Insulation is a non-conductive material, or a material resistant to the flow of electric current. It is often called a dielectric in radio frequency cables. Insulation resists electrical leakage, prevents the wire’s current from coming into contact with other conductors, and preserves the material integrity of the wire by protecting against environmental threats such as water and heat. Both the safety and effectiveness of the wire depend on its insulation.
Following is a list of insulation materials with information on the typical uses, advantages, and disadvantages for each option.
Polyvinyl Chloride (PVC)
PVC is a relatively inexpensive and easy-to-use material, with the potential to be used in diverse applications. The maximum temperature range is -55°C to 105°C and is flame, moisture, and abrasion resistant. It also holds up against gasoline, ozone, acids, and solvents. It can also be used for medical and food related purposes as it is odorless, tasteless, and non-toxic. PVC can be used in both heavy and thin wall applications. PVC should not be used when flexibility and an extended flex life are required at low temperatures. When used in retractile cord applications, it also shows below average flexibility. PVC displays high attenuation and capacitance loss, meaning that power is lost when used in an electrical system.
Semi-Rigid PVC (SR-PVC)
This is mainly used as a primary insulation and is very abrasion resistant. (For 30-16 gauge, a 10 mil. wall meets UL style 1061, 80°C, 300 volts.) Semi-Rigid PVC is also heat, water, acid, and alkali resistant, as well as flame retardant.
Plenum Polyvinyl Chloride (Plenum PVC)
Plenum PVC is suitable for use in building spaces behind dropped ceilings or raised floors which are left open to allow for air circulation. Standard PVC is considered a non-plenum insulation option because it does not exhibit the qualities necessary for safe usage in plenum areas. To be plenum-rated the insulation must meet more stringent fire safety regulations.
This compound is used most in coaxial and low capacitance cables because of its exemplary electric qualities. Many times it is used in these applications because it is affordable and can be foamed to reduce the dielectric constant to 1.50, making it an attractive option for cables requiring high-speed transmission. Polyethylene can also be cross-linked to produce high resistance to cracking, cut-through, soldering, and solvents. Polyethylene can be used in temperatures ranging from -65°C to 80°C. All densities of Polyethylene are stiff, hard, and inflexible. The material is also flammable. Additives can be used to make it flame retardant, but this will sacrifice the dielectric constant and increase power loss.
This material is very similar to Polyethylene, but has a wider temperature range of -30°C to 80°C. It is used primarily for thin wall primary insulations. Polypropylene can be foamed to improve its electrical properties.
Polyurethane is known for its extreme toughness, flexibility, and flex life, even in low temperatures. It also has excellent ratings for chemical, water, and abrasion resistance. This material works well in retractile cord applications and can be a good option for salt-spray and low-temperature military purposes. Polyurethane is a flammable material. The flame retardant version sacrifices strength and surface finish. Polyurethane’s main disadvantage though, is its poor electrical properties, making it suitable for jackets only.
Chlorinated Polyethylene (CPE)
CPE displays very good heat, oil, and weather resistance. Many times CPE serves as a lower cost, more environmentally friendly alternative to CSPE. Its reliable performance when exposed to fire also makes it a favorable alternative to PVC insulation. Chlorinated Polyethylene is commonly found in power and control cables and industrial power plant applications.
Nylon is usually extruded over softer insulation compounds. It serves as a tough jacket, exhibiting strong abrasion, cut-through, and chemical resistance, especially in thin wall applications. It is also extremely flexible. One disadvantage of Nylon is its absorption of moisture which degrades some of its electrical properties.
Thermoplastic Rubber (TPR)
In many applications, TPR is used to replace true thermoset rubber. It has improved colorability, higher processing speeds, and a wider usable temperature range. It also displays excellent heat, weather, and age resistance without curing. TPR is not cut-through resistant, but can be used in applications where other properties of rubber are preferred.
This is a synthetic thermoset rubber that must be vulcanized to obtain its desired qualities. It exhibits supreme abrasion, cut-through, oil, and solvent resistance. Neoprene is also known for its long service life and wide ranges of temperature and usability. It is remarkably flame retardant and self-extinguishing. >Military products often incorporate Neoprene. This material is especially desirable for hand-held cordsets.
Styrene Butadiene Rubber (SBR)
This is a thermoset compound with qualities similar to Neoprene. It has a temperature range of -55°C to 90°C. SBR is primarily used in Mil-C-55668 cables.
This material is extremely heat resistant and flame retardant and can be used in temperatures up to 180°C. It is moderately abrasion resistant. Silicone is also extremely flexible. Benefits include a long storage life and good bonding properties necessary in many electrical applications.
Fiberglass is the most widely used glass insulation. It can be used continuously in temperatures up to 482°C. This material is moisture and chemical resistant, but only fairly abrasion resistant. Its common applications include heat treating, glass and ceramic kilns, foundries, and extensive applications in aluminum processing.
Ethylene Propylene Rubber (EPR)
EPR is known for its excellent thermal characteristics and electrical properties, allowing a smaller cross-sectional area for the same load carrying capacity of other cables. It is commonly used in high-voltage cables. The flexibility of this material also makes it appropriate for temporary installations and applications in the mining industry. These rubbers are also valuable for their heat, oxidation, weathering, water, acid, alcohol, and alkali resistance. EPR can be used in the temperature range of -50°C to 160°C. EPR is not as tear resistant as other insulation options. It is also relatively soft and may require more care during installation to avoid damage.
Rubber insulation generally refers to both natural rubber and SBR compounds, each available in a variety of formulas for use in a wide range of applications. Because formulas vary, so do temperature ranges and some other basic characteristics. While this type of insulation has poor oil, and ozone resistance, it exhibits good low-temperature flexibility, good water and alcohol resistance, good electrical properties, and excellent abrasion resistance.
Chlorosulfonated Polyethylene (CSPE)
CSPE works well as low-voltage insulation. It is known for its ability to perform through a wide temperature range as well as for its resistance to chemicals and UV rays. This insulation material can be found in appliance wire, lead wire, coil leads, transformer leads, and motor lead wire. Chlorosulfonated Polyethylene is sometimes referred to as Hypalon, a registered trademark of Dupont.
Ethylene Propylene Diene Monomer (EPDM)
This synthetic rubber insulation displays outstanding heat, ozone, weather, and abrasion resistance. EPDM also exhibits excellent electrical properties. Further benefits include excellent flexibility at both high and low temperatures, from -55°C to 150°C, as well as good dielectric strength. EPDM replaces silicone rubber in some applications.
PFA has temperature ratings ranging from 250°C to 65°C. It also has a very low dissipation factor, making it an electrically efficient option. It does not exhibit thermoset qualities, limiting it to use only in select applications. PFA is also an expensive material, though it can be processed in long lengths.
PTFE is a thermoplastic material that can be used across a wide temperature range of
-73°C to 204°C. It is extremely flexible, as well as, water, oil, chemical, and heat resistant. The mechanical properties of PTFE are low compared to other plastics.
Fluorinated Ethylene Propylene (FEP)
This material is widely used due to its processing characteristics and wide range of applications. It is also highly flame resistant. Improved data transmission can also be achieved when FEP is foamed. Pricing and processing are also being improved. FEP is commonly used in plenum cable and military applications.
ETFE Tefzel and ECTFE Halar
These materials are stronger and more flexible than PFA or FEP and can become thermoset through irradiation. Foaming ECTFE and ETFE improves data transmission and reduces weight. ETFE and ECTFE lack many of the electrical advantages of FEP.
Polyvinylidene Fluoride (PVDF)
PVDF is flexible, lightweight, and thermally stable, as well as chemical, heat, weather, abrasion, and fire resistant. It is also a relatively low cost insulation option. This insulation is used in a wide range of industries and applications. It is often found in cables meeting the UL Standard 910 Plenum Cable Flame Test, deeming the cables suitable for use in a building’s space for air circulation, typically behind dropped ceilings or raised floors. PVDF is also commonly called Kynar, a registered trademark of Arkema Inc.
Thermoplastic Elastomers (TPE)
Thermoplastic elastomers consist of a mix of polymers, typically a plastic and a rubber, to combine the benefits of each material into one insulating product. TPE can be molded, extruded, and reused, similar to a plastic, while maintaining the flexibility and stretch of rubber. TPE is commonly used in applications where conventional elastomers are unable to provide the necessary range of physical properties. They are found increasingly in automotive applications and household appliances. Disadvantages of TPE include poor chemical and heat resistance, low thermal stability, and higher cost than other types of insulation.