It’s hard to disagree that outwardly attractive decorative lighting fixtures in the park will not look very nice if electrical wires are connected to them by air. Besides this, the overhead electric line will create many problems during use. land plot for its intended purpose. In such a situation, there is only one correct solution - laying the electrical cable in a trench underground.
The advantages of this method are: good protection of the power cable from damage during falling trees, strong winds, snowfall or other precipitation. Electrical lines laid in a trench underground are less susceptible to electromagnetic influences created by adjacent cables, remote control and signaling circuits of the railway track, as well as other underground communication systems.
Which cables are suitable for underground installation?
Naturally, there is also back side these rules, since they were written back in the last century, but no one takes this into account. At the same time, most electricians understand this, but do not want to argue about this - it will cost themselves more. Therefore, you need to know what is stated in these rules, and what electrical cables can be used for laying in underground trenches? The PUE has an unequivocal statement on this matter.
- Electrical wire or cable should only be used in the area specified in technical documentation for the use of such products.
- For power lines that are laid underground or in water, it is necessary to use mainly products with a high degree of protection - armored cables. The metal sheath of such a wire must have an outer covering that is resistant to chemical and mechanical influences.
Naturally, such formulations are slightly unusual for ordinary people who, from the entire amount of information, understand that they need to use a special cable. Simply put, the power wire used in the trench must have high-quality protection from moisture and external mechanical influences. In addition, they must have increased tensile strength, which is necessary for high-quality resistance to soil movement. Wiring falls under these parameters with marking standards VBBShv or AVBBShv.
If you simply open the specification of any modern wire and read all its characteristics, then most of the cables fully comply with the standards for use in underground trenches. Modern power cables are fully compliant with moisture protection and tensile strength. The only thing they do not have is armor protection, but such a degree of protection is unlikely to be needed when laying underground lighting network on a summer cottage.
In general, any situation can arise, and the same PUE simply describes the rules for laying power cables. In practice, for work on a summer cottage, in principle, any high-quality conductors with a suitable cross-section will be suitable. The situation is completely different with the correct installation of high-voltage wires.
Requirements for cables laid underground
Listing all the requirements for underground electrical wiring is long and simply pointless. Therefore, most of them will be considered next, which really concerns the laying of power cables in trenches.
- Depth, on which the cable must pass underground. If someone thinks that they can simply sprinkle the electrical wire with earth and this will be enough to prevent it from being damaged by a shovel when carrying out any earthworks, then this is not so. In reality, the depth to which the wire should be immersed in the ground depends on the freezing of the soil and the proximity of groundwater, which often cause irreparable damage power lines in the trench. The PUE clearly states that the cable must be buried at least 75 cm in the ground, but it is important to take into account that this applies to low-power power systems.
- High security underground electrical wiring from mechanical damage. To do this, the cable is inserted into a special pipe or corrugated hose. Do not think that this is reinsurance; such safety measures help avoid damage to wires by ice in winter time years and during ground movement. In addition, according to experts, a cable laid in a pipe is easier to replace if the latter fails. But in this situation, it all depends on how long the power system lay underground, since very often the pipe can collapse over time.
- Adding sand to the trench– is also a fairly important factor that provides additional protection for underground cables from mechanical damage. Thanks to the sand cushion, the wire will not come into contact with solid soil particles. In this case, the backfill is carried out in several stages: to the bottom of the trench and on top of the laid wires. Thus, the electric cable turns out to be between two sand layers. It is very important that the bedding, like the backfill, is compacted well.
- Installation of warning tape, which acts as a kind of beacon warning that there are electrical cables underground. The tape is laid over the cable in the trench at a distance of approximately 25 cm above power network. This is due to the fact that the bayonet of the shovel will not reach such a depth. In the case of high-voltage underground electrical wiring, bricks or concrete plates, laid on top of the wires.
It is important that underground cables are not too stretched - do not skimp on wire footage. This is necessary so that when the ground moves, it does not occur. electrical network break. According to the technology of underground cable laying, it is provided to leave a reserve, which is achieved by laying cables in small waves.
This concerns the most significant requirements in accordance with which electrical lines are laid underground. In addition to the above-mentioned PUE standards, There are also other regulations which can be found very often.
- Laying wires under roads - they must be made in thick-walled metal pipe. This is due high blood pressure on the ground of cars and trucks passing along the road, which can cause soil movement. And, as you know, this can lead to breakage of electrical wires.
- Cables laid parallel to each other. In such a situation, everything will depend on the power characteristics of the electrical network. But in general, it is important to realize that several wires cannot be inserted into one pipe, since if one cable breaks down, the adjacent wire may also be damaged. According to the standards, each wire must be placed in an armored sleeve and located no closer than 15 cm from the adjacent cable.
Also backfilling of cables in the ground cannot be carried out without verification. It is imperative to ensure the integrity of the wiring and only then finally fill the trench with earth. Wherein visual inspection It is not enough to ring the wires using instruments. In addition, the protection of underground electrical wiring plays an important role, which will be discussed in more detail.
Requirements for PUE protection
Protection of electrical lines is considered the most important condition for laying wires in a trench underground. At the same time, according to the PUE, underground electrical wiring is subject to a whole list of requirements.
- At the entry point electric line Into the house, the cable is placed in a coupling made of asbestos-cement, which protrudes at least 60 cm from each side of the wall.
- Throughout the entire duration of underground electrical wiring, the cables are protected by bricks laid across the wires or an asbestos-cement pipe. This is necessary to protect the electrical network from soil subsidence.
- When laying several wires in one trench, the distance between adjacent cables should not be less than 10 cm for a 10 kV network, 25 cm if it is a 20-35 kV high-voltage network and 50 cm between wires of different organizations.
- Wires laid in a trench must be covered with a layer of soil with mechanical protection or warning tape laid.
- The signal tape must not be laid directly on the cable. From the wire to the beacon there must be at least 25 cm vertically. If several wires are laid in a trench, the tapes are laid separately above each cable.
- If the cable line crosses other communication systems, the warning tape should be laid no closer than 200 cm from adjacent communications.
Requirements for checking the electrical network for current leakage
After laying the cable in the trench, it is required to check for current leakage. To do this, in different places of the underground power route take a soil sample.
- If a current leak is detected in any area, then apply additional protection or replacing wires with durable electrical wiring samples.
- When passing the route in soil with an aggressive environment, it is necessary to use a cathodic vapor barrier.
After completing the excavation work for laying the underground electrical network and checking it for current leakage electrical installation organization and representatives of the customer draw up an act for hidden work. Based on this document, repair work will be carried out in the future if necessary.
The main stages of laying underground electrical networks
Ground laying work electrical cables usually carried out in a trench following certain steps.
The installation of an underground electrical network is carried out in accordance with the specified procedure and only certified teams of specialists with sufficient skills to carry out earthworks related to electricity.
External or internal gasket cable lines(CL) is carried out by the company "MasterEnergoService" using modern materials, as well as innovative technologies.
The range of services includes:
- coordination of adopted design decisions;
- installation of lines;
- maintenance, repair of equipped lines (if necessary).
It is carried out on objects of varying complexity in the ground in prepared trenches or along specialized structures: tunnels, channels, trays, boxes, cable ladders.
In addition, we carry out cable laying on overhead lines with mandatory consideration of all normalized requirements of current standards.
Cabling
We provide services for laying cable lines in Moscow and the Moscow region. In general, this is a responsible job for which specialists should be responsible. high level to ensure the reliability of cable lines. There are many ways to lay cables in the world. In order for you to understand what we are talking about, we will tell you about the most well-known and reliable methods.
External cable routing
Outdoor cabling used in cities to hide power lines underground. Cable laying is carried out in trenches, collectors, and also along the walls of buildings.
Laying cables in the ground
If you want to laying cables in the ground, it is necessary to provide for the presence of a geological basis during design. Topographical survey will help determine the location of existing communications and utility networks and select the most appropriate route for the future cable line.
When designing the installation of cable lines in the ground, the type of soil on the site, the complexity of the terrain, climate features, and the level of groundwater flow are taken into account.
For an underground line, a special brand of cable is selected - preferably armored, the shell of which is resistant to chemicals, mechanical damage.
Design calculations take into account the construction length and the corresponding number of connecting or branching cable joints of a suitable type.
Laying cables in trenches
If planned laying cables in trenches, then it is advisable to provide line protection.
The cost of these works includes excavation and leveling activities, as well as the transportation of “extra” soil. The trenches themselves can be secured with special fasteners before laying the line. The depth of the trenches depends on the characteristics of the cable line: power, cable brand, soil type, presence of intersections with existing engineering networks, communications.
Cable depth
If you need to lay a cable in the ground, pay attention to the installation depth. Remember, regardless of whether you use trenches, cable ducts or laying cables in trays, this must be taken seriously. Cable depth should be at least 0.7 m. Also, under no circumstances place an unprotected cable in water; it is better to place it in a HDPE pipe.
Intersection with deep communications
Before starting cable laying work, you need to familiarize yourself with the geological basis in order to correctly position all communications. We must remember that everything intersection with deep communications are regulated in order to maintain security zones, as well as to create the necessary conditions for repairs. In addition, when laying in parallel, the cables should be located 10 cm from each other.
Internal cable routing
One of the most popular methods is internal cable routing, it involves the installation of materials inside the building. This method differs significantly from external laying, both in the mechanics of execution and in cost. First of all, there are many strict rules that must be followed when installing internally. For example, you must remember that the shell of all materials must have a fireproof layer.
Cable laying techniques
As we already said at the beginning of our material, there are many ways and techniques for laying cables. Let us remember, for example, hidden installation cable, which is mainly used indoors. For this type of laying, wall grooves are used - recesses in which the cable is hidden. The advantages of this method, of course, include an aesthetic appearance and safety, protecting the cable from external damage. You can also run the cable in a conduit or tray, which is very common in many office buildings. This is one of the fastest and economical ways, which is convenient for further use.
If you have a need to lay a cable or need advice, the professionals of MasterEnergoService are ready to help you resolve all issues. With us you will find responsible and efficient specialists whose experience you can only be amazed at. Contact us right now!
Laying (installation) of power cable
The power cable is an indispensable element that is always present in the electrical installation process. Therefore, every professional electrician knows how to lay (install) a power cable. The whole process, like others, is preceded by the development and approval of a project in which the type, cross-section of the cable, and method of its installation are determined.
There are several types and methods of laying (installing) power cables. These include laying cables in trenches, open and hidden installations inside buildings and structures, external cable routing along the walls of buildings.
Underground laying of power cables involves manual or mechanized installation at a given depth using a cable laying machine. When using this method, pay attention to protecting the cable from various mechanical damage.
Open and hidden cable installation is carried out inside buildings. Open means laying cables over walls and ceilings, hidden means laying inside walls, foundations, floors, and in cable ducts.
External installation is the laying of power cables along the external walls of buildings or on supports. This type of installation is further divided into open and hidden.
Cable line repair
Execute cable line repair The specialists of the MasterEnergoService company will help with varying complexity. According to your application and the surveys carried out, we will carry out everything necessary measures, including:
- CL measurements before the start of repair work and after its completion;
- replacement of damaged sections of a cable line running openly (through trays, cable risers, overhead lines) or closed (in blocks, boxes, pipes, trenches, tunnels);
- changing connecting or branching couplings;
- cleaning, repair cable channels, designs;
- relocation of cable lines sections.
In addition, from the MasterEnergoService company you can order repairs of the following structures: cable duct, cable wells and pits, cable entries.
Tell us what needs to be done, and we will tell you how much it costs!
Laying the power cable in the ground (in trenches) is the most economical. For this purpose, armored cables are used steel tapes with an outer cover of cable yarn. There can be no more than six of them in one trench. The clear distance between the cables should be from 100 to 250 mm. If the cables belong to different organizations, then this distance is increased to 0.5 m.
The depth of laying cables with voltage up to 35 kV from the planning mark must be at least 0.7 m, and when crossing roads - 1 m, but not less than 0.5 m from the bottom of the drainage ditch. If these distances cannot be maintained, then the cables are laid in pipes or separated from each other by a fireproof partition.
Distances (dimensions) from cable lines to engineering structures and places of objects are standardized. For example, cables cannot be laid closer than 0.6 m from the foundations of buildings; 0.5...1 m – from pipelines; 2 m – from heating mains; 3...10 m – from railways; 1 m – from road ditches; 10 m – from the axis of the outermost wire and from the support of an overhead line above 1 kV; 1 m – from the overhead line support to 1 kV, etc.
If cables intersect with engineering structures, then, starting from the size, install mechanical protection cables Most often, this cable is laid in pipes. These pipes must allow cable replacement without disrupting the normal operation of the structure crossed by the line.
If the cables are laid before the structure is erected, then empty pipes are laid next to them for new cables if the existing ones are damaged.
In cases where it is impossible to maintain the dimensions, as well as under a durable, improved coating, the cables are laid in pipes and blocks. This is the least economical way to install cables. The blocks are made from asbestos-cement concrete and ceramic pipes or from special prefabricated reinforced concrete structures.
The blocks provide 10% spare pipes or channels, but not less than one. When the route turns and in places where more than 10 cables cross, special wells are installed in the ground. The same wells are also installed on straight sections of pipes or blocks. The distance between them depends on the permissible force when pulling the cable.
Unarmored cables with a thickened lead hermetic sheath (for example, SGT) are laid in blocks longer than 50 m. For sections up to 50 m long, armored cables without external covers can be used.
A line with more than six cables should be laid in channels; and more than 20 are in the tunnels. Removable slabs are laid on top of the channels. Outside buildings and in explosive installations, channels are covered with sand or soil.
In channels up to 0.9 m deep, cables can be placed at the bottom; in deeper channels and tunnels - on cable structures. The height of the tunnel must be at least 1.5...1 m, and the passage between structures must be at least 1 m. There may be local narrowing of passages up to 0.8 m for a length of up to 0.5 m. Devices are installed in the tunnels automatic fire extinguishing and smoke notification. To prevent water from entering the tunnel, automatic drainage mechanisms, etc. are installed.
Tunnels, where in addition to cables there are other communications (water supply, heating networks, etc.), are called collectors.
In all cable structures(tunnels, channels, collectors) it is allowed to use not armored cables. Armored cables with a non-flammable coating should be used in switchgears. Protective covers made from flammable materials fibrous materials on cables laid in structures are not allowed. To prevent corrosion and improve heat transfer, the armor is painted black.
Support structures for cable laying are installed every 0.8...1 m. Glassine, roofing felt, etc. are laid between unarmored cables with a metal hermetic sheath and support (fastening) structures. soft materials.
IN production premises cables are laid so that they are accessible for repair, and those laid openly, for example, on trays, are accessible for inspection. In places where mechanical damage is possible, as well as everywhere at a height of up to 2 m, the cables are protected. In floors and interfloor coverings, cables are laid in pipes or ducts. Embedding of cables in building structures (“embedded”) is not permitted.
Otherwise, cable laying in industrial premises is similar to cable wiring. The difference is that in in this case Not only unarmored cables are used, but also cables with armor without protective covers made of flammable materials. In addition, the cable cross-section is not limited. Cable route under water, for example, at the intersections of rivers, canals, bays, etc. are chosen in areas with a bottom and banks that are little susceptible to erosion. The cables are buried by 0.5...1 m. Underwater obstacles are bypassed or trenches and passages are provided in them.
Cables crossing streams, their floodplains and drainage ditches are placed in pipes embedded in the ground. In this case, the same cables are used as when laying in the ground.
Without pipes, cables are laid under water in a lead sheath with armor made of flat or round wires with an external protective coating. Cables with rubber (plastic) insulation and a hermetic vinylite sheath. Cables with paper-oil insulation and an aluminum hermetic sheath are not suitable for underwater installation.
When crossing rivers with fast current It is necessary to use cables with double armor made of round wires, which can easily withstand significant tensile loads. It is allowed to cross unnavigable and non-raftable rivers with a slow flow with cables with tape armor. The cable exits from the water with a margin of 10...30 m in pipes and wells.
In drying out peat bogs, for laying cables, a route of neutral soils is poured 1.5 m on both sides of the outer cables. There must be a layer of soil of at least 0.3 m under and above the cable. Small water depressions can be filled with soil or passed over piles with or without flooring. You can lay the cable in pipes, blocks or closed trays above the swamp 0.3 m above the standing water level. All these structures are attached to piles.
In permafrost areas there are a number of unfavorable factors: cracks, heaving, subsidence, landslides, etc. Cables are laid in these areas, as well as in cases of deep seasonal freezing underground: in trenches (up to 4 cables), in embankments, cable trays, channels and collectors; or above the ground; open on the surface (air suspension), in protective boxes, on overpasses, in galleries, on walls and structures of engineering structures and under permanent pedestrian bridges.
Trenches are made in rocks (at a depth of at least 0.4 m), dry sand and other soils with minor frost cracks and low heaving. In other cases, in trenches it is necessary to use cables with an aluminum hermetic sheath and the most durable armor made of flat wires (AP, AAP).
Cables with tape armor are allowed when carrying out a number of measures to combat uneven soil heaving and frost cracks: embanking, backfilling trenches with sand or gravel-pebble soil, installing drainage ditches or slots, sowing the cable route with grasses or planting shrubs and snow retention. All this is very expensive and labor-intensive.
In areas with active development of hillocks, heaving and landslides, cables are not laid directly in the ground at all. Channels and underground cable trays are made waterproof.
Overground laying of cables with a number of up to 20 is carried out on wooden, and more than 20 - on reinforced concrete overpasses. In particularly difficult conditions (permafrost, polar night and low temperatures), cables are laid along the side surfaces of ducts of heating networks, water supply systems and other devices.
I. I. Meshcheryakov
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.
Cables are laid parallel to class I roads (roadway width 15 m with four lanes), as well as class II roads (roadway width 7.5 m with two lanes). outside cuvette 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.
Clear distance from the cable line to the grounding devices of the supports air lines power transmission 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 section 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 electric arc if it occurs.
When power cable lines cross each other, high voltage cables are laid under the cables low voltage,
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 mineral wool 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 event that 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. Install under the ends of the steel shaft screw jacks, 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 to cover the cable after laying, bricks or reinforced concrete slabs are prepared and laid along the route to protect the cable after it has been laid and covered.
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 |
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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. At manual drive rotate the winch 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 unrolled 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, mentioned above, and then to 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 carried out in extreme cases by a qualified team of workers with great experience laying cables, since with this method the cable is most likely damaged as a result of 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 the margin required for cutting and connecting the cable is determined depending on the method of making the connection with like cores (of the same color) or unlike wires ( 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.
Use of rigid cables with single-wire conductors in cramped switchgear conditions electrical devices It 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.
We discussed above different ways unwinding and laying of the cable, as well as the reasons causing 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 properly preheated.
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 power transformer power 20 kV * A, primary winding voltage 220/380 V, secondary - from 7 to 98 V at 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 turning on 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 permissible loads for air, taking into account the correction factor for air temperature during warming 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 heated cables have different section cores, then the maximum permissible current for heating is selected using a 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 “snake” trench and have more slack (3%) than a similar cable laid in normal conditions(i.e. without heating), since as it cools it will stretch somewhat.
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 large quantities When covering cables, a continuous flooring is made with an extension of at least 50 mm beyond the outer cables in both directions.
Backfilling of a trench, as a rule, is done with earth 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 fine soil. On landscaped streets, city squares and other areas with an improved road base, trenches and pits are filled exclusively with sandy soil to avoid subsequent subsidence after restoration road surface. The final filling of the trench with soil and its compaction is carried out using mechanisms.