# IEC 60584-1 vs ASTM E230 — Thermocouple Standard Comparison

> European and American thermocouple standards compared: tolerance classes, EMF reference tables, testing requirements and how to specify dual compliance.


> IEC 60584-1 and ASTM E230: same EMF data, different class names.

## Tolerance class equivalents

| **IEC 60584-1** | **ASTM E230** | Type K at 1000 °C | Type N at 1000 °C | Notes |
| --- | --- | --- | --- | --- |
| Class 1 | Special Limits | ±4.0 °C | ±4.0 °C | Approx. 2× better than Class 2 |
| Class 2 | Standard Limits | ±7.5 °C | ±7.5 °C | Standard industrial grade |
| Class 3 | — | ±12.5 °C | — | IEC-only, rarely used for base metals |

## How to specify dual compliance

1. State both standards on the purchase order — for example "IEC 60584-1 Class 1 and ASTM E230 Special Limits".
2. Confirm the MTC will reference each standard separately, so both audiences find their own clause.
3. Check the colour code against the instrument the cable will actually be connected to.

## Key differences

**EMF reference tables:** IEC 60584-1 and ASTM E230 use the same underlying ITS-90 temperature scale. The EMF values are **identical for all practical purposes** (differences are below 1 µV). A wire manufactured to IEC Class 1 will meet ASTM Special Limits and vice versa.

**Tolerance definition:** IEC expresses tolerance as a fixed value (±X °C) in the low range and a percentage of reading (±Y%) in the high range. ASTM uses the same mathematical formula but uses different terminology: "Special Limits of Error" ≈ IEC Class 1, "Standard Limits of Error" ≈ IEC Class 2.

**Testing requirements:** ASTM E230 references ASTM E220 (calibration method) and ASTM E1350 (homogeneity testing). IEC references IEC 60584-2 (tolerances) and IEC 60584-3 (extension cable). The testing procedures produce equivalent results.

**Dual certification:** We can supply the same batch certified to both IEC 60584-1 Class 1 and ASTM E230 Special Limits. No additional testing is required — we simply issue two MTCs referencing the respective standard.