Laying concrete mortar at sub-zero temperatures requires special measures to prevent water from freezing. This will lead to a loss of strength and reduce the reliability of the structure being built. There are many technologies for maintaining a constant temperature of mixture components. An effective way to ensure normal hardening is the use of a specially created heating wire PNSV. The question of domestic use is interesting. The main parameters, characteristics, and practical issues are considered.
Basics of laying and installation technology
- a step-down transformer;
- trunk cables;
- cold end wires;
- thermal protection means.
During the cold season, when the ambient temperature drops below the freezing point of water, problems arise with the hydration of the concrete solution. Simply put, the mixture partially freezes rather than completely hardens. After the ambient temperature rises, the thawing process begins, the solidity of the mixture may be disrupted, which will negatively affect the solidity of the structure, its resistance to water penetration, which will lead to a decrease in durability.
Consequences of pouring mortar in the cold, in this case even the Aquabarrier waterstop or other waterproofing will not help
To avoid these consequences, it is imperative to electrically heat the concrete mixture in winter. In this isothermal process, there are no disturbances in its structure, which has a positive effect on the strength of the structure being built.
The principle of operation is quite simple: when voltage is applied, the wire heats up, which in turn heats the concrete mixture. Since it is recommended to limit heating to a voltage of 70 V, a step-down transformer (hereinafter referred to as PT) of appropriate power will be required.
Transformer substation KTPTO 80 for working with thermal conductor
Before installation, it is necessary to calculate the length of the heating wire. In this case, it is necessary to take into account its type and characteristics, the voltage of the transformer substation, the volume of the concrete mixture, the ambient temperature, as well as the nature of the structure (pouring of a column, beam is expected), etc.
To heat a concrete mixture with a volume of one cubic meter, about 1200-1300 W are needed. If we use a wire of this brand with a cross-section of 1.20 mm, then we will need a heating device of 30-45 m (to accurately calculate the length, you need to know the temperature conditions).
In addition, it is necessary to take into account the current strength; for normal operation of a cable immersed in a solution, 14.0 - 18.0 Amperes are permissible (depending on the connection diagram).
Electrical diagram for connecting PNSV A) star B) triangle
After purchasing the necessary heating material, the production of the heating system begins:
- The purchased coil or reel is cut into heating sections, the lengths of which are determined by the specifications, in the required quantity. It is possible to manufacture sections from segments, ensuring reliable connection contact;
- The ends are stripped to 4 cm, and “cold ends” are connected to them - pieces of insulated aluminum conductor of sufficient length to connect to the transformer. A reliable insulated connection must be located inside the heated volume;
- Heating sections are placed in the formwork. Measures are being taken to ensure the correct location, absence of sagging, and care for the boundaries of the future monolith. If reinforcement is used, you can tie it to it; It is not allowed to cross or touch wire sections within the formwork. The distance between the wires is at least 15 cm.
- To improve the uniformity of heat distribution, it is recommended to wrap the wire with thin metal foil 0.2÷0.5 mm thick;
- All marked “Cold ends” after installation should be located at one edge;
When heating concrete on construction sites, ensuring electrical safety requirements, it is necessary to take measures to fence off the dangerous area and limit the presence of unauthorized persons in it.
Once completely dry, using floor or wall heating is not dangerous.
Heating technology and laying scheme
Before installing the concrete heating system in winter, formwork and reinforcement are installed. After this, the PNSV is laid out with an interval between the wires of 8 to 20 cm, depending on the outside temperature, wind and humidity. The wire is not stretched and is attached to the fittings with special clamps. Bends with a radius of less than 25 cm and overlaps of current-carrying conductors should not be allowed. The minimum distance between them should be 1.5 cm, this will help prevent short circuits.
The most popular installation scheme for PNSV is a “snake”, reminiscent of a “warm floor” system. It provides heating of the maximum volume of concrete mass while saving heating cable. Before pouring the solution into the formwork, you must make sure that there is no ice in it, the temperature of the mixture is not lower than +5°C, and the installation of the connection diagram is carried out correctly, and the cold ends are brought out to a sufficient length.
The PNSV wire comes with instructions, which you need to read before heating the concrete. The connection is made through sections of busbars in two ways through a “triangle” or “star” circuit. In the first case, the system is divided into three parallel sections connected to the terminals of a three-phase step-down transformer. In the second, three identical wires are connected into one node, then three free contacts are similarly connected to the transformer. The power supply is installed no further than 25 m from the connection point, the heated area is surrounded by a fence. The system is connected after the entire volume of mortar has been completely filled. The technology for heating concrete with a PNSV heating cable includes several stages:
- Heating is carried out at a rate of no more than 10°C per hour, which ensures uniform heating of the entire volume.
- Heating at a constant temperature continues until the concrete reaches half its technological strength. The temperature should not exceed 80°C, the optimum is 60°C.
- Cooling of the concrete should occur at a rate of 5°C per hour, this will help avoid cracking of the mass and ensure its solidity.
If the technological requirements are met, the material will gain a grade of strength corresponding to its composition. At the end of the work, the PNSV remains in the thickness of the concrete and serves as an additional reinforcing element.
It should be noted that using a KDBS or VET cable is much easier, since they can be connected directly to a 220 V network through a panel or socket. They are divided into sections, which helps to avoid overload. But these cables are more expensive than PNSV, so they are less often used in the construction of large facilities.
Another popular technology is the use of formwork with heating elements and electrodes, when the reinforcement is inserted into the solution and connected to the network using a welding machine or another type of step-down transformer. This heating method does not require a special heating cable, but is more energy-consuming, since water in concrete acts as a conductor, and its resistance increases significantly during hardening.
Types of heating wires and cables
The description of the operating features of conductors of this type is that they are connected to the electrical network through step-down transformers. The wires are laid in the thickness of the concrete mass and, heating up with the passage of current, maintain the required temperature regime. Laying occurs at the reinforcement stage. The cables are attached to the fitting sections.
Laying the wire together with reinforcement
Important! The concrete solution hardens completely in 26-28 days. In the cold season at sub-zero temperatures, the water included in the solution freezes. Hardening of the concrete mixture slows down. When temperatures change (as they rise), the ice melts again. There is no need to talk about the quality of concrete.
PNSV cable and similar products can help get rid of the problem and maintain the temperature of the solution within acceptable limits. The use of this technology makes it possible to reduce the setting and hardening time of concrete by 5-6 times. In this case, the structure of the solution does not change, the concrete does not crack or swell.
A cable that has two cores and is used for sectional concrete is KDBS. The advantage of this model is its direct connection to 220 V. There is no need to use a step-down transformer. Laying is carried out according to the required pattern, without cutting, using couplings.
Attention! Dismantling the KDBS after the concrete has hardened is impossible; it itself costs from 60 to 280 rubles per linear meter.
Heating cable KDBS
VET is a Finnish cable with two cores, which similarly allows you to connect yourself to a 220 V network using a special plug and does not require transformation of the supply voltage. Used at temperatures up to -250C. Conductor consumption – 5 l.m. (linear meters) per 1 cubic meter of heated volume, but not less than one kilowatt per 1 m3.
For your information. The price of BET ranges from 76 to 530 rubles per linear meter. It is worth considering that the shorter the product length, the higher the cost.
PNSV is a single-core wire. It can be used several times. When connecting, if the total length of the conductor does not withstand the supply voltage of 220 V, it is necessary to use a step-down transformer.
Most often, PNSV wires are used for electrical heating of concrete. This is due to its relatively low cost and simple installation. Below is the appearance of the thermal wire, its design features and the explanation of the markings.
Appearance of the PNSV wire (A), explanation of the markings (B) and design (C)
As an alternative, an analogue can be used - PNSP, the main difference of which is insulation; it is made of polypropylene, which allows a slight increase in the maximum heat release power.
Table of main parameters of PNSV and PNSP wires
Please note that wires of this type can be used as floor heaters, which operate on the principle of a warm floor.
The main difficulty associated with the use of thermal wires of this type is the need to calculate their length. Small miscalculations can be corrected by adjusting the voltage level coming from the warm-up transformer.
Details on how the installation of PNSV is carried out, as well as a description of the related procedures (calculation of the length of wires, laying diagram, drawing up a technological map, etc.) will be given in another section.
The main disadvantage of the thermal wires described above is the need for additional equipment that allows you to regulate the heat generation power by changing the voltage. The task can be significantly simplified by using two-core sectional self-regulating thermal cables, namely the Finnish VET or the domestic KDBS.
Main elements of the heating cable design
Designation:
- A – Outputs of heating cores.
- B – Installation cable used to connect the KDBS to a 220V network; for this purpose, you can use any connecting wire, for example APV.
- C – Coupling for connecting the heating section.
- D – End insulator sleeve.
- E – Heating section of fixed length.
Structurally, the VET cable is practically no different from the domestic analogue discussed above; as for the main technical characteristics, they are shown in the comparative table below.
Table of comparative characteristics of VET and KDBS cables
As for marking, domestic products of this type are coded in the following form: ХХКДБС YY, where ХХ is the linear power characteristic, and YY is the section length. An example is the marking 40KDBS 10, which indicates a power of 40 W per meter, and the section itself is ten meters long.
Since such concrete heaters are supplied not in coils, but in ready-made sections, the issue of cutting is eliminated. All that is needed to assemble a winter concreting installation is to calculate the power of the segment based on how many cubes of concrete are in the structure, and then select a cable of the appropriate length.
Let's start with a brief guide to calculations and small installation recommendations:
- The instructions for the concrete TMT technology indicate that heating a cubic meter of mixture requires from 500 to 1500 W (depending on the air temperature). Electricity consumption can be significantly reduced if you use a few simple technical techniques:
- Use special additives for the mixture to lower the freezing point of the solution.
- Insulate the formwork.
- If a beam or ceiling is being poured, the heating cable is calculated based on 4 linear meters per 1 m2 of surface area. When constructing volumetric elements, such as I-beams, electric heating is laid in tiers, with a distance between them of no more than 40.0 cm.
- The cable protection allows it to be wound to the fittings.
- The distance from the surface of the structure to the electric heater placed inside must be at least 20.0 cm.
- In order for the concrete mixture to heat up evenly, the heaters must be placed at the same distance.
- There must be at least 40.0 mm between different contours.
- Crossing heating conductors is prohibited.
The undoubted positive qualities of products of this type include:
- To organize concrete heating using this method, you do not need expensive additional equipment (ET).
- Unlike drying with electrodes, the likelihood of electric shock is minimal.
- Easy installation and simple calculation of segment length.
VET cable is significantly more expensive than the wire for heating concrete PNSV. Domestic KDBS, for example, produced by the ETM company in Krasnoyarsk, improves the situation somewhat, but not by much. That is why these cables are used in the construction of small concrete and reinforced concrete structures.
As a conclusion.
We have described only one method of heating concrete; in fact, there are many more. These will be discussed in other publications.
In conclusion, we consider it necessary to answer the question that appears repeatedly on the Internet, why it is impossible to use nichrome wires to heat concrete. Firstly, this pleasure would be very expensive, and secondly, it is prohibited by safety regulations. This is why there is no need for a calculator to calculate the number of turns of nichrome to heat a pipe or concrete.
Operating principle and types of wires
After installing the reinforcing frame, the heating cable is placed directly on the working surface. The cross-sectional area and maximum allowable stress depend on the specific situation. Then the concrete mixture is poured, followed by connecting the heating cable to the power supply network (or transformer). The concrete gradually heats up, begins to harden faster and (most importantly) evenly. The structure remains homogeneous, therefore eliminating the possibility of bubbles and cracks.
Three main types of cables are used to heat concrete:
- A two-core cable for concrete in sections (KDBS) can be switched to a 220 V electrical network, so there is no need to use a step-down transformer. Of the three products, it is much easier to install, no trimming is required, and the presence of convenient couplings ensures easy installation according to the desired pattern. On the other hand, KDBS has a high cost (from 1000 rubles per 1 linear meter). The second disadvantage is related to single use. Once the concrete mixture has hardened, it will not be possible to dismantle the product.
- Two-core cable made by Finnish BET. Again, it does not require a step-down transformer and is connected directly to the mains. It is characterized by efficiency, and to heat one cube of concrete mass, no more than 20-25 linear meters are needed.
- A single-core heating wire with a steel conductor and polyvinyl chloride insulation (PNSV) is the cheapest product for heating the concrete mass (about 20-50 rubles per 1 running meter), therefore it is most used in the construction of private houses. The power supply circuit must have a step-down transformer. However, if a number of conditions are met, direct switching to the network is possible. After the concrete has been heated, the wire can be reused (as a “warm floor” or an “anti-ice” system).
Let's take a closer look at the most popular and simple PNSV wire.
Features of PNSV heating wires
Structurally, the product consists of one steel core, the diameter of which ranges from 1-3 mm. The cross-sectional area of a round conductor can reach 4 square meters. mm. Polyvinyl chloride or polyester is used as insulation, which eliminates strong kinks, protects the wire from fractures and increases resistance to fire.
The most common are wires of small diameter - about 1.2 mm, but since the cost of the product is minimal, it is better not to save money and take a 3 mm PNSV cable. This is especially true if you plan to manually compact the cement mortar. In this situation, the insulation will be much stronger, so even during power failures, the possibility of overheating is eliminated.
Be sure to pay attention to another distinctive characteristic of heating cables - cold ends. These structural parts are located outside the concrete slab, and for their production they use conventional aluminum current-carrying conductors (ACV). Their main task is to connect the heating cable embedded in concrete with the electrical network.
Features of KDBS and VET cables
PNSV is not ideal, and the main disadvantage of the heating cable is associated with the extreme need to use additional equipment - a transformer used to lower the voltage and regulate the power of heat generation. Simply put, to prevent the device from burning itself out, you have to reduce the voltage.
The use of two-core sectional conductors simplifies the task of heating the concrete mixture. These products are characterized by self-regulating properties. We are talking about the domestic KDBS or the Finnish VET. There is no need to connect additional devices for heating. It is enough to switch to a 220 V electrical network and enjoy the result.
In the image below you can see the cable structure for heating concrete:
Let's decipher the notation:
- A – stripped heating cores;
- B – cold termination (regular installation cable, for example, with aluminum conductors, which is necessary for connecting to the network, but is not used as a heating element);
- C – coupling for fixing the installation cable with heating sections;
- D – end sleeve for insulation;
- E – heating cable for heating concrete of a specified length.
The design of the Finnish VET cable is almost identical to KDBS, but the technical and operational characteristics are still different. Their comparison is shown in the table below:
| Parameter name | VET | KDBS |
| Operating voltage, V | 220-230 | 220-240 |
| Linear power, W/m | 35-45 (depending on model and length) | 40 |
| Insulation resistance, Ohm | 103 | 103 |
| Bending radius, mm | 25 | 35 |
| Diameter, mm | 6 | 7 |
| Heating section length, m | 3,3-85 | 10-150 |
| Dust and moisture protection class | IP67 | IP67 |
To mark domestic heating cables KDBS, the general marking scheme AAKDBS BB is used, where AA is the linear power value, BB is the length of the heating section. For example, if you see the marking 40KDBS 20, then it indicates that the power of one linear meter of this cable is 40 W, and the length of the heating section is 20 m.
Installation of sectional heating cable
Today, there are many options for online calculators that are convenient and allow you to instantly get the exact power, quantity, and cross-section of the heating cable. The calculation below illustrates the logic and provides a methodology for carrying out calculations of the most general form.
| Room name | Power W/m2 |
| Non-residential | 110÷120 |
| Residential | 110÷130 |
| Plumbing | 120÷150 |
| Unheated loggia | 180 |
The option of using it as the only element of the heating system will require 160÷200 W/m2.
For example: an electric heated floor is calculated, the required heating area is 10 m2, there is a PNSV of 1.2. Characteristics taken from parameter tables:
- The power of the bedroom floor heater, for the need to provide 120 W/m2, W: 10*120=1200;
- Heater element length 1200 W, specific power 20 watts per linear meter, meters: 1200/20=60;
- On one square meter you need to lay (fulfilling the requirements of the specifications), meters of wire: 60/10=6;
- The ohmic resistance of 60 meters of wire, the resistivity of one meter of steel core is 0.15 Ohms will be, Ohm: 60*0.15=9;
- A heating section connected to a 220V network with a wire with a diameter of 1.2 mm. cannot be less than 110 meters long (specifications). Otherwise, the result will be: the resistance of the shortened element decreases, the current increases, which causes overheating, and the likelihood of destruction increases. The active resistance of the heating section is, Ohm: 110*0.15=16.5. The recommended effective heating current is, A: I=U/R=220/16.5=13.33. Rounded 13 amps.
- The calculated 60 meters of wire are shorter than the normalized length of the section and cannot be directly powered by the network. A voltage step-down transformer is required. You can calculate it like this:
- Secondary winding: voltage, V: U=I*R=13*9=117, power, W: P=U*I=117*13=1521
- Total transformer power, W: 1521*1.25=1901.3
Total: to install a heated floor with an area of 10 m2, you need:
- 60 meters of wire PNSV 1.2;
- Step-down transformer with a power of 2 kilowatts, secondary winding voltage 110÷120 volts.
A welding machine may be a suitable option when selecting a transformer.
The use of a thermostat will increase the comfort of using a heated floor and will allow you to use electrical energy more economically.
Description and design of the PNSV wire
For the PNSV wire, the abbreviation decoding describes the following design features:
- P – wire;
- H – for heating;
- C – steel current-carrying conductor (sometimes galvanized or not);
- B – polyvinyl chloride insulation.
For example, wire pnsv 1*1.2 stands for heating wire with a steel core in a PVC sheath, having one core with a cross-section of 1.2 mm2. The range of sections for use is from 1 to 6 mm2, most often the maximum is 1.4 mm2.
Interesting. A solid core reduces the flexibility of the conductor; with increasing cross-section, this indicator noticeably decreases. If we compare the minimum bending radii (for the wire in question this is 5 outer diameters), then its flexibility is comparable to cables that have class 3 of this parameter. The core insulation ranges from 0.8 to 1 mm.
PNSV design
The conductor is steel, single-wire, round in shape.
Insulation - PVC plastic or polyethylene.
P - WireH - HeatingC - Core - steel, single-wire, round B - PVC insulation
How to replace it
It is permissible to replace the PNSV cable with a PTPZh wire. This is a two-wire broadcast (for radio) conductor, with plastic insulation and galvanized steel conductors. Core diameter – 1.2 mm2. The conductors are arranged in parallel and covered with insulation made of high pressure polyethylene.
PTPZh, appearance
For heating, you can take a 0.6 mm2 core. Also suitable as a replacement:
- PNSP;
- VET;
- KDBS.
The choice of an analogue directly depends on the scope of the proposed work. With the correct calculation of the length and choice of connection diagram, the PNSV will ensure reliable heating of the concrete. Reasonable price and ease of use make this heating conductor accessible for purchase and installation. The ability to change the heating temperature by adjusting the voltage supply will smooth out all small miscalculations when determining the required length.
Design elements of PNSV wires:
Core - steel, single-wire, round
Insulation - PVC plastic or polyethylene
AREA OF APPLICATION of PNSV wires
The wires are intended for heating during fixed installation of oil and gas industry objects, monolithic concrete and reinforced concrete, as well as for floor heaters at voltages up to 380 V AC with a nominal frequency of 50 Hz or DC up to 1000 V.
OPERATING CHARACTERISTICS of PNSV wires
Wires are resistant to changes in ambient temperature: from -60° to 50°C Maximum permissible operating temperature: 80°C Wires must be laid at an ambient temperature not lower than -15°C Wires are resistant to water and a 20 percent aqueous solution table salt or a 30 percent solution of alkalis Ca(OH)2 or NaOH. The bending radius of the wires during installation must be: at least 5 outer diameters Minimum bending radius: 25 mm Mounted wires must not intersect or touch each other, the distance between the wires must be: at least 15 mm Mode of operation of the wires - intermittent or long-term Wiring power supply to the heating section is carried out by the “cold” ends, the junction of the heating wire and the “cold” end is recommended to be taken outside the heated zone. It is recommended to connect the “cold” end to the heating wires by soldering using a copper wire bandage, using terminal boxes or sleeves. Any other method is allowed that ensures reliable connection during operation. To achieve uniformity of the thermal field, it is recommended to cover the mounted wires with metal foil 0.2-0.5 mm thick. It is allowed to manufacture heating sections from 2-3 pieces of wires, while the connection of the conductive cores of the pieces can be made in any way that ensures quality connections Electrical insulation resistance of wires, recalculated per 1 km of length and measured at a temperature of (20±5)°C: not less than 1 MOhm
Warranty period: 2 years from the date of commissioning Service life of PNSV wires: at least 16 years
Regulatory document: TU 16.K71-013-88
Allowable voltage, kV: 0.220;0.380;1
Core - steel, single-wire, round
Insulation - PVC plastic or polyethylene
AREA OF APPLICATION of PNSV wires
The wires are intended for heating during fixed installation of oil and gas industry objects, monolithic concrete and reinforced concrete, as well as for floor heaters at voltages up to 380 V AC with a nominal frequency of 50 Hz or DC up to 1000 V.
OPERATING CHARACTERISTICS of PNSV wires
Wires are resistant to changes in ambient temperature: from -60° to 50°C Maximum permissible operating temperature: 80°C Wires must be laid at an ambient temperature not lower than -15°C Wires are resistant to water and a 20 percent aqueous solution of table salt or 30 percent solution of alkalis Ca(OH)2 or NaOH.
The bending radius of the wires during installation must be: at least 5 outer diameters Minimum bending radius: 25 mm Mounted wires must not intersect or touch each other, the distance between the wires must be: at least 15 mm Mode of operation of the wires - intermittent or long-term Power supply to the heating section is carried out by “cold” ends, the junction of the heating wire and the “cold” end is recommended to be taken outside the heated zone. It is recommended to connect the “cold” end to the heating wires by soldering using a copper wire bandage, using terminal boxes or sleeves.
Any other method is acceptable that ensures reliable connection during operation. To achieve uniformity of the thermal field, it is recommended to cover the mounted wires with metal foil 0.2-0.5 mm thick. It is possible to manufacture heating sections from 2-3 pieces of wires, while the connection of the conductive cores of the segments can be made in any way that ensures the quality of the connection. Electrical resistance wire insulation, recalculated per 1 km length and measured at temperature (20±5)°C: not less than 1 MOhm
Warranty period: 2 years from the date of commissioning Service life of PNSV wires: at least 16 years
Specifications
| Main characteristics | Units | PNSV 1x1.2 |
| Insulation material | PVC - plastic or polyethylene | |
| Electrical resistance of the conductor | Ohm/km | 140 |
| Electrical resistance of wire insulation | MOhm/km | 1 |
| Number of cores in the wire | PC | 1 |
| Nominal conductor diameter | d | 1,2 |
| Core insulation thickness | s | 0,8-0,17 |
| Wire outer diameter | D | 2,8 |
| Max. permissible operating temperature | t°C | 80 |
| Length of heating section of wires | m | 110 |
| Weight | kg/km | 13 |
Heating wires, in particular PNSV, have the following parameters and indicators:
- operating temperature range – -60 to 500C;
- permissible air temperature during installation work – up to minus 150C;
- resistance to electric current – 0.15 Ohm/m;
- working wire consumption – 60 m/m3;
- current when heating concrete (inside the mass) – 15-17 A.
Carefully! The heating current can only be measured when the product is laid deep in concrete. Connecting the wire outdoors is strictly prohibited - the wires will melt and the fittings will be energized.
Technical characteristics of PNSV
| Parameter | Meaning |
| Mains voltage | 380 V |
| Recommended supply voltage | 60-70 V |
| Ambient temperature | -60~50°C |
| Operating temperature | ≤80°C |
| Specific power | 1.5-2.5 kW/m3 |
| Wire consumption per cubic meter of solution | 50-60 l.m. |
| Cycle of keeping structures under tension | 2-4 days |
| Wire section length | |
| PNSV 1.0 mm | 80 m |
| PNSV 1.2 mm | 110 m |
| PNSV 1.4 mm | 140 m |
| Specific heat dissipation power of the wire | |
| for reinforced structures | 30-35 W/rm |
| for unreinforced structures. | 35-40 W/rm |
| Average core resistance value | |
| PNSV 1.2 mm | 0.15 Ohm/m |
| PNSV 1.4 mm | 0.10 Ohm/m |
| PNSV 2 mm | 0.05 Ohm/m |
| PNSV 3 mm | 0.02 Ohm/m |
You can buy PNSV wire in coils (coils) of 1000 m. The price of PNSV wire starts from 900 rubles/km for PNSV 1.2 mm to 5000 rubles/km for PNSV 3 mm.
Application area
It is used to heat the mass during installation work at industrial facilities in the oil and gas industries, reinforced concrete products and monolithic concrete structures.
In addition, the conductor can be used:
- during the construction and construction of buildings and structures at the initial (foundation) stage;
- for heating water pipelines and sewer pipes;
- for arranging heated floors;
- heating soil in greenhouses.
The product is resistant to water, 30% alkaline solutions (Ca(OH)2, NaOH), salt compounds (up to 20%).
The properties are determined by the requirements of TU 16.K71-013-88, OKP code 35581304. Used for warming up:
- Monolith, reinforced concrete in the construction of industrial facilities;
- Objects, buildings, structures of industrial complexes for various purposes, construction mechanisms;
- Can be used in heating systems for domestic and industrial building structures.
The PNSV marking indicates the design, area of use, materials: “P” heating wire, single “C” steel conductor, insulated with polychlorine “B” vinyl.
| Index | Meaning |
| Operating environment temperature, °C | -60 ÷ 50 |
| Operating heating temperature, °C, maximum | 80 |
| Installation is carried out at temperatures above °C. | -15 |
| Insulation resistance of a wire 1 km long, more, mOhm: | 1 |
| Insulation thickness, mm | 0.8 |
| Specific power (voltage 220 V, 20°C), W/meter | 20 |
| Service life, years | 16 |
The physical and chemical characteristics of the materials give the parameters values that ensure:
- Lack of reaction when interacting with water, chemically active aqueous solutions of salt, alkalis, the solution concentration of which reaches 20÷30%;
- Strength that allows bending on a roller, the size of which is equal to ten wire diameters, without loss of mechanical properties for at least three cycles;
- Possibility to operate in constant long-term heating modes or pulsed, short-term repeated heating modes.
When performing installation work, you need to take into account the following restrictions:
- Bending is carried out with a radius less than five diameters;
- Crossing at any angle or touching in the heated volume is not allowed;
- It is prohibited to place wires no closer than 15 cm from each other.
| Dependence of characteristics on diameter | |||||
| Nominal parameter values | Nominal wire diameter, mm | ||||
| 1 | 1.1 | 1.2 | 1.3 | 1.4 | |
| Constructive: | |||||
| Outer diameter (dimensions), mm | 2.6 | 2.7 | 2.8 | 2.9 | 3 |
| Estimated mass of length 1 km, kg | 18 | 18.5 | 19 | 19.5 | 20 |
| Electrical: | |||||
| Resistance of 1 meter of conductor, Ohm | 0.22 | 0.18 | 0.15 | 0.13 | 0.11 |
| Heating section length, (for 220 V, m | 80 | 95 | 110 | 125 | 140 |
Cable manufacturers and their characteristics
- Kama cable. The company produces wires of various price segments and purposes:
- energy;
- metallurgy;
- coal;
- mechanical engineering;
- oil industry.
Products are manufactured in accordance with the requirements of Russian Federation standards and international standards BS and DIN.
- OJSC RybinskKable. The company produces cables with copper and aluminum conductors. In addition, the plant produces:
- power wires for laying with an operating voltage of 1 kV;
- power conductors for non-stationary installation;
- for shipbuilding;
- for construction equipment;
- for the automotive industry.
- Uralcable. Basic products are aimed at consumers of the national economy, these include:
- oil and gas industry;
- auto, aircraft, shipbuilding;
- energy.
Each manufacturer has a wide range of products that will suit each consumer’s needs. Prices and characteristics of a specific model must be clarified with the manufacturer before placing an order.
Pros and cons of PNSV
Heating concrete in this way is quite beneficial. This is explained by both the low cost of the wire and the relatively low electricity consumption. Separately, it is necessary to note the resistance of the wire to alkaline and acidic influences, which allows the use of this method when adding various additives to the mixture.
Main disadvantages:
- complexity of calculations when calculating the length of the wire;
- the need to use PT.
Step-down stations are quite expensive, and given the length of the process, it is not profitable to rent them (such services cost 10% of the cost of the product). The use of welding machines makes it possible to heat small structures, but since it is not designed for this mode of operation, its failure and subsequent expensive repairs are quite likely.
Delivery of PNSV
Nobody likes to wait - that’s why we try to deliver cable products as quickly as possible. The speed of delivery of PNSV wire is achieved through cooperation with large transport companies. In addition, we have our own logistics division.
MANUFACTURERS
How to connect and lay wire
Regardless of which wire is used, psv with core 1 2 or another, the following requirements must be taken into account:
- calculate the total length of the heating conductor, taking into account the circuit, the volume of the solution to be heated, and the influence of external conditions;
- select the type of connection: single-phase, three-phase (star or delta);
- calculate the sectional connection based on a heating current of 15 A for each section being mounted;
- provide for the use of step-down stations: KTP TO - 80/86, SPB - 80, with body grounding, which provide heating of 20-30 m3 of the working mixture;
- perform uniform laying around the perimeter, maintaining a distance from wire to wire from 15 to 50 mm;
- “hot” contact connections are made in concrete, while the working (hot) sections of the PNSV are connected to “cold” conductors made of copper or aluminum, which, in turn, are connected to the transformer.
Attention! When connecting “hot” and “cold” wires, the connection points are insulated. Connection without adapter wires to the transformer is unacceptable.
Small nuances that will help in your work:
- When calculating the required amount of cable, it is necessary to take into account that the connection is not made in one whole piece. For this, the wires are divided into sections of 16-28 m. To calculate Lmax, you need to know the conductor resistivity (p), which depends on the cross-section. To calculate, you can use Ohm's law (U=I*R) or use an online calculator.
- The voltage supplied to the PNSV usually ranges from 70 to 100 V. This provides the required temperature and heating current.
- It is recommended to lay a layer of foil metal gasket up to 2.5 mm thick between the reinforcement mesh and the heating element. This will increase heating efficiency and eliminate direct contact of the fittings with the wire.
In each individual case, the specific conditions associated with the technology of concrete laying are taken into account. In this case, the heating temperature will depend on the weight of the solution, thermal insulation, the direction and speed of air masses (wind), the size of the formwork and the grade of concrete.
Connection diagram
Connections for heating concrete mixtures can be made using two types of circuits: star and triangle.
Turning on conductors
In the first case, one ends of 3 segments of equal length are connected to a common point, and the three remaining ends are connected to the terminals of the PTS. In the second case, the wire is divided into three equilateral conductors, they are connected in parallel. Each set is connected in series and three clamps from the output of KTP TO - 80/86 are connected to common points.
After all joints and connections have been made, the concrete solution is placed in place, and the assembled structure is connected to the network. Power supply to the heating elements is possible only after the solution has been completely laid. It is not recommended to do it any other way.
Power supply block diagram
At home, when working with small volumes of concrete solutions, you can connect the PNSV to a welding machine and heat it by supplying direct current.
Using a welding machine for heating
Warm-up technology
Concrete should be heated using three stages: preliminary, intermediate and final. They are divided by time and temperature as follows:
- preliminary (warm-up) – the temperature is maintained up to 100C for 2 hours;
- intermediate - heating is carried out according to an isotherm (the temperature is constant), while the temperature should not rise above 80 degrees;
- the final stage is when the solution cools; the process speed should not be more than 5 degrees per hour.
When working with concrete, you should not heat it after 50% hardening.
Recommendation. Work on processing concrete surfaces and blocks without waiting for complete hardening can be carried out using any cutting or drilling tool, with the exception of shock loads.
How to connect correctly
To carry out the procedure yourself, you must follow certain rules, since to obtain a good result, installation should be done not by eye, but by accurate calculations.
Connection
Note! It is necessary to take into account the volume of concrete, the area of work, temperature conditions, wind speed in the area where concrete work is being carried out, the required time for warming up the concrete, as well as the electrical connection diagram. Connection features:
Connection features:
- at the very beginning, the required amount of wire is calculated, depending on the parameters discussed above;
- the PNSV wire should be connected in separate sections. Connecting in one piece is impractical, as this does not give the expected effect;
- the type of connection can be three-phase or two-phase, as well as in delta or star circuits;
- Important during the work are the selection of wire length and compliance with the current load. In a separate section, the current strength should not exceed 15 Am;
- correspondence of the supplied voltage to the temperature of the wire. Most often, power is connected within the range of 70-100 W, using a step-down transformer for this. The most popular transformer model when carrying out concrete work using a heating wire has become the KTPTO-80 brand.
PNSV is a wire for heating concrete, which at a very reasonable price allows you to solve problems associated with concrete work in winter. However, it does not impose any special requirements for connection and operation.
