Extension and compensating cables are used for the electrical connection between the open ends of a thermocouple and the reference junction in those installations where the conductors of the thermocouple are not directly connected to the reference junction.
Extension cables are manufactured from conductors having the same nominal composition as those of the corresponding thermocouple. They are designated by a letter “X” following the designation of the thermocouple, for example “JX”.
Compensating cables are manufactured from conductors having a composition different from the corresponding thermocouple. They are designated by a letter “C” following the designation of the thermocouple, for example “KC”. Different alloys may be used for the same thermocouple type, they are distinguished by additional letters such as, for example, KCA and KCB.