High Temperature Cable Guide: Insulation Types, Ratings & Selection

High temperature cable is engineered to operate reliably in environments where standard PVC and THHN-insulated wire would degrade, melt, or fail. These cables use specialized insulation and jacket materials — PTFE (Teflon®), PFA, FEP, ETFE, polyimide (Kapton®), silicone rubber, fiberglass, mica, and cross-linked polyolefin — that maintain their electrical and mechanical properties at sustained temperatures from 150°C to over 550°C. High temperature insulation is also used in plenum-rated (CMP, CL2P, CL3P, FPLP) and tray-rated (Type TC) cables where flame resistance and low smoke properties are critical. This guide covers insulation types, temperature ratings, construction methods, applicable standards, and selection criteria for high temperature wire and cable.

Why Standard Cable Fails at High Temperatures

Standard building wire insulation materials have well-defined thermal limits. THHN/THWN conductors are rated to 90°C in dry locations — a rating determined by the overall nylon/PVC insulation system, not the PVC alone. Cross-linked polyethylene (XLPE) typically tops out at 90°C continuous with a 130°C emergency rating. When these materials are exposed to temperatures above their rating, the insulation softens, loses dielectric strength, becomes brittle over time, and eventually cracks or melts — creating short circuits, ground faults, and fire hazards.

High temperature cable replaces these conventional insulation materials with compounds specifically formulated to resist thermal degradation. The result is cable that maintains flexibility, dielectric strength, and mechanical integrity at temperatures where standard cable would fail within hours or days.

High Temperature Insulation Materials

The insulation material determines the cable's maximum operating temperature, chemical resistance, flexibility, and cost. Each material occupies a specific niche in the temperature spectrum.

PTFE (Polytetrafluoroethylene)

PTFE — commonly known by the brand name Teflon® — is the benchmark high temperature insulation. It is rated for continuous operation at 260°C (500°F) and can withstand brief excursions above 300°C. PTFE offers outstanding chemical resistance (virtually inert to all common chemicals, solvents, and acids), a low coefficient of friction, excellent dielectric properties, and UV resistance. The tradeoffs are cost (PTFE is among the most expensive insulation materials) and limited flexibility compared to silicone.

PTFE cannot be melt-processed like most thermoplastics. Instead, it is manufactured using ram extrusion (where PTFE resin is compacted and pushed through a die under high pressure) or tape wrapping (where thin PTFE tape is spirally wrapped around the conductor and sintered). This specialized manufacturing contributes to PTFE wire's higher cost compared to melt-extruded fluoropolymers like FEP.

PTFE-insulated wire is widely used in aerospace, semiconductor manufacturing, laboratory equipment, industrial ovens, and chemical processing where both extreme heat and aggressive chemical exposure are present.

PFA (Perfluoroalkoxy)

PFA-insulated cable is rated for continuous operation at 260°C (500°F), matching PTFE's temperature rating. Unlike PTFE, PFA is a melt-processable fluoropolymer, allowing it to be conventionally extruded over conductors. This gives PFA a smoother, more uniform wall thickness and better flex life than ram-extruded PTFE, while retaining nearly identical chemical resistance and dielectric properties.

PFA is often specified where the application demands PTFE-level thermal and chemical performance but requires a smoother surface finish, better flexibility, or more consistent concentricity. It is common in semiconductor fab wiring, analytical instrumentation, and chemical processing equipment. PFA is more expensive than FEP but less costly to process than PTFE in many configurations.

Polyimide (Kapton®)

Polyimide film — best known by the DuPont trade name Kapton® — is rated for continuous operation at 240°C to 260°C depending on the specific formulation, with short-term survival above 400°C. Polyimide is applied as a thin tape wrap over the conductor rather than extruded, resulting in an exceptionally thin, lightweight insulation wall that saves space and weight in tight wiring harnesses.

Polyimide excels in applications requiring extreme temperature resistance in a minimal cross-section: aerospace wiring harnesses, motor and transformer windings, miniature electronics, and space-rated cable. It has excellent dielectric strength for its thickness, good chemical resistance, and inherent radiation resistance. The primary limitations are susceptibility to hydrolysis (degradation from moisture combined with heat over long periods) and higher cost than fluoropolymer insulations. Polyimide-insulated wire is also less flexible than silicone and can be prone to cracking if subjected to sharp bends or mechanical stress at low temperatures.

Polyimide is commonly specified under MIL-DTL-16878 (Type EE and similar designations) and SAE AS22759 for aerospace wire. It is also widely used as a wrapping tape over other insulation layers and as a high-temperature tape shield carrier in place of standard Mylar® in cables rated above 150°C.

FEP (Fluorinated Ethylene Propylene)

FEP-insulated cable is a fluoropolymer closely related to PTFE but with a lower melting point, allowing it to be melt-extruded rather than ram-extruded like PTFE. FEP is rated for continuous operation at 200°C (392°F). It shares many of PTFE's properties — excellent chemical resistance, low friction, strong dielectric performance — but at a lower cost and with better processability.

An important note on FEP temperature ratings: FEP cable with tinned copper conductors is commonly available rated at 200°C for non-UL applications. However, UL-listed FEP cable with tinned copper conductors is typically rated at 150°C, since tin plating has a lower oxidation threshold. For UL-listed 200°C FEP cable, nickel-plated or silver-plated conductors are required.

FEP is commonly used for hookup wire, instrumentation cable, and plenum-rated cables where both high temperature performance and flame resistance are required. Many plenum cables (CMP, CL2P, CL3P, FPLP) use FEP insulation for its low smoke generation and flame-spread characteristics, making FEP one of the most widely used high temperature insulation materials across both industrial and building wire applications.

Foam FEP (Foamed Fluorinated Ethylene Propylene)

Foam FEP is a specialized variant of solid FEP where gas micro-bubbles are incorporated into the insulation during extrusion, creating a cellular structure with a lower dielectric constant than solid FEP. Standard solid FEP has a dielectric constant of approximately 2.1; foaming reduces this to approximately 1.4–1.7, depending on the foam density. This lower dielectric constant translates directly to reduced signal loss, lower capacitance, and improved impedance control — making foam FEP the insulation of choice for high-frequency data cables, coaxial cables, and plenum-rated network cables where signal integrity is critical.

Foam FEP is rated for continuous operation from -80°C to +200°C, matching solid FEP's temperature range. It retains solid FEP's chemical resistance and flame properties while offering reduced weight (important in aerospace and robotics), increased flexibility (the foam structure is softer and more pliable than solid FEP), and improved high-frequency electrical performance. The tradeoff is that foam FEP is typically used only as conductor insulation, not as an overall cable jacket, since the cellular structure is less mechanically robust than solid FEP.

Foam FEP is widely used in plenum-rated (CMP, CL2P) data cables where low smoke, low flame spread, and high-frequency performance must all be achieved simultaneously. It is also common in aerospace wiring, medical instrumentation, and high-speed data interconnects.

ETFE (Ethylene Tetrafluoroethylene)

ETFE-insulated cable is rated for continuous operation at 150°C (302°F). It offers better mechanical strength and abrasion resistance than PTFE or FEP, making it suitable for applications where the cable is subject to physical abuse in addition to heat. ETFE also has good chemical resistance and radiation resistance, making it popular in aerospace, nuclear, and automotive wiring.

Silicone Rubber (SR)

Silicone rubber (SR) insulated cable is rated for continuous operation at 150°C to 200°C depending on the formulation, with some specialty grades rated to 250°C. Silicone's primary advantage is flexibility — it remains soft and pliable across a wide temperature range (typically -60°C to +200°C), making it the preferred choice for applications requiring frequent flexing, tight bend radii, or operation in both extreme cold and heat.

Silicone-insulated cable is common in appliance wiring (ovens, ranges, commercial cooking equipment), medical devices, lighting fixtures, and industrial heating elements. The main drawback is lower mechanical strength — silicone is softer and more susceptible to cut-through and abrasion than fluoropolymer insulations.

SRML (Silicone Rubber with Motor Lead)

SRML wire is a silicone rubber insulated, fiberglass braided wire rated for 150°C to 200°C depending on the specific construction. The fiberglass outer braid provides mechanical protection and improved abrasion resistance over standard silicone wire, addressing silicone's primary weakness. SRML is commonly used for motor leads, transformer connections, lighting fixture wiring, and appliance internal wiring where both flexibility and ruggedness are needed at elevated temperatures.

Fiberglass / MG Wire (Glass Braid)

Fiberglass insulation, often applied as a braided or served layer, is rated for continuous operation at 200°C to 450°C+ depending on the construction. Fiberglass is inherently non-combustible and provides excellent thermal resistance. It is often used in combination with other insulation layers — for example, TGGT wire uses a dual fiberglass braid over a PTFE primary insulation.

MG wire (mica/glass) takes fiberglass insulation to the extreme, combining mica tape with a fiberglass braid for continuous ratings up to 550°C. MG wire is used in high-heat industrial applications such as furnaces, kilns, foundries, and glass manufacturing where no polymer-insulated cable can survive.

Fiberglass-insulated cable is used in furnaces, kilns, glass manufacturing, foundries, and other extreme-heat industrial environments. The downsides are limited flexibility (fiberglass braid is stiffer than polymer insulations) and susceptibility to moisture absorption, which can degrade dielectric performance in humid environments.

Mica Tape

Mica tape is used as a fire-barrier insulation layer, rated to withstand temperatures above 800°C for short durations. Mica-wrapped cables are common in fire survival circuits — applications where the cable must continue to function during a fire to power emergency systems (fire pumps, emergency lighting, alarm circuits). Mica is typically used as part of a composite insulation system rather than as the sole insulation.

Cross-Linked Polyolefin (XLPE / XLPO)

Cross-linked polyolefin insulations are rated for 90°C to 125°C continuous, placing them at the lower end of the "high temperature" spectrum. However, the cross-linking process (typically irradiation or chemical cross-linking) gives these materials significantly better thermal aging, chemical resistance, and mechanical properties compared to standard thermoplastic insulation. XLPE is widely used for medium voltage cable, automotive wire, and building wire applications where a modest temperature upgrade over PVC is needed without the cost of fluoropolymers.

Temperature Ratings at a Glance

Common High Temperature Cable Types

TGGT (Teflon®/Glass/Glass/Teflon®)

TGGT is a high temperature appliance wire constructed with a PTFE primary insulation, dual fiberglass braid, and a PTFE outer jacket. It is rated for 250°C continuous and is UL Style 5107/5128 (depending on voltage rating). TGGT is the standard wire for commercial oven wiring, industrial heating elements, kiln controls, and appliance internal connections where temperatures exceed the capability of standard appliance wire.

TGGT is available in single-conductor configurations from 20 AWG through 8 AWG, typically with nickel-plated copper conductors. The nickel plating prevents copper oxidation at elevated temperatures, which would otherwise increase conductor resistance and weaken terminations.

PFA Wire

PFA wire is rated for 260°C continuous and offers a melt-processable alternative to PTFE. PFA can be extruded with tighter dimensional tolerances and a smoother finish, making it preferred for applications where concentricity and surface quality matter (semiconductor tools, high-purity chemical systems, analytical instruments). PFA hookup wire is available with nickel-plated or silver-plated copper conductors.

FEP Hookup Wire

FEP hookup wire is rated for 200°C (non-UL) or 150°C (UL-listed with tinned copper conductors) and is available in a wide range of sizes and colors for electronic and instrumentation wiring. FEP wire is commonly used in laboratory equipment, medical devices, semiconductor manufacturing tools, and any application where the cable must resist both heat and chemical attack. For UL-listed FEP wire rated at the full 200°C, nickel-plated or silver-plated conductors are required.

ETFE Wire

ETFE wire rated at 150°C offers the best abrasion resistance among fluoropolymer insulations. ETFE is widely used in aerospace wiring harnesses (SAE AS22759 types), automotive under-hood applications, and nuclear facility cable where radiation resistance is required in addition to elevated temperature performance.

PTFE Hookup Wire (MIL-W-16878)

MIL-spec PTFE hookup wire is rated for 200°C to 260°C depending on the specific type designation. It uses solid or stranded silver-plated or nickel-plated copper conductors with ram-extruded or tape-wrapped PTFE insulation. These wires are specified in aerospace, defense, and high-reliability electronics where consistent performance at extreme temperatures and in harsh chemical environments is mandatory.

Silicone Rubber (SR) Appliance Wire

Silicone rubber appliance wire (UL 3512, UL 3530, and similar styles) is rated for 150°C to 200°C. It is the standard choice for appliance internal wiring (ovens, ranges, dryers, commercial cooking equipment) where flexibility and heat resistance are both required. Silicone wire is softer and easier to route than PTFE or fiberglass-insulated wire, making it preferred for assembly applications.

SRML Wire

SRML wire adds a fiberglass outer braid to silicone rubber insulation, providing the flexibility of silicone with better abrasion and cut-through resistance. SRML is commonly specified for motor leads, transformer connections, and industrial heating equipment where the cable is subject to mechanical contact or vibration in addition to heat.

MG Wire (Mica/Glass)

MG wire is rated for continuous operation at 550°C, making it one of the highest-rated wire types available. It uses a mica tape primary insulation with a fiberglass braid outer covering, over nickel-plated or nickel-clad copper conductors. MG wire is used in applications where no polymer insulation can survive: furnace wiring, kiln controls, glass manufacturing, foundry equipment, and high-temperature industrial process connections.

RTD Wire (Resistance Temperature Detector)

RTD wire is specialized cable designed for connecting resistance temperature detectors (RTDs) and thermocouples to instrumentation systems. RTD cable typically uses high temperature insulation (FEP, PFA, PTFE, or fiberglass) to ensure accurate temperature measurement in hot environments without the cable itself affecting readings. RTD cable is available in 2-wire, 3-wire, and 4-wire configurations with shielding options, and is essential in process control, HVAC, food processing, and industrial monitoring applications.

High Temperature Multi-Conductor Cable

Multi-conductor high temperature cables combine two or more insulated conductors within an overall jacket, with both insulation and jacket rated for elevated temperatures. Construction varies: some use FEP-insulated conductors in a fiberglass or PTFE jacket, while others use silicone or ETFE throughout. These cables are used for instrumentation, control, and power wiring in high temperature environments such as steel mills, glass plants, chemical processing, and power generation facilities.

Belden, Alpha Wire, and other specialty manufacturers offer high temperature multi-conductor cables in various configurations for industrial applications.

Mineral-Insulated (MI) Cable

Mineral-insulated cable uses magnesium oxide (MgO) powder as insulation, packed between copper conductors and a seamless copper or alloy outer sheath. MI cable is rated for continuous operation at 250°C (with some constructions rated higher) and can survive temperatures exceeding 1000°C during fire exposure. MI cable is inherently non-combustible, waterproof, and immune to radiation.

MI cable is used in fire survival circuits, nuclear power plants, high-rise building fire alarm and emergency power systems, and industrial installations where cable must survive a fire and continue to function. The tradeoffs are high cost, difficult termination (requires specialized sealing glands), and limited flexibility.

High Temperature Insulation in Plenum, Riser, and Tray Cable

High temperature insulation materials — particularly FEP — are not limited to dedicated high temperature cable. They also serve as the primary insulation in several common building and industrial cable types where flame resistance and low smoke generation are the driving requirements:

Plenum Cable (CMP, CL2P, CL3P, FPLP): Plenum-rated cables are required in air-handling spaces (above drop ceilings, under raised floors) where building air circulates. FEP insulation is the most common choice for plenum cables because it meets the strict flame spread and smoke generation requirements of UL 910 (the Steiner Tunnel test). Many CMP-rated network cables (Cat5e, Cat6, Cat6A), CL2P/CL3P low-voltage cables, and FPLP fire alarm cables use FEP-insulated conductors. While these cables are not marketed as "high temperature cable," their FEP insulation inherently provides elevated temperature performance.

Tray Cable (Type TC): Tray cables rated for cable tray installation under NEC® Article 336 may use high temperature insulation materials depending on the application environment. High temperature tray cable constructions using XLPE, ETFE, or FEP insulation are specified for industrial environments where cable trays run through hot areas — near boilers, process equipment, or in petrochemical facilities. For more information, see our Tray Cable Applications & Selection Guide.

Fire Alarm Cable (FPLP, FPLR): Fire alarm cables in plenum spaces (FPLP) typically use FEP insulation. Fire alarm circuits in general may also use high temperature insulation where the cable routes through hot mechanical rooms or near heating equipment. See our Fire Alarm Cable Guide for detailed information on types and ratings.

Conductor Plating for High Temperature Service

At temperatures above 150°C, bare copper conductors begin to oxidize at an accelerated rate. Copper oxide is a semiconductor with significantly higher resistance than pure copper, causing increased resistance at termination points, reduced current-carrying capacity, and weakened crimps and connections over time. High temperature cables address this with plated conductors:

Always match the conductor plating to the insulation temperature rating. Using tin-plated conductors in a 260°C-rated PTFE cable would create a weak point — the tin would oxidize long before the insulation reached its thermal limit. This is why FEP cable with tinned copper may be rated at 200°C for non-UL applications but only 150°C when UL-listed — UL's testing accounts for the conductor plating's thermal limitation.

Conductor Stranding for High Temperature Cable

The stranding type affects a cable's flexibility, current-carrying efficiency, and suitability for high temperature service. Common conductor constructions used in high temperature wire include:

Solid Conductor: A single wire. Solid conductors are used in smaller gauges (typically 20 AWG and smaller) for hookup wire and fixed installations. Solid wire is easier to terminate but has limited flexibility and will break if repeatedly flexed.

Stranded Conductor: Multiple individual wires twisted together. Standard stranded conductors (Class B per ASTM B8) provide a good balance of flexibility and cost. Most high temperature cables 18 AWG and larger use stranded conductors.

Finely Stranded (Flexible) Conductor: Higher strand counts (Class K, Class M) using finer individual wires yield significantly greater flexibility. Finely stranded conductors are specified for portable cords, robotic cable, and any application where the cable must flex during service. In high temperature applications, finely stranded silicone and PTFE wire is used for appliance leads, motor connections, and instrumentation cable that must be routed through tight spaces.

Rope Lay / Concentric Conductor: Bundles of stranded groups twisted concentrically. Rope lay stranding provides the highest flexibility in larger conductor sizes and is used in welding cable, mining cable, and heavy-duty portable cables that must flex while carrying high current.

In high temperature cables, the conductor stranding interacts with the plating: finer strands have more total surface area, which means the plating quality (tin, silver, or nickel) is even more critical since oxidation of the individual strand surfaces can degrade the conductor's effective cross-section more rapidly than in a solid or coarsely stranded wire.

Shielding in High Temperature Cable

Many high temperature cable applications require shielding for electromagnetic interference (EMI) protection, signal integrity, or noise immunity. The shield construction must also withstand the same elevated temperatures as the insulation and jacket. Common shielding options for high temperature cable include:

Aluminum/Mylar® Foil Shield: A thin aluminum foil laminated to a polyester (Mylar®) carrier, typically with a drain wire for grounding. Foil shields provide 100% coverage and are effective against high-frequency interference. Standard aluminum/Mylar® foil is limited to approximately 150°C. For higher temperatures, aluminum/polyimide (Kapton®) foil replaces the Mylar® carrier, extending the shield rating to 200°C or higher.

Braid Shield: Interwoven strands of tinned copper, silver-plated copper, or nickel-plated copper braided around the cable core. Braid shields provide good coverage (typically 80–95%) and excellent low-frequency shielding effectiveness. For high temperature applications, nickel-plated copper braid is used above 200°C, and stainless steel braid for extreme temperatures or corrosive environments.

Spiral (Serve) Shield: Conductors spirally wrapped around the cable core. Spiral shields offer excellent flexibility and long flex life (making them preferred for portable and robotic cables), with coverage up to 97%. However, they are less effective against high-frequency interference than braid or foil shields. Tinned copper, silver-plated copper, and nickel-plated copper serve shields are available depending on the temperature requirement.

Combination Foil + Braid: Many high-performance cables combine a foil inner shield (for high-frequency coverage) with a braid outer shield (for low-frequency coverage and mechanical strength). This combination is common in high temperature instrumentation cables, RTD cables, and data cables where comprehensive EMI protection is needed at elevated temperatures.

Applicable Standards and Ratings

High temperature cable is governed by several overlapping standards depending on the application:

UL 758 (Appliance Wiring Material): Covers the majority of high temperature hookup and appliance wire types. UL assigns "Style" numbers (e.g., UL 5107 for TGGT) that define the construction, voltage rating, and temperature rating of each wire type. All UL-listed high temperature wire has been tested to verify its temperature rating under controlled conditions.

UL 44 (Thermoset-Insulated Wires and Cables): Covers higher-voltage thermoset (rubber, XLPE, EPR) insulated power cables, some of which carry elevated temperature ratings.

UL 910 (Steiner Tunnel Test): The plenum cable fire test standard. FEP-insulated plenum cables must pass this test for CMP, CL2P, CL3P, and FPLP listings.

NEC® Article 310 (Conductors for General Wiring): NEC Table 310.16 lists ampacity values for conductors based on insulation temperature rating. Higher temperature ratings allow higher ampacity for a given conductor size, which can allow downsizing conductors in high-ambient-temperature environments.

NEC® Article 424 (Fixed Electric Space-Heating Equipment): Governs wiring for electric heating equipment, including temperature limits for conductors at terminations and within heating appliances.

NEC® Article 336 (Type TC Cable): Covers tray cable installation requirements, including high temperature tray cable constructions for industrial environments.

MIL-W-16878 / MIL-DTL-16878: U.S. military specification for insulated wire, defining numerous types of high temperature wire with specific insulation materials, conductor platings, and test requirements.

SAE AS22759: Aerospace wire specification covering PTFE, ETFE, and other high temperature insulated wire types for aircraft and aerospace applications.

IEC 60245 (Rubber Insulated Cables): International standard covering silicone and rubber insulated cables, commonly referenced for silicone appliance wire.

NEC® Ampacity and Temperature Rating Benefits

One often-overlooked benefit of high temperature cable is its impact on NEC® ampacity calculations. NEC® Table 310.16 provides ampacity values at three temperature columns: 60°C, 75°C, and 90°C. Conductors with higher-rated insulation can carry more current for a given size.

More importantly, in high ambient temperature environments, standard cables must be derated (their ampacity reduced) per NEC® Table 310.15(B)(1). Cables with higher temperature-rated insulation require less derating because they have a larger thermal margin between the ambient temperature and their rated limit. In a 50°C ambient environment, a 90°C-rated cable has only 40°C of thermal headroom, while a 200°C-rated cable has 150°C. This can allow significant conductor downsizing in hot environments like boiler rooms, process areas, and rooftop equipment.

Important: Even when the conductor insulation is rated well above 90°C, NEC® installations may still be limited by the termination temperature rating at equipment lugs and connectors, which is typically 75°C or 90°C per NEC® 110.14(C). The higher insulation rating helps with ampacity derating in hot environments, but the final ampacity used must account for the weakest link in the system — which is often the termination, not the conductor.

Applications by Industry

Industrial Heating and Process

Furnaces, kilns, industrial ovens, heat treating equipment, and process heaters all require cable rated for the ambient temperatures inside the equipment enclosure and along the wiring path. TGGT (250°C) is the standard for oven internal wiring. MG wire and fiberglass-insulated cable handle kiln and furnace connections where temperatures exceed 250°C. Silicone wire and SRML are used for control wiring and motor leads routed near hot process equipment.

Food Service and Commercial Cooking

Commercial ovens, ranges, fryers, and warming equipment generate sustained heat that exceeds the capability of standard appliance wire. TGGT and silicone appliance wire are specified for internal connections, with high temperature multi-conductor cable used for control and power feeds within the appliance enclosure.

Aerospace and Defense

Aircraft and aerospace systems use PTFE, FEP, and ETFE-insulated wire almost exclusively. Engine compartments, avionics bays, and external wiring harnesses experience wide temperature swings (from -65°C at altitude to over 200°C near engines) combined with exposure to fuels, hydraulic fluids, and de-icing chemicals. MIL-spec wire (MIL-DTL-16878, SAE AS22759) defines construction and test requirements for aerospace applications.

Automotive

Under-hood and exhaust-area wiring in vehicles requires cable rated for at least 125°C to 200°C. XLPE, ETFE, and silicone-insulated automotive wire handles the heat generated by engines, exhaust systems, and turbochargers. Electric vehicles introduce additional high temperature requirements around battery packs, motor controllers, and charging systems.

Power Generation

Gas turbines, steam turbines, boiler rooms, and heat recovery steam generators (HRSGs) all create high ambient temperature zones where conventional cable cannot survive. High temperature cable is used for instrumentation, control, and power wiring routed through or near these hot zones. MI cable is specified for fire-critical circuits in power plants.

Glass and Metals Manufacturing

Glass forming, steel mills, aluminum smelters, and foundries produce extreme radiant and ambient heat. MG wire, fiberglass, and PTFE-insulated cable, often with additional heat-reflective or ceramic fiber overbraid, is used for instrumentation and control wiring near molten material and high-temperature processes.

Process Control and Instrumentation

RTD wire and thermocouple extension cable with high temperature insulation are essential for accurate temperature measurement in industrial processes. These cables must maintain stable electrical characteristics at elevated temperatures to ensure measurement accuracy. FEP, PFA, and PTFE-insulated RTD cables are standard in chemical plants, refineries, food processing, and pharmaceutical manufacturing.

Semiconductor and Cleanroom

Semiconductor manufacturing tools (diffusion furnaces, CVD chambers, etch tools) operate at temperatures from 200°C to over 1000°C internally. PTFE, PFA, and FEP-insulated wire is standard for wiring within and between process tools, combining high temperature performance with the chemical purity required in cleanroom environments.

High Temperature Cable by Type

Selection Guide: Choosing the Right High Temperature Cable

1. Determine the maximum operating temperature — Identify the highest sustained temperature the cable will experience along its entire routing path, not just at the equipment. Account for heat rise in conduit, cable tray stacking, and proximity to other heat sources. Add a safety margin of at least 10–20% above the expected maximum.
2. Assess chemical exposure — If the cable will contact oils, solvents, fuels, acids, or caustic chemicals, fluoropolymer insulations (PTFE, PFA, FEP, ETFE) provide the best resistance. Silicone offers moderate chemical resistance but is vulnerable to certain solvents and fuels.
3. Evaluate flexibility requirements — For applications requiring frequent flexing, tight bends, or field routing in confined spaces, silicone rubber (SR) provides the best flexibility. SRML adds abrasion resistance. PFA offers the best flexibility among the 260°C fluoropolymers. PTFE and fiberglass are stiffer and more suited to fixed installations.
4. Check mechanical requirements — If the cable will be pulled through conduit, run in cable tray, or exposed to foot traffic, choose insulations with good abrasion and crush resistance (ETFE, XLPE, SRML) or add a protective overbraid or conduit.
5. Verify applicable standards — Determine which UL, NEC®, MIL, or industry-specific standards apply. Aerospace applications require MIL-spec or SAE wire. Commercial appliances require UL-listed appliance wire. Building installations must comply with the NEC®. Pay attention to UL temperature ratings vs. non-UL ratings, especially for FEP with tinned copper conductors.
6. Match the conductor plating — Select tin (up to 150°C), silver (up to 200°C), or nickel (up to 260°C+) plating based on the insulation temperature rating and termination requirements.
7. Consider cost vs. service life — Fluoropolymer-insulated cable costs more upfront but offers longer service life and lower maintenance costs in harsh environments. PFA is a premium choice where PTFE-level performance with better processability is needed. Silicone is a cost-effective middle ground for moderate temperatures. Fiberglass and MG wire are economical for very high temperatures in fixed installations.

Frequently Asked Questions

What is the highest temperature rating available for wire and cable?

MG wire (mica/glass) is rated for continuous operation at 550°C. Fiberglass-insulated cable can also operate at 450°C or higher in specialized constructions. For polymer-insulated cable, PTFE and PFA at 260°C continuous are the standard upper limits. Mineral-insulated (MI) cable can survive fire temperatures exceeding 1000°C, though its continuous rating is typically 250°C.

Can I use THHN wire in a 100°C environment?

THHN is rated for 90°C in dry locations. Operating it at 100°C ambient exceeds its rating and will cause premature insulation degradation. For a 100°C ambient, you need cable rated to at least 125°C (with appropriate derating applied) — XLPE, silicone, or a fluoropolymer insulation.

What is the difference between PTFE, PFA, and FEP insulation?

All three are fluoropolymers with excellent chemical resistance and dielectric properties. PTFE is rated to 260°C and must be ram-extruded or tape-wrapped during manufacturing. PFA matches PTFE's 260°C rating but is melt-processable, yielding a smoother finish and better flexibility. FEP is rated to 200°C and is also melt-extruded, making it the most economical fluoropolymer option. For applications at or below 200°C, FEP offers excellent performance at lower cost. Above 200°C, PTFE or PFA is required.

Why are some FEP cables rated 200°C and others 150°C?

The difference is typically the conductor plating and UL listing status. FEP cable with tinned copper conductors can operate at 200°C in non-UL applications, but UL-listed FEP cable with tinned copper is rated at 150°C because UL testing accounts for the tin plating's oxidation temperature. FEP cable with nickel-plated or silver-plated conductors can achieve 200°C even with a UL listing.

What is foam FEP and when should I use it?

Foam FEP is a variant of solid FEP where gas micro-bubbles are incorporated during extrusion, reducing the dielectric constant from approximately 2.1 to 1.4–1.7. This results in lower signal loss, reduced capacitance, and improved impedance control — making it ideal for high-frequency data cables, coaxial cables, and plenum-rated network cables. Foam FEP is rated for 200°C continuous (same as solid FEP) and retains solid FEP's chemical resistance and flame properties. It is typically used only as conductor insulation, not as a cable jacket.

Why do high temperature cables use nickel-plated conductors?

At temperatures above 150°C, bare copper oxidizes rapidly. Copper oxide is a poor conductor, which increases resistance at terminations and degrades current-carrying capacity over time. Nickel plating forms a stable, conductive barrier that resists oxidation up to 260°C and beyond. Silver plating is used for temperatures up to 200°C and offers superior conductivity for RF and aerospace applications.

What is the difference between SR and SRML wire?

SR wire uses silicone rubber insulation only, offering maximum flexibility. SRML wire adds a fiberglass outer braid over the silicone insulation, providing significantly better abrasion and cut-through resistance at the cost of slightly reduced flexibility. SRML is preferred for motor leads, transformer connections, and any installation where the wire may contact sharp edges or experience vibration.

Is high temperature cable required in a boiler room?

It depends on the ambient temperature. NEC® Table 310.15(B)(1) provides ampacity correction factors for ambient temperatures above 30°C. If the boiler room ambient exceeds the rating of standard cable (90°C for THHN), then yes, high temperature cable is required. Even when the ambient is below the cable rating, high temperature cable may be economically advantageous because it requires less derating, allowing smaller conductors.

Can high temperature cable be run in conduit?

Yes, provided the conduit fill and ampacity calculations account for the installation. Most PTFE, PFA, FEP, and silicone-insulated single-conductor wire is suitable for conduit installation. Multi-conductor high temperature cables can also be run in conduit, though the additional insulation thickness may increase the conduit size required. Check NEC® Chapter 9, Table 1 for conduit fill limits.

Are plenum cables considered high temperature cable?

Plenum cables (CMP, CL2P, CL3P, FPLP) frequently use FEP insulation, which is rated for 200°C. While these cables are marketed and installed primarily for their flame and smoke properties rather than their temperature rating, their FEP insulation inherently provides elevated temperature performance. However, the overall cable assembly (including the jacket) may have a lower system temperature rating than the individual conductor insulation.

Related Resources

• Plenum vs. Riser Cable: CMP, CMR, CL2P & CL3P Ratings Explained
• Fire Alarm Cable: Types, Ratings & NEC Requirements
• Tray Cable Applications & Selection Guide
• How to Read a Cable Print Legend: Markings, Codes & What They Mean
• UL Listings for Wire & Cable: What to Look For
• AWG Wire Gauge Guide: Sizes, Ampacity & Selection
• How to Choose the Right Cable for Your Project

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Disclaimer: This guide is provided for informational purposes only and is not installation advice. Installing wire & cable can be dangerous and pose a risk of possible electric shock or other hazards. Specifications, availability, and pricing are subject to change without notice. Always verify product specifications with the manufacturer's current datasheet before ordering. Consult a licensed professional and your local authority having jurisdiction (AHJ) before specifying or installing cable. Images are for illustration purposes and may not reflect actual installed products.

The information on this page is provided for general reference only and may contain errors or omissions. NEC® is a registered trademark of the National Fire Protection Association (NFPA®). UL® is a registered trademark of Underwriters Laboratories. Teflon® is a registered trademark of The Chemours Company. All other trademarks, product names, and brand names referenced on this page are the property of their respective owners. Ramcorp Wire & Cable is not affiliated with or endorsed by these organizations unless explicitly stated.