It is difficult to disagree that outwardly attractive decorative lighting in the park will not look very nice if you bring electrical wires to them. Besides of this, an overhead electrical line will create many problems during the use of the land plot for its intended purpose. AT such The situation remains only one correct way out - laying the electric cable in the trench underground.
The advantages of this method are: good security of the power cable from damage during falling trees, strong wind, snow or other precipitation. Electric lines laid in a trench under the ground are less susceptible to electromagnetic effects created by adjacent cables, remote control circuits and railway signaling systems, as well as other underground communications systems.
- 1 What cables are suitable for laying underground?
- 2 Requirements for cables laid underground
- 3 Requirements for the PUU to protect
- 4 Requirements for checking the mains for leakage current
- 5 The main stages of the laying of underground power grids
What cables are suitable for laying underground?
Most experts in the field of electrical systems say that power cables laid in the ground should be made using special materials, including those used for insulation. At the same time, this statement is confirmed by the established standards of the EMP. Argue with the rules of the device electrical installations, and even more so to break them strictly contraindicated.
Naturally, there is reverse side of these rules, since they were written in the last century, but no one takes this into account. Moreover, most electricians understand this, but they don’t want to argue about this - it will be more expensive for themselves. Therefore, you need to know what is written in these rules, and what electrical cables can be used for laying in trenches under the ground? In the PUE there is an unequivocal statement about this.
- The electric wire or cable should be used only in that area which is stated in the technical documentation for the operation of such products.
- For power lines, which are laid under the ground or in water, it is necessary to use mainly products with a high degree of protection - armored cables. The metal sheath of such a wire must have an external cover that is resistant to chemical and mechanical stress.
Naturally, such formulations are slightly unusual for ordinary people, who, from the whole amount of information, understand that you need to use a special cable. Simply put, the power wire used in the trench must have high-quality protection from moisture and external mechanical influences. In addition, they must have increased tensile strength, which is necessary for a qualitative opposition to the movement of soils. These parameters include wiring. with labeling standards VBBSHv or AVBBShv.
If you just open the specification of any modern wire and read all its characteristics, then most of the cables fully comply with the standards of use in trenches under the ground. Modern power cables are fully consistent with the moisture and durability of the strength of the impact on the gap. The only thing they do not have this armor protection, but such a degree of security is unlikely to need when laying underground lighting network on the summer cottage.
In general, any situation may arise, and the same EIR simply describes the rules for laying power cables. In practice, for work on the summer cottage, in principle, fit any high-quality conductors suitable for the cross section. Quite otherwise, the situation is with the correct laying of high-voltage wires.
Requirements for cables laid underground
List all requirements for underground wiring for a long time and just meaningless. Therefore, further will be considered most of them, which really concerns the laying of power cables in the trenches.
- Depthon which the cable should go underground. If it seems to someone that it is possible to simply put electricity on the electric wire with earth and this will be enough so that it will not be damaged by a shovel during any excavation work, then this is not so. In reality, the depth at which the wire must sink into the ground depends on the freezing of the soil and the proximity of groundwater, which often cause irreparable damage to the lines of force in the trench. It is clearly stated in the OES that the cable in the ground should lie at least 75 cm, but it is important to bear in mind that this applies to low-power power systems.
- High security underground wiring against mechanical damage. To do this, the cable is pushed into a special pipe or corrugated hose. Do not think that this is a reinsurance such security measures allow you to avoid damage to the wires by ice in the winter season and during the movement of the ground. In addition, according to experts, the cable laid in the pipe is easier to replace if the latter fails. But in this situation, it all depends on how long the power system has lain underground, since very often the pipe can collapse over time.
- Sand bedding - also quite important factor providing additional protection of underground cables against mechanical damage. Thanks to the sand pad, the wire will not come into contact with hard soil particles. In this case, the filling is carried out in several stages: at the bottom of the trench and on top of the laid wires. Thus, the electrical cable turns out to be between two sand layers. It is very important that the backfill, as well as the backfill, be properly rammed.
- Installation of signal tape, which plays the role of a kind of beacon, warning that underground, there are electrical cables. The tape is settled 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 shovel bayonet will not be enough at such a depth. In the case of high-voltage underground wiring, bricks or concrete slabs laid over the wires are used as a beacon.
It is important that the underground cables are not too tight - you should not save on the length of the wires. This is necessary so that during the movement of the ground does not occur. open circuit. Under the technology of underground wiring it is provided to leave a margin, which is achieved by laying the cables in small waves.
This is with regard to the most significant requirements, in accordance with which the laying of electrical lines under the ground. In addition to the above standards of EIR, there are also other regulationswhich can be met very often.
- Wiring under the roads - they must be made in a thick-walled metal pipe. This is due to the increased pressure on the ground of cars and trucks passing on the road, which can cause ground movement. And, as you know, this can lead to breakage of electrical wires.
- Cables laid parallel to each other. In such a situation, everything will depend on the power characteristics of the electrical network. But in general, it is important to realize that several wires cannot be wired into one pipe, since in case of breakdown of one cable, the adjacent wire can be damaged. According to the norms, each wire should be placed in the armor sleeve and be located no closer than 15 cm from the row of the laid cable.
Also cabled in the ground can not be carried out without checking. It is imperative to ensure the integrity of the wiring and only then finally fill the trench with earth. In this visual inspection is not enough to ring the wires with the help of devices. In addition, an important role is played by the protection of underground wiring, which will be discussed in more detail.
Requirements for the PUU to protect
Protection of electrical lines is considered the most important condition for laying wires in a trench under the ground. In this case, according to the EMP to the underground wiring is presented whole list of requirements.
- At the location of the electrical line in house the cable is placed in the sleeve, from asbestos cement, which protrudes at least 60 cm on each side of the wall.
- Throughout the duration of the underground wiring, the cables are protected with bricks laid across the wires or asbestos-cement pipe. This is necessary to protect the grid from subsidence of the soil.
- When laying multiple wires in one trench, the distance between adjacent cables should not be less 10 cm for a 10 kV network, 25 cm, if it is a high voltage network of 20-35 kV and 50 cm between the wires of different organizations.
- The wires laid in the trench should be filled with a layer of soil with the installation of mechanical protection or signal tape.
- Signal tape must not be laid directly on the cable. From the wire to the lighthouse, must be at least 25 cm vertically. In the case of laying several wires in a trench, the tapes are laid separately above each cable.
- In case of a cable line crossing other communication systems, the signal tape is placed no closer than 200 cm from adjacent communications.
Requirements for checking the mains for leakage current
After laying the cable in the trench, it must be checked for leakage. For this purpose in different places of the underground power route take a sample of the soil.
- If a leakage of current is detected at any site, then additional protection or replacement of wires with resistant samples of electrical wiring is applied.
- With the passage of the route in the ground with an aggressive environment you need to use a cathode vapor barrier.
After completion of the earthworks for laying the underground power grid and checking it for leakage current, the electrical installation organization and the customer’s representatives draw up an act for hidden works. On the basis of this document further repairs will be carried out if necessary.
The main stages of the laying of underground power grids
Land works for laying electrical cables in a trench are usually carried out with certain steps.
- Choose a route for laying and make a breakdown of it directly on the ground. Prepare project documentation, according to which land work is carried out taking into account the location of communications, other organizations.
- With the help of earthmoving cars, and in especially difficult places the trench arrangement will be carried out manually.
- Along the bottom of the trench, a 10 cm layer of sand is poured. Such a sandy pillow can also be equipped with sifted soil.
- If necessary, additional measures to protect the cable are laid metal or asbestos-cement pipes into which the wire will be inserted.
- The cable is being prepared for installation. Unpack the drum and place it on the cable layer. Part of the wire is leveled and placed near the moat.
- Perform direct cable laying on a sand pad or in pipes.
- If necessary, install the coupling, the location of which is fixed on the cable routing.
- If envisaged by the project, then wire protection is performed using concrete slabs or red bricks, over which the signal tape is laid.
- A layer of clean soil is poured over the cable and an act of completion of the hidden works is drawn up.
- The insulation material is tested for leakage current by measuring the resistance of the latter.
- Conduct the final backfill of the trench.
- Install reference columns and warning security signs.
Laying of the underground power network is performed in accordance with the specified procedure and only certified teams of specialistswith sufficient skills for land work related to electricity.