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Common Insulation Materials used for Thermocouple Wires and Cables
Contents
Introduction to Thermocouple Wire Insulation Materials
Choosing the right insulation material for thermocouple wire is a crucial decision that hinges on various factors including the operating temperature range, required flexibility, chemical resistance, and mechanical durability. From the high temperature range of ceramic fibre to the chemical resistance of PFA, each insulation material has a unique set of properties tailored to specific requirements. This article explores some of the characteristics and applications of the most popular types of thermocouple cable insulation materials including: Heat Resistant PVC, Flame Retardant PVC, PFA, Fibreglass, Ceramic Fibre, Silicone Rubber, and XLPE.
Heat Resistant (HR) PVC (Polyvinyl Chloride)
PVC insulated thermocouple cables are extremely common and are widely used in many industries and applications. They are a cost effective choice especially over longer runs of cables.
All our Heat Resistant (HR) PVC cables are suitable for use in the temperature range -30°C to +105°C. The grade of PVC used on these cables is to BS7655:Part 4 Section 4.2 Type 5/UL Style 105°C rated (15,000 hours at 105°C).
We offer a wide variety of HR PVC cables from simple bellwire to screened and armoured types in virtually all of the thermocouple combinations.
Properties:
- Temperature Range: -30°C to +105°C
- Flexibility: Good flexibility
- Chemical Resistance: Good resistance to chemicals and moisture
- Abrasion Resistance: Good
- Cost: Generally economical
Applications:
- Used in environments where moderate heat resistance is required
- Common in industrial settings for general-purpose thermocouples
Flame Retardant (FR) PVC (Polyvinyl Chloride)
By incorportaing flame retardant compounds, these FR PVC insulated thermocouple cables have excellent properties for the reduced propagation of flame.
The Oxygen Index Value of the overall sheath is typically not less than 30% in accordance with ISO 4589 which allow fire resistance properties.
Properties:
- Temperature Range: -30°C to +75°C
- Flame Retardancy: Contains additives to reduce flammability
- Chemical Resistance: Good resistance to chemicals and mositure
- Abrasion Resistance: Good
- Cost: Slightly higher than standard HR PVC
Applications:
- Suitable for applications requiring fire safety measures
- Used in commercial buildings and public infrastructure
Did you know?
We have over 4 million metres of Thermocouple and RTD cable in stock and available for immediate despatch, including single and multipair, with and without armour.
Call us now on 01895 252222 to discuss your requirements.
PFA Insulated Cables (Perfluoroalkoxy)
PFA insulated thermocouple cables are known for their excellent resistance to virtually all known chemicals, oils and fluids. As well as being ideal for higher temperature applications up to 250°C, it is also excellent for cryogenic temperatures down to –75°C.
PFA insulated cables are resistant to mechanical stress and wear, making them suitable for demanding environments and they maintain thei flexibility even at low temperatures, which helps in easy routing and installation.
All our PFA cables are made in extruded form and are therefore gas, steam and water tight which makes them most suitable for applications such as autoclaves or sterilizers.
Properties:
- Temperature Range: -75°C to +250°C, short term up to 300ºC
- Flexibility: Good flexibility
- Chemical Resistance: Outstanding resistance to chemicals and solvents
- Abrasion Resistance: Good
Applications:
- Ideal for high-temperature and chemically aggressive environments
- Used in chemical plants, semiconductor manufacturing and food processing
Fibreglass Insulated Thermocouple Cables
Fiberglass insulated thermocouple cables are designed for use in high-temperature applications where other types of insulation may not withstand the extreme conditions.
They are available in standard fibreglass which is suitable for continuous use up to 480ºC and a high temperature fibreglass which will withstand temperatures up to 800ºC.
Whilst they may require additional coatings or treatments to address specific limitations such as adding stainless steel braiding for mechanical protection, their overall performance makes them ideally suited to industries such as aerospace, metallurgy, power generation, and industrial processing.
Properties:
- Temperature Range: up to 480°C for standard fibreglass or 800ºC using high temperature variant
- Flexibility: Less flexible compared to polymers
- Chemical Resistance: Good, but can be affected by moisture absorption
- Durability: Excellent high-temperature durability
Applications:
- Used in high-temperature industrial processes such as kilns, furnaces, and ovens
- Suitable for harsh environments where high heat and mechanical strength are needed
Ceramic Fibre
Ceramic fibre insulated thermocouple cables are designed for extremely high-temperature applications where even materials like fiberglass may not suffice. These cables are used in environments that demand exceptional heat resistance and stability such as metallurgy, aerospace, power generation, and high-temperature manufacturing.
While they may be more expensive and require careful handling, their benefits in terms of withstanding temperatures up to 1200ºC make them a top choice for the most demanding applications.
Properties:
- Temperature Range: Extremely high, up to 1200°C
- Flexibility: Brittle, not very flexible
- Thermal Conductivity: Low (excellent insulator)
- Chemical Resistance: Good, but can degrade over time with exposure to some chemicals
- Can be stainless steel braided to provide more abrasion resistance
Applications:
- Primarily used in ultra-high-temperature environments
- Common in furnaces, refractory installations, and high-temperature sensors
Silicone Rubber Insulated Thermocouple Cable
Silicone rubber insulated thermocouple cables offer a good balance of high-temperature resistance, flexibility, and durability, making them suitable for a wide range of applications. They provide reliable performance in automotive, aerospace, industrial, HVAC, and medical fields, where moderate high-temperature stability and mechanical flexibility are crucial and are also ideal for applications where, for short periods of time, the temperature can fluctuate, which would cause other cables to become inflexible and brittle.
Silicone rubber cables also have excellent properties for the reduced propagation of flame by incorporating flame retardant silicone rubber compounds.
Properties:
- Temperature Range: -40°C to +200ºC
- Flexibility: Remains flexible at low temperatures, which is beneficial for cold environments
- Moisture Resistance: Excellent water and moisture resistance
- Flame Retardancy: Contains additives to reduce flammability
Applications:
- Suitable for applications requiring flexibility and moisture resistance
- Common in medical equipment, food processing, and outdoor applications
Did you know?
We have over 4 million metres of Thermocouple and RTD cable in stock and available for immediate despatch, including single and multipair, with and without armour.
Call us now on 01895 252222 to discuss your requirements.
Cross-linked polyethylene (XLPE) and Low Smoke Zero Halogen (LS0H)
Cross-linked polyethylene (XLPE) and Low Smoke Zero Halogen (LS0H or LSZH) are types of insulation used in electrical and thermocouple cables, offering distinct properties that make them suitable for various applications.
XLPE is chemically stable and has a high tensile strength whilst retaining good flexibility and maintains high insulation resistance over a wide range of temperatures and environmental conditions. LS0H materials produce minimal smoke when exposed to fire, improving visibility and reducing harm during evacuation. It does not release toxic halogen gases (like chlorine or fluorine) when burned, which can be corrosive and harmful to humans.
We combine XLPE with LS0H in a single cable to provide thermocouple cables for use in situations where there is a risk of fire and the emission of smoke and gases could threaten life and property.
Properties:
- Temperature Range: -30°C to +70ºC
- Low smoke and halogen free when burned
- Moisture Resistance: Very good
- In accordance with BS6425 Pt 1 1990 and IEC 60754.1: 1996, the acidic gas evolved during combustion of our XLPE / LS0H cables is less than 0.5%
- Abrasion Resistance: Good
Applications:
- LS0H insulation focuses on fire safety, emitting low smoke and no toxic halogen gases, making it ideal for use in public buildings, transportation, and other areas where safety is paramount
MICA
Whilst Mica is not a common thermocouple cable insulation, we do use Mica on the cores of some of our XLPE / LS0H insulated thermocouple cables for applications where it is essential that the cable continues to function during a major crisis involving fire.
Mica is a naturally occurring mineral with exceptional thermal, electrical, and mechanical properties.
Properties:
- Non-combustible: Mica is inherently non-combustible and does not support flame propagation
- Low Smoke and Toxicity: Produces minimal smoke and toxic gases when exposed to fire, enhancing safety
Kapton® Insulated Thermocouple Wire
Kapton® is a polyimide film developed by DuPont, known for its excellent thermal, chemical, and mechanical properties. Kapton® insulated thermocouple cables are widely used in high-temperature and harsh environments.
Suitable for temperatures ranging from -75ºC to +285ºC, it is flame retardant with resistance to chemicals and radiation.
Kapton® thermocouple cables have excellent physical, electrical and mechanical properties over high temperatures and excellent abrasion resistance.
Properties:
- Temperature Range: -75°C to +285ºC
- Flame retardant
- Abrasion Resistance: Excellent
- Resistant to most chemicals, oils, solvents, and radiation, ensuring longevity in aggressive environments
Applications:
- Aerospace: used in spacecraft, satellites, and aircraft for temperature measurement and control due to its ability to withstand extreme temperatures and radiation
- electronics: Employed in high-performance electronic devices and circuits, particularly in environments exposed to high temperatures and chemicals
Other Insulation Materials for Thermocouple Wire
FEP (Fluorinated Ethylene Propylene)
FEP (Fluorinated Ethylene Propylene) insulated thermocouple extension cable is suitable for use over the temperature range -65ºC to210°C. FEP insulated cables are particularly suited to the automotive industry where the flexibility of FEP is an advantage in routing cables.
PTFE (Polytetrafluoroethylene)
Very similar to PFA and FEP, PTFE thermocouple cables have an operating temperature range of -75ºC to +250ºC and are extremely resistant to chemicals and oils and in a 'single shot' construction are widely used in autoclave applications due to their ability to withstand ingress of moisture.
Nextel
Nextel is a brand name of 3M and is a ceramic fibre material some of which like Nextel440 have a slightly higher temperature rating than standard ceramic fibre. Not widely used as a thermocouple cable insulation material.
Tefzel
Tefzel is a brand name for ethylene-tetrafluoroethylene (ETFE), a type of fluoropolymer known for its excellent mechanical, chemical, and electrical properties. It has a moderate temperature rating of 150ºC but has excellent resistance to abrasion, chemicals moisture. It is used in marine applications and medical sterlizing equipment.
Summary
Each of these materials has unique properties that make them suitable for specific applications. The choice of insulation depends on the environmental conditions and specific requirements of the thermocouple application.
General Purpose: Heat Resistant PVC
Resistance to Oils and Chemicals: PFA, PTFE, Kapton®
High Temperature: Fibreglass, Ceramic Fibre
Flame Retardant: FR PVC, XLPE/LS0H, Mica