The problem of freezing of sewer communications of external sewerage is best solved at the design stage, using insulation and placing its main part below the freezing depth of the soil. But due to the great depth (more than 1m) or the presence of additional communications, this becomes impossible. The risk of freezing is also subject to parts of water pipes and drains in places where they exit the house and come into direct contact with the ground. Therefore, all these communications need to be protected from possible freezing not only with a layer of thermal insulation, but also with heating elements.
There are several ways to build thermal insulation for sewerage systems with heating, without it, with your own hands or with the help of specialists. One of the most popular and effective heating of sewerage systems is heating with a heating cable.
Heating cables (types)
Produced in one- and two-wire versions. The basis of this type of product is a conductive (heating) core, which, when an electric current passes, releases heat according to the Joule-Lenz law. The heating core is insulated, as a rule, with a heat-resistant material (for example, fluoroplastic). Some types use double insulation. Next is a metal shielding braid in the form of a mesh of thin conductors or just foil. This shell protects it from mechanical damage, and is also a screen. The surface of the wire is covered with a heat-resistant sheath.
This cable works as follows. If it is single-core, then the power supply must be carried out from two sides (as shown in the figure below on the left), and the wire should be evenly distributed in a loop along the entire length, which is extremely inconvenient. The problem of two-way power supply is solved in two-core products, although the principle of operation is similar, but it is more convenient to install and connect (in the figure below, on the right). In addition, for both types, it is necessary to use temperature control of its surface using temperature controllers.
It is a kind of resistive, or rather a modified version of a two-wire. The modification consists in the fact that short sections of heating spiral wires are added to it, located with a certain step. Now, unlike its predecessor, it can be cut into pieces of the desired length with a certain step.
It is a wire with two parallel copper strands, between which there is a semiconductor. This design is covered with protective, electrically insulating and shielding shells. The specific resistance to electric current of a semiconductor is directly proportional to its temperature. That is, the higher its heating temperature, the resistance between the two cores increases and vice versa. As with previous products, heat is released according to the same law (Joule-Lenz), but not in the current-carrying cores, but in the semiconductor separating them. Since its conductivity depends on temperature, the magnitude of the current will also change, and, consequently, the power. In fact, this wire is its own heater and thermostat in any of its sections along its entire length. Accordingly, the amount of heat in each area will be released differently, so that regardless of external conditions, the temperature of its surface will be almost the same at each point.
Such a heating cable consists of an insulated conductive core wound around a ferromagnetic core, which is a pipe. Alternating current creates an alternating magnetic flux, which induces eddy currents in it, and they heat it up.
Such heating is considered obsolete and is now used extremely rarely. This is due not only to low efficiency, but also to the fact that it can only be used for metal pipes.
Which heating cable to choose for heating sewer pipes
To resolve this issue, let’s compare the advantages and disadvantages of the above wires for heating. Resistive single-wire, two-wire, and zonal can be generalized because of their similarity.
Resistive and zone heating cables
Advantages of resistive (including zonal) heating cables:
- The simplicity of the device;
- Relatively low cost;
- Long-term use resistivity stability;
- Long service life if properly installed.
- The inability to change the length (in zonal this problem is partially solved, but the length changes in steps);
- The need for a thermostatic device;
- If the heating wires are close together, if they are intertwined, and even if the surface is dirty, the insulation overheats significantly. Overheating of the insulation leads to its premature aging and possible short circuit;
- Requirements for installation.
Advantages of a self-regulating cable:
- Does not require a separate thermostat;
- The ability to cut the footage of any length (not less than 1.5 m and not more than indicated in the passport);
- During installation, the approach and crossing of wires is allowed, which greatly simplifies the laying;
- Temperature control occurs independently at each point, along the entire length. This completely eliminates its overheating;
- The surface temperature along the entire length is almost the same.
- Compared with resistive, this product has a high cost.
After analyzing the advantages and disadvantages of different types of cables, we can conclude that self-regulating will be much more efficient. When heating sewer systems and drains with it, in addition to the above advantages, significant energy savings can be achieved. To do this, you need an additional thermostat to control the temperature of the external environment.
Choosing a cable for a sewer system
The required heating power is directly related to the heat loss of the heated pipe. It is very important to make the correct selection of power for the sewer system of the desired diameter and the conditions for its heat transfer.
Important! Incorrect power selection can lead to:
- If the power is too high, overheating, as a result of which the service life of the heating system will decrease. In the worst cases, plastic drains can melt. (When using a self-regulating heating cable, overheating is completely eliminated).
- If the power is too low, the system will not be able to withstand low temperatures, which will lead to freezing of drains.
- To reduce the economic efficiency of heating.
- Increasing the likelihood of electric shock to a person or animal.
- Reduced service life of both the heating system and the sewage system itself.
When you build a sewer with your own hands, design its heating and thermal insulation, you can be guided by the table below. It displays the average heat loss depending on the pipe diameter, insulation layer and temperature difference.
We take the power per unit length equal to or slightly greater than the number that we find at the intersection of the desired thickness and temperature difference. Next, we multiply the length of the pipeline by this number and by a safety factor of 1.3, then divide by the cable power according to the passport — this will be the required length.
Reliability of the heating cable
The reliability of a self-regulating cable directly depends on the quality of the heating matrix (semiconductor material between current-carrying cores). The lower the quality, the faster it ages — as a result, the specific heat release and self-regulation decrease. The service life of such a low quality matrix is 3-4 years.
Proven manufacturers who care about their reputation, such as Fujikura, Pentair, Devi, Hemstedt, use quality materials for production. This, of course, translates into a higher price, but its work throughout the entire service life (15 … 20 years) is worth it.
The main stages of laying the heating cable
In private homes and in production, installation of heating is carried out at the stage of insulation of sewer pipes. It is necessary to securely seal the joints to avoid moisture seepage. The cable can be laid on the outside of the pipeline (under thermal insulation) or inside it.
This method of heating the sewer system has many more disadvantages:
- Increased risk of blockage
- The heating cable is constantly exposed to the aggressive environment of drains (accordingly, you need to fork out for a purchase with a more stable outer sheath);
- It is extremely difficult to apply this method on extended communications;
- An additional tee is required.
However, the method of laying inside the pipe can sometimes be the only possible solution. Advantages:
- It is possible to heat pipes with low thermal conductivity or old systems with significant deposits on the walls;
- It is convenient to heat partially in places where the sewerage passes through the foundation;
- It is convenient to heat water pipes and drains without thermal insulation.
The main stages of installation:
- In order to introduce the cable into the sewer, a special coupling-nipple is installed.
- If there is no tee or inspection hole, you can cut a small section, and then mount an adapter of the desired diameter.
- Insert the cable to the required depth.
- The sewer pipe must be sealed. It is necessary to screw the nut with the nipple and check the tightness.
- Connect the cable to the mains. To do this, it is necessary to provide a power socket nearby or a circuit breaker in advance.
When installing a heating cable outdoors, there are two ways — this is laying in a «wave» («spiral») or along the pipe. Regardless of the method, it fits along the entire length. A higher concentration of laying should correspond to places with a higher probability of freezing. Further, it is displayed in a warm place, and only then an electrical connection is made.
This is the most versatile and probably the most effective way. Of course, for this you need to spend time and have the relevant experience in reserve. But this method allows heating the sewer with the possibility of further modifying it at low cost.
- For short lengths, the cable is laid in a spiral wound around the pipe. (calculated length is distributed over the entire pipeline).
- For long distances. We divide the route by the number of sections, a multiple of two (approximately).
- With a margin in length, we fasten the pre-cable product.
- We wrap the resulting loops around the pipe in the opposite direction, one from one.
- We wind the coil in increments of 30-50 cm.
It is attached to the pipe with adhesive or aluminum tape in increments of 0.5-1m or along the cable along the entire length. The aluminum tape is sealed to ensure complete cable sealing.
Laying along the pipe
This is an easier installation method, but slightly worse in terms of heating efficiency. The principle of such laying can be seen in the figure below. With one (left) and two (right) heating elements. Fastening the cable product to the pipe through 0.5-1m or along the entire length is similar to the previous method.
When laying a sewer pipe system in the ground, the same insulation and additional heating are required. In addition, it is recommended to use an outer protective shell. It is recommended not to stick the heating self-regulating cable with a strip of foil, but wrap it completely around the pipe, as shown in the figure below.
Recommendations of the installation masters
- To increase savings when heating the pipes of the sewerage system with a self-regulating cable, you need to use an additional thermostat to control the ambient temperature.
- It is necessary to ensure a reliable connection of sewer joints, to prevent the passage of moisture.
- It is strictly forbidden to mount cable products with conventional insulation internally.
- The permissible temperature of the pipe material, as well as its insulation, must be higher than the temperature to which the cable will be heated.
- The angles of rotation of the heating cable must correspond to those prescribed in its passport.
- During installation, the air temperature at which the laying is carried out must be higher than the permissible one.
- At the time of the first inclusion of a self-regulating cable in the power grid, its power consumption will exceed the nameplate several times. After that, in a few minutes, the indicator will return to normal.
At first glance, the installation of a self-regulating heating cable to protect the pipes of the sewerage system is very simple, but this requires knowledge of the relevant codes and regulations. By following them, you will be able to mount an efficient and reliable heating system.