Cable laying method, application scope and technical requirements

First, the laying of cables and basic requirements

The laying methods of cables generally include direct laying, cable trench laying, cable tunnel laying, pipe laying and overhead laying. Among them, there are two kinds of cable trenches: ordinary cable trenches and sand-filled cable trenches. Overhead laying sub-cables overhead cableways (ie cable bridges), along the construction, the construction of the use of brackets or ladders laying and cable suspended several. Various laying methods have advantages and disadvantages. The laying method is determined by the specific circumstances. Generally consider the development planning of cities and enterprises, the density of existing buildings, the length of cable lines, the conditions for the laying of cables, and the influence of the surrounding environment.

There are different technical requirements for different cable laying methods, but there are common basic requirements for various laying methods. The main points are as follows.

1 The maximum difference between the lowest point and the highest point of the laying of the oil-impregnated insulated cable shall not exceed the requirements of Table 2-11. If it exceeds the regulations, other types of cables suitable for high drop may be selected, such as non-dripping impregnated paper insulation or plastic insulation, and if necessary, oil plugging intermediate joints may also be used.

2 To prevent damage to the cable insulation, the cable should not be excessively bent. The ratio of the minimum permissible bending radius of various cables to the outer diameter of the cable shall be not less than: 15 times for paper-insulated cables and 10 times for rubber- or plastic-insulated cables.

3 The spacing of cable support points should meet the following requirements:

When laid horizontally, the outer diameter of the cable is greater than 50mm is 1000mm, the outer diameter of the cable is less than 50mm is 600mm;

When laying vertically, it should be fixed every 1000~1500mm.

4 In places where mechanical damage may occur, such as entering buildings and tunnels, passing through floors and walls, leading from the channel to poles, equipment, wall surfaces, etc., a section of cable less than 2m above the ground shall be piped or protected. Cover, the inner diameter of the steel pipe is 1.5 times the outer diameter of the cable, and the protection pipe is buried in the ground not less than 100mm.

5 The cables laid in the workshop, in the tunnel and not in the sand cable trench shall be bare armored or non-flammable outer sheath cables. If there is a connector in the cable, measures should be taken around the connector to prevent the spread of fire.

Table 2-11 Maximum permissible difference of oil-impregnated paper-insulated cable, m cable level ky whether or not armored lead-free aluminum-clad cable grade kV yes or no armored lead-free aluminum package 1 to 3 armored 25256 to 10 no or pinned 1520 No outfit 202520~35 No outfit or 5 -

Second, laying directly buried

1. Scope of application

The direct burial laying is to bury the cable directly in the ground, which has the advantages of low investment, convenient construction and good heat dissipation conditions, and is the most economical and widely used laying method. With this laying method, a certain sand interval is required between the cables laid side by side, so that when one cable fails, the possibility of spreading another cable is reduced, which improves the reliability of the power supply. However, this type of laying cable is susceptible to erosion by corrosive substances in the ground, and it is inconvenient to find faults and troubleshoot the cables, and it is particularly difficult to repair the accident when the soil is frozen in winter. This method is suitable for underground accessibility, soil does not contain serious acid, alkali, salt, corrosive media, the number of cable is less than the number of places, such as suburban or vehicle traffic is not very frequent places.

2. skills requirement

1 Directly buried cables should generally use armored cables. The use of short lengths of armored cable is only permitted when repairing the cable, but mechanical protection must be added. When selecting a buried cable line, it should be noted that the soil around the buried cable should not contain substances that corrode the metal sheath of the cable.

2 The distance from the cable surface to the ground should not be less than 0.7m. In regions where the depth of soil freezing is greater than 0.7m in winter, the depth of burial may be appropriately increased to allow the cable to be buried below the permafrost. It may be lighter when it is introduced into a building or intersects with underground obstacles, but it must not be less than 0.3m and protective measures should be taken.

3 The minimum clear distance when cables are horizontally close to each other is: 0.1m for 10kV and below; 0.25m for 10kV and above; 0.5m for cables (including communication cables) for different service departments. If the cables are separated by a partition It can be reduced to 0.1m, and no regulation is required when the tube is worn.

4 The minimum clear distance when the cables cross each other is 0.5m, which is reduced to 0.25m when they are separated by partitions within 1m before and after the intersection, and is not specified when the pipes are crossed.

5 When the cable is laid directly, the bottom of the trench must have a good soil layer and there should be no stones or other hard debris. Otherwise, soft soil or sand layers of 100mm should be laid. After the cable is applied, a 100mm soft soil or sand layer is placed on top. The concrete protection plate is then covered along the entire length of the cable, covering a width of more than 50 mm on either side of the cable. In special circumstances, bricks are also allowed instead of concrete protection plates.

6 In order to facilitate maintenance, it is forbidden to lay the cables above or below the pipes in parallel, and it is forbidden to lay one cable in parallel on the other cable. The minimum distance between the cable and the underground pipeline approaching and crossing is 2m when approaching the thermal pipeline (including the petroleum pipeline), 0.5m when crossing, and 0.5m when approaching or crossing with other pipelines. If appropriate measures are taken for the heat pipes so that the soil temperature at the embedded cable site does not exceed 10°C at any time, and appropriate protective measures are taken for other pipes, the above net distance is not specified.

7 Pipes should be protected by steel pipes when crossing urban streets, roads, railways or drains. The inner diameter of the tube is not less than 1.5 times the outer diameter of the cable and not less than 100mm. The depth of the pipe roof from the bottom of the track or the road surface shall not be less than 1m, the distance from the bottom of the drainage ditch shall not be less than 0.5m, and the depth from the road surface of the urban street shall not be less than 0.7m. Both ends of the pipe should extend 2m from the road and track. In the city streets, the road should be extended. When the cable crosses the DC electrified railway, proper corrosion protection measures should be taken.

8 Cable protection box outside the joint box should be protected against mechanical damage (except for plastic cable middle joints).

9 Cable routes laid in suburbs and open areas should be erected with signs of cable location.

Third, the cable trench laying

1. Scope of application

In the production facilities of power plants, substations and general industrial and mining enterprises, cable trenches can be laid. However, it is not advisable to use cable trenches in areas where the groundwater level is too high. Otherwise, water will accumulate in the ditch for a long time and it is inconvenient to maintain. If the water contains corrosive media, it will damage the cables. This is the case in chemical companies. There are two types of cable trenches, and common cable trenches can be used in general locations. The structure is shown in Figure 2-2. Sand-filled cable trenches can be used in explosion and fire hazard areas where there is an explosive medium that is heavier than air. There is no need to install a cable bracket in the cable trench.

2. skills requirement

1 The cable trench is generally made of brick. The place where the top of the trench is flush with the ground can be covered with a reinforced concrete cover plate (or steel plate), and the cable can be directly placed on the bottom of the trench or supported by a cable support. In order to keep the cable trench dry, measures should be taken to prevent groundwater from flowing into the trench. An appropriate number of water pools should also be installed in the trench.

2 The minimum allowable distance listed in Table 2-12 should be maintained in the cable.

Table 2-12 Minimum allowable distances for various parts of cable trenches, mm

Name minimum allowable distance

When there are cable supports on both sides, the horizontal clearance (channel width) between brackets is 500 (300mm when the groove depth is less than 600mm)

With a cable support on one side, the horizontal clearance between the rack and the wall (channel width) 450 (300mm when the groove depth is less than 600mm)

The uppermost bracket supports the distance from the top to the top of the trench 150 to 200

The lowest bracket is spread to the bottom of the ditch with a clearance of 50-100

Vertical distance between layers of cable support

1OkV and below 150

20kV or 35kV200

Horizontal clearance between cables 35

3 In the sand-filled cable channel, the cables are laid in parallel in the ditch. The distance between the cables is not less than 35mm, and the inter-layer spacing is not less than 100mm. The middle is filled with sand.

The full length of the 4 ditch should be equipped with a continuous grounding wire, with two ends of the grounding wire connected to the grounding electrode.

IV. Cable tunnel laying

1. Scope of application

The laying of the cable tunnel is convenient for maintenance and inspection. It is easy to find anomalies in the operation and it is not vulnerable to various external damages, and it can accommodate more cables at the same time. However, it has serious water seepage. The explosive mixture that is heavier than air will threaten safety when it enters the tunnel. This method is applicable to the main power lines with low groundwater level and relatively concentrated distribution cables. Generally, more than 30 large-section cables are laid.

2. skills requirement

1 Cables The minimum allowable distance listed in Table 2-13 should be maintained within the tunnel.

Table 2-13 Minimum allowable distance of various parts of the cable tunnel, mm

Name minimum allowable distance

Tunnel height 1900

When there are cable brackets on both sides, the horizontal clearance between the brackets (channel width) 1000

With a cable support on one side, the horizontal distance between the bracket and the wall (channel width) 900

Vertical distance between layers of cable support

10kV and below 200


Horizontal clearance between cables 35

2 The whole length of the tunnel shall be provided with a continuous grounding wire, and two ends of the grounding wire shall be connected to the grounding electrode.

3 The tunnel should have good ventilation and drainage facilities.

V. Laying pipe laying

1. Scope of application

A number of cables are laid in the streets of the city. Pipelines may be used when cable trenches and cable tunnels are not suitable. Pipe laying has the following advantages:

1 Reduce external damage to the cable and mechanical damage;

2 Elimination of chemical corrosion of cables by harmful substances in the soil;

3 repair or replace the cable quickly and easily;

4 New cables can be laid at any time without having to open the road.

2. skills requirement

1 The cable laid in the pipe should use thick bare leaded or plastic sheathed cable. The tube should be made of a material that does not have a chemical effect on the metal sheathing of the cable. The inner surface of the tube should be smooth, and the inner diameter of the tube should not be less than 1.5 times the outer diameter of the cable and not less than 100 mm.

2 In order to facilitate inspection and laying of cables, cable manholes should be installed at intervals. The distance between cable manholes can be determined according to the length and geographical location of the cables. Generally, it should not be more than 200m. The size of the manhole needs to consider whether it is convenient to install, maintain and repair the middle connector of the cable. The row pipe leading to the manhole should not be less than 1/1000 incline so that the water in the pipe flows into the well.

6. Overhead laying

1. Scope of application

Inside the industrial and mining enterprises, especially power plants, chemical plants, and general underground pipelines and drainage ditch, there are many corrosive media in factories and nearby soils in acid and alkali factories. Therefore, in many occasions, Directly buried and cable trenches are not suitable for laying methods, and overhead laying methods are often used. The path for laying overhead cables is large, the configuration is flexible, and the crossover with the pipeline is easy to handle. It is not affected by conditions such as groundwater, underground corrosive media, and accumulation of explosive dangerous substances that are heavier than air, nor is it restricted by underground pipes and gutters. There are three forms of cable overhead laying.

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