Method for drying electrical cables with paper or other insulation. Electrical Wire Insulation Drying Oven Drying paper insulation. types of moisture. Kinetics of the drying process

The reliability and uninterrupted operation of any cable is primarily due to the quality of the insulating coating of its cores, expressed in its electrical strength.

For cables up to 3 kV, plastic insulation can be used: polyvinyl chloride, polyethylene, polyimide (Kapton). For cables up to 35 kV, paper insulation is used, which is characterized by high electrical characteristics, relatively high allowable temperature, long service life and low cost. Thus, it is cable paper that occupies a leading position in the issue of insulation of current-carrying conductors.

Cable paper for insulation is grade K-12 (thickness 0.125 mm) and K-17 (thickness 0.175 mm). It is made from unbleached, sulphated pulp, usually natural color, but for marking in multicore cables, the top tape is made of colored paper.

Overlay is carried out by winding unimpregnated wrapping tape in one of the following ways: end-to-end, with negative or positive overlap. Insulating layers are superimposed on twisting-insulating equipment, which simultaneously twists and seals the core if it is multi-wire.

If each core is lead-coated separately and intended for a single-core cable, then after twisting and insulating machines they are sent directly to the dryer. In other cases, insulated cores are wound on drums and fed to equipment for general twisting into a cable. The difference between the twisting of insulated conductors and non-insulated conductors differs only in their smaller number and large twisting pitch. In the process of twisting, the gaps between the cores are simultaneously filled, for which either paper bundles or sulphate paper are used, the thickness of which is up to 0.08 mm. In addition, belt insulation is applied on top. The point of filling the free space until a rounded shape is achieved is to make it difficult to move the impregnating composition along the cable, which makes it possible to increase the dielectric strength of the cable.

For the manufacture of 1 km of a 35 kV cable with a cross section of 3 * 95 mm 2, 2 tons of cable paper are required. Since the humidity of the latter is about 7-9%, which is about 140-180 kg of water, additional removal of excess moisture is required. For this, the cable from the equipment for general stranding enters special vacuum boilers. Here, not only drying is carried out, but also the removal of excess air, which can significantly reduce the electrical and physical characteristics of the insulating paper coating. Drying is carried out at a temperature of more than 100 ° C, and after 2-3 hours moisture and air begin to be pumped out of the boiler. The total duration of the process depends on the design features of the cable and the equipment used. To speed up and improve the quality of drying, the cores are simultaneously heated by electric current.

At the end of drying, impregnation with a special composition is carried out, which makes it possible to increase the electrical strength of the insulating coating made of paper, and then cooling in the open air follows.

Electrical machines are subjected to drying when wetting the insulation of windings and other current-carrying parts. e.g. during transport, storage, installation and repair, as well as when the unit is stopped for a long time.

Drying the insulation of the windings of electrical machines without special need causes additional unjustified costs, and if the drying mode is not maintained correctly, the winding is also damaged.

The purpose of drying is to remove moisture from the insulation of the windings and increase the resistance to a value at which the electric machine can be energized. The absolute resistance, MΩ, of insulation for electrical machines that have undergone major repairs must be at least 0.5 MΩ at a temperature of 10 - 30 ° C.

For newly installed electrical machines, this value must not be lower than the values ​​​​given in Table. 2, and for electric motors with voltages above 2 kV or more than 1000 kW, in addition, it is necessary to determine the ratio R60 / R15 with a megohmmeter ka6c.

If the obtained data indicate an unsatisfactory condition of the insulation, the electrical machines are dried.

The removal of moisture from the insulation of the winding of an electrical machine occurs due to diffusion, which causes moisture to move in the direction of the heat flow from the hotter part of the winding to the colder one.

The movement of moisture occurs due to the difference in humidity in different layers of insulation, from layers with higher humidity, moisture moves to layers with lower humidity. The difference in humidity, in turn, is created by the difference in temperature. The greater the temperature difference, the more intense the drying of the insulation. For example, by heating the internal parts of the winding with current, it is possible to create a temperature difference between the internal and external layers of insulation and thereby speed up the drying process.

To accelerate the drying of windings heated to the limiting temperature, it is advisable to periodically cool to ambient temperature. Therefore, the efficiency of thermal diffusion is the greater, the faster the surface layers of the insulation are cooled.

Tab. 1. Approximate drying time for electrical machines

During the drying process, it is necessary to heat the windings and steel gradually, since with rapid heating the temperature of the internal parts of the machine can reach a dangerous value, while the heating of the external parts will still be insignificant.

The winding temperature rise rate during drying should not exceed 4 - 5°C per hour. According to the PTE of electrical installations of consumers, the measurement of insulation resistance relative to the machine body and between the windings is carried out for windings of electrical machines with a voltage of up to 660 V inclusive at 1000 V, and for electrical machines with a voltage above 660 V - with a megaohmmeter at 2500 V.

However, according to GOST 11828 - 75, the resistance of the windings of electrical machines for a rated voltage up to 500 V inclusive is measured with a megohmmeter designed for 500 V, windings of electrical machines for a rated voltage above 500 V - with a megohmmeter for 1000 V. Therefore, PTE to some extent tighten the requirements for testing insulation with a megaohmmeter.

Produced at a winding temperature of 75°C. If the winding insulation resistance was measured at a different temperature, but not lower than 10 °C, it can be recalculated to a temperature of 75 °C.

Before drying the insulation of the windings of electrical machines, the room must be cleaned of debris, dust and dirt. Electrical machines must be carefully inspected and purged with compressed air. During drying, the insulation resistance of each winding of the electrical machine is measured with respect to the grounded machine housing and between the windings (Fig. 1).

Each time before the measurement, it is necessary to eliminate residual charges in the insulation; for this, the winding is grounded to the housing for 3-4 minutes. In addition, when drying the windings of electrical machines, it is necessary to measure the temperature of the windings, the ambient air, and the drying current. In practice, as a result of drying the windings of electrical machines, the insulation resistance at a temperature of 750 ° C should not be lower than the data in Table. 2.

Tab. 2. The smallest permissible insulation resistance of the windings of electrical machines after drying

Drying of the windings of electrical machines by the method of inductive losses in steel

In recent years, rational methods have been introduced for drying electric motors by inductive losses in the stator steel when the machines are stationary, not related to the passage of current directly in the windings. With this drying method, there are two varieties: losses in the active steel of the stator and losses in the stator housing.

Heating of electric motors is carried out by magnetization reversal losses in the active steel of the stator of the AC motor or the inductor of the DC machine from the alternating magnetic flux created in the machines in the stator core and the machine housing.

It is created by a special magnetizing winding wound on the machine body along its outer surface with the conductors pulled under the frame (Fig. 1, a) or onto the housing and end shields (Fig. 1, b), an alternating magnetic flux can also be created by inductive losses in the active steel of the stator and the body of the electric machine (Fig. 1, c).

The rotor of an asynchronous or synchronous machine must be removed in order to be able to wind magnetizing turns on the stator.

Rice. 1. Drying of electrical machines due to inductive losses in steel: o-in the machine body, b - in the body and end shields, c - in the body and stator active steel

The magnetizing winding is made with an insulated wire, the cross section and the number of turns are determined by the appropriate calculation.

During the drying process, the insulation resistance of the windings of electrical machines decreases in the first period of drying, then increases and, having reached a certain value, becomes constant. At the beginning of drying, the insulation resistance is measured every 30 minutes, and when a steady temperature is reached, every hour.

The results are recorded in the drying log and at the same time curves (Fig. 2) are plotted for the dependence of the insulation resistance and winding temperature on the duration of drying. Measurements of insulation resistance, winding and ambient temperature continue until the electrical machine is completely cooled down.

Drying of the windings of the electrical machine is stopped after the insulation resistance is practically unchanged at a constant temperature for 3-5 hours and ka6c is not lower than 1.3.

Rice. Fig. 2. Dependence curves of insulation resistance 2, absorption coefficient 3 and winding temperature 1 of the electric machine on the duration of drying

Drying the insulation of the windings of an electric motor in a drying oven

Reliable and uninterrupted operation of the cable largely depends on the quality of the insulation. It must have such dielectric strength that the possibility of electrical breakdown at the voltage for which this cable is designed is excluded.
Impregnated paper insulation of cable cores has high electrical characteristics, long service life, relatively high allowable temperature. All this and low cost have provided impregnated cable paper with a leading position in cable insulation.
Paper for insulation of cable cores for voltages up to 35 kV inclusive is produced with a thickness of 0.125 mm grade K-12 and 0.175 mm grade K-17 from unbleached, sulphate pulp of predominantly natural color (GOST 645-59). To color the phases in multi-core cables, the upper tape is used from colored paper.
Cable paper is applied by winding the core with unimpregnated paper tapes. There are the following ways of winding multilayer paper insulation: end-to-end, with positive overlap and with negative overlap.
End-to-end winding is characterized by the fact that when the tape is applied, the edge of one turn comes into contact with the edge of the adjacent one. This winding method is rarely used, since it has a serious drawback: when the insulated core is bent, the inner part of the tapes bulges in the compression zone, and the outer part diverges in the tension zone.
In positive overlap winding, one edge of the tape overlaps the edge of the tape of the previous turn. This winding method reduces the flexibility of the strand and often causes wrinkles and even cracks in the paper at the overlap when the strand is bent. This method is used in cables only for winding the lowest layers of insulation located directly at the core, since this excludes the possibility of coincidence in the first layers of paper tapes, which is very important for ensuring the dielectric strength of the insulation. The use of a positive overlap for the outer mites gives greater smoothness to the outer layer of insulation.
The most common way is the negative overlap winding, i.e. with a gap. The presence of a gap between the tapes allows the cable to be bent within certain limits without the danger of damaging the paper insulation. The gap between two adjacent turns in this case is in the range of 0.5-2 mm. The gaps between the turns of adjacent tapes located on top (vertically) should not coincide in order to avoid deterioration of the electrical characteristics of the insulation. However, when applying a large number of tapes, it is not possible to avoid gap coincidences, therefore, the number of coincidences of insulation tapes according to GOST 340-59 on power cables with impregnated paper insulation should not exceed that specified in the standards.
According to the requirements of GOST 340-59, in the insulation of cables of 6 kV and above, more than three tapes located one above the other and two tapes directly adjacent to the core are not allowed to coincide.
In the process of insulating the cores, in addition to the coincidence of the gaps between the tapes, tears of the tapes may appear.
The coincidence of longitudinal cracks or cuts over a length of more than 50 mm in two tapes located one above the other is considered as one.

It should be noted that the development of sliding discharges will be most difficult in cases where the gaps are located under the middle of the tape of the next layer, while the gaps adjacent vertically will be covered with only one layer of paper, and this place will naturally be electrically weakened. For this reason, the isolation technology provides for gap bridging by the next layer by about one third of the width of the tapes.
Of great importance is the width of the paper tapes used for winding. A wide tape hinders the development of sliding discharges between the tapes, allows you to increase the winding step, and hence productivity. However, an excessive increase in the width of the tapes does not ensure a tight winding of the cores, leads to the appearance of wrinkles, cracks and breaks in the paper tapes when the cable is bent. The width of the tapes is usually set depending on the diameter of the wrapped core, while the larger the diameter of the core or cable, the greater the allowable width of the paper tapes.
The width limits of paper tapes for conductors, depending on their diameter, established by the factories of the domestic cable industry, are given in Table. 2-4.
In the case of a sector core, the width of paper tapes is selected according to the equivalent diameter, which is equal to the perimeter of the core divided by π.
The application of paper insulation should be tight, without folds or wrinkles. The presence of folds, wrinkles, leaks in the insulation leads to the formation of voids, air inclusions, which reduce the reliability of the insulation under operating conditions.
The sharp edges of the sectors of the cores cause uneven winding density of the paper insulation, as well as an increase in the electric field strength. An increase in the radius of curvature of the edges of the sector conductors leads to a more uniform distribution of the electric field and an increase in the electrical strength of the insulation.
The thickness of the insulating layer, normalized by GOST 340-59, is given in Table. 2-5 and 2-6.
The deviation of the insulation thickness between the cores or | M1chzhdu the residential and shell is allowed no more than: for cables 1 kV - minus 0.18 mm, for cables above 1 kV minus 0.24 mm.
Paper tape insulating layer is usually | are superimposed in different directions, and the layer of insulation adjacent to the core is superimposed in the direction of the twisting of the wires of the upper layer of the core. Reversing the direction of the applied tapes of the insulating layer makes it possible to obtain cables without excessive rigidity and a tendency to twist. Paper insulation is applied on a twisting and insulating machine, which simultaneously twists the stranded core and seals it.
The insulated cores of cables, in which each core is leaded separately, come from the twisting and insulating machines directly to the dryer. Insulated cores for multi-core cables from twisting and insulating machines are wound onto drums and sent to machines for general twisting of cores into a cable. The twisting of insulated cores into a cable differs from the twisting of uninsulated cores only in a smaller number of twisted cores and a large twisting pitch. With a general twisting of insulated conductors into a cable, they are given two movements - one rotational around the cable axis and the other rectilinear
The general twist is characterized by two main parameters: the pitch and the direction of the twist, which are of great importance, as will be seen later, when connecting cables to each other.

The pitch of the total twisting of the cores is the length of the manufactured cable per revolution of the twisting device. The step length is determined by the factory standard depending on the diameter of the cable under the sheath.

Each core of its color makes a complete revolution around the cable axis during one step, consistently occupying any position in the cross-sectional area of ​​​​the circle from 0 to 360 ° (like a clock hand). Each next step of the twisting device is a repetition of the previous one both in the length of the step and in the sequence of placement of the cores in the cross-sectional area of ​​the circle.
Thus, the construction length of the cable manufactured by the factory:
where ι is the pitch length of the total twist; n is the number of steps. When twisting insulated cores, the gaps between the cores are simultaneously filled with paper bundles or sulphate paper with a thickness of not more than 0.08 mm and belt insulation is applied over the twisted cores. The paper bundle, filling the free space between the cores to a round shape, makes it difficult to move the impregnating composition along the cable and thereby increases the electrical strength of the cable. The twisting of insulated cores at all plants of the cable industry of the Soviet Union is carried out in one direction - to the right. This is determined by the conditions for laying and connecting individual construction lengths to each other during the construction of cable lines.
Since 2 tons of cable paper with a moisture content of 7-9% (about 140-180 kg of water) are consumed for the manufacture of insulation of 1 km of a 35 kV cable with a cross section of 3X95 mm2, the cable from general twisting machines enters special vacuum boilers for drying and removing moisture from the paper insulation and air, the presence of which reduces the electrical and physical characteristics of paper insulation.
Drying is carried out at a temperature above 100 ° C, and after 2-3 hours air and water vapor begin to be pumped out of the boiler. The drying time depends on the design of the cable and equipment. To speed up and improve the quality of drying, the process is carried out with simultaneous heating of the cores of the inner part of the cable with electric current.
After the drying process is completed, the paper insulation of the cable is impregnated with an impregnating composition.
After the end of the process of impregnation with a heated composition in a vacuum boiler, the baskets with the cable are installed for cooling in the open air in the drying and impregnation department. At the same time, the volume of the impregnating composition in the insulation (as a result of cooling) decreases and, as a result, the insulation is additionally replenished with the composition in the basket.
Impregnation with oil-rosin composition significantly increases the electrical strength of the paper insulation of cables.
The impregnating composition is made from mineral oils and rosin. For the impregnation of cables up to 35 kV inclusive, a very viscous mineral oil of the P-28 brand (GOST 6480-53) is used, obtained from the residues of oil distillation, called brystok, which is characterized by high resistance to oxidation and low gas emission during ionization.

The most important characteristic of the impregnating composition is the viscosity. The composition must, on the one hand, be less viscous in order to ensure complete impregnation of the paper, as well as cable laying without preheating at a temperature of at least 0 ° C, otherwise, when the cable is bent, the individual tapes of cable paper will not be able to slide relative to each other, which will break the paper tapes and damage the insulation in these places. On the other hand, when laying on steep and vertical sections of the route, the impregnating composition, which is not viscous enough, will gradually drain from the upper sections to the lower part of the cable. As a result, the upper section of the cable is devoid of part of the impregnating composition, which degrades the quality of the insulation of this section. At the same time, an increased pressure of the impregnating composition is created in the lower section of the cable, which can lead to rupture of the cable sheath.
For the impregnation of cables, the composition MP-1 is used, which has a viscosity of 6-7.5 according to Engler1 at 70 ° C, and MP-2, which has the same viscosity at 80 ° C. The main electrical characteristics of impregnating (oil-rosin) compositions and cable paper are given in Table. 2-8.
Comparison of the data in Table. 2-8 shows that the dielectric strength of the impregnated cable paper is 1.3-2.2 times that of the impregnating compound and 13-16 times that of the unimpregnated cable paper.
Impregnation of cables with depleted insulation, intended for vertical laying, is carried out with a less viscous composition MP-2. Insulation depletion is carried out in the same boilers after the impregnating composition has been removed from them.
In cables with individually lead-coated conductors with depleted insulation, the impregnating composition should not leak out at a temperature of 85 ° C and in cables with a common lead sheath - at a temperature of 75 ° C.
Depletion of paper with an impregnating composition leads to a decrease in the electrical strength of the insulating layer, so the paper insulation of cables with depleted impregnation thickens.
The thickness of the insulation of cables 1-3 kV with depleted impregnation is the same in thickness with the insulation of cables of the same voltage with normal impregnation. This is explained by the fact that the thickness of the insulation for cables for these voltages is determined by the requirement of mechanical strength, under which the resulting thickness of the paper insulation has a sufficient margin for electrical strength.
At present, cables with depleted insulation are rarely used for vertical and steep sections of the route, since the use of belt-insulated cables and cables with separately lead-coated cores for a cable line at a line operating voltage of 10 kV requires the use of special couplings.
In this regard, at present, much attention is paid to impregnating compositions containing synthetic ceresin as one of the components.
In accordance with GOST 340-59, in 20-35 kV cables over the core, in 6-10 kV cables with separately leaded cores over the insulation and in cables with a common lead sheath over the belt insulation, shielding must be performed by applying a layer of semi-conductive paper. Shielding, the arrangement of conductive surfaces in relation to the insulating material of the cable, is one of the best ways to regulate, limit and reduce the strength of the electric moth.

In cables with viscous impregnation, with a difference in levels along the laying route and under the action of heating, the impregnating composition moves in the radial and longitudinal directions. This leads to the formation of gas inclusions and the occurrence of ionization processes in them, which can lead to damage to the cable insulation.
The use of semiconductor screens along the core and under the lead sheath, where the increase in volume due to the pressure of the impregnating composition and the low elasticity of the tit under operating conditions reaches from 0.5 to 20% of the insulation volume, significantly improves the ionization characteristic of the cable and increases the reliability of its operation.
Under the lead sheath of cables according to GOST 340-59, every 300 mm, the designations of the manufacturer and the year of manufacture of the cable must be clearly marked on the surface of the insulation or on a special tape. In cables under a lead sheath with a diameter of less than 20 mm, instead of a special tape, a tape or thread of the color assigned to the manufacturer is allowed.
In multi-core cables, the upper insulation tape of one core must be made of natural-colored paper, the second core - red or natural-colored paper with a red stripe, the third core - any other color or natural-colored paper with a stripe of any other color. In four-core cables, the top tape of the neutral core must be made of natural-colored paper.
The distinctive coloring of the cores was introduced to determine the direction of the phase sequence of a three-phase system, to ensure the correct connection of the same phases to each other according to their colors during the installation of individual building lengths of the cable, as well as to connect the same-name phases of the busbars of the equipment of the switchgear of electrical installations with cable lines.
Plastic core insulation is used for cables up to 3 kV, manufactured in accordance with GOST 16442-70*. Polyvinyl chloride and polyethylene are used as plastics.
Polyvinyl chloride is a solid polymerization product of vinyl chloride, it is flame retardant and highly resistant to heat aging, water, alkalis, dilute acids and other active chemicals, oils and gasoline. In its pure form, polyvinyl chloride is not used due to its rigidity and brittleness at low temperatures.
To increase the elasticity and frost resistance of polyvinyl chloride, hard-to-evaporate organic filler liquids (plasticizers) are added to it; to improve the electrical insulation characteristics and reduce the cost, kaolin, talc, calcium carbonate, etc. are added to it; to increase resistance at high temperatures - stabilizers; to increase its light fastness - special dyes.
Cables with PVC insulation are most widely used for voltages up to 1,000 V. The disadvantage of PVC insulation is its thermoplasticity. Heating of the core by load currents can cause some softening of the insulation and displacement of the core from the central position during operation. The dielectric strength of insulation made of polyvinyl chloride plasticate, in addition, depends on the time spent under AC voltage.
In order to avoid an increase in dielectric losses in the insulation, these cables can be manufactured for voltages not exceeding 10 kV.
Cables with PVC insulation are made in a sheath only from PVC. The thickness of the sheaths, depending on the diameter of the cable under the sheath, is 1.8-2.6 mm.

Cables laid in the ground are provided with the usual protective covers and armor.
Polyethylene is one of the synthetic polymers that has the greatest application and promising wide use as cable insulation, especially cables for steep and vertical sections of the route. Polyethylene has good mechanical properties and a wide temperature range resistance to acids, alkalis, moisture and has high 9lwhtroieolation characteristics.
Depending on the density, polyethylene is classified into low, medium and high density.
Compared to low density polyethylene, high density polyethylene has a higher melting point and greater mechanical strength. With the introduction of carbon black or graphite into it, semi-conductive polyethylene can be obtained for shielding purposes.
Cables with polyethylene insulation are mass-produced by the domestic industry for voltages up to 10 kV and experimentally 20, 35 kV.

Unlike cables with impregnated paper insulation, the electrical calculation of cables with plastic insulation is carried out not according to the maximum, but according to the average electric field strength, since the field strength in cables with plastic insulation depends markedly on the core radius.
The operating field strength of the developed designs of plastic-insulated cables produced by the cable industry has magnitudes.
The thicknesses of the insulating layer applied by hot pressing for cables up to 3 kV with plastic insulation are given in Table.
For cables of 10 kV and higher with polyethylene insulation, the choice of screens is the most important issue in the reliability of the cable. The shield must be well bonded to the polyethylene insulation and have the same thermal expansion coefficient as the insulation, so that no voids form between the semi-conductive layers and the cable insulation when the cable load changes. These cables are shielded both on the core side and on the sheath side. In this case, the core is pressed with a thin layer of semi-conductive polyethylene, on which the main polyethylene insulation is applied, shielded from above with colloidal graphite or semi-conductive polyethylene.
Plastic insulation for a voltage of 6 kV is shielded from the side of the shell, for which purpose semi-conductive and metal (copper or aluminum) screens are applied over the core insulation.
On 6 and 10 kV cables with plastic insulation and a sheath, the conductivity of the screen tapes must ensure the magnitude of the earth fault current that occurs under operating conditions

→ ?

Hello!

Can you tell me the method and how you can dry the plinths of the BKT boxes. And how to get rid of it in the future.

In general, the topic of raw plinths has already been raised, pages:

It is best to dry the terminal devices in a damp cabinet with a household electric hair dryer. It is household, since during drying it is important to withstand a low temperature and not melt the insulation of cross-connects or cables. ☺

Since this is a long time, not serious, it requires a voltage of 220 volts and a hair dryer is not designed for long-term operation, the skirting boards are dried with blowtorches or gas burners. This should be done carefully, not bringing the burner close to the wires and constantly monitoring the temperature of the plinths with your hand, since the insulation of the cross-connects easily melts, causing short messages. Accordingly, neat and responsible people are sent to such work.

This process is not described in official manuals, since dampness in switch cabinets occurs due to violations of construction and operation technologies. Given that you are from Belarus, I will refer you to TCP 206 - 2009 (02140) "Rules for the technical operation of linear cable structures of subscriber lines of local telephone networks" →
9.2 Inspection and preventive maintenance of line-cable structures →
9.2.7 During preventive maintenance of the RS, the following work is carried out: ... →
- installation, alignment, compaction and filling of the cabinet board (or sealing the board with putty);

In the official document, this process is described dryly, incompletely and without explanation. Meanwhile, it is the leakage of the sealing of the cabinet floor that is the main reason for dew deposition on the plinths. A small hole in the floor or between incoming cables is enough to make the cabinet damp. Builders have the concept of "dew point", and in simple terms, relatively warm and humid air from a basement, a well or even a closet pit, getting into the cabinet space, cools down, and dew falls on all cabinet surfaces.

In our area (Vitebsk region), the cabinet floor was made three-layered. First there were boards or plywood (fibreboard and cardboard are not suitable, they warp over time). Two halves were cut out: the back and the front, and cuts were made on them under the existing cables. The boards are installed in the cabinet, and all the cracks are plugged with tow or rags. Next, the floor is covered with an even, 1-2 cm, layer of dry sand, this is the second layer.

While all these works are being carried out, bitumen is usually heated. After leveling the sand, the bottom is sealed with bitumen. They try to fill it evenly, in all corners and between the cables. Same when filling pay attention to the temperature of the bitumen, because if you fill it with too liquid and hot, you can melt the internal insulation of the incoming cables.

As some alternative, bituminous chips can be used. In this case, the sand is covered with an even layer of crumbs, then it is heated from above, right in the cabinet, with a blowtorch or gas burner.

I am a little surprised that in Belarus all this is not used everywhere, since in the Vitebsk region the mandatory sealing of the bottom of the cabinet has been the norm for ten years already (although a freebie in the wilderness is always possible). Cabinets are really dry. It is worth noting that the RUES in most cases sealed the bottom of the cabinets at the expense of construction organizations. Builders, when putting the cable into operation, are obliged to restore or re-sealing the cabinet bottom. I don’t have Belarusian documents on this subject, but I can cite a Russian one (and they, as a rule, are word for word). Guidelines for the construction of linear structures of local communication networks, M., 2005 3.20 Distribution cabinets:

3.20.6 The channels of the pipeline introduced into the cabinet and into the cabinet well must be carefully sealed to prevent accidental penetration of water and explosive gases through the wells into the cabinet and the room.

→

Thank you very much for your advice. Let's fix our wardrobes.