The principle of operation, characteristics and installation of a heating cable for sewer pipes

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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.

Frozen sew­er pipe

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)

resistive

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.

Zonal

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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.

self-regulating

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.

Inductive

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.

Flaws:

  • 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.

Self-regulating cable

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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.

Flaws:

  • 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:

  1. 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).
  2. If the pow­er is too low, the sys­tem will not be able to with­stand low tem­per­a­tures, which will lead to freez­ing of drains.
  3. To reduce the eco­nom­ic effi­cien­cy of heat­ing.
  4. Increas­ing the like­li­hood of elec­tric shock to a per­son or ani­mal.
  5. 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.

Internal installation

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:

  1. In order to intro­duce the cable into the sew­er, a spe­cial cou­pling-nip­ple is installed.
  2. If there is no tee or inspec­tion hole, you can cut a small sec­tion, and then mount an adapter of the desired diam­e­ter.
  3. Insert the cable to the required depth.
  4. The sew­er pipe must be sealed. It is nec­es­sary to screw the nut with the nip­ple and check the tight­ness.
  5. Con­nect the cable to the mains. To do this, it is nec­es­sary to pro­vide a pow­er sock­et near­by or a cir­cuit break­er in advance.
The main stages of instal­la­tion of a heat­ing self-reg­u­lat­ing cable inside a pipe

outdoor installation

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.

Spiral laying

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.

Instal­la­tion prin­ci­ple:

  1. For short lengths, the cable is laid in a spi­ral wound around the pipe. (cal­cu­lat­ed length is dis­trib­uted over the entire pipeline).
 Coil­ing method for short dis­tances
  1. For long dis­tances. We divide the route by the num­ber of sec­tions, a mul­ti­ple of two (approx­i­mate­ly).
  2. With a mar­gin in length, we fas­ten the pre-cable prod­uct.
  3. We wrap the result­ing loops around the pipe in the oppo­site direc­tion, one from one.
  4. 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

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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

  1. 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.
  2. It is nec­es­sary to ensure a reli­able con­nec­tion of sew­er joints, to pre­vent the pas­sage of mois­ture.
  3. It is strict­ly for­bid­den to mount cable prod­ucts with con­ven­tion­al insu­la­tion inter­nal­ly.
  4. 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.
  5. The angles of rota­tion of the heat­ing cable must cor­re­spond to those pre­scribed in its pass­port.
  6. Dur­ing instal­la­tion, the air tem­per­a­ture at which the lay­ing is car­ried out must be high­er than the per­mis­si­ble one.
  7. 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.

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