Laying cable lines in cable blocks, pipes and reinforced concrete trays

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Section 2. Sewerage of electricity

Cable lines up to 220 kV. Laying cable lines in cable blocks, pipes and reinforced concrete trays

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Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE)

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2.3.102. For the manufacture of cable blocks, as well as for laying cables in pipes, it is allowed to use steel, cast iron, asbestos-cement, concrete, ceramic and similar pipes. When choosing a material for blocks and pipes, one should take into account the level of groundwater and their aggressiveness, as well as the presence of stray currents.

Oil-filled single-phase low pressure cables must be laid only in asbestos-cement and other pipes made of non-magnetic material, and each phase must be laid in a separate pipe.

2.3.103. The allowable number of channels in blocks, the distances between them and their size should be taken in accordance with 1.3.20.

2.3.104. Each cable block must have up to 15% of redundant channels, but not less than one channel.

2.3.105. The depth of laying cable blocks and pipes in the ground should be taken according to local conditions, but not less than the distances given in 2.3.84, counting to the top cable. The laying depth of cable blocks and pipes in closed areas and in the fields of industrial premises is not standardized.

2.3.106. Cable blocks must have a slope of at least 0,2% towards the wells. The same slope must be observed when laying pipes for cables.

2.3.107. When laying pipes for cable lines directly in the ground, the smallest clear distances between pipes and between them and other cables and structures should be taken as for cables laid without pipes (see 2.3.86).

When laying cable lines in pipes in the floor of the room, the distances between them are taken as for laying in the ground.

2.3.108. In places where the direction of the route of cable lines laid in blocks changes, and in places where cables and cable blocks go into the ground, cable wells should be constructed to ensure convenient pulling of cables and their removal from blocks. Such wells should also be built on straight sections of the route at a distance from one another, determined by the maximum allowable tension of the cables. With the number of cables up to 10 and voltage not higher than 35 kV, the transition of cables from the blocks to the ground is allowed to be carried out without cable wells. In this case, the exit points of the cables from the blocks must be sealed with waterproof material.

2.3.109. The transition of cable lines from blocks and pipes to buildings, tunnels, basements, etc., should be carried out in one of the following ways: by direct insertion of blocks and pipes into them, by constructing wells or pits inside buildings or chambers near their outer walls.

Measures must be provided to prevent water and small animals from penetrating through pipes or openings from trenches into buildings, tunnels, etc.

2.3.110. Channels of cable blocks, pipes, exit from them, as well as their connections must have a treated and cleaned surface to prevent mechanical damage to cable sheaths during pulling. At the exits of cables from blocks to cable structures and chambers, measures should be taken to prevent damage to the sheaths from abrasion and cracking (the use of elastic linings, compliance with the required bending radii, etc.).

2.3.111. With a high level of groundwater in the outdoor switchgear, preference should be given to above-ground methods of laying cables (in trays or boxes). Above-ground trays and slabs for their covering must be made of reinforced concrete. Trays must be laid on special concrete pads with a slope of at least 0,2% along the planned route in such a way as not to impede the runoff of storm water. If there are openings in the bottoms of above-ground trays that ensure the release of storm water, it is not required to create a slope.

When using cable trays for laying cables, passage through the territory of the outdoor switchgear and access to the equipment of machines and mechanisms necessary for performing repair and maintenance work should be provided. For this purpose, crossings through the trays should be arranged using reinforced concrete slabs, taking into account the load from passing vehicles, while maintaining the location of the trays at the same level. When using cable trays, it is not allowed to lay cables under roads and crossings in pipes, channels and trenches located below the trays.

The exit of cables from the trays to the control and protection cabinets must be carried out in pipes that are not buried in the ground. Laying of cable jumpers within one cell of the outdoor switchgear is allowed in a trench, and in this case, the use of pipes to protect cables when they are connected to control cabinets and relay protection is not recommended. Protection of cables from mechanical damage must be carried out in other ways (using an angle, channel, etc.).

See other articles Section Rules for the installation of electrical installations (PUE).

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