Cables and wires with PVC insulation. Review of cable laying and protection technologies. The wire is heating up - what to do? Why is the socket heating up?

Outside the window is the 2015th year of the so-called “Our Era”, and every year of this very Era brings us something new. Over the past ten years, we have already become accustomed to the fact that every new year brings us joy with new devices that use the so-called “electric current” for their functioning. The machines, mechanisms and devices of modern man have become smaller, smarter and faster compared to those of a century ago. A lot of previously unseen things have appeared in devices, which could take hours to list, but with all this, our numerous mechanical assistants still contain separate, or better said, separately laid wires, cables, cords, or in scientific terms - conductors electric current. In this short story we will talk about the development of these same conductors, or more precisely, the materials used in conductors. The emphasis is on insulation materials, since it is this part of the conductor that determines its lifespan, reliability and security. The very concept and word “Cable” probably has German, Germanic roots, because this word does not appear in more ancient languages. The analogue of the German “Kabel” is the Russian “Wire” - the meaning of this word is clearer to us, because we can easily guess what “conduct” is and who the “conductor” is. Now that we have defined the concepts, we can move on to the history of this very “Wire”. We will not go deep into history until the time of experiments with “electricity”. We will limit ourselves only to the times when the first conductor production appeared in Russia. On the 21st of October 1832, Pavel Lvovich Schilling installed in St. Petersburg, with the help of mechanic I. A. Shveikin, the first electromagnetic telegraph in history. To operate the telegraph, reliable conductors of electric current were needed. First underwater electrical cable It was a thin wire covered with two layers of insulation, silk and hemp, and the first layer (silk) was impregnated with a special resinous composition, onto which hemp was then wound, and everything was again impregnated with the same resinous composition. Thus, we can say that the first wires in Russia, with the exception of the current-carrying core, were completely environmentally friendly, made from natural products(silk, resin, hemp). The first underground telegraph cables were made in approximately this way: the wires were insulated with one or two layers of cotton yarn and then impregnated with special compounds (for example, wax, lard and rosin). The protective shell was glass, tubes connected by rubber couplings, or steel sleeves; in some cases, glass tubes were placed in wooden gutters (for underground installation). For air lines Communications and the first power transmission used insulators made from very environmentally friendly materials - glass and porcelain.

In the early 40s of the 19th century, due to the need to manufacture a large number of insulated conductors, special machines for wrapping wires with yarn. During these same years, as insulating materials Rubber and gutta-percha began to be used, which retained their properties well in water. Rubber has been known for a long time, but its ability to greatly change properties with slight changes in temperature prevented its use for insulation purposes. Only after the introduction of the vulcanization method in 1939 did rubber acquire the properties possessed by the material well known to us as “rubber”. Thus, the use of wires in underground and mass conditions became the impetus for the complication of the design of the insulation and cable sheath - they are coming into use materials such as glass and rubber. If glass can still be called an environmentally friendly material (it is chemically resistant, easily recyclable, non-toxic when burned, and in general normal person cannot set it on fire), then it is difficult to call rubber a pure material. Not only does rubber production use sulfur, but during the entire period of its use rubber emits terrible and clearly not environmentally friendly odors. The rapid increase in the length of underwater and underground telegraph lines placed increasingly serious demands on improving the quality of insulation. A significant step towards solving this problem was the invention in 1848 of a press for seamless application of rubber and gutta-percha insulation on copper conductors. But even more important was to create special coating materials that would enhance the mechanical strength of the insulation (in particular, rubber and gutta-percha) while maintaining its flexibility and elasticity. This problem was solved by the construction of a lead press in 1879, with the help of which the insulated wire was covered with a seamless lead sheath. In the early 50s, ebonite was first obtained, used in the manufacture of various electrical appliances and devices. Ebonite (from the ancient Greek “??????” - ebony) - highly vulcanized rubber with a high sulfur content (30-50% based on the mass of rubber), usually dark brown or black in color; chemically inert, has high electrical insulating properties, however, those who still have cutlery with ebonite handles from Soviet times and who accidentally overheated them should remember what a terrible smell ebonite emits when it gets into the flame of a fire. In 1878, a process engineer Maxim Mikhailovich Podobedov organized in Russia Vasilyevsky Island in the city of St. Petersburg, the first handicraft workshops for the production of conductors with silk and cotton insulation, which employed several people. There he also created a small enterprise “Russian production of insulated electrical conductors Podobedovs, Leburde and Co.” In the 90s of the nineteenth century, multilayer oil-impregnated paper insulation began to receive increasing use for power cables. About the material of current-carrying conductors or conductors for I couldn’t find the first information providers in Russia on the Internet, but I dare to suggest that copper and aluminum were outlandish things at that time and steel should have been a much cheaper and, most importantly, more accessible and usable material. In general, today, at the beginning of the twenty-first century, the material most often used as a conductor is copper. Other materials used are aluminum, steel, sometimes gold, silver, and in rare special cases, superconducting materials. Some materials are used in conductors for other than their intended purpose (for example, for heat dissipation): nichrome, constantan and others. For the reason that the materials of the current-carrying core have remained unchanged for more than a hundred years (nothing more practical than copper has yet been invented ), the main “progress,” if you can call it that, occurs in the materials and structure of the insulation of the core and the outer sheath of the wire-cable. Over the twentieth century, this part of the wire has changed very much and, in my opinion, not in better side, judging by the care for the environment of our Nature. Let's take a closer look at the insulation and sheath of the wire.

After an era of experiments with natural silk, hemp, various resins, special cable (electrical insulating) paper, wood, ceramics, glass and even cotton fabric, an era of openly disregarding Nature has come. Even rubber, compared to some modern materials, may seem like a small harmless lamb against the backdrop of a pack of bloodthirsty wolves. The main one of these wolves is Poly-Vinyl-Chloride, abbreviated as PVC in Russian or PVC in English. The production of PVC on a large scale began in the 30s of the twentieth century in Germany; in 1931, the BASF concern produced the first tons of this material. At the same time, successful developments in this area were carried out in the United States of America and England. After the end of World War II, Poly Vinyl Chloride became the most popular material for the manufacture of pipes, profiles, floor coverings, films, cable insulation and many other plastic products! Usually this fact is presented by advertising agents of plastic windows as an advantage of the material. Who would have thought, but yes (!), plastic windows are made from PVC! Let's think about whether this PVC is so good? The chemical formula of PVC is [-CH2-CHCl-]n. PVC, as the name implies, contains Chlorine. PVC belongs to the group of thermoplastics; pure PVC is a powder that consists of 43% ethylene (a petrochemical product) and 57% combined chlorine. The melting point of PVC is 150 – 220°C, however, when heated above 135°C, destruction processes begin in it, accompanied by the elimination of atomic chlorine with the subsequent formation of hydrogen chloride, causing intense destruction of macro-chains. PVC begins to deform at already 65 – 70 °C! If you delve into the history of chemical weapons, you will find the fact that chemical weapons very often used chlorine in their composition. Conclusions on whether PVC is like a time bomb and why Western countries are actively promoting PVC products all over the planet, I suggest you do it yourself. The main official problem associated with using PVC, is the difficulty of its disposal - when it is incompletely burned, highly toxic organochlorine compounds are formed, for example the poisonous substance phosgene and dioxins, which are carcinogens. PVC is the most dangerous plastic produced today. Despite its danger, some people, without knowing about it, heat and burn things containing PVC. Doing this in enclosed spaces is not exactly extremely dangerous - but in general it is strictly prohibited if you want to live! This article is not intended to indicate how many harmful PVC things surround us in everyday life (and there are very, very many of them!), the emphasis of this article refers to the fact that most wires and cables produced today use poisonous Poly-Vinyl-Chloride as the insulator and sheath of the wire. If you imagine how many devices have electrical wires, and that all these wires are made of PVC, then it’s better not to think what will happen to the owners of all this “slow-action equipment” when it heats up to a high temperature. But it really does get warm often. Haven't you noticed? Better notice. As a guide, 60 degrees Celsius is the pain threshold for the skin of an average person. If a PVC wire is laid near hot surfaces, it is better to remove it from there or replace it with a wire made from other materials, which will be mentioned below. PVC materials are promoted to the market under the guise of caring for us, they are supposedly safer than others. However, if you look at the types of cables, you will notice that among PVC cables there are a lot of cables made of simple PVC plastic compounds, for which it is not indicated that it is low-smoke or does not propagate fire. So, PVC is not a panacea for all ills? Fire resistance would be much easier to ensure with metal shells and housings, ceramic and glass inserts, and much more than with chemical weapons in wires! Fire safety is just an excuse, not the real reason!

I think you can skip exotic types of insulation and sheathing like silk, because now no one makes pure natural wires for a long time. Well, maybe some Kulibin uncle Vasya in his garage naked copper wire winds silk scarves, which is very unlikely :-) I suggest you dive into a little market research of alternatives to harmful PVC wires available today. I conducted a mini-research at the beginning of February 2015 by browsing popular stores of wholesalers and retailers of cable products in the Russian Federation. For installation small parts Inside the devices there is a very convenient wire (from now on I will simply call all cable products the word “wire”, let the techies forgive me, but I’m a lover of the Russian language) such as MPM and MPO. Judging by technical specifications, they are quite capable of replacing a cloud of PVC trash in modern devices for the following reasons:1. The insulation shell is made of Poly-Ethylene (PE), I will talk about it below; 2. Availability of different colors and sizes (which is important for some modern collectors, but was absolutely unimportant a hundred years ago). Poly-Ethylene (PE) does not contain chlorine, has the simplest chemical formula of all plastics known to our industry, and is the safest plastic known today. Yes, of course, when burning, even PE will smoke nasty chemicals, but this chemical will be much less toxic than PVC - you will have a chance in case of a fire to run out and not die in a few days from poisoning, as happened with visitors to the Lame Horse club , most of who died not from burns, but from poisoning by combustion products of Foam-Poly-Styrene (PPS). The destruction temperature of PE is approximately 80 degrees Celsius. The melting point is 120 degrees, lower than 150 degrees for PVC, but there is a greater chance of survival :-) MPO wire has more thick layer isolation. In all other respects, these two wires are the same. However, finding this wire on the open market (for mere mortals, not legal entities with wholesale purchase volumes) I failed. Here are the alternatives to MPO and MPM that I found. Let's start with “weak” wiring, such as telephone lines. 1. Wire "TRP". Has 2 copper cores, insulation made of transparent or colored PE. It is quite suitable for installation purposes if you need a cross-sectional area of ​​0.4 or 0.5 square millimeters (sq. mm.). If you need one wire, you can split (cut) the pair lengthwise.2. Wire "PRPPM". It also has 2 cores, you can also halve it if desired. The color is only black. But everything is made from Poly-Ethylene.3. Wire "P-274M" is used for field communication. 2 cores of 0.5 sq. mm. Also everything is made of PE. Black color. Each of the two cores contains 3 steel cores and 4 copper cores. Next comes a specific cable for relaying, but if you have nothing else, it can also be adapted somewhere.4. Wire "PTPG". Two wires, transparent, again, all made of PE. Wires made of galvanized steel. It can also be suitable for those purposes where a transparent shell is important. Next - power cables, suitable for a household network with an alternating voltage of 220 volts.5. Runway wire. One core, black, PE, nominal AC voltage- up to 380 V.6. Wire "PRKA". One core, rated alternating voltage - up to 660 V; insulation made of Silicon-Organic-Rubber (Silicone) of increased hardness. Operating temperature: from -60 C° to +180 C° (heat resistant)! Ideal choice for replacement in all our residential 220-volt wires. And it costs cheap (1 meter with 1 residential section of 1.5 sq. mm costs about 13 rubles today). Why weren't things made from it from the very beginning? Riddle...7. Wire "PVKV". One core, again 660 volts alternating, also made of Silicon-Organic-Rubber (Silicone) of increased hardness, also heat-resistant up to 180 degrees Celsius, good price.8. Wire "RKGM". 1 core, 660 volts alternating, heat-resistant (up to +180 degrees), insulation made of Silicon-Organic-Rubber (Silicone), braid (outer shell) made of fiberglass (!), impregnated with heat-resistant varnish. And finally, a wire for extreme sports enthusiasts. 9. Wire "Energoterm-400". Insulation made of mica-containing heat-resistant tapes, winding with glass tape, up to 660 volts alternating. Operating temperature: from -60° C to +400° C! The price, however, is appropriate. So, having taken a brief excursion into the history of materials related to electrical conductors, we can clearly see where and because of whom this world is heading. Polyethylene wires can be used in “light” devices where the risk of fire is almost impossible (for example, a manipulator such as a mouse, keyboard, etc.). Other devices can use silicone heat-resistant insulators! Even if this is not enough, you can improve the design of the devices - use additional metal, ceramic or glass screens, shells and casings. Yes, the weight of the devices will obviously be greater, but environmental friendliness will increase significantly. I wish our industry and our government to quickly realize this and understand what needs to be done.

Periodically, a situation arises when the wire heats up; very few people know what to do in this case. First you need to find out what is the reason for this phenomenon? The fact is that the electrical energy passing through the wire is partially converted into heat. The magnitude and speed of this transformation directly depends on the power of the electric current. The higher the power, the more the wire can heat up and cause undesirable consequences.

Overheating of wires - melting of insulation

First of all, the insulation of the wires melts, and they become very dangerous, especially for workers who repair and maintain the lines. When an electric current with a constant value passes through the cable, heating occurs only to a certain limit. Thus, if you control the current value, you can ensure the safety of the insulation. Severe overheating of the insulation can cause ignition and lead to a fire. If wires without insulation overheat, they may develop too much tension, leading to...

In modern conditions, the laying of electrical lines, in most cases, is done with wire with copper conductors. Aluminum wires, due to many negative qualities, are practically not used, although they are found in old lines. The ideal option is to use multi-core cable, capable of withstanding significant short-term loads.

It should be remembered that overheating of the wire in many cases does not occur along the cable line, but in places of twisting and soldering in sockets, junction boxes and electrical panels.

Prevention of overheating of wires

If the wire heats up, you need to know to eliminate this problem. To avoid emergency situation on cable lines, you need to follow certain simple rules:

• To avoid damage to the insulation, you need to choose the correct cross-section. The electrical line must be laid in such a way as to prevent it from being accidentally damaged by any sharp objects during repair work. For this purpose, a diagram of electrical networks is drawn up. In addition, the joints must be reliably protected from moisture.
• The cable must be laid in a special box, or under baseboards. In this case, it can be easily inspected and replaced.
• When, it is necessary that the places of soldering and twisting be placed in such a way that they are completely accessible for prevention or repair. Typically, distribution boxes are used for these purposes.
• The ends must be thoroughly cleaned and then securely insulated. It is at the junctions that points of increased resistance are created, causing overheating.

Why does the outlet get hot?

One of the sources of fires in housing and communal services and cultural and educational, office and administrative buildings are electrical networks.

Currently, the most common brands of electrical wires in the housing and communal services sector for supplying electricity to consumers are: cables with PVC insulation(Table 1)

Table 1

Brief characteristics of the physical and mechanical properties of polyvinyl chloride

Polyvinyl chloride ( PVC) is a thermoplastic polymer that is solid at ordinary temperatures and amorphous, i.e. a shapeless structure in which its properties (mechanical, electrical, etc.) under natural conditions are the same in all directions.

The electrical insulating properties of PVC are relatively low (26...28 MV/m). However, due to a number of positive characteristics (resistance to acids, alkalis and salt solutions), PVC has found wide use as an insulator, in particular, in the insulation of electrical wires and cables.

The long-term operating temperature of PVC is 80...90°C. Above 1-40°C, PVC begins to decompose with the release of hydrogen chloride. Wherein physical and mechanical properties PVC deteriorates: volumetric decreases electrical resistance and mechanical strength (the relative elongation at break decreases and fragility increases). The released hydrogen chloride has a harmful effect on humans (especially during fires) and causes corrosion of materials located nearby. At elevated temperatures, PVC burns, but does not support combustion. The self-ignition temperature of PVC is 454...495°C. When PVC burns, thick and dense smoke is produced and a large number of heat. The calorific value of PVC insulation is 5949 kcal/kg. For comparison, we can provide data on the calorific value of wood, in particular oak, - 2500 kcal/kg. This means that when 1 kg of PVC insulation is burned, 2.4 times more heat is released than from high-calorie wood.

A noticeable deterioration in the properties of PVC is observed when exposed to light, mainly due to ultraviolet radiation. To protect PVC from light exposure, various types of pigments (soot, titanium dioxide, etc.) are added to it, which, being a screen, absorb ultraviolet radiation.

Main causes of damage to PVC insulation

The main causes of damage to the insulation of PVC electrical wiring and cables include:
manufacturing defects;
mechanical damage;
natural aging of insulation during operation;
light exposure;
current overload of wires;
exposure to an aggressive environment.
Factory defects in PVC insulation are mainly associated with a decrease in the plasticizer content in the polyvinyl chloride plastic compound. Thus, according to data, reducing the plasticizer in IRM-40 plastic compound to 20 parts by mass leads to the formation of cracks in the insulation at a temperature of -15°C during installation bending of wires.

Behind last years at hidden gasket electrical wiring in residential buildings power cables are laid in special flexible corrugated pipes with high level insulation resistance (at least 100 MOhm and 500 V for 1 min) and fire resistance (the ability to ignite at a temperature of at least 650°C). Unfortunately, some Ukrainian manufacturers deliberately violate the production technology of these products, producing pipes from recycled materials, changing physical characteristics products. According to the data, this leads to increased fragility of the material and loss of strength during temperature changes, which, of course, negatively affects the durability and safe operation electrical networks.

Mechanical damage to insulation occurs mainly during transportation and careless storage of cable products and installation of electrical wiring (especially on bends when laying through walls and interior partitions).

In our opinion, the aging of insulation during long-term operation is the main cause of fires. The underlying process that leads to insulation aging is the natural removal (loss) of plasticizer from PVC plastic. The further performance of the electrical wire insulation depends on this.

As PVC insulation ages, a decrease in the cold resistance of cables and wires is observed, which may indicate a failure of their operation. In case of mechanical stress on electrical wiring or cable when low temperatures(-1 5°C or less) cracking of the insulation is observed. In addition, during long-term operation of electrical wires, a change in the geometric dimensions of the insulation is observed, mainly a decrease in the outer diameter. Studies have shown that what occurs during aging PVC insulation the loss of plasticizer is accompanied by an increase in density and shrinkage of the insulation. Obviously, measuring the outer diameter of electrical wiring during operation under certain conditions can serve as an indicator for diagnosing PVC insulation.

Light effects on insulation can be explained by penetration ultraviolet rays in the thickness of thermoplastic polymer PVC. The author's research shows that in the absence of light exposure to electrical wires, the relative elongation and strength of PVC insulation decreases slightly. Noticeable difference in mechanical characteristics There is no insulation pigmented in different colors. The most effective in terms of optical fastness is Blue colour, least - red and natural. Pigmentation of insulation in various colors subject to atmospheric aging (on outdoors), protects it from destructive aging for no more than 2...2.5 years. When exposed to atmospheric conditions, cracking in the microstructure of the material occurs intensively. Not only the number of cracks is growing, but also their sizes. Intensity solar radiation decreases from the outer surface to the inner one. All this leads to a decrease in both mechanical and electrical characteristics of the insulation. Thus, we can conclude that laying electrical wiring openly in the air is undesirable. And if this cannot be avoided, then electrical wiring and power cables should be laid in pipes (metal, smooth or corrugated from plasticizer).

Current overload in the wires of the electrical network can occur mainly in two possible frequent cases: during a short circuit due to the tight contact of the phase and neutral wires exposed for any reason and during mechanical, even minor damage to the insulation or due to its aging.

In the first case, as a result of a direct short circuit, the electrical network is protected by the device protective shutdown(of course, with his reliable operation). The possibility of fires in such cases is, as a rule, unlikely (of course, if there are no flammable objects at the site of the short circuit). In the second case, the development process current overload happens gradually. And this is very dangerous, since the protective shutdown device may not immediately react (or even not have time to do so at all) to a current overload.

Note. The allowable heating of the conductor is not more than 55°C. In cases of active loads, it is necessary to use a neutral core of the same cross-section or a symmetrical 4-wire cable.
Table 2

Observations have established that even microscopic damage to the insulation causes a point leakage current and local heating of the insulation. Over time, dust and other types of dirt accumulate between conductors that have mechanical damage to the insulation, and insects settle in a place insulated from leakage currents. All this, when moistened, becomes an electrically conductive medium. In subsequent operation of the electrical wiring between phase and neutral wires arises electrical circuit: first, the insulation is charred at the point of damage, the leakage current and circuit temperature increase, which ultimately leads first to a local ignition of the insulation, the appearance of a stable arc and a fire.
In this regard, it is impossible not to note cases of fires when the electrical network is overloaded due to the fact that instead of calibrated fuse links, the notorious “bugs” with cross-sections significantly exceeding the cross-sections of the calibrated inserts are installed in the fuses. In this case, when the electrical network is overloaded, the insulation ignites and a fire becomes inevitable. It has been experimentally established that a current of 300 mA releases energy that is insufficient to ignite standard building materials. Therefore, a residual current device with such rated current leakage is an effective means of fire protection, especially in areas where flammable materials are stored.

Exposure to an aggressive environment. This may include:
humidification of wires;
overheating of wires from extraneous heat sources;
actions of rodents;
saturation of indoor air with toxic gases, etc.

Wetting of the insulation occurs when laying electrical wiring in rooms when the requirements of the PUE are violated, which stipulate that when crossing wires or running in parallel, for example, with water pipes, the distance between them should be at least 50 mm. The author of the article has already analyzed the cause of the accident when, as a result of constant condensation on the surface of the water supply PVC pipes The insulation of the wire touching the pipe has become unusable over a long period of use and has ceased to provide resistance to electric current.
When laying electrical wires near extraneous heat sources, a decrease in the outer diameter of the wire with PVC insulation is observed, which accelerates the aging process.
Damage to the insulation of electrical wires and cables by rodents is observed in cable ducts located on open switchgears of substations and in basements residential buildings.

In rooms with high air saturation with toxic gases, such as cowsheds and, especially, pigsties and poultry houses, mines, etc., they are used special methods laying wires and cables with protected insulation. Due to the limited scope of the article, this issue is not considered by the author.

Review of new technologies for laying and protecting electrical wiring and cables

It is obvious that in order to prevent fires, the insulation of electrical wiring and electrical power cables must have a combination of fire-fighting properties and, most importantly, the ability to prevent the spread of combustion, emit smoke, corrosive substances and toxic products when exposed to an open flame.

Some foreign companies produce and supply power cables with single-wire and multi-wire copper conductors (Fig. 1). The insulation and outer sheath of the cables are made of self-extinguishing and highly flammable PVC plastic. Limits permissible temperature cable environment: with installation and operational bends from -5°С to +50°С; subject to operation in a fixed (stationary) state from -30°C to +70°C. The cable is recommended for use in power supply and distribution and power installations, connecting houses and street lighting. Maximum permissible stresses:
single-phase AC systems - 1.4 kV;
three-phase systems with a grounded conductor - 1.2 kV.
Test voltage 4 kV, alternating current 50 Hz.

XLPE cables

A new generation of power forces is known low voltage cables from so-called cross-linked polyethylene. Their characteristics: they are resistant to aggressive soils; more environmentally friendly and reliable in operation. Their damage rate is reduced to a minimum. XLPE insulated cables(Fig. 2) are much more reliable and require lower costs for installation, reconstruction and operational maintenance. One of the main advantages of cables with XLPE insulation is the large throughput by increasing the permissible core temperature. Additional load currents, depending on installation conditions, are 15...30% greater than for paper-insulated cables. This is achieved by increasing the operating temperature of the cores to 90°C (instead of 70°C) and high thermal stability current during a short circuit in the electrical network.

The cable is also noted for its high moisture resistance, which does not require the use of a metal sheath. However, when introducing these cables into production, one should also take into account the opinion and concerns of some domestic experts in the field of cable products regarding the fire safety of such cables. Obviously, in all cases, when purchasing such cables, one should require certificates from suppliers for their quality.

Protection pipes and laying systems

An important role in ensuring the safe and long-term operation of electrical wires and cables with PVC insulation is played by protective pipes(metal and plastic). So, plastic, smooth, hard and corrugated are recommended flexible pipes made of PVC material, designed for the convenience of laying power and signal electrical networks indoors and outdoors. The main advantages of the material of such pipes (Fig. 3) is that it does not support combustion, its degree of protection is IP65. Installation temperature -5...+60°С, operating temperature -25...+60°С, melting +650°С. Insulation resistance more than 100 MOhm.
Laying electrical wires and cables in plastic pipes protects them from dust, dirt, ultraviolet radiation and mechanical influences. The pipes have successfully passed certification tests in domestic state laboratories and comply with clause 2.1. GOST 12.1.044-89 according to the flammability group as “heavy flammable”

In conclusion, it can be noted that to ensure trouble-free and long-term operation it is necessary to carry out in accordance with requirements of the PUE in a timely manner, mandatory comprehensive preventive tests of electrical networks and electrical equipment, in particular measuring the insulation resistance of power and lighting electrical wiring, checking the values ​​of short circuit currents of the phase-zero loop, testing protective equipment, as well as measuring the resistance of the main grounding conductors and grounding lines of the equipment.
We can also recommend thermal imaging monitoring of the thermal state of electrical equipment, which has become widespread in recent years. The use of this method of control makes it possible to detect defects in insulation of wires and cables with elevated temperatures in places of damage at the earliest stage of their occurrence, as well as to foresee the degree of its subsequent development and develop recommendations for eliminating such defects.

IN modern world There are many ways to transmit something wirelessly, but wiring is still used, and quite often. So, after reading the article, you will learn everything you need about wire insulation.

Materials used to insulate wires

There are two types of wire insulation materials. The first is PVC, and the second is insulated with rubber. Both have their pros and cons.

PVC (polyvinyl chloride) insulation

Another name is vinyl. This material is widely used in wiring insulation, because It is resistant to alkali and acid, does not allow current to pass through it, and is also insoluble in water. These properties guarantee good protection wiring from external influences.

PVC is used to create the sheath of both wiring and cables. On this moment They even produce special PVC tape for insulation individual parts wires.

The price of PVC insulation can be considered a plus. Another advantage of this type of shell is that the polymer does not burn and does not react to sharp changes temperatures

Even during the production of this material, plasticizers may be added to it. Because of them, the resistance to alkali and various acids decreases, however, thanks to them, the wire sheath becomes more elastic, and resistance to ultraviolet radiation also appears.

Rubber insulation

Rubber casing is used in industrial areas. It has many advantages, which include:

• This type of shell is moisture resistant.
• Rubber insulation has significant elasticity.
• If you measure the insulation resistance, you can see that it is quite high.
• This shell does not respond to high temperatures.

In the production of rubber shells, both natural and artificial and synthetic materials are used. The latter serve for a long time, are resistant to various chemicals and high sub-zero temperatures.

Another advantage of this material is its elasticity, thanks to which you can conduct wiring with a rubber sheath anywhere. Over time, the rubber will begin to age, causing the shell to crack. This means you can easily get electrocuted.

If the shell will be exposed to high temperatures, it is recommended to use vulcanized rubber for insulation. More often, wiring with this type of sheath is used due to its elasticity. That is, where it is necessary.

Wire insulation methods

There are several ways to insulate wires. Today we will talk about the most common ones, there are only four of them:

• Insulation using special tape.
• Sheath PVC type
• Sheath for wiring using heat shrink tubing.
• Insulation using terminals.

Special tape for insulation

Another name is electrical tape. Every home has it. If you don’t have electrical tape on your farm, it won’t be difficult to purchase it, because... it's inexpensive.

It is usually used to partially insulate a wire. Often in some place the shell bends or cracks on its own, for example due to old age. Today we will not talk about how to strip wires of insulation, but will consider cases of spontaneous damage to the wire sheath.

I would like to note that it is necessary to wind the electrical tape at an angle, first in one direction and then in the other direction. To understand how to do this correctly, you should look at a photo of insulating wires using electrical tape.

When heated too much, the tape will begin to melt, although this disadvantage has a plus in the form of moisture resistance. Also, the thickness of the wire insulation in this place will be greater.

There is cotton tape for creating a sheath for electrical wiring. On the contrary, it can withstand high temperatures, but is not moisture resistant.

Heat shrink tubing

The material from which these tubes are made is polymer. I note that it is best to use this type of shell on low-voltage equipment, when the voltage is not higher than 1 kV.

In order to use this method of creating a casing for electrical wiring, you need to follow some steps:

• First you need to prepare a piece of heat-shrinkable tubing. To do this, measure the exposed section of the electrical wire, after turning off the electricity. We cut off a piece of tube, it is better if it is a little larger than needed. About 2-3 centimeters.
• Next, take a piece of tube and put it on the end of one of the wires.
• After completing the second step, you need to twist the wiring.
• The last step is to transfer the heat-shrinkable tube to the junction of the wiring and use a hair dryer to secure the result.

After these steps, the heat shrink tube will be pressed tightly against the wiring. If you don't have a hair dryer, a lighter will do. It should be carefully kept at a small distance from the junction of the wires.

This type of insulation is more convenient than electrical tape. It also adheres better to electrical wiring. However, if you need to remove the heat shrink tubing, you will have to clean it off.

There are different tubes. It all depends on the desired temperature that the tube must withstand, as well as on the voltage. To find out the characteristics of the tube, you need to look at the markings that manufacturers put on at the factory for the manufacture of these products.

There are tubes of different diameters, colors, and also for certain cable sections. This plus allows you to select the most suitable heat shrink tube.

Wiring insulation using terminals

To create the shell, terminals are used - these are small clamps that are widely used, including for connecting wiring. Terminals can and should be used to insulate wiring in distribution box.

It is better not to use terminals together with aluminum wiring with screws, because... Due to strong pressure on the wire, this metal will begin to leak. A short may eventually occur due to the weakening of the connection and increasing resistance. If you do insulate using terminal blocks, do not forget to inspect the electrical wiring connection at least once a year.

It is strictly prohibited to connect wiring made of materials such as copper and aluminum using twists. Due to the incompatibility of these metals, at least a short circuit will occur, or at most a fire. This will put your life at risk.

Important! After finishing, be sure to check the wire insulation.

So today you have learned everything you need to know about insulating electrical wiring. We examined the materials and methods for creating a wire sheath. I hope that after reading this article, you have decided which wire insulation is best for you.

Photo of the wire insulation process

Although more and more wireless devices are appearing every day, wires are still the main means of transmitting electrical current.
Various types of insulation are used in the production of wires and cables. Each type of wire insulation determines the scope of application of certain cable products.
During the installation of wires or cables, it becomes necessary to insulate the places where they are connected or connected to electrical appliances. How can this be done?

Previously, paper was used to insulate cables, but now, with a huge amount of modern materials it is used extremely rarely. The paper was wound in several layers, soaked in oil and rosin. This helped resist the effects of moisture.
In production conditions, reliable insulation is made from fluoroplastic. PTFE tapes are wound around the wires and baked. A shell is formed that is not afraid of not only chemical or temperature, but also mechanical influence.

PVC (polyvinyl chloride) is also called vinyl insulation. Polyvinyl chloride is resistant to alkalis and acids, does not conduct current, and does not dissolve in water, therefore it is widely used in the manufacture of insulating materials. Used for the manufacture of insulation for wires and cables. PVC electrical tape is also produced to insulate wire connections.
One of advantages of PVC insulation - its cheapness. Polymer insulation is quite elastic and resistant to temperature changes and does not burn in air. In production PVC materials can add plasticizers, they slightly worsen the insulating properties and resistance to chemicals, but increase elasticity and resistance to ultraviolet rays.

If the connecting cable uses vinyl insulation covering the wires, then . It can consist of 2-5 aluminum or copper cores. The shell can be vinyl or rubber.
The service life of PVA cables exceeds 6 years. During this entire time they do not require replacement. They are resistant to corrosion and mold, withstand frosts down to -40° and heat up to +40°. Their operating resistance is about 270 Ohms per 1 km.
Cables with PVC sheath and aluminum conductors are used in urban electrical networks, for supplying electricity in production and in residential apartment buildings. PVA cables with copper conductors have become widespread when connecting almost all household appliances and other equipment to the network. low power, they are used for electrical wiring in private houses and apartments.

Application of rubber insulation

In industrial applications, rubber sheathing is often used to insulate cables. To her positive qualities include:

• Moisture resistance.
• Elasticity.
• High resistance.
• High temperature resistance.

Rubber insulation is made on the basis of natural and synthetic materials. High-quality synthetic braid has best performance— ages longer, withstands the effects of aggressive chemical substances and negative temperatures. The rubber bends easily, so the wires can be laid in any conditions. But over time, the rubber insulation ages, cracks and begins to conduct current. In high temperature environments, it is recommended to use vulcanized rubber for insulation. Rubber insulated cables are most often used where cable flexibility is required. These are power cables of cranes, descents to control panels of crane beams. Connecting welding transformers, both from the power side and from the low voltage side to the electrode “holder” and the neutral wire.

Wire insulation methods

Insulation electrical wires designed mainly to ensure that there is no leakage of currents. For this reason, it is made from non-conductive (insulating) materials. Depending on the operating conditions and design features of the cables or wires, the type of insulation is selected. At electrical installation work The following types are used.

• Insulating tape.
• PVC tube.

Insulation tape

Insulating electrical wires with electrical tape does not lose its relevance. Insulating tape is inexpensive and is sold at any hardware store in a wide variety.

It must be wound at an angle, starting from the edge of the original wire insulation. With a parallel connection, an empty winding tube is made at the end of the twist, bent and continued movement in the opposite direction.

Common PVC insulating tape melts when exposed to high heat, but does not allow moisture to pass through. Cotton insulating tape, on the other hand, can withstand high temperatures, but dries out over time and can peel off when wet.

PVC is also used to make cambrics - tubes for insulating wires and cables. In order for the tube to fit tightly, you need to choose the correct diameter of the tube.

How to properly insulate twisted wires, watch the video:

Heat shrink tubing

Heat-shrinkable tubes are made from polymers (PVDF, PET, silicone and others). They are used primarily on low-voltage equipment, when the voltage direct current does not exceed 1 kV.

If you want to use heat shrink for wires, then you need to perform a number of steps.

1. Cut off a piece of heat-shrink tubing that completely covers the exposed section of the wire (connection), with a margin of about 2 cm.
2. Then you need to put a tube on one of the ends of the wires to be connected.
3. Twist the conductors.
4. After this, the tube is moved to twist and heated with a construction hairdryer.

As a result of heat shrinking, the insulation is pressed tightly against the wires. If you don’t have a hairdryer, you can use a lighter, carefully holding it at a short distance.
This is done when insulating twisted wires connected in series. If the connection of wires is parallel (the so-called bundle of wires), then first twist it and then put on the tube.
In most cases, heat shrink tubing is easier to use than electrical tape. The tube can be quickly put on; it fits the wire connection more tightly and does not unwind. But it is more difficult to remove it if necessary. You just have to peel it off or cut it off.
Manufacturers put markings on the tubes that show what temperature it can withstand and what voltage it is suitable for. Tubes are produced in different diameters and colors, so for different brands and cable sections it is always possible to select the appropriate insulation and color marking.
How to properly insulate wires using heat shrink tube, watch the video:

Terminal Applications

It is used as insulation in a dielectric shell. Terminals are sold in the form of caps or blocks that clamp the wires. If you want to insulate the wires in the distribution box, then the choice of terminals is one of the connection options.

But a lot depends on the load. At high loads, it is better to use soldering for connections, and put an insulating tube on top.
Tightening aluminum wire with screw terminals is not recommended because aluminum will begin to leak under constant pressure. As a result, the connection weakens, resistance increases and a short circuit occurs. If you decide to connect aluminum wires terminals with screws, then an inspection must be done at least once a year.
Connecting copper and aluminum wires by twisting is unacceptable. When current passes between metals, an electric potential arises, the wires heat up, which can cause short circuit or worse - a fire.
However, in one case, twisting can be done - if copper wire cover with tin-lead solder (tin). But more often they use for joining both aluminum and copper. terminal blocks or (screw, nut and washer).

Insulation resistance

Between cable cores and external environment Current leakage may occur. One of the goals of isolation is to prevent their occurrence. The value that shows how well a wire is insulated is called insulation resistance.
The higher the resistance, the more reliably the wires through which current flows are protected. Each brand of cable has its own value for this indicator. Insulation resistance is established by GOST or technical specifications(THAT).
The resistance is measured at a given temperature (about +20°) with a special device (megaohmmeter). If measurements are taken at negative temperatures, then its value will be underestimated, and in the case of hot conditions – overestimated. After readings are taken, they are entered into the “Wire Insulation Measurement” protocol, compared with standard values ​​and conclusions are drawn about whether the cables are suitable or not for further use. Electrical wiring that fails the test must be repaired or replaced. The periodicity of testing wire insulation is stipulated by the Rules. Also, checking the insulation of wires is carried out after completion of electrical installation work, repair work, after the wiring gets wet or overheated.
How to correctly check the insulation resistance of conductors using a megohmmeter, watch the video: