Thermocouple Wire Colour Coding

A Quick Guide to Thermocouple Wire Colour Coding

What are Thermocouple Colour Codes?

There are numerous different thermocouples in the market. To be able to identify them, they are assigned different colours. However, not everyone has an easy time differentiating the different thermocouples. The main reason for this is because there are different colour code systems. It is essential to know the origin of a particular device when applying thermocouples to use the right colour codes.

The old standard thermocouple colour code that was commonly used in the UK and Europe is the IEC colour code. BS EN 60584 is the current standard of colour code commonly used in the UK and Europe. Even though it is rare, you may also come across the American ANSI colour coding in the UK and Europe.

If you have trouble differentiating different types of thermocouples, worry no more because the purpose of this article is to help you out.

Thermocouples and Their Working Principle

Thermocouples are devices used for measuring temperatures. Due to their robust nature, thermocouples are capable of measuring a wide temperature range. However, the range varies from one type of thermocouple to the other.

Thermocouples wires have polarity because of the Seebeck effect that needs one to connect to the correct terminals. When connecting a thermocouple leads to an electrical circuit, a sensor, which to be specific is a voltmeter, is connected to one of the conductors. Changes in temperatures cause voltage differences that can be measure using a thermocouple.

IEC Thermocouple Colour Codes

Thermocouple colour coding confuses a lot of people, even though it may seem straightforward. This article can help you correctly identify thermocouple types. You will gain knowledge on thermocouples applications, including:

  • Controllers
  • Transmitter
  • Transducers
  • Thermistors

Thermocouples types are assigned single letters: J, K, T, N, E, and R/S. Every thermocouple type has its unique colour for identification purposes. Type J and K are the most common thermocouples in the plastics industry.


K Type Thermocouple

The jacket and connector housing of this thermocouple is green. The positive lead is a non-magnetic nickel-chromium (NiCr) alloy with green insulation, while the negative magnetic lead is an alloy of nickel and aluminium (NiAl) with white insulation. Type K thermocouples are widely known for being accurate and reliable. Also, Type K thermocouples are capable of measuring temperatures of up to 1100⁰C.

J Type Thermocouple

Type J thermocouples have black jacket and connector housing. The positive lead has black insulation, while the negative lead has white insulation. The positive lead is iron (Fe); therefore, it is magnetic, while the negative lead is a non-magnetic copper-nickel alloy (CuNi). Even though Type J thermocouples are common, they cannot compare to Type K thermocouples when it comes to temperature range. The temperature range of type J thermocouples is 0 to 600⁰C. However, the cost pretty the same. Class 1 accuracy for Type K and Type J thermocouples have the same accuracy for temperature ranges of -40 to +375°C, which is ±1.5°C. As for class 2, the tolerance is wider.

T Type Thermocouple

It has a brown jacket and connector housing. The lead with brown insulation is the positive one, while the negative lead has white insulation. The positive lead is copper (Cu), while the negative lead is CuNi. Both leads are non-magnetic.

N Type Thermocouple

Both the jacket and thermocouple connector housing are pink. The NiCr positive lead insulation is pink, and for the nickel-silicon (NiSi) negative lead is white.

E Type Thermocouple

The positive leg has purple insulation, while the negative leg has white insulation. As for the jacket and connector housing, they are purple. The positive lead is NiCr, and the negative lead is CuNi, which ate both non-magnetic.

R / S Type Thermocouple

The jacket and connector housing are orange. The positive lead has orange insulation, while the insulation colour of the negative lead is white.

The accuracy of thermocouples is not affected by the length of the thermocouple wiring. This is because the voltage drops used to get temperature measurements are low. However, it is essential to shield and ground sensors at one end to prevent electrical noise if the distance between a thermocouple and the instrument is large.

If you want to learn more about thermocouples, you can visit

Measuring temperatures

Thermocouples are used for measuring temperatures. Some types of thermocouples can measure temperatures of up to 2000⁰C. The main parts of a thermocouple are the jacket, connector housing, positive leg, and negative leg.

Thermocouples are assigned different colour codes so that people can differentiate them. However, different countries use different colour code systems, making it difficult for some people to identify the thermocouple type they are using. The International standard thermocouple colour code used is the IEC 60584-3.