Zone cable for heating. How is a resistive heating cable made? Benefits of a roof heating system

Sectional cable

In the classical concept, a cable is a device for transporting electricity or an electrical signal from point “A” to point “B”, however, with heating cables, everything is a little different. Their main task is to radiate heat throughout its entire length or in certain areas. There are currently three types of heating cables on the market: resistive, zonal and self-regulating heating cables. Of these options, the latter is the most expensive, but often the most promising in terms of use in almost all areas.

Principle of operation

The difference between a self-regulating cable and a resistive and zonal cable lies in the design and principle of operation. In short, a resistive cable is a long boiler, with no way to shorten it. In this case, current conductors are heating elements.

Resistive cable.

The zonal heating cable can be cut the current in it is supplied through parallel conductors, between which a heating element of high resistance wire is wound. Through certain sections, this wire touches one of the conductive cores and provides heating of the "zone" section

Zone heating cable device

The self-regulating heating cable is a smarter design. Inside the braids and screens (depending on the modification) is the main element of the cable - two copper conductors, between which is located heating matrix. It looks like ordinary dense polyethylene, but it has qualities that bring cable heating to a whole new level. This matrix is a semiconductor, and it changes its properties as the temperature changes.

Self-regulating cable. What is inside

Underfloor heating example

Let's say you make underfloor heating with such a cable. But in different rooms, usually, there is a different initial floor temperature, for example, in the bathroom it is one, and in the hallway it is different. Moreover, in the same room, the initial floor temperature can vary significantly, and if you use a resistive or zonal cable, you can achieve a comfortable floor balance, but only by dividing the rooms into "cold" and "warm" zones. To do this, it will be necessary to install additional thermostats and thermal sensors ... Not a very pleasant prospect, especially considering the shortcomings that we will write about below.

Arrangement of a warm floor with a cable

A self-regulating cable allows you to exclude the thermostat from the circuit altogether. He himself regulates where it is necessary to heat more strongly, and where weaker due to its matrix. Let's say you came home from the cold and left your snow-covered boots on the floor with a self-regulating cable. So, the area with the boots will heat up more than all other areas exactly until it heats up your boots to the set temperature.

This significantly saves electricity due to the fact that it heats up only the area that needs heating.

Plumbing example

Using a heating cable to heat a water pipe

So that in severe frost the water in the water supply does not freeze, you wrapped it. Any valve (water meter, coarse filter, etc.) has a complex geometric shape that does not allow the cable to touch the metal directly. If you use a self-regulating heating cable, then the main electricity consumption will go to heating exactly those areas that touch the metal, because. where heat transfer is most pronounced. At the same time, the efficiency of the cable increases several times compared to other cable heating systems.

Roof heating example

When heating the roof from icing, you will almost never be able to guess in which area there will be the most dangerous area for the occurrence of icicles. By using this solid state matrix cable, you can be sure that the area with the most ice/water will be warmed.

Roof heating with self-regulating cable

Helpful Hint: If you are going to use cable for roof heating, you should choose a type that is UV resistant and can handle high temperatures well, as the temperature of the roof in summer rises to 50-60 degrees. For example, Raychem ETL-10 can withstand temperatures of 65 degrees.

Advantages

In addition to the main ones listed, there are a few more "chips" that complete the picture.

The cable can be cut to any length, starting from 20 cm. This will not affect its properties in any way. There will be no cold areas, as well as areas with high temperatures
Can be crossed during installation. This is especially true when heating plumbing units. The cable at the crossing point does not overheat and does not fail
Remains functional when broken. If for some reason the current-carrying core inside the cable breaks, then it will still heat up to this point
In the case of heating pipes with a self-regulating cable, there are modifications to be placed inside the pipe, which significantly increases the efficiency
Does not require a heat sensor and thermostat. Plugs directly into an outlet or switch
Ease of connection, there are special kits for connecting to electricity, inside the pipe, sealing the end of the cable.

Flaws

Well, where do without them? The main one is, of course, the price. Depending on the modification, it is 2-3 times more expensive than the same power/length for resistive and zonal heating cables.

The second significant drawback is that a self-regulating cable cannot quickly heat / thaw a particular area. It just won't get hotter than the rated temperature. This cable is designed more to be on all the time, good, low power consumption allows you to survive it painlessly for your wallet

The third drawback, but rather a feature of this heating element, is an increased starting load. Let's say your cable is marked 50W m.p. (50 watts per linear meter) - this means that when the cable is connected to the network, the load will be 80-100 watts per meter until the cable warms up for the first time (1-5 minutes) - this feature should be taken into account when laying wiring of the appropriate section.

Connection

Some models of self-regulating heating cables have additional braids and protective screens. We will consider connecting a cable with two insulating braids.

We cut and remove the first insulation to a length of 40 mm;
Under it is a copper braid (ground) - we twist it into a bundle;
Under the braid there is an internal insulation - it must be stripped to the internal matrix (it is black) for a length of 30 mm;
After that, the matrix itself is carefully cut off, exposing the current-carrying wires, to the same length of 30 mm;
Heat-shrinkable tubes, 25 mm long, are put on the wires (current-carrying and ground), they are seated with a hair dryer, but most often with a lighter J;
The current-carrying wires can then be combined with another heat shrink tube and seated together;
The cable is ready to be connected.

Cable cutting procedure

As you can see, there is no fundamental difference in connecting this cable from a conventional power cable with grounding. There are differences in the termination of the termination of such a cable. Because the heating cable is the final element and is not connected to anything - its end must be properly terminated. Manufacturers of self-regulating heating cables sell special kits for cutting and terminating them. The work is as follows:

The first layer of insulation is stripped to a length of 20mm;
A heat shrink tube is put on the copper braid 10 mm longer;
After shrinkage, until the tube has cooled down, the free end is clamped with pliers;
All this after cooling is smeared with a layer of silicone sealant
Another larger diameter heat shrink tube is put on this entire structure to overlap the inner tube by 20 mm in both directions.
Shrinks with a hair dryer until extruded silicone appears at the end.
The tube is bent and clamped with pliers until it cools down

The order of work on the termination of the cable

After such manipulations, the cable can safely go to the most dangerous and wet places. He is no longer afraid of moisture.

The "warm floor" heating system has long proved its efficiency and comfort, therefore it is widely used all over the world. The fundamental question is, what source of energy is used to produce heat? As long as there is a modern difference in energy prices, it is cheaper for a person to burn solid fuels or hydrocarbons, heat water with the heat received, and then pump it through the pipes of a warm floor. But it is much more convenient to use a heating cable as a warm floor, rather than a complex system of pipelines, collector assemblies and pumps. The dominance of hydrocarbons in the energy market will not last forever, and more convenient for transmission and use of electrical energy will inevitably be used for heating more and more.

Heating cable as a warm floor

Theoretical educational program of cable heating

As is known from the school physics course, an electric current is nothing more than a directed movement of charged particles under the influence of an electric field. If any substance has such free charged particles that can move, then it is called a conductor, and if not, then a dielectric. Those substances that can change the number of particles depending on some external factors are called semiconductors. In common metals, charge is carried by electrons, in electrolytes by cations and anions, and in gases by electrons and ions.

Any conductor does not allow the flow of charged particles to pass freely, but exerts a certain resistance to it, which is physically explained by the fact that the particles collide with the atoms of the conductor, “loosen” them, losing their energy, and as a result, the energy of the electric current is partially converted into the internal energy of the conductor, which expressed in its heating.

The ability of a conductor to resist the flow of electric current is quite logically called resistance.

Heating cables are based on the property of conductors with resistance to heat up when an electric current flows.

As can be seen from the formula, the resistance depends on the resistivity, which refers to the reference data (it is unchanged for a particular material), the length of the conductor and its cross-sectional area. The specific resistances of various conductors can be viewed in the table.

Resistivity of main conductors

Obviously, for the transmission of electrical energy, it is necessary to use materials that have the lowest resistivity - then the percentage of losses will be low. These are aluminum, copper and steel of large section for the manufacture of cables, wires, power lines. In electronics, silver, gold, tin, platinum are used.

If the conductors are used for heating, then the properties that are harmful to the transfer of energy loss turn out to be very useful for generating heat, which is why materials with high resistivity are selected: tungsten, nichrome, galvanized steel, various alloys that the heater manufacturer can keep secret.

To estimate the amount of thermal energy that a conductor can release when an electric current flows through it, the Joule-Lenz law, discovered back in the 19th century, is applied.

Joule-Lenz law

According to this law, the amount of heat Q is equal to the work A, and it directly depends on the square of the current strength - I, resistance - R, and the time interval Δt.

From the above diagram it can be seen that a current flows in a closed circuit, measured by an ammeter, and it will be the same in each of its sections. There is a heating element R in the water tank, the resistance of which is so much greater than other conductors that they can simply be neglected. According to the Joule-Lenz law, a certain amount of heat will be released at the resistance R, it will begin to heat the water in the tank, while no heat will be released in other parts of the circuit. A rheostat can change the current in the circuit, and the amount of heat generated will change accordingly.

Scheme of an experiment confirming the operation of the Joule-Lenz law

It is the effect of this law that we see on the example of electric kettles, irons, boilers, where the resistance of their thermoelectric heaters - heating elements, is much greater than electrical wiring. Therefore, they give off more heat. The heating cable is the same heating element, only having a longer length, so heat is not released locally, but along the entire length of the cable. The heat released by the cable is transferred to the building structures, including the floor covering. Heating cables can be laid in the screed material, in tile adhesive, in special metal assemblies. Leading power cables with low resistance are called "cold" or mounting ends.

Classification of heating cables

It would seem, what is easier? You need to take a material that has a high resistivity, make a cable out of it, calculate the heat generated by it, and you're done. But in reality, this is far from the case; heating cables must meet a set of specific requirements, which will be discussed below.

In cable heating systems (KSO), completely different in design, materials used, cable power density can be used, depending on the purpose:

Room heating. First of all, the "warm floor" system is used, but warm walls and even a warm ceiling are also used. Usually electric underfloor heating is made for comfort or additional heating in addition to the main system. As the main source of heat, their use is not recommended due to unprofitability and in most cases is unacceptable, since no power supply organization will issue a permit for the allocated power.

On the warm floor it is comfortable not only to walk, but also to sit on it

Heating of roofs and gutters is most effective with heating cables, as they save you from costly repairs to the roof, and also eliminate injuries from falling icicles.

Roof heating prolongs its life

Heating of the porch, stairs, ramps, entrance to the garage, space under the gate of the entrance to the territory of the house. In winter, the comfort and safety benefits of using CSR in these areas are tangible.

On the heated porch it will never be slippery

Heating of pipelines in private houses. Pipes must always be laid below the freezing depth of the soil, but it happens that at the exit points, passage through the foundation, even thermal insulation does not help protect pipes from freezing. Heating cables are your best bet.

Pipe heating

Resistive heating cable

The very name of this type of cable means that it is a resistive load - a kind of elongated conductor with a constant resistance, which is greater than the resistance of "cold cables": power and installation. Heating occurs with conductive copper or special alloy heating wires enclosed in insulation. Over the insulation, a screen made of copper braid or foil sheath is necessarily applied along with a drainage core.

The screen performs very important functions:

The screen reduces electromagnetic radiation, which is characteristic of any conductors with current, especially alternating ones.
The shield is connected to ground (PE conductor), which is part of the potential equalization system (PSS). If an insulation breakdown occurs, the leakage currents will close to the screen and go to the ground, which will protect a person from electric shock. In addition, this will cause the circuit breakers and residual current devices (RCDs) to operate.

Resistive cables in their design are:

Structure of resistive heating cables

Single-core resistive cable - one conductive core is used for heating. This is the most inexpensive type of heating cables and requires careful laying, since the beginning and end of this cable must converge at one point and be connected to special control devices - thermostats.
A two-core heating cable in the central part has two cores enclosed in a screen. In this case, either both conductors can be heating, or one conductor is heating, and the other is supplying or, as it is called, returnable. At the end of a two-core cable section there is a special end sleeve that connects two heating wires and insulates the cable. The advantages of a two-core cable are obvious - to lay it, you just need to lay it in a serpentine pattern, without the need to return it back to the thermostat. The level of electromagnetic radiation in a two-core cable is much less than a single-core cable, since the currents flow in the heating conductors in the opposite direction. Obviously, these cables are more expensive.

Resistive cables are sold in ready-made sections that have a fixed length, which must not be changed at all. Why? The fact is that the most important characteristic of any heating cable is the specific power released by one linear meter of the cable. It should be in the range of 10-20 W / m and in no case more, as this will lead to overheating of the cable and its failure. For example, when a resistive cable is shortened by half, the resistance is halved, which, according to the Joule-Lenz law, leads to a twofold increase in the amount of heat, and the cable material is not designed for this.

Fixed length resistive cable kit with mounting kit

The length of the section is selected based on the calculations. Manufacturers produce kits with section lengths from 10 to 110 meters, so it is always possible to select the required cable with the required power density. There are resistive cables on reels that can be cut to any length, but this is the prerogative of specialists who are able to do the necessary calculations.

Advantages of resistive heating cable:

Reasonable cost.
Permanence of characteristics.
The absence of inrush currents does not require the use of special type C circuit breakers.

The disadvantages of a resistive cable are:

With illiterate installation, there is a danger of local overheating, which will lead to cable failure.
Impossibility to reduce the length of the heating cable without changing the characteristics.
The cable must be provided with the necessary heat transfer parameters.

Resistive zonal (sectional) cable

The evolution of resistive heating cables was the invention of the zonal (sectional) cable, in which two conductors of low resistance, enclosed in insulation, pass through the center. A coil of high resistance wire is wound over the conductors. After a certain interval (usually 1 meter), this wire is connected alternately to one and then to another central conductor. Obviously, in this case, each section (zone) will be an independent heating element, similar to the parallel connection of resistors.

The resistive heating cable differs from other heating elements in its small dimensions and ease of installation. As a heating element in the device, a conductor is used, which has a high resistance. In this article, we will consider the device and the principle of operation of a resistive heating cable.

Design features

How is the conductor arranged? Its design is based on steel cores (one or two), depending on this, the resistive heating cable is divided into two types: with one and with two cores. The conductive core is insulated with a special material. In some types, the design includes two layers of insulation. A protective screen made of metal (shielding braid) is applied to the insulating material. Its purpose is protection against mechanical damage, as well as use as a ground. For complete protection, an outer protective shell is used.

The resistance heating cable with one core has one heating conductor, which occupies the entire length of the structure. The use of such a device is considered the most cost-effective, as it is resistant to high temperatures of plastic. Power is supplied from both sides of the device. Such a scheme may form some boundaries in the installation plan, since it becomes necessary to return the heating conductor to the point of its connection. There is also a need to use additional power systems.

The two-core design includes two wires: heating and current-carrying. Electric current is applied to one end of the wire, and a coupling is installed at the other end. When drawing up a project, this design option is much more comfortable to use.

Principle of operation

The principle of operation of the design is described, which states that with a uniform electric current along the entire length of the circuit, heat will be generated in any area. The higher the resistance in this area, the stronger the heat. In other words, the principle of operation is similar to an electric heater: a current flows through the conductor, which generates heat. It will be stronger if the resistance of the conductor and the strength of the electric current will be greater.

Therefore, the resistance heating cable contains a heating element which is made up of low cross-section alloys with high resistance. It is sold in a certain length, each piece of conductor has a constant resistance and the ability to release the same amount of heat.

The principle of operation of a single-core conductor is as follows: since the connection to electricity occurs from two ends, the resistive heating cable is pulled in a loop so that the two ends of the product are in one place. Such a connection is shown in the diagram below (left):

The principle of operation of a two-core resistive cable is different from the previous one. The use of two cores allows you not to bring the two ends of the product to one place. The diagram on the right shows the correct connection.

As a rule, this principle of operation makes it possible to use the device in the household and heat pipes of small dimensions. And in order for the work to take place correctly, it is permissible to use pipes with a diameter of not more than 40 mm.

Advantages and disadvantages

The principle of operation of a resistive cable has its pros and cons. The advantages of the product are as follows:

affordable cost;
simple device;
with proper installation, it lasts for several decades;
significant indicators of resistivity;
with prolonged use, the stability of the parameters is maintained.

In Heatus zonal cables, heating elements 1 meter long are located in zones. In the border areas marked with special marks, it is allowed to cut this cable. These design features play an important role: the cable can be easily cut to different lengths, which is required when installing on steps, walkways, roofs. Independence from a fixed length allows you to save on product purchases; the zonal cable took over this advantage from the self-regulating cable.

Silicone rubber is used as internal and external insulation. This material has excellent flexibility, so the elastic heating cable can be easily fixed on any difficult surfaces: valves, tanks, roofing elements and non-standard heating objects.

The Heatus zonal heating cable is reliably insulated with a silicone sheath, which allows it to be installed at low temperatures (up to -60°C). In addition, it has high heat resistance up to (+230°C), protected from chemical agents, ultraviolet and moisture.

The heating element is made of high resistance alloys (nichrome filament) and is protected by a double sheath of silicone rubber. The silicone braid of the cable also provides reliable electrical insulation. The cable is difficult to damage mechanically, but even if damaged, it does not absorb water under the sheath, like a resistive and self-regulating cable.

The zone cable has a parallel structure. This design allows the cable to maintain its full performance, even with partial damage.

Products are manufactured in South Korea under the control of the ISO quality management system.

The durability of the Heatus cable is ensured by the nickel-chromium alloy of the heating core and the parallel structure of the conductor. The zonal cable inherited the last property from resistive cables with constant power, which reliably and for a long time protect industrial and domestic facilities from freezing.

Under the Heatus brand, two modifications of the zonal electric cable are produced: with and without braid. This allows the manufacturer to offer the consumer products from various price categories. At the same time, the lower price for a zone cable without grounding does not affect its service life in any way. That is why Heatus products are so in demand in situations that require flawless operation for several decades: floor heating, ground heating in production and anti-icing.

Theoretical educational program of cable heating

Any conductor does not allow the flow of charged particles to pass freely, but provides it with a certain resistance, which is physically explained by the fact that the particles collide with the atoms of the conductor, “loosen” them, losing their energy, and as a result, the energy of the electric current is partially converted into the internal energy of the conductor, which expressed in its heating.

The ability of a conductor to resist the flow of electric current is quite logically called resistance.

To estimate the amount of thermal energy that a conductor can release when an electric current flows through it, the Joule-Lenz law, discovered back in the 19th century, is applied.

Joule-Lenz law

According to this law, the amount of heat Q is equal to the work A, and it directly depends on the square of the current strength - I, resistance - R, and the time interval Δt.

From the above diagram, it can be seen that a current flows in a closed circuit, measured by an ammeter, and it will be the same in each of its sections. There is a heating element R in the water tank, the resistance of which is so much greater than other conductors that they can simply be neglected. According to the Joule-Lenz law, a certain amount of heat will be released at the resistance R, it will begin to heat the water in the tank, while no heat will be released in other parts of the circuit. A rheostat can change the current in the circuit, and the amount of heat generated will change accordingly.

Scheme of an experiment confirming the operation of the Joule-Lenz law

Classification of heating cables

In cable heating systems (KSO), completely different in design, materials used, cable power density can be used, depending on the purpose:

. First of all, the system is used warm floor", but also used warm walls and even warm ceiling. Usually electric underfloor heating is made for comfort or additional heating in addition to the main system. As the main source of heat, their use is not recommended due to unprofitability and in most cases is unacceptable, since no power supply organization will issue a permit for the allocated power.

Heating of roofs and gutters is most effective with heating cables, as they save you from costly repairs to the roof, and also eliminate injuries from falling icicles.

Heating of the porch, stairs, ramps, entrance to the garage, space under the gate of the entrance to the territory of the house. In winter, the comfort and safety benefits of using CSR in these areas are tangible.

Heating of pipelines in private houses. Pipes must always be laid below the freezing depth of the soil, but it happens that at the exit points, passage through the foundation, even thermal insulation does not help protect pipes from freezing. Heating cables are your best bet.

Resistive heating cable

The screen performs very important functions:

The screen reduces electromagnetic radiation, which is characteristic of any conductors with current, especially alternating ones.
The shield is connected to ground (PE conductor), which is part of the potential equalization system (PSS). If an insulation breakdown occurs, then the leakage current will close to the screen and go into the ground, which will protect a person from electric shock. In addition, this will cause the circuit breakers and residual current devices (RCDs) to operate.

Resistive cables in their design are:

Single-core resistive cable - one conductive core is used for heating. This is the most inexpensive type of heating cables and requires careful laying, since the beginning and end of this cable must converge at one point and be connected to special control devices - thermostats.
A two-core heating cable in the central part has two cores enclosed in a screen. In this case, either both conductors can be heating, or one conductor is heating, and the other is supplying or, as it is called, returnable. At the end of a two-core cable section there is a special end sleeve that connects two heating wires and insulates the cable. The advantages of a two-core cable are obvious - to lay it, you just need to lay it in a serpentine pattern, without the need to return it back to the thermostat. The level of electromagnetic radiation in a two-core cable is much less than a single-core one, since the currents flow in the heating conductors in the opposite direction. Obviously, these cables are more expensive.

Resistive cables are sold in ready-made sections that have a fixed length, which must not be changed at all. Why? The fact is that the most important characteristic of any heating cable is the specific power released by one linear meter of the cable. It should be in the range of 10-20 W / m and in no case more, as this will lead to overheating of the cable and its failure. For example, when shortening a resistive cable by half, the resistance is halved, which, according to the law Joule-Lenz leads to a twofold increase in the amount of heat, and the cable material is not designed for this.

Fixed length resistive cable kit with mounting kit

The length of the section is selected based on the calculations. Manufacturers produce kits with section lengths from 10 to 110 meters, so it is always possible to select the required cable with the required power density. There are resistive cables on reels from which you can cut off any length, but this is the prerogative of specialists capable of making the necessary calculations.

Advantages of resistive heating cable:

Reasonable cost.
Permanence of characteristics.
The absence of inrush currents does not require the use of special type C circuit breakers.

The disadvantages of a resistive cable are:

With illiterate installation, there is a danger of local overheating, which will lead to cable failure.
Impossibility to reduce the length of the heating cable without changing the characteristics.
The cable must be provided with the necessary heat transfer parameters.

Resistive zonal (sectional) cable

The evolution of resistive heating cables was the invention of the zonal (sectional) cable, in which two conductors of low resistance, enclosed in insulation, pass through the center. A spiral of high resistance wire is wound over the conductors. After a certain interval (usually 1 meter), this wire is connected alternately to one and then to another central conductor. Obviously, in this case, each section (zone) will be an independent heating element, similar to the parallel connection of resistors.

Advantages of zone cable:

The same power density of the cable along the entire length.
performance stability.
When starting, it does not consume large currents.

Disadvantages of zonal resistive cable:

Danger of local overheating.
The need for heat transfer.
Higher price compared to conventional resistive cables.

Heating mats

To facilitate the process of laying a warm floor, the manufacturer makes special ones, where the cable with the required pitch is attached to the polymer mesh. It is very convenient to lay such mats on a flat base before laying ceramic tiles. They can be mounted directly into the layer of tile adhesive, this is their main advantage. True, we must carefully monitor that there are no air cavities left that will cause local overheating.

In rooms with complex geometry, it may be difficult to lay mats. This is their main drawback.

Prices for different types of heating mats

heating mat

Self-regulating heating cable

The flagship among all heating cables is the self-regulating heating cable, which can change the heating temperature, and, therefore, the heat release depending on the ambient temperature.

A special polymer matrix with the properties of a semiconductor is pressed between the two conductors. As the temperature decreases, the matrix shrinks, but many heat-conducting paths with high resistance are formed in it. The flowing current causes the matrix and cable to heat up. With an increase in temperature, the polymer expands and the number of current flow paths decreases, and, in the end, there comes a moment when the currents become negligible, which leads to the cessation of cable heating. Each section of the cable works independently.

Self-regulating cable "chooses" where and how to heat

On top of the semiconductor polymer there is a layer of heat-resistant insulation, then a copper or steel shield, and another layer of insulation. Each cable has its own linear (specific) power dependence on temperature and is selected based on operating conditions and purpose.

Advantages of self-regulating cables:

Energy savings, which occurs due to heating only insufficiently warm areas.
Independence of specific power from cable length.
This cable "forgives" installation errors. Even the overlap of the cable will not lead to its overheating and failure.

Disadvantages of self-regulating cables:

These cables have high starting currents, especially if there are long cold runs. This obliges to install class C circuit breakers, which allow tenfold current surges in comparison with the nominal one.
The polymer semiconductor matrix has a limited service life.
The high price of such cables often makes their use a dubious benefit.

Heating cable as a warm floor

When planning the arrangement in the premises, you first need to decide what function it will perform.

Heating cable for underfloor heating direct action

Direct underfloor heating is usually placed in a thin layer of screed directly in front of the floor covering, for example in a layer of tile adhesive. The main task of such floors is to quickly warm up the floor surface to a comfortable temperature of 24-27 °C. Mats with a thin cable are ideal for this purpose, as well as a resistive single-core or two-core heating cable. The required characteristics can be found in the table.

The required installed power is achieved by cable laying spacing so that as much cable is laid per square meter as will provide the required power. Depending on the area of the room, the total length of the heating cable is calculated. The method for calculating the underfloor heating is given in.

In underfloor heating with direct action, thermal insulation may not be used, or be of minimal thickness, since their task is to heat the surface, and not the main heating. When heating wooden floors, a heater is used between the lags, as well as a special metal mesh that distributes heat and a foil screen that reflects heat towards the floor covering.

Heating cable for thermal storage underfloor heating

Accumulating warm floors require mandatory thermal insulation, as they heat a concrete screed of considerable thickness: from 5 to 15 cm, which will accumulate heat. It is better to heat such floors during reduced electricity tariffs, and at other times the heat will be gradually released into the room. A thick layer of insulation will significantly reduce heat leakage down.

Such floors are best done in those rooms where coatings with high thermal resistance will be laid: parquet board, laminate, carpet. Then the heat transfer will occur very gently, which will only increase comfort. Such a floor heating system can already act as the main heating.

The underfloor heating cable is laid in the middle layer of the screed, for a more even distribution of heat energy. The table shows that the cable for such a system should be used with a higher power density in combination with a metal mesh that will help distribute heat and be a reinforcing element of the screed. Given that the cable will be hidden in a thick layer of screed, which will provide heat dissipation, it is best to use a two-core resistive cable with a power density of 20 W / m for storage underfloor heating. A self-regulating cable can also be used, but its price is 3-5 times higher than a resistive one.

The use of such heating systems is limited for two reasons:

The cost of heating with electric energy is still high compared to gas heating.
The power allocated to an apartment or house may simply not be enough to heat the accumulating warm floors.

General requirements for underfloor heating cables

Temporary technical requirements from 2003 regulate the order heating cables. We will make the most important excerpts from this voluminous document.

For personal use, it is recommended to use KSO only for comfort and to supplement the main heating system.
In direct-acting underfloor heating and for underfloor heating made of wood, the cable should not have a rated power of more than 2 kilowatts.
In thermal storage floors and when heating external stairs and ramps, the maximum rated power of the cable is 4 kilowatts.
The iron rule must be observed: one room - one cable. The exception is premises over 25 sq. m.
The heating cable must not pass into other rooms.
The heating cable must not be laid under fixed furniture.
Heating cables are always supplied with mounting plates and other accessories. It is they who must be used, no amateur performance is welcome.

The cable must be laid in the form of a snake and the following rules must be observed:
- Touching, crossing, twisting and looping on the cable is not allowed.
- From the boundaries of the laying zone to the edges of the cable there must be a distance that is not less than the laying step.
- From metal structures and wiring elements, the cable must have a distance of at least 50 mm, from wooden structures - 30 mm, and from elements of other heating systems - at least 500 mm.
- The laying step should always be more than 6 - 10 outer diameters.
- The distance between the sections of the laid cable must be greater than or equal to the laying pitch.
- The entire hot part of the cable must be in a homogeneous material.
- For a cable inside the screed, the pitch is not more than 20 cm, and in direct action floors - 10 cm.
All cables must be connected through a thermostat with a temperature sensor. Direct connection to the mains is only permitted in exceptional cases for self-regulating cables.

should be located at a distance of 0.5-1.5 meters above the floor.
The floor temperature sensor must be located at a distance of at least 0.5 meters from the walls, connected only with a copper wire placed in a corrugated plastic or metal tube.
All connections of the heating and supply cables must be made on thermostats, in junction boxes and electrical panels using terminals. No twists are allowed.
Power cables must be protected by circuit breakers of the appropriate ratings, and to protect people, it is mandatory to use an RCD with a differential trip current of not more than 30 mA.

The installation of the KSO must be carried out only by qualified personnel with the appropriate permit.

Prices for heating cable and accessories

Heating cable and accessories

Conclusion

The heating cable is recommended for underfloor heating. The most preferred application is a direct heating system or "thin floor".
Among heating cables, it is best to use a two-core resistive cable in terms of price-quality ratio.
The choice of the desired cable with the required power density, its length and laying step are obtained as a result of calculations.
It is unacceptable to change the length of a resistive cable section (except for zonal cable).