Laying the cable in the ground is the most economical. In addition, unlike overhead lines, installation of the cable in the ground is not exposed to heavy snowfalls, stormy winds and is not damaged by felled trees. Cable lines are less susceptible than overhead lines to dangerous and interfering electromagnetic influences. Which are created in communication, signaling, automation and telemechanics circuits by various power lines and contact networks of electric railways, as well as to the effects of atmospheric overvoltages (lightning discharges).

Laying a cable in the ground using technology

For cable lines laid in the ground, mainly armored cables should be used. The metal sheaths of these cables must have an outer sheath to protect them from chemical attack.

If unarmored cables are being laid, then you must first lay asbestos-cement or PVC pipes, which will reliably protect it from accidental mechanical damage during subsequent excavations. If the cable is armored, then its use will also require laying pipes at the intersection of railway and tram rails, highways and dirt roads, under carriageways of streets, at intersections with underground structures and other cables so that the ends of the pipes extend 1 m beyond the intersection, as well as when entering a cable into a building or structure.

Laying the cable in the ground. Which cable should you choose?

To prolong the durability and increase the reliability of the cable, it is protected with insulation. Today, two types of insulation are used: impregnated paper (ASB) and plastic (VBbshV and AVBbshV cables). The advantages of impregnated paper include good electrical performance at a relatively low cost. Such a cable has proven itself well in high temperature conditions, it is quite durable. But such a design of an electric cable has its drawbacks, which call into question the possibility of their use underground. Their main disadvantage is increased hygroscopicity. Accordingly, if the question arose of how to lay a paper impregnated electrical cable underground, then you need to know that it must be protected with a completely sealed sheath. Another, most significant, disadvantage of such a cable is the feature of impregnation of its shell, which eventually flows down to the lower part of the cable, which significantly reduces the durability and insulating strength.

Laying the cable in the ground, cable AVBbShv

Plastic insulated cable has the most acceptable technical characteristics for underground applications. In addition, VBbshV and AVBbshV are widely used to supply electricity in conditions of high humidity and fire hazard. Since polyethylene or polyvinyl chloride is used for the production of the insulating part of such a cable, the most dangerous conditions for its operation are constant or periodic contact with sharp and edges of solids of various origins. If such a cable is not properly protected before laying in the ground, then after a while it can get mechanical damage and fail.

Based on the foregoing, we can conclude that armored copper cable VBbshV and armored aluminum cable AVBbshV are considered optimal for conducting electric current underground. Their advantage is that they are sufficiently protected from all possible mechanical damage by steel armor. Due to this, laying such a cable into the ground does not require the use of a solid pipe, which greatly simplifies the process.

Laying the cable in the ground, safety precautions and sequence of actions

How to lay the cable underground and avoid unpleasant situations and accidents during its operation, it is recommended to carry out the laying process in the sequence given below.

The cost of the construction of cable lines and networks, their durability, as well as reliability and uninterrupted operation depend on the correct choice of the route. The route of underground cable lines is chosen on the basis that the length of the cable laid between the given points is the smallest and the convenience of the work on laying the cable and its further maintenance and operation is ensured.

Any electrical work related to excavation of the earth and laying the cable in the ground must be started only after obtaining permits for laying the cable, since other engineering systems can be laid in the ground, and you can damage them, or lay the cable in violation of existing standards. If earthworks are carried out in settlements, then before they begin, the customer is obliged to issue a permit for the performance of the works provided for by the project with the territorial administration authorities and transfer it to the contractor. The contractor is obliged to obtain a work order on the basis of a permit.

The order specifies:

a) surname, name, patronymic and position of the person responsible for the conduct of work
b) the deadline for the completion of construction work at the facility, linked to the submitted project for the production of work
c) organizations responsible for the restoration of road surfaces, transplanting green spaces and the timing of these works
d) organizations whose representatives must be called to the site before the start of earthworks

Working documentation, an order for the right to work and a copy of a written notification document must be located at the place of work. Excavation work within the protection zones of existing underground structures (power cables and communications, pipelines, etc.), as well as overground structures at their intersection (railways, highways), when laying cables along the side of the road, etc. is allowed only if written permission of the organization operating these structures and in the presence of its representative, as well as the responsible executor of the work.

Safety precautions before starting work

The performance of work in such places must be coordinated and reflected in the design documentation. The construction organization is obliged, no later than three days before the start of earthworks, to notify in writing about the upcoming work, and one day - to call representatives of interested organizations to the place of work to clarify the location of their structures and agree on measures to prevent damage to these structures. Excavation work is prohibited until the arrival of the representatives.

Before digging a trench, the route should be inspected to identify places on the route containing substances that have a destructive effect on the cable sheath (salt marshes, lime, water, bulk soil containing slag or construction waste, areas located closer than 2 m from sewage, cesspools and garbage pits etc.). If it is impossible to bypass these places, the cable should be laid in clean neutral soil in asbestos-cement pipes with their additional sealing. When backfilling the cable with neutral soil, the trench should be additionally widened on both sides by 0.5-0.6 m and deepened by 0.3-0.4 m.

If in the course of excavation work underground structures are found that are not indicated in the working drawings, the work should be stopped immediately until the purpose of these structures is clarified and the further work is coordinated with their owners.

Laying the cable in the ground, distances in the light to buildings and populations

When laying in the ground in parallel with other operated cables or utilities near buildings and structures, clear distances must be observed (at least):

• between cables up to 10 kV - 0.1 m (the same distance with parallel laying of newly laid cables)
• from cables 35 kV - 0.25 m
• from cables operated by other organizations and communication cables - 0.5 m
• from cable to forest plantations - at least 3 m, from tree trunks - 2 m and from artisan plantings - 0.60 m
• from the foundations of buildings and structures - 0.6 m
• from pipelines, water supply, sewerage, drainage, low and medium pressure gas pipelines - 1 m
• from high pressure gas pipelines and heat pipelines - 2 m
• from the electrified railway - 10.75 m
• from tram tracks - 2.75 m
• from the road from the curb - 1 m
• from the curbstone - 1.5 m
• from the extreme wire of the 110 kV overhead line - 10 m
• from the support of 1 kV overhead line - 1 m

Laying the cable in the ground, clear distances from the cable to forest plantations

In case of accidental damage to any underground structure, the responsible work performer is obliged to immediately stop work in this place, take measures to ensure the safety of workers, and report the incident to his manager and the emergency service of the operating organization. If gas is found in trenches or pits, work in them must be stopped immediately, and people must be removed from the danger zone. The work can be continued only after the termination of further gas supply. All structures damaged during the development of trenches (ditches, drainage channels, arches, canals, embankments, improved coatings, fences, etc.) must be restored. On arable land, reclamation of the fertile soil layer should be carried out.

The scope and conditions for the implementation of reclamation works are determined by the design documentation. Signal cables can be laid without restriction in the same trench with power cables with an operating voltage of up to 500 V. Signal cables when crossing them with power cables and other underground structures should also be laid at a distance of 0.5 m from these structures, if this distance is due to local conditions it is impossible to withstand, it is allowed to reduce it to 0.3 m. At the same time, at the intersection of the signal cable with power cables, it must be laid in an asbestos-cement pipe. The distance between crossing signal cables must be at least 0.1 m.

Layout and layout of the route, preparation of trenches for cable laying

Before the cable is laid, the route is broken down, which in the design process is selected taking into account the least amount of construction work, maximum use of mechanisms, ease of maintenance and minimum costs for protecting cables from corrosion, hazardous influences and damage from lightning strikes. The breakdown of the route is carried out in accordance with the working drawings, deviation from which is allowed only by agreement with the customer or the design organization.

The route of the cable is chosen as straight as possible. Areas with calcareous soils, sewage, landfills and other corrosive hazardous areas should be avoided. Locations of existing underground structures are determined by technical documentation or with the help of cable detectors and by drilling (more on this below). On the slopes of ravines, steep ascents and descents above 30 ° and up to 45 °, the trench should be dug in a zigzag manner ("snake"), with a maximum deviation from the centerline of 1.5 m at a length of 5 m. For slopes from 30 ° to 45 ° a cable with ordinary armor is laid, and with slopes over 45 ° - with wire armor.

The marking and breakdown of the route of the underground cable line is carried out in accordance with the working drawings with the help of pegs in the center of the future trench and at its turns, as well as on straight sections after about 50 m along its length, stakes are driven in, which serve as starting points for breaking the trench ... At a distance equal to half the width of the trench from the pegs, pull a cord that marks the line of one of the edges of the trench.

Consider the following when staking out alignments:

a) the intersection of streets by underground structures of the GTS should be carried out at an angle of 90 ° to the axis of the street, only if this is impossible, a deviation from a right angle within no more than 45 ° is allowed;
b) the intersection of rail tracks (railway and tram) by underground structures of the GTS should be carried out only at an angle of 90 °;
c) in gardens, parks and squares, the layout of routes should be made in the presence of a representative of the gardening and green building sector, taking into account the least damage to green spaces.

When laying out the route of laying cables in the ground, it is necessary to observe the distances from ground and underground structures specified in the design documentation. When working within the security zones of underground communications, the responsible performer of work is obliged to instruct the foreman and machinists working on the mechanisms on the conditions of work, show the places of passage of underground communications according to drawings and in nature, to mark the boundaries within which it is prohibited to work with the help of earthmoving mechanisms, as well as use percussion mechanisms.

If the cable route is planned in places where there are already existing cables or other underground structures that are not accurately indicated on the street drawing, then before proceeding with the digging of the trench, it is necessary to check the location of these structures in relation to the route. For this purpose, test pits are cut along the entire route - pits, which should have a length of 1 m along the axis of the future trench.

What is pitting

In the event that underground structures run parallel to the future route, pits should be dug perpendicular to its axis every 20 m. The length of each pit should exceed the width of the projected trench on each side of it by at least 0.3 m. The depth of the pits, if the structures in question are not found, must exceed the depth of the trench by 0.2 m. The drilling must be carried out in the presence of a representative of the organization operating the underground structures. Underground structures opened during pitting and during the development of trenches must be protected with a special box and suspended in the manner specified in the working drawings. The route of the laid underground cable can be specified with a special cable detector. With a cable laying depth of up to 2 m, the device determines its location with an accuracy of 10 cm and works independently of road surfaces.

Cable trench depth

The depth of the cable trench depends on where it will go. If the cable is laid under the road on which the transport is moving, then the depth of the route must be at least 1.25 meters. It is necessary to dig a trench carefully, since there may be engineering systems in the ground that are not plotted on the geofence diagram, such an incident occurs very often. If the cable route runs in an urban environment, in the immediate vicinity of buildings, structures or at intersections with utilities located in the ground, digging is performed only by hand.

The depth of the trench should not be less than 70cm, the width of the trench depends on the number of cables that will be laid. The depth of laying communication cables in soils of I-III categories must be at least 0.8 m, and in rocky soils - at least 0.5 m in the absence of an alluvial soil layer and 0.7 m in its presence. In settlements, the depth of the cable trench is increased to 1.0-1.2 m. The classification of soils is given in GOSTs. When digging a trench by hand, it is dug so that the side walls of the trench have a certain slope.

For free passage of workers along the edge of the trench during the development of the soil, the earth thrown out of the trench is placed on one side of the trench at a distance of at least 0.3 m from its edge, and asphalt, cobblestones and other materials - on the other side at a distance of 1 m. The bottom of the trench they are leveled and cleaned of stones and rubble, and before rolling and laying a cable in stony and rocky soils, they are covered with a layer of sand or loosened soil up to 10 cm thick. This layer is called the "lower bed". Arrangement of bedding (cushions) of fine earth (sand) without stones is carried out along the entire length of the trench. To do this, along the entire trench, fine earth or sand must be prepared for backfilling the trench. In soft soils, beds can be omitted and the pipes are laid on the leveled soil of the bottom of the trench. When digging trenches, it is necessary to ensure that the size of the torn section (especially in cities and towns) allows the work to be completed during the working day.

During the production of work, the trench passing through city streets and driveways is fenced along the entire length. Safety notices and signs are installed on the fences, and special lighting at night and in the evening. The name and telephone number of the organization performing the work is also indicated on the fences. In case of openings requiring closure of the passage, the direction of the detour must be clearly indicated. In places where pedestrians move, the trench is covered with temporary bridges 1 m wide made of solid boards with 1 m high guardrails. Excavation sites in urban conditions should be fenced off with slingshots on portable stands, and, if necessary, or at the request of the territorial administration, with inventory boards or a blank fence. ... By agreement with the owner of the work site, signal plastic tapes can be used. If it is necessary to carry out earthworks on the carriageway, the organization performing this work must agree with the local traffic police on a scheme for fencing the place of work and placing road signs indicating the types of work and the timing of their implementation.

Laying cables in the ground, fencing work sites

To ensure the normal passage of vehicles and pedestrians when digging streets, roads and driveways over trenches, transport bridges and pedestrian bridges with handrails should be installed. The length of bridges and bridges should span the trench beyond the natural slope so that they do not collapse during use.

Opening and restoration of road and street covers

Opening of street covers is carried out on an area determined by the size of trenches, taking into account the norms for additional opening of covers, given in the following table.

Norms for additional opening of street covers:

When carrying out works in parks and squares, the upper vegetation cover is considered as street cover. The materials obtained from the opening of the street covers, as well as other upper layers of the soil, in order to avoid backfilling and clogging with the soil removed from the trench, should be piled at a distance of at least 1 m from the edge of the trench on the side opposite to the dump of soil. Temporary paving of trenches on the roadway must be carried out by the construction company performing the excavation work immediately after their completion. The final restoration of street coverings is carried out by specialized organizations under contracts with construction organizations.

Laying the cable in the ground, protecting the cable from mechanical damage

In cases where it is necessary to protect cables from mechanical damage, from the effects of aggressive soils and stray currents, they must be laid in pipes. For this purpose, steel, cast iron, asbestos-cement, ceramic and plastic pipes are used. The pipe material is defined in the project. It is allowed to replace some types of pipes with others, but this must be stipulated in the project.

The pipes must meet the following requirements:

—their inner surface should be smooth
- pipe ends on the inside must be rounded with a radius of at least 5 mm and not have protrusions, breaks, burrs
- pipe connections must be strictly aligned
- ends of pipes at the points of entry (exit) into the tunnels, the channels must be sealed flush with the inner surfaces of the walls

When pipes are formed into blocks, the clear distance between the pipes vertically and horizontally must be at least 10 cm.In this regard, the lower pipes of the block must be laid to a great depth so that the upper pipes of the block are from the planning mark at a depth of 0.7 m. The width of the trench depends on the number of cables that will be laid. For the convenience of installing the couplings, there should be trench extensions (pit). The depth of the pit is made 10 cm deeper than the bottom of the trench. In the event of a forced suspension of work in the middle part of the pipeline span, the canals must be temporarily closed with plugs, and the trench must be protected with earth rolls to protect it from rain and melt water.

Laying the cable in the ground, methods of sealing joints when connecting pipes

Before joining the pipes, the inner and outer surfaces of the channels must be cleaned of dirt and their ends must be brought together. If, at the same time, a discrepancy in the inner and outer diameters is revealed due to poor-quality sorting, the pipe is replaced. Docking of pipes can be done in different ways.

When connecting asbestos-cement pipes, three methods of sealing joints are used:

- with a sheet steel collar
- using a polyethylene sleeve
- with the use of asbestos-cement couplings

Sheet steel cuffs

To seal the joints of asbestos-cement pipes by the first method, it is necessary to deliver cement mortar of grade 50 (in a volume that can be consumed before it dries) and sand to the trench. The pipes laid on the bottom of the trenches are aligned end-to-end. Under the joints of the ends, slightly stepping back from them, pour a soft soil with a tubercle, which is tamped with light blows of the ends. The joint of the two ends is wrapped with a waterproofing tape to prevent moisture from entering the pipeline. A cuff of 60 mm wide sheet steel is placed on the waterproofing tape (bandage), which has a tongue on one side and three slots on the other. Depending on the outer diameter of the pipe, the tongue is inserted into one of the slots, tightened with pliers and folded in the opposite direction. The width of the applied waterproofing tape should be 20 mm greater than the width of the metal sleeve. Then the entire joint is coated with a cement-sand mortar of grade 50.

For joining asbestos-cement pipes in the second way, polyethylene couplings with an inner diameter for the pipe size are used. After laying the pipes in the trench, the ends of them are wiped with a rag to the width of the coupling. It is best to put on the coupling when it is heated; for this, it is immersed in water heated to boiling and kept there for 10 - 15 minutes. Then the heated sleeve is removed with a weeding hook from the tank, shaken off and, using a screwdriver, pushed onto the end of the first pipe to the protrusion in the middle of the cuff, and then from the other side to the end of the second pipe to the protrusion. After the cuff has cooled, it narrows and fits snugly around the pipe junction. Since plastic becomes soft in hot water, the muff is very easy to put on, you just need to do everything quickly, without letting it cool down.

Cable laying in the ground, polyethylene sleeves

If there is a high water level in the trench, then the joint is waterproofed using a bituminous compound. The inner surface of the coupling from one side to the partition is coated with a bitumen compound and pushed onto the end of the pipe. The end of the second pipe is coated with a bitumen compound to the width of the sleeve up to the partition and is introduced into the sleeve before joining. Sealing the joint is performed in the same way as described earlier.

In some cases, joints of asbestos-cement pipes are sealed with asbestos-cement couplings, the inner diameter of which is greater than the outer diameter of the pipe. The gap between the pipe and the coupling is clogged with resin tow and sealed with cement mortar or bitumen mastic.

Cable laying in the ground, asbestos-cement couplings

Concrete pipes are connected to each other by inserting the protrusion of one pipe into the socket of the other. Around the joint, a belt of grade 50 cement mortar is applied. When sealing the joints of asbestos-cement and concrete pipes, cement mortar must be coated not only from above, but also from the bottom of the pipeline in order to avoid leakage and deterioration of the pipeline strength. For better adhesion of the cement mortar to the pipes, their joints are moistened with water before sealing.

Transporting the cable and preparing it for laying

Correctly organized transportation of cables guarantees their safety, and, consequently, the durability of the cable lines. Within storage areas, the reels are rolled manually, with both ends of the cable securely attached to the reel. The drums with the cable are rolled in the direction of the cable winding, indicated by the arrow on the drum. Violation of this rule causes loosening of the cable winding on the drum neck and loosening of the turns.

Delivery of cables and materials (pipes, blocks, etc.) to the place of work is carried out, as a rule, before the start of work. When transporting or moving cable drums, you must take measures to prevent damage to the drum and cable. Before transportation and laying, the drums with the cable are checked, which begins with an external inspection, the integrity of the drum shell, the bolts holding the drum are checked. And also the sealing of the ends of the cable and the safety of the metal bushings (at the hole) on the cheeks of the drum, the factory marking on the outside of the cheek of the drum and the cable passport, sealing of the ends of the cable. The results of the inspection are documented in an act, which is subsequently attached to the executive documentation of the cable line. Cables that have not passed the incoming inspection are not subject to laying.

Laying the cable in the ground, transporting the cable

To avoid possible damage to the cable, drums with cable must not be dropped from a car, cable carts, conveyors. It is recommended to store them under a canopy. It is also allowed to store the cable in the open air (for a period of up to 1 year) in drums sheathed with boards. Plastic cables with no outer sheath should not be stored outdoors in unshielded drums. They should be stored with hermetically sealed ends. To protect the lower part of the drum from possible flooding during rains, the drums are installed on wooden pads. Transportation, unloading and movement of drums with a cable is carried out only in a vertical position.

In-ground cable routing, cable testing and measurement

Before laying the cable, the insulation resistance of the cores is measured, and the insulation resistance of the communication cables is measured and the cores are checked for breakage and their communication with each other and with the metal sheath. Since during the transportation and reloading of the cable to the object, the cable insulation may already be damaged, and you will carry out the electrical installation of the damaged cable into the pipes, and then you will have to look for the place of damage to the cable. To check the conductors for a break and to communicate them with each other and with a metal shell, a special telephone with a light bulb is used.

With a long cable length, it is advisable to replace the phone with some other device (ammeter, voltmeter). The detected faulty cores are checked a second time, and then separated from the bundle and tied up. A list of all damaged cores is compiled, indicating the number of the pair of cores, the twist in which it is located, and the nature of the damage.

Electrical checks of cables in a plastic sheath are performed in the same way, only in the circuit, instead of a metal sheath, a bare copper core is used as a "ground". To control the insulation of the cable cores, its resistance is measured with cable devices or megohm meters. The data obtained are compared with the standard insulation resistance for a particular cable at a temperature of 20 ° C. The insulation resistance of the measured cable is considered satisfactory if it is equal to or greater than the standard.

Laying cables in the ground, checking cables

Measurement of the insulation resistance of the conductors and testing them for breakage at signal and control cables is carried out using a megohmmeter. Depending on the type of megohmmeter, it can measure the insulation resistance value up to 500-1000 MΩ. When testing the conductors for a break with a megohmmeter, if the tested core does not have a break, then when the handle of the megohmmeter is rotated, the arrow of its device will remain at zero. In the event of a break, the arrow will deviate to the left, indicating the magnitude of a large resistance, which will indicate the presence of a break in the core.

At the end of the electrical tests, the cable cores are cut off and the metal sheath of both ends of the cable on the drum is sealed; the ends of cables with a non-metallic sheath are carefully insulated with PVC tape or in another way to prevent moisture from entering the cable. When loading drums, as well as when rolling them on the ground, make sure that the direction of rotation of the drum coincides with the direction of the arrow on the drum cheek.

High quality, stable and reliable operation of the constructed cable lines can be ensured provided that the technology of their laying is observed. All electrical work on laying the cable in the trench must be carried out in accordance with the PUE and PTEEP. Since compliance with the rules and regulations is a guarantee of trouble-free operation of the power system, electrical wiring, electrical installations and electrical equipment. Before the start of laying the cable lines, the construction work on the construction of the routes must be completely completed. For example, before laying cables in the ground, the construction organization completely finishes digging trenches, arranging inputs and intersections.

Pulling must be carried out with due regard for precautions so as not to damage the cable sheathing on the edge of the pipe (the edges must be pre-rounded and not have sharp edges or burrs). The further electrical installation of the cable into the laid pipes depends on how you prepared the cable route and laid the pipes. If you have poorly tamped the sand or docked the pipes poorly, it will be very problematic to lay the cable, since when pulling the cable into the pipes, its passage can be difficult and will lead to cuts in the cable insulation.

When laying cables, a number of technological operations can be distinguished, for which special control is established in order to improve the quality of work and increase the reliability of operation of installed cable lines.

Most often, damage to cables occurs when the technology of their laying is violated:

- in case of non-observance of the distances between cables laid in parallel, between cables and underground structures;
- non-observance of the depth of their laying;
- unwinding cables from drums, pulling cables with a force exceeding the permissible load;
- in case of unacceptable bends and twists of cables; low ambient temperatures.

When several cables are laid in parallel, the minimum distances established between them are observed under the conditions of mutual permissible heating or possible damage to cables by an arc during a short circuit on one of these cables.

Laying cables at a shallow depth increases the possibility of their mechanical damage during various excavation works near cable lines. During the rolling of cables from the drums, they may be damaged as a result of tightly laid coils sticking to each other. Rapid rotation of the drums in this case leads to jerks and breaks in the cables. Therefore, the cable is unwound at a minimum speed, using various devices for braking the rotating drums. Damage can occur due to the falling of the turns when the cable is not wound correctly on the drum or the rules for rolling the drums are violated. In this case, the turn coming off the drum is pinched by the adjacent turns. In this case, when unwinding the cable, the drum is temporarily stopped and the jammed turn is released.

Slack in the form of a "snake"

When laying cables in a trench along the entire length, a slack in the form of a "snake" is provided to compensate for the change in cable length caused by temperature fluctuations in them during operation. In this case, the cable length is 2-3% longer than the trench length. During laying, near the pits for the couplings, reserves of the ends of the construction lengths of cables are left. The reserves of cables are provided for compensators that protect the couplings from damage when the soil is displaced, as well as from temperature deformation of the cables.

Before proceeding with the laying of the cable, stones, debris and unnecessary objects are removed from the trench, water is pumped out, etc. After that, the bottom of the trench is leveled and the bed is filled with sand or shallow earth 100 mm thick. At the same time, the device of passages through the wall of buildings is carried out.

To install the cable in pipes, it is required to use a special elastic steel cable, with the help of which the cable is pulled through the pipes. First, the cable is pulled into the pipe so that it goes through it and comes out on the other side of the cable route for 10-15 meters, because with the help of this cable, the cable is installed into the pipes.

To attach the cable to the cable, you will need a special metal stocking, which is a cylinder woven from thin steel wires and has clefts on one side for fastening with a rope or cable.

When put on, the stocking expands and easily slides over the sheath of the cable, and when pulled, it contracts, tightly covering the cable. Metal cable stockings are made of three types: end-for termination at the end of the cable, through (open at both ends) - for pulling the cable in the well to the required length and split-for fastening at any point of the cable. For a more reliable fastening of the stocking with a cable, screws are screwed into the stocking pulled over the cable sheath, or the end of the stocking is tied with soft wire, and then wrapped with insulating tape over the knitting.

If the cable is laid along a busy channel, then it is connected to a hemp rope, and the cable stocking is wrapped along its entire length with insulating tape in two or three layers, which protects the cable in the channel from scratches and abrasions. A cable with a capacity of up to 100 pairs is pulled into the sewer by hand. Pull the cable by the cable laid in the pipes very carefully so as not to damage the cable sheath. If, when pulling the cable, it rested on an obstacle and does not go further, then you should not tie the cable to a car or tractor, since instead of a cable you can pull out bare wires, which will only be suitable for delivery to the collection point for non-ferrous metals. If the cable does not go through, then you should gently pull it back and try to pull it out again.

Laying the cable in the ground, repeated electrical measurement

After you have pulled the cable through the pipes, you need to make sure to repeat the electrical measurement. Measurement of the insulation resistance of electrical wiring (measurement, control, power, signaling circuits, etc.) is carried out with a megohmmeter for a voltage of 1000 V. The insulation resistance must be at least 0.5 MΩ. The duration of the application of the test voltage is 1 min. Based on the results of checking the insulation resistance, an act is drawn up. The funnels that you installed on the pipes before laying the cable must be covered with polyurethane foam.

Work performed after the cable is laid in the trench

At the end of the laying of the cable in the trench, a check is made for the compliance of the work with the requirements of the project. At the same time, an external examination of the condition of the cable is carried out and the correctness of the termination of its ends is checked. Before backfilling the trench with soil, permanent landmarks (buildings, fences) are identified and an executive drawing of the route of the laid cable lines is drawn up.

In the absence of local permanent landmarks (in open places or outside the city), reinforced concrete or metal poles-relays are installed on the cable route at a distance of 100-150 m from one another on straight sections of the route, as well as at the turns of the route and at the couplings. On the plan, in addition to the route of the laid cable, other underground and aboveground structures are applied. For example, water and gas pipes crossing the cable and running in parallel, other cables, roads, ditches, etc., located in a strip of 20-30 m from the cable. Drawing up an executive plan facilitates the operation of the cable in the future and allows you to more accurately and quickly determine the places of its damage. On the laid cables, as well as on all couplings and terminations, the tags are strengthened. The cable labels indicate the voltage, brand, section, number or name of the cable. On the tags of couplings and fittings - the section, the cutting date and the name of the cable operator.

After laying the cable in the trench, leveling it and tying it to the landmarks, sprinkle it on top with a layer of sand or fine earth 100 mm thick. It is not allowed to cover the cable with soil containing debris, bricks, slag, etc.

Laying the cable in the ground, backfilling the trench with soil

Backfilling of trenches with soil is carried out sequentially in separate layers with a thickness of no more than 0.2 m. Moreover, each layer is carefully compacted with rammers and sprinkled with water. Within the limits of the carriageway of streets, roads and squares with improved coverage, backfilling of trenches is carried out only with sand in order to avoid sedimentation of the coverage after restoration.

Before backfilling the trench, the laid pipeline must be carefully inspected by a foreman (foreman) with the participation of a representative of the customer, and its compliance with the technical requirements must be recorded by an act for hidden work. Before commissioning, the patency of the channels should be checked with a test cylinder.

Video, laying a cable in the ground