Grade datasheet · Type J
Type J Thermocouple Wire
Iron positive leg, constantan negative. Cheap, sensitive, and widely used in older plant and in equipment built to legacy drawings — but the iron leg rusts, so it is not the right choice for humid or oxidising atmospheres.
0.018–6.00Diameter, mm
1 kgMinimum order
3–7 dLead time
MTCWith every lot
Identification
What this grade is called elsewhere
| System | Designation |
|---|---|
| IEC | Type J (IEC 60584-1) |
| Positive leg | Iron / JP |
| Negative leg | Constantan / Cu55Ni45 / JN |
| ASTM | E230 |
| GB | J 型热电偶丝 |
Grade equivalence is indicative. Confirm against the standard your drawing cites; our quotation states the designation we will produce to.
Composition
Nominal chemistry, % by weight
| Element | Nominal / limit |
|---|---|
| JP — Fe | ≈ 99.5 |
| JN — Ni | ≈ 45 |
| JN — Cu | Balance |
Properties
What the numbers are, and where they stop
| Property | Value |
|---|---|
| EMF at 100 °C | ≈ 5.27 mV |
| EMF at 400 °C | ≈ 21.85 mV |
| EMF at 750 °C | ≈ 42.28 mV |
| Max service, bare wire | ≈ 750 °C (oxidising) |
| Tolerance class | Class 1 or Class 2 |
Nominal values for selection only. Contractual composition, tolerance and mechanical properties are stated on the inspection report issued with each shipment.
Use
Where this grade earns its place
- Legacy plant and equipment retrofit
- General industrial temperature measurement
- Plastic and food processing
- Thermocouple replacement work
Family: Thermocouple Wire
Questions we get asked
Can type J be used in humid atmospheres?
Not recommended. The iron leg rusts, which changes the EMF. Use type T or type E where moisture is present.
Do you supply the constantan negative leg to match?
Yes — same-melt pairing for every thermocouple order.
Send the specification — diameter, grade, temper, quantity.
We come back with a confirmed lead time and the documentation we can issue for the shipment. 100 g sample at cost; orders from 1 kg.
Request a quotation Order a 100 g sample