- Self-regulating cable device description
- Calculation of the power of a self-regulating cable
- Installation of the heating system inside the pipeline
- Fastening the cable over the pipe
Severe cold can damage the water supply system laid at a shallow depth or passing through an unheated part of the house. To reduce this risk, a self-regulating heating cable for heating pipes is used, which is mounted on top of the pipes or laid inside the water supply system..
Self-regulating cable device description
The self-regulating cable is a flexible heating element. The general protective function is performed by the upper shell made of polymeric material. The subsequent metal braid is designed for grounding, shielding and mechanical protection. The thermoplastic winding used behind it creates a reliable sheath for two twisted conductors and a conductive matrix containing finely dispersed graphite.
1 – external polymer insulation; 2 – metal braid; 3 – internal insulation; 4 – self-regulating conductive matrix; 5 – conductors
When the supply voltage is applied, the matrix is heated and expanded. Graphite grains lose a lot of microcontacts with each other, the resistance of the cable section increases, limiting the heating process. The lower temperature causes a new cycle of heat generation. This happens independently at each point of the cable, and this makes it possible to maintain different temperatures in different areas, while significant energy savings are achieved. The use of this technology increases the resistance to voltage surges, it becomes possible to cut the cable of various lengths or mount it with an overlap, for example, on locking and adjusting equipment.
Calculation of the power of a self-regulating cable
When deciding on the power of a cable for heating a pipeline with a length of more than 7-10 m, it is necessary to take into account many factors: the type of pipe, its location, length, diameter, thermal insulation used and the minimum ambient temperature. To calculate the self-regulating cable, you can use the manufacturers tables. You can calculate the required cable length for heating pipes up to 10 m using a simplified version:
- if installation is planned on top of the pipe, then the power should be approximately 17 W / m;
- when laid inside a water pipe, the indicator should be 10 W / m.
Installation of the heating system inside the pipeline
For pipes with a diameter of up to 50 mm and in the absence of direct access, if it is, for example, an existing water supply system laid underground, the method of installing the cable inside the pipe is used. If the installation of the cable will be carried out in a pipe with tap water, then such a cable must comply with the SanPiN standards. When buying such a cable, ask the seller for a certificate. The installation of the cable into the pipe is easy. Along with the cable, you must purchase an adapter sleeve for a pipe of the corresponding diameter.
If you need to warm up the pipe for entering water into the house, then it is enough to insert a self-regulating cable into the pipe from the entrance to the house to the depth of freezing. To do this, you will need a cable with a length equal to the height of the input plus the height of the floor above ground level, and plus the depth of freezing of the soil.
Fastening the cable over the pipe
With external mounting, there are three possible cable layouts. Linear is most suitable for small pipe diameters up to 35 mm, since self-regulating cable has a restriction on the minimum bending radius. Laying is carried out along the pipe. If one heating element is not enough, then two cables are installed on opposite sides of the water pipe. The second method involves an undulating fixation of the heating element. It is used on medium pipe diameters and gives savings in cable usage compared to linear installation of two self-regulating elements. The third way is spiral. Most effective method for protecting medium to large pipe diameters.
All three methods involve the use of aluminum tape. Plastic pipes are wrapped with them before the cable is fixed – this avoids local overheating of the pipe and ensures uniform heat distribution. The heating element is fixed every 30–40 cm with a self-adhesive heat-resistant mounting tape, and the use of wire or cable clips in this case is unacceptable. After securing the cable, wrap the elements with aluminum tape again. To reduce heat loss, it is necessary to protect the structure with heat-insulating material for pipes.
Self-regulating cable is more expensive than other types of pipeline frost protection, but significant energy savings, higher reliability and ease of use make it preferred.