Thermocouple wiring — insulation limits What is the maximum recommended service temperature for fibre-glass insulation on thermocouple extension/compensation wires in typical industrial use?

Introduction / Context:
Thermocouples often run through hot environments; however, it is usually the insulation and jacket that limit allowable service temperature, not the thermoelements themselves. Fibre-glass sleeves are common for moderate-to-high temperatures.

Given Data / Assumptions:

• Typical E-glass or high-temperature glass braid with appropriate binders is considered.
• Continuous service temperatures are lower than short-term excursion limits.

Concept / Approach:
Standard glass fibre insulation for thermocouple leads is widely rated around 500 °C for continuous service. Above this, ceramic fibre or mineral insulation is preferred. Lower options (e.g., 250 °C) are associated with certain polymeric insulations; higher options (750–1000 °C) exceed glass fibre’s binder and softening constraints.

Step-by-Step Solution:
Identify the commonly published continuous rating for glass fibre insulation.Select the closest matching value from the options → 500 °C.

Verification / Alternative check:
Manufacturers’ datasheets for glass braid thermocouple wires consistently specify ~500 °C continuous capability.

Why Other Options Are Wrong:

• 250 °C: more consistent with high-temperature polymers, not glass braid.
• 750–1000 °C: above glass fibre’s practical continuous limits; mineral/ceramic solutions are used instead.

Common Pitfalls:

• Confusing the thermocouple hot junction capability with wire insulation limits.

Final Answer:
500 °C