Laying cable ducts in the ground. Crossing and bringing together cables in the ground

SCOPE, DEFINITIONS

2.3.1. This chapter of the Rules applies to cable power lines up to 220 kV, as well as lines carried out by control cables. Cable lines of higher voltages are carried out according to special projects. Additional requirements for cable lines are given in Chapter. 7.3, 7.4 and 7.7.

2.3.2. A cable line is a line for transmitting electricity or its individual pulses, consisting of one or more parallel cables with connecting, locking and end couplings (terminals) and fasteners, and for oil-filled lines, in addition, with feeding devices and an oil pressure alarm system.

2.3.3. A cable structure is a structure specifically designed to house cables, cable couplings, as well as oil-feeding devices and other equipment designed to ensure the normal operation of oil-filled cables. cable lines. Cable structures include: cable tunnels, channels, ducts, blocks, shafts, floors, double floors, cable overpasses, galleries, chambers, feeding points.

A cable tunnel is a closed structure (corridor) with supporting structures located in it for placing cables and cable couplings on them, with free passage along the entire length, allowing for cable laying, repairs and inspections of cable lines.

A cable channel is a closed and buried (partially or completely) impenetrable structure in the ground, floor, ceiling, etc., designed to accommodate cables, the installation, inspection and repair of which can only be done with the ceiling removed.

A cable shaft is a vertical cable structure (usually rectangular in cross-section), the height of which is several times greater than the side of the section, equipped with brackets or a ladder for people to move along it (through shafts) or a completely or partially removable wall (non-through shafts).

A cable floor is a part of a building bounded by a floor and a ceiling or covering, with a distance between the floor and the protruding parts of the ceiling or covering of at least 1.8 m.

A double floor is a cavity bounded by the walls of a room, the interfloor ceiling and the floor of a room with removable slabs (over all or part of the area).

A cable block is a cable structure with pipes (channels) for laying cables in them with associated wells.

A cable chamber is an underground cable structure, covered with a blind removable concrete slab, intended for laying cable couplings or for pulling cables into blocks. A chamber that has a hatch to enter it is called a cable well.

A cable overpass is an overhead or ground-based open horizontal or inclined extended cable structure. The cable rack can be pass-through or non-pass-through.

A cable gallery is an above-ground or above-ground, fully or partially closed (for example, without side walls) horizontal or inclined extended cable passage structure.

2.3.4. It is called a box - see 2.1.10.

2.3.5. It's called a tray - see 2.1.11.

2.3.6. An oil-filled cable line of low or high pressure is a line in which the long-term permissible excess pressure is:

0.0245-0.294 MPa (0.25-3.0 kgf/cm2) for low-pressure lead-sheathed cables;

0.0245-0.49 MPa (0.25-5.0 kgf/cm2) for low pressure cables in aluminum sheath;

1.08-1.57 MPa (11-16 kgf/cm2) for high pressure cables.

2.3.7. A low-pressure oil-filled cable line section is the section of the line between the stop couplings or the stop and end couplings.

2.3.8. A feeding point is an above-ground, above-ground or underground structure with feeding devices and equipment (power tanks, pressure tanks, feeding units, etc.).

2.3.9. A branching device is the part of a high pressure cable line between the end of a steel pipeline and the single-phase end couplings.

2.3.10. A feeding unit is an automatically operating device consisting of tanks, pumps, pipes, bypass valves, taps, an automation panel and other equipment designed to provide oil replenishment to a high-pressure cable line.

GENERAL REQUIREMENTS

2.3.11. The design and construction of cable lines must be carried out on the basis of technical and economic calculations, taking into account the development of the network, the responsibility and purpose of the line, the nature of the route, the installation method, cable designs, etc.

2.3.12. When choosing a cable line route, you should, if possible, avoid areas with soils that are aggressive to the metal sheaths of cables (see also 2.3.44).

2.3.13. Above underground cable lines, in accordance with the current rules for the protection of electrical networks, security zones must be installed in the size of the area above the cables:

for cable lines above 1 kV, 1 m on each side of the outer cables;

for cable lines up to 1 kV, 1 m on each side of the outer cables, and when cable lines pass in cities under sidewalks - 0.6 m towards buildings and 1 m towards the roadway.

For submarine cable lines up to and above 1 kV, in accordance with the specified rules, a security zone must be established, defined by parallel straight lines at a distance of 100 m from the outermost cables.

Security zones of cable lines are used in compliance with the requirements of the rules for the protection of electrical networks.

2.3.14. The cable line route should be selected taking into account the lowest cable consumption, ensuring its safety under mechanical stress, providing protection from corrosion, vibration, overheating and from damage to adjacent cables by an electric arc in the event of a short circuit on one of the cables. When placing cables, avoid crossing them with each other, with pipelines, etc.

When choosing the route of a low-pressure oil-filled cable line, the terrain is taken into account for the most rational placement and use of feed tanks on the line.

2.3.15. Cable lines must be constructed in such a way that during installation and operation the occurrence of dangerous mechanical stresses and damage in them is excluded, for which:

cables must be laid with a reserve length sufficient to compensate for possible soil displacements and temperature deformations of the cables themselves and the structures along which they are laid; It is prohibited to lay cable reserves in the form of rings (turns);

cables laid horizontally along structures, walls, ceilings, etc. must be rigidly secured at the end points, directly at the end seals, on both sides of bends and at connecting and locking couplings;

cables laid vertically along structures and walls must be secured in such a way that deformation of the shells is prevented and the connections of the cores in the couplings are not broken under the influence of the cables’ own weight;

structures on which unarmored cables are laid must be made in such a way that the possibility of mechanical damage to the cable sheaths is excluded; in places of rigid fastening, the sheaths of these cables must be protected from mechanical damage and corrosion using elastic gaskets;

cables (including armored ones) located in places where mechanical damage is possible (movement of vehicles, machinery and cargo, accessibility to unauthorized persons) must be protected in height by 2 m from the floor or ground level and by 0.3 m in earth;

when laying cables near other cables in operation, measures must be taken to prevent damage to the latter;

cables must be laid at a distance from heated surfaces that prevents heating of the cables above the permissible level, while protection of the cables from the breakthrough of hot substances in the places where valves and flange connections are installed must be provided.

2.3.16. Protection of cable lines from stray currents and soil corrosion must meet the requirements of these Rules and SNiP 3-04.03-85 “Protection of building structures and structures from corrosion” of the State Construction Committee of Russia.

2.3.17. The designs of underground cable structures must be calculated taking into account the mass of cables, soil, road surface and load from passing traffic.

2.3.18. Cable structures and structures on which cables are laid must be made of fireproof materials. It is prohibited to install any temporary devices in cable structures or store materials and equipment in them. Temporary cables must be laid in compliance with all requirements for cable laying, with the permission of the operating organization.

2.3.19. Open laying of cable lines should be carried out taking into account the direct effect of solar radiation, as well as heat radiation from various types of heat sources. When laying cables at latitudes greater than 65°, protection from solar radiation is not required.

2.3.20. The radii of the internal bending curve of cables must have a multiple of at least those specified in the standards or technical specifications for the corresponding brands of cables in relation to their outer diameter.

2.3.21. The radii of the internal bending curve of the cable cores when performing cable terminations must have, in relation to the given diameter of the cores, a multiple of not less than those specified in the standards or technical specifications for the corresponding brands of cables.

2.3.22. Tensile forces when laying cables and pulling them in pipes are determined by the mechanical stresses permissible for cores and sheaths.

2.3.23. Each cable line must have its own number or name. If a cable line consists of several parallel cables, then each of them must have the same number with the addition of the letters A, B, C, etc. Openly laid cables, as well as all cable couplings, must be equipped with tags with the designation on the cable tags and end couplings brand, voltage, section, number or name of the line; on the coupling tags - coupling numbers and installation dates. Tags must be resistant to impact environment. On cables laid in cable structures, tags must be located along the length at least every 50 m.

2.3.24. Security zones of cable lines laid underground in undeveloped areas must be marked with information signs. Information signs should be installed at least every 500 m, as well as in places where the direction of cable lines changes. Information signs must indicate the width of the security zones of cable lines and the telephone numbers of cable line owners. (see Appendix "Requirements for information signs and their installation")

SELECTION OF LAYING METHODS

2.3.25. When choosing methods for laying power cable lines up to 35 kV, you must be guided by the following:

1. When laying cables in the ground, it is recommended to lay no more than six cables in one trench power cables. If there are a larger number of cables, it is recommended to lay them in separate trenches with a distance between groups of cables of at least 0.5 m or in channels, tunnels, overpasses and galleries.

2. Laying cables in tunnels, along overpasses and in galleries is recommended when the number of power cables running in one direction is more than 20.

3. Laying cables in blocks is used in conditions of very tight spaces along the route, at intersections with railway tracks and driveways, when there is a possibility of a metal spill, etc.

4. When choosing methods for laying cables across urban areas, initial capital costs and costs associated with maintenance and repair work, as well as the convenience and cost-effectiveness of maintaining structures, should be taken into account.

2.3.26. In the territories of power plants, cable lines must be laid in tunnels, ducts, channels, blocks, along overpasses and in galleries. Laying power cables in trenches is allowed only to remote auxiliary facilities (fuel depots, workshops) with a number of no more than six. In the territories of power plants with a total capacity of up to 25 MW, laying cables in trenches is also allowed.

2.3.27. In the territories of industrial enterprises, cable lines must be laid in the ground (in trenches), tunnels, blocks, channels, along overpasses, in galleries and along the walls of buildings.

2.3.28. In the areas of substations and distribution facilities, cable lines must be laid in tunnels, ducts, channels, pipes, in the ground (in trenches), ground reinforced concrete trays, along overpasses and in galleries.

2.3.29. In cities and towns, single cable lines should, as a rule, be laid in the ground (in trenches) along impassable parts of streets (under sidewalks), along courtyards and technical strips in the form of lawns.

2.3.30. In streets and squares saturated with underground communications, it is recommended to lay 10 or more cable lines in a stream in collectors and cable tunnels. When crossing streets and squares with improved surfaces and heavy traffic, cable lines should be laid in blocks or pipes.

2.3.31. When constructing cable lines in permafrost areas, one should take into account the physical phenomena associated with the nature of permafrost: heaving soil, frost cracks, landslides, etc. Depending on local conditions, cables can be laid in the ground (in trenches) below the active layer, in active layer in dry, well-draining soils, in artificial embankments made of large-skeletal dry imported soils, in trays on the surface of the earth, on overpasses. It is recommended to jointly lay cables with pipelines for heating, water supply, sewerage, etc. in special structures (collectors).

2.3.32. The implementation of different types of cable laying in permafrost areas should be carried out taking into account the following:

1. For laying cables in earthen trenches, the most suitable soils are draining soils (rock, pebble, gravel, crushed stone and coarse sand); heaving and subsidence soils are unsuitable for laying cable lines in them. Cables can be laid directly in the ground if the number of cables is no more than four. Due to soil, permafrost and climatic conditions, laying cables in pipes laid in the ground is prohibited. At intersections with other cable lines, roads and underground communications, cables should be protected with reinforced concrete slabs.

Laying cables near buildings is not permitted. The entry of cables from the trench into the building in the absence of a ventilated underground must be carried out above the zero mark.

2. Laying cables in channels may be used in places where the active layer consists of non-heaving soils and has a flat surface with a slope of no more than 0.2%, ensuring surface water drainage. Cable ducts should be made of waterproof reinforced concrete and covered on the outside with reliable waterproofing. The channels must be covered from above with reinforced concrete slabs. Channels can be made buried in the ground or without burial (on top of the ground). In the latter case, a cushion with a thickness of at least 0.5 m of dry soil must be made under the channel and near it.

2.3.33. Inside buildings, cable lines can be laid directly along building structures (open and in boxes or pipes), in channels, blocks, tunnels, pipes laid in floors and ceilings, as well as along machine foundations, in shafts, cable floors and double floors.

2.3.34. Oil-filled cables can be laid (with any number of cables) in tunnels and galleries and in the ground (in trenches); the method of laying them is determined by the project.

CABLE SELECTION

2.3.35. For cable lines laid along routes passing in different soils and environmental conditions, the choice of cable designs and sections should be made along the section with the most severe conditions, if the length of sections with easier conditions does not exceed the construction length of the cable. If there are significant lengths of individual sections of the route with different laying conditions, appropriate designs and cable sections should be selected for each of them.

2.3.36. For cable lines laid along routes with different cooling conditions, cable sections must be selected according to the section of the route with the worst cooling conditions, if its length is more than 10 m. It is allowed for cable lines up to 10 kV, with the exception of underwater, to use cables of different sections, but no more than three, provided that the length of the shortest segment is at least 20 m (see also 2.3.70).

2.3.37. For cable lines laid in land or water, armored cables should be used predominantly. The metal sheaths of these cables must have an outer covering to protect them from chemical attack. Cables with other designs of external protective coatings (unarmoured) must have the necessary resistance to mechanical stress when laid in all types of soil, when pulled in blocks and pipes, as well as resistance to thermal and mechanical stress during maintenance and repair work.

2.3.38. Pipelines of oil-filled high-pressure cable lines laid in the ground or water must be protected against corrosion in accordance with the design.

2.3.39. In cable structures and production premises, if there is no danger of mechanical damage in operation, it is recommended to lay unarmored cables, and if there is a danger of mechanical damage in operation, armored cables should be used or protected from mechanical damage.

Outside cable structures, it is allowed to lay unarmored cables at an inaccessible height (at least 2 m); at a lower height, laying unarmored cables is permitted provided they are protected from mechanical damage (ducts, angle steel, pipes, etc.).

For mixed installation (ground - cable structure or industrial premises), it is recommended to use the same grades of cables as for installation in the ground (see 2.3.37), but without flammable outer protective coverings.

2.3.40. When laying cable lines in cable structures, as well as in industrial premises, armored cables should not have protective coverings made of flammable materials on top of the armor, and unarmored cables on top of metal sheaths.

For open installation, it is not allowed to use power and control cables with flammable polyethylene insulation.

The metal sheaths of cables and the metal surfaces on which they are laid must be protected with a non-flammable anti-corrosion coating.

When laying in rooms with an aggressive environment, cables that are resistant to this environment must be used.

2.3.41. For cable lines of power plants, switchgears and substations specified in 2.3.76, it is recommended to use cables armored with steel tape protected by a non-flammable coating. At power plants, the use of cables with flammable polyethylene insulation is not allowed.

2.3.42. For cable lines laid in cable blocks and pipes, as a rule, unarmored cables in a reinforced lead sheath should be used. In sections of blocks and pipes, as well as branches from them up to 50 m long, it is allowed to lay armored cables in a lead or aluminum sheath without an outer covering of cable yarn. For cable lines laid in pipes, the use of cables in a plastic or rubber sheath is allowed.

2.3.43. For installation in soils containing substances that have a destructive effect on cable sheaths (salt marshes, swamps, bulk soil with slag and building materials, etc.), as well as in areas dangerous due to the effects of electrocorrosion, cables with lead sheaths must be used and reinforced protective covers of types B, B or cables with aluminum sheaths and especially reinforced protective covers of types B, B (in a continuous moisture-resistant plastic hose).

2.3.44. Where cable lines cross swamps, cables must be selected taking into account geological conditions, as well as chemical and mechanical influences.

2.3.45. For installation in soils subject to displacement, cables with wire armor must be used or measures must be taken to eliminate the forces acting on the cable when the soil moves (soil reinforcement with sheet piling or pile rows, etc.).

2.3.46. Where cable lines cross streams, their floodplains and ditches, the same cables should be used as for laying in the ground (see also 2.3.99).

2.3.47. For cable lines laid over railway bridges, as well as other bridges with heavy traffic, it is recommended to use armored cables in an aluminum sheath.

2.3.48. For cable lines of mobile mechanisms, flexible cables with rubber or other similar insulation that can withstand repeated bending should be used (see also 1.7.111).

2.3.49. For submarine cable lines, cables with round wire armor should be used, if possible of the same construction length. For this purpose, the use of single-core cables is permitted.

In places where cable lines pass from shore to sea in the presence of strong sea surf, when laying cables in sections of rivers with strong currents and eroded banks, as well as at great depths (up to 40-60 m), a cable with double metal armor should be used.

Cables with rubber insulation in a polyvinyl chloride sheath, as well as cables in an aluminum sheath without special waterproof coatings, are not allowed for installation in water.

When laying cable lines through small non-navigable and non-floating rivers with a width (including the floodplain) of no more than 100 m, with a stable bed and bottom, the use of cables with tape armor is allowed.

2.3.50. For oil-filled cable lines with a voltage of 110-220 kV, the type and design of cables are determined by the project.

2.3.51. When laying cable lines up to 35 kV on vertical and inclined sections of the route with a level difference exceeding that allowed by GOST for cables with viscous impregnation, cables with a non-draining impregnation mass, cables with depleted impregnated paper insulation and cables with rubber or plastic insulation must be used. For the specified conditions, cables with viscous impregnation may only be used with stop couplings placed along the route, in accordance with the permissible level differences for these cables according to GOST.

The difference in vertical elevations between the locking couplings of low-pressure oil-filled cable lines is determined by the corresponding technical specifications for the cable and the calculation of recharge under extreme thermal conditions.

2.3.52. In four-wire networks, four-core cables must be used. Laying neutral conductors separately from phase conductors is not permitted. It is allowed to use three-core power cables in an aluminum sheath with a voltage of up to 1 kV using their sheath as a neutral wire (fourth wire) in four-wire networks alternating current(lighting, power and mixed) with a solidly grounded neutral, with the exception of installations with an explosive atmosphere and installations in which, under normal operating conditions, the current in the neutral wire is more than 75% of the permissible long-term current of the phase wire.

The use of lead sheaths of three-core power cables for this purpose is allowed only in reconstructed urban areas. electrical networks 220/127 and 380/220 V.

2.3.53. For cable lines up to 35 kV, it is allowed to use single-core cables if this leads to significant savings in copper or aluminum compared to three-core cables or if it is not possible to use a cable of the required construction length. The cross-section of these cables must be selected taking into account their additional heating by currents induced in the sheaths.

Measures must also be taken to ensure equal distribution of current between parallel-connected cables and safe touching of their shells, to prevent heating of metal parts in the immediate vicinity and to securely fasten the cables in insulating clasps.

FEEDING DEVICES AND OIL PRESSURE ALARM FOR CABLE OIL-FILLED LINES

2.3.54. The oil-feeding system must ensure reliable operation of the line in any normal and transient thermal conditions.

2.3.55. The amount of oil in the oil-feeding system must be determined taking into account the consumption for feeding the cable. In addition, there must be a supply of oil for emergency repairs and for filling the longest section of the cable line with oil.

2.3.56. Feeding tanks for low pressure lines are recommended to be placed in enclosed spaces. It is recommended to place a small number of feeding tanks (5-6) at open feeding points in light metal boxes on portals, supports, etc. (at an ambient temperature of at least minus 30°C). Feed tanks must be equipped with oil pressure indicators and protected from direct exposure to solar radiation.

2.3.57. Feeding units for high-pressure lines must be located in enclosed spaces with a temperature not lower than +10°C, and located as close as possible to the point of connection to the cable lines (see also 2.3.131). Several feeding units are connected to the line through an oil manifold.

2.3.58. When laying several high-pressure oil-filled cable lines in parallel, it is recommended that each line be topped up with oil from separate feeding units, or a device should be installed to automatically switch the units to one or another line.

2.3.59. It is recommended that the feeding units be provided with electricity from two independent power sources with a mandatory automatic transfer switch (ATS) device. Feeding units must be separated from one another by fireproof partitions with a fire resistance rating of at least 0.75 hours.

2.3.60. Each oil-filled cable line must have an oil pressure alarm system that ensures registration and transmission to duty personnel of signals about a decrease or increase in oil pressure above permissible limits.

2.3.61. At least two sensors must be installed on each section of the low-pressure oil-filled cable line, and on the high-pressure line - a sensor on each feeding unit. Emergency signals must be transmitted to a point with permanent personnel on duty. The oil pressure alarm system must be protected from the influence of electric fields of power cable lines.

2.3.62. Feeding points on low pressure lines must be equipped with telephone communication with control centers (electricity network, network area).

2.3.63. The oil pipeline connecting the manifold of the feeding unit with the high-pressure oil-filled cable line must be laid in rooms with a positive temperature. It is allowed to lay it in insulated trenches, trays, channels and in the ground below the freezing zone, provided that a positive ambient temperature is ensured.

2.3.64. Vibration in the switchboard room with devices for automatic control of the feeding unit should not exceed permissible limits.

CABLE CONNECTIONS AND TERMINATIONS

2.3.65. When connecting and terminating power cables, coupling designs that comply with their operating and environmental conditions should be used. Connections and terminations on cable lines must be made in such a way that the cables are protected from the penetration of moisture and other harmful substances from the environment into them and that the connections and terminations can withstand the test voltages for the cable line and comply with GOST requirements.

2.3.66. For cable lines up to 35 kV, end and connecting couplings must be used in accordance with the current technical documentation for couplings, approved in accordance with the established procedure.

2.3.67. For connecting and locking couplings of low-pressure oil-filled cable lines, only brass or copper couplings should be used.

The length of sections and installation locations of locking couplings on low-pressure oil-filled cable lines are determined taking into account the replenishment of the lines with oil in normal and transient thermal conditions.

Stop and half-stop couplings on oil-filled cable lines must be placed in cable wells; When laying cables in the ground, it is recommended to place connecting couplings in chambers that are subject to subsequent backfilling with sifted earth or sand.

In areas with electrified transport (metropolitan, trams, railways) or with soils that are aggressive to the metal shells and couplings of cable lines, the couplings must be accessible for inspection.

2.3.68. On cable lines made with cables with normally impregnated paper insulation and cables impregnated with a non-drip compound, cable connections must be made using stop-transition couplings if the laying level of cables with normally impregnated insulation is higher than the laying level of cables impregnated with a non-drip compound (see also 2.3 .51).

2.3.69. On cable lines above 1 kV, made with flexible cables with rubber insulation in a rubber hose, cable connections must be made by hot vulcanization and coated with anti-damp varnish.

2.3.70. The number of couplings per 1 km of newly constructed cable lines should be no more than: for three-core cables 1-10 kV with a cross-section of up to 3x95 mm2 4 pcs.; for three-core cables 1-10 kV with sections 3x120 - 3x240 mm2 5 pcs.; for three-phase cables 20-35 kV 6 pcs.; for single-core cables 2 pcs.

For cable lines 110-220 kV, the number of connecting couplings is determined by the design.

The use of undersized cable sections for the construction of long cable lines is not permitted.

GROUNDING

2.3.71. Cables with metal sheaths or armor, as well as cable structures on which cables are laid, must be grounded or neutralized in accordance with the requirements given in Chapter. 1.7.

2.3.72. When grounding or neutralizing the metal sheaths of power cables, the sheath and armor must be connected by a flexible copper wire to each other and to the housings of the couplings (end, connecting, etc.). On cables of 6 kV and above with aluminum sheaths, grounding of the sheath and armor must be carried out with separate conductors.

It is not required to use grounding or neutral protective conductors with a conductivity greater than the conductivity of the cable sheaths, however, the cross-section in all cases must be at least 6 mm2.

The cross-sections of grounding conductors of control cables should be selected in accordance with the requirements of 1.7.76-1.7.78.

If an external end coupling and a set of arresters are installed on the structure support, then the armor, metal shell and coupling must be connected to the grounding device of the arresters. In this case, using only metallic cable sheaths as a grounding device is not allowed.

Overpasses and galleries must be equipped with lightning protection in accordance with RD 34.21.122-87 "Instructions for the installation of lightning protection of buildings and structures" of the USSR Ministry of Energy.

2.3.73. On oil-filled low-pressure cable lines, the end, connecting and locking couplings are grounded.

On cables with aluminum sheaths, feeders must be connected to the lines through insulating inserts, and the housings of the end couplings must be insulated from the aluminum sheaths of the cables. This requirement does not apply to cable lines with direct input into transformers.

When using armored cables for low-pressure oil-filled cable lines in each well, the cable armor on both sides of the coupling must be welded and grounded.

2.3.74. The steel pipeline of oil-filled high-pressure cable lines laid in the ground must be grounded in all wells and at the ends, and those laid in cable structures - at the ends and at intermediate points determined by calculations in the project.

If it is necessary to actively protect a steel pipeline from corrosion, its grounding is carried out in accordance with the requirements of this protection, and it must be possible to control the electrical resistance of the anti-corrosion coating.

2.3.75. When a cable line transitions into an overhead line (OHL) and if there is no grounding device at the overhead line support, cable couplings (mast) can be grounded by attaching the metal sheath of the cable, if the cable coupling at the other end of the cable is connected to a grounding device or the grounding resistance of the cable sheath complies with the requirements of Chapter. 1.7.

SPECIAL REQUIREMENTS FOR CABLE FACILITIES OF POWER PLANTS, SUBSTATIONS AND DISTRIBUTION DEVICES

2.3.76. The requirements given in 2.3.77-2.3.82 apply to cable facilities of thermal and hydroelectric power plants with a capacity of 25 MW or more, switchgears and substations with a voltage of 220-500 kV, as well as switchgears and substations of particular importance in the power system (see. also 2.3.113).

2.3.77. The main electrical connection diagram, the auxiliary diagram and the operating current diagram, equipment control and layout of the equipment and cable management of a power plant or substation must be carried out in such a way that in case of fires in the cable management or outside it, disruptions to the operation of more than one unit of the power plant are excluded, simultaneous loss of mutually redundant connections of switchgears and substations, as well as failure of fire detection and extinguishing systems.

2.3.78. For the main cable flows of power plants, cable structures (floors, tunnels, shafts, etc.) must be provided, isolated from the process equipment and preventing access to the cables by unauthorized persons.

When placing cable flows at power plants, cable routes must be selected taking into account:

preventing overheating of cables from heated surfaces of technological equipment;

preventing damage to cables during dust emissions (fires and explosions) through the safety devices of dust systems;

preventing the laying of transit cables in hydraulic ash removal technological tunnels, chemical water treatment rooms, as well as in places where pipelines with chemically aggressive liquids are located.

2.3.79. Mutually redundant critical cable lines (power, operating current, communications, control, alarm systems, fire extinguishing systems, etc.) must be laid in such a way that during fires the possibility of simultaneous loss of mutually redundant cable lines is excluded. In areas of cable facilities where the occurrence of an accident threatens it great development, cable flows should be divided into groups isolated from one another. The distribution of cables into groups depends on local conditions.

2.3.80. Within one power unit, it is permitted to construct cable structures with a fire resistance limit of 0.25 hours. In this case, technological equipment that can serve as a source of fire (oil tanks, oil stations, etc.) must have fences with a fire resistance limit of at least 0.75 h, eliminating the possibility of cables catching fire in the event of a fire on this equipment.

Within one power unit of a power plant, it is permitted to lay cables outside special cable structures, provided that they are reliably protected from mechanical damage and dust, from sparks and fire during repairs of process equipment, and that normal temperature conditions for cable lines are ensured and their maintenance is convenient.

To provide access to cables when they are located at a height of 5 m or more, special platforms and passages must be constructed.

For single cables and small groups of cables (up to 20), operational platforms may not be constructed, but it must be possible to quickly replace and repair cables under operating conditions.

When laying cables within one power unit outside special cable structures, it should be ensured, if possible, that they are divided into separate groups running along different routes.

2.3.81. Cable floors and tunnels in which cables of various power units of a power plant are located, including cable floors and tunnels under block control panels, must be divided block by block and separated from other rooms, cable floors, tunnels, shafts, ducts and channels by fireproof partitions and ceilings with a fire resistance limit not less than 0.75 hours, including in places where cables pass.

In places where cables are supposed to pass through partitions and ceilings, in order to ensure the possibility of replacement and additional laying of cables, a partition made of fireproof, easily pierced material with a fire resistance rating of at least 0.75 hours must be provided.

In extended cable structures of thermal power plants, emergency exits must be provided, located, as a rule, at least every 50 m.

Cable facilities of power plants must be separated from outgoing network cable tunnels and collectors by fireproof partitions with a fire resistance rating of at least 0.75 hours.

2.3.82. The entry points of cables into the rooms of closed switchgears and into the rooms of control and protection panels of open switchgears must have partitions with a fire resistance rating of at least 0.75 hours.

The entry points of cables to the control panels of the power plant must be closed with partitions with a fire resistance rating of at least 0.75 hours.

Cable shafts must be separated from cable tunnels, floors and other cable structures by fireproof partitions with a fire resistance limit of at least 0.75 hours and have ceilings at the top and bottom. Extended shafts, when passing through ceilings, but at least after 20 m, must be divided into compartments by fireproof partitions with a fire resistance limit of at least 0.75 hours.

Walk-through cable shafts must have entrance doors and be equipped with ladders or special brackets.

LAYING CABLE LINES IN THE GROUND

2.3.83. When laying cable lines directly in the ground, the cables must be laid in trenches and have a backfill on the bottom and a layer of fine earth on top that does not contain stones, construction waste and slag.

Cables along their entire length must be protected from mechanical damage by covering them at voltages of 35 kV and above with reinforced concrete slabs with a thickness of at least 50 mm; at voltages below 35 kV - with slabs or ordinary clay bricks in one layer across the cable route; when digging a trench with an earth-moving mechanism with a cutter width of less than 250 mm, as well as for one cable - along the cable line route. The use of silicate, as well as clay hollow or perforated bricks is not allowed.

When laid at a depth of 1-1.2 m, cables of 20 kV and below (except for city power supply cables) may not be protected from mechanical damage.

Cables up to 1 kV should have such protection only in areas where mechanical damage is likely (for example, in places of frequent excavation). Asphalt surfaces of streets, etc. are considered as places where digging is carried out in rare cases. For cable lines up to 20 kV, except for lines above 1 kV that supply power receivers of category I*, it is allowed in trenches with no more than two cable lines to use signal plastic tapes instead of bricks that meet the technical requirements approved by the USSR Ministry of Energy. It is not allowed to use warning tapes at the intersections of cable lines with utility lines and above cable couplings at a distance of 2 m in each direction from the crossed utility line or coupling, as well as at the approaches of lines to switchgears and substations within a radius of 5 m.

____________
* According to local conditions, with the consent of the line owner, it is allowed to expand the scope of application of signal tapes.

The signal tape should be laid in a trench above the cables at a distance of 250 mm from their outer covers. When placing one cable in a trench, the tape must be laid along the axis of the cable; with a larger number of cables, the edges of the tape must protrude beyond the outer cables by at least 50 mm. When laying more than one tape across the width of a trench, adjacent tapes must be laid with an overlap of at least 50 mm wide.

When using signal tape, laying cables in a trench with a cable cushion, sprinkling the cables with the first layer of earth and laying the tape, including sprinkling the tape with a layer of earth along the entire length, must be carried out in the presence of a representative of the electrical installation organization and the owner of the electrical networks.

2.3.84. The depth of cable lines from the planning mark must be no less than: lines up to 20 kV 0.7 m; 35 kV 1 m; when crossing streets and squares, regardless of voltage 1 m.

Oil-filled cable lines 110-220 kV must have a laying depth from the planning mark of at least 1.5 m.

It is allowed to reduce the depth to 0.5 m in sections up to 5 m long when entering lines into buildings, as well as where they intersect with underground structures, provided that the cables are protected from mechanical damage (for example, laying in pipes).

The laying of 6-10 kV cable lines across arable land must be done at a depth of at least 1 m, while the strip of land above the route can be occupied for crops.

2.3.85. The clear distance from a cable laid directly in the ground to the foundations of buildings and structures must be at least 0.6 m. Laying cables directly in the ground under the foundations of buildings and structures is not allowed. When laying transit cables in basements and technical undergrounds of residential and public buildings, one should be guided by the SNiP of the Gosstroy of Russia.

2.3.86. When laying cable lines in parallel, the horizontal clear distance between the cables must be at least:

1) 100 mm between power cables up to 10 kV, as well as between them and control cables;

2) 250 mm between 20-35 kV cables and between them and other cables;

3) 500 mm* between cables operated by different organizations, as well as between power cables and communication cables;

________________

4) 500 mm between oil-filled cables 110-220 kV and other cables; in this case, low-pressure oil-filled cable lines are separated from one another and from other cables by reinforced concrete slabs placed on edge; in addition, the electromagnetic influence on communication cables should be calculated.

It is allowed, if necessary, by agreement between operating organizations, taking into account local conditions, to reduce the distances specified in clauses 2 and 3 to 100 mm, and between power cables up to 10 kV and communication cables, except for cables with circuits sealed by high-frequency telephone communication systems, up to 250 mm, provided that the cables are protected from damage that may occur during a short circuit in one of the cables (laying in pipes, installing fireproof partitions, etc.).

The distance between control cables is not standardized.

2.3.87. When laying cable lines in a planted area, the distance from the cables to the tree trunks must, as a rule, be at least 2 m. It is allowed, in agreement with the organization in charge of the green spaces, to reduce this distance provided that the cables are laid in pipes laid by digging .

When laying cables within a green area with shrub plantings, the specified distances can be reduced to 0.75 m.

2.3.88. When laying in parallel, the horizontal clear distance from cable lines with voltages up to 35 kV and oil-filled cable lines to pipelines, water supply, sewerage and drainage must be at least 1 m; to gas pipelines of low (0.0049 MPa), medium (0.294 MPa) and high pressure (more than 0.294 to 0.588 MPa) - at least 1 m; to high pressure gas pipelines (more than 0.588 to 1.176 MPa) - at least 2 m; to heating pipes - see 2.3.89.

In cramped conditions, it is allowed to reduce the specified distances for cable lines to 35 kV, with the exception of distances to pipelines with flammable liquids and gases, to 0.5 m without special cable protection and to 0.25 m when laying cables in pipes. For oil-filled cable lines 110-220 kV in a convergence section with a length of no more than 50 m, it is allowed to reduce the horizontal clear distance to pipelines, with the exception of pipelines with flammable liquids and gases, to 0.5 m, provided that a protective wall is installed between the oil-filled cables and the pipeline , eliminating the possibility of mechanical damage. Parallel laying of cables above and below pipelines is not permitted.

2.3.89. When laying a cable line parallel to a heat pipe, the clear distance between the cable and the wall of the heat pipe channel must be at least 2 m, or the heat pipe throughout the entire area of ​​proximity to the cable line must have such thermal insulation so that additional heating of the ground by the heat pipe in the place where the cables pass does not occur at any time of the year. exceeded 10°C for cable lines up to 10 kV and 5°C for lines 20-220 kV.

2.3.90. When laying a cable line parallel to railways, the cables must, as a rule, be laid outside the road exclusion zone. Laying cables within the exclusion zone is allowed only in agreement with organizations of the Ministry of Railways, and the distance from the cable to the axis of the railway track must be at least 3.25 m, and for an electrified road - at least 10.75 m. In cramped conditions It is permissible to reduce the specified distances, while the cables throughout the approach area must be laid in blocks or pipes.

With electrified roads on DC blocks or pipes must be insulating (asbestos-cement, impregnated with tar or bitumen, etc.)*.

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2.3.91. When laying a cable line parallel to tram tracks, the distance from the cable to the axis of the tram track must be at least 2.75 m. In cramped conditions, this distance can be reduced, provided that the cables throughout the approach area will be laid in insulating blocks or pipes specified in 2.3.90.

2.3.92. When laying a cable line parallel to highways of categories I and II (see 2.5.145), the cables must be laid on the outside of the ditch or the bottom of the embankment at a distance of at least 1 m from the edge or at least 1.5 m from the curb stone. Reducing the specified distance is allowed in each individual case in agreement with the relevant road departments.

2.3.93. When laying a cable line in parallel with an overhead line of 110 kV and above, the distance from the cable to the vertical plane passing through the outermost wire of the line must be at least 10 m.

The clear distance from the cable line to the grounded parts and grounding conductors of overhead line supports above 1 kV must be at least 5 m at voltages up to 35 kV, 10 m at voltages 110 kV and above. In cramped conditions, the distance from cable lines to underground parts and grounding conductors of individual overhead line supports above 1 kV is allowed at least 2 m; in this case, the distance from the cable to the vertical plane passing through the overhead line wire is not standardized.

The clear distance from the cable line to the overhead line support up to 1 kV must be at least 1 m, and when laying the cable in the approach area in an insulating pipe, 0.5 m.

In the territories of power plants and substations in cramped conditions, it is allowed to lay cable lines at distances of at least 0.5 m from the underground part of overhead communication supports (current conductors) and overhead lines above 1 kV, if the grounding devices of these supports are connected to the substation grounding loop.

2.3.94*. When cable lines cross other cables, they must be separated by a layer of earth at least 0.5 m thick; this distance in cramped conditions for cables up to 35 kV can be reduced to 0.15 m, provided that the cables are separated throughout the entire intersection area plus 1 m in each direction with slabs or pipes made of concrete or other equal strength material; in this case, communication cables must be located above power cables.

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* Agreed with the USSR Ministry of Communications.

2.3.95. When cable lines cross pipelines, including oil and gas pipelines, the distance between the cables and the pipeline must be at least 0.5 m. This distance can be reduced to 0.25 m, provided that the cable is laid at the intersection plus at least 2 m in each direction in pipes.

When an oil-filled cable line crosses pipelines, the clear distance between them must be at least 1 m. For cramped conditions, a distance of at least 0.25 m is allowed, but provided that the cables are placed in pipes or reinforced concrete trays with a lid.

2.3.96. When cable lines up to 35 kV cross heat pipes, the distance between the cables and the ceiling of the heat pipe in the clear must be at least 0.5 m, and in cramped conditions - at least 0.25 m. In this case, the heat pipe at the intersection plus 2 m in each direction from the outer cables must have such thermal insulation that the temperature of the ground does not increase by more than 10 ° C in relation to the highest summer temperature and by 15 ° C in relation to the lowest winter temperature.

In cases where the specified conditions cannot be met, one of the following measures is allowed: deepening the cables to 0.5 m instead of 0.7 m (see 2.3.84); use of a cable insert with a larger cross-section; laying cables under the heat pipeline in pipes at a distance of at least 0.5 m from it, while the pipes must be laid in such a way that cable replacement can be done without excavation work (for example, inserting pipe ends into chambers).

When an oil-filled cable line crosses a heat pipe, the distance between the cables and the ceiling of the heat pipe must be at least 1 m, and in cramped conditions - at least 0.5 m. In this case, the heat pipe at the intersection plus 3 m in each direction from the outermost cables must have such thermal insulation so that the ground temperature does not rise by more than 5°C at any time of the year.

2.3.97. When cable lines cross railways and highways, the cables must be laid in tunnels, blocks or pipes across the entire width of the exclusion zone at a depth of at least 1 m from the roadbed and at least 0.5 m from the bottom of drainage ditches. In the absence of an exclusion zone, the specified laying conditions must be met only at the intersection plus 2 m on both sides of the road surface.

When crossing cable lines electrified and subject to electrification on direct current* railways blocks and pipes must be insulating (see 2.3.90). The intersection must be at a distance of at least 10 m from the arrows, crosses and points of connection of suction cables to the rails. The intersection of cables with the tracks of electrified rail transport should be made at an angle of 75-90° to the axis of the track.

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* Agreed with the Ministry of Railways.

The ends of blocks and pipes must be recessed with jute braided cords coated with waterproof (crumpled) clay to a depth of at least 300 mm.

When crossing dead-end industrial roads with low traffic intensity, as well as special paths (for example, on slips, etc.), cables, as a rule, should be laid directly in the ground.

When the route of cable lines crosses a newly constructed non-electrified railway or highway, relocation of existing cable lines is not required. At the intersection, reserve blocks or pipes with tightly sealed ends should be laid in the required quantity in case of cable repairs.

In the case of a transition of a cable line into an overhead line, the cable must exit to the surface at a distance of at least 3.5 m from the base of the embankment or from the edge of the canvas.

2.3.98. When cable lines cross tram tracks, the cables must be laid in insulating blocks or pipes (see 2.3.90). The intersection must be carried out at a distance of at least 3 m from the switches, crosses and points of connection of suction cables to the rails.

2.3.99. When cable lines cross vehicle entrances to courtyards, garages, etc., cables must be laid in pipes. Cables at intersections of streams and ditches should be protected in the same way.

2.3.100. When installing cable boxes on cable lines, the clear distance between the cable box body and the nearest cable must be at least 250 mm.

When laying cable lines on steeply inclined routes, installing cable couplings on them is not recommended. If it is necessary to install cable joints in such areas, horizontal platforms must be made underneath them.

To ensure the possibility of reinstalling the couplings in the event of their damage on the cable line, it is necessary to lay the cable on both sides of the couplings with a reserve.

2.3.101. If there are stray currents of dangerous quantities along the cable line route, it is necessary to:

1. Change the cable line route in order to bypass dangerous areas.

2. If it is impossible to change the route: provide measures to minimize the levels of stray currents; use cables with increased resistance to corrosion; carry out active protection of cables from the effects of electrocorrosion.

When laying cables in aggressive soils and areas with stray currents of unacceptable values, cathodic polarization must be used (installation of electrical drains, protectors, cathodic protection). For any methods of connecting electrical drainage devices, the standards for potential differences in the suction sections, provided for by SNiP 3.04.03-85 “Protection of building structures and structures from corrosion” of the State Construction Committee of Russia, must be observed. It is not recommended to use cathodic protection with external current on cables laid in saline soils or saline bodies of water.

The need to protect cable lines from corrosion should be determined based on the combined data of electrical measurements and chemical analyzes soil samples. Protection of cable lines from corrosion should not create conditions that are dangerous for the operation of adjacent underground structures. The designed corrosion protection measures must be implemented before the new cable line is put into operation. If there are stray currents in the ground, it is necessary to install control points on cable lines in places and at distances that make it possible to determine the boundaries of dangerous zones, which is necessary for the subsequent rational selection and placement of protective equipment.

To monitor potentials on cable lines, it is allowed to use the cable exit points on transformer substations, distribution points, etc.

LAYING CABLE LINES IN CABLE BLOCKS, PIPES AND REINFORCED CONCRETE TRAYS

2.3.102. For the manufacture of cable blocks, as well as for laying cables in pipes, it is allowed to use steel, cast iron, asbestos-cement, concrete, ceramic and similar pipes. When choosing material for blocks and pipes, you should take into account the level of groundwater and its aggressiveness, as well as the presence of stray currents.

Oil-filled single-phase low-pressure cables must be laid only in asbestos-cement and other pipes made of non-magnetic material, and each phase must be laid in a separate pipe.

2.3.103. The permissible number of channels in blocks, the distances between them and their size must be taken in accordance with 1.3.20.

2.3.104. Each cable unit must have up to 15% redundant channels, but not less than one channel.

2.3.105. The depth of installation of cable blocks and pipes in the ground must be taken according to local conditions, but not be less than the distances given in 2.3.84, counting to the top cable. The depth of installation of cable blocks and pipes in closed areas and in the floors of industrial premises is not standardized.

2.3.106. Cable blocks must have a slope of at least 0.2% towards the wells. The same slope must be observed when laying pipes for cables.

2.3.107. When laying pipes for cable lines directly in the ground, the smallest clear distances between pipes and between them and other cables and structures should be taken as for cables laid without pipes (see 2.3.86).

When laying cable lines in pipes in the floor of a room, the distances between them are taken as for laying in the ground.

2.3.108. In places where the direction of the route of cable lines laid in blocks changes, and in places where cables and cable blocks pass into the ground, cable wells should be constructed to ensure convenient pulling of cables and their removal from the blocks. Such wells should also be constructed on straight sections of the route at a distance from one another determined by the maximum permissible tension of the cables. When the number of cables is up to 10 and the voltage is not higher than 35 kV, the transition of cables from blocks to the ground can be carried out without cable wells. In this case, the places where cables exit from the blocks must be sealed with waterproof material.

2.3.109. The transition of cable lines from blocks and pipes to buildings, tunnels, basements, etc. must be carried out in one of the following ways: by directly introducing blocks and pipes into them, by constructing wells or pits inside buildings or chambers near their outer walls.

Measures must be taken to prevent the penetration of water and small animals from trenches into buildings, tunnels, etc. through pipes or openings.

2.3.110. The channels of cable blocks, pipes, their outlets, as well as their connections must have a treated and cleaned surface to prevent mechanical damage to the cable sheaths during pulling. At cable exits from blocks to cable structures and chambers, measures must be taken to prevent damage to the sheaths from abrasion and cracking (use of elastic linings, compliance with the required bending radii, etc.).

2.3.111. If the groundwater level is high on the territory of the outdoor switchgear, preference should be given to above-ground methods of laying cables (in trays or boxes). Aboveground trays and slabs for their covering must be made of reinforced concrete. The trays must be laid on special concrete pads with a slope of at least 0.2% along the planned route in such a way as not to interfere with the flow of storm water. If there are openings in the bottoms of the above-ground gutters that allow for the release of storm water, there is no need to create a slope.

When using cable trays for laying cables, passage through the territory of the outdoor switchgear and access to the equipment of machines and mechanisms necessary for performing repair and maintenance work must be ensured. For this purpose, crossings over the trays must be arranged using reinforced concrete slabs, taking into account the load from passing traffic, while maintaining the location of the trays at the same level. When using cable trays, laying cables under roads and crossings in pipes, channels and trenches located below the trays is not allowed.

The cable exit from the trays to the control and protection cabinets must be carried out in pipes that are not buried in the ground. Laying cable jumpers within one open switchgear cell is allowed in a trench, and in this case the use of pipes to protect cables when connecting them to control and relay protection cabinets is not recommended. Cables must be protected from mechanical damage by other means (using an angle, channel, etc.).

LAYING CABLE LINES IN CABLE STRUCTURES

2.3.112. Cable structures of all types must be carried out taking into account the possibility of additional laying of cables in the amount of 15% of the number of cables provided for by the project (replacement of cables during installation, additional laying in subsequent operation, etc.).

2.3.113. Cable floors, tunnels, galleries, overpasses and shafts must be separated from other rooms and adjacent cable structures by fireproof partitions and ceilings with a fire resistance limit of at least 0.75 hours. Extended tunnels must be divided by the same partitions into compartments no more than 150 m long, if available power and control cables and no more than 100 m in the presence of oil-filled cables. The area of ​​each double floor compartment should be no more than 600 m2.

Doors in cable structures and partitions with a fire resistance limit of 0.75 hours must have a fire resistance limit of at least 0.75 hours in electrical installations listed in 2.3.76, and 0.6 hours in other electrical installations.

Exits from cable structures must be provided outside or into premises with production categories G and D. The number and location of exits from cable structures must be determined based on local conditions, but there must be at least two. If the length of the cable structure is no more than 25 m, it is allowed to have one output.

Doors of cable structures must be self-closing, with sealed doorways. Exit doors from cable structures must open outward and must have locks that can be unlocked from cable structures without a key, and doors between compartments must open in the direction of the nearest exit and be equipped with devices that keep them in the closed position.

Walk-through cable racks with service bridges must have entrances with stairs. The distance between the entrances should be no more than 150 m. The distance from the end of the overpass to the entrance to it should not exceed 25 m.

Entrances must have doors that prevent free access to the overpasses for persons not involved in cable maintenance. Doors must have self-locking locks that can be opened without a key. inside overpasses.

The distance between the entrances to the cable gallery when laying cables no higher than 35 kV in it should be no more than 150 m, and when laying oil-filled cables - no more than 120 m.

External cable racks and galleries must have main load-bearing building structures (columns, beams) made of reinforced concrete with a fire resistance limit of at least 0.75 hours or rolled steel with a fire resistance limit of at least 0.25 hours.

Load-bearing structures of buildings and structures that can be dangerously deformed or reduce mechanical strength when groups (streams) of cables laid near these structures on external cable overpasses and galleries burn, must have protection that provides a fire resistance limit of the protected structures of at least 0.75 hours.

Cable galleries must be divided into compartments by fireproof fire partitions with a fire resistance limit of at least 0.75 hours. The length of the gallery compartments should be no more than 150 m when laying cables up to 35 kV and no more than 120 m when laying oil-filled cables. The above requirements do not apply to external cable galleries that are partially closed.

2.3.114. In tunnels and canals, measures must be taken to prevent process water and oil from entering them, and drainage of soil and storm water must also be ensured. The floors in them must have a slope of at least 0.5% towards the water collectors or storm drains. The passage from one tunnel compartment to another, when they are located at different levels, must be carried out using a ramp with an inclination angle of no higher than 15°. The construction of steps between tunnel compartments is prohibited.

In cable channels constructed outdoors and located above the groundwater level, an earthen bottom with a drainage bedding 10-15 cm thick of compacted gravel or sand is allowed.

Drainage mechanisms must be provided in tunnels; In this case, it is recommended to use automatic start-up depending on the water level. Starting devices and electric motors must be designed to allow them to operate in particularly damp places.

When crossing overpasses and walk-through galleries from one mark to another, a ramp must be made with a slope of no more than 15°. As an exception, staircases with a slope of 1:1 are allowed.

2.3.115. Cable ducts and double floors in switchgears and rooms must be covered with removable fireproof slabs. In electrical machinery and similar rooms, it is recommended to cover the channels with corrugated steel, and in control panel rooms with parquet floors - with wooden boards with parquet, protected from below with asbestos and asbestos with tin. The covering of ducts and double floors must be designed to allow the movement of related equipment over it.

2.3.116. Cable ducts outside buildings must be backfilled on top of removable slabs with a layer of earth at least 0.3 m thick. In fenced areas, backfilling of cable ducts with earth on top of removable slabs is not necessary. The weight of an individual floor slab removed manually should not exceed 70 kg. The slabs must have a lifting device.

2.3.117. In areas where molten metal may be spilled, liquids containing high temperature or substances that have a destructive effect on the metal sheaths of cables, the construction of cable channels is not allowed. In these areas, it is also not allowed to install hatches in sewers and tunnels.

2.3.118. Underground tunnels outside buildings must have a layer of earth at least 0.5 m thick on top of the ceiling.

2.3.119. When laying cables and heat pipes together in buildings, additional heating of the air by the heat pipe at the location of the cables at any time of the year should not exceed 5°C, for which ventilation and thermal insulation on the pipes must be provided.

1. Control cables and communication cables should be placed only under or only above power cables; however, they should be separated by a partition. At intersections and branches, it is allowed to lay control cables and communication cables above and below power cables.

2. Control cables may be laid next to power cables up to 1 kV.

4. Various groups of cables: working and backup cables above 1 kV of generators, transformers, etc., supplying power receivers of category I, it is recommended to be laid at different horizontal levels and separated by partitions.

5. The dividing partitions specified in paragraphs 1, 3 and 4 must be fireproof with a fire resistance rating of at least 0.25 hours.

When using automatic fire extinguishing using air-mechanical foam or sprayed water, the partitions specified in clauses 1, 3 and 4 may not be installed.

On external cable overpasses and in external partially enclosed cable galleries, the installation of dividing partitions specified in clauses 1, 3 and 4 is not required. In this case, mutually redundant power cable lines (with the exception of lines to electrical receivers of special group I category) should be laid with a distance between them of at least 600 mm and are recommended to be located: on overpasses on both sides of the span supporting structure (beams, trusses); in the galleries on opposite sides of the aisle.

2.3.121. Oil-filled cables should, as a rule, be laid in separate cable structures. It is allowed to lay them together with other cables; in this case, oil-filled cables should be placed in the lower part of the cable structure and separated from other cables by horizontal partitions with a fire resistance limit of at least 0.75 hours. The same partitions should be used to separate oil-filled cable lines from one another.

2.3.122. The need for the use and scope of automatic stationary means of detecting and extinguishing fires in cable structures must be determined on the basis of departmental documents approved in the prescribed manner.

Fire hydrants must be installed in the immediate vicinity of the entrance, hatches and ventilation shafts (within a radius of no more than 25 m). For overpasses and galleries, fire hydrants must be located in such a way that the distance from any point on the axis of the overpass and gallery route to the nearest hydrant does not exceed 100 m.

2.3.123. In cable structures, the laying of control cables and power cables with a cross-section of 25 mm2 or more, with the exception of unarmored cables with a lead sheath, should be carried out along cable structures (consoles).

Control unarmored cables, power unarmored cables with a lead sheath and unarmored power cables of all designs with a cross-section of 16 mm2 or less should be laid on trays or partitions (solid or non-solid).

It is allowed to lay cables along the bottom of the channel with a depth of no more than 0.9 m; in this case, the distance between a group of power cables above 1 kV and a group of control cables must be at least 100 mm, or these groups of cables must be separated by a fireproof partition with a fire resistance rating of at least 0.25 hours.

The distances between individual cables are given in table. 2.3.1.

Filling power cables laid in channels with sand is prohibited (for an exception, see 7.3.110).

In cable structures, the height, width of passages and the distance between structures and cables must be no less than those given in table. 2.3.1. Compared to the distances given in the table, a local narrowing of passages up to 800 mm or a reduction in height to 1.5 m over a length of 1.0 m is allowed with a corresponding reduction in the vertical distance between cables for one-sided and two-sided structures.

Table 2.3.1. Shortest distance for cable structures

	Smallest dimensions, mm, when laying
Distance	in tunnels, galleries, cable floors and overpasses	in cable ducts and double floors
Clear height		Not limited, but not more than 1200 mm
Horizontally in the clear between structures when they are located on both sides (passage width)		300 at a depth of up to 0.6 m; 450 at a depth of more than 0.6 to 0.9 m; 600 at a depth of more than 0.9 m
Horizontally in the light from the structure to the wall with a one-sided arrangement (passage width)
Vertically between horizontal structures *:
for power cables voltage:
110 kV and above
for control and communication cables, as well as power cables with a cross-section of up to 3x25 mm2 and voltage up to 1 kV
Between supporting structures (consoles) along the length of the structure
Vertically and horizontally in the clear between single power cables with voltages up to 35 kV***	Not less than cable diameter
Horizontally between control cables and communication cables***	Not standardized
Horizontally in the clear between cables with voltage 110 kV and above		Not less than cable diameter
____________________ * The useful length of the console should be no more than 500 mm on straight sections of the route. ** When cables are arranged in a 250 mm triangle. *** Including for cables laid in cable shafts.

2.3.124. Laying of control cables is allowed in bundles on trays and in multilayers in metal boxes, subject to the following conditions:

1. The outer diameter of the cable bundle must be no more than 100 mm.

2. The height of the layers in one box should not exceed 150 mm.

3. Only cables with the same type of sheaths should be laid in bundles and multilayers.

4. Fastening of cables in bundles, multilayered in boxes, cable bundles to trays should be done in such a way that deformation of the cable sheaths under the influence of its own weight and fastening devices is prevented.

5. For fire safety purposes, fire barrier belts must be installed inside the boxes: in vertical sections - at a distance of no more than 20 m, as well as when passing through the ceiling; in horizontal sections - when passing through partitions.

6. In each direction of the cable route, a reserve capacity of at least 15% of the total capacity of the boxes should be provided.

Laying power cables in bundles and multi-layers is not allowed.

2.3.125*. In places saturated with underground communications, it is allowed to construct semi-through tunnels with a height reduced in comparison with that provided in the table. 2.3.1, but not less than 1.5 m, subject to the following requirements: the voltage of the cable lines must be no higher than 10 kV; the length of the tunnel should be no more than 100 m; the remaining distances must correspond to those given in the table. 2.3.1; There should be exits or hatches at the ends of the tunnel.

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* Agreed with the Central Committee of the Trade Union of Power Plant and Electrical Industry Workers.

2.3.126. Oil-filled low-pressure cables must be mounted on metal structures in such a way that the possibility of forming closed magnetic circuits around the cables is excluded; the distance between fastening points should be no more than 1 m.

Steel pipelines of high-pressure oil-filled cable lines can be laid on supports or suspended on hangers; the distance between supports or hangers is determined by the line design. In addition, pipelines must be fixed on fixed supports to prevent thermal deformations in the pipelines under operating conditions.

The loads taken by the supports from the weight of the pipeline should not lead to any movement or destruction of the support foundations. The number of these supports and their locations are determined by the project.

Mechanical supports and fastenings of branching devices on high-pressure lines must prevent swinging of branching pipes and the formation of closed magnetic circuits around them, and insulating gaskets must be provided in places where supports are fastened or touched.

2.3.127. The height of cable wells must be at least 1.8 m; The height of the chambers is not standardized. Cable wells for connecting, locking and semi-locking couplings must have dimensions that ensure installation of the couplings without tearing.

Coastal wells at underwater crossings must be sized to accommodate backup cables and feeders.

A pit must be installed in the floor of the well to collect groundwater and storm water; a drainage device must also be provided in accordance with the requirements given in 2.3.114.

Cable wells must be equipped with metal ladders.

In cable wells, cables and couplings must be laid on structures, trays or partitions.

2.3.128. Hatches for cable wells and tunnels must have a diameter of at least 650 mm and be closed with double metal covers, the bottom of which must have a device for closing with a lock that can be opened from the side of the tunnel without a key. Covers must have provisions for their removal. Indoors, the use of a second cover is not required.

2.3.129. Special protective covers must be installed on connecting couplings of power cables with a voltage of 6-35 kV in tunnels, cable floors and channels to localize fires and explosions that may occur during electrical breakdowns in the couplings.

2.3.130. End couplings on high-pressure oil-filled cable lines must be located in rooms with positive air temperatures or be equipped with automatic heating when the ambient temperature drops below +5°C.

2.3.131. When laying oil-filled cables in galleries, it is necessary to provide heating for the galleries in accordance with the technical specifications for oil-filled cables.

The premises of oil-feeding units of high-pressure lines must have natural ventilation. Underground feeding points may be combined with cable wells; in this case, wells must be equipped with drainage devices in accordance with 2.3.127.

2.3.132. Cable structures, with the exception of overpasses, wells for connecting couplings, channels and chambers, must be provided with natural or artificial ventilation, and the ventilation of each compartment must be independent.

The calculation of ventilation of cable structures is determined based on the temperature difference between incoming and exhaust air of no more than 10°C. At the same time, the formation of hot air bags in narrowing tunnels, turns, bypasses, etc. must be prevented.

Ventilation devices must be equipped with dampers (dampers) to stop the access of air in the event of a fire, as well as to prevent freezing of the tunnel in winter. The design of ventilation devices must ensure the possibility of using automatic shutdown of air access to structures.

When laying cables indoors, overheating of the cables due to increased ambient temperature and the influence of technological equipment must be prevented.

Cable structures, with the exception of wells for connecting couplings, channels, chambers and open overpasses, must be equipped with electric lighting and a network for powering portable lamps and tools. At thermal power plants, the network for powering the tool may not be installed.

2.3.133. Cable laying in collectors, technological galleries and along technological overpasses is carried out in accordance with the requirements of SNiP Gosstroy of Russia.

The shortest clear distances from cable overpasses and galleries to buildings and structures must correspond to those given in Table. 2.3.2.

The intersection of cable racks and galleries with overhead power lines, intra-plant railways and roads, fire passages, cable cars, overhead communication and radio lines and pipelines is recommended to be performed at an angle of at least 30°.

Table 2.3.2. The shortest distance from cable overpasses and galleries to buildings and structures

Construction	Normalized distance	Smallest dimensions, m
When following in parallel, horizontally
Buildings and structures with blank walls	From the design of an overpass and gallery to the wall of a building and structure	Not standardized
Buildings and structures with walls with openings
In-plant non-electrification quoted railway	From the design of overpasses and galleries to the approach dimensions of buildings	1 m for galleries and passage overpasses; 3 m for impassable overpasses
Intra-factory highway and fire routes	From the structure of the overpass and gallery to the curb stone, outer edge or base of the road ditch
Cable car	From the design of the overpass and gallery to the size of the rolling stock
Overhead pipeline
When crossing, vertically
In-plant non-electrified bathroom railway	From the bottom mark of the overpass and gallery to the rail head
In-plant electrified railway	From the bottom mark of the overpass and gallery:
	to the rail head
	to the highest wire or supporting cable of the contact network
Intra-factory highway (fire passage)	From the bottom mark of the overpass and gallery to the road surface (fire passage)
Overhead pipeline	From the structure of the overpass and gallery to the nearest parts of the pipeline
Overhead power line	From the design of the overpass and gallery to the wires
Overhead communication and radio link

Location of overpasses and galleries in hazardous areas - see Chapter. 7.3, location of overpasses and galleries in fire hazardous areas - see Ch. 7.4.

When running parallel overpasses and galleries with overhead communication and radio lines, the shortest distances between the cables and wires of the communication and radio lines are determined based on the calculation of the influence of cable lines on the communication and radio lines. Communication and radio wires can be located under and above overpasses and galleries.

Minimum height of cable overpass and gallery in impassable part of the territory industrial enterprise should be taken from the calculation of the possibility of laying the bottom row of cables at a level of at least 2.5 m from the planning ground level.

LAYING CABLE LINES IN PRODUCTION PREMISES

2.3.134. When laying cable lines in industrial premises, the following requirements must be met:

1. Cables must be accessible for repair, and if laid openly, they must be accessible for inspection.

Cables (including armored ones) located in places where machinery, equipment, cargo and vehicles are moved must be protected from damage in accordance with the requirements given in 2.3.15.

2. The clear distance between the cables must correspond to that given in table. 2.3.1.

3. The distance between parallel power cables and all kinds of pipelines, as a rule, should be at least 0.5 m, and between gas pipelines and pipelines with flammable liquids - at least 1 m. At shorter approach distances and at intersections, the cables must be protected from mechanical damage (metal pipes, casings, etc.) throughout the entire approach area plus 0.5 m on each side, and, if necessary, protected from overheating.

Cable crossings of passages must be carried out at a height of at least 1.8 m from the floor.

Parallel laying of cables above and below oil pipelines and pipelines with flammable liquids in a vertical plane is not allowed.

2.3.135. Laying of cables in the floor and interfloor ceilings should be done in channels or pipes; Tightly sealing cables in them is not allowed. The passage of cables through ceilings and internal walls can be carried out in pipes or openings; After laying cables, gaps in pipes and openings must be sealed with easily pierced fireproof material.

Laying cables in ventilation ducts is prohibited. It is allowed to cross these channels with single cables enclosed in steel pipes.

Open cable routing in staircases is not permitted.

UNDERWATER CABLE LINES

2.3.136. When cable lines cross rivers, canals, etc., cables should be laid primarily in areas with a bottom and banks that are less susceptible to erosion (crossing streams - see 2.3.46). When laying cables across rivers with unstable beds and banks prone to erosion, the cables should be buried in the bottom taking into account local conditions. The depth of cables is determined by the project. Laying cables in areas of piers, moorings, harbours, ferry crossings, as well as regular winter moorings of ships and barges is not recommended.

2.3.137. When laying cable lines at sea, data on the depth, speed and style of water movement at the crossing point, prevailing winds, bottom profile and chemical composition, and water chemistry must be taken into account.

2.3.138. Cable lines must be laid along the bottom in such a way that they do not become suspended in uneven places; sharp protrusions must be removed. Shallows, rock ridges and other underwater obstacles on the route should be avoided or trenches or passages provided in them.

2.3.139. When cable lines cross rivers, canals, etc., the cables, as a rule, must be buried in the bottom to a depth of at least 1 m in coastal and shallow areas, as well as on shipping and rafting routes; 2 m when crossing oil-filled cable lines.

In reservoirs where dredging is periodically carried out, cables are buried in the bottom to a level determined in agreement with water transport organizations.

When laying oil-filled cable lines of 110-220 kV on navigable rivers and canals, in order to protect them from mechanical damage, it is recommended to fill the trenches with sandbags, followed by throwing stones.

2.3.140. The distance between cables buried in the bottom of rivers, canals, etc. with a reservoir width of up to 100 m is recommended to be at least 0.25 m. Newly constructed underwater cable lines must be laid at a distance from existing cable lines of at least 1.25 depth reservoir, calculated for the long-term average water level.

When laying low-pressure cables in water at a depth of 5-15 m and at a flow speed not exceeding 1 m/s, the distance between the individual phases (without special phase fastenings to each other) is recommended to be at least 0.5 m, and the distance between the extreme cables of parallel lines - at least 5 m.

For underwater installations at a depth of more than 15 m, as well as at flow speeds of more than 1 m/s, the distances between individual phases and lines are taken in accordance with the design.

When laying oil-filled cable lines and lines up to 35 kV in parallel underwater, the horizontal distance between them in the clear must be at least 1.25 times the depth calculated for the long-term average water level, but not less than 20 m.

The horizontal distance from cables buried in the bottom of rivers, canals and other bodies of water to pipelines (oil pipelines, gas pipelines, etc.) must be determined by the project depending on the type of dredging work performed when laying pipelines and cables, and be at least 50 m. It is allowed to reduce this distance to 15 m in agreement with the organizations in charge of cable lines and pipelines.

2.3.141. On banks without improved embankments, a reserve of at least 10 m in length for river installations and 30 m for sea installations must be provided at the location of the underwater cable crossing, which is laid in a figure eight pattern. On improved embankments, cables must be laid in pipes. As a rule, cable wells should be installed at the point where cables exit. The upper end of the pipe must go into the coastal well, and the lower end must be at a depth of at least 1 m from the lowest water level. In coastal areas, pipes must be firmly sealed.

2.3.142. In places where the channel and banks are subject to erosion, it is necessary to take measures against exposure of cables during ice drifts and floods by strengthening the banks (paving, fender dams, piles, sheet piles, slabs, etc.).

2.3.143. Crossing cables with each other under water is prohibited.

2.3.144. Underwater cable crossings must be marked on the shores with signal signs in accordance with the current rules of navigation on inland shipping routes and sea straits.

2.3.145. When laying three or more cables up to 35 kV in water, one backup cable must be provided for every three workers. When laying oil-filled cable lines from single-phase cables in water, a reserve must be provided: for one line - one phase, for two lines - two phases, for three or more - according to the design, but not less than two phases. Reserve phases must be laid in such a way that they can be used to replace any of the existing operating phases.

LAYING CABLE LINES IN SPECIAL STRUCTURES

2.3.146. The laying of cable lines on stone, reinforced concrete and metal bridges must be carried out under the pedestrian part of the bridge in channels or in fireproof pipes separate for each cable; measures must be taken to prevent storm water from flowing through these pipes. On metal and reinforced concrete bridges and when approaching them, it is recommended to lay cables in asbestos-cement pipes. In places of transition from bridge structures to the ground, it is recommended to lay cables in asbestos-cement pipes.

All underground cables when passing over metal and reinforced concrete bridges must be electrically insulated from the metal parts of the bridge.

2.3.147. The laying of cable lines on wooden structures (bridges, piers, piers, etc.) must be carried out in steel pipes.

2.3.148. In places where cables pass through expansion joints of bridges and from bridge structures to abutments, measures must be taken to prevent the occurrence of mechanical forces in the cables.

2.3.149. Laying cable lines along dams, dikes, piers and moorings directly in an earthen trench is allowed if the earth layer is at least 1 m thick.

When transmitting large powers, it is not always possible to use one cable, and we are forced to lay several parallel cables. This design solution is not very good compared to running a single cable.

Previously, I had the opportunity several times to provide two cables running in parallel. At the same time, I connected them to one circuit breaker. If I had to make a similar decision now, I would make it completely differently.

What is the danger of connecting several parallel cables to one machine?

In normal mode, the entire load is distributed equally among all cables. In this case, the cable lines must be of the same cross-section and the same length. Let's imagine this situation. For some reason one cable fails. Of course, not as a result of short circuit current, since the machine will disconnect the line. The load from the damaged cable is redistributed to other cables and thus they themselves become overloaded and fail.

How can you protect parallel running cables?

Let's consider two options:

• two parallel operating cables;
• three cables running in parallel.

The first thing you need to do is install its own protective circuit breaker on each cable. In this case, the rated current of the machine must be less than the permissible cable current.

But I think this solution is not enough. Why wait for other cables to overload? Other circuit breakers must be turned off immediately.

For example, BA88 series circuit breakers allow the installation of additional devices such as independent releases and emergency contacts.

The emergency contact signals us about the state of the circuit breaker and gives a command to operate the independent release.

Algorithm for this scheme:

Circuit breaker No. 1 triggered -> emergency contact No. 1 switched -> independent release triggered (No. 2, No. 3)

The only difficulty may arise when turning on the circuit breakers. In this regard, the protection scheme for three parallel operating cables is more practical. When turned on, the circuit breaker is the last to turn on. In the first scheme, the machines must be turned on simultaneously.

How to lay electrical cables, we recommend reading the second section of PUE 6. “Outdated” version. The provisions listed in the document are advisory in nature. Those who comply with the requirements for laying electrical cables will certainly avoid violations. The information is presented within one document, all you have to do is read it. Let's see how power electrical cables are laid.

How and where to lay the cable

First, look at the end of PUE 6, it will dispel doubts: the endless list of approvals will convince readers: what appeared before their eyes was not a piece of paper, a real document that had seen the hands of many builders and officials. New demands may appear, but given that humanity is just overcoming the Stone Age, it’s enough not to slide into the Paleozoic. PUE 6 electrical lines classifies:

1. The first part examines types of electrical wiring, choice, typical conditions: premises, street, attic.
2. Lines with voltage below 35 kW (separately before/after 1 kV).
3. Lines with voltage below 220 kV (including cables up to 35 kV).
4. Overhead cable lines (up to/above 1 kV).

The first to discuss the scope of application is PUE 6 (section 2). The requirements below must be met for cables with a cross-section of phase conductors up to 16 square millimeters. Unfortunately, it is omitted whether to use copper or aluminum. We conclude: it is always good until proven otherwise. Let's first consider the classification of electrical wiring:

• By nature of occurrence:
  1. Open. It can be stationary, portable, mobile. It is laid outdoors along the surfaces of structures, between supports. Along the way, insulators, rollers, pipes, boxes, sleeves, baseboards, and posts are used.
  2. Closed. It is laid inside the walls: hidden by plaster, grooves, inside concrete (walls, floor, ceiling) as a monolith, using cavities.
• External electrical wiring is laid along external walls. The suspended length is no more than 100 meters (four spans of 25 meters each). Others concern overhead lines and underground routes.

It is permissible to lay the electrical cable in the bathroom floor. Another question concerns the protection measures provided (grounded grid). The matter is limited to trifles.

Laying wires inside buildings

Among general requirements the inadmissibility of laying nearby circuits with voltages up to/above 42 volts is indicated, with rare exceptions (see clause 2.1.16). Relevant to today's reality, when I wanted to illuminate the bathroom without restrictions with a constant 12 volts. Fortunately, the DIN rail adapter sells for 800 rubles. It turns out that it is forbidden to merge into one branch. Wire your home from 12 volts. Safe, allows the use of a minimum wiring cross-section.

PUE 6 gives the answer here: use fireproof partitions between the wires. Much more interesting would be the requirement for the phase and neutral (return) wires to be connected together (it is prohibited to use adjacent pipes). Village residents should know: cables are not laid in combustible cavities or niches in wooden walls. Many people use ceramic insulating rollers (the distance to the plane is more than 10 mm, or by placing fireproof material).

When laid open, the distance from the floor is at least 2.5 meters. We bet that in private houses the villagers do not comply with the requirement. Only for high-risk areas. There is no obligation to reduce the voltage, placing the upper limit at 42 volts, placing the electrical cable for internal installation at a height of two meters. But it can be done. Remember the 12 volt adapter, put in switchboard. It will definitely be enough to provide lighting for a village house. As for sockets, protected installation (cable ducts) should be used. When the protection level of the box is IP20 and higher, the height is not standardized. Connections are allowed in the form:

• crimping;
• terminal blocks;
• welding;
• rations.

By the way, bare twists are prohibited even for grounding circuits. The insulation of joints is no worse than linear sections. Next come the obvious requirements: absence of tension, accessibility of components and connections (to service specialists). A combustion-protected cable must be laid under the cladding: many installers have forgotten. YouTube will give you any number of stories: the cladding of PVC panels hides traditional PVC for several cores. The mentioned part of the PUE is inactive, the installation process itself does not become less dangerous. Draw your own conclusions: we are building for government inspectors, officials, by and large, don’t care about the consequences (we are required to comply with the letter of the law), we are building for ourselves (so that we are guaranteed nothing will happen).

Thus, laying an electrical cable in a wooden house is a delicate art. Aluminum corrugation is useful. It is clear that plastic is not always suitable for reasons of lack of fire resistance. Take comfort: aluminum corrugation is easy to ground, certainly improves the electromagnetic environment of the house, simplifies the replacement of wiring, and protects against fire. Like other metal parts of the building, hoses, pipes, cable channels are zeroed. Can serve as a screen. Read more about the standards for laying electrical cables in the table. 2.1.3 PUE 6, regarding the peculiarities of installation in various climatic conditions (heat, dampness), many rules are prescribed in section 2.1.

Increased attention is paid to places where they intersect with pipelines. The electrical cable is laid leaving a gap of at least 5 cm. If there is hot water or something flammable (read gas) in the pipeline, the distance doubles. Moreover, 25 cm of protection against mechanical damage should be provided on each side of the intersection. On a parallel pipeline or cable, the distance is taken to be 10 or 40 cm minimum depending on the contents (gas, kerosene, hot water, steam).

External building wiring

Rules for laying external electrical wiring

Finally, the color marking of the electrical cable for external installation from the substation will be a novelty:

1. Yellow – phase A.
2. Green – phase B.
3. Red – phase C.
4. Blue – neutral working wire.
5. With yellow and green stripes - neutral protective wire.
6. The reserve tire is marked with transverse stripes to the main ones.

The color differs (slightly) from PVS cables, which are not intended to carry three-phase lines. Laying an electrical cable in the ground at the dacha is carried out by other types. The marking of pipes is in accordance with GOST R IEC 61386.24, examples of cables will be provided by GOST 16442. The latter document will indicate which brand of electrical cable is unsuitable for laying in the ground. Installation details are indicated in PUE 6, starting in paragraph 2.3.83. It is said that the cable line lies no closer than 0.7 meters to the surface. The bottom is filled with bedding (sand, crushed stone), and the top is covered lightly with soil, freed from various types of debris.

Selecting the wiring cross-section (cable cores)

According to PUE 6, the cable is divided into two categories by core cross-sectional sizes:

• Within 6 square millimeters for copper, 10 for aluminum is selected from tables 1.3.4 and 1.3.5 directly. As for long-term operation.
• Otherwise, when the core thickness is higher, you need to multiply the tabulated current by a correction factor of 0.875 / √ TPV. Where TPV is the relative duration of equipment activity in the operating cycle. Simply put, the equipment works less over a period of time, the core is thinner.

Please note that the figures indicated in the table are widely quoted in the literature without indicating the source. PUE 6 says: the maximum long-term current of the core is determined by the type of cable (the number of conductors in the insulation), the laying method discussed above. By grouping the data, readers can easily choose an electrical cable for laying over the air or underground. It’s nice that the parameters are graded according to the type of insulation and voltage. There is not enough space to call the information exhaustive, some of which has been removed from official circulation by current legislation.

It has become difficult to find requirements for the cross-section of the cable neutral conductor three-phase network. PUE 6 directly says: it must be at least 50% of the phase phase, sometimes it increases to 100%. Correction factors for selecting the current limit depending on the ambient temperature will seem useful. You will see that depending on the conditions, the cable cross-section can be reduced, or, conversely, it will have to be increased. Correction factors are introduced for soil type. It is important for those who want to lay the route correctly.

Many readers will like Table 2.1.1, indicating the smallest cross-sections of copper and aluminum cores. For stationary cable laying on rollers indoors, the value is at least 1 square millimeter of copper. The current can reach 17 A (PVC cords with PVC insulation), approximately 3.7 kW of power. I wanted LED bulbs connecting with a thinner section is not possible. Let’s assume that PUE 6 was released long before home-based sources appeared in our area. Surely engineers will have to reconsider the measurements and make adjustments to the type of light bulbs.

Cable blocks

The permissible current of cable units depending on the structure is widely discussed. The laying process is described in section 2.3 (now removed). It is said that cast iron, concrete, and asbestos-cement pipes are suitable for the cable block. Calculation of the number of channels and structuring is carried out in accordance with clause 1.3.20, with 15% (at least 1 piece) set aside as a reserve (in case it is necessary to lay an additional line).

The depth of the cable blocks is selected in accordance with clause 2.3.84. In most cases it is 0.7 - 1 meter. There are allowances for reducing the distance to half a meter over a section length of no more than 5 meters. It will allow you to correctly lay channels, which should have a slope of 0.2% towards the wells (the depth increases). When laying, we take into account: the minimum distance between the lines is determined by the voltage, and increases with increasing voltage.

The definition of cable units is hushed up, so readers probably have a mountain-sized question. Meanwhile, the structures are formed by channels of various kinds connecting the wells. Thanks to the structure, underground installation of electrical cables is carried out without the involvement of construction equipment. The main thing is that there is no need to open expensive coatings. We bet they're using some kind of cable ducts underneath the Piazza.

Similar technology helps lay cables under river beds. A special unit drills an arched tunnel in the ground that goes out to the opposite bank. The cable is laid inside. If necessary, the walls are, of course, reinforced. Makes it possible in the future to freely repair a section of the route, change certain cores (add, replace, remove). It is clear that underwater types of cable laying are not available to most private owners; you need to know in case you need to go through a difficult section.

Conclusion

We remind you that the specified PUE 6 is “outdated”. You can still be guided when carrying out work. Simply put, atheists say: There is no God, God doesn’t care much about what is said. Similarly, the installation of electrical cables in the apartment is carried out in accordance with documents certified by professionals.

Typically, cables in a trench are laid in one row at specified distances from buildings and structures. The shortest distance between the cables and the oil or gas pipeline is at least 0.5 m. At intersections, cables up to 1 kV are laid on top of cables of higher voltage, since the probability of damage in cables up to 1 kV is greater and with such placement in case of accidents in cables up to 1 kV will not damage higher voltage cables. When cables cross other cable lines, there must be a layer of soil at least 500 mm thick between them. If this distance cannot be maintained, then concrete slabs (bricks) are laid between cables up to 35 kV or the cable is placed in a pipe or corrugated hose. Bricks or a concrete slab are laid on a layer of earth at least 150 mm thick, which is poured on top of the cables. When crossing railway tracks and highways, cables are laid in tunnels, blocks or pipes across the entire width of the exclusion zone at a distance of at least 1 m from the roadbed and at least 0.5 m from the bottom of the drainage ditch.
In places where they intersect and approach obstacles, asbestos-cement, plastic, concrete, ceramic, cast iron and corrugated plastic pipes should be used to protect cables. The use of steel pipes is allowed only for passages made by piercing the soil. To prevent water from accumulating in pipes, they should be laid with a slope of at least 0.2%. The internal diameter of pipes longer than 5 m must be at least one and a half times the external diameter of the cable, but not less than 100 mm. It is not allowed to leave a cable laid in a trench unattended unless it is covered with earth and protected with slabs or bricks. Cables intended for voltages above 1000 V must, with rare exceptions, be covered on top with red gapless bricks or special plates. The route of each line must be plotted on the site plan.
When crossing streets, squares, highways and railways, the laying depth is increased to 1 m. Reducing the laying depth to 0.5 m is allowed when introducing cables into a building, as well as when the line crosses underground structures, provided that the cables are protected from mechanical damage (for example, when installation in pipes). The laying of 6-10 kV cable lines across arable land is carried out at a depth of at least 1 m, while the land above the route is used for crops.
The width of the bottom of the trench for laying power cables up to 10 kV must be at least: 300 mm - for one or two cables; 400 mm - for two or three cables; 500 mm - for three or four cables; 630 mm - for four to five cables and 800 mm - for five to six cables. In the case of developing a trench using an earth-moving mechanism, it is allowed to reduce the width of the trench for laying one cable up to 10 kV to the width of the cutter, but not less than 150 mm. Failure to maintain the distances between cables causes unacceptable heating during their operation, which can cause cable failure.
At turns, a trench is dug so that bending the cables does not damage their insulation. Cables in an aluminum sheath, especially large sections, are quite difficult to bend to the required radius; To do this, use a special device similar to a manual pipe bender.

Dimensions of cable trenches and placement of cables in them with brick protection from mechanical damage: a - one, b - two, c - three, d - four, d - five
Cable laying at intersections of roads and railways is carried out in an open (trenching) or closed (puncture, horizontal drilling) way. Piercing the soil for the passage of cables under structures without digging an open trench is carried out using horizontal drilling, punching or a pneumatic punch type D-4601.
The trench before laying the cable must be inspected to identify places on the route containing substances that have a destructive effect on the metal cover and cable sheath (salt marshes, lime, water, bulk soil containing slag or construction waste, areas located closer than 2 m from cesspools and garbage pits, etc.). If it is impossible to bypass these places, the cable must be laid in clean neutral soil.
When laying cables in ground and water, it is necessary to take into account the calculated ambient temperatures, which are given in table.
Design ambient temperatures

When laid in the ground in parallel with other cables or utility lines in use near buildings and structures, clear distances must be maintained (at least):

1. between cables up to 10 kV - 0.1 m (the same distance when laying newly laid cables in parallel);
2. from 35 kV cables - 0.25 m (Fig. 6);
3. from cables operated by other organizations and communication cables - 0.5 m (Fig. 7);
4. from tree trunks - 2 m and from bush plantings - 0.75 m (Fig. 8);
5. from the foundations of buildings and structures - 0.6 m (Fig. 9);
6. from pipelines, water supply, sewerage, drainage, low and medium pressure gas pipelines - 1 m (Fig. 0);
7. from high-pressure gas pipelines and heat pipelines - 2 m (Fig. 1);
8. from the electrified railway - 10.75 m (Fig. 2);-
9. from tram tracks - 2.75 m (Fig. 3);
10. from the highway, from the edge - 1 m
11. from the curb stone - 1.5 m (Fig. 4);
12. from the outermost wire of a 110 kV overhead line - 10 m (Fig. 5);
13. from the support of a 1 kV line - 1 m (Fig. 6);

It is possible to reduce the listed distances in cramped conditions, but this must be specified in the project and measures must be provided to protect cables in pipes or blocks. When crossing other cable lines or utilities and structures, the clear distances must be no less than:

1. from cables with voltage up to 10 kV - 0.25 m (Fig. 7);
2. from pipelines, heat pipelines, gas pipelines - 0.5 m (Fig. 8);

From railway tracks, tram tracks, highways - 0.6 m.

Rice. 9. Laying cables near the foundation of buildings and structures:
1 - cable 1-10 kV; 2 - foundation

Rice. 6. Laying 1-10 kV cables in parallel with 35 kV (20 kV) cables: 1 - 20 kV cable; 2 - cable 35 kV; 3 - 10 kV cable; 4 - sand; 5 - reinforced concrete slabs
Note. The distance between cables operated by different organizations must be at least 500 mm. If the required distance cannot be maintained, partitions made of fireproof materials (brick, concrete) are installed between the cables, or one of the cables in the area of ​​inaccessible approach is laid in a pipe

Rice. 10. Laying cables parallel to pipelines, water pipes, sewerage, drainage, low and medium pressure gas pipelines
1 - pipeline; 2 - cable 1-10 kV

Rice. 7. Laying 1-10 kV cables with communication cables and with power cables up to 10 kV operated by other organizations: 1 - 10 kV cable; 2 - cable 1 kV; 3 - communication cable or power cable of another organization; 4- sand;
1 - tray; 2 - cable 1-10 kV

Fig.2. Laying cables in parallel with the electrified railway: 1 - 1-10 kV cable; 2 - rail head
5 - bricks or slabs

Rice. 8. Laying cables near bushes and trees: 1 - 1-10 kV cable



Note. When laying cables near the supports of overhead lines 220 kV and higher, the distance to them is taken according to the cable line design or according to the overhead line design (depending on which line was built later).
Rice. 7. Crossing cable routes with voltage up to 10 kV: 1 - cable up to 10 kV; 2 - bricks
Rice. 6. Laying cables next to an overhead power line up to 1 kV: 1 - overhead line support; 2 - cable 1-10 kV
Rice. 5. Laying cables next to an overhead power line with a voltage of 110 kV: 1 - overhead line support; 2 - cable 1-10 kV.

Rice. 8. Crossing of cables with pipelines, water and gas pipelines: 1 - cable up to 10 kV; 2 - pipeline

Rice. 4. Laying cables parallel to the road: 1 - road surface; 2 - curbstone: 3 - cable 1-10 kV

Fig.3. Laying cables parallel to the tram tracks: 1 - rail head; 2 - cable 1-10 kV.

When laying cables over bridges, it is necessary to use cables in an aluminum or plastic sheath, under the pedestrian part of the bridges - in pipes made of fireproof material. Cables must be electrically isolated from metal parts of bridges.
On the cables at the points of transition through expansion joints of bridges and with the structure of bridges on the abutments, compensators must be made in the form of a semicircle.
For complex descents from bridges to abutments, the design organization must develop sketches for difficult locations.
For underwater installation, cables with round and flat armor are used. Installation of couplings in water is prohibited, i.e. When crossing rivers, it is necessary to lay a cable of the same construction length.
Underwater cable installation must be carried out by a specialized installation organization according to a previously agreed upon work plan.
When laying cables in places where the soil is subject to displacement (including in bulk soils), the cables must have wire armor.
In places where cables turn and branch, trenches are made so that the bending radius of the cables is not less than the permissible one (Fig. 9).
On slopes from 20 to 50°, cables are laid in trenches by fastening the cables to reinforced concrete piles.
In Fig. Figure 10 shows an example of cable laying on slopes. Distance A between fastenings should be no more than 15 m for cables with flat tape armor and 50 m for cables with wire armor. Dimension H does not exceed the maximum permissible level differences for cables. The places where the cables are attached to the slab are filled with bitumen mass. Instead of reinforced concrete piles, pillars made of coniferous wood treated with an antiseptic composition can be used.



Rice. 9. Rotation and branching of cable routes: a - rotation of cables; b - cable branching; c - cable branch

Rice. 10. Fastening the cable on slopes eroded by rain and melt water with a slope of 20 to 50°: 1 - subsided soil or sand; 2 - brick or slabs; 3 - reinforced concrete pile; 4 - asbestos-cement slab; 5 - bracket for fastening the cable

Cables are laid with a reserve of 1...2% (“snake”) of its length to eliminate the possibility of dangerous mechanical stresses arising from soil displacement and temperature deformations, especially in the spring when the ground thaws. Laying the cable in a “snake” pattern when laying with the help of mechanisms is carried out in the process of transferring it from the rollers to the bottom of the trench.
After inspecting the cable route, a representative of the operating organization is allowed to backfill the cable with sand or fine earth that does not contain stones, construction waste and slag.
If the project provides for the protection of cables with red clay bricks or asbestos-cement slabs, then the powder above the cable must be at least 100 mm. When laying signal and warning tape over the cables, which must also be indicated in the design, the powder must be at least 300 mm, i.e. the tape must be at a depth of 400 mm from the planning mark. A smaller depth of laying of the tape is allowed in sections up to 5 m long when introducing cables into a building, as well as at intersections with underground structures and communications, provided that the cables are protected from mechanical damage (in pipes, reinforced concrete slabs). In these cases, the tape must be inserted 300 mm into the pipe or under the slab on each side of the intersection.
Signal and warning tape made of polyvinyl chloride plastic must be red, 0.5... 1 mm thick and at least 150 mm wide. One tape can be laid over two cables.
With a larger number of cables, it is necessary to lay an additional number of tapes so that the edges of the tape cover the cable, taking into account the “snake”.
After filling the cables and laying bricks (slabs) or warning tape, representatives of construction and electrical installation organizations, together with representatives of the operating organization, draw up an act for hidden work, which is an official document authorizing the filling of trenches with soil. Backfilling of routes without the specified document is prohibited. The routes are backfilled immediately after the act is signed.
The final backfilling of the pits must be done after installing the connecting couplings and testing the cable line with increased voltage.
It is prohibited to fill trenches with soil containing stones, metal waste, etc.

Page 12 of 18

In the ground

There is a trench in the ground power cables of 1-20 kV are laid at a depth of 0.7 m, and 35 kV - 1 m from the planning mark of the ground surface and are placed closer to buildings in the sidewalk area. The shallow location of power cable lines laid in the ground and their accessibility are often the cause of mechanical damage during excavation work. Protection of electrical power cables from mechanical damage is carried out with reinforced concrete slabs for cables of 20-35 kV along the entire length, and for cables up to 10 kV - with bricks or slabs, while cables with voltages above 1000 V are protected along the entire length, and cables up to 1000 V are protected only in frequent excavation sites.

Rice. 21. Parallel laying of power cables up to 10 kV together with control cables.
1 - power cable up to 10 kV; 2 - control cables; 3 - soft soil or sand; 4 - brick or reinforced concrete slabs.
When laying cable lines up to 10 kV in parallel, the horizontal clear distance between them, as well as between them and the control cables, is taken to be at least 100 mm (Fig. 21).
When laying cable lines with voltages above 10 kV and up to 35 kV inclusive, the distance between them and other cables must be at least 250 mm. The distances given are minimum due to mutual heating conditions and the possibility of arc damage in the event of damage.
The clear distance between power cables and communication cables, as well as between cables operated by different organizations, is set to at least 500 mm. If, due to local conditions, the required distances cannot be maintained, then, by agreement between the operating organizations, it is allowed to reduce these distances to 100 mm, and between power cables with voltage up to 10 kV and communication cables (except for cables with a circuit sealed with high-frequency telephone systems) to 250 mm provided that the cables are protected from arc damage. Protection
protection of parallel laid cables from damage by an electric arc during a short circuit in the power cable is carried out by installing fireproof partitions between the cables.
The distance between the cable and the body of the cable line couplings is set to 250 mm. If it is impossible to maintain this distance, it is necessary to take measures to protect the cables closest to the coupling from damage (for example, installing a fireproof partition between the cable and the coupling, deepening the couplings, etc.).
When laying cables along buildings parallel to the building line, the distance from the building foundations to the nearest cable is set to at least 600 mm.
According to the conditions of the minimum number of intersections, power cables laid along buildings are located in the following sequence from the building line: distribution line cable with voltage up to 1000 V, distribution line cable with voltage above 1000 V, supply line cable more than 1000 V. Cable laying when installing cable inputs into buildings at This arrangement of the line does not lead to the need to relocate nearby cables lying in the trench.
When laying cables in an area of ​​green spaces, the distance from tree trunks to the nearest cable, according to the conditions for ensuring the safety of green spaces, is taken to be at least 2 m, and from bushes - at least 1 m.
For a cable line located parallel to the heat pipe, the clear distance between the cable and the heat pipe must be at least 2 m, or the heat pipe throughout the entire area of ​​proximity to the cable line is insulated in such a way that additional heating of the ground by the heat pipe at the point where the cables pass at any time of the year does not exceed 10°C for cable lines with voltage up to 10 kV and 5°C for lines 35 kV.
When laying cables in parallel with other pipelines, the horizontal distance between the cable and the pipeline is taken to be at least 500 mm, and with oil and gas pipelines at least 1 m. If, due to local conditions, this distance cannot be maintained, it can be reduced to 250 mm, in this case, to protect against mechanical damage, cables are laid in pipes throughout the entire approach area. Parallel laying of cables above and below pipelines (in a vertical plane) is not allowed.
When laying cables parallel to railways, they are usually located outside the road exclusion zone (Fig. 22,a). Laying cables within the exclusion zone (Fig. 22.6) is allowed only in agreement with organizations of the Ministry of Railways, while the distance A (Fig. 22) between the cable and the nearest rail of the railway with diesel traction is taken equal to at least 3 m, and on electrified roads - at least 10 m.

Rice. 22. Laying cable lines parallel to railways.
a - laying the cable outside the right-of-way; b - cable laying in the right-of-way; c - laying the cable parallel to the tram tracks; 1 - power cable; 2- railway rail; 3- cuvette.
In cramped conditions, it is permissible to reduce the specified distances, while the cables along the entire approach area must be laid in blocks or pipes. When laying cables through electrified railways, insulating blocks or pipes (asbestos-cement pipes impregnated with tar or bitumen) are used.
When laying cables parallel to tram tracks (Fig. 22, c), the distance from the cable to the nearest rail is set to at least 2 m. In cramped conditions, this distance can be reduced, while the cables throughout the approach area are laid in insulating blocks or pipes.
Parallel to class I roads (carriageway width is 15 m with four lanes), as well as class II (carriageway width is 7.5 m with two lanes), cables are laid on the outside of the ditch at a distance of at least
1 m from it (Fig. 23). Reducing this distance is allowed in each individual case in agreement with the relevant road authorities.
If a cable line is laid in parallel with an overhead power line (OHL) with a voltage of 110 kV or higher, the distance from the cable to the vertical plane passing through the outermost wire of the line is set to at least 10 m.
The clear distance from the cable line to the grounding devices of the supports of overhead power lines with voltages over 1000 V is taken to be at least 10 m. The distance to the supports of lines with voltages up to 1000 V should be 1 m, and when laying cables in the convergence area in a pipe, 0.5 m .
Cable lines crossing streets and areas, which usually have improved coverage, are carried out in blocks or pipes at a depth of at least 1 m. In order to reduce the length of the route, the intersection is performed perpendicular to the structure being crossed.
When crossing cable lines at vehicle entrances to courtyards and garages, cables are laid in pipes, and when crossing dead-end industrial roads with low traffic volumes, as a rule, directly in the ground.

Rice. 23. Laying cables parallel to roads.
1 - power cables, 2 - shoulder, 3 - ditch, 4 - roadway.
When cable lines cross railways and highways, the cables are laid in tunnels, blocks or pipes across the entire width of the exclusion zone at a depth of at least 1 m from the roadbed and at least 0.5 m from the bottom of drainage ditches. In the absence of an exclusion zone, this method of laying is carried out only at the intersection plus 2 m on both sides of the road surface.
When crossing electrified and subject to DC electrification railways, cables are laid in insulating blocks or pipes. The intersection point is set at a distance of less than 10 m from the switches, crosses and points of connection of the suction cables to the rails.
In the case of a cable line transition into an overhead line, the cable exit to the surface is made no closer than 3.5 m from the base of the embankment or from the edge of the canvas.
New cable lines laid in the ground, as a rule, intersect with existing previously laid lines, as well as with other underground structures. At such intersections, the cables are protected from mechanical damage and the action of an electric arc if it occurs.
When power cable lines cross each other, cables high voltage laid under low voltage cables,
At intersections, the cables are separated by a layer of soil at least 500 mm thick (Fig. 24). If, due to local conditions, it is not possible to maintain this distance, then it is allowed to reduce it to 250 mm, provided that the cables are separated throughout the entire intersection area plus 1 m in each direction using fireproof partitions, slabs or pipe sections.
When cable lines cross pipelines, including oil and gas pipelines, the distance between the cable and the pipeline is assumed to be at least 0.5 m. This distance can be reduced to 0.25 m provided that the cable is laid at the intersection site plus 2 m in each direction in the pipes.
When cable lines cross heat pipes, the distance between the cables and the ceiling of the heat pipe in the clear must be at least 0.5 m; in this case, the heat pipeline at the intersection plus 2 m in each direction from the outer cables is equipped with such thermal insulation that the ground temperature does not increase by more than 10 ° C in relation to the highest summer temperature and by 15 ° C in relation to the lowest winter temperature (Fig. 25). In case of intersection of the steam pipeline, the channel is completely backfilled with mineral wool at the intersection points and plus 2 m on both sides of the outer cables. This measure is carried out in addition to the main thermal insulation applied to the steam pipeline. In the case where the above temperatures cannot be met, the following are allowed: cable deepening up to 0.6 m instead of 0.7 m; use of a cable insert with a larger cross-section; the cables are laid under the heat pipeline in pipes at a distance of at least 0.5 m from it.



Rice. 24. Mutual intersection of power cables.
a - with separation by a layer of earth; b - with their separation by brick or reinforced concrete slabs; c - with confinement of one group of crossed cables into a pipe; 1 - high voltage cable; 2 - low voltage cable or low current cable; 3 - soil; 4 - brick or slab; 5-pipe.
In cramped city conditions, it is not always possible to deliver a drum with cable to its installation site for unrolling. Usually, drums with cable (preliminarily delivered to the route, and left temporarily in the nearest courtyards and other places where they do not interfere with the movement of vehicles, pedestrians, and only at the time of laying the cable are rolled up to the trench and set up for unwinding. Rolling of drums with cable should be done in casing in the direction of cable winding, indicated by an arrow on the drums so that the turns of the cable tightly wound on the drum do not loosen or unravel when rolling the drum.Rolling of drums with cable without casing can only be allowed on flat surfaces (improved road surface) or on flooring from boards laid along the rolling line, and provided that the cable is tightly wound onto the drum, the upper end of the cable is securely fastened and the edges of the drum cheeks rise above the cable turns by at least 100 mm. In all cases of rolling, it is necessary to ensure that under the drum did not hit stones, bricks and other objects that could damage the cable.

Rice. 25. Cables crossing heat pipes.
a - cables above the heat pipeline; b - cables under the heat pipeline; 1 - power cable; 2 - heat pipe; 3 - pipe; 4- thermal insulation.
The drum is installed in such a way that its rotation when winding the cable occurs against the direction of the arrow on the cheek of the drum. Then a steel shaft with a diameter of 60 mm with a drum weight of up to 2500 kg, a shaft with a diameter of 70 mm with a weight of up to 3500 kg, and a 75 mm shaft with a drum weight of up to 5000 kg are passed through the axial hole of the drum. Screw jacks are installed under the ends of the steel shaft, with the help of which the drum is raised 150-200 mm from the ground surface. The raised drum must stand firmly on supports and rotate freely without moving along the shaft. Carefully, so as not to damage the upper turns of the cable, remove the casing. The nails remaining at the end of the drum cheeks are removed or hammered in so as to exclude the possibility of snagging and damage to the cable when rotating the drum, as well as to the hands of workers rotating the drum.
To roll out cable from a drum weighing up to 3 tons, it is recommended to use a drum lifter (Fig. 26), the use of which speeds up the installation of the drum.



Rice. 26. Drum lifter.
1 - drum with cable; 2 - drum lifter lever.
This design of the drum lifter differs favorably from the jacks discussed above in that it does not require edging the drum or adjusting each of the two supports of the installation. The drum lifter is brought under the steel axle threaded through the drum, leveled and, using it as a lever, the drum is lifted and given the position and direction necessary for rolling out the cable.
Before laying the cable, pipes laid in places where they intersect or approach other underground utilities are first secured and sprinkled with earth; prepare passages for the entry of cables into buildings through foundations and walls; remove stones from the trench (if any) and level the bottom of the trench; backfill 100 mm thick at the bottom of the trench with fine soft earth or mountain sand and prepare along the route fine sifted earth or mountain sand for dusting the cable after laying; bricks or reinforced concrete slabs are prepared and laid along the route to protect the cable after laying and dusting.
The preparation of the trench for cable laying is documented with an acceptance certificate for installation.
Cable laying work consists of the following technological operations: rolling out the cable from the drum, laying the cable in a trench, removing the as-built drawing, backfilling the cable with a layer of soft earth or sand at least 100 mm thick, laying coatings that protect the cable from mechanical damage, backfilling the trench.
When unwinding the cable from the drum using any of the methods described below, measures are taken to eliminate the possibility of damage to the cable as a result of sticking of cable turns tightly superimposed on each other. When adjacent turns are glued together and the drum rotates quickly during unwinding, unacceptable bends and damage to the cable turn unwinding from the drum are possible. Therefore, the cable should be unwinded at a minimum speed, and to regulate the speed of rotation of the drum, it should be braked if necessary. Experienced workers or electricians standing at the drum observe the correct winding of the cable and the timely separation of glued adjacent turns from each other. A worker standing at the drum picks up a coil of cable coming off the drum and, if it is glued to adjacent coils, forcibly tears it away from them. Kink and damage to the cable when unwinding from the drum can also be due to the sinking of turns as a result of incorrect winding (usually during rewinding) or rolling of the drum with incomplete use of its capacity over a significant distance and thereby violating the direction of rolling (against the direction indicated by the arrow).
In this case, the coil coming off the drum may be pinched by adjacent coils that have moved out of place. The worker standing at the drum must notice this in a timely manner, eliminate the pinching, release the jammed coil, or temporarily stop the unwinding.
Cable rolling can also be done from a moving vehicle, by pulling with a drive or manual winch over rollers, by pulling manually on rollers, or by hand without rollers.
When rolling out a cable from a drum installed on a vehicle moving at a speed of 0.6-1 km/h, the cable is simultaneously laid in a trench. The vehicle in this case can be a car equipped with an RKB-Z loader, a TKB-5 cable conveyor trolley towed by a car or tractor, a special cable car, as well as a car with cable jacks installed on it.



Rice. 27. Rolling out the cable on rollers using a winch.
1 - cable layer; 2 - roller; 3 - electric winch.

When rolling out a cable from a conveyor or vehicle, rotation of the drum in accordance with the above must be done manually by experienced workers or assemblers. Workers moving behind the machine take the reeled cable and lay it at the bottom of the trench. The distance between the edge of the trench and the machine must be no less than the depth of the trench for all soils except loam, in which this distance is equal to the depth of the trench multiplied by 1.25. The method of unwinding and laying cables from moving vehicles is used in field conditions and in places where there are no other underground structures crossing the trench, and under which the reeled cable must be laid. The use of this method is also possible in the absence of obstacles to traffic along the route. In the cramped conditions of the city with its saturation of underground communications, the use of the method of unwinding and laying cables from moving vehicles is impossible. The disadvantages of this method are also the difficulties associated with loading the drum, installing the structure, jacks in the car body, and irrational use of the car.
The most widely used method is to roll out the cable by pulling it with a cable using a drive or hand winch along rollers. In this method, the drum with the cable is installed on the TKB-5 conveyor trolley or on ordinary cable screw jacks at one end of the trench, and winches with a cable for pulling the cable at the other end.
Rollers for rolling out cables on straight sections of the route are installed at the bottom of the trench at a distance of 3 to 5 m from each other, and at turns of the route, corner rollers or a guide chute are installed (Fig. 27). The corner rollers or the guide channel are secured with braces so that they do not move when the cable is pulled.

Rice. 28. Clamp for attaching the cable to the cable.
1 - conical sprocket with three sector recesses; 2 - body; 3 - head; 4 - traction cable; 5 - casing; 6 - cable core; 7 - cable.
When laying several cables in one trench, the rollers are installed so that they do not interfere with laying the laid cable in its place at the bottom of the trench. The bending radius of the corner rollers and guide grooves must be no less than the bending radius allowed for the given cable. After installing the drum with the cable, ensuring its free rotation along pre-installed rollers, the steel winch cable is unwound, the end of which is passed through all intersections, and attached to the upper end of the cable unwound from the drum. At the ends of the pipes through which the cable is pulled (during the rolling process), detachable mounting funnels are installed to reduce friction when the cable enters the pipe channel.
The method of connecting the cable to the outer end of the cable is determined by the tensile force and, depending on the value of this force, the connection can be made using a special wire stocking, a canvas belt, or directly by the wires using a special clamp (Fig. 28). The permissible length of the cable to be pulled, at which it is possible to use a wire stocking or a tarpaulin belt, depends on the weight and cross-section of the cable and is limited to a length of no more than 100 m for cable ends with a cross-section of 120-185 mm 2. The wire stocking is put on the cable sheath and firmly fixed at the end with a wire bandage along an applied resin tape for a length of at least 500 mm.

Table 4
Calculated tensile forces per 100 m of cable

Core cross-section, mm 2				Core cross-section, mm 2	Tension force, kgf, at cable voltage, kV

Note. The numerator shows the tensile forces for three-core cables with aluminum conductors, and the denominator for cables with copper conductors.
The required tensile force on straight sections of the route depends on the mass of the cable (accepted according to the reference book for electrical cables) and the friction coefficient, i.e.
P=kq,
where P is the tensile force of the cable; q - cable mass; k - friction coefficient,
The value of the coefficient of friction when unwinding and pulling the cable is: 0.8 when pulling “along the ground (bottom of the trench); 0.25 when pulling on rollers, when sliding on the ground is excluded, since the number of rollers is set in sufficient quantity; 0.35 when pulling on rollers, when sliding on the ground between the rollers is not excluded; 0.03-0.04 - on ice.
Tensile forces per 100 m of cable for approximate calculations when laying heavy three-core armored cables with voltages up to 10 kV in a trench with a coefficient of 0.35 according to [L. 6] are given in table. 4.
The tensile strength of copper conductors is 26 kgf/mm, and that of aluminum stranded conductors is 16 kgf/mm, respectively. The maximum permissible tensile force is assumed to be equal to 7b of the strength of the cable cores.
The diameter of the steel cable, taking into account the tensile force for laying the cable, is selected according to the following data:

Let, for example, you need to determine the tensile force of a construction length of 250 m of a cable with a cross section of 3X185 mm 2, voltage 10 kV, ASB grade, laid on rollers.
Using the formula given above and substituting the values ​​of the quantities, we get:

where 7763 kg is the mass of 1 km of length of ASB brand cable with a cross-section of 185 mm 2 and a voltage of 10 kW; 0.35 is the value of the friction coefficient in the presence of cable sliding on the ground between the rollers.
To take into account the additional effort required when moving away (starting to move),

The obtained value of the tensile force allows you to select the diameter of the cable, equal to 7.7 mm, as well as the lifting capacity of the winch.
The tensile strength of three-core cables with aluminum conductors will be:
185-3-16=8880 kgf.
The maximum permissible tensile force on the cores for this cable is correspondingly equal to: P = 8880/6 = 1480 kgf, which, as can be seen, significantly exceeds the required tensile force P required for rolling the cable we have adopted along the rollers.
The choice of the load capacity and drive of the winch for rolling out the cable, depending on the tensile forces and laying conditions, is made according to table. 3.
After attaching the cable to the upper end of the cable, begin rolling out the drum. By turning on the winch drive motor or rotating the winch manually, they provide the necessary tensile force to unwind the cable from the drum, roll it out onto the rollers and the bottom of the trench. When rolling out a cable using mechanisms, the tensile force acting on the cable is monitored using a dynamometer or other control device. When manually driven, the winch rotates smoothly, without jerking. The cable, unwound from the drum by the pull of the cable, must, without bending, sliding freely along the rollers, cross other underground structures located on its path above the marks without snagging or friction.
If it is necessary to pull the cable through pipes, along with the installation of mounting funnels, measures are taken for preliminary cleaning, and, if possible, measures for purging them. For pipes longer than 10 m, the cable being pulled is lubricated with grease.
When unrolling a cable using a cable and winches for tension, two experienced installers must be at the drum and monitor its unwinding. If necessary, they slow down the drum or release the cable coil coming off the drum that is stuck together or pinched by adjacent turns. A winch with a drive (electric or motor) has one worker who monitors the operation of the winch and controls the pulling force using a dynamometer. If cable rolling is carried out using a manual winch, then it is necessary to have two workers to rotate it and control the tensile force. An experienced worker is assigned to monitor the end of the cable being laid moving along the rollers, to direct it under the underground structures crossing the trench, as well as to communicate with the winch control and give a signal to stop or start the winch. The cable is rolled out at a speed of 0.6-1 km/h.
After the cable has been rolled out and the winch has stopped, the cable is disconnected, and then the cable is removed from the rollers and transferred to its place at the bottom of the trench. The cable is laid along its entire length with normal slack, a snake, which compensates for changes in the cable length caused by temperature fluctuations in the cable during operation; in this case, the cable length will be approximately 2-3% greater than the length of the trench. When laying several cables in a trench, their ends are positioned so that the distance between the centers of the couplings (to be installed) is at least 2 m.
The method of mechanized unwinding and laying of cable described above is the simplest, most reliable and therefore has great advantages over other methods, especially on straight routes and in the presence of intersections under which the cable unwound from the drum must be laid.
If it is impossible to use mechanisms due to local conditions, the cables are rolled out and laid manually. When rolling out and laying the cable manually, the drum is also installed at the end of the trench, and the cable is pulled by workers placed along the route, at the command of the work manager. The number of workers during manual laying is determined based on the load on each worker not exceeding 35 kg. When rolling out and laying the cable, make sure that the cable is not damaged as a result of unacceptable bends or twists, and for this, at all critical places: at the drum, in places where the route turns, where the cable passes through pipes, at intersections with other underground structures - Experienced workers or electricians should be posted. The drum with the cable must have a brake in the form of a board, pressed, if necessary, against the cheek of the drum, and experienced electricians must be assigned to regulate the speed of rotation of the drum and monitor the correct winding of the cable. When laying cables, ensure the consistency and simultaneity of the actions of all workers along the entire scope of work, for which it is recommended that for large installations, have local radio installations on the route and carry out commands using a loudspeaker or telephone. The signal is also provided by flags and other conventional signaling means. The technology for manual cable laying is determined depending on the width of the trench and the presence of intersections with other underground structures in it along a wide trench (at least 0.5 m) workers carry the cable moving along the trench, and in a narrow trench workers carry the cable, moving along the edge of the trench. One of the workers takes hold of the end of the cable, and the people stationed at the drum begin to rotate the drum. At certain equal intervals of 3-5 m (depending on the weight of the cable and based on the load of no more than 35 kg), the cable is picked up by workers who carry it in their hands, not allowing the cable to drag along the ground after rolling out the entire construction length of the drum, the end of the cable is laid to the bottom of the trench by the first worker, then successively by the second, third, and so on, until the entire cable is correctly laid on the bottom of the trench and in its place.
If there are intersections of the trench with other underground communications, under which it is necessary to pull the cable, workers are placed in the gap between two adjacent rollers on which the cable is laid. Workers, standing still in a bent position, simultaneously and on command gradually move the cable being laid along the rollers, as shown in Fig. 29, a. The method of manual unwinding and laying of cables described above, when a cable drum is installed at the end of a trench, has a significant drawback, since it requires a significant number of workers, especially when laying heavy cables.
If, however, the drum with the cable to be unwound and laid is placed not at the end, but in the middle of the trench, then the required number of workers can be reduced by approximately 2 times. With this method of rolling out and laying cables with installing a drum in the middle of the trench, the cable is unwinded from the upper end of the drum and laid first on one side of the trench in the same way and in the same technological sequence discussed above, and then on the other side of the trench. In this case, the cable is wound up not from above, but from below the drum with a loop brought through the drum (Fig. 29.6). If there are underground structures under which the cable to be laid must be laid, unwind the entire cable from the drum in a loop, bring the end of the cable under the first intersection and, standing still, gradually move the cable along the rollers along the trench through all other intersections until The entire loop is selected. Cable laying using loops can only be done in extreme cases by a qualified team of workers with extensive experience in cable laying, since with this method cable damage is most likely due to unacceptable bends, kinks and twists. When forced to use this method, the most experienced, disciplined workers or electricians are placed on loops and turns.



Rice. 29. Cable laying without the use of mechanisms (manually).
a - unwinding the cable from the drum and moving the cable along the rollers; b - unwinding the cable from the bottom of the drum with a loop brought through the drum.
The placement of cable drums along the laying route and the rolling out of the cable are carried out using the factory markings of the upper end of the cable, as follows. Construction lengths of cable are laid sequentially one after another, and the upper end of one drum is placed against the lower end of another drum if the marking of the upper end of both drums is the same (“P” or “O”). If the upper end of one drum is marked “P” and the other “O”, then rolling out the cable from these drums should be done with their upper ends facing each other.
When laying the cable, provide a reserve of cable ends along the length necessary to complete the connection and termination, install compensators that protect the coupling from damage during soil displacements, as well as temperature deformations of the cable. The cable reserve in the compensators is also calculated in such a way that in the event of damage to the connection it was possible to install a new coupling without the need to lay the insert and install two couplings. For cables up to 10 kV inclusive, the length of the cable reserve in the compensators of the couplings can be taken equal to 350 mm (which corresponds to half the length of the coupling for the largest cross-section of the cable 240 mm 2 type SS-110, equal to 690 mm) and for cables 20-35 kV, respectively 400 mm.
The length of reserve required for cutting and connecting the cable is determined depending on the method of making the connection with the same cores (same colors) or dissimilar cores (different colors).
When constructing power cable lines, the connection of individual cable lengths to each other is usually carried out using any conductors without taking into account the color, and phasing in order to ensure the same phases with the switchgear buses is carried out when installing the end coupling. The cable margin left at the ends (overlap) during installation, depending on the method of connection, is:
when making connections with any wires of different colors

when making a connection with the same cores of the same color

where I is the pitch length of the total cable twist (mm), the value of which for large cross-section power cables is 3000 mm; 3 - the number of phases (cores) involved in calculating the length of the margin of each end; 2 is the number of cable ends to be connected.
When laying a cable with single-wire conductors of large cross-section (150 mm 2 and above), which has a rigid structure, it is necessary to replace this cable with a multi-core cable of normal flexibility of a similar brand at the site where the line being constructed enters the building, switchgear cell.
The use of rigid cables with single-wire conductors in cramped conditions of the switchgear of electrical devices is not always possible due to the small dimensions of the cells, leaning panels and assemblies and the difficulties arising in connection with this when installing the end coupling and making the connection.
Above, we discussed different methods of unwinding and laying cables, as well as the reasons that cause damage to the cable.
When laying a cable with impregnated paper insulation, the most serious, irreparable type of defect in work, leading to damage to the cable throughout its entire construction length, is unwinding and laying at a negative ambient temperature of a cable that has not been preheated appropriately.
At negative temperatures below 0°C, the oil-rosin composition with which the paper cable insulation is impregnated loses its viscosity and lubricity. The frozen mass does not lubricate, but rather glues the layers of paper insulation tapes together. Bending of the cable during unwinding and laying under these conditions leads to rupture of the paper insulation, a decrease in its electrical strength and subsequent electrical breakdown after the cable line is put into operation. Therefore, laying cables with impregnated paper insulation at temperatures below 0°C without preheating is not permitted. The cable can be heated in a heated room, in a special greenhouse, or by electric current. The most convenient, high-quality and fastest way is to heat the cable with electric current.
This method consists in passing an electric current through the conductive cores of a heated cable, the source of which is a power transformer with a power of 20 kV * A, the voltage of the primary winding is 220/380 V, the secondary winding is from 7 to 98 V in 10 steps. The transformer is fixed in a ring frame, which makes it easy to transport. The value of the electric current passing through the cable cores is set depending on the cross-section and voltage of the heated cable. The only drawback of this method is the need to break the sealing of the cable ends, since to create an electric current circuit it is necessary to short-circuit the conductors of the inner end of the cable after cutting them, and connect the outer end to a current source - a power transformer.
After connecting the cable cores to each other, it is necessary to restore the sealing of the inner end of the cable by soldering a lead cap. The lead cap must be soldered in such a way that the shorted wires do not reach the bottom of the cap by 30-40 mm, since with a smaller distance the cap can be torn by the cable wires during its installation.
The outer end of the cable on the drum is cut into a temporary funnel and filled with bitumen mass so that the place where the core insulation is cut is filled with the mass and is 50 mm from the surface of the mass poured into the funnel. It must be borne in mind that after heating the cable and subsequent cooling, a vacuum is formed inside it, as a result of which intensive suction of outside air and moistening of the insulation is possible if a tightness is not created when sealing the ends of the cable. Therefore, after the cable has finished heating, the funnel is cut off and a lead cap is also soldered onto this end of the cable.
When connecting the heating cable, make sure that the load does not exceed the maximum permissible value for a given cable cross-section, taken from the tables of permissible loads for air, taking into account the correction factor for air temperature during warm-up.
If several cables are laid in a trench, then several drums can be simultaneously heated from one transformer by connecting their current-carrying conductors in series and increasing the circuit voltage accordingly. If the cables to be heated have different core cross-sections, then the maximum permissible current for heating is selected for the cable having a smaller core cross-section. When turning on the cable for warming up, use an ammeter to ensure that the current does not exceed the permissible values ​​for the given cable cross-section. Along with monitoring the current value, the temperature of the outer covers of the upper turns of the cable on the drum is monitored.
The temperature of the armor or metal sheath of the outer turns of the cable at the end of warming up should not exceed + 25°C for cables of 20-35 kV, +35°C for cables of 6-10 kV and +40°C for cables of 3 kV and below. To monitor the heating temperature, a thermometer is installed between the two upper turns of the cable on the drum, the lower end of which is pressed tightly against the outer cover and insulated with felt or cotton wool. The cable is laid after heating is completed at the maximum possible speed (from 30 to 60 minutes depending on the outside temperature) so that the cable does not have time to cool. In cases where cable laying, carried out at a low temperature, for some reason is delayed and requires a lot of time, the cable is reheated before unwinding begins or the cable is laid “under current”.
The heated cable should be laid in a trench in a “snake” pattern and have more slack (3%) than a similar cable laid under normal conditions (i.e., without heating), since it will stretch somewhat when cooling.
After the installation of the cable is completed, check the correct placement of the cable in the trench, in the pipe provided for crossing driveways, streets, as well as at the approaches and inputs to the switchgear of substations, compliance with the dimensions in places where cable lines approach and intersect with each other, as well as with underground structures located in operation by other organizations.
To draw up as-built drawings, the route of laying and entering cables into the electrical room is photographed before backfilling the trench. In accordance with the requirements [L. 4] for topographic and geodetic work, as-built drawings for cable laying are signed by the surveyor who surveyed the route, representatives of the customer and the construction and installation organization. The correctness of the survey and the correspondence of the as-built drawing to nature after control measurements and inspection are certified by technical supervision. The as-built drawing of the route is included in the as-built documentation presented upon commissioning of the line.
As a cable line construction project, as-built cable laying drawings are prepared on a scale of 1:500, and in some cases, where there are a large number of cable lines, on a scale of 1:200 or even 1:100. The location of each laid cable line is “tied” to permanent structures, which are usually buildings, and in areas where there are no permanent landmarks, reinforced concrete or metal poles (benchmarks) are installed at a distance of 100-150 m from each other on straight sections of the route, at all turns and at connecting couplings.
The as-built drawings also indicate sections of the route where cables are laid at a depth of more than 1 m and less than 0.7 m, the location of occupied and reserve pipes laid in connection with approaches and intersections of other underground communications.
After checking the quality of the laying, filling the cable with a layer of soft earth or sand 100 mm thick, laying slabs or red (non-silicate) bricks to protect the laid cable from mechanical damage, a hidden work report is drawn up, drawn up by the construction and installation organization and a representative of the operating organization. The technical supervision representative gives permission to backfill the trench, while monitoring the quality of the backfill and the thoroughness of soil compaction over the laid cables.
Before covering the cable with a layer of earth or sand, laying protective slabs or bricks, it is not allowed to leave the cable unattended due to a break in work. The brick is laid on top of the cable bedding so that with one cable the middle of the covering is on the cable axis (in one layer across), and with a large number of cables, a continuous flooring is made from the covering with an extension of at least 50 mm beyond the outer cables in both directions.
The trench is usually backfilled with soil previously removed from the trench, provided that it does not contain lumps of frozen soil, stones, construction waste, slag, etc. If the soil removed from the trench does not meet the specified requirements, then the trench is backfilled with imported fines. earth. On landscaped streets, city squares and other areas that have an improved road base, trenches and pits are filled exclusively with sandy soil to avoid subsequent subsidence after restoration of the road surface. The final filling of the trench with soil and its compaction is carried out using mechanisms.