B

Sources disagree

More than one authority states this, and they do not state the same thing. Both are reproduced with the source each came from — deciding between them is yours, not ours.

Source document

thermometricscorp.com says source document is ANSI/ASTM Thermocouple Color Codes, as of 2026-08-19.

Type | Positive conductor | Negative conductor | Positive color | Negative color | Extension-grade jacket | Thermocouple-grade jacket shown in legacy assets | T | Copper | Constantan | Blue | Red | Blue | Brown | J | Iron | Constantan | White | Red | Black | Brown | E | Chromel | Constantan | Purple | Red | Purple | Brown | K | Chromel | Alumel | Yellow | Red | Yellow | Brown | N | Nicrosil | Nisil | Orange | Red | Orange | Brown | S | Platinum 10% rhodium | Pure platinum | Black | Red | Green | None established in legacy asset | R | Platinum 13% rhodium | Pure platinum | Black | Red | Green | None established in legacy asset | B | Platinum 30% rhodium | Platinum 6% rhodium | Gray | Red | Gray | None established in legacy asset |

https://thermometricscorp.com/thermocouple-color-codes.html

assets.omega.com says source document is ANSI and IEC Color Codes, as of 2026-08-19.

B B Do Not Insert in Metal NONE – PLATINUM- Platinum- Tubes. Beware of – – Contamination. 0 to 1820°C 0 to 13.820 ESTABLISHED 30% RHODIUM 6% RHODIUM High Temp. Common Use 32 to 3308°F Pt-30% Rh Pt-6% Rh in Glass Industry

https://assets.omega.com/pdf/test-and-measurement-equipment/temperature/sensors/thermocouple-probes/tc_colorcodes.pdf

tc.co.uk says source document is Thermocouple Colour Code Standards, as of 2026-08-19.

What is the Colour Code for a Type B Thermocouple? In the UK and Europe, the most widely used colour code for Type B thermocouple cable is to the international IEC 60584-3 standard which is as follows: Positive Leg = Grey, Negative Leg = White, Outer Sheath (Jacket) = Grey, Thermocouple Connector Colour = Grey

https://www.tc.co.uk/thermocouple-information/thermocouple-colour-code.html