Laying a power cable in the ground: the rules of the PUE, the technology of digging trenches and laying cable lines

To transmit electricity to consumer objects, a power cable is laid in the ground. This technology is highly reliable. It replaces the air power supply, the wires of which cause a lot of trouble during operation and look unaesthetic. So, lamps in the park will not look very nice if wires are brought to them through the air. To solve the problem, you have to dig trenches and lay cables.

Technology features

Underground conduction of power lines is a laborious process. The repair of such communications is difficult, therefore all work is carried out in accordance with the PUE for laying the cable in the ground (the rules for the installation of electrical installations).

Do not use wires that are not intended for burial. For this, special armored cables with a waterproofing layer are used. They are protected from water and mechanical damage, tear resistant and resist ground movement. The wire is selected as follows:

1. For installation in soil with normal acidity, armored products AVBbShv with aluminum veins and VBbShv with copper conductors are used.
2. If the cable needs to be laid in swampy soil, salt marshes, places with a lot of construction waste or slag, then products with lead armor or aluminum sheath AABl, AAB2l, ASB, ASPl, AVBbsh, etc. are used.
3. To connect small summer cottages, farm buildings or baths to electricity, you can use ordinary PVC-coated wires. They have sufficient strength and resistance to moisture and corrosive environments. Sometimes for installation on the site, types such as NYM, SIP or VVG are used. But these products are not intended for underground installation and quickly lose their useful properties.
4. In the regions of the Far North, PvKShp cables with increased resistance to low temperatures are used for underground laying.

Armored items have three shells, while conventional items have one. The former are more expensive, but they also last much longer.

Fundamental rules

A route should first be developed along which the high-voltage cable will be laid in the ground. Although when installing along a straight line, the wire consumption will be minimal, it is not always possible to do this. On the way, the following obstacles may arise:

1. Large trees, past which the track must pass at a distance of at least 1.5 m. They must be skirted along an arc path.
2. Places with increased human and traffic load: parking lots, paths for pedestrians, entrances of waste collection equipment. It is better to go around such spaces around the perimeter. If you cannot get around them, then the wires are placed in special protective cases. They are also used at the intersection of communication lines and where there are solid foundations (large stones, old foundations, etc.). ).
3. In places where the route passes near the foundations of buildings, the line of force must be laid at a distance of at least 60 cm from them, otherwise the solid foundation may damage the cable when the ground moves.
4. Crossings with power lines should be avoided. If this cannot be done, then both wires must be protected by cases and pass one above the other at a height of at least 15 cm. HDPE, metal or corrugated pipes are used as cases.

Laying description

Along the planned path, they dig a trench with a depth of 70 to 80 cm. Its width depends on the number of threads being laid. If one cable is laid, that it is 20 cm, if two or more, then a distance of more than 10 cm is maintained between them. When the trench is dug carry out the following work:

1. Stones, glass, brick and other solid objects are removed from the bottom and walls. They can damage the insulating layer and destroy the entire line.
2. The bottom is leveled and tamped so that there are no strong drops.
3. A sand layer 10 cm thick is poured onto the bottom. An inexpensive quarry can be used, but must first be sieved to remove rocks, glass, and other objects. The sand is trampled down so that there are no pits and humps.
4. Inspect the buried power cable and check the insulation. Cases are immediately put on it and brought to places of increased stress.
5. The wire is placed in a trench. It should not be pulled, the laying is done in small waves. Cases are placed in the right places.
6. To eliminate possible damage during installation, the cable is examined. The casings are checked with a megameter to find damage. If there is no such device, then you can simply ring the wires for an open circuit using a multimeter. The cable should also be tested “to ground”. If it "earths", then the insulation is damaged somewhere. Such places need to be found and damage repaired.
7. It is necessary to sketch a plan of the route and mark on it the distance from reliable objects: corners of houses, boundaries of sites, etc. This is necessary in order to facilitate access to damaged areas when repairing the cable.
8. Then a layer of sand about 10 cm thick is poured over the cable and tamped down with your feet.
9. The top is covered with a layer of earth, from which stones and other sharp objects were removed. The layer thickness should be 15 cm.
10. A signal tape is laid from a bright polymer material with the inscription "Caution, cable!". This is done in order to protect the wire from damage during construction work.
11. The trench is finally covered with soil, making the backfill slightly above the surface of the earth, since the soil settles over time.
12. Before connecting to the load, the electrical parameters of the cable are checked, after which the installation is considered complete.

Installation tips

Repairing an underground power line is a complex and labor-intensive process, so it is better to immediately lay the cable in a trench as reliable as possible. Armored products can be stowed without a protective sheath, which does not contradict the standard. This power supply will last for many years. But it is better to place VVG or NYM in a double-walled corrugated hose along the entire length of the trench.

In the right places of the track, a hard case is additionally put on the wire. In this form, it will last longer, since the main load will fall not on the conductive cores, but on the pipes.

A hose placed in plastic, cement or corrugated pipes is easier to replace. To do this, the old wire is tied to a new one and pulled out until it snaps into place. But this is not always possible, since the corrugated hose quickly collapses under the influence of water, ice and soil loads.

The rules do not preclude laying the cable in a paper sheath, but this option is short-lived, since the paper in the ground quickly collapses. Stronger insulation is preferable PVC or polyethylene.

The greatest strength is the laying of a whole piece of cable without connections. If this is not possible, then both pieces are pulled out, install a sealed junction box and connect the wires in it. This is the most reliable method as you can always reconnect the contacts.

Entering inside the house

The rules prohibit laying a cable line into a house, a bathhouse or an outbuilding under a foundation, even a tape of shallow depth. Usually, when pouring a foundation, pipe sections, the so-called mortgages, are bricked into it, through which the cable is led into the building. They should protrude a few centimeters from the foundation. The pipe diameter is usually 4 times the cable cross-section. To prevent animals from getting inside, the mortgages are poured with polyurethane foam. If they were not made, then holes for the cable are drilled in the foundation.

When an armored cable is introduced into a house, it must be grounded. To do this, a wire is connected to the armor, connected to the zero phase on the shield. If this is not done, then during breakdown, the wire will be energized. People or animals touching the armor will be electrocuted. If the phase is zeroed, then in the event of a breakdown, an automatic switch will operate, turning off the power supply until the damage is corrected.

Underground routing keeps the cable free from wind, snow or falling trees, which are often the cause of damage. The soil protects power lines from the effects of electromagnetic radiation from power lines, railway signaling and other sources. Although the cost of the work is high, it pays off with the durability of the cable and the savings in repairs.