Thermocouple Color Codes (IEC and ANSI)
Choose a thermocouple type to see its IEC and ANSI extension cable colours, so you can identify cables and connect polarity correctly.
Thermocouple extension cable colours
| Type | IEC sheath and + | IEC − | ANSI jacket | ANSI + | ANSI − |
|---|---|---|---|---|---|
| Type K | Green | White | Yellow | Yellow | Red |
| Type J | Black | White | Black | White | Red |
| Type T | Brown | White | Blue | Blue | Red |
| Type E | Violet | White | Purple | Purple | Red |
| Type N | Pink | White | Orange | Orange | Red |
| Type R | Orange | White | Green | Black | Red |
| Type S | Orange | White | Green | Black | Red |
| Type B | Grey | White | Grey | Grey | Red |
Reading Thermocouple Cable Colours
In the IEC system the positive conductor and the outer sheath share the type colour, and the negative conductor is always white. In the ANSI system the negative conductor is always red, which is the opposite of most electrical practice.
R and S types use copper based compensating cable, and type B is often connected with plain copper because its output near room temperature is negligible. Older national codes (BS, DIN, JIS, NF) used different colours, so check before reusing old cable.
Frequently Asked Questions
What colour is a type K thermocouple?
IEC: green sheath and positive, white negative. ANSI: yellow jacket and positive, red negative.
Why is the negative thermocouple wire red in ANSI?
It is a historical convention of the ANSI MC96.1 standard; in IEC 60584-3 the negative is white instead.
Can I use copper cable to extend a thermocouple?
No, except type B in some cases. Copper creates new junctions at the terminals and causes errors; use matching extension or compensating cable.
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