These are one of the most common types of heating cables available on the market today. The general construction is that there are two bus-wires (Live and Neutral) carrying the supply voltage.
A conductive matrix is extruded over the bus-wires. This is actually the heating element and not an insulating layer.
To provide electrical insulation, a layer of thermoplastic is then extruded over the matrix and conductors.
As an option, a further layer of metallic braiding is normally applied to the cable. This layer provides both mechanical protection and also an earth path for earth leakage detection. As a final option, a layer of thermoplastic or fluoropolymer is extruded over the final cable. This final layer provides UV and further mechanical protection. In some industries, the fluoropolymer layer is preferred because of its resistance to acids and chemicals (e.g. oil refineries).
If the temperature drops, the heating cable will start increasing its output again. This is the main principle of self-regulating heaters.
Typically self-regulating cables come in various output ranges, and a maximum temperature that they can withstand. For example the graph above, the maximum operating range is up to 65°C.
The great advantage of self-regulating cables is that they can be cut anywhere along its length. This allows long reels to be provided to site and the cable can be pulled from the reel and installed very quickly without knowing the exact length of the equipment to be heated.