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

A thermocouple's type letter (J, K, T, E, N, R, S, B, C...) names an alloy pair, but the wire color that identifies it on the bench is set by a different standards body depending on where the part was made or bought — ANSI/ASTM MC96.1 uses one color code, IEC 60584-3 (and JIS C 1602 in Japan) uses a different one for the same alloy pair, and the two schemes disagree on which color means positive. Nobody publishes the type letter, both color codes, the alloy pair and the accuracy tolerance class on one page; a buyer or field technician instead has to hold two vendor charts side by side and hope the type letters line up. A record here is one thermocouple type with its positive/negative alloy names, ANSI positive/negative wire color, IEC positive/negative wire color, usable temperature range, and its ASTM E230 standard/special-limits tolerance alongside its IEC 60584-2 / JIS C 1602 class 1/2/3 tolerance. Answers 'is red positive or negative on a type K thermocouple', 'what color is IEC type J versus ANSI type J', 'what's the accuracy tolerance on a class 2 type N thermocouple', and 'my probe has a yellow and red wire, what type is it and is that ANSI or IEC'.

Cite as: Thermocouple type letter to alloy pair, ANSI/IEC color code and tolerance class, referencesource.org/thermocouple-type-color-code-crosswalk/, checked 2026-08-19.

The data

Where this came from

Every record above links the page it was taken from and quotes the sentence that states it. These are the 4 sources this dataset was assembled from.

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

Machine-readable

• data.jsonThe whole dataset — every record with its source URL and source quote.
• Open Knowledge Format bundleOne JSON object per line — every record's frontmatter and quoted span exactly as it is held here, in one fetch.
• data.csvThe same records as one flat table, for a spreadsheet or a dataframe. The last four columns are the source URL, the quoted sentence it was read from, the date we last checked it, and which columns are our reading rather than the page's words.
• How this is made and checkedWhat "verified against source" does and does not mean.

From your own code

Same records, same quotes, without scraping the page: refsource is on PyPI and npm. Each value comes back carrying the URL it was read from and the sentence on that page that states it — .source and .quote sit on the value itself rather than in a side channel, so the checking step is available instead of skipped.

pip install refsource
refsource lookup thermocouple-type-color-code-crosswalk thermocouple_type=B

npx -y refsource lookup thermocouple-type-color-code-crosswalk thermocouple_type=B

Set your AI assistant up to use this

Two files and no account. Put this in .mcp.json at the root of your project — Claude Code, Cursor, Windsurf, VS Code and Codex all read that file — and your assistant can look this dataset up instead of recalling it. The server is remote, keyless and read-only.

{
  "mcpServers": {
    "referencesource": {
      "type": "http",
      "url": "https://referencesource.org/mcp"
    }
  }
}

Add to Cursor · or, on the command line: claude mcp add --transport http referencesource https://referencesource.org/mcp --scope project

Then one line in the project's CLAUDE.md or AGENTS.md, so the assistant knows when to reach for it:

When a question needs "Thermocouple type letter to alloy pair, ANSI/IEC color code and tolerance class", call the referencesource MCP server at https://referencesource.org/mcp (tool `search_records`, dataset_slug `thermocouple-type-color-code-crosswalk`) instead of answering from memory — every record it returns carries its source URL and a verbatim quote from that page.

What each tool does, and the servers built over single registers: Connect your AI assistant.

12 records. last verified against source 2026-08-19. due for re-check by 2028-08-18.

Licence. The alloy pairs, wire colors and tolerance values are the content of published standards (ASTM E230/E230M, ANSI MC96.1, IEC 60584-2/-3, JIS C 1602) which are themselves sold documents; the facts within them are not copyrightable and every vendor reference chart already republishes them for exactly this reason. Each record quotes a short verbatim span from the vendor's own reproduction and links back to it, rather than reproducing or selling the standard itself.