What Is High Temperature Wire?
High temperature wires are for applications where temperatures exceed 150 degrees Celsius in normal use. Applications for heat-resistant wire include internal wiring of furnaces, cooking appliances, and industrial heating applications. Common insulation and jacket materials used for high temperature lead wires include silicone, perfluoroalkoxy (PFA), polytetrafluoroethylene (PTFE), mica, and fiberglass.
Factors to Consider When Selecting Heat-resistant Wire
The most important characteristic of high temp wire is the ability to withstand the maximum operating temperature at the point of application. Secondly, consider the wire's ampacity, (maximum current rating) at that temperature. Note that for a given American Wire Gauge (AWG) size, the ampacity of high temperature cable is higher than for standard electrical wires because of the higher allowable operating temperature. Other points to consider include flexibility, abrasion, and chemical resistance.
Conductor Materials
Pure copper corrodes more easily at high temperatures, so high temperature wire uses the following heat-resistant conductor materials:
- Tin-plated copper: Suitable for moderately high temperatures up to 180ºC
- Nickel-plated copper: For high temperatures up to 450ºC
- Nickel wire: Able to withstand very high temperatures above 450ºC
Common Types of High Temperature Wire
Silicone Insulated Wires (180ºC)
You can use silicone insulated single conductors for operating temperatures up to 180ºC. Silicone can withstand 250ºC for a short time and it has good low-temperature properties down to -25ºC. This material is self-extinguishing and has good flame-retardant properties. The addition of a fiberglass jacket impregnated with a high temperature saturant improves abrasion resistance and heat resistance. Examples include silicone rubber cable, silicone rubber motor lead (SRML), and silicone fixture (SF-2) wire.
Teflon Glass Glass Teflon (TGGT) Wires (250ºC)
Teflon® is a polytetrafluoroethylene (PTFE) originally developed by DuPont. TGGT wire has PTFE tape insulation covered by a high temperature sealant impregnated fiberglass jacket. You can use this wire continuously at 250ºC. In some instances, manufacturers place a ceramic tape on top of the PTFE wire insulation (TCGT).
High Temperature Mica Glass Wires (450ºC)
Mica is an excellent high temperature insulate. Mica glass (MG) insulation has multiple layers of a mica and glass composite tape usually covered by a fiberglass jacket impregnated with a high temperature saturant. Mica insulated wire protects cables at temperatures of up to 450ºC. Flame 1000 high temperature cable has a mica thermal tape covered by a PTFE moisture barrier and a fiberglass jacket. While its maximum sustained operating temperature is 450ºC, this wire has excellent flame reactance, passing the IEEE 383 1000ºC vertical tray flame test for a minimum of two and a half hours.
Thermocouple Wires
Thermocouple wires use carefully selected alloys to form a thermoelectric junction that's sensitive to temperature. Each wire is a different material. Standard thermocouple types include Types E, J, K, N, R, and T. The only application for these cables is measuring temperature and you must use a compatible extension wire if there's a need to extend the thermocouple wire from the point of measurement to the measuring instrument. Depending on the cable you can use thermocouple cables for measurements between -270ºC and 1260ºC.