To keep heat for water in pipe of solar system.

It consists of two parallel metal bus wires encased in a semi conductive polymer matrix forming a heating unit with a polyolefin jacket as metallic shield. For corrosive and some hazardous environments, additional Fluor plastics over jackets can also be used. As the electric current flows from one of the copper wires, passes the conductive polymer and arrives in the other copper wire, a close circuit is established. The electric power causes PTC polymer to heat up and consequently raises the resistance value. When the PTC polymer reaches the transition temperature, its resistance value takes a step increase, which is high enough to cut off the current and keep the temperature from going any higher, and the purpose of self-temperature regulating is served.