Thermocouple Extension Wire Explained

Whilst the insulation of a particular cable might be suitable for continuous operation at elevated temperatures, extension grade conductor accuracy is specified up to 392°F (200°C) in accordance with ANSI MC96.1.

This temperature limit applies at all termination and transition junctions where extension grade conductors connect to thermocouple grade wire or instrumentation, not to the process temperature or the entire cable length; sustained exposure of extension grade conductors above this temperature may affect measurement accuracy.

In practice, this really applies to PFA and Fiberglass insulated cables, because PVC cables are rated below the 392ºF limit.