Outer plastic jacket This outer jacket works by shielding or protecting the heating cableagainst mechanical and moisture damage. It is, however, important to note that the plastic outer jacket is not present on all heating cables. Inner plastic insulation This acts as the main layer of insulation (electrical) between the outside and the live-current heater. The heating cablealso has bus wires which connect the heater to the power source. The conductive core This is where the real magic of self-heating occurs. The conductive core is made of a unique plastic material. This plastic is electrically insulating at high temperature and conductive at low temperatures. This property of the plastic leads to what is commonly referred to as the positive temperature coefficient or simply, the PTC element. This means that, as the temperature increases, so does the resistance of the heating cable. To understand this better, consider the following equation:R= kT, where T is the temperature, k is a constant ratio, and R is the resistance. The actual process is a bit complex and this is a simple equation to show you the general idea. As electricity flows through the plastic material, some of it is absorbed by the resistive plastic, which turns it into heat. It works the same way as to how the tungsten coil absorbs electricity to produce light in an incandescent light bulb.
