How to lay the cable underground - practical tips
First of all, you need to tell you about what regulatory documents can affect how you will install electrical wiring in an earthen trench. So, the basic rules for laying cables in the ground are described in chapter PUE 2.3 starting with paragraph 83, as well as SNiP 3.05.06-86, “Unified technical guidelines for the selection and use of electric cables” and other regulatory documents. In the article, we consider the features of laying cable lines with voltage up to 1000V. We single out the most important:
- The cable laying depth in the ground according to PUE 2.3.84 must be at least 0.7 m for cables up to 20 kV, at the intersection with the carriageway - at least 1 m. For entry into the building and at the intersection with underground structures, laying at a depth of 50 cm is allowed with protection from mechanical damage, that is, laying in a pipe (at such a depth, the cable must be armored). Moreover, the length of such a section should be no more than 5 meters.
- According to PUE 2.3.85. PIt is forbidden to draw the line with the foundation of the house. The minimum distance from the foundation should be 60 cm. If you need to lay the cable from the house to the bathhouse, garage or other building, lay the cable as described above, and the passage through the wall (foundation) must be done in rigid PVC, HDPE or in a steel pipe.
- According to PUE 2.3.86, the distance between two cables in one trench should be no less than 10 cm, on the basis of which the width of the trench is chosen. 50 cm need to step back from the cables of other organizations and communication cables.
- At least 2 meters should be backed off from trees to lay electrical wiring in a trench, and at least 75 cm from shrubs (according to clause 2.4.87). This distance can be reduced when laying the cable in the pipe, for example, if you dig under the tree).
- In all cases where damage to the cable line is possible - lay it in the pipes. In other cases - directly in the ground at the depth indicated above.
- The distance to pipelines and sewerage during parallel installation should be at least 1 m (paragraph 2.3.88), to the heat pipe - 2 m (paragraph 2.3.89). Up to a gas pipeline with a pressure of 0.0049-0.588 MPa - not less than 1 m, with a pressure of more than 0.588 MPa - 2 meters. Laying above and below the pipelines is not allowed.
- When crossing cables, they should be separated by a 50 cm thick layer of earth (paragraph 2.3.94-95).
- According to paragraph 2.3.37, you must use predominantly armored cables, for example, (A) VBBSHV. Unarmored cables must be resistant to mechanical stress.
- According to the “Uniform Requirements ...” and GOST 16442-80, which we mentioned above, it is permissible to use (A) VVG in the ground directly (without a pipe). But only if there is no tensile load and if it is not a marshland, bulk or heaving soils or vertical sections of the line, as well as in trenches in the soil with low and medium corrosive activity. However, laying the cable in PVC, HDPE or steel pipes allows in which case it is easy to replace the cable without opening the ground.
- To avoid strain on the line due to stretching and ground pressure - lay the cable with a snake with a margin of 1-2% in length, and when laying in heaving soil or when laying a hot cable (if the work is done in cold weather), the margin should be 3-4 %
- If you need to do it yourself electrical cable connection underground, use special couplings as shown in the photo.
- For additional protection of the power line underground (for example, with severe subsidence), you can use a pipe or a special cable structure made of brick (laid across the trench, as in the photo below). Do not use hollow bricks. Note that protection against mechanical damage by bricks or concrete plates of cables up to 20 kV laid at a depth of 1 meter or more is optional, according to clause 2.3.83 of the Electrical Code. At the same time, cables up to 1 kV MUST have such protection only in those places where frequent excavations are likely.
- Be sure to lay the signal tape with the inscription: "Caution, cable!" Yourself on top of the conductor laid in the ground.
Given these requirements and rules, you can be sure that laying the cable in the trench will not endanger you and the home electrical wiring line! Of course, this is not all the restrictions that exist in the rules of the EMP and SNiP, but for home conditions the provided requirements will be enough even when connecting the site from the pole to the house.
DIY styling technology
So we come to the main issue of the article, in which we will consider how to properly lay the electric cable in the ground on our own. To make the instruction convenient and understandable, we will provide it in stages.
- Draw a diagram of the wiring in the trench, on which mark the exact distance from the house, garden buildings and plantings, according to regulatory documents. If the underground electrical installation will be used to connect street lighting in the country, be sure to indicate the location of the lights.
- Mark the territory of the summer cottage with pegs and a rope, and then dig a trench according to the marking. After excavation work, remove stones, possible glass fragments or pieces of metal from the prepared trench, which may subsequently cause damage to the electrical wiring underground. Install lighting poles immediately if necessary.
- On a tamped bottom, make an even pillow of sand or fine soil, previously cleaned of small stones, glass fragments, bricks and other objects that could damage the insulation.
- Lay the conductor in the ground as shown in the photo. For laying electrical wiring in a trench, it is recommended to use cable AVBBSHV with aluminum conductors or a more expensive option - VBBSHV, with copper conductors, or VVG-ng-LS, in the cases described above.
- Check the finished cable line with a megohmmeter that will detect insulation damage and high voltage leaks (measure insulation resistance) Do not forget to discharge the cable to the ground or shorting the conductors after resistance measurements.
- Use the pipe following the rules and recommendations described above. If you need laying in a pipe (depth 50 cm, excavations often occur, laying under a tree, etc.), then use HDPE, PVC, steel or asbestos-cement pipes.The last type of pipe is cut lengthwise into two parts, making them look like a pencil case, after which the wire is laid. This technology will allow you to quickly release the wiring during its repair.
- Take a picture of the net from the trenches to know exactly where the cable runs in the ground in the garden. By the way, the drawing is also better to save, because on it there are signs of all distances when laying a line from the house, fencing, etc.
- Fill the trench with sand or fine soil, cleared of sharp objects. The layer should be uniform, about 15 cm. After filling it must be carefully tamped.
- Lay a signal tape on the sand with a sign that electrical wiring has been completed underneath.
- Fill the remaining ground over the tape, making a slide that, after several rains, will settle and level with the surface.
- Measure again using a megger.
That's the whole technology of laying the cable underground at the cottage. As you can see, drawing a line at home is not so difficult. More time and effort will be spent on earthwork - digging a trench.
Practical advice from specialists
In addition to the above instructions, we recommend that you familiarize yourself with some tips for laying cable in a trench:
- Use only a special armored vehicle. Brands such as KG, PUNP, Ball screw or PVA can not be used because they do not have sufficient protection.
- The diameter of the metal pipe that will pass through the foundation of the private house (if necessary) should be 3 times larger than the diameter of the email itself. cable.
- If the depth of freezing of the earth in your region is deeper than 70 cm (the depth of the trench), be sure to fasten the protective pipe so that it does not tear or deform.
- Do not use a plastic corrugated pipe to protect the electrical wiring underground. Within a year, the corrugation will collapse and all its protective properties, which are already weak, will disappear.
- Try not to lay the conductor under heavy traffic areas such as roads, parking and entry into the courtyard. If this is inevitable - do not forget about laying in pipes and protecting with bricks.
- There is no consensus or rules in the regulatory documentation regarding the minimum cable cross-section for laying in the ground. In practice, a cross section of 10 mm is most often used.2 for copper and 16 for aluminum. Focus only on calculation of cable cross-section by power and current, and also note that the line must be armored.
Nuances when laying in the winter
Well, the last thing I would like to talk about is whether it is possible to lay the cable underground at low temperatures, and in particular in winter. Electrical work in winter is allowed, but the following rules and regulations must be considered:
- Before laying the wiring in the trench, you need to warm the conductor in a warm room or using a transformer. We do not recommend using the latter method if you have not encountered it before, because this requires certain skills.
- After heating, you need to quickly lay the power line with a margin of 3-4% in length. If the outdoor temperature is not lower than -10 aboutYou have an hour of time, from -10 to -20 aboutC - no more than 40 minutes, below -20 aboutC - half an hour maximum. If the temperature is lower in winter, electrical installation is prohibited.
- It is allowed to lay the cable underground without preheating in the following cases: if the temperature is not lower than -5 aboutC, and the high pressure conductor itself; if the temperature is not lower than -7 aboutC and cable protected by insulation, -15 aboutC if PVC insulation or rubber, -20 aboutC in the event that the insulation of the cores is represented by a polyethylene sheath or rubber and an additional lead sheath.
That's all I wanted to tell you about how to do the cable laying in the ground with your own hands.We hope our practical tips, instructions and the provided standards will help you with installation at home!