An essential factor to take into account when organizing a building or remodeling project that involves electrical installations is the efficient layout of cables. The technique selected has an impact on maintenance and upcoming changes in addition to the effectiveness of electrical distribution. Choosing the right kind of trench for cable laying is one of the most important choices, and it greatly depends on the quantity of cables being installed.
The size and layout of the trench that is needed depend on how many cables need to be installed. A small trench might be sufficient for smaller projects with fewer cables. This type of trench is perfect for upgrades or renovations where there is limited space because it reduces excavation and the disturbance of existing structures. It ensures effective resource use without sacrificing functionality or safety during installation and is more affordable and manageable.
On the other hand, a wider trench is required for larger projects or those involving a significant number of cables. This lowers the possibility of interference or damage during installation and maintenance by enabling the correct separation and arrangement of cables. Additionally, a broader trench makes it easier to access future repairs and upgrades and can accommodate future growth of electrical systems without causing significant disruptions.
Furthermore, the overall robustness and lifespan of the electrical infrastructure are impacted by the type of trench that is selected. Trenches that are carefully chosen guarantee that cables are sufficiently shielded from external elements like moisture, temperature changes, and physical impact. In order to minimize the need for expensive repairs or replacements over time, this protection is essential for preserving the integrity and dependability of electrical connections.
- The importance of size
- Nuances and recommendations
- Depth and width
- Depth determination depending on power
- Distance between cables
- Footage between trenches
- Distance from other engineering networks
- Table of dimensions
- Video on the topic
- Group laying of cables in cable structures according to PUE
- Selection of cable cross-section
- Laying cables in the ground – entry in a trench
The importance of size
An increasingly common way of wiring electrical networks is through underground installation. It is very practical, safe, and has a straightforward circuit. The primary factor, however, is that the cables are always buried, which guards against vandalism.
The dimensions of the trenches that will be used to lay wires must first be determined. The smooth functioning of the entire system depends on how this stage is handled, so it should be approached responsibly.
The length, width, and depth of the wire depend on its kind and size. The operation of the power transmission network may be adversely affected if the hole is small and narrow.
Nuances and recommendations
Prior to beginning installation work, review the following guidelines and recommendations:
- It is worth checking whether the route intersects with utility networks. All the necessary data can be obtained after studying the geological basis of the route being laid;
- It is important that there are no communication networks at the installation site, otherwise they can be damaged during the digging process;
- Do not forget that the depth depends on the type of terrain in which it will pass;
- If the installation is planned under a highway, then the depth must be at least 1.25 meters;
- If the cable is installed under the lawn, you can dig a hole up to 90 cm deep.
Important considerations should be made when excavating. For example, utility lines should not run underground as this could damage them. The size and quantity of wires, whether or not a protective sheath is used, the kind of soil, the terrain, and other factors must all be considered when determining the pit’s dimensions.
The number of cables involved in the trench will determine the type of trench that will work best for you. Every variety, including duct banks, direct burial, and open trenches, has unique benefits. Open trenches are convenient for maintenance and access, but they can disturb surface areas and need a lot of room. With their enclosed conduits, duct banks neatly arrange cables, but they require careful planning to allow for future growth. Even though direct burial is easier and less expensive, it does not have duct protection and might require extra environmental shielding. Making informed decisions about your cable infrastructure needs guarantees effective installation, future accessibility, and long-term dependability.
Depth and width
Trenches are dug continuously along the entire length of the route when laying underground. Prior to anything else, it is important to determine the pit’s width and depth.
At what depth in the cable should it be placed? The accepted standard depth is between 70 and 90 cm. It is preferable to run the wires inside pipes or a protective shell if it is not feasible for it to burst to this extent.
An internal region made of soft polyethylene and an outer surface made of rigid polypropylene can be used as a shell for corrugated or special-shaped pipes.
As previously mentioned, the type of area determines the depth. Its indicator can be standard, no more than 90 cm, in areas with lawns. Digging deeper is preferable in areas where roads are covered, though, to prevent future road collapse.
The depth on average soil should be at least 0.7 meters. In unfavorable circumstances—for instance, loamy or extremely unstable soil—the depth may drop to 1.3 meters.
It’s important to accurately calculate the width in addition to the depth. It should be within 25–30 cm for a single cable. A minimum of 10 centimeters should separate any two or more lines that are laid. The cables and the wall must be separated by at least 15 centimeters.
Depth determination depending on power
Power indicators are a recommended consideration when calculating trench depth. The table below displays all of the parameters:
| Power | Depth indicator |
| At entrances to structures, if there is an intersection with underground structures | 50 cm |
| 20-35 kV | 70 cm |
| From 35 to 110 kV, at all street intersections, on driveways, installation in areas with arable soil | 1 meter |
| From 110 kV and more (oil-filled lines) | 1.5 meters |
Distance between cables
Six cables may be installed in a single trench when installing a line. However, they need to be placed a specific distance apart to prevent short circuits and complete electrical line failure. The distance between the wires needs to be at least 10 cm.
However, don’t overlook the cable power indicator, as it determines the spacing between the lines in a parallel horizontal installation:
- Between power wires with a power rating of up to 10 kV there should be no more than 10 cm;
- Between 20-35 kV lines the gap should be 25 cm;
- The distance between cables used in production, between power wires and communication lines should be 50 cm;
- Between oil-filled wires with a power of 110-220 kV and other communications there should be 50 cm or more.
Reinforced concrete slabs are installed on the ribs to divide oil-filled cable lines from one another.
Footage between trenches
Parallel trench laying is possible, but there needs to be a specific spacing requirement between them. This is necessary for power lines to operate normally. 50 cm is the normalized distance.
The kind of cables used or their power ratings have no bearing on the distance. Though it occasionally reaches 0.7–0.9 meters, the minimum should be 0.5 meters. Each and every dimension is computed using the PUE.
Distance from other engineering networks
There must be a certain spacing between utility networks when laying lines in trenches next to them:
- If there is a water supply, drainage, or sewerage system parallel to the highway, then the distance between these objects should be no more than 1 meter;
- If a gas pipe with a pressure indicator from 0.0049 to 0.0058 MPa is installed in parallel, then the distance should be at least 1 meter, but if the pipe pressure is higher than 0.0058 MPa, then the distance will be at least 2 meters;
- The distance between the line and the heating main is 2 meters;
- If the power transmission network is laid along railways, then it is better to install it in the exclusion zone;
- If the power line is laid along tram tracks, it should be built at a distance of 2.75 meters;
- If in forest plantations, park areas, then there should be an indentation of about 2 meters between trees and cables. This indicator can be reduced, but it should be at least 0.45 meters, and the wires must be laid in pipes;
- If the electrical network is laid along highways of I and II categories, then it is better to install the cable from the outer area of the sole or ditch from the edge of the road surface at a distance of at least 1 meter. The distance between the line and the curbstone is 1.5 meters.
It is preferable to place the electric wire 60 centimeters away from building foundations if they are adjacent to them. There should be a minimum of 2 meters between the power line and the supports of the power transmission line, which should have a voltage of 1 kV or less, and 5 meters between them and the ground.
Table of dimensions
Table: Earthworks volumes and trench dimensions
| Trench type | Width in mm | Height in mm | Volume of excavation work per 100 m of trench, m3 | Volume of fine sifted earth or sand per 100 meters of trench, m3 | Laying depth | |
| Digging a trench | backfilling | |||||
| T-1 | 200 | 900 | 18 | 12 | 6 | 700 |
| T-2 | 300 | 27 | 18 | 3 | ||
| T-3 | 400 | 36 | 24 | 12 | ||
| T-4 | 500 | 45 | thirty | 15 | ||
| T-5 | 600 | 54 | 36 | 18 | ||
| T-6 | 700 | 63 | 42 | 21 | ||
| T-7 | 800 | 72 | 48 | 24 | ||
| T-8 | 900 | 81 | 54 | 27 | ||
| T-9 | 1000 | 90 | 60 | thirty | ||
| T-10 | 300 | 1250 | 37.5 | 28.5 | 9 | 900 |
| T-11 | 500 | 62.5 | 47.5 | 15 | ||
| T-12 | 600 | 75 | 57 | 18 | ||
| T-13 | 800 | 100 | 78.6 | 24 | ||
| T-14 | 900 | 112 | 85 | 27 | ||
| T-15 | 1000 | 125 | 95 | thirty | ||
Table – choosing the trench type based on how many cables up to 10 kV are installed in it:
| Trench type | Number of cables, pcs | |||||||
| with cable diameter, mm | ||||||||
| To 10 | Up to 20 | Up to 30 | Up to 40 | Up to 50 | Up to 60 | Up to 70 | Up to 80 | |
| T-1 | 1;2 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| T-2 | 2 | 2 | 2 | 2 | 2 | |||
| T-10 | ||||||||
| T-3 | 3 | 3 | 3 | 3 | 2 | 2 | ||
| T-4 | 4 | 4 | 4 | 3 | 3 | 3 | ||
| T-11 | ||||||||
| T-5 | 5 | 5 | 4 | 4 | 3 | |||
| T-12 | ||||||||
| T-6 | 6 | 6 | 5 | 5 | 4 | |||
| T-7 | 6 | 5 | 5 | 4 | 4 | |||
| T-13 | ||||||||
| T-8 | 6 | 6 | 5 | 5 | ||||
| T-14 | ||||||||
| T-9 | 6 | 6 | ||||||
| T-15 | ||||||||
This section contains important and helpful information about trench cable laying.
| Number of Cables | Recommended Trench Type |
| Few (1-2 cables) | A shallow trench can suffice, typically 12-18 inches deep, to protect and organize cables without excessive digging. |
| Several (3-5 cables) | A deeper trench, around 18-24 inches, may be needed to accommodate more cables comfortably, allowing for easier maintenance and future expansions. |
| Many (6 or more cables) | A trench depth of 24 inches or more is advisable, ensuring ample space for multiple cables, organized in layers if necessary, to prevent overcrowding and facilitate accessibility. |
The quantity of cables involved has a major influence on selecting the appropriate kind of trench for cable laying. A shallow trench is adequate for small-scale projects or limited cable requirements. They require less excavation and cause less disturbance to the surrounding area because they are quicker and easier to dig.
A medium-depth trench finds equilibrium when working with a moderate quantity of cables. It offers enough room for cables to be installed comfortably without requiring a lot of excavation. In residential and small commercial settings where a moderate amount of wiring is needed, this kind of trench is frequently used.
Larger projects involving a large number of cables require a deep trench. This kind of trench makes it possible to install numerous cables side by side with plenty of space between them, making maintenance and organization easier. When extensive electrical or communication wiring is required for industrial or large-scale commercial projects, deep trenches are frequently used.
It is imperative to take into account various factors such as soil type, drainage requirements, and future accessibility for maintenance and repairs, regardless of the trench depth selected. When the trench is planned properly, it can accommodate future expansions or modifications without causing significant disruptions, in addition to meeting the immediate needs.
