When installing an electric cable in a private house or cottage, the question arises as to how best to do it – by air (from pole to house) or underground (dig a trench and lay from the healing site to the shield at home). Installation of air SIP (self-supporting insulated wire) is always much faster and several times cheaper. But there can often be situations when you have to wind the power cord in the house just underground.
Which cable to lay in the ground, we will consider a little later. So let’s move on to consider the installation of the cable. First, the minimum distance from the trench with the cable to the foundation of the house should be 60 cm. This trench can be dug close to the foundation of the house, excavation of the trench under the cable near the foundation of the house is prohibited. After laying in the ground, the cable should not fall on the line of force of the foundation, directed at 45 degrees from the base. Normalized deviations from plants and trees in your area are also required. How deep to bury the cable in the ground?
The depth of the cable is 0.7 m. And this is the distance from the surface to the top of the cable. Given that there will be a sand cushion of 10-15 cm under it, the total depth of the trench should be at least 0.9 m.
The main reason for this depth of the trench under the cable is to ensure the optimal temperature for the cable. If you lay it as close as possible to the ground, the main advantage of the underground laying is lost – no influence of ambient temperature and weather conditions, because the top layer of soil warms up much more, and moisture after good rains simply will not reach the cable sheath if it lies on 70cm. The advantages of such a bookmark depth are the pressure. The deeper the cable is buried, the more evenly the pressure is distributed on it from above. If you enter the house passes from the support across the road, then you need to bury the cable to an even greater depth – at least 1 meter.
The bottom layer of the trench (under your cable) must be covered with sand. The sand must be carefully compacted. The cable cannot be laid in a trench without sand filling. Otherwise, sharp stones and other foreign elements in the ground due to some can damage the insulation. The layer of sand should be under the cable and above it.
The cable itself should be laid in the trench “snake” making small wavy bends, with a margin of 1-2%. This stock is just provided by a snake. These bends are needed to protect against stretching and deformation. If the cable is laid in a perfectly straight straight line, the temperature deformations that will accompany the operation of the cable line will sooner or later damage the input.
On top of the laid cable, as we mentioned above, a small layer of sand is filled in, preferably at least 10 cm. After that, to protect against possible digging of the ground with a shovel, as well as to mark the route, use a signal tape. If suddenly someone decides to dig in the place where you have the cable laid, the signal tape with the inscription “carefully cable” will report the danger. That is, when excavating, you must first bump into the tape with a bayonet, but do not reach the cable. The signal tape is laid at a distance of 25 cm from the cable line. Due to the lack of signal tape, you can use any handy materials. The main thing is to lay something that will warn – the presence of the bottom of the cable.
Mechanical protection of cable, brick or asbestos-cement slabs is also recommended. Bricks should be used as protection when it comes to input from a substation to a high-rise building, factory or other large facility. Silicate or perforated brick can not be used.
After performing the above work, finally fill the trench with earth. Briefly summarize the rules of cable instillation:
trench depth 0.9 meters for underground cable laying
sand pillow (bottom) 10-15cm in the trench under the cable
sand pillow (top) over the cable in the trench 10-15cm
cable line (ground input)
final burial of the trench under the cable soil
Each layer after laying is compacted manually or mechanically.
So you get the right cable.
Now let’s move on to consider the cable itself, which is designed for laying underground. For this purpose, special power cables of several major brands are used. Depending on the corrosion activity of the soil, its type, and operating conditions of the cable in general, choose one or another brand of power cable. For example, wet and acidic soil has a high corrosion activity, and in some cases the cable may be subjected to tensile load, and then it requires additional strength. Armored cables meet these requirements and do not require additional protection during installation.
Usually for laying in the ground the armored copper cable of the VBbShv brand or the armored aluminum AVBbShv cable is used.
Thanks to the armor made of steel tapes, the laying of this cable is carried out without additional protective pipes, because it is the armor that provides the cable with protection from both mechanical influences and rodents.
VBbShv and AVBbShv are deciphered as follows:
A – aluminum cores;
V – isolation of veins from polyvinylchloride plastic;
B – armor of two steel strips;
b – without a protective cushion superimposed under the armor, which protects against corrosion and mechanical damage layers under the armor;
Shv – a hose from PVC of plastic;
That is VBbShv (copper) and AVBbShv (aluminum, the letter “A” speaks about existence of an aluminum vein)
These cables include the following elements:
1. Conductive cores (copper or A – aluminum), which can be from 1 to 5, and there is an option 3 + 1, when the fourth core, intended for grounding, has a smaller cross section.
The veins in turn can be 1 or 2 classes: single-core (cross section from 2.5 to 625 sq.mm) or multi-core (cross section from 2.5 to 240 sq.mm).
2. PVC insulation, providing color and digital (for cables with a cross section of 70 sq. Mm and above) marking of cores: white or yellow, red or crimson, blue or green, brown or black, or yellow-green, numbers 0, 1, 2, 3, 4.
3. Belt insulation from PVC tapes.
4. Two steel or galvanized steel strips forming armor.
5. In cables with a cross section above 6 square meters. mm bitumen is used.
6. In cables with a cross section above 6 sq. Mm additionally used winding polyethylene terephthalate film.
7. Protective hose made of PVC plastic.
Laying of VBbShv cable is admissible even in soil chemically active in relation to metal, it can be mounted near railway and tram tracks which can be sources of wandering currents. The cable of the VBbShv brand can be laid in places of the increased explosion danger, it is steady against temperature differences, and the range of admissible temperatures – from minus 50 to plus 50 degrees Celsius, it makes possible application of a cable in any climatic zone.
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