U.S. Thermocouple Types, Polarity and Color Codes
Look up common ANSI thermocouple conductor colors and polarity, distinguish extension from sensor identification, and avoid mixing U.S. and IEC color systems.
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Common ANSI conductor colors
Confirm the identification system before using a thermocouple color. In the common U.S. ANSI convention the negative conductor is red; IEC uses a different convention. Connector color, cable jacket and individual conductor insulation describe different parts of an assembly.
| Thermocouple type | Positive conductor | Negative conductor | Common alloy description |
|---|---|---|---|
| J | White | Red | Iron / copper-nickel |
| K | Yellow | Red | Nickel-chromium / nickel-aluminum |
| T | Blue | Red | Copper / copper-nickel |
| E | Purple | Red | Nickel-chromium / copper-nickel |
| N | Orange | Red | Nickel-chromium-silicon / nickel-silicon |
Read the assembly identification
The table is limited to individual conductor colors in the stated ANSI system and common base-metal types. It is not a temperature-range table. Sensor sheath, junction construction, extension-grade wire and insulation have their own limitations.
- Read the type marking on the probe, cable and connector.
- Confirm ANSI versus IEC in the product documentation.
- Identify positive and negative conductors in that system.
- Match the extension cable and input channel to the required thermocouple type.
A yellow conductor identified under ANSI must not be interpreted using an IEC table. Generic copper extension wire changes the intended thermoelectric junction arrangement and cannot be substituted merely because continuity is present.
Keep measurement setup with the reading
Record probe type, polarity, extension-cable designation, input type, cold-junction compensation arrangement and grounded/ungrounded junction information. A type letter alone does not establish usable range or accuracy for the whole assembly.
Store the setup and measured units in test records and link cable endpoints with the cable register. Use RTD wiring for resistance sensors; RTDs and thermocouples require different measurement methods.