Type J Thermocouple Wire: Iron / Constantan, −40 … +750 °C
Iron (Fe 99.5%)
Constantan (CuNi 55/45)
±1.5°C (0–275°C) / ±0.4% (275–750°C)
Higher EMF output than Type K in the 0–400°C range. Cost-effective due to iron positive leg. Good for reducing atmospheres.
Iron leg oxidises rapidly above 550°C. Not for oxidising atmospheres above 750°C. Not for vacuum or sulphur-containing atmospheres.
Technical Specifications
| Property | Specification |
|---|---|
| Diameter Range | φ0.025mm – φ5.0mm |
| Tolerance | ±0.005mm (fine) / ±0.02mm (standard) |
| Temperature Range | −40 … +750 °C |
| Standards | IEC 60584-1 Class 1 / ASTM E230 / DIN EN 60584 |
| Surface Finish | Bright / Oxidised / Electro-polished |
| Packaging | DIN 125 spool / Coil / Custom reel |
| Coil Weight | 5kg / 10kg / 20kg standard |
| Traceability | Furnace batch number engraved on spool |
Available Product Forms
Bare Wire →
Solid single-strand, φ0.025–5.0 mm, bright or oxidised.
Stranded Wire →
Multi-strand for flexibility and vibration resistance. 7/19/37 strand.
How to specify Type J Thermocouple Wire
- Confirm the alloy for your operating temperature — Iron / Constantan, rated −40 … +750 °C.
- Check the atmosphere before ordering — Iron leg oxidises rapidly above 550°C. Not for oxidising atmospheres above 750°C. Not for vacuum or sulphur-containing atmospheres.
- Choose the product form — Bare Wire or Stranded Wire. For Type J Thermocouple Wire the deciding factor is the service condition: higher EMF output than Type K in the 0–400°C range. Cost-effective due to iron positive leg. Good for reducing atmospheres.
- Fix the conductor diameter within φ0.025mm – φ5.0mm (±0.005mm (fine) / ±0.02mm (standard)).
- Quote against IEC 60584-1 Class 1 and request the MTC / EMF calibration certificate with the furnace batch number — state which Type J Thermocouple Wire form you need so the certificate scope matches the delivered conductor.
Frequently Asked Questions
What is the maximum temperature for Type J?
+750 °C, and only in suitable atmospheres. The iron positive leg oxidises rapidly above 550 °C.
What atmospheres suit Type J?
Reducing atmospheres. Type J is not for oxidising service above 750 °C, nor for vacuum or sulphur-containing atmospheres.
Why choose Type J over Type K?
Higher EMF output than Type K in the 0–400 °C range and a lower cost, thanks to the iron positive leg.
Where is Type J commonly used?
Plastics and rubber processing, food equipment and HVAC plant — applications that sit in the 0–400 °C band under reducing conditions.
Bottom line: Type J is a cost-effective instrument for the 0–400 °C band in reducing conditions, with higher EMF output than Type K in that range. Its ceiling is +750 °C and the iron leg oxidises rapidly above 550 °C, so it should not be used in oxidising, vacuum or sulphur-bearing service.