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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
External wiring. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electric installation work External wiring lay outdoors: along the outer walls of buildings and structures, under awnings, cornices; it is stretched between supports to supply electricity to utility buildings (baths, sheds, garages, etc.). With the help of external wiring, a branch is carried out from the power line to enter the power line into the building. To supply electricity to outbuildings, wiring must be carried out on load-bearing supports, and its metric parameters are allowed as follows: total length of the branch - no more than 100 m; the distance between the supports or between the support and the building - no more than 25 m; height - at least 3,5 m. The input of a branch into the building is carried out similarly to the input of electricity into the building in general. Unprotected insulated wires of external electrical wiring should be hung in such a way that it is impossible to touch the wires in places where people can be present, for example, on balconies or near windows. From such places, wires laid openly along the walls should be at a certain distance: with horizontal laying - no closer than 0,5-1 m from a window or balcony; when laying vertically from the electrical wiring to the window, there must be a distance of at least 0,75 m, to the balcony - 1 m, and from the ground - 2,75 m. If the electrical wires are laid on the supports of the overhead line (VL), then the distance from the wires of the overhead line to the balconies and windows of the building must be at least 1,5 m with the maximum approach of the wires of the overhead line in strong winds. Laying wires of external electrical wiring on the roofs of buildings is unacceptable, with the exception of inputs to the building and branches to these inputs. Under the terms of electrical safety, unprotected insulated wires of external electrical wiring should be considered as uninsulated. The distance from electrical wires crossing fire lanes and ways for transporting goods to the ground must be at least 6 m, and in the impassable part - at least 3,5 m. The distance between the wires (with a span of up to 6 m) must be at least 0,1 and 0,15 m (with a span of more than 6 m). The distance from the electrical wires to the walls of the building and supporting structures must be at least 5 cm. Laying of wires and cables of external electrical wiring in pipes, ducts and flexible metal hoses must be carried out with a seal. Laying wires in steel pipes and ducts in the ground outside the building is unacceptable. In cases where the branch from the power line is carried out using a cable, it is more logical to carry out the input using the same conductor. To enter the cable into the building, a hole is punched in the foundation wall at a depth of at least 0,5 m. A tube with a diameter of 1,5-2 cable diameters (but not less than 5 cm) is passed into it. The length of the tube is selected so that it passes through the entire thickness of the foundation wall and has protrusions on both sides: 5 cm inside the building and 60 cm outside. The pipe is laid with a slope towards the outer trench (approximately 5 °) and carefully insulated (compacted with cement mortar with sand, clay or oil-soaked cable yarn), which prevents water from entering the building. Only one cable can be inserted through one tube, and if the input is carried out by several cables, a separate tube is mounted in the foundation wall for each. At the entrance to the building (in the trench), it is necessary to leave a supply of cable (1 m), which can be useful for re-cutting the ends. The stock is laid in a semicircle with a radius of 1 m and must be covered with a brick or concrete slab. Cable laying in the ground should be carried out in asbestos-cement non-pressure pipes with a diameter of 100 mm at a depth of at least 0,5 and not more than 2 m from the ground surface. Pipes should be laid with a slope towards the street. Only one cable can be pulled into one pipe. Cable laying in the ground can be done as shown in fig. 41.
The ends of asbestos-cement pipes, as well as the cables at the outlet of the pipes, should be sealed with non-combustible or slow-burning materials. In the basement or underground, it is allowed to lay cables with a voltage of up to 1000 V with impregnated paper insulation without an outer cover or with plastic insulation and a sheath. Horizontal sections of supply lines may be laid in the voids of reinforced concrete structures (without pipes) and in plastic pipes in a layer at the stage of floor preparation. It is allowed to lay hidden lines in the floor of the overlying floor in plastic pipes laid in monolithic concrete. When making an input through a wall on porcelain insulators, the passage of wires through the wall must be made in plastic or rubber pipes (Fig. 42), with each of the insulated input wires placed in a separate insulating tube. The distance between the wires in the walls must be at least 5 cm if they are brick or concrete, and at least 10 cm if they are wooden.
Porcelain funnels are put on the outer ends of the insulating tubes, bushings are put on the inner ones; the gaps between the surface of the hole in the wall and the insulating tube are sealed with alabaster or cement mortar. To prevent moisture from accumulating in the holes inside the wall and getting into the porcelain funnels and rubber tubes, the passages through the walls are arranged with a slight (about 5 °) slope to the outside, and the inlets of the funnels and bushings are sealed after laying the wires. Entering the overhead electrical line into the building Before proceeding to get acquainted with the technical parameters and technological operations of introducing an overhead electrical line into a building, it must be remembered: the installation of the input can only be carried out by a qualified electrician who has a permit to work with high voltage, the necessary skills and the professional tools and special equipment necessary for this work . Theoretical knowledge on this issue is needed in order to control the quality of the work of an electrician and, if necessary, provide him with all possible assistance. Conventionally, the input of an overhead power line into a building can be divided into two sections: a branch from the main power line to the input and the input itself. A branch from the main power line is a section of wires from a power line support (power line) to ceramic or porcelain insulators on the outer wall of a building. Accordingly, the section of wires from these insulators to the input device (meter or knife switch) inside the building is called the input. The physical parameters of the branch wires depend on the distance of the power transmission line support from the input: - in the event that the overhead line support is removed from the input section at a distance of up to 10 m, the branch can be made with bare wires with a conductor cross section of at least 4 mm2; - if this distance exceeds 10 m, then only insulated wires with a core cross section are used for the branch: aluminum - at least 16 mm2, copper - at least 6 mm2; - instead of a wire for a branch, you can use a cable laid on a cable; the cross section of the cable conductors should not be less than 2,5 mm2 if the conductors are copper, and not less than 4 mm2 if the conductors are aluminum. When arranging a branch section passing over the carriageway, the wires must be located at a height of at least 6 m; if the branch line does not cross the carriageway, 3,5 m is sufficient (Fig. 43).
At the approach of the branch wires to the building entry insulator, the height can be reduced to 2,75 m. Instead of a wire, a cable can be used as a material for making a branch from a power line. The laying of a cable branch is fundamentally different from a wire one: the cable is lowered along the power line support to the ground, and before entering the building it is laid in a trench about 0,7 m deep. At the same time, at the descent site (at a height of 2 m from the ground), the cable must be reliably protected from accidental mechanical damage, therefore it is covered with a metal pipe or other protective structure, and the last 0,5-0,6 .0,6 m cable before entering the building. If the installation of a branch involves pulling the cable along the wall of the building, then a trench for its placement is dug no closer than XNUMX m from the foundation wall. The direct entry of the line into the building can be made on porcelain insulators through the wall, pipe-resistant through the wall, pipe-resistant through the roof, in a pipe through the foundation (cable entry). The most common is the entry through the wall on porcelain insulators - this is the easiest method to perform, moreover, in this case it is easier to monitor the condition of the input and make the necessary repairs (Fig. 44). The input of wires into the building is shown in fig. 45.
Wires should be introduced through porcelain funnels (each wire in a separate funnel). Such an input can only be carried out if the height of the building meets the input conditions, namely: the input site must be at least 2,75 m above ground level, and the input site must be located below the level of the insulators. The minimum distance from the input wires (with the largest sag) with the largest deviation (in strong wind) to trees, bushes should be at least 1 m. Insulators are attached to the wall on hooks: if the walls are wooden (log, block), then the hooks are screwed into previously prepared holes with a diameter and depth slightly less than the corresponding hook dimensions; if the wall is brick or concrete, then the hook is installed on the cement mortar in a punched hole 10 cm deep and 2,5 times the diameter of the hook itself (after attaching the hooks and before attaching the wires, at least 1 day must pass, since the cement mortar must harden and gain initial strength); if the walls are frame-panel, plank, etc., then the hooks are installed on a segment of a wooden block with a thickness of at least 6-7 cm, which is screwed to the wall. Regardless of the angle formed by the wall plane and the input wires, the distance from the current-carrying wire to the protruding parts of the building must be at least 0,2 m, the same distance must be maintained between the wires. When entering wires into a log or wooden panel house, the distance between the funnels (insulators) must be at least 10 cm, and from the centers of the holes for the hooks of the insulators to the centers of the holes for the funnels - 15-20 cm. The input wires from the overhead line are mounted on insulators using clamps, bandage twisting (knitting) or twisting the ends of the wire. For aluminum wires, aluminum clamps should be used. To connect aluminum and steel-aluminum wires with a cross section of 16-50 mm2, bolted die clamps of the PAB type are used. The end fastening of the aluminum stranded wire of the branch to the insulator can be carried out with PAB-type flat clamps or with the help of bandage knitting (metric parameters of the bandage are shown in Fig. 44). In both cases, the end fastening is carried out in such a way that the end of the branch wire is at least 0,2 m - this is necessary to connect the input wire to the branch wire. Such a critical connection as the connection of input and branch wires must be very strong, which fully ensures the CCA clamp. Attention! It is strictly forbidden to connect the input wire to a stretched branch wire, as this may cause a break in the branch wires. The power line is entered into the building with a copper or aluminum cable or insulated wire in a non-combustible sheath. The cross section of the wire or cable must be at least 4 mm2 for aluminum and 2,5 mm2 for copper. In a brick building or a building with gypsum concrete walls, each wire is introduced through a separate porcelain funnel. The minimum distance between the funnels should be 5 cm. The vertical distance from the center of the holes for the hooks of the input insulators to the center of the holes for the funnels should be within 10-15 cm. However, the height of the building does not always allow the input of the power line through the wall on porcelain insulators (it should be remembered that, in accordance with the "Electrical Installation Rules", the place for entering the wire into the building should be at a height of 2,75 m from ground level). In this case, the input is carried out using a pipe rack - a steel pipe with an upper end bent down. From the pipe rack, the wire inside the building can be laid in two ways: through the wall and through the roof; each of these methods has its own characteristics. What else do you need to know about the pipe stand itself? For its manufacture, water and gas pipes with a diameter of 20 mm are usually used for the input of two wires and a diameter of 32 mm for the input of four wires. The length of the pipe rack must ensure the distance from the injection point to the ground (2,75 m). After sawing off the required section of the pipe, its edges must be processed (cleaned) with a file from burrs that can damage the wire insulation. The inner surface of the pipe rack should be protected from corrosion by a coating of bitumen, bituminous varnish or oil paint. To prevent atmospheric precipitation from getting inside the pipe rack, its upper end is bent down by 180 °. A traverse is welded perpendicularly to the curved end (steel angle 50 cm long, section 45 x 45 mm, 5 mm thick), onto which two vertical pins are welded for installing lead-in insulators. When introducing an electric line into a building on a metal pipe rack, it is necessary to perform zeroing (connect the pipe to the zero core), for which a metal bolt is welded to the pipe rack, placing it close to the input insulators. The mounted pipe rack will be constantly under load from the tension of the branch wires. To compensate for this load, braces made of round steel with a diameter of 5 mm are used; the guy is fixed in rings or on bolts specially welded on the pipe rack closer to the upper bend. During installation, a steel wire or cable with a diameter of 3-4 mm is laid in the pipe rack to pull the wires inside the pipe rack with their help. In order to facilitate pulling, the wires are wiped with a rag, and the pipe rack is blown with dry talc. The ends of the pipe, after pulling the wires, are poured with chatterton (bitumen) or portland cement moisture-resistant putty is stuffed into the pipe. The pipe rack is mounted on the wall using brackets and screws (in concrete or brick walls, nests are specially arranged for screws, as for hooks for insulators). The pipe rack is installed on the roof with steel wire braces. All bolted connections of pipe racks, especially fasteners, must be made using locking devices (spring washers, lock nuts, wire); this necessary precaution will not be superfluous, because a pipe rack mounted on a roof or on a wall will be constantly exposed to gusts of wind and sway, as a result of which self-unscrewing of the nuts may occur. In addition, all bolted connections (after the final installation of the bushing) must be liberally lubricated with technical petroleum jelly or other grease to protect against corrosion. A more convenient way to enter the pipe through the wall (Fig. 46).
The passage of wires through the wall in this case is arranged not in an insulating tube with a porcelain funnel, but in a pipe rack, for which its lower end is bent so that it is located in the wall with a slope of 5 ° to the outside; from the inside, a porcelain sleeve is put on the end of the pipe. Due to the temperature difference, condensation moisture can accumulate on the inner walls of the pipe rack; to remove it, a hole with a diameter of 5 mm is drilled at the lower point of the pipe bend. If the height of the building into which the power line is entered is insufficient to enter the pipe rack through the wall (the distance from the ground surface to the lowest point of the pipe rack is less than 2 m), then the pipe rack is used through the roof (Fig. 47).
The inconvenience of this method lies both in the complexity of the installation of the pipe stand itself, and in the need for high-quality installation of the passage through the roof (to ensure safety and reliable waterproofing). In this case, the pipe rack is attached to the roof surface with braces (steel wire 5 mm in diameter) installed on four sides of the pipe rack. Fixing guy wires on the pipe rack and roof is similar to the previously described guy fixing - using rings or bolted connections. In this case, it should be borne in mind that the tension force of each of the stretch marks must be the same: this is the only way to achieve a vertical position of the pipe rack and its resistance to weather phenomena (wind). The presence of braces does not at all mean a refusal to install braces, because these two elements perform different functions: the bracing holds the pipe rack, and the bracing compensates for the tensile force of the branch wires. The passage of the input conductors through the roof and the ceiling is carried out in the pipe of the same pipe rack, on which a porcelain sleeve is already put on from the inside of the room. The gaps between the pipe and the roof are carefully sealed with any waterproofing mastic (for example, bituminous). On fig. 48 shows the entry of wires from the building into the garage through the roof.
Basic rules for entering electrical wires into a building The entry of electrical wires into the building through the walls should be carried out in insulating pipes through porcelain funnels in such a way that water cannot accumulate and penetrate into the room. The distance from the wires with the largest sag to the ground and the carriageway of the streets, which should be at least 6 m, can be reduced to 3,5 m when crossing the overhead line of the impassable part of the street, footpaths, sidewalks, in hard-to-reach areas, and in inaccessible areas ( slopes of mountains, rocks, cliffs) - up to 1 m. The horizontal distance between the wires of the overhead line and the wires of the communication line and radio, television cables and descents from the radio antennas at the inputs must be at least 1,5 m. The wires of the overhead line in the span from the support to the input and the wires of the input of the overhead line into the building should not intersect with the wires of the branches from the communication lines and radio to the inputs and should not be located below the wires of the communication lines and radio. The distance between the wires at the input insulators, as well as from the wires to the protruding parts of the buildings, should not be less than 0,2 m. VL wires are allowed to be introduced through roofs in steel pipes. The distance from the input wires to the roof must be at least 2,5 m. The pipe (stand) is bent 180 ° with the hole down so that moisture cannot penetrate inside the pipe. Sometimes, in order to make the rack more stable against the force created by the stretched wires of the introductory span of the overhead line, it is reinforced with braces. Steel wire with a diameter of 6-8 mm is used as braces. Open laying of wires on the roof of a residential building is unacceptable. Laying flat wires in a hidden way is allowed along the outer walls. Author: Korshevr N.G.
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