What is the difference between thermocouple wire cable and extension grade wire?
Thermocouple grade wire is used to manufacture thermocouple probes. Thermocouple grade wire is normally used for the junction and inside the stem sheath. This is because the thermocouple grade wire has a better accuracy specification than extension grade wire.
Extension grade wire is a less expensive, lower grade wire. It is used to extend the signal from the thermocouple probe to the control system or digital display. Extension grade wire is more economical due to a lesser grade metal being used. Extension grade wire should not be used in the process itself and should not see the temperature extremes & temperature cycling as standard grade wire.
In many industrial applications a sensor is located in a process pipe far away from the control room. This means the wires must be run a considerable distance back to the control room to get the temperature reading. Using more expensive thermocouple grade wire to accomplish this is unnecessary. Extension grade wire will do the job.