Thermocouple Wire Colour Code

Thermocouples of all different types have their own colour coding to aid identification however this is not necessarily as easy as it may seem. As well as each thermocouple type having its own colour code, there are various national and international standards each having their own colour code system. It is important to positively identify which standard is being used before you can identify the thermocouple type. Don’t worry though, we are always here to help you.

The primary standard used within the UK and Europe is often referred to simply as the IEC colour code. Strictly speaking this is a little vague as this refers to the IEC standard IEC584 and more specifically IEC584-3. This is now an old standard and the current standard used within the UK and Europe is BS EN 60584 and the part of this standard which deals with colour codes is BS EN60584-3:2008.

Outside Europe

Other countries outside of Europe have their own standards and on occasion, these find there way into the UK market. The most notable is the American ANSI colour coding with comply with the specification ANSI MC96.1.

Obsolete codes

Other colour codes which are now officially obsolete but may still be used, particularly on older machinery, are the old British Standard colour code which complied with BS1843:1952 and BS4937:1993 also the German DIN colour codes which complied with DIN 43714.

Japan & France

Other countries to have their own standards include Japan and France but these are rarely seen if ever.

thermocouple temperature sensors from Process Parameters with wire colour code explained to aid identification

Thermocouple diagram to aid identification

IEC thermocouple colour codes

The main purpose of this document is to deal with the IEC thermocouple colour codes used within the UK and Europe. This is by far the most common thermocouple colour code system used today and is the standard colour coding we supply for our thermocouples unless otherwise requested. What follows is specifically for IEC colour code and is not applicable to the other standards mentioned.

Basics of the IEC colour code system
  • For all thermocouple types the negative conductor is always identified by a white insulation.
  • The positive conductor is insulated with a colour, for example type K has a green insulation, type J has a black insulation. This colour is different for each type.
  • The jacket colour of the cable (where the cable has a jacket) is the same colour as the positive conductor insulation. Therefore, for type K the jacket is green, for type J the jacket is black.
  • Thermocouple connectors are colour coded to the jacket colour of the thermocouple. So again, a type K thermocouple connector would have a green casing and a type J would be black.

As mentioned already, the thermocouple colour coding system seems straight forward at first glance but there are some pitfalls to be aware of and these will be described as follows. Within these notes we will also provide additional tips on positive identification of the thermocouple type. To learn more about thermocouples follow this link: What is a Thermocouple?

a chart showing the types of thermocouple colour code against different national standards such as the IEC standard IEC584
Click to expand the image

Thermocouple Types and Temperature Ranges

J Type Thermocouple Colour Code

The colour coding for type J is as follows:-

Positive Leg = Black Insulation
Negative Leg = White Insulation
Jacket = Black Insulation
Thermocouple Connector Housing = Black

The colour coding for type J within the IEC system is unique and there are no other types which are similar. It is also completely unique when compared to other standards.

For some cables, particularly glass fibre insulation, the colour coding is not very clear. This may be because the cable manufacture uses a colour tracer rather than dying the insulation completely. If the colour coding is unclear you can again use a magnet. For type J the positive conductor is strongly magnet as it is pure Iron.

With respect to other colour coding standards, there are a couple of other difficulties in identifying type J.

For the American ANSI standard, the colour coding is Red and White with a Black jacket. This is identical to the standard that is used for Two Wire Platinum Resistance Thermometers. It is not unusual for a customer to request a type J thermocouple in fact they have a Pt100 and vice versa.

The German standard for type J is still relatively commonly used as it is a common type in plastics machines but there may be cause for confusion as the colour code, Red and Blue with a Blue jacket, is identical to the American ANSI colour code for type T! Again the simplest method to confirm the thermocouple type is by using a magnet to test. The positive leg will be strongly magnetic.

T Type Thermocouple Colour Code

The colour coding for type T is as follows:-

Positive Leg = Brown Insulation
Negative Leg = White Insulation
Jacket = Brown Insulation
Thermocouple connector housing = Brown

Both conductors for type T are not magnetic so this is not a way of positively identifying type T. Of course, you could use a magnet to test for either type K or type J and this would rule out the cable being type T by elimination.

The positive conductor of type T is pure copper. Many cable manufacturers plate the conductor to help protect it but it is often possible to scrape the plating away to expose the copper conductor. No other thermocouple uses Copper as a conductor so this can aid positive identification.

E Type Thermocouple Colour Code

The IEC colour coding for type E is as follows:-

Positive Leg = Purple Insulation
Negative Leg = White Insulation
Jacket = Purple Insulation
Thermocouple Connector Housing = Purple

K Type Thermocouple Colour Code

The colour coding for type K is as follows: –

Positive Leg = Green Insulation
Negative Leg = White Insulation
Jacket = Green Insulation
Thermocouple Connector Housing = Green

K Type Thermocouple Colour Code: Note that the colour coding for type K is exactly the same as for type KCA/KCB compensating cable. This can cause confusion as at first glance the two cables would look identical however it is not possible to manufacture a thermocouple from KCA/KCB cable. This is simply a lower cost cable which allows the user to connect a type K thermocouple to their instrument under certain conditions.

How can I positively identify whether I have a type K cable or a KCA/KCB cable?

By using a magnet, test the negative leg of the cable. The negative conductor of type K is weakly magnetic whereas the negative of KCA/KCB is not. The magnetic pull is very slight for type K so needs some care to notice it.

Type K colour code issues with other standards:

The issue of type K and types KCA/KCB having the same colour code is also true for the German standard colour code system. Use the magnet test as described above.

A highly unlikely problem is that of type K and type E colour coding when using the now obsolete British Standard colour coding. Both positive and negative for type K and type E are the same colours (Brown and Blue) and the only difference is the jacket colour of the cable. Assuming the cable has a jacket then check this first. Type K would be red and type E would be brown. If there is not a jacket then you can use the magnet test as above. Type E will not have a magnetic conductor.

N Type Thermocouple Colour Code

The IEC colour coding for type N is as follows:-

Positive Leg = Pink Insulation
Negative Leg = White Insulation
Jacket = Pink Insulation
Thermocouple Connector Housing = Pink

R / S Type Thermocouple Colour Code

The IEC colour coding for type R/S is as follows:-

Positive Leg = Orange Insulation
Negative Leg = White Insulation
Jacket = Orange Insulation
Thermocouple Connector Housing = Orange

More About Thermocouples