Electric heating of concrete using PNSV wire - calculation and connection diagram

During the construction of monolithic concrete structures, several technologies are used that are required to create optimal temperature conditions. This can be the use of special wires for heating or automatic machines, as well as greenhouses. The first option is the most in demand, since in comparison with analogues it is less energy-intensive and financially costly.

Why do you need concrete heating

If the water in the concrete solution freezes, it will not gain technological strength

Electric heating of concrete is required in the cold season, when the ambient temperature drops below the freezing point of water, which entails the hydration of the concrete solution. The mixture does not solidify as required, but partially freezes.

With the arrival of heat, an active thawing process begins, as a result, the solidity of the structure is violated, which negatively affects the durability and resistance to moisture penetration into the cavities of monolithic blocks.

In order to prevent undesirable and dangerous consequences for human health and life, it is imperative that concrete is heated in winter with special wires. The calculation of the footage and laying schemes are carried out at the design stage of the building.

The principle of operation and types of heating wires

The most common heating wire is PNSV type. This is due to the ease of installation and reasonable price in comparison with analogues.

An analogue of PNSP is also often used. Its main structural difference lies in the insulating material. Composition - polypropylene, due to which it is possible to increase the maximum power of the heat dissipator.

The table shows the main technical and physical characteristics of PNSP and PNSV wires.

Wire brandEstimated weight of 1,000 meters of wire, kgOptimum length of the heating section at 220 V, mNominal outer diameter, mmRated value of electrical resistance of 1 meter of heating conductor, Ohm
PNSV191102,80,12
PNSV18,5952,70,18
PNSV18802,60,22
PNSP16,41302,80,11
PNSP12,71002,60,12
PNSP14,51102,70,14
PNSP11,1852,50,18
PNSP9,6752,40,22

Heating wires of PNSP and PNSV types are also used for the organization of heated floors in residential premises.

The main difficulty that builders face when using heating wires is the need to calculate the required length. Minor errors are corrected by regulating the voltage supplied to the heating transformer.

Varieties and features of KDBS and VET cables

Heating wire PNSV

Despite the wide distribution, the described types of heat cables have a significant drawback - the need to use special expensive equipment that regulates the heat release power by changing the voltage.

The solution to the problem is the use of two-core sectional self-regulating thermal cables. The domestic modification was named KDBS, and the European - BET (manufacturer - Finland). For their full-fledged and uninterrupted functioning, additional equipment is not required, they are connected directly to a 220 V network.

There are practically no differences in the design of the domestic and European models. The table shows a comparative analysis.

Technical featuresKDBSBET
Degree of protectionIP67IP67
Section size, m10 to 1503.3 to 85
Nominal diameter, mm76
Recommended bending radius3525
Insulating material resistance, Mohm / m103103
Linear power, W / m40Depending on the model and length, it ranges from 35-45
Working voltage, Volt220-240220-230

Domestic models have their own marking characteristics. They are coded in the following form: ХХКДБС YY, where ХХ are linear power indicators, and YY is the section length.

Electric heating of concrete with PNSV wire

Pouring the solution into the mold prepared for heating

After carrying out and approving all calculations and schemes, they begin to warm up. The technology is as follows:

  1. The heating element spreads out evenly at the pouring point. It is important that the parts of the cable do not come into contact with each other. The heating object should not go beyond the boundaries of the structure and interact with the formwork.
  2. Before leading the ends of the cable beyond the heating boundaries, the cold ends are securely connected to the heating outputs by soldering. For maximum protection, the soldering points are additionally wrapped with metal foil.
  3. A test check is carried out using a megohmmeter and a measured current load is measured in phases.
  4. If the system is operational and there are no complaints about the implementation of the project, the structure is poured with concrete.
  5. Current is supplied through the step-down transformer substation.

This is the simplest method that allows you to effectively warm up concrete with a wire without violating the features of operation.

Installing the wire

Wire laying diagram

The wire is laid inside the formwork even before the concrete is poured into the cavities. As a rule, it is fixed with soft aluminum wire to the armature, but according to safety rules, this approach is not welcomed in implementation. The minimum bending radius is at least 25 cm, due to the high rigidity of the steel core. This rule is especially true when the ambient temperature drops, despite the fact that vinyl insulation retains its physical properties at temperatures down to -30 degrees. At -10 degrees, a steep bend can damage the integrity of the insulating layer.

For uniform heating, the wires are laid parallel to each other with an interval of no more than 15 cm. For 5 cbm. concrete requires about 30 m of cable type PNSV 1.2.

At a voltage of 220V, about 17 meters of cable are required, and at 380V at least 31 meters. With this approach, the entire system will warm up evenly. If a section of a greater length is laid, the heat release will occur no further than 5-6 meters from the point of connection to the supply network.

The cable is connected to the mains outside the formwork. As a rule, this is done with the help of aluminum conductors, with which the ends of the PNSV are tightly wrapped in several turns.

Advantages and disadvantages

In this way, heating monolithic concrete structures is beneficial due to economical energy consumption and low cost of cables. Special attention should be paid to the resistance of the wire to chemical attack (acid and alkaline), which allows them to be used when adding various additives to the building mixture.

Despite the significant advantages, there are also disadvantages:

  • the need to use special equipment - PT;
  • difficulty in calculating the required cable length.

The cost of special equipment - step-down stations - is high. The use process is short-lived, and the rental cost is usually about 10% of the unit's cost. The use of welding machines seems to be possible when heating small structures.

Installation of sectional heating cable

Heating wire in formwork

When installing a sectional heating cable, there is no issue with cutting, since heaters are sold in ready-made sections, and not in coils.For concreting in winter, it is required to calculate the power of the heating element based on the concrete cubes used in the monolithic concrete structure.

An instruction is attached to the TMT technology of concrete, where it is indicated that 1 cbm for heating. the building mixture will require from 500 to 1500 watts. It all depends on the weather conditions outside. If you use a few simple techniques, you can significantly reduce your electricity bill:

  • pre-insulate the formwork;
  • use special nozzles for the mixture, which allow you to lower the freezing point of the solution.

If floors or beams are to be poured, the calculation of the required material is carried out from 4 running meters for each square meter of the surface. If three-dimensional structures are to be erected, for example, I-beam concrete beams, electric heating is laid in tiers with an interval of no more than 0.4 meters. The protection of the heating wires allows them to be securely fastened to the fittings.

The interval between the electric heater and the surfaces of the structure must be at least 20 cm. For uniform heating, the distance between the cables must be the same.

Pros and cons of segmented cable

KDBS cable for heating concrete

Segmented wires have undeniable advantages in comparison with their counterparts:

  • simple calculation of the length of the required heating element, ease of installation;
  • the probability of electric shock is minimal;
  • to organize the heating of the building material, additional use of expensive equipment is not required.

The disadvantages include the relatively high cost.

Post-processing concrete

Soon after warming up the concrete monolithic structures, it is impossible to start processing them. The building material must be pre-hardened and achieve optimum brand strength.

Shock loads are also contraindicated. Cutting is allowed. For this, equipment is used, equipped with diamond attachments, after which cracks do not form. In general, the heating of concrete with heating wires resembles the work and arrangement of underfloor heating.

The use of nichrome cables for heating the concrete mixture is prohibited by safety regulations. In addition, this approach will cost the customer large financial costs.

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