Understanding Thermocouple Wire Colors and Coding

Thermocouple wire

The thermocouples that you use in your daily work are composed of two wires of different metals that conduct electricity. They are connected at the tip of the unit and further down the shaft. The resulting voltage that develops between the two points after heating or cooling is proportionate to the temperature difference and can be used to accurately measure the temperature of fluids or substances within sealed or contained areas.

Wherever you are in the country, continent, or world, if you rely on thermocouples to read temperatures, then you need to be sure that they are accurate, but also that they are the best fit for any given application. We will share some top ways to quickly identify the thermocouple you’re working with, while also helping to demystify the coding system. Let’s get into it!

What Do Thermocouple Wire Codes Mean?

The letter codes that are assigned various colors generally point to the type of metal used in the wiring and the range of temperature that the thermocouple can most accurately sense or withstand. Types J, K, N, E, and T thermocouple wires are nickel-based (base metal) while R, S, and B are platinum-based (noble metal). 

Noble metals generally resist oxidation, corrosion, moisture, and acidic environments, while base metals more readily oxidize and corrode in the same situations. Clearly, they will have different ideal applications and uses. Together, these eight thermocouple types are defined and accepted by the American National Standards Institute (ANSI) and the International Electrotechnical Commission (IEC).

Type J: Widely-used, versatile, and affordable, J types have an extreme temperature limit of roughly 1300°F (700°C)

Type K: Commonly used because of its high temperature range, K types can withstand approximately 2350°F (1285°C).

Type N:  Known to provide better EMF stability, N types can be used with temperatures up to about 2350°F (1285°C). 

Type E: Providing a large EMF output, E types offer temperature limits of 1600°F (870°C).

Type T: Best used in sub-zero cryogenic settings, T types can also handle up to 700°F (370°C).  

The following three noble-metal types include varying amounts of platinum and rhodium, making them more costly and susceptible to contamination if temperatures spike.

Type R, Type S: These thermocouples can withstand high temperatures of up to 2700°F (1480°C). 

Type B: Use this thermocouple up to 3100°F (1700°C).

The best thermocouple for your project is the one that most closely meets temperature ranges common to your application.

How to Identify a Thermocouple by Wire Color

The insulation on thermocouple wire is the first place to start. In the US, the outermost jacket of insulation is typically brown for most thermocouple types. Thermocouple color codes come into play once the jacket is removed and you can more closely examine the wires inside. Their individual insulation layers will tell you which wire is positive, which is negatively charged, and once those two pieces of data are put together, you can accurately determine the type of thermocouple and its capacity. The list in the below section can help you to properly identify thermocouple type by color and by country.

Under ANSI guidelines, a red wire is always negatively charged, while the second, positively charged wire’s color will shift, helping you to determine the type of thermocouple you have. IEC standards lay out that a white wire is always the negative component. The same is primarily true in Japan. British thermocouple specifications outline blue as the negative wire, and other countries vary colors by type.

Thermocouple Color Codes by Country

You want to be sure that the reading you’re getting is accurate, but it’s also vital that the thermocouple wires are calibrated to meet the needs of the industry and application you’re working in.

Various national and international agencies have adopted coding standards to make it easier to quickly identify a thermocouple. ANSI and IEC color codes are generally accepted. At the same time, some individual countries retain their own unique coding system.

Here are a few helpful lists of thermocouple wire colors and codes, broken up by major country and international standards:

Thermocouple Wire Colors (ANSI-US and Canada)
Thermocouple Type Thermocouple Jacket Color Extension Grade Jacket Color Positive Lead Color Negative Lead Color
K Brown Yellow Yellow Red
J Brown Black White Red
N Brown Orange Orange Red
R -- Green Black Red
S -- Green Black Red
T Brown Blue Blue Red
E Brown Purple Purple Red
B -- Gray Gray Red
C -- Red Green Red
Thermocouple Wire Colors
International Electrotechnical Commission (IEC/IEC-584-3)
Thermocouple Type Thermocouple Jacket Color Intrinsically Safe Jacket Color Positive Lead Color Negative Lead Color
K Green Blue Green White
J Black Blue Black White
N Pink Blue Pink White
R Orange Blue Orange White
S Orange Blue Orange White
T Brown Blue Brown White
E Purple Blue Purple White
B Gray -- Gray White
C -- -- -- --
Thermocouple Wire Colors
By Various Countries
 Country Thermocouple Type Thermocouple Extension Jacket Color Positive Lead Color Negative Lead Color
Britain/Czechoslovakia (BS1843) K Red Brown Blue
J Black Yellow Blue
N Orange Orange Blue
R Green White Blue
S Green White Blue
T Blue White Blue
E Brown Brown Blue
B -- -- --
C -- -- --
Netherlands/Germany (DIN 43710) K Green Red Green
J Blue Red Blue
N -- -- --
R White Red White
S White Red White
T Brown Red Brown
E Black Red Black
B Gray Red Gray
C -- -- --
Japan (JIS C 1610) K Blue Red White
J Yellow Red White
N -- -- --
R Black Red White
S Black Red White
T Brown Red White
E Purple Red White
B Gray Red Gray
C -- -- --
France (NFC 42-324) K Yellow Yellow Purple
J Black Yellow Black
N -- -- --
R Green Yellow Green
S Green Yellow Green
T Blue Yellow Blue
E Purple Yellow Purple
B -- -- --
C -- -- --

Contact RAM Sensors for Expert Advice on Identifying Thermocouple Wire

Depending on the source of your equipment, the color coding standards may vary. Perhaps you know what colors to look for in the US, but what about in other countries? Contact us today for expert help in both identifying a thermocouple and determining the best type for your application.