Thermocouple Wires and Extension Cables

Extension Cable

• Made from the same material as the thermocouple itself
• Such cables are marked with the letter “X” after the sensor type designation, e.g., “KX.”

Extension cable color markings

• Color markings for extension cables have been highly varied, and mismatched color codes according to different standards have caused most errors during thermocouple installation.
• The main “cause of error” has been the red conductor, which has different polarity in various standards.
• In IEC-584-3, there is no red color, and the negative (-) conductor is always white.

Compensating Cable

• Made from a different material than the thermocouple but provides the same voltage as the thermocouple at low temperatures
• Such cables are marked with the letter “C” after the sensor type designation, e.g., “KC.”
• Different alloys for the same thermocouple type are marked with an additional letter, e.g., “KCA” and “KCB.”
• The term compensating cable originates from the time when rotating coil instruments were used, where the circuit resistance was known, and the cable was used to equalize the circuit resistance. It is still sometimes referred to as an equalizing cable.

Thermocouple Wires

• Made from the same material as the thermocouple
• Available insulated (e.g., fiberglass, PVC, Teflon, etc.) or as bare wire
• Thermocouple wires can be used like a complete thermocouple by connecting the wire ends together through twisting, welding, melting, or other reliable methods