Cable laying in the ground: methods, depth, norms

You can run the cable through the site underground. This is a more labor-intensive process, but more reliable in terms of safety – there is less chance that someone will borrow it. This moment is especially relevant in summer cottages and garden plots. But the laying of the cable in the ground is carried out in accordance with certain rules prescribed in the PUE. These rules and explanations to them are set out below. 

What cables to use

If we talk about GOST, then it says that it is necessary to lay armored cables in the ground, covered with a waterproofing layer on top. That is, underground entry into the house from a pole, with a sufficiently large allocated power, it is desirable to make an armored cable. This is AVBbShv (armored with aluminum conductors and armor made of two galvanized steel strips, covered with a protective layer) or VBBbShv (the same, but with copper conductors), PvBShv is also armored, but with XLPE insulation and the same steel tapes as armor. Suitable AASHp, AASHv, AAB2l, AAP2lShv, ASShl and so on. These types of cable products are used on lands with normal acidity.

Cable laying in the ground with increased chemical activity – salt marshes, swamps, a large amount of construction debris, slag – requires lead armor or an aluminum sheath. In this case, you can use AABL, AASHv, AAB2l, ASB, AApl, ASPl, AAP2l, AASHp, AVBbShv, AVBbShp, APvBbShv and others.

If you need to connect a small dacha, in which there is nothing to electrical appliances, a bathhouse, a barn or other outbuildings (a pigsty, a chicken coop, etc.), you can use a regular cable in a PVC sheath, since it is strong enough and precisely sealed. For lighting distribution on the site, NYM, SIP are often used, VVG is enough for several years. But these products are not designed for laying underground and they quickly fail.

More serious cables are, of course, more expensive, but they last much longer. If we take into account the laboriousness of laying them, it is more expedient to use special cables, and these are AASHv, AASHp, AAP2l, AVVG, AABL, APsVG, ASB, AApl, APvVG, APVG, ASPl, etc.

In the regions of the Far North, underground laying uses special products with increased resistance to frost – PvKSHp.

Basic rules and technology

First you need to develop a route for laying the cable. It is clear that when laying in a straight line, it will require a smaller amount. But, unfortunately, this is not always possible. When laying the route, it is desirable to avoid:

• Walking near large trees. It is advisable to lay the track at a distance of at least a meter from large trees. If the tree is right on the track, it is advisable to bypass 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 stretch the cable into it.
  

• It is highly desirable to bypass places with increased load: parking areas, places for the entrance of a sewage truck, footpaths, etc. Such zones can be bypassed around the perimeter.
• If places with increased load cannot be bypassed, cases are used to improve protection. Cases are also needed at the intersection with drainage trays, at the intersection of water supply lines, gas pipelines and other communications. If there are sections of the track somewhere 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 case everywhere.
• If the route of underground cable laying runs along the foundation, it must be at least 60 cm from it. Laying the cable in the ground closer to the foundation is prohibited – ground or building movements 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 should protrude beyond the intersection by at least 1 meter on both sides, and the cables should be at least 15 cm one above the other.

If it was not possible to avoid all the difficult places – it’s not scary. In these areas, it is possible to lay the cable not in the ground, but in a corrugated pipe, HDPE pipe or in a metal one. 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 junctions.

The order and technology of laying the cable in the ground

A trench is being dug along the marked 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 should be at least 10 cm. After the trench has been dug:

• Remove all hard and sharp objects, roots, stones, etc. They can damage the insulation and cause line failure.
• Level the bottom and tamp it down a little. It is not required to bring to the level, but there should not be sharp drops.
• Pour a layer of sand 10 cm, level it. Sand can be used cheap, quarry, but it must be sieved – so that foreign objects do not get in – stones, pieces of glass, etc. Sand is also compacted. You can just crush it with your feet. There should be no obvious humps and depressions.
• Check the integrity of the insulation, if there is damage somewhere, repair it. Cases (pieces of pipes) are first put on the cable, they are dragged to places of increased load.
• Further, 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 on the track.
  

• It is advisable to check the laid cable – there may be damage during installation. If there is a megger – excellent, 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. You also need to check them on the “ground”. If somewhere “earths” – damaged insulation. You need to look for damage and fix it.
• If all the parameters are normal, draw a route plan, preferably on a scale, with reference to landmarks. Put down the distances from reliable objects to the route (from the corner of the house, the edge of the site, etc.). Laying the cable in the ground is also inconvenient because it is difficult to access if repairs are needed. If you have a plan with dimensions, everything will be much easier.
• After that, fill the laid cable with sand. It is also sieved and a layer is poured – about 10 cm, compacted. It is not necessary to ram hard, you can compact with your feet.
• Next, a layer of 15-20 cm of previously excavated earth is covered. When backfilling, remove stones and other foreign objects. The layer is also leveled and compacted.
• Install signal tape. This is a bright polymer tape with the inscription “caution cable!”. During earthworks, it can save electrical wiring laid underground from damage.
  

• After that, they continue to fill the ditch with soil, pouring it a little above ground level, since after a while the rock will compact and settle.

And the last step is to check 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.

Nuances and features

Laying a cable in the ground is a labor-intensive process. Why is it worth digging a trench, and then it’s also not easy to carry the cable. Burying is a little easier, but also not the most pleasant experience. If after a couple of years the insulation wears out, you will have to repeat everything again, which will please few people. It is clear that it is better to do everything once and more reliably. The fact is that it is possible to lay the cable in a trench without a protective sheath. This will not be against the rule. And if you lay an armored high-quality cable, it will serve for a long time.

But if you are laying a conventional VVG or NYM, for greater reliability, it is better to lay it in a double-walled corrugated hose DKS throughout. In the right places, you additionally put on cases made of more rigid pipes or the same DCS but of a larger diameter. Often, asbestos-cement or plastic thick-walled pipes are also used. With such a cable laying 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 conductive cores.

Laying the cable in the ground in plastic or asbestos-cement pipes, corrugated hose has another plus: it is likely that, if necessary, it can be replaced simply by 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 “creeps” in its place. But this is far from always possible: over time, both the pipe and the corrugated hose can collapse – the impact of ice, soil loads contribute to the destruction of protective shells.

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

How to connect two pieces

It is more reliable to lay the cable in the ground in whole pieces – without connections. If one piece of the required length could not be found, bring both parts to the surface to connect, put a sealed junction box and connect the conductors in it. It is not worth making couplings without experience and special equipment, burying them underground – they will quickly fail, you will have to dig out, redo. And a serviced connection is always convenient – you can redo the contacts if you need to.

How to enter into the house

When entering a house, bathhouse, outbuilding, the passage of a 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 immured into it. This is a piece of pipe that protrudes a few centimeters beyond the foundation. A cable is inserted into it.

The cross section of this mortgage should be 4 times the cable cross section. And so that living creatures do not climb into the remaining gap, after laying the mortgage is sealed. For sealing, you can use the old grandfather method – rags soaked in cement milk, or fill everything with mounting foam.

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

Another option: in a metal pipe, raise the cable to a certain height along the wall of the house. They usually raise it to the mark 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 through it into the house. This method is suitable if your foundation is a monolithic slab or you just don’t want to break the solidity of the tape.

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

If there are multiple cables

If several cables are laid underground at the same time, the distance between them must be at least 10 cm.

How to tighten into a corrugation or pipe

There are two types of corrugations for underground cable laying – with and without a probe. It’s easier to take with a probe. This is a thin wire to which the wiring is tied to tighten it inward. The wire is pulled out, the cable is pulled in its place. Everything is simple.

If the pipe or corrugation is without a probe, problems may arise. If the cable is stiff enough, it is quite possible to simply tuck it inside. This is usually easy, but can be quite time consuming.

With a soft conductor, such a trick will not work – it will twist and cling to the walls. But in this case, too, there is a way out. First, twine or a thin rope is threaded into the pipe. A cable is tied to it and pulled inward.

How to thread twine? With a vacuum cleaner. You fix one edge of the twine well, the rest is unfolded, but without lumps and loops, you put it in the pipe. On the other hand, connect the vacuum cleaner, close the second inlet. Due to the creation of a rarefied atmosphere, the twine flies out from the other side.

Cable laying under the road

If the route is located in such a way that it must be carried out under the road, you will have to take permission from the organization on whose balance sheet this road is located. This point is obligatory in settlements, since other communications may be located under the road and they can be damaged by unauthorized work. If we are talking about a summer house and a holiday village, then it is necessary to coordinate with the administration of the village.

The rules for laying the cable under the road do not change – the depth of the trench is 70-80 cm, a sand cushion and backfill, it is desirable to lay it in an asbestos-cement pipe or a double-walled corrugation of the DKS. In general, there are no differences, all the rules and regulations are the same.

Difficulties may arise when it is necessary to lay a cable under asphalt. If this is a solid track, you are unlikely to be allowed to destroy the surface, and if they do, then restoring the asphalt is an expensive pleasure. In this case, there is also a way out – there is special equipment with which a puncture is made under the road. The service is also not cheap, but it costs much less than the cost of asphalt restoration.