Self-regulating heating cables

While resistance heating cables heat evenly along their whole length and any blockage affecting the heat delivery in any of its parts leads to local overheating, the structure of self-regulating cables ensures the automatic regulation of the heating output depending on the local temperature, and this at any point along its length.

The cable is formed by two copper conductors between which there is a semi-conductive heating core. When the ambient temperature rises, the resistance of the heating core increases and its output thus decreases. The opposite is true when the temperature drops - the output of the cable increases. The cables can thus touch and cross one another or pass through environments with different temperatures without there being a danger of overheating or burning. The structure enables the reduction of the cable to any length and the double insulation with a protective screen provides high dielectric strength, protection against humidity and resistance against mechanical damage. These cables are offered in four output strengths – 10, 15, 20 and 30 W/m. They are mainly used for the anti-freeze protection of pipes (10 and 15 W/m), or roofs, eaves troughs and downpipes (20 and 30 W/m).

As it is possible to cut self-regulating cables to any length (only the maximum length is limited depending on the protection), circuits are not produced in a range of types but it is necessary to use accessories for the cables (KIT No.4) which enable the ending of cables (the closing of the electric circuit) and the connection of connecting conductors (known as cold ends).
Even though self-regulating heating cables change their output depending on the ambient temperature, they never switch themselves off completely. Therefore, it is necessary to use suitable regulation even with self-regulating cables.

Self-regulating cables and floor heating
As was stated above, self-regulating cables cannot overheat because of their construction. In the case of electric floor heating, heating cables mustn’t generally be installed into surfaces where the dissipation of heat cannot be guaranteed. There is a danger that the cable could overheat and thus its life span could be reduced – therefore, self-regulating cables might seem to be a good option. Such cables could be laid within the whole surface and if, for example, the furniture was moved, there would be no danger that the cables will overheat. Heating systems with self-regulating cables keep periodically reappearing on the market. The self-regulating property of the cables is presented here as a great advantage and the cables are often described as "intelligent heating cables".

This idea is logical, of course, as the cables really cannot overheat, but in practice a different problem emerges. If the thermal resistance of the layer above the floor heating is increased (for example by using materials with lower thermal conductivity such as wood, laminate or carpet), standard resistance cables will ‘heat through’ this layer – the temperature below the bottom side of the wear layer will increase and the heat will gradually start penetrating the covering. However, self-regulating cables react to temperature increases by decreasing their output, which means that in this case they will basically stop heating. The same effect occurs when a higher temperature is required in the room – also in this case, it is necessary to heat the floor to a higher temperature. The end result is that there is a very real danger that the self-regulating cables will not be capable of heating the building – this experience was recorded e.g. in Scandinavian countries where experiments were carried out concerning the use of self-regulating cables for floor heating in the 1990s and where such applications have now been completely abandoned.