Description
Self-regulating cables are heating cables with a semi-conductive matrix consisting of a mixture of graphite and polymer powder extruded onto two suitably cross-sectioned conductors. This matrix is subsequently irradiated to fix its molecular structure and form a memory of its initial construction.
The matrix is then covered with a polyolefin or other thermoplastic or fluoropolymer sheath, thus forming the base cable.
This cable is then covered with a tinned copper or stainless steel braid for mechanical protection and earthing and, finally, by a final jacket of fluoropolymer or polyolefin or other thermoplastic material.
Upon construction, the graphite molecules tend to link together and form chains that are randomly arranged within the matrix. These chains are conductive and can be assimilated to many small electrical resistances placed in parallel between the two conductors.
When the two conductors are energised at one end and insulated at the opposite end of the circuit, an electric current passes through these micro heating elements and produces a certain amount of heat.
As the temperature of the heating cable increases (due to both the power produced and the external ambient temperature), the polymer molecules expand and tend to break the graphite chains and, as a result, the power produced in the microcircuits decreases.
As a result of the irradiation undergone during construction, the matrix has memorised its initial molecular arrangement and the phenomenon is reversible. Consequently, when the temperature of the cable decreases, the material tends to return to its initial condition and the power produced increases.
