Most countries developed their own thermocouple wire color codes years ago. Today, there are two governing bodies that are globally recognized for setting the accepted color codes standards: ASTM International (formerly known as American Society for Testing and Materials or ASTM) and International Electrotechnical Commission (IEC). ASTM E230-03 is the standard adopted by the United States. The standard recognized in Europe is IEC 584-3.
The table provided below defines the thermocouple calibration types in the left column (i.e., Type J, K, E, T, N, S) and the alloy combination for the positive (+) and negative (-) leads. The standard insulation colors for the different thermocouple leads are illustrated in the remaining columns below the country.
Important: The color chart represents the standards for thermocouple extension accuracy wire. For standard limit and special limit accuracy thermocouple wire, ASTM calls out a different jacket color – brown.
For additional information on the different thermocouple calibration types and temperature ratings, read this blog.