Thermocouple Wire Colors

Thermocouple Wire Identification

Insulated Thermocouple Wire combinations use guidelines according to ANSI color coding. You will see in the table below, that commonly, negative wires are red, the outer sheath for thermocouple grades is brown and the positive lead is color coded according to thermocouple type. For extension grade cables this positive leg color is also carried over to the outer insulation color. Fiberglass insulated wires follow the same system but have a colored tracer rather than a solid color.

We have large stocks of Thermocouple Wire (Cable) in all thermocouple types (K, J, T, N, R/S, E etc.) in PVC, Fiberglass, PFA, Silicone Rubber, XLPE and Ceramic Fiber insulation. Our thermocouple wire is ANSI standard color coded and to ANSI tolerances, although other color codes are also available.

We also have an extensive range of data sheets available for all our Thermocouple Grade Wire and Thermocouple Extension Wire.

Thermocouple Wire Colors, Ranges and Tolerances

United States
International Color Code
to IEC 60584-3
Temperature Range Limits of Error*
Thermocouple Grade Extension Grade Thermocouple Grade Extension Grade Standard Special
K ANSI MC96.1 Type K Thermocouple Wire Thermocouple Wire IEC K -454 to 2300°F
-270 to 1260°C
32 to 392°F
0 to 200°C
±2.2°C or ±0.75% ±1.1°C or 0.4%
T Thermocouple Wire  Type T Thermocouple Wire TX Thermocouple Wire IEC T -454 to 700°F
-270 to 370°C
32 to 392°F
0 to 200°C
±1.0°C or ±0.75% ±0.5°C or 0.4%
J Thermocouple Wire JJ Thermocouple Wire JX Thermocouple Wire IEC J -346 to 1400°F
-210 to 760°C
32 to 392°F
0 to 200°C
±2.2°C or ±0.75% ±1.1°C or 0.4%
N Thermocouple Wire NN Thermocouple Wire NX Thermocouple Wire IEC N -454 to 2300°F
-270 to 1260°C
32 to 392°F
0 to 200°C
±2.2°C or ±0.75% ±1.1°C or 0.4%
E Thermocouple Wire EE Thermocouple Wire EX Thermocouple Wire IEC E -454 to 1600°F
-270 to 870°C
32 to 392°F
0 to 200°C
±1.7°C or ±0.5% ±1.0°C or ±0.4%
S -- Thermocouple Wire SX Thermocouple Wire IEC S -58 to 2700°F
-50 to 1480°C
32 to 392°F
0 to 200°C
±1.5°C or ±0.25% ±0.6°C or ±0.1%
R -- Thermocouple Wire RX Thermocouple Wire IEC R -58 to 2700°F
-50 to 1480°C
32 to 392°F
0 to 200°C
±1.5°C or ±0.25% ±0.6°C or ±0.1%

* whichever is greater

Thermocouple extension wire is manufactured from conductors having approximately the same thermoelectric characteristics as thermocouple wire but the accuracy is for a more limited range. Extension wire can offer a cost advantage.
For base metal thermocouples, the wire is the same composition as the corresponding thermocouple.
For noble metal thermocouples, the wire is an entirely different alloy which matches the noble metal characteristics over a specified temperature range.

The maximum temperatures are limited by the type of insulation used.

What are Special Limits of Error (SLE) and Standard Limits of Error?

As can be seen from the table above, there are two accuracy classes of wire available. Cables with a Standard Limit of Error use standard thermocouple grade wire and this accuracy grade is suitable for the majority of uses. However, certain applications require a higher accuracy and so use cables with a Special Limit of Error (SLE). These wires use a purer form of the thermocouple alloys which in turn improve the accuracy as listed above.

As a company speciliaising the manufacturer of custom built thermocouples, TC can offer cable or complete assemblies made using SLE wire.

Color Codes and Tolerances for Thermocouple Wires and Extension Wire

IEC 60584-3 provides tolerances and identification for a common international system for thermocouple wire identification and tolerances based essentially on thermoelectric emf as opposed to a datum of the emf of the thermo elements against platinum. Tolerances are defined as the maximum allowable deviation in microvolts, caused by the introduction of extension or compensating extension wire into the circuit. Color codes and tolerances are well established in the United States and have been in use as a national standard for years. In other parts of the world, there are alternative color code systems and tolerances, either in use, or in the process of being implemented. One such color code system is that established by the IEC.

In the United States, color codes and tolerances are defined in ANSI 96.1 (1982) and ASTM E-230. Extension wire and compensating extension wire is indicated with the letter “X” after the thermocouple type per these standards.

The color code for thermocouple grade wire includes a brown overall jacket whereas the color code for thermocouple extension wire typically includes an overall jacket in the color of the positive wire. For some insulations, colors may appear as a stripe or trace strand. High temperature braided insulation is not normally color coded. The table above shows the color coding adopted by the ASTM and IEC.


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