Do I need thermocouple extension or compensating cable?

Thermocouple extension cables are made from the same conductor material as the thermocouple and are designated with the letter 'X' after the thermocouple type, so KX, TX, JX etc.

Thermocouple compensating cables are made from lower cost conductor materials which have the same thermoelectric properties as the thermocouple, provided that the interconnection point to the thermocouple material is below a certain temperature – as shown below. Compensating cables are designated by the letter 'C', so KC, NC, RC, SC etc.

Compensating cables ar available for Type K, N, R and S thermocouples with the cost saving advantage most noticeable for Types N, R and S unless a Type K thermocouple has a very long run of cable. For Types R and S however, extension cables are not available, so compensating cables for these types is the standard method for connecting them to instrumentation.

There is usually a 3rd letter added to the compensating cable (A or B), so KCB, RCA etc. which designates slightly different characteristics as explained below.

Thermocouple Extension and Compensating Cables

Thermocouple Colour Codes to IEC 60584-3 and ANSI MC96.1
Thermocouple
Type		 Extension and Compensating Cable Type International Colour Code to IEC 60584-3 Notes
Extension
Cable

Compensating

Cable
K KX   IEC60584-3 Type K Thermocouple

Type KX Thermocouple extension cable conductors are made from the same constituent elements as the Type K thermocouple combination and therefore minimises potential errors when connecting to a sensor.
  KCA IEC60584-3 Type K Thermocouple

This compensating cable conductor combination is little known and generally not available. It should not be confused with the more popular Type KCB as shown below.
  KCB IEC60584-3 Type K Thermocouple This popular compensating cable conductor combination (once known as Type V) is made with Copper vs Copper-Nickel conductors, and should only be used when the ambient temperature of the interconnection point between the cable and its Type K sensor is below 100°C. If suitable to your requirements it can save money where long runs are necessary.
N NX   IEC60584-3 Type N Thermocouple

Type NX extension cable conductors are made from the same constituent elements as Type N thermocouples. Although there is a designated compensating cable for Type N, it is not at present readily available.
  NC IEC60584-3 Type N Thermocouple

This compensating cable is the most recent cable type and is for use with Type N thermocouples. It should only be used when the ambient temperature of the interconnection point between the cable and its Type K sensor is below 150°C. If suitable to your requirements it can save money where long runs are necessary.
R   RCA IEC60584-3 Type R Thermocouple

Type RCA compensating cable is suitable for connecting to Type R thermocouples where the ambient temperature of the interconnection point between the cable and its Type R sensor is below 100°C.
  RCB IEC60584-3 Type R Thermocouple Type RCB compensating cable is suitable for connecting to Type R thermocouples where the ambient temperature of the interconnection point between the cable and its Type R sensor is below 200°C, however this increased range is achieved with a lesser degree of accuracy than Type RCA as shown above.
S   SCA IEC60584-3 Type R Thermocouple

Type SCA compensating cable is suitable for connecting to Type S thermocouples where the ambient temperature of the interconnection point between the cable and its Type S sensor is below 100°C. SCA is in fact the same material as Type RCA.
  SCB IEC60584-3 Type R Thermocouple Type SCB compensating cable is suitable for connecting to Type S thermocouples where the ambient temperature of the interconnection point between the cable and its Type S sensor is below 200°C, however this increased range is achieved with a lesser degree of accuracy than Type SCA as shown above. SCB is in fact the same material as Type RCB.
What is multipair thermocouple cable? What is thermocouple cable? How do I identify a thermocouple cable?