Rules for laying cables in cable structures. Power cable construction Cable constructions

The listed products serve primarily for fastening and mounting trays, perforated profiles, boxes and other structures intended for laying cable routes and wires.

Such products create a single structure that makes it possible to simply and with high reliability fasten both elements of electrical structures under the cable, and the cable itself directly on ceilings, walls, floors, load-bearing beams, columns, etc. Examples of installation of load-bearing structures.

Cable shelves and racks are used when laying routes, wires, lines from trays in a horizontal position (on columns, walls, etc.), when designing a route in several tiers.

The GEM stand is attached to the bearing surface (vertical) with brackets. A minimum of two staples are required to secure one element. The shelf is installed in it using the K1156 key and a dovetail.

In the graph below, you can see the comparative load characteristics of load-bearing models.

Supporting structure "rack-shelf"

Load characteristics of the supporting structure "rack-shelf"

Types and application of racks

To install shelves, use models K1150-K1155. They differ in length and, accordingly, the number of holes. They are fastened to the wall or column with brackets K 1157. Fastening by welding is allowed to metal structural elements. Perforated holes for fastening shelves are arranged in 50 mm increments.

The analogue of the described models are cable racks S-400 and S-2200.

For installation of cable shelves, perforation has certain differences: there is no fixing tongue.

Cable shelves models K1160-K1164

Shelves have different lengths and different load capacity. Made with perforations. Its pitch is 30 mm, the hole has a size of 10 * 20 mm.

The need for the use and volume of automatic stationary means for detecting and extinguishing fires in cable structures should be determined on the basis of departmental documents approved in the prescribed manner.

Fire hydrants must be installed in the immediate vicinity of the entrance, hatches and ventilation shafts (within a radius of no more than 25 m). For flyovers and galleries, fire hydrants should be located in such a way that the distance from any point on the axis of the flyover and gallery route to the nearest hydrant does not exceed 100 m.

2.3.123

In cable structures, the laying of control cables and power cables with a cross section of 25 mm or more, with the exception of unarmored cables with a lead sheath, should be carried out along cable structures (consoles).

Control unarmoured cables, unarmoured power cables with a lead sheath and unarmoured power cables of all designs with a cross section of 16 mm or less should be laid along trays or partitions (solid or non-solid).

It is allowed to lay cables along the bottom of the channel at a depth of not more than 0.9 m; in this case, the distance between a group of power cables above 1 kV and a group of control cables must be at least 100 mm, or these groups of cables must be separated by a fireproof partition with a fire resistance of at least 0.25 hours.

The distances between the individual cables are given in table. 2.3.1.

Backfilling of power cables laid in channels with sand is prohibited (for an exception, see 7.3.110).

In cable structures, the height, width of passages and the distance between structures and cables must be at least those given in Table. 2.3.1. Compared with the distances given in the table, local narrowing of the passages up to 800 mm or a decrease in height up to 1.5 m over a length of 1.0 m is allowed with a corresponding decrease in the vertical distance between the cables with one-sided and two-sided arrangement of structures.

Table 2.3.1. Minimum distance for cable installations

2.3.124

Laying of control cables is allowed in bundles on trays and in multilayers in metal boxes, subject to the following conditions:

1. The outer diameter of the bundle of cables should be no more than 100 mm.

2. The height of the layers in one box should not exceed 150 mm.

3. Only cables with the same type of sheaths should be laid in bundles and multilayers.

4. Fastening cables in bundles, multilayered in boxes, bundles of cables to trays should be carried out in such a way that deformation of the cable sheaths under the action of its own weight and fastening devices is prevented.

5. For the purpose of fire safety, fire protection belts should be installed inside the ducts: in vertical sections - at a distance of no more than 20 m, as well as when passing through the ceiling; on horizontal sections - when passing through partitions.

6. In each direction of the cable route, a capacity margin of at least 15% of the total capacity of the boxes should be provided.

Laying of power cables in bundles and multilayer is not allowed.

2.3.125

*. In places saturated with underground utilities, it is allowed to perform semi-through tunnels with a height reduced in comparison with that provided for in Table. 2.3.1, but not less than 1.5 m, subject to the following requirements: the voltage of the cable lines must not exceed 10 kV; the length of the tunnel should be no more than 100 m; other distances must correspond to those given in table. 2.3.1; at the ends of the tunnel there should be exits or hatches.

___________________

* Agreed with the Central Committee of the trade union of workers of power plants and the electrical industry.

2.3.126

Oil-filled low-pressure cables must be fastened to metal structures in such a way that the possibility of the formation of closed magnetic circuits around the cables is excluded; the distance between the attachment points should be no more than 1 m.

Steel pipelines of high-pressure oil-filled cable lines can be laid on supports or suspended on hangers; the distance between supports or hangers is determined by the line project. In addition, pipelines must be fixed on fixed supports to prevent thermal deformations in pipelines under operating conditions.

The loads taken by the supports from the weight of the pipeline should not lead to any movement or destruction of the foundations of the supports. The number of these supports and their locations are determined by the project.

Mechanical supports and fastenings of branching devices on high-pressure lines should prevent the branching pipes from swinging, the formation of closed magnetic circuits around them, and insulating gaskets should be provided at the points of fastenings or touches of the supports.

2.3.127

The height of cable wells must be at least 1.8 m; chamber height is not standardized. Cable wells for connecting, locking and semi-locking couplings must have dimensions that ensure the installation of couplings without breaking.

Shore wells at underwater crossings should be sized to accommodate backup cables and feeders.

In the floor of the well, a pit should be arranged to collect groundwater and storm water; a drainage device shall also be provided in accordance with the requirements given in 2.3.114.

Cable wells must be equipped with metal ladders.

In cable wells, cables and couplings must be laid on structures, trays or partitions.

2.3.128

The hatches of cable wells and tunnels must have a diameter of at least 650 mm and be closed with double metal covers, of which the lower one must have a locking device that can be opened from the side of the tunnel without a key. Covers must be equipped with tools for their removal. Indoors, the use of a second cover is not required.

2.3.129

On the couplings of power cables with a voltage of 6-35 kV in tunnels, cable floors and channels, special protective covers must be installed to localize fires and explosions that may occur during electrical breakdowns in the couplings.

2.3.130

Terminations on high-pressure oil-filled cable lines should be located in rooms with a positive air temperature or be equipped with automatic heating when the ambient temperature drops below +5°C.

2.3.131

When laying oil-filled cables in the galleries, it is necessary to provide heating of the galleries in accordance with the specifications for oil-filled cables.

The premises of the oil-feeding units of the high-pressure lines must have natural ventilation. Underground feeding points are allowed to be combined with cable wells; in this case, the wells must be equipped with drainage devices in accordance with 2.3.127.

2.3.132

Cable structures, with the exception of overpasses, wells for couplings, channels and chambers, must be provided with natural or artificial ventilation, and the ventilation of each compartment must be independent.

The calculation of the ventilation of cable structures is determined based on the temperature difference between the incoming and outgoing air of no more than 10 ° C. In this case, the formation of hot air bags in the narrowing of tunnels, turns, detours, etc. must be prevented.

Ventilation devices must be equipped with dampers (gates) to stop air access in the event of a fire, as well as to prevent the tunnel from freezing in winter. The design of ventilation devices should ensure the possibility of using automation to stop air access to buildings.

When laying cables indoors, overheating of the cables must be prevented due to the increased ambient temperature and the effects of process equipment.

Cable structures, with the exception of wells for couplings, channels, chambers and open overpasses, must be equipped with electric lighting and a network for powering portable lamps and tools. At thermal power plants, the network for powering the tool may not be performed.

2.3.133

Cable laying in collectors, technological galleries and technological overpasses is carried out in accordance with the requirements of SNiP Gosstroy of Russia.

The smallest clear distances from cable racks and galleries to buildings and structures should correspond to those given in Table. 2.3.2.

The intersection of cable racks and galleries with overhead power lines, internal railways and roads, fire lanes, cable cars, overhead communication and radio lines and pipelines is recommended to be carried out at an angle of at least 30 °.

Table 2.3.2. The smallest distance from cable racks and galleries to buildings and structures

The location of overpasses and galleries in hazardous areas - see Ch. 7.3, the location of overpasses and galleries in fire hazardous areas - see Ch. 7.4.

With parallel passage of flyovers and galleries with overhead communication and radio links, the smallest distances between cables and wires of a communication line and radio link are determined based on the calculation of the effect of cable lines on communication lines and radio link. Communication and radio communication wires can be located under and above flyovers and galleries.

The smallest height of the cable overpass and gallery in the impassable part of the territory of an industrial enterprise should be taken into account the possibility of laying the lower row of cables at a level of at least 2.5 m from the planning ground level.

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On cable structures, wires and cables are laid openly along walls and ceilings.
Before laying, inspect the condition of the cables on the drums. Then, using a megohmmeter, the integrity of the core insulation is determined.
For laying cables, load-bearing structures assembled from perforated metal profiles and fasteners (brackets, bolts, nuts and washers) are used. Single cables are laid on hanging hooks fixed in racks (Fig. 1).
Cables with an outer diameter of more than 18 mm, laid horizontally or vertically, must have supports 4-10 m long. At the same time, cables laid on horizontal straight sections are not fixed on supports, and cables laid on vertical sections are fixed on each support.
Regardless of the arrangement of the supporting cable structures, the cables are fixed at a distance of no more than 0.5 m from junction boxes, couplings and end fittings.

Rice. 1. Prefabricated cable structures of the "Christmas tree" type: a - rack; b - shelf; in - bracket; g - suspension; d - fire-resistant partitions; e - stand with pendants; 1 - language; 2 - shank; 3 - oval hole of the shank; 4 - cable; 5 - asbestos-cement partition; 6- connector; 7 - suspension
When securing unarmoured cables, care must be taken not to damage their sheath. For this, elastic gaskets are used for supports and brackets, which should be 5-6 mm wider than them.
Indoor cables with a PVC sheath are laid in places where they cannot be damaged by rodents, or they are protected by boxes or nets.
Cable structures of the "herringbone" type, manufactured in factories, consist of perforated racks and shelves. Trough-shaped racks are made of sheet steel 2.5 mm thick and 400, 600, 800, 1200 and 1800 mm high. Depending on the height, the racks have 8, 12, 16, 24 and 36 shaped holes for placing cable shelves with different or equal distances within one rack.

Rice. 2. Installation of cable structures:
a - wall-mounted;: b - single-sided ceiling; a - double-sided ceiling; g - block (double) structures; 1 - shelf; 2- rack; 3 and 4 - corners

Cable shelves are made in lengths of 160, 250, 350 and 450 mm. The oval holes of the shelves allow cables to be fastened at a certain distance from each other, the special design of the joint between the shelf and the rack does not require welding (the exception is the structures used for vertical cable routing).
Cable structures are painted or galvanized. Galvanized structures are used in outdoor installations, in damp, especially damp and hot rooms, as well as in rooms with a chemically active environment of internal electrical installations, in cable mezzanines, basements and tunnels (regardless of the environment), in other cases, painted structures are used.
Cable structures with hangers consist of racks and embedded hangers. Racks with a height of 600, 800, 1200 and 1800 mm are manufactured at the MEZ by transverse cutting of factory-made perforated profiles (channels). Embedded hangers of three sizes during assembly of structures are inserted into the oval holes of the racks with the narrow side of the shank, and then turned by 90 ° are set to a horizontal position.
When laying cable lines, they tend to combine routes, combining cables into common streams placed on common structures. At the same time, cable structures are installed along the walls of rooms and cable structures, and also suspended from ceilings, beams and other building elements of buildings.
Depending on the installation method and the number of cables to be laid, single and block structures are used from racks and shelves or racks and embedded suspensions: wall, ceiling one-sided and two-sided, double (Fig. 2). In wall and ceiling blocks, cable structures in the MEZ are combined into transportable length sections (up to 6 m) with the help of General connections (girders).
Cable structures, depending on the place of their installation in rooms and cable structures, are welded to embedded elements or metal structures.
Cable racks can be attached to building bases by shooting with dowels using special overhead brackets.

Technical conditions for laying cable lines.

Cable lines must be designed in such a way that during installation and operation, the possibility of dangerous mechanical stresses and damages in them is excluded. To this end:
cables are laid with a margin in length sufficient to compensate for possible soil displacements and temperature deformations of both the cables themselves and the structures along which they are laid;
cables laid horizontally along structures, walls, floors, are rigidly fixed at the end points, directly at the end fittings, on both sides of the bends and at the connecting and locking couplings;
cables laid vertically along structures and walls are fixed in such a way that the deformation of the shells is prevented and the connections of the cores in the couplings are not broken under the action of the cable's own mass;
structures on which unarmored cables are laid are made in such a way that the possibility of mechanical damage to the cable sheaths is excluded; in places of rigid fastening, the sheaths of these cables are protected from mechanical and corrosion damage by elastic gaskets;
cables (including armored ones) located in places where mechanical damage is possible (movement of vehicles, mechanisms and goods, accessibility for unauthorized persons), protect in height by 2 m from the floor or ground level and by 0.3 m in the ground;
cables are laid from heated surfaces at a distance that prevents them from heating above the permissible level, while providing for the protection of cables from the breakthrough of hot substances at the installation sites of valves and flange connections;
cables protect against stray currents and soil corrosion;
designs of underground cable structures are selected taking into account the mass of cables, soil, road surface and the load from passing vehicles;
when laying cables, they withstand certain bending radii;
when laying cables on vertical and inclined sections of routes, the maximum allowable level differences are taken into account;
tensile forces when laying cables and pulling them in pipes are limited depending on the mechanical stresses allowed for conductive cores and sheaths.

Rice. 3. Attaching cables to structures:
a - one with a diameter of 22-34 mm with a single-blade bracket; b - one with a diameter of 12-60;. mm two-arm bracket; a - two with a diameter of up to 20 mm with a bracket; g ~ two overlays with a diameter of more than 20 mm; 5 - three 12-20 mm staples; 1 - cable; 2 - single-arm bracket; 3 - bolt; 4 - cable shelf; 5 - Thai;
6 and 7 - two-leg brackets; 5 - overlay
To compensate for temperature changes in cables and structures along which they are laid, in cable structures and industrial premises, cables are laid with a margin of 1-2% of the total length of the route.
For rigid fastening of cables laid horizontally along structures, brackets, clamps or linings are used, the size of which is chosen depending on the outer diameter of the cables (Fig. 3). On the vertical sections of the route, the distance between the points of rigid fastening of the cables is assumed to be 1 m.
In places of rigid fastening of unarmored cables with a lead or aluminum sheath, elastic gaskets made of non-combustible material (for example, asbestos sheet, polyvinyl chloride sheet) are tried on structures. Unarmored cables with a plastic sheath or a plastic hose are attached to the structure with brackets (clamps) without gaskets. To protect cables in places where mechanical damage is possible, cut steel pipes or sheet metal casings are used.
The radii of the internal bending curve of the cables during laying are allowed at least the following multiplicity / in relation to their outer diameter:
stranded in a lead sheath. . . , . ... , fifteen
single-core in an aluminum or lead sheath and stranded in an aluminum sheath. . . . , . . , . 25
with plastic insulation in aluminum sheath... 15
plastic and rubber insulation:
single-core. ..... . ,.,......, ten
stranded, . .. . . . -, . . , . 7.5
Excessively tight bends can damage the insulation and sheaths of the cables. In paper insulation, paper tapes are displaced and torn. Plastic and rubber insulation breaks when sharply bent, and wrinkles or cracks appear on the shells.
The maximum allowable level difference between: the highest and lowest points of the location of cables with voltage up to 1 kV with paper insulation and with their pro-; masonry on vertical and inclined sections should be no more than 25 m. The difference in levels for cables with plastic and rubber insulation is not limited.
The limitation of the level difference between the highest and lowest points of the cables is associated with the movement of the impregnating composition. It happens barely: in a blowing way. The cable cores are heated by electric current and there is a volumetric expansion of all materials from which the cable is made. The impregnating composition has the highest coefficient of volumetric expansion of the materials included in the cable construction. Therefore, it is filtered through the cable paper, penetrates the metal sheath and creates an overpressure in the cable, which leads to the expansion of the sheath and an increase in its volume. In a cable laid vertically or obliquely, under the action of gravity, the impregnating composition drains (between the wires of the cores, along the surface of single-wire cores, in the gaps between the paper insulation and the sheath), as a result of which an excess amount of the impregnating composition accumulates in the lower part of the cable, and in voids are formed in the upper part, filled with volatile substances and gases. The greater the level difference between the highest and lowest points of the cable location, the higher the hydrostatic pressure of the impregnating composition column on the metal sheath of the cable and the termination or termination. Under significant pressure, deformation of the shell can occur, the tightness of the end seal can be broken and, as a result, the impregnating composition can leak out. The presence of air and vacuum inclusions in cable insulation is accompanied by a sharp deterioration in electrical strength. When using cables with aluminum sheaths, which have greater mechanical strength than lead sheaths, the highest allowable level difference increases.
For cables with depleted-impregnated insulation, the largest allowable difference in levels increases to 100 m with lead sheaths and is not limited with aluminum sheaths.
The indicated level difference is not limited for cables with paper insulation impregnated with a non-flowing composition.
Cables are laid, as a rule, at a positive ambient temperature. Unwinding, carrying and laying cables at low temperatures is carried out after preheating.

In cable tunnels, channels, shafts and industrial premises, cables are laid along cable structures and in boxes. Cable structures, ducts and fasteners necessary for laying and fastening cables are produced by industrial enterprises of Glavelektromontazh.

Prefabricated cable structures consist of racks with special holes in which consoles are installed, made with and without perforation. Prefabricated cable structures are intended for direct laying of armored cables over them. When laying unarmored cables on prefabricated cable structures, solid fireproof partitions made of asbestos-cement boards under metal cable trays should be laid.

Cable ducts are produced in the KP and KKB series. Boxes of the KP series (Fig. 5) are used for multilayer laying of control cables under and above service platforms in the main building and auxiliary facilities of power plants, as well as in galleries along overpasses and in cable floors. The set of boxes includes straight, angled and tee sections, which makes it possible to assemble any cable route from them. The gearbox box section consists of a body, a cover and fasteners.

Boxes block series KKB (Fig. 5) are used for joint laying of power and control cables both inside the main building and auxiliary structures, and across the territory of power plants and outdoor switchgear. The boxes have an angle steel frame and a steel sheet lining. Cable consoles are installed inside the boxes. For the possibility of completing the cable route, elements of straight and corner boxes are produced.

Installation of cable structures should be started after the completion of plastering, whitewashing and painting of walls and building structures along which the cable route passes.

To fasten cable structures along the entire length of the cable route, guide strips 50x5 mm are laid from strip steel, two in number for tunnels and channels 900 and 1200 mm high and one for channels less than 900 mm high. These strips are also used as grounding lines and therefore must be securely welded along the entire length and connected along the route in two places to a common ground loop. The guide strips are welded to the embedded parts or attached to the building base with dowels fired with a mounting gun.

Fig 5. Left KP series box: 1-pin; 2 - cover; 3 - clamping bar; 4 - gasket; 5 - box body; 6 - cables or wires; 7 - cable structure bracket: 8 - insulating tube; 9-nut: 10-pillar On right- Cable boxes of the KKB series: a - box assembly; b - self-supporting span of the box; 1.2-corner box for horizontal rotation by 225 ° type KKB-UGN; 3 - direct type KKB-P; 4. 5 - angular type KKB-UN; 6 - direct type KKB-PO

Prefabricated cable structures are welded to the guide strips vertically and at the same height so that the corresponding shelves of all structures are on the same straight line. The distance between cable structures is maintained within 800-1000 mm. In places where the cable route turns, the distance between the structures is chosen in such a way that the permissible bending radius of the cables is maintained.

Metal trays are installed over cable structures when unarmored cables are laid through them. Trays are attached to structures with bolts or wedges or welded by electric welding. The connection of the trays is also carried out by bolts or welding. On the vertical sections of the cable route, the distance between the supporting structures should be no more than 2 m for cables of all brands, except for unarmored cables with rubber insulation of small sections, for which this distance should be no more than 0.7 m.

KP series cable ducts are installed on cable shelves, brackets or suspended on cables. The connection of the duct sections and the continuous earthing circuit are carried out by means of bolts or by welding. Boxes of the KKB series are self-supporting and can be attached to the supports assembled in blocks with a distance between the supports from 3 to 12 m. To increase fire safety, fire barriers are provided in the boxes KP and KKB. The boxes must be grounded in each room at least in two places.

Staples, buckles and other parts are used to fasten cables to structures.

In industrial premises and cable structures, various designs are used for laying cables and wires. The installation of structures at the facility is a significant amount of electrical work, so the structures must meet a high degree of prefabrication and have a small mass. Cable structures are produced in normal and chemically resistant versions (galvanized or painted with chemically resistant varnishes).

Prefabricated cable structures (Fig. 30) are designed for laying electrical cables, as well as installing trays and boxes on them. They are installed along the walls of rooms, canals, tunnels, wells and other building structures. The distance between the cable structures on the horizontal sections of the route is 0.8-1 m, on the vertical sections - 2 m.

The structure of the cable structure includes racks, shelves, brackets and a key. Racks are made with a height of H 400-1800 mm (Fig. 30, a) from sheet steel with perforation, which has a pitch of 50 mm, which allows you to install shelves with distances between them of 100, 150 mm, etc. Cable construction does not require welding of shelves to the racks. The shelf is inserted into the rack and mechanically secured with a key. The reliability of the mechanical engagement of the shelf with the rack provides the necessary electrical contact for grounding the shelves. Racks are attached to building bases with brackets by shooting or welding to embedded parts.

Rice. 30. Prefabricated cable structures:
a - cable rack, b - shelf, c - bracket for attaching the cable rack, d - key for attaching the shelf to the rack

To obtain a cable structure of the required height, the racks can be vertically joined together in any combination. The shelves are made with a length (overhang) of 160-450 mm (Fig. 30, b), which allows you to complete the rack with shelves of different lengths.

For laying single cables, cable structures are used, consisting of perforated channels and embedded hangers (Fig. 31), which are inserted into the channel perforation hole with the narrow side of the shank and rotated by 90 °. Hangers are produced in three standard sizes for cables with an outer diameter of 20, 35 and 50 mm.

Rice. 31. Cable structures for single cables:
1 - perforated channel, 2 - embedded suspension

For fastening cables to various bases, single-blade and two-blade brackets are used (Fig. 32).

Rice. 32. Clips for cables:
a, b - single-arm and two-arm for fastening with screws and bolts, c - two-arm for shooting.

Trays are used for laying power and control cables and wires with voltage up to 1000 V and are made of perforated bent metal sheet. The width of the tray is 50, 100, 200 and 400 mm, the length is 2 m. The range of trays includes elements ready for assembly that provide the creation of a route with the necessary turns and branches in the horizontal and vertical planes (Fig. 33).

Rice. 33. Trays:
1, 2 - straight lines with a width of 50, 100 or 200, 400 mm, 3 - angled, 4. 5 - transitional and hinged connectors, 6 - clamps, 7 - hangers

The trays are connected with bolts, which ensures a reliable electrical circuit, which is necessary for the grounding network. Mount trays on brackets, hangers and prefabricated cable structures. Trays mounted on supporting structures are fixed in such a way that the possibility of slipping, overturning and falling them is excluded.

When trays intersect with other communications, the trays are laid indented from the walls, if this is not possible, bypasses are performed.

Boxes have a purpose similar to trays.

For straight sections of the route, a straight box is used, for branching into four directions - a cruciform box, for changing the direction of the route in the horizontal and vertical planes - an angular one, for entering electrical devices - a connecting one. In addition, the box set includes: an end cap for closing the end of the box and a clamp for fixing wires and cables. The boxes are made single-channel with a length of 2 and 3 m and are calculated for uniformly distributed loads (the distance between the attachment points is 3 m).

The boxes are designed for laying wires and cables in them with a bending radius of up to 50 mm.

test questions

1. List the advantages and disadvantages of tunnels and channels.
2. What is the design and purpose of collectors?
3. List the advantages and disadvantages of a block sewer.
4. Why have they become less likely to use cable laying in trenches?
5. Why is the laying of cables on overpasses and galleries so widespread?
6. What is the purpose of prefabricated cable structures?