# B — Thermocouple type letter to alloy pair, ANSI/IEC color code and tolerance class

For B, positive-leg alloy is Platinum 30% rhodium; negative-leg alloy is Platinum 6% rhodium; ansi/astm positive-leg color is Gray; ansi/astm negative-leg color is Red; ansi extension-grade jacket color is Gray, verified against its source on 2026-08-19.

- **Type letter:** B _(verified: appears in the quote below)_
- **Positive-leg alloy:** Platinum 30% rhodium _(verified: appears in the quote below)_
- **Negative-leg alloy:** Platinum 6% rhodium _(verified: appears in the quote below)_
- **ANSI/ASTM positive-leg color:** Gray _(verified: appears in the quote below)_
- **ANSI/ASTM negative-leg color:** Red _(verified: appears in the quote below)_
- **ANSI extension-grade jacket color:** Gray _(verified: appears in the quote below)_
- **Source document:** ANSI/ASTM Thermocouple Color Codes _(verified: appears in the quote below)_
- **Usable temperature range:** 0 to 1820°C _(per assets.omega.com, not stated by the source above)_
- **IEC 60584-3 positive-leg color:** Grey _(per tc.co.uk, not stated by the source above)_
- **IEC 60584-3 negative-leg color:** White _(per tc.co.uk, not stated by the source above)_
- **IEC 60584-3 outer sheath colour:** Grey _(per tc.co.uk, not stated by the source above)_

## What the source says

> 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 |

## 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.

### 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 |

Source: 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

Source: 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

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


## Source

- https://thermometricscorp.com/thermocouple-color-codes.html
- https://assets.omega.com/pdf/test-and-measurement-equipment/temperature/sensors/thermocouple-probes/tc_colorcodes.pdf
- https://www.tc.co.uk/thermocouple-information/thermocouple-colour-code.html

Last verified: 2026-08-19. Review by: 2028-08-18.
Part of [Thermocouple type letter to alloy pair, ANSI/IEC color code and tolerance class](https://referencesource.org/thermocouple-type-color-code-crosswalk/).