Thermocouple colour codes — IEC 60584-3 and ANSI MC 96.1
Thermocouple colour codes identify the thermocouple type (B, E, J, K, N, R, S or T) by the insulation colour of each conductor. The international standard IEC 60584-3 uses a white negative conductor for all types, while the American standard ANSI MC 96.1 uses a red negative conductor. The same colour can mean different things under different standards, so always identify the standard before connecting.
IEC 60584-3 — the international colour code
IEC 60584-3 defines the colour codes for thermocouple extension wires and compensating cables, also written thermocouple color codes in American English. The negative conductor is always white; the positive conductor and the outer sheath carry the type colour.
| Type | Conductor pair (+ / −) | Positive (+) | Negative (−) | Sheath |
|---|---|---|---|---|
| K | NiCr / NiAl | Green | White | Green |
| J | Fe / CuNi | Black | White | Black |
| T | Cu / CuNi | Brown | White | Brown |
| E | NiCr / CuNi | Violet | White | Violet |
| N | NiCr / NiSi | Pink | White | Pink |
| S / R | S: Pt-10%Rh / Pt R: Pt-13%Rh / Pt | Orange | White | Orange |
| B | Pt-30%Rh / Pt-6%Rh | Grey | White | Grey |
Thermocouple wires intended for high temperatures normally have sheaths which cannot be coloured. A coloured identification fibre is sometimes integrated into the sheath instead.
ANSI MC 96.1 — the American colour code
Under ANSI MC 96.1 the negative conductor is always red. The positive conductor carries the type colour. Extension-grade wire uses a type-coloured jacket, while thermocouple-grade wire has a brown overall jacket for every type.
| Type | Positive (+) | Negative (−) | Extension-grade jacket |
|---|---|---|---|
| K | Yellow | Red | Yellow |
| J | White | Red | Black |
| T | Blue | Red | Blue |
| E | Violet | Red | Violet |
| N | Orange | Red | Orange |
| S / R | Black | Red | Green |
| B | Grey | Red | Grey |
Types R, S and B are normally supplied as extension or compensating cable only.
Older national standards — DIN, BS, NF C and JIS
Before IEC 60584-3, most industrial countries had their own colour codes. Equipment wired to these standards is still in service worldwide, so the older codes remain relevant when extending or replacing sensors on existing installations. The table below gives the positive conductor, the negative conductor and the sheath for each type under each standard.
| Type | DIN 43714 (Germany — replaced by IEC) | BS 1843 (UK — replaced by IEC) | NF C 42-324 (France — replaced by IEC) | JIS C 1610 (Japan) |
|---|---|---|---|---|
| K | + Red− GreenSheath Green | + Brown− BlueSheath Red | + Yellow− VioletSheath Yellow | + Red− WhiteSheath Blue |
| J | + Red− BlueSheath Blue | + Yellow− BlueSheath Black | + Yellow− BlackSheath Black | + Red− WhiteSheath Yellow |
| T | + Red− BrownSheath Brown | + White− BlueSheath Blue | + Yellow− BlueSheath Blue | + Red− WhiteSheath Brown |
| E | + Red− BlackSheath Black | + Brown− BlueSheath Brown | + Yellow− VioletSheath Violet | + Red− WhiteSheath Violet |
| N | Not defined | + Orange− BlueSheath Orange | Not defined | Not defined |
| S / R | + Red− WhiteSheath White | + White− BlueSheath Green | + Yellow− GreenSheath Green | + Red− WhiteSheath Black |
| B | + Red− GreySheath Grey | Not defined | Not defined | + Red− GreySheath Grey |
Red means the opposite thing in America and Japan: under ANSI MC 96.1 the red conductor is always negative, while under JIS C 1610 the red conductor is always positive. Identify the standard before you wire a thermocouple, or the polarity will be reversed.
Extension wires and compensating cables — KX versus KCA
Extension wires are made from the same alloys as the corresponding thermocouple and are marked with the letter X — KX for type K, for example. Their tolerances equal thermocouple class 1 or class 2 to IEC 60584 within a limited temperature range, typically −25 to 200 °C.
Compensating cables are produced from substitute alloys and are marked with the letter C plus a letter identifying the alloy — for example KCA, SCA or SCB. Compensating cables carry the same thermoelectric behaviour over a defined ambient range and cover class 2 duty within it — KCA, for instance, from 0 to 150 °C. Where class 1 tolerances are required, choose extension wire in the thermocouple’s own alloys.
The cable sheathing can limit the range further. PVC sheathing, for example, limits the ambient temperature at the cable location to below 100 °C. Connectors should carry the same colour marking as the corresponding cable.
Frequently asked questions
What colour is type K thermocouple wire?
Under IEC 60584-3, type K has a green positive conductor, a white negative conductor and a green sheath. Under ANSI MC 96.1, type K has a yellow positive conductor and a red negative conductor, with a yellow extension-grade jacket.
Why do IEC and ANSI thermocouple colours differ?
They were developed by different standards bodies. IEC 60584-3 is the international standard and uses white for the negative conductor; ANSI MC 96.1 is the American standard and uses red for the negative conductor. The same colour can indicate opposite polarity under different standards, so the standard must be identified before wiring.
Is red positive or negative on a thermocouple?
It depends on the standard. Under ANSI MC 96.1 red is always the negative conductor. Under JIS C 1610 red is always the positive conductor. IEC 60584-3 does not use red at all — its negative conductor is white for every type.
What is the difference between extension wire and compensating cable?
Extension wire (marked X, for example KX) uses the same alloys as the thermocouple and can meet class 1 tolerances. Compensating cable (marked C, for example KCA) uses substitute alloys, qualifies only for class 2 tolerances and has a narrower ambient temperature range.
What do the thermocouple letters B, E, J, K, N, R, S and T mean?
Each letter identifies a standardised conductor pair — type K is NiCr/NiAl and type J is Fe/CuNi, for example — with tolerances defined in IEC 60584. The letter determines the temperature range, the output signal and the colour code.
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