation. The points of connection of the grounding jumper with the aluminum sheath of the cable are covered with asphalt varnish or hot bitumen after soldering.

The connection of grounding conductors with each other and their connection to the installation structures is carried out by welding, and the connection to the bodies of apparatus and machines is carried out by welding or a reliable bolted connection. Locknuts, spring washers, etc. are installed to prevent loosening of contact during shocks and vibrations.

Contact surfaces on grounded electrical equipment at the points of connection of grounding conductors, as well as contact surfaces between grounded equipment and the structures on which it is installed, must be cleaned to a metallic sheen and covered with a thin layer of petroleum jelly.

4.3 Measuring the resistance of earthing devices

protective earth electrical equipment resistance

Grounding reliably performs its protective functions only if its resistance is sufficiently small. For example, in networks with a dead-earthed neutral, a large resistance of the grounding device can lead to the fact that the strength of the current that has arisen during insulation breakdowns is insufficient to trigger the tripping protective equipment. Therefore, PUE strictly limit the resistance of grounding devices.

When grounding electrical installations with voltages up to 1000 V with a solidly grounded neutral, it is necessary to securely connect the neutrals of their power sources (generators, transformers) to the ground electrode, which should be located in close proximity to them. If the transformer substation is located inside the workshop, it is allowed to take out the ground electrodes on the outer side of the building wall. The resistance of the grounding device to which the neutrals of generators and transformers are connected must be no more than 4 ohms, but if their power is 100 kVA and lower, then the resistance, then the resistance of the grounding device should not exceed 10 ohms; during parallel operation of power supplies, the grounding resistance can reach 10 Ohm only if their total power does not exceed 100 kV * A.

Figure 6. - Electrical measuring device:

Cylinder;

aluminum frame;

Arrow;

Scale

After the completion of all installation work, it is mandatory to measure whether the grounding resistance meets the requirements of the PUE. Most often, measurements are made using an ammeter and a voltmeter or an MS-08 device.

Electrical measuring instruments - ammeters and voltmeters, which use the orientation effect of a magnetic field on a current-carrying circuit, are arranged as follows. Rice. 6 on a light aluminum frame 2 of a rectangular shape with an arrow 4 attached to it, a coil is wound. The frame is reinforced on two semiaxes OO`. It is held in the equilibrium position by two thin spiral springs 3, the moment of elastic forces of which is proportional to the angle of deflection of the arrow. The coil is placed between the poles of a permanent magnet with specially shaped tips. Inside it is a cylinder 1 made of soft iron. This design provides a radial direction of the magnetic induction line in the area where the turns of the coil are located (Fig. 7, i.e. at any position of the coil, the moment of the forces of the magnetic field is maximum and at a constant current strength is the same. The vectors F and -F correspond to the forces of the magnetic field that act on the coil and create a torque. The current-carrying coil rotates until the moment of elastic forces of the spring balances the moment of forces of the magnetic field. When the current strength is doubled, the arrow also rotates through an angle twice as large, since the maximum moment of the forces M of the magnetic field is directly proportional to the current strength: M~I. Having established which angle of rotation of the arrow corresponds to the known value of the current strength and calibrating the electromagnetic device, it can be used to measure in DC and AC circuits. Ammeters and voltmeters are the most common switchboard instruments due to the simplicity of the device and relatively good overload tolerance. The disadvantages of these devices are low accuracy, high power consumption (up to 10 W), limited frequency range, and sensitivity to external magnetic fields.

Figure 7. Scheme of the action of forces in an electrical measuring device

Figure 8. - Scheme for measuring ground resistance using

ammeter and voltmeter

Panel ammeters produce class 1.0; 1.5; 2.5 for currents up to 300 A with direct connection and up to 15 A with external current transformers. Panel voltmeters of the same accuracy classes are available for voltages up to 600 V with direct connection and up to 750 kV with voltage transformers.

With direct connection of measuring devices fig. 8 between the ground electrode (G), the resistance of which relative to the ground must be measured, the auxiliary current electrode (T) passes a single-phase alternating current Ix and measures it with an ammeter, and, having immersed the auxiliary potential rod (P) in the ground between the electrodes Z and T, measure the voltage with a voltmeter Ux between it and ground electrode Z.

Grounding resistance measurements using an ammeter, voltmeter and transformer are performed in the following order. Electrodes P and T are hammered into the ground (steel rods pointed at the ends about 1 m long). an ammeter and a voltmeter are connected with separate wires to the ground electrode and these electrodes. A voltmeter checks the absence of voltage between the ground electrode and the P rod. If the device shows any voltage, changing the direction of the spacing of the rods or proportionally increasing the distance between them, they achieve its zero value. After that, a rheostat with resistance R is fully introduced and the transformer Tr is connected to the network. With the help of a rheostat, the current strength is gradually increased and the readings of the ammeter and voltmeter are monitored (a simultaneous report on the instruments is made at the moment when their readings can be recorded with the greatest accuracy). According to the measurement data, the resistance of the ground electrode is calculated using Ohm's law:

R 3= U x /I x .

At least three measurements are made and the arithmetic mean of the obtained values ​​is taken for calculation.

The advantage of such a measurement is the accuracy and the possibility of determining small, very small resistances (up to hundredths of an ohm); the disadvantages are the need for two measuring instruments and a transformer, the influence of mains voltage fluctuations on the measurement accuracy, the lack of a direct report and increased danger to people making measurements. This method is mainly used to measure the resistance of earthing conductors of power plants and large district transformer substations.

Grounding resistance can also be measured with the MS-08 instrument (Fig. 9), which has three scales (10 ... 1000, 1 ... 100 and 0.1 ... 10 Ohm), whose operation is based on the principle of simultaneous measurement of current and voltage with a magnetoelectric logometer.

Figure 9. - Simplified diagram of the MS-08 device:

Ratiometer;

Generator;

Current interrupter;

Rectifier

A logometer is an indicating device that measures the ratio of two electrical quantities, in most cases the ratio of two currents. It is used to measure electrical and non-electrical quantities that are independent of current (resistance, phase shift, frequency, temperature, pressure, displacement in space).

The deviation of the pointer of most measuring mechanisms is determined by the current that passes through this mechanism and may depend on the measured value. For example, in an electrothermometer, the current depends on the resistance in the circuit, since a resistor is included in it, the resistance of which changes with a change in the measured temperature. But according to Ohm's law, current is also proportional to voltage. Consequently, the reading of the device will depend not only on the measured value x, but also on the voltage of the power source, changes in which will cause corresponding errors in the readings of the device. To eliminate the effect of voltage in such measurements, ratiometers are widely used.

A ratiometer can have a measuring mechanism of almost any system, but magnetoelectric ratiometers are widely used.

In a logometer of any system, the rotating and counteracting moments are created by electromechanical forces and are equally dependent on voltage, so a change in voltage does not change the ratio of moments, and therefore does not affect the readings of the device.

Logometer 1 has a potential current frame fixed at an angle and located in the field of a permanent magnet. The current strength in the potential loop, connected in parallel to the ground electrode Z, is proportional to the voltage drop U x on it, and the current in the frame connected in series is proportional to the current I x flowing through the ground electrode. The deflection angle of both frames of the ratiometer in a constant magnetic field is proportional to the ratio U x /I x , equal to the resistance of the earth electrode. The device has a manually operated DC generator 2, a current interrupter 3, a rectifier 4 and a variable resistor R, which serves to increase the resistance of the potential circuit to 1000 ohms. Terminals I are located on the external panel of the device. 1, E 1, E 2and I 2. When the generator handle is rotated, a direct current is generated, which is converted by the breaker into an alternating current and through terminal I 2and the auxiliary potential rod P first goes into the ground, and then through the tested ground electrode Z and terminals I 1, E 1, connected by a jumper, returns to the breaker and further along the current winding of the ratiometer to the generator. Passing in the ground, an alternating current creates an alternating voltage drop between the ground electrode and the rod P, which through the terminals E 1and E 2falls on the rectifier 4 and then - on the potential frame of the ratiometer.

Auxiliary electrodes P are hammered at certain distances into dense soil to a depth of at least 0.5 m with direct impacts and without buildup. The switching circuit of the MS - 08 device is determined by the estimated value of the resistance of the ground electrode. To measure high resistances, it is installed as close as possible to the ground electrode and switched on according to the diagram, fig. 10 a. To measure low resistances or if the device cannot be installed near the ground electrode, remove the jumper between terminals I 1and E 1, and turn on the device according to the scheme, fig. 10 b.

Figure 10. - Scheme of measurement by the MS - 08 device of large (a) and

small (b) resistances:

Switch;

variable resistance

Next, the resistance of the potential circuit is compensated, for which switch 1 is set to the “Adjustment” position and, by rotating the generator handle at a frequency of 120 ... 135 rpm, using variable resistance 2, the arrow of the device coincides with the red line on its scale. The switch is then moved to the " ×1" and, continuing to rotate the generator knob, take off the values ​​​​from the scale of 10 ... 1000 Ohm. If the deviation of the arrow is not significant, the switch is moved to the position " ×0.1" ( scale 1…100 Ohm) or " × 0.01 "(scale 0.1 ... 10 Ohm). During these switchings, they strive to ensure that the arrow deviates by at least 2/3 of the scale, after which, without stopping the rotation of the generator handle, the reading is taken and multiplied by the coefficient of the scale used.

When measuring the grounding resistance with the MS - 08 instrument, there is no need for an alternating current network, which is especially important during repair and field work. In addition, no calculations are required, i.e. the measured value is read directly on the scale. The disadvantages of the device are a significant weight (about 13 kg) and a relatively high error (up to 12.5%).

These measurements are compared with the requirements of the PUE. If the resistance is less than or equal to the value given in the EMP, the grounding device is considered serviceable.

4.4 Installation of the internal earth network

Before backfilling the trenches, steel strips or round rods are welded to the outer ground loop, which are then inserted into the building where the equipment to be grounded is located. The inputs connecting the ground electrodes with the internal ground network must be at least two and they are made of steel conductors of the same dimensions and cross sections as the connections of the ground electrodes to each other. As a rule, the input of grounding conductors into the building is laid in fireproof metal pipes protruding on both sides of the wall by about 10 mm.

In workshops of industrial enterprises and buildings of transformer substations, electrical equipment to be grounded is located in a variety of ways, therefore, to connect it to the grounding system, grounding and zero protective conductors must be laid in the room.

The latter are used:

zero working conductors (except for explosive installations), as well as metal structures of the building (columns, trusses);

conductors specially designed for this purpose;

metal structures for industrial purposes (frames of switchgear, crane runways, elevator shafts, framed channels), steel pipes for electrical wiring;

aluminum cable sheaths;

metal casings of busbars, boxes and trays;

metal fixed pipelines for any purpose (except for pipelines of combustible and explosive substances and mixtures, sewerage and central heating).

It is forbidden to use metal sheaths of tubular wires, carrying cables, metal hoses, armor and lead sheaths of cables as zero protective conductors, although they themselves must be grounded or grounded and have reliable connections throughout.

If natural grounding lines cannot be used, then steel conductors are used as grounding or zero protective conductors, the minimum dimensions of which are presented in Table 2. Grounding conductors in the premises must be accessible for inspection, therefore they (with the exception of steel pipes of hidden electrical wiring, cable sheaths) laid out openly.

The passage through the walls is carried out in open openings, fireproof non-metallic pipes, and through the floors - in segments of the same pipes protruding under the floor by 30 ... 50 mm. Grounding conductors must be carried out freely, with the exception of explosive installations, where the openings of pipes and openings are sealed with easily penetrating fireproof materials.

Before laying, steel tires are straightened, cleaned and painted on all sides. The joints after welding the joints are covered with asphalt varnish or oil paint. In dry rooms, nitro enamels can be used, and in rooms with damp and caustic fumes, paints that are resistant to a chemically active environment should be used.

Table 2 - Minimum dimensions of earthing conductors

Conductor type Laying location In the building In the outdoor installation and in the ground Round steel Diameter 5 mm Diameter 6 mm Rectangular steel Section 24 mm 2, thickness 3 mm Section 48 mm 2, thickness 4mmSteel gas pipeWall thickness 2.5mmWall thickness 2.5mm in NU and 3.5mm in the groundSteel thin-walled pipeWall thickness 1.5mm2.5mm in NU in the ground is not allowedAngular steelShelf thickness 2mmShelf thickness 2.5mm in NU and 4 mm in the ground

In rooms and outdoor installations with a non-aggressive environment in places accessible for inspection and repair, it is allowed to use bolted connections of grounding and zero protective conductors, provided that measures are taken against their weakening and corrosion of the contact surfaces.

Openly laid grounding and zero protective conductors must have a distinctive paint: on a green background, yellow stripes 15 mm wide at a distance of 150 mm from each other. Grounding conductors are laid only parallel to the inclined structures of the building.

Conductors with a rectangular cross section are attached with a wide plane to a brick or concrete wall (Fig. 11 using a construction and assembly gun or a pyrotechnic frame. Grounding conductors are attached to wooden walls with screws. Supports for fixing grounding conductors must be installed in compliance with the following distances: between supports in straight sections - 600 ... 1000 mm, from the tops of corners at turns - 100 mm, from the floor level of the room - 400 ...

In damp, especially damp and rooms with caustic vapors, it is not allowed to fasten grounding conductors directly to the walls, they are equated to supports fixed with dowels fig. 12 With or embedded into the wall.

Figure 11. - Fastening of grounding conductors with dowels

directly to the wall (a) and with a gasket (b)

Figure 12. - Fastening of flat (a) and round (b) conductors

grounding with supports

4.5 PUE requirements for grounding electrical installations

Grounding or grounding should be carried out in all AC electrical installations with a voltage of 380 V and in DC electrical installations with a voltage of 440 V or more. voltage above 42 V and in direct current devices with voltage above 110 V, and in explosive installations - at any voltage of alternating and direct currents.

At voltages up to 1000 V in electrical installations with a solidly grounded neutral, zeroing must be performed. In these cases, grounding of cases of electrical receivers without grounding is prohibited.

To be grounded or grounded:

Cases of electrical machines, transformers, devices, lamps;

Secondary windings of measuring transformers;

Frames of switchboards, shields and cabinets;

Metal structures of switchgear, cable structures and couplings, sheaths and armor of control and power cables, metal sheaths of wires, steel pipes for electrical wiring, busbar housings, trays, boxes, cables and steel strips with cables and wires mounted on them;

Electrical equipment installed on overhead line supports;

Metal cases of mobile and portable electrical receivers;

Electrical equipment placed on moving parts of machine tools and machines;

Metal cases of power permanently installed electrical receivers, as well as metal pipes of electrical wiring to them;

Cases and parts of electrical wiring on staircases of residential and public buildings, in house, dock and public sanitary facilities, baths and other similar premises. In bathrooms, the metal bodies of the tubs must be connected to the plumbing pipes.

It is allowed not to perform special grounding or grounding:

Cases of electrical equipment installed on grounded or grounded metal structures of panels or cabinets, machine beds and other bases;

Metal parts on wooden poles of overhead lines (if grounding does not require protection against atmospheric surges).

Figure 13. - Connecting the receivers to the grounding line

There are certain requirements for grounding and grounding of electrical receivers of various types.

1.Each grounded part of the electrical installation must be connected to the grounding line by a separate branch fig. 13. Serial connection to the ground conductor of several parts is prohibited.

2.The cross section of copper and aluminum conductors for grounding various parts of the electrical installation must correspond to the values ​​\u200b\u200bspecified in table 3.

.Grounding branches to single-phase electrical receivers must be carried out by a separate conductor; it is forbidden to use a neutral working wire for this purpose.

.The connection of grounding branches to metal structures should be carried out by welding, and to the bodies of apparatus and machines - by bolts. The contact surfaces must be cleaned to a metallic sheen and lubricated with a thin layer of Vaseline.

.The metal cases of mobile and portable power receivers are grounded with a special conductor of a flexible wire, which should not simultaneously serve as a conductor of the working current. It is forbidden to use the zero working wire of the electrical installation for this purpose.

.The connection of the grounding conductor to the grounding or neutral contact of the socket outlet should be carried out with a separate conductor. The plug for turning on a portable electrical receiver must have an elongated grounding pin that comes into contact with the grounding contact of the outlet before the current-carrying contacts are connected.

.The cores of wires and cables for grounding portable and mobile installations must have cross sections equal to the cross sections of the phase wires and be in a common sheath with them.

Table 3. - Minimum allowable cross-section of grounding

conductors, mm 2

Type of conductorCopperAluminumUninsulated conductor with open laying46Insulated wire1.52.5Grounding and neutral conductor of the cable and stranded wire in a common protective sheath with phase conductors11.5

Grounding is not subject to:

Rail tracks that go beyond the territory of power stations, substations of industrial enterprises;

Casings of electrical equipment installed on grounded metal structures, if cleaned and unpainted places are provided on the support surfaces to ensure tight electrical contact;

Cases of electrical measuring instruments, relays and other devices installed on shields, shields, cabinets and walls of switchgear chambers;

Cases of electrical receivers having double insulation with respect to current-carrying parts. For devices with double insulation, the case is made of insulating material, and the live parts have their own insulation. Thus, if the insulation of the current-carrying part of the receiver is damaged, then the danger of electric shock does not arise, since the insulating case or insulating gaskets between the case and the internal insulated current-carrying parts reliably protect a person from electric shock;

Removable or opening parts of metal grounded frames and chambers of switchgears, fences, cabinets.

It is forbidden to ground the metal cases of permanently installed lighting electrical equipment and portable receivers in rooms without increased danger of residential and public buildings. In the grounding network, the welding seams connecting its individual sections to each other are most often damaged. The integrity of the welds is checked by hammer blows on the welds. The defective seam is cut down with a chisel and re-welded with autogenous arc or thermite welding.

Before starting the repair of the grounding network, the resistance of the grounding conductor to current spreading is checked. If it is above the norm, then measures are taken to reduce it. For this, the number of grounding electrodes is increased or layers of salt and earth 10…15 mm thick are laid alternately around them within a radius of 250 ... 300 mm. Each laid layer is watered. In this way, the earth is cultivated around the upper part of the ground electrode every 3-4 years.

5. Safety

5.1 Organization of the electrician's workplace

Electricians for the maintenance of electrical equipment often have to perform various plumbing and assembly operations. Therefore, they must clearly know the safety rules for carrying out such work and be able to organize their safe implementation.

Before starting work, you should check the state of the tool with which it will be performed. A defective tool must be replaced with a good one. The hammer should be firmly seated on the handle, which is wedged with a wedge of mild steel or wood. It is impossible to correct a hammer with a weakened handle by hitting it about miles or other objects, this leads to even greater loosening of the handle. Handles must also be firmly attached to scrapers, files and other tools. Weakly attached handles easily jump off the tool during operation, while the sharp shank of the tool can severely injure the hand. Do not use hand tools without a handle. Wrenches must match the dimensions of the nuts and bolt heads; it is not allowed to use wrenches with crumpled and cracked jaws, to increase the keys with pipes, other keys or in any other way, it is necessary to monitor the serviceability of the vise, pullers.

Proper organization of the workplace ensures rational movements of the worker and reduces to a minimum the time spent on finding and using tools and materials.

At the workplace of the workshop electrician on duty, there should be: technological equipment, organizational equipment, job description, electrical diagrams of the main electrical installations, power supply circuits for the workshop or section, an operating log, safety instructions, inspection schedules and a shift-hour index-calendar of the electrician's location. The workplace should be designed in accordance with the requirements of technical aesthetics.

The workplace is a part of the space adapted for the worker or group to perform their production tasks. The workplace, as a rule, is equipped with basic and auxiliary equipment (machines, mechanisms, power plants, etc.), technological (tools, fixtures, instrumentation) equipment. At socialist production enterprises, requirements are imposed on all jobs, the fulfillment of which ensures an increase in labor productivity and contributes to the preservation of the health and development of the worker's personality.

The workplaces where workers of electrical professions work are different depending on what actions and operations they perform installation, assembly, adjustment, etc. The workplace of an electrician can also be outdoors, for example, during the construction or repair of air and cable electrical networks, substations, etc. In all cases, there should be an exemplary order at the workplace: adaptation tools (it is allowed to use only serviceable tools) must be placed in the appropriate places, the tool must also be put there after finishing working with it, there should not be anything superfluous that is not required for performance at the workplace. of this work, the equipment and maintenance of the workplace must strictly meet all the requirements of labor protection, safety, industrial sanitation and hygiene and exclude the possibility of a fire.

All of the above general requirements apply to the student's work must. It can be a mounting table or workbench (when performing electrical and insulating work), a winding machine (when performing winding work), a special workbench or table (when performing plumbing and assembly work), etc. Depending on the type of electrical work performed (installation, assembly, operation, etc.), the workplace must be equipped with appropriate tools and devices. Typically, the following tools are placed at the workplace:

fastening-clamping pliers, round-nose pliers, pliers, vice;

cutting - fitter's knife, wire cutters, hacksaw, impact hammer, chisel, punch.

In addition, general metalwork tools are used, as well as many types of metal-cutting tools, since electrical work is often associated with cutting metal, bending pipes, cutting various materials, threading, etc.

Factories produce sets of tools for performing certain types of electrical work. Each set is placed in a closed bag made of leatherette (IN-3) or in a folding bag made of artificial leather (NIE-3), the weight of the set is 3.25 kg.

So, a general-purpose electrical installation tool kit includes the following:

universal pliers 200 mm, wiring pliers with elastic covers;

pliers (nippers) 150 mm with elastic covers;

various locksmith and assembly screwdrivers (with plastic handles) - 3 pcs.;

metalwork hammer with a handle weighing 0.8 kg;

monter's knife;

fitter's awl;

voltage indicator;

ruler meter folding metal;

light goggles;

gypsum;

trowel;

cord twisted with a diameter of 1.5-2 mm, length 15 m.

At the workplace, strictly observe the following rules:

1. Be attentive, disciplined, careful, accurately follow the oral and written instructions of the teacher (master)
2. Do not leave the workplace without the permission of the teacher (master).
3. Place devices, tools, materials, equipment in the workplace in the order indicated by the teacher (master) or in a written instruction.
4. Do not keep items in the workplace that are not required for the task.

5.2 Safety requirements before starting work

Before starting work, the electrician must:

a) present to the manager a certificate of testing knowledge of safe working methods, as well as a certificate of testing knowledge when working in electrical installations with a voltage of up to 1000 V or more than 1000 V, receive an assignment and be instructed at the workplace on the specifics of the work performed;

b) put on overalls, special footwear and a helmet of the established sample. After receiving the task from the work manager and familiarizing, if necessary, with the activities of the work permit, the electrician is obliged to:

a) prepare the necessary personal protective equipment, check their serviceability;

b) check the workplace and approaches to it for compliance with safety requirements;

c) select the tools, equipment and technological equipment necessary for the performance of work, check their serviceability and compliance with safety requirements;

d) get acquainted with the changes in the power supply scheme for consumers and current entries in the operational log.

The electrician should not start work in case of the following violations of safety requirements:

a) malfunctions of technological equipment, fixtures and tools specified in the instructions of manufacturers, in which their use is not allowed;

b) untimely carrying out of the next tests of the main and additional protective equipment or the expiration of their service life established by the manufacturer;

c) insufficient lighting or cluttered workplace;

d) the absence or expiration of the work permit when working in existing electrical installations.

Detected violations of safety requirements must be eliminated on their own before the start of work, and if it is impossible to do this, the electrician is obliged to report them to the foreman or responsible work manager.

a) pronounce the necessary shutdowns and take measures to prevent the supply of voltage to the place of work due to erroneous or spontaneous switching on of the switching equipment;

b) apply grounding to live parts;

c) protect the workplace with inventory fences and hang warning posters;

d) by means of switching devices or by removing the fuses, disconnect current-carrying parts on which work is performed, or that is, which are touched during work, or protect them during work with insulating pads (temporary fences);

e) take additional measures to prevent the erroneous supply of voltage to the place of work when performing work without the use of portable grounding;

f) on the starting devices, as well as on the bases of the fuses, post posters “Do not turn on - people are working!”;

g) hang posters on temporary fences or apply warning signs “Stop - life is dangerous!”;

h) to check the absence of voltage in dielectric gloves;

i) apply portable grounding clamps to grounded current-carrying parts using an insulated rod using dielectric gloves;

j) when performing work on live parts under voltage, use only dry and clean insulating means, and also hold the insulating means by the gripping handles no further than the restrictive ring.

Change of fuse links in the presence of a knife switch should be carried out with the voltage removed. If it is impossible to remove the voltage (on group shields, assemblies), it is allowed to change the fuse links under voltage, but with the load disconnected.

The electrician must change the fuse links of the fuses under voltage in goggles, dielectric gloves, using insulating pliers.

Before starting the equipment, temporarily disconnected at the request of non-electrical personnel, you should inspect it, make sure that it is ready to receive voltage and warn those working on it about the upcoming inclusion.

Connecting and disconnecting portable devices that require breaking electrical circuits under voltage must be carried out when the voltage is completely removed.

When working on wooden poles of overhead power lines, an electrician should use claws and a safety belt.

When performing work in hazardous areas, an electrician is not allowed to:

a) repair electrical equipment and networks under voltage;

b) operate electrical equipment with faulty protective grounding:

c) turn on an automatically disconnected electrical installation without finding out and eliminating the reasons for its disconnection;

d) leave open the doors of rooms and vestibules separating explosive rooms from others;

e) replace burnt out electric bulbs in explosion-proof lamps with lamps of other types or higher power;

f) turn on electrical installations without the presence of devices that turn off the electrical circuit during abnormal operating modes;

g) replace the protection (thermal elements, fuses, releases) of electrical equipment with another type of protection with other nominal parameters for which this equipment is not designed.

When working in electrical installations, it is necessary to use serviceable electrical protective equipment: both basic (insulating rods, insulating and electrical clamps, voltage indicators, dielectric gloves), and additional (dielectric overshoes, rugs, portable grounding devices, insulating stands, protective stands, protective devices, posters and safety signs).

Work in conditions with increased danger should be carried out by two people in the following cases:

a) with full or partial removal of voltage, performed with the imposition of grounding (disconnection and connection of lines to individual electric motors, switching on power transformers, work inside switchgears);

b) without removing the voltage, which does not require the installation of grounding (electrical tests, measurements, change of fuse links, etc.);

c) from ladders and scaffolds, as well as where these operations are difficult due to local conditions;

d) on overhead power lines.

Measurement of insulation resistance with a megger should only be carried out on a completely de-energized electrical installation. Before measurement, make sure that there is no voltage on the equipment under test.

When working near existing crane or hoist trolls, electricians must comply with the following requirements;

a) turn off the trolleys and take measures to eliminate their accidental or erroneous switching on;

b) ground and short-circuit the trolleys among themselves;

c) protect with insulating materials (rubber mats, wooden shields) the places where the trolls can touch if it is impossible to relieve the voltage. Hang a poster on the fence "Dangerous for life - voltage 380 V!".

When servicing lighting networks, electricians must comply with the following requirements:

a) replacement of fuses and burnt out lamps with new ones, repair of lighting fittings and electrical wiring to be carried out with the mains voltage removed and during daylight hours;

b) cleaning of fittings and replacement of lamps mounted on supports should be carried out after removing the voltage and together with another electrician;

c) the installation and testing of electricity meters connected through instrument transformers should be carried out together with an electrician who has a safety qualification group of at least IV;

d) when servicing lamps from aerial platforms or other moving means of scaffolding, use safety belts and dielectric gloves.

When adjusting switches and disconnectors connected to wires, electricians should take measures to prevent the possibility of unforeseen switching on of drives by unauthorized persons or their spontaneous switching on.

To check the contacts of oil switches for simultaneous switching on, as well as to illuminate closed containers, electricians should use a voltage in the mains not higher than 12 V.

During work, the electrician is prohibited from:

a) rearrange temporary fences, remove posters, groundings and enter the territory of fenced areas;

b) apply the voltage indicator without re-checking after its fall;

c) remove the guards of the winding leads during the operation of the electric motor;

d) use for grounding conductors not intended for this purpose, as well as connect grounding by twisting the conductors;

e) use current clamps with a remote ammeter, as well as bend over to the ammeter when reading readings while working with current clamps;

f) touch devices, resistances, wires and instrument transformers during measurements;

g) take measurements on overhead lines or trolleys, standing on a ladder;

h) use metal stairs for maintenance and repair of electrical installations;

i) use hacksaws, files, metal meters, etc. when working under voltage;

j) use autotransformers, choke coils and rheostats to obtain step-down voltage;

k) use stationary lamps as hand-held - portable lamps.

For access to the workplace, electricians must use the equipment of the access system (ladders, ladders, bridges). In the absence of fencing of workplaces at a height, electricians are required to use safety belts with a nylon halyard. At the same time, electricians must comply with the requirements of the "Standard instructions for labor protection for workers performing steeplejack work."

5.4 Safety requirements in emergency situations

In the event of a fire in an electrical installation or a danger of electric shock to others as a result of a cable (wire) break or short circuit, it is necessary to de-energize the installation, take part in extinguishing the fire and inform the foreman or work manager about this. Flames should be extinguished with carbon dioxide fire extinguishers, asbestos blankets and sand.

5.5 Safety requirements at the end of work

a) transfer information to the shift worker about the condition of the serviced equipment and electrical networks and make an entry in the operational log;

b) remove tools, devices and personal protective equipment in the places provided for them;

c) put the workplace in order;

d) make sure that there are no sources of fire;

e) report all violations of safety requirements and malfunctions to the foreman or responsible work manager.

Types of damage to the human body by electric current:

A characteristic case of getting under voltage is contact with one pole or phase of a current source. The voltage acting on a person in this case is called the touch voltage. Particularly dangerous are the areas located on the temples, back, backs of the hands, shins, back of the head and neck.

Increased danger is represented by premises with metal, earthen floors, damp. Particularly dangerous are rooms with vapors of acids and alkalis in the air. Safe for life is a voltage not higher than 42 V for dry rooms heated with non-conductive floors without increased danger, not higher than 36 V for rooms with increased danger (metal, earthen, brick floors, dampness, the possibility of touching grounded structural elements), not higher than 12 B for especially dangerous premises with a chemically active environment or two or more signs of premises with increased danger.

In the case when a person is near a live wire that has fallen to the ground, there is a danger of being struck by step voltage. Step voltage is the voltage between two points of the current circuit, located one from the other at a step distance, at which a person simultaneously stands. Such a circuit is created by a current flowing along the ground from the wire. Once in the zone of current spreading, a person must connect his legs together and, slowly, leave the danger zone so that when moving, the foot of one leg does not go completely beyond the foot of the other. In case of an accidental fall, you can touch the ground with your hands, which increases the potential difference and the danger of injury. The effect of electric current on the body is characterized by the main damaging factors:

1. an electric shock that excites the muscles of the body, leading to convulsions, respiratory and cardiac arrest;
2. electrical burns resulting from the release of heat when current passes through the human body; depending on the parameters of the electrical circuit and the condition of the person, reddening of the skin, a burn with the formation of bubbles or charring of tissues may occur; when the metal is melted, metallization of the skin occurs with the penetration of pieces of metal into it.

Bibliography

1.Nesterenko V.M., Mysyanov A.M. Technology of electrical work: textbook. allowance for the beginning prof. education. - M.: Academy, 2002. - 592 p.

2.Sibikin Yu.D., Sibikin M.Yu. Maintenance, repair of electrical equipment and networks of industrial enterprises: Proc. for the beginning prof. education. - M.: IRPO; Academy, 2000. - 432 p.

Grounding devices of electrical installations with voltage up to 1 kV in networks with dead-earthed neutral

Where should the grounding conductor be connected if a CT is installed in the PEN conductor connecting the neutral of the transformer or generator with the PEN RU bus up to I kV?
Answer . It must not be connected directly to the neutral of the transformer or generator, but to the PEN conductor, if possible immediately on the CT. In this case, the division of the PEN conductor into RE and N conductors in the TN-S system must also be carried out behind the CT. The CT should be placed as close as possible to the neutral terminal of the transformer or generator.
What should be the resistance of the grounding device to which the neutrals of the generator or transformer are connected, or the outputs of the single-phase current source?
Answer . It should be no more than 2, 4 and 8 ohms at any time of the year, respectively, at 660, 380 and 220 V of a three-phase current source or 380, 220 and 127 V of a single-phase current source. This resistance must be provided taking into account the use of natural grounding conductors, as well as grounding conductors for repeated grounding of a PEN- or PE-conductor of an overhead line up to 1 kV with a number of outgoing lines of at least two.
What should be the resistance of the ground electrode located in close proximity to the neutral of the generator or transformer, or the output of a single-phase current source?
Answer. It should be no more than 15, 30 and 60 ohms, respectively, at line voltages of 660, 380 and 220 V of a three-phase current source or 380, 220 and 127 V of a single-phase current source. With a specific earth resistance ρ > 100 Ohm×m, it is allowed to increase the indicated norms by 0.01 ρ times, but not more than tenfold.
At what points in the network should the PEN-conductor be re-grounded?
Answer . Must be performed at the ends of overhead lines or branches from them with a length of more than 200 m, as well as at the inputs of overhead lines to electrical installations in which automatic power off is applied as a protective measure in case of indirect contact.
What should be the total spreading resistance of grounding conductors (including natural ones) of all repeated groundings of the PEN conductor of each overhead line at any time of the year?
Answer . It should be no more than 5, 10 and 20 ohms, respectively, at line voltages of 660, 380 and 220 V of a three-phase current source or 380, 220 and 127 V of a single-phase current source. In this case, the spreading resistance of the grounding conductor of each of the repeated groundings should be no more than 15, 30 and 60 ohms, respectively, at the same voltages. With a specific earth resistance ρ > 100 Ohm × m, it is allowed to increase the indicated norms by 0.01ρ times, but not more than tenfold.
W grounding devices in electrical installations with voltage up to 1 kV with isolated neutral
What condition must be met by the resistance of the earthing device used for the protective earthing of the HFC (open conductive part) in the IT system?
Answer . Must meet condition:
R ≤ U pr /I
where R is the resistance of the grounding device, Ohm;
U pr - touch voltage, the value of which is assumed to be 50 V; I - total earth fault current, A.
What are the requirements for the resistance values ​​of the grounding device?
Answer . As a rule, it is not required to take the value of this resistance less than 4 ohms. The resistance of the grounding device is allowed up to 10 ohms, if the condition is met
R ≤ U pr /I,
and the power of generators or transformers does not exceed 100 kVA, including the total power of generators or transformers operating in parallel.
Earthing switches
What can be used as natural grounding conductors?
Answer . Can be used:
o metal and reinforced concrete structures of buildings and structures in contact with the ground, including reinforced concrete foundations of buildings and structures with protective waterproofing coatings in non-aggressive, slightly aggressive and medium-aggressive environments;
o metal water pipes laid in the ground;
o well casing pipes;
o metal sheet piles of hydraulic structures, conduits, embedded parts of gates, etc.;
o rail tracks of mainline non-electrified railways and access roads in the presence of a deliberate arrangement of jumpers between the rails;
o other metal structures and structures located in the ground;
o metal sheaths of armored cables laid in the ground. Aluminum cable sheaths are not allowed to be used as grounding conductors.
Is it allowed to use pipelines of flammable liquids, flammable or explosive gases and mixtures and sewerage and central heating pipelines as grounding conductors?
Answer . Use is not allowed. These restrictions do not exclude the need to connect such pipelines to a grounding device in order to equalize potentials.
Grounding conductors

What section should have a grounding conductor connecting a working (functional) grounding conductor to the main grounding bus in electrical installations up to 1 kV?
Answer . Must have a cross section of at least: copper - 10 mm> 2, aluminum - 16 mm 2, steel - 75 mm?.
Main ground bus

What should be used as the main ground bus inside the input device? Answer . PE bus should be used.
What are the requirements for the main ground bus?
Answer . Its cross section must be at least the cross section of PE (PEN) - the conductor of the supply line. It should be, as a rule, copper. It is allowed to use it from steel. The use of aluminum tires is not allowed.
What are the requirements for installing a main ground bus?
Answer . In places accessible only to qualified personnel, for example, switchboard rooms of residential buildings, it should be installed openly. In places accessible to unauthorized persons, for example, entrances and basements of houses, it must have a protective shell - a cabinet or box with a door that can be locked with a key. A sign must be placed on the door or on the wall above the tire.
How should the main ground conductor be made if the building has several separate inputs?
Answer . Must be performed for each input device.

Protective conductors (PE conductors)

Which conductors can be used as PE conductors in electrical installations up to 1 kV?
Answer . Can be used:
- specially provided conductors, cores of multi-core cables, insulated or uninsulated wires in a common sheath with phase wires, permanently laid insulated or uninsulated conductors;
- HRC of electrical installations: aluminum sheaths of cables, steel pipes of electric wires, metal sheaths and supporting structures of bus ducts and complete prefabricated devices;
- some third-party conductive parts: metal building structures of buildings and structures (trusses, columns, etc.), reinforcement of reinforced concrete building structures of buildings, provided that the requirements given in the answer to question 300 are met, metal structures for industrial purposes (crane rails, galleries, platforms, elevator shafts, lifts, elevators, channel framing, etc.).
Can third-party conductive parts be used as PE conductors?
Answer . They can be used if they meet the requirements of this chapter for conductivity and, in addition, simultaneously meet the following requirements: the continuity of the electrical circuit is ensured either by their design or by appropriate connections protected from mechanical, chemical and other damage; their dismantling is not possible unless measures are taken to preserve the continuity of the circuit and its conductivity.
What is not allowed to be used as PE conductors?
Answer . It is not allowed to use: metal sheaths of insulating pipes and tubular wires, carrying cables for cable electrical wiring, metal hoses, as well as lead sheaths of wires and cables; gas supply pipelines and other pipelines of combustible and explosive substances and mixtures, sewerage and central heating pipes; water pipes with insulating inserts in them.
In what cases is it not allowed to use zero protective conductors as protective conductors?
Answer . It is not allowed to use zero protective conductors of equipment powered by other circuits as protective conductors, as well as use the HFC of electrical equipment as zero protective conductors for other electrical equipment, with the exception of shells and supporting structures of busbars and factory-made complete devices that provide the ability to connect protective conductors to them. conductors elsewhere.
What should be the smallest cross-sectional areas of protective conductors?
Answer . Must comply with the data in table 1
Table 1

Section of phase conductors, mm 2	The smallest section of protective conductors, mm
S≤16	S
16	16
S>35	S/2

It is allowed, if necessary, to take the cross-section of protective conductors less than required, if it is calculated according to the formula (only for disconnection time ≤ 5 s):
S ≥ I √ t/k
where S is the cross-sectional area of ​​the protective conductor, mm 2 ;
I - short-circuit current, providing the time for disconnecting the damaged circuit by the protective device or for a time not exceeding 5 s, A;
t is the response time of the protective device, s;
k - coefficient, the value of which depends on the material of the conductor, its insulation, initial and final temperatures. The values ​​of k for protective conductors under various conditions are given in Table. 1.7.6-1.7.9 of Chapter 1.7 of the Electrical Installation Rules (seventh edition).

Combined zero protective and zero working conductors (PEN-conductors)
In what circuits can the functions of zero protective (PE) and zero working (N) conductors be combined in one conductor (PEN-conductor)?
Answer . Can be combined in multi-phase circuits in the TN system for permanently laid cables, the cores of which have a cross-sectional area of ​​at least 10 mm 2 for copper or 16 mm 2 for aluminum.
In which circuits is it not allowed to combine the functions of the zero protective and zero working conductors?
Answer . Not allowed in single-phase and direct current circuits. A separate third conductor must be provided as a zero protective conductor in such circuits. This requirement does not apply to branches from overhead lines up to 1 kV to single-phase electricity consumers.
Is it acceptable to use third party conductive parts as the only PEN conductor?
Answer . Such use is not permitted. This requirement does not exclude the use of open and third-party conductive parts as an additional PEN conductor when connecting them to a potential equalization system.
When the zero working and zero protective conductors are separated, starting from any point of the electrical installation, is it allowed to combine them beyond this point along the distribution of energy?
Answer . Such association is not allowed.
Connections and connection of grounding, protective conductors and conductors of the control and potential equalization system
How should the grounding and zero protective conductors and potential equalization conductors be connected to the HRC?
Answer . Must be made by bolting or welding.
How should each HRE of an electrical installation be connected to a zero protective or protective earth conductor?
Answer . Must be done with a separate branch. Serial connection to the protective conductor of the HFC is not allowed.
Is it possible to include switching devices in the circuits of PE- and PEN- conductors?
Answer. Such inclusion is not allowed, except for the cases of supplying electrical receivers with the help of sockets.
What are the requirements for sockets and plugs of a plug connection if the protective conductors and/or potential equalization conductors can be disconnected using the same plug connection?
Answer . They must have special protective contacts for connecting protective conductors or potential equalization conductors to them. Portable electrical receivers
What measures can be taken to protect against indirect contact in circuits supplying portable electrical receivers?
Answer . Depending on the category of the premises according to the level of danger of electric shock to people, automatic power off, protective electrical separation of circuits, extra low voltage, double insulation can be applied.

What are the requirements for connecting to a neutral protective conductor in the TN system or to grounding in the IT system of metal cases of portable electrical receivers when using automatic power off?

Answer . To do this, a special protective (PE) conductor must be provided, located in the same sheath with phase conductors (the third core of the cable or wire - for single-phase and direct current electrical receivers, the fourth or fifth core - for three-phase current electrical receivers), attached to the body of the electrical receiver and to protective contact of the plug. The use of a zero working (N) conductor for these purposes, including one located in a common sheath with phase conductors, is not allowed.
How should socket outlets with a rated current of not more than 20 A of outdoor installation, as well as indoor installation, be additionally protected, but to which portable power receivers used outside buildings or in rooms with increased danger can be connected?
Answer . RCDs with a rated residual current not exceeding 30 mA must be protected. It is allowed to use hand-held power tools equipped with RCD plugs.
Mobile electrical installations
What should be applied for automatic power off?
Answer. To be used: an overcurrent protective device in combination with an RCD reacting to differential current, or a continuous insulation monitoring device acting to trip, or an RCD reacting to the housing potential relative to earth.

Posted on 08/14/2011 (valid until 02/22/2013)

Any part of an electrical installation and another installation is called the intentional electrical connection of this part with a grounding device.

Protective earth called grounding of parts of an electrical installation in order to ensure electrical safety.

Working grounding called the grounding of any point of the current-carrying parts of the electrical installation, necessary to ensure the operation of the electrical installation.

Zeroing in electrical installations with voltages up to 1 kV, it is called the deliberate connection of parts of an electrical installation that are not normally energized with a dead-earthed neutral of a generator or transformer in three-phase current networks, with a dead-earthed output of a single-phase current source and with a dead-earthed midpoint of the source in DC networks.

ground electrode called a conductor (electrode) or a set of metal-connected conductors (electrodes) that are in contact with the ground.

deaf-earthed neutral is the neutral of a transformer or generator, connected to a grounding device directly or through a small resistance (for example, through current transformers).

GOST R 50571.2-94 provides for the following types of grounding systems for electrical networks: TN-S, TN-C, TN-C-S, IT, TT. For buildings, you can mainly find TN-S, TN-C, TN-C-S schemes. Schemes IT, TT are typical, as a rule, for local areas inside the building and provide telecommunication systems powered by direct current. The letters and graphic symbols used in the above designations of the types of grounding systems and in the figures are deciphered in Table. 6.1 and 6.2.

Grounding (zeroing) of computer equipment, telecommunication facilities and technological equipment provides a solution to two main tasks:

Protection of personnel from electric shock in case of damage to the insulation and short circuit of one of the wires of the supply line to the equipment case or from the appearance of a potential dangerous for humans on the equipment case for any other reason (for example, due to inductive or capacitive couplings);

Protection of equipment and information exchange lines (including local area networks) from interference that occurs from supply networks due to the potential difference between different points of the ground circuits and stray currents in the ground circuits due to external electromagnetic fields and other reasons.

Table 6.1. Letter designations grounding systems and grounding conductors

Table 6.2. Symbols of conductors

The first task is solved with the help of protective grounding devices, performed in accordance with Ch. 1.7 PUE, GOST R 50571.10-96, GOST R 50571.21-2000, GOST R 50571.22-2000. The second task is solved by laying special grounding or zero protective conductors connected to a single electrical connecting network.

In accordance with GOST R 50571.10-96, in the case when grounding is required both for protection and for the normal operation of the electrical installation, the requirements for protective measures should be observed in the first place.

The presence of closed loops and connections between grounding systems for various purposes may be accompanied by the occurrence of intersystem grounding noise, which cannot be eliminated by installing uninterruptible power supplies and other power conditioning (improvement) devices without galvanic isolation. In some cases, formally fulfilling the requirements of GOST 464-79 for the organization of a separate grounding system for telecommunications facilities, a separate grounding system is created, for example, for a corporate digital telephone exchange. This ignores the fact that the standard requires a separate earthing system for the pole of the DC power system. Powering the equipment from a common AC network with a solidly grounded neutral and performing a seemingly isolated grounding just leads to a situation where ground loops are formed, causing unstable operation of the equipment. The ground loop, in contrast to the jargon "ground loop" (connection of horizontal ground electrodes in the ground), is undesirable and is formed when there is a connection between two ground electrodes (Fig. 6.1).

Rice. 6.1. Ground loop

In the resulting circuit, ground electrode 1 - electrical connection (conductor) - ground conductor 2 - environment (earth) currents from external electromagnetic fields can be induced or stray currents of third-party loads can flow. All this leads to electromagnetic interference in the operation of the equipment. Local computer and telecommunication networks often include communication equipment (antennas, modems, etc.) and are subject to interference, including from lightning discharges, so high noise immunity is important for them. Due to this circumstance, special attention should be paid to the elimination of contours in the design and operation of electrical installations of buildings.

In practice, there is also an erroneous grounding of a separate electrical receiver or a group of electrical receivers to a separate ground electrode that is not connected to the neutral of the transformer (Fig. 6.2). This grounding scheme resembles a TT scheme, with the only difference that this violates clause 1.7.39 of the PKE, which reads: “In electrical installations up to 1 kV with a solidly grounded neutral or a solidly grounded output of a single-phase current source, as well as with a solidly grounded midpoint in three-wire DC networks must be grounded. The use in such electrical installations of grounding the housings of electrical receivers without their grounding is not allowed ... ". This requirement is due to the fact that it is impossible to ensure electrical safety with such a scheme. On fig. 6.2 shows the removal of the potential in case of a short circuit to the body of the power receiver, grounded to a separate ground electrode.

Rice. 6.2. Removal of the potential on the non-zeroed body of the equipment

The potential on the case will be due to the voltage drop in the phase conductor to the short circuit point and the voltage drop in the resistance of the ground electrode 2, in the environment (in the ground and structures) and in the resistance of the earth electrode 1. The resistance of the short circuit circuit will be more resistance circuit "phase-zero", based on the parameters of which a circuit breaker is selected, and short circuit will most likely not be tripped by the overcurrent protection action. In this case, a potential close to phase voltage which will pose a threat to human life. Disconnection of short circuit will occur due to the action of thermal protection circuit breaker, but the short circuit disconnection time will exceed the normalized values.

The characteristics of the protection devices and the impedance of the "phase-zero" circuit must ensure automatic power off within the specified time in case of short circuits to open conductive parts.

This requirement is met if the following condition is met:

Z s I a

where Z s is the total resistance of the phase-zero circuit; I a - current, less than the short-circuit current, causing the protection device to operate in a time that is a function of the rated voltage Uo; Uo - rated voltage (effective value) between phase and earth.

The maximum permissible outage times for TN systems are:

Uo = 220 V, off time - 0.4 s;

Uo = 380 V, off time - 0.2 s.

Thus, improperly performed grounding leads to the formation of unwanted loops and causes electromagnetic interference in the operation of equipment, as well as a threat to human life.