The construction of high quality, commercial grade, Self Regulating Cables is basically the same until you get to the outer jacket or exterior insulator. In the middle of a 2 conductor Self Regulating Cable there are two conductors usually made of Copper and coated with something like Tin or Nickel. The two coated Copper conductors are surrounded by a semi-conductive heating matrix or Polymer which some call the “self regulating component”. The semi-conductive heating matrix or Polymer is covered by either a first adhesive inner jacket and then a Polyolefin jacket or just a Polyolefin jacket. In either case, the polyolefin jacket is surrounded by a metallic shield usually constructed of Tinned Copper which is covered by an outer jacket made of either Polyolefin, or Fluoropolymer (“Teflon” is DuPont’s brand name for Fluoropolymer).
Other than cost (Fluoropolymer is significantly higher than Polyolefin) the only significant difference between high quality, commercial grade, CR (Polyolefin) and CT (Fluoropolymer) Self Regulating Cables is the outer jacket. Knowing the difference between CR and CT, what they are designed to do and the applications for which they are suited can result in a great deal of savings because of the cost variation.
Companies specializing in Self Regulating Cables should be able to tell you which cable is best suited for your application and explain to you, in layman’s terms, the reasons the cable they recommend is best. However it is wise to trust, but verify, the information provided because sometimes even those that know better fail to effectively communicate. I have been surprised at the number of times I have seen a CT jacketed cable in a specification for snow melting in asphalt, concrete or under brick or stone pavers or for snow and ice melt on roofs and in rain gutters and downspouts when a CR jacketed cable would perform equally as well and cost substantially less.
In the world of Self Regulating Cables the CR (Polyolefin or sometimes called Modified Polyolefin) Outer Jacket is designed to be used where exposure to aqueous inorganic chemicals is anticipated and, the CT (Fluoropolymer) Outer Jacket is best suited for those applications where exposure to organic chemicals or corrosives is likely.
A very simplistic definition of organic compounds is those that contain carbon like the chemicals found in living organisms. Similarly, a simplistic definition of inorganic compounds is those from a mineral, and not a biological, origin that do not contain carbon. While there are a few exceptions to these simplistic definitions I think that they serve our needs for a discussion pertaining to Self Regulating Cables.
According to Wikipedia, “Aqueous” means dissolved in water and an “Aqueous Solution” means a solution in which the solvent is water. Examples of aqueous solutions include: soda, saltwater, rain, etc.
Summarizing, Self Regulating Cables which have a CR (Modified Polyolefin or Polyolefin) Outer Jacket are suitable for all applications where they may be exposed to Inorganic compounds (minerals such as Sodium, Ozone, Carbon Monoxide, etc. ) that are dissolved in water (Aqueous Inorganic Chemicals) as well as where they are exposed to oil and gasoline. Acceptable applications for CR Self Regulating Cables include roof snow and ice melting, rain gutter and downspout heating, snow melting off of asphalt, concrete and paver surfaces, warming of floors, heating of buildings, warming of pipes. and other applications where the cable will not be subjected to organic or corrosive compounds.
CT (Fluoropolymer or “Teflon” by DuPont) Outer Jacketed Self Regulating Cables best serve the needs of industrial applications where there is potential for the cable to be exposed to Organic and corrosive compounds such as Methane, Butane, Acetone, Toluene, Acetylene, Ethyl Alcohol, Acid, etc