By Wu Peng, Senior Process Instrumentation Engineer · Last reviewed September 18, 2026
Two thermocouple color codes are in daily use, and they disagree about almost everything. Under ANSI MC96.1, the code followed in North America, the negative lead is red on every type. The positive lead carries the type color: yellow on Type K, white on Type J, blue on Type T.
Under IEC 60584-3, the code used across Europe and on most export projects, the negative lead is white on every type. The type color moves to the positive lead and the outer sheath: green on Type K, black on Type J, brown on Type T.
That difference is not cosmetic. A green jacket means Type K to an engineer trained on IEC, and Type R or S extension cable to one trained on ANSI. A white conductor is the positive lead of a Type J in the United States and the negative lead of every type under IEC.
This page puts both current thermocouple color code charts in one place and adds the legacy British and German charts that still turn up on older plant. It also lists the colors that collide, so you can spot them before a sensor is wired backwards.
Contents
- Two codes in use
- ANSI colors by type
- IEC colors by type
- Where the codes collide
- Legacy codes in service
- Color is not proof
- Ordering the right cable
- FAQ
Two codes in use
ANSI MC96.1 is the American color standard, and ASTM E230 carries the same convention into the tolerance tables most US suppliers quote. IEC 60584-3 is the international standard; the British version, BS EN 60584-3, is identical to it, which is why UK and European cable looks the same. Almost every color argument on a project comes down to which of these two documents the cable was made to.
The two standards are built on opposite starting points. Clause 6.1 of IEC 60584-3 makes white the negative conductor for every thermocouple type. The type is therefore identified by the positive lead and by the sheath, which clause 6.3 assigns from the same table.
ANSI does the reverse: red is the negative lead for every type, and the type is identified by the positive lead and the jacket. Neither code is ambiguous on its own. The trouble only starts when cable from both worlds lands in the same marshalling cabinet.
One consequence of the IEC rule is worth stating early, because it catches people who assume color carries more information than it does. IEC assigns color by thermocouple type and nothing else. It does not distinguish extension cable from compensating cable.
The first is built from the sensor’s own alloys; the second substitutes cheaper metals that follow the curve only while the joint stays below a stated temperature. A green IEC cable can be either, so you have to read the printed designation on the jacket.
The difference between the two is covered in our guide to thermocouple extension and compensating cable. Where the color could be confused with another IEC cable code, the standard allows the type to be marked with a label or tag instead. That is another reason the jacket alone is not the last word.
ANSI colors by type
The table below is the North American thermocouple wire color code. Read it as the colors you will find on extension-grade cable. That is the cable running from the sensor head back to the instrument, and therefore what you see in a cabinet.
| Type | Positive lead | Negative lead | Jacket |
|---|---|---|---|
| K | Yellow | Red | Yellow |
| J | White | Red | Black |
| T | Blue | Red | Blue |
| E | Purple | Red | Purple |
| N | Orange | Red | Orange |
| R and S | Black | Red | Green |
| B | Gray | Red | Gray |
Thermocouple-grade wire is the alloy pair rated to sit at the sensing junction itself. On the base metal types it is jacketed brown rather than in the type color. Two types also break the pattern that the jacket matches the positive lead. Type J runs white and black; Types R and S run black and green.
The one rule with no exception in this table is red. Every ANSI type puts red on the negative lead, and that is the single fact a North American technician can carry across the whole table. It is also the assumption that old German cable breaks, as the legacy section shows.
IEC colors by type
The international code is easier to memorize, because the negative lead never changes and the sheath repeats the positive color.
| Type | Positive lead | Negative lead | Sheath |
|---|---|---|---|
| K | Green | White | Green |
| J | Black | White | Black |
| T | Brown | White | Brown |
| E | Purple | White | Purple |
| N | Pink | White | Pink |
| R and S | Orange | White | Orange |
| B | Gray | White | Gray |
The current edition also lists Type C, the tungsten-rhenium pair, in red, and Type A in dark blue. Both are specialty items rather than stock cable.
Type N is where the two codes look least alike. The American code puts Type N in orange, the international code in pink. If a project drawing says orange and the cable on the drum is pink, nothing is wrong. One was made to ANSI and the other to IEC, and both are Type N.
Where the codes collide
Most published charts show the two codes in separate tables and leave the reader to compare them. The table below runs the comparison in reverse. It starts from the color in front of you and lists what that color means under each standard.
Three colors agree. The rest do not, and two of them invert a polarity convention rather than simply renaming a type.
| What you see | Under ANSI MC96.1 | Under IEC 60584-3 |
|---|---|---|
| Red conductor | Negative lead, every type | Not used on conductors; red is the Type C sheath |
| White conductor | Positive lead of a Type J | Negative lead, every type |
| Green jacket | Type R or S cable | Type K |
| Brown jacket | Thermocouple grade, type not implied | Type T |
| Yellow jacket | Type K | Not assigned |
| Blue jacket | Type T | Not assigned; Type A is dark blue |
| Orange jacket | Type N | Not assigned; Type N is pink |
| Black jacket | Type J | Type J |
| Purple jacket | Type E | Type E |
| Gray jacket | Type B | Type B |
Black, purple and gray mean the same type under both standards. Everything above them in the table does not.
The two rows at the top of the table are the ones that cause wiring errors rather than paperwork errors. A technician who learned that red is negative finds no red at all on an IEC cable, so the habit never fires. A technician who learned that white is negative will wire an ANSI Type J backwards, because white is the Type J positive lead.
Reversed leads do not look like a fault at first glance. The reading sits below the terminal temperature and moves the wrong way when the process heats up.
Legacy codes in service
Plant older than the current standards keeps its original cable until something forces a change, so two withdrawn codes are still worth recognizing. The British code, BS 1843 of 1952, was replaced by BS 4937 Part 30 in 1993. That document is itself now inactive, and the current British standard is BS EN 60584-3. The German code was withdrawn in favor of the IEC colors in the same period.
| Legacy code | Type K | Type J |
|---|---|---|
| BS 1843 (old UK) | Brown positive, blue negative, red jacket | Yellow positive, blue negative, black jacket |
| Old German DIN | Red positive, green negative, green sheath | Red positive, blue negative, blue sheath |
Published charts do not agree on which DIN number to cite for the German colors, with 43710 and 43714 both in circulation. The colors themselves are consistent across the suppliers who still stock legacy cable.
The German row is the important one. Red marks the positive lead, which is the opposite of the ANSI rule that a North American technician is most confident about. On a machine imported from Germany in the 1980s, trusting red to be negative reverses the sensor.
The British code has a trap of its own that lives entirely inside the standard. Types K and E both use brown and blue conductors, so the conductors alone cannot separate them. Only the jacket does: red for Type K, brown for Type E. If the jacket has been cut back or has faded in a hot cabinet, that distinction is gone.
Older Japanese and French codes exist as well. The published references disagree about their document numbers in the same way they disagree about the German one. Rather than reproduce numbers that suppliers cite three different ways, take the practical position. On legacy cable, treat color as a hint and confirm the type another way before you rely on it.
Color is not proof
Color identifies cable that was made to a known standard and has not been modified since. Three common situations break that assumption. A repair may have spliced in whatever was on the shelf that day.
The cable may predate the code the drawing quotes. And under IEC the color tells you the type but not the grade. It cannot say whether the run is true extension cable or the cheaper compensating cable, which is only valid below a stated ambient temperature.
When the color is in doubt there are two checks that do not depend on it. The first is identifying the alloy pair itself, which works because Alumel is magnetic while Chromel is not. The method for each type is set out in our guide to thermocouple types and their characteristics.
The second is a two-point check against known temperatures, described step by step for Type K in the Type K guide. Neither takes long, and both settle the question that a faded jacket cannot.
Polarity has its own test that needs no color at all. Warm the sensing end by hand or with hot water and watch the reading. It should rise.
If it falls, the leads are reversed somewhere between the junction and the instrument, and the error grows as the plant warms up.
Ordering the right cable
Most color disputes are avoided at the purchase order rather than in the field. The line that belongs to this page is the color code standard the cable is to be made to. It matters most on export projects, where the plant standard and the local supplier default to different codes.
The rest of a cable order, including which grade to specify and how far a given gauge will run, is covered in the companion guide to thermocouple extension wire. It also explains why Types R and S are supplied with compensating cable rather than true extension cable. For the sensor itself, our thermocouple assemblies are built to the type, sheath and connection you specify.
The range and tolerance behind each type are set out for the base metal group in the Type J, T and E guide and for the noble metal group in the Type S, R and B guide. If you are starting further back, how a thermocouple works explains why the two legs have to stay distinguishable in the first place.
Application note
Why there is no case study on this page. We checked our project records for a color code job and found none, which is itself informative. Color questions arrive during commissioning, from a technician at a cabinet, rather than as a line on a request for quotation: the cable is usually bought with the sensor or from a local cable house. Settling the color code on the purchase order is what turns that decision into a record.
FAQ
Is red positive or negative on a thermocouple?
Under ANSI MC96.1, the North American code, red is the negative lead on every thermocouple type without exception. Under IEC 60584-3 the negative lead is white and red is not used on conductors at all. On older German cable red marks the positive lead. Red on its own never settles polarity until you know which code the cable was made to.
What is the color code for a K type thermocouple?
Under ANSI the positive lead is yellow, the negative lead is red, and extension cable has a yellow jacket. Under IEC the positive lead and the sheath are green and the negative lead is white. Under the withdrawn British code BS 1843 a Type K is brown positive, blue negative, in a red jacket.
What color is a J type thermocouple?
Under ANSI a Type J is white positive and red negative in a black jacket. That makes it the type where the US jacket color does not repeat the positive lead. Under IEC the positive lead and sheath are black and the negative lead is white. A white conductor therefore means positive on American cable and negative on international cable.
What color is type R thermocouple wire?
Under ANSI, Type R and Type S cable is black positive and red negative in a green jacket. Under IEC both are orange positive, white negative, with an orange sheath. Note that these two types are normally supplied with compensating cable rather than true extension cable, which is covered in the extension wire guide.
Request a quote
Tell us the application and we configure one assembly, not a shelf part. Give us the thermocouple type, the color code your plant works to and the cable grade you need. We supply the sensor and the cable to match. Reach our application engineers or use the form below.
Written and technically reviewed by Wu Peng and the Instranova engineering team.