Wire that is used in a thermocouple from the point of sensing to the point of cold junction compensation (cjc end) where the signal is measured. A thermocouple is a sensor for measuring temperature, that consists of two dissimilar metals that are joined together at the sensing end.

Different thermocouple types (e.g. J, K, T, E, etc) use different mixtures of metals in the wire. At the cjc end, the millivolt value provided by the thermocouple represents the difference in temperature of the sensing end as compared to the cjc end (also called the reference end).