How to lay a cable under the road and what requirements need to be taken into account

Options for protecting cables under the road

When laying the cable under the road surface, avoid placing the line near trees - you need to retreat from them by a radius of about 1.5 m. If you cannot retreat this distance, lay it closer, but place it inside a metal pipe. You should also avoid places with increased load on the ground, such as various parking lots, roads, and entrances. They need to be walked around the perimeter. We'll talk about how exactly they lay it under the road later.

If places with increased load cannot be avoided, then you need to use pipes, for example, a smooth HDPE pipe, a corrugated pipe or an asbestos-cement pipe, they are called cases. If there are no harmful factors, you can lay the line without pipes.

The cable is laid in a trench, it is dug to a depth of 70-80 cm. If a single cable is laid, then its width is 20-30 cm. If there are several lines, there should be a distance of 10 cm between them. The bottom of the trench is covered with a cushion of sand 10 cm high. When backfilling it, you need to remove all stones, debris, bricks, and other sharp and dangerous objects from the soil. Their presence in the ground can puncture the insulation.

There is no need to pull the cable, it needs to be laid freely, in waves, as shown in the picture:

It is necessary to provide for possible future land works. To avoid damaging the line when digging, it is worth laying down a warning tape, for example this:

Avoid connecting the conductor underground; this should be done in special couplings. If you do not have the skills to install such couplings, you should not do it yourself; if possible, try to do the installation without connections - with a single cable.

In any case, it is better to use a protective pipe of any type as additional protection, this will increase the reliability of the line. In addition, in this way it is possible to lay VVG and similar brands for not very critical electrical installations. As an option, you can use corrugation, it has a probe (metal wire) for pulling wires. If it is not there, then it will not be possible to push through a long soft wire.

Basic rules and technology

First you need to develop a cable route. It is clear that when laying in a straight line, less of it will be required. But, unfortunately, this is not always possible. When laying a route, it is advisable to avoid:

• Walking near large trees. It is advisable to lay the route at a distance of at least a meter from large trees. If the tree is located directly on the road, it is advisable to go around it along an arc or a trajectory close to it. In principle, the optimal distance is 1.5 m. If such an arc does not fit into the site, you can dig small trenches on both sides of the tree, drive a metal pipe into the ground between them, and pull the cable into it.

  
  If there are more plants, they must be bypassed

• It is highly advisable to bypass areas with increased traffic: parking areas, access areas for sewage disposal vehicles, pedestrian paths, etc. Such zones can be bypassed along the perimeter.
• If areas with increased load cannot be bypassed, cases are used to improve protection. Cases are also needed at intersections with drainage trays, at intersections of water supply lines, gas pipelines and other communications. If there are sections of the route with a ditch depth of less than 50 cm or in places where it was not possible to remove solid objects (old foundation, large stones, etc.), it is worth laying a protective cover everywhere.
• If the route of underground cable laying runs along the foundation, it must be at a distance of at least 60 cm from it. Laying the cable in the ground closer to the foundation is prohibited - movements of the soil or building can damage the power line.
• It is advisable to avoid crossing with other cables. If it is impossible to bypass the intersection, both cables must be in a case. They must protrude beyond the intersection by at least 1 meter in both directions, and the cables must be at a distance of at least 15 cm one above the other.

If you couldn’t avoid all the difficult places, don’t worry. In these areas, you can lay the cable not in the ground, but in a corrugated pipe, HDPE pipe or metal pipe. They are called cases. When using several pieces of metal pipes in a row, they must be welded. This is done so that they do not damage the shell at the junction points.

The procedure and technology for laying cables in the ground

They dig a trench along the intended route. Its depth is 70-80 cm, the width when laying one cable is 20-30 cm, when laying two or more, the distance between the threads laid at the bottom of the trench must be at least 10 cm. Use these criteria to decide. After the trench has been dug, you must:

• Remove all hard and sharp objects, roots, stones, etc. They can damage the insulation and may cause the line to fail.
• Level the bottom and compact it a little. It is not necessary to bring it to level, but there should not be any sudden changes.
• Pour a 10 cm layer of sand and level it. You can use cheap sand from a quarry, but it must be sifted to prevent foreign objects from getting in - stones, pieces of glass, etc. Compact the sand too. You can just crush it with your feet. There should be no obvious humps or depressions.
• Check the integrity of the insulation, if there is damage somewhere, repair it. Cases (pieces of pipes) are first put on the cable and dragged to places of increased load.
• Next, the actual laying of the cable in the ground begins - it is laid in a trench with sand. You can’t pull it - it should lie in light waves. Cases are placed in the right places along the route.

  
  The waves will allow the line not to break during frost heaving or other soil movements

• It is advisable to check the laid cable - damage may occur during installation. If you have a megometer, great, use it to check the integrity of the shell. If there is no such device, you can ring the wires for a break with a conventional multimeter or tester. It is also necessary to check them for ground. If it “grounds” somewhere, the insulation has been damaged. It is necessary to look for damage and repair it.
• If all the parameters are normal, sketch out a plan for the route, preferably to scale, with reference to landmarks. Set the distances from reliable objects to the route (from the corner of the house, the edge of the plot, etc.). Laying the cable in the ground is also inconvenient because if repairs are necessary, it is difficult to gain access. If you have a plan with dimensions, everything will be much easier.
• After this, fill the laid cable with sand. It is also sifted and a layer is poured - about 10 cm, compacted. There is no need to tamp down too much; you can compact it with your feet.
• Next, a layer of 15-20 cm of previously excavated soil is poured. When backfilling, remove stones and other foreign objects. The layer is also leveled and compacted.
• Lay down warning tape. This is a bright polymer tape with the inscription “be careful with the cable!” During excavation work, it can save underground electrical wiring from damage.

  
  The warning tape will warn of possible excavation work

• Afterwards, they continue to fill the ditch with soil, pouring it slightly above ground level, since after some time the rock will compact and settle.

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All technical data and characteristics. And the last stage is checking the electrical parameters before connecting to the load. This completes the laying of the cable in the ground. Once again, the entire procedure can be seen in the video.

2.3.15

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

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

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

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

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

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

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

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

Features of HDPE pipes

Features of using HDPE pipes:

• HDPE pipes have very simple installation;
• Corrugated pipes are suitable for laying electrical network cables;
• If the installation is done correctly, the pipes form a tight connection;
• HDPE pipes return to their previous linear size over time. The use of a probe allows you to simplify cable pulling.
• HDPE pipes have a high elasticity index (more details: “HDPE pipes - application and technical characteristics”). Therefore, they can be used all year round; changes in soil temperature will not affect them.

For laying signal or power cables, double-wall corrugated pipes are optimal. Their use allows you to protect the line from any external influences.

There are two different types of pipes in the manufacture of which low-density polyethylene was used: products that comply with the GOST standard, and other products from the secondary market. The second option is of worse quality. You can choose it if your budget is limited.

Advantages of low pressure polyethylene pipes:

• Long service life (manufacturers claim 50 years);
• No welding is required to connect individual pipes;
• Lightweight design;
• Over time, the product does not lose its performance characteristics;
• External factors do not have a negative impact on HDPE pipes;
• To lay cables in such pipes, no additional grounding is required;
• Wide range of operating temperatures - from -25 oC to +70oC;
• HDPE pipes do not have a negative impact on the environment, as they do not emit toxic waste or condensate;
• Pipes made of low-pressure polyethylene are easily deformed; there is no need to use additional fasteners and connecting parts to lay the pipeline. But you should understand that if the pipe is strongly bent, the cable will not fit into it.

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HDPE pipes are gaining increasing popularity in various areas of life. This is due to the abundance of their advantages without harm to the environment. If you approach the installation and installation process correctly, the object will last for several decades without the need for repairs. They also use HDPE pipes for electrical wiring in the house (for more details: “Characteristics of PVC pipes for electrical wiring, advantages and rules of use”).

Specifics and standards

The distance from the cable to the gas pipeline, as well as other parameters that relate to the transportation of electricity through an electric cable and gas fuel through a gas pipeline, are provided for by special instructions for construction, operation and safety.

Electric cable

The rules for the design of electrical installations provide for a variety of difficulties and subtleties that may arise when placing electrical power panels. They can be group, external or internal.

It is impossible to answer the question of what distance should be maintained between the gas pipeline and the electric cable without taking into account the specific features of the engineering project, because the standards depend on several parameters in each specific case.

Laying high voltage cables underground

Recommendations have been made to the prescribed standards several times. This happened as isolation methods improved, transportation changed, and networks developed and branched out.

Electric cable in the ground

In the case of a pipeline, the distance is regulated according to separate principles. It all depends on the type and variety of the special structure, its technical equipment, the required level of pressure in the gas main, as well as the place and method of its installation:

1. In SP 62.13330.2011 “Gas distribution systems”, supplemented and revised SNiP 42-01-2002 (attached to it is a table of minimum distances from gas pipelines, which organically follow from the safety standards and regulations specified in the code).
2. The PB (FNiP) approved in 2013 provides for industrial safety features for those facilities that use hydrocarbon fuel in a liquefied state.
3. The Decree of the Government of the Russian Federation, adopted on November 20, 2000 (No. 878), specifies the distances required to be maintained in public and residential buildings. The main function of this regulation is to prevent dangerous situations. They can arise due to incorrect placement of gas pipes in relation to other systems.

Laying electrical cables underground

Norms

The distance between the cable and the gas pipeline is also determined by the specifics of electricity transmission. Gas pipelines can be of underground and above-ground types, electricity can be transmitted through underground cable or overhead overhead lines. The distance from the communication cable in the airspace depends on the security zone of the power line, the power and operating mode of the electrical installation.

Overhead power line

In an underground cable network, everything depends on the voltage class and insulation safety, the proximity of other objects, their size and purpose. A safety zone is provided for power lines, the dimensions of which are marked in the form of a geometrically calculated polygon. The underground cable can be equipped with additional devices that make it possible to reduce the distance.

In addition to the Decree of the Government of the Russian Federation No. 169, which determines the procedure for installing security zones, rules for the design and provision of electricity transportation and the organization of safety measures, there is GOST 13109-97 “Electric energy”, GOST 14254-2015 “Degrees of protection provided by shells”, technical rules operation of consumer electrical installations (PTEEP) and SNiP 21-01-97 “Fire safety of buildings and structures”.

Corrugation

The rules for electrical installations have been repeatedly edited and adjusted. They are aimed at preventing possible violations due to non-compliance with distances. The Ministry of Energy regulations, for example, stipulate a minimum distance between sockets for electrical appliances and the gas pipe in the room.

It is set at 50 cm to prevent the possibility of household gas explosion if sparking occurs in the outlet. In other cases there are many nuances

Particular attention is paid to the distance from the cable to the above-ground or underground location of natural gas or energy transportation facilities

Medium pressure gas pipeline

Nuances and features

Laying cables in the ground is a labor-intensive process. It takes a lot to dig a trench, and then carrying the cable is also not easy. Burying is a little easier, but also not the most pleasant experience. If after a couple of years the insulation becomes leaky, you will have to repeat everything again, which will not make anyone happy. It’s clear that it’s better to do everything once and more reliably. The fact is that you can lay the cable in a trench without a protective sheath. This will not contradict the norm. And if you install a high-quality armored cable, it will last a long time.

For greater reliability, it is advisable to lay the cable in double-walled special corrugation or asbestos-cement pipes

But if you are laying a regular VVG or NYM, for greater reliability, it is better to lay it in a double-walled corrugated hose DKS along its entire length. In the right places, you additionally put on cases made of stiffer pipes or the same booster tube but of a larger diameter. Asbestos-cement or plastic thick-walled pipes are also often used. When laying the cable in this way in the ground, the risk of its premature failure is much lower - most of the loads fall on the pipes, and not on the protective sheath and conductors.

Laying the cable in the ground in plastic or asbestos-cement pipes or corrugated hoses has one more advantage: there is a high probability that, if necessary, it can be replaced by simply tightening it in place of the old one. The new one is tied to the old one, the old one is pulled out, and the new one “crawls” in its place. But this is not always possible: over time, both the pipe and the corrugated hose can collapse - the effects of ice and soil loads contribute to the destruction of the protective shells.

This is what a cable not intended for laying in the ground may look like after a few years.

From all this it follows that although laying cables in paper insulation does not contradict the standards, it is better to use plastic insulation - PVC or cross-linked polyethylene. Paper, even with special impregnations, deteriorates much faster than polymers, which brings the replacement period closer. Laying cables in the ground still requires significant effort and labor, so it is better to lay more durable materials.

How to enter the house

When entering a house, bathhouse, outbuilding, passing the cable under the foundation is unacceptable. Even if it is a shallow strip foundation. In general, when pouring the tape to enter the cable into the house, mortgages are embedded in it. This is a piece of pipe that protrudes a few centimeters beyond the foundation. The cable is inserted into it.

The cross-section of this embed should be 4 times larger than the cable cross-section. And to prevent living creatures from getting into the remaining gap, after laying the mortgage is sealed. To seal, you can use the old-fashioned method - a rag soaked in cement milk, or fill everything with polyurethane foam.

Entry of underground power cable through the foundation

If a mortgage was not made during construction, you will have to drill a hole in the foundation, insert and seal a pipe. Further, all the technology is the same.

Another option: raise the cable in a metal pipe to a certain height along the wall of the house. They usually raise it to the level where the introductory cabinet hangs. At this height, install a mortgage in the wall (the same metal pipe with the same parameters and rules) and lead the cable into the house through it. This method is suitable if your foundation is a monolithic slab or you simply don’t want to disturb the solidity of the tape.

How to introduce an underground cable into a house through a wall

When using an armored cable, the armor must be grounded. To do this, a wire in a sheath is welded/soldered to the armor, it is in the shield. If this is not done, when the phase breaks through, it will most likely end up on the armor. If someone touches the armor, at best they will receive an electrical injury, at worst they may die. If the protective metal shell is grounded (or rather, zeroed), the breakdown will trigger the machine, which will turn off the power until the causes are identified and eliminated.

2.3.111

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

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

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

Puncture of the road within the cottage village

Horizontal directional drilling using the puncture method is in demand in the individual housing construction segment. HDD makes it possible to quickly lay utility lines without causing serious damage to roads within the village. Allowed installation:

• Low-voltage and high-voltage power supply lines;
• Water supply and sewerage;
• Gas pipeline sections.

Horizontal directional drilling does not harm agricultural land, does not affect the integrity of wells and the quality of water in a populated area. HDD does not violate the integrity of dirt roads, asphalt sections, sidewalks; does not violate the aesthetics of the design of personal plots. Work in the residential sector is carried out in a short time due to the characteristics of the soil, the lack of dense vehicle traffic and the small number of underground communications. The Techservice company offers Chinese DDW installations to customers, we provide fast delivery of DDW and carry out warranty (post-warranty) repairs.

Stages of laying cable lines in the ground

The work is performed in the following order.

1. The laying route is selected and laid out on the ground. A project is drawn up, according to which excavation work is coordinated with all organizations and enterprises whose communications may be in the ground.
2. Using earthmoving equipment, a trench is dug. In particularly complex and critical cases (if there are other utilities nearby), excavation work is carried out manually.
3. A sand bedding is placed along the entire length of the power line at the bottom of the trench. Such a pillow can also be made of fine earth, cleared of stones and construction debris.
4. In the event that additional cable protection is required (provided for by the project), asbestos-cement or PVC pipes are laid.
5. The cable is being prepared for installation. The drums are unpacked and installed on cable laying machines. Short length - laid and leveled next to the trench.
6. The actual installation of the power line is carried out, including the broaching of the pipes.
7. If necessary, connecting couplings are installed. Their locations are marked on the laying diagram.
8. If provided for by the project, the power line is protected with concrete slabs or red bricks, and warning tape is laid.
9. The cable is covered with a layer of earth cleared of stones and a hidden work report is drawn up.
10. The insulation is tested for breakdown, its resistance is measured, and then the trench is completely backfilled with soil.
11. Benchmarks and safety warning signs are installed.

All work is carried out strictly in the specified order by teams, which must include certified specialists with the necessary skills and knowledge

Particular attention should be paid to safety regulations

Cost of work

The price of the work includes taking out the route in kind by a surveyor, drilling a well, welding and pulling pipes, digging and backfilling pits, caulking holes, blowing construction thread into each pipe, and drawing up as-built documentation. The price also includes VAT 20%. Activities for improvement and restoration of the territory are paid separately.

The cost of work does not depend on the category of soil, the presence of intersections with existing communications, the time of year, or the remoteness of the site. The final price for HDD across the road is calculated after preparing the project and selecting the type (diameter) of pipes.

Cost calculator

m

Total price: 33,000 rub.

2.3.25

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

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

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

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

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

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, a whole list of requirements is imposed on underground electrical wiring.

​

• At the point where the electric line enters the house, the cable is placed in an asbestos-cement coupling, which protrudes at least 60 cm on 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 and laid with mechanical protection or warning tape.
• 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.

2.3.13

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

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

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

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

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

The essence and advantages of HDD puncture technology

Laying utility networks by HDD puncture under the road consists of drilling a pilot well followed by back drilling with an expander to obtain a drilling channel of the designed diameter. A pipeline is then connected to the expander and pulled through the well.

Pipelines under roads of any category must be laid in a protective case. The process is controlled using an electronic location system. The curvature of the well trajectory is limited only by the permissible bending angle of the drill rods.

Advantages of the technology:

• work is carried out without digging and backfilling trenches, regardless of weather conditions or time of year;
• there is no destruction of the road surface with the embankment, adjacent sidewalks, or pedestrian paths;
• damage to the surrounding landscape and landscaped areas in cities, cottage villages, and dacha communities is minimized;
• does not interfere with the movement of cars, passenger transport, or pedestrians, which is especially important in areas with difficult road conditions or in cramped urban conditions;
• the duration of work, the number of involved equipment and labor, and financial costs are reduced;
• soil does not accumulate on the surface in large quantities;
• puncture length up to 800 m, diameter up to 1,000 mm.

When HDD punctures under the road, due to reverse excavation, strengthening bentonite solution is not used, because The canal walls are held in place by compaction. With the help of HDD it is possible not only to lay, but also to replace old pipes.

Laying cables in the ground: which cable is better to use

Most electricians argue that laying cables in a trench should be done using special material, including the wire itself - this is what not only they say, but also the so-called PUE (electrical installation rules). It is useless to argue with these rules and it would be wrong to violate their instructions. BUT! There is also another side to the coin, which the rules written in the last century do not take into account. Everyone understands this, but they don’t try to argue with them - it will cost you more, so it’s better to play it safe a little. So what do these rules say? What cable is prescribed to be used when installing underground electrical wiring?

The PUE has a clear answer to this.

• PUE 2.1.48. Wires and cables should only be used in those areas specified in the standards and specifications on the cable.
• PUE 2.3.37. For cable lines laid in land or water, armored cables should be used predominantly. The metal sheaths of these cables must have an outer covering to protect them from chemical attack.

Agree, for the average person this is too confusing a formulation, from which one can only understand that the cables must be special. In general, in simple terms, they must have serious protection from water and no less high-quality protection from mechanical damage. In addition, they must be very tensile strength in order to successfully withstand ground movements. In most cases, according to the same PUE, cable and wire products marked VBBShv and AVBBShv fall into this category.

Now let’s just open the specification for any modern wire and read what is written there - for example, VVG or the same PVS, and ShVVP too. Their characteristics are fully suitable for underground installation - they are 98% waterproof, like the prescribed wires, they are quite tensile strength. The only thing they don’t have is armor protection - but, excuse me, what kind of armor protection can we talk about when installing lighting wiring in the garden?

In general, situations are different, and the same PUE simply mean laying a power cable - practice shows that, in principle, any cable of a suitable cross-section is suitable for arranging a personal plot. Another thing is the correctness of its installation. We’ll talk about this later.

Electrical cable laying

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.

1. The depth at which the cable must run 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 during any excavation work, 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 causes irreparable damage to the 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.
2. High protection of underground electrical wiring from mechanical damage. To do this, the cable is inserted into a special pipe or corrugated hose. You should not think that this is reinsurance; such safety measures allow you to avoid damage to wires by ice in the winter season and when the ground moves. 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.
3. Adding sand to the trench is also a fairly important factor, providing 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.
4. Installation of a signal 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 the 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 slabs laid on top of the wires are used as a beacon.

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, the electrical network does not 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 requirements that can be found very often.

1. Laying wires under roads - they must be made in a thick-walled metal pipe. This is due to increased pressure on the ground from cars and trucks passing along the road, which can cause soil movement. And, as you know, this can lead to breakage of electrical wires.
2. 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 inspection. It is imperative to ensure the integrity of the wiring and only then finally fill the trench with earth. In this case, a visual inspection is not enough; it is better 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.

2.3.124

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

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

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

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

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

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

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

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

Brief information about the layer of plastic sewerage into asphalt (trencher) is presented. He cuts asphalt in the city with a milling cutter to a depth of 40 cm, lays plastic pipes and fills the gap with high-strength concrete. The only obstacles with this installation method can be tram rails and hatches. The top of the gap is first closed temporarily with a special tape, then covered with asphalt. Restoration of the road surface - complete and strengthened at the cut site. The speed of sewerage construction is up to 500 m per shift.

Improvements in telecommunications equipment make it possible to significantly reduce the area occupied by station equipment, while increasing power many times over.

Unfortunately, such trends are practically not observed in relation to linear structures. The development of networks of telecom operators, as well as departmental networks, leads to the fact that the existing cable duct is overloaded, and additional cable laying is impossible. In addition, it should be taken into account that fiber-optic cables must be laid in free channels of the cable duct, into which other fiber-optic cables can subsequently be laid. In a cable duct occupied by a cable with metal conductors, joint laying of fiber-optic cables is allowed only in a protective polyethylene tube. However, there is often no space in the channels for laying cables in polyethylene tubes. In such a situation, you have to carry out the reporting of cable channels, and this is a very expensive procedure. Most often, there is a need to report channels in central areas, which are already oversaturated with underground communications (these are, as a rule, areas with high business activity).

It should be noted that digging entails numerous inconveniences: it creates obstacles to the movement of vehicles and pedestrians, and worsens the appearance of the streets. In places where communications from third parties intersect, it is necessary to involve representatives of these organizations. Work often has to be carried out in a short time, including at night. For the movement of pedestrians through the excavation zones, temporary crossings with fences are installed, and lighting is provided at night. In addition, upon completion of work, remediation measures are carried out, as well as restoration of the road surface (asphalting, laying tiles, etc.). Current instructions recommend manual work on digging trenches and pits in cramped urban conditions. This creates additional problems, especially in winter. City authorities are reluctant to allow excavation in the central areas of the city. Thus, there is a whole range of problems that hinder the development of wired networks in areas where they are most needed. The search for ways to solve these problems forces us to turn to the experience of foreign partners. One of the effective methods is the use of microtrench laying of fiber-optic cables.

Microtrenching mechanisms

The microtrenching technique is based on the use of specialized mechanisms. They are a cutter on a tractor chassis for removing road surfaces and a device for removing dust, sand, gravel and other small fractions. These mechanisms can be combined into one or, conversely, separated, accordingly distributing the technological operation of preparing the trench for cable installation into two stages - opening the asphalt and cleaning the microtrench. A compressor, as well as a vacuum or water pump, can be used as a cleaning device. Accordingly, foreign particles are blown out by an air stream, sucked out, or washed away by a water stream supplied under pressure.

As a rule, cable laying in the ground is carried out in a trench to a depth of 1.2 m (except for rocky and other dense soils of category IV and higher) in accordance with current standards. This depth is considered sufficient to reliably protect line cable structures operated outdoors from unauthorized access and the influence of environmental factors. In urban environments, to streamline communications, cable ducts are built, which provide additional protection for linear cable structures.

Various developers of fiber-optic cables offer different technology options for laying cables in a microtrench. These options have a common technological operation - deepening. The idea of ​​microtrench technology is to provide reliable cable protection while significantly reducing excavation work. Additional protection from the most likely external mechanical and temperature effects is provided by the road surface itself.

Diagram of functional devices when laying an optical cable in a microtrench

There are technologies for laying specially designed fiber-optic cables directly into a microtrench, as well as laying special channels for the subsequent installation of fiber-optic cables in them.

Laying fiber optic cables directly into the ground

Using specialized mechanisms, a microtrench up to 15 mm wide and 40 to 100 mm deep is made in the roadbed, into which a specialized fiber-optic cable is laid. The laid cable is covered with a porous rubber bundle; the diameter of the bundle is selected so that it fits tightly into the trench and serves as a spacer. After this, the trench is filled with bitumen.

The cable intended for this installation method is a monotube design and consists of one metal module made of copper alloy, which contains optical fibers inside. The internal space of the module with fibers is filled with a hydrophobic compound. The outer diameter of the module is 5 mm. The module contains bundles of optical fibers. For identification, the optical fibers in one bundle have different colors, and each bundle has a winding of colored synthetic threads. The number of optical fibers in a bundle is up to 12 pieces. The cable can contain up to 5 bundles of optical fibers. Thus, the number of optical fibers in the cable can reach sixty. The outside of the cable is covered with a protective polyethylene sheath. The outer diameter of the cable is 7 mm, weight is about 110 kg/km.

Fiber optic cable for microtrench installation

This design of the fiber optic cable provides high resistance to temperature fluctuations and mechanical stress. The permissible breaking force is 1 kN. The permissible bending radius during installation is 70 mm. Operating temperature range - from -40 to +70°C.

It should be noted that, as in the case of other fiber optic cables, installation work must be carried out at an ambient temperature of at least -5°C.

To splice building lengths of fiber-optic cable, special couplings have been developed for installation on the ground surface so that the coupling hatch is flush with the road surface. These are through-type couplings. The round body is made of stainless steel and is designed for splicing up to two construction lengths of cable, that is, it has 4 cable entries. There are modifications of couplings for splicing fiber-optic cables of various capacities. The coupling body has a round shape, the diameter is designed in such a way as to ensure the possibility of laying out the technological supply of optical fibers inside the coupling body.

Cable entries are located in the lower part of the coupling body and are sealed mechanically by crimping the coupling pipe around the metal cable module using a crimping tool. Then, the junction of the protective polyethylene cable sheath and the cable entry of the coupling can be additionally protected with heat-shrinkable tubing to prevent moisture from penetrating under the sheath. This sealing method provides reliable long-term protection of the coupling from moisture penetration.

Microtrench laying of cable channels

The method of preparing a microtrench for installation is similar to the method of laying a cable directly into the ground, with the exception of the size of the microtrench. To lay channels, a microtrench is made 100 mm wide and about 250 mm deep. 1-2 channels are laid into it, containing up to 7 subchannels for laying cables: one central and 7 peripheral. The internal diameter of the channels is 10 mm. After laying the channels, the microtrench is filled with lightweight concrete, and then the asphalt surface is restored. To locate the couplings and technological reserve of the fiber-optic cable, special microwells are installed, which are plastic or metal boxes buried in the ground and embedded in asphalt. The microwell neck is closed with a lid or hatch with a lock that prevents unauthorized access. The channels with cables are inserted through the walls with subsequent sealing of the entry point. The coupling is fixed on the wall of the microwell, and the technological supply of the cable is laid out in the shape of a figure eight. Due to the small outer diameter of the cable, the minimum permissible bending radius of the cable is about 150 mm.

Cross-section of microtrenches with laid cable

The construction of traditional cable duct inspection devices involves a significant amount of excavation work, including digging a pit, removing excess soil, and compacting the soil at the bottom of the pit to avoid subsidence under the weight of the reinforced concrete structure. During construction, equipment is also needed to unload the reinforced concrete elements of the well.

Since microwells are located on the ground surface, and their size and weight are much smaller than standard cable duct inspection devices, significantly lower construction costs are required. First of all, this is achieved by significantly reducing the volume of excavation work, as well as by reducing labor costs.

For this technique, special microcables have been developed, which are typical cables of the loose tube design, but with optical modules of reduced diameter. Thanks to the use of such technological solutions and the improvement of cable materials, it was possible to reduce the outer diameter of the cable to 7.2 mm without reducing mechanical strength, that is, resistance to tensile and crushing forces, impact, torsion, bending, as well as temperature fluctuations. This cable contains up to 6 optical modules, each of which can contain up to 12 optical fibers. Thus, the total number of optical fibers in the cable can reach 72. Modifications of these cables are also available, containing 8 and 12 optical modules and, respectively, 96 and 144 optical fibers.

Since the bulk of underground communications are located in sewers and sewers, which are located at a depth of at least 1 m, and the depth of the microtrench is much less, the likelihood of damage to third-party communications during the installation process is significantly reduced. The process of approving construction work at the design stage is also simplified.

When using standard methods for constructing cable ducts, the installation speed is up to 300 m per day. The use of microtrench technology makes it possible to increase the construction speed to several kilometers per day, without taking into account the time for constructing inspection devices, where the advantages of this method are even more obvious.

As a result of installing one channel, you can get a cable duct ready for laying fiber-optic cables with a capacity of up to five thousand optical fibers.

Prospects

Broad prospects for the use of microtrench technology for laying fiber-optic cables are due to the absence of the need to purchase additional expensive equipment and attract foreign specialists to set it up and train personnel. The road construction equipment necessary for the implementation of this method is available in institutions involved in the operation of roads. The advantage of this laying technology is that there is no need for long interruptions in traffic. In the case of work on streets with insignificant traffic flow, traffic may not be blocked at all, even in the case of a transverse intersection.

In conclusion, it should be noted that microtrench technology for laying fiber-optic cables is much cheaper than traditional methods of constructing cable ducts. The use of this technique can significantly reduce labor costs and time for construction work, as well as increase labor efficiency through mechanization. Widespread implementation of microtrench technology in practice will make it possible to intensify the development of interstation networks in megacities and thereby improve the quality of customer service.

2.3.31

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

Options for laying fiber optic cables “on the road” and their design

Rice. 1. Schematic representation of a paved road and possible locations for laying cables

Taking into account the above-mentioned natural gravity of the routes for laying cable communication lines to roads, in the general case, three options for the execution of their linear part are possible, which differ in the location of the cable and its design. Cable laying can be done, see fig. 1:

• directly into the road surface (1);
• into the mini-trench of the shoulder (2);
• along the road immediately beyond the right-of-way, usually at a distance of 15 - 30 m from the edge of the roadway (3).

Laying within the right-of-way, but outside the roadside, is permissible if the communication line being created is intended to solve service problems necessary for the correct functioning of the route. This possibility is not specifically identified as a separate option due to the fact that from the point of view of performing construction work, with the exception of organizational issues, it is practically no different from laying an alienated strip outside its boundaries.

It is possible to lay it directly in the road surface in its side part at a depth of about 10–15 cm in a groove about 2 cm wide, followed by filling with tar. This technology was actively promoted by the German company Siemens at the very beginning of the 2000s and was partially in demand in the city. As a prototype of the cable used for this, Fig. 1b, due to the need to ensure high lateral strength, a deep sea cable module was selected. It differed from the widespread traditional “land” products in that it contained a thick-walled copper or aluminum tube, which served as a power base and waist insulation. Due to the high cost of such products (at least 1.5 times more compared to traditional structures with armor made of round steel wire due to the use of a continuous reinforcing coating made of non-ferrous metal of large thickness), this direction of development has not received.

Rice. 2. Schematic representation of cable options for laying along paved roads: a) traditional modular design in single-layer armor made of round steel wire; b) with continuous tubular armor; c) armorless with a tube for pneumatic laying

Laying outside the right-of-way is carried out directly into the ground and should only be done with a cable armored with steel wire. The wire has a predominantly round cross-section; the more efficient square-cross-section wire is not used due to the technological difficulties of applying it to the cable body. The most common designs are with single-layer armor, Fig. 2a, when laying in rocky soils and when there is a risk of frozen soil deformations, 2-layer wire armor can be used, which allows the permissible tensile force of the cable to be increased to 20 tons.

STANDARDS, REQUIREMENTS AND FEATURES OF LAYING CABLES OF DIFFERENT TYPES

The main guidelines are the PUE standards (in particular, 2.1 and 2.3), SNiP 3.05.06-85 and GOST R 52868. These and other construction and electrical installation rules are taken into account when drawing up a project for laying trays, choosing their materials, design features and sizes.

The presence of a project and its strict adherence during installation is a mandatory requirement; any deviations are agreed upon separately.

The rules for the design of electrical installations allow the joint placement of wires for different purposes in trays with a total voltage of up to 440 V. The main guideline when checking the admission or prohibition of the joint installation of circuits for different purposes are clauses 2.1.15 and 2.1.16 of the PUE.

According to the norms, an exception is made in any case for:

• mutually redundant lines with different power sources;
• emergency and work lighting circuits with more than 8 wires and lighting circuits with different voltages (up to 42 V and above 42 V) without separate insulation;
• automation and fire alarm circuits, metering and measuring instruments, secondary communications and relay protection lines; stationary electrical networks with voltage up to 42 V, laid separately in accordance with TB requirements.

One-sided laying of low-current and power lines is permitted provided they are separated by non-flammable asbestos partitions. In this case, according to the norms, power lines are placed on top.

Redundant low-current cables are laid in different trays or also separated by partitions. Chaotic and arbitrary arrangement of cables with different voltages and purposes is prohibited.

General requirements include laying in one row, without rings, filling the free space by no more than 50-60%. Unarmored cables with voltages up to 1 kV can be laid in a single layer without gaps, multi-layered or in bundles with a diameter of no more than 100 mm and gaps of 20 m and above.

The number of wires in one bundle is limited to 12; the requirements for the distances between single wires of larger cross-sections largely coincide with the rules for laying wires along structures.

Thus, the gap between single power conductors is maintained within 5 mm, in bundles - 20. Arbitrary arrangement is allowed if the total cross-section of all wires is within 40% of the cross-section of the open tray.

Fastening wires and cables in bundles to each other is mandatory; in horizontal structures, there is no need for additional support (tying step in bundles is 4.5 m), in vertical structures, clamps are placed every 2 m at least (tying step – 1 m).

Requirements of power engineers for electrical installation work

All rules are spelled out in regulatory documents. Based on SNiP, GOST, PUE, we can highlight the main restrictions when performing installation:

• It is forbidden to lay the power line directly under the foundation of the house; it is necessary to retreat at least 60 cm from it. If laying under the foundation cannot be avoided, then it is necessary to protect the line with a steel pipe.
• The cable is laid to a depth of 70 cm or more. A depth of 50 cm is allowed, provided that the length of the underground line does not exceed five meters and the electrical wires are additionally protected by a pipe.
• The width of the trench depends on the amount of wiring that will be laid in it. Please note that the distance between the two lines should not be less than 10 cm.
• The distance from trees should be at least two meters, and 75 centimeters should be retreated from bushes. This rule may not be observed if the wires are additionally protected by a pipe.
• You also need to retreat 1 and 2 meters from the water supply and gas pipelines, respectively.
• If the cable has intersections underground, they must be separated by a layer of soil at least 50 cm thick.
• To install the line, you should choose an armored conductor. This will protect the network from rodents.
• To construct additional protection for power lines underground, construct a fence of bricks, laying them across (hollow bricks cannot be used). An asbestos cement pipe is also used to protect against severe soil subsidence.

Not all the rules and restrictions specified in regulatory documents are listed above. But for home installation, this is enough to carry out safe electrical work and protect residents and home wiring from emergencies.

Similar: How to hide wires in a wall or box

Requirements for checking the line in case of current leakage.

Next, the cable laying work is tested for current leakage. To do this, soil is sampled in several places along the route.

• PUE clause 2.3.101 If the soil is dangerous, then it is necessary to apply leakage protection in areas with leaks: replace cable sections with samples resistant to electrical corrosion or change the route to bypass dangerous areas
• SNiP clause 2.3101 When laying a route in aggressive soils, cathodic polarization must be used (installation of protectors, electrical drains, cathodic protection).
• SNiP clause 3.70 After checking the line for current leakage is completed, the customer, together with electricians and representatives of the construction organization, draws up an act for hidden work. This is the main document according to which the road repairs will be carried out.

Technology of laying cables in metal pipes: installation process

Installing cables in pipes is quite labor-intensive and expensive, so it is used when it is necessary to guarantee the cable protection from mechanical stress. Bookmarking is carried out in several stages:

• marking the upcoming route;
• preparation and installation of pipes;
• cabling.

To complete the first point, the installation location is determined and preparatory work is carried out. When installing on the walls of buildings, foundations, partitions, grooves, holes for electrical appliances, transitions, etc. are made. Lengths and bends are measured, the necessary documentation is drawn up and sent to the electrical installation workshop. There the pipes are cleaned, painted, and cut to size. The joints must be processed so that there are no burrs. If necessary, make bends. Finished products are labeled, packaged and sent to the customer.

The installation is carried out in such a way as to prevent the ingress of dust, oil and other substances. To prevent water from accumulating, the laying is made at an angle of at least 2 degrees towards the boxes. Fastening by welding is prohibited; for this you need to use staples, clamps, pads, and clamps. The distance between the fasteners should not be greater than that indicated in the table.

All connections and inputs must be sealed. Then the electrical equipment is installed.

At the final stage, tightening is performed. Check the cleanliness of the pipes, if necessary, they are blown with compressed air, and plastic bushings are put on the ends. Wires and cables are assembled in groups, the cores are tied to steel wire with a diameter of 2-5 mm and pulled through.

Construction of the trench

First, the terrain is marked; the future route must be removed from the foundation, gas pipeline, etc. at the distance specified in the PUE. Then the ground is cleared of plants and debris. Earth-moving equipment is used to dig trenches; where this is not possible, they are dug by hand. The depth is determined by the operating voltage. The bottom is cleaned of debris if necessary, leveled and lined with a sand cushion. Signal tape must be laid on top of the route.

Trenchless method of laying cables in the ground

This is a complex and expensive method, carried out with specialized equipment. It is produced in places where it is impossible to dig a trench due to any circumstances, for example, laying under a reservoir. The bottom line is that horizontal drilling is carried out using an adjustable drill head. Then the channel expands, a HDPE pipe is pulled in which there is a steel cable, and a cable is laid through it using a cable.

Laying cables under the road

In the case where the route must pass through an asphalt road, in order not to disturb its surface, another method of passage is used - a puncture. The rod with the tip is pushed through the soil under the road using machinery. The tip, passing through the thickness, compacts the earth around itself, preventing it from crumbling. This passage is called the starting passage. After the rod has reached the surface, an expander is attached to it and pulled in the opposite direction. The passage widens, and the earth around is compacted even more. A cable line is pulled through it.

2.3.23

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

The main advantages of laying an optical cable on the side of the road

Using the roadside as a location to install fiber optic cable has several advantages over traditional off-right-of-way installations. Among the most significant among them, the following factors deserve special mention:

• high laying speed, which is illustrated by the data in Table 1;
• ease of installation of wells, determined by their prefabricated design, low weight and small dimensions;
• minimizing the risks of frozen deformations and prolonged exposure to moisture, determined by the structure and conditions of formation of the roadside;
• ease of connection to the information system of technological controllers for various purposes, facilitating the ongoing operation of highways and making road traffic more efficient.

Table 1. Typical parameters for the construction of the linear part of a fiber-optic communication system

It is of no small importance that the risks of damage to cables and wells by construction equipment during operation are reduced to almost zero (the availability factor of the linear part of the system reaches “five nines” or 0.99999) simply due to the absence of construction work carried out by third parties on the side of the roads.

From a financial point of view, a road telecommunications network at the construction and operation stages costs the customer and operator at least tens of percent less. If in terms of capital costs this statement is not unexpected due to the simplicity and low cost of construction mechanisms, as well as good weight and size indicators of cables, then in terms of operation everything is not so obvious and requires additional comments.

The added benefit of lower operating costs for organizations designing, building and operating technology information systems directly results from the ease of adding individual fibers to a line and/or feeding them to an intermediate point along the route as the need arises. A fiber-optic long-distance communication line is a highly capital-intensive facility; building up the traffic transmitted over it to its design capacity sometimes takes ten years or more. Given the high cost of borrowing, the ability to implement a fiber-on-demand approach allows the operator to save significant financial resources.

Requirements when preparing to lay cables

This stage of work requires the involvement of surveyors. And here the following requirements must be met:

• SNiP clause 3.66 states that you must first inspect the trench to identify places that could destroy the cable. This could be salt marshes, water, sharp objects (slag or construction waste). You also need to ensure that the cable does not pass closer than 2 m from the cesspools. If all requirements cannot be met, then the cable must be laid in an asbestos-cement pipe coated with a bitumen compound. To do this, the trench needs to be expanded.
• PUE 2.3.83 indicates that a sand cushion must be poured onto the bottom of the trench. The pillow should be compacted. In general, each layer of soil must be compacted when laying cables. If large or sharp inclusions accidentally get into the cushion, they can damage the cable during compaction.

2.3.113

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

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

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

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

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

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

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

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

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

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