Under IEC 60584-1, type K and N thermocouples run to 1,200 °C (tolerance class 2), type J to 750 °C and type E to 900 °C. Types R and S go to 1,600 °C and type B to 1,700 °C. A metal protection tube is good for up to about 1,200 °C, depending on the steel. Above that you're measuring with a platinum type, and it needs a gas-tight ceramic tube, preferably high-purity alumina.
Whichever limit is lower sets the limit of the assembly: the wire or the tube. WIKA says so plainly in its data sheet for ceramic-tube thermocouples, and it's the reason this page covers both.
Temperature ranges by thermocouple type
| Type | IEC 60584-1 class 1 (°C) | IEC 60584-1 class 2 (°C) | ASTM E230 (°C) | Usual protection tube (WIKA) |
|---|---|---|---|---|
| K, N | −40 to 1,000 | −40 to 1,200 | 0 to 1,260 | Metal |
| J | −40 to 750 | −40 to 750 | 0 to 760 | Metal |
| E | −40 to 800 | −40 to 900 | 0 to 870 | – |
| R, S | 0 to 1,600 | 0 to 1,600 | 0 to 1,480 | Gas-tight ceramic |
| B | – | 600 to 1,700 (class 2 and 3) | 870 to 1,700 | Gas-tight ceramic |
WIKA fits base-metal types (K, J and N) with metal tubes as a rule, and platinum types (R, S and B) with ceramic ones. Type T isn't in WIKA's table and we don't quote a range for it here.
Thin wire, lower limit
The 1,200 °C figure for type K assumes heavy wire. ASTM E230 gives suggested upper limits for thermocouples in conventional closed-end protection tubes, and they drop as the wire gets thinner:
| Wire (AWG) | Diameter (mm) | Types K and N (°C) |
|---|---|---|
| 8 | 3.25 | 1260 |
| 14 | 1.63 | 1090 |
| 20 | 0.81 | 980 |
| 24 | 0.51 | 870 |
| 28 | 0.33 | 870 |
| 30 | 0.25 | 760 |
So a 3.25 mm (8 AWG) type K wire is rated to 1260 °C, while a 0.25 mm (30 AWG) wire stops at 760 °C. The same applies to platinum types: WIKA notes that their long-term stability rises with wire diameter and offers them in Ø0.35 and Ø0.5 mm. If you want to run near the top of the range, use the thicker wire, and size the insulator bore for it (see insulator sizes by wire diameter).
Metal or ceramic protection tube
WIKA puts metal protection tubes at up to 1,200 °C, depending on the material. Its own table of tube steels shows how much that depends on the grade:
| Material no. | AISI | Upper limit in air (°C) |
|---|---|---|
| 1.0305 (carbon steel) | – | 550 |
| 1.4571 | 316Ti | 800 |
| 1.4749 | 446 | 1,150 |
| 1.4841 | 310 / 314 | 1,150 |
| 1.4762 | – | 1,200 |
WIKA also notes that metal tubes can turn porous or scale at high temperature, and offers a gas-tight ceramic inner tube inside the metal one to keep aggressive gases off the wire. Above 1,200 °C, or where you want no metal near a platinum element, the tube itself is ceramic.
Ceramic tubes are brittle. WIKA's ceramic-tube thermocouples are closed and hemispherical at the tip and cemented into a metal support tube, which carries the process connection. It also advises preheating C 799 tubes before installation, pushing them in slowly, and supporting long horizontal tubes against bending.
Which ceramic: C 530, C 610 or C 799
- C 799 (alumina, over 99% Al₂O₃). WIKA: gas-tight, high-purity, usable up to 1,600 °C, only partially resistant to changes in temperature, not resistant to alkali vapours. The choice for platinum types and for anything above 1,200 °C.
- C 610 (mullite, 50–65% Al₂O₃). WIKA: gas-tight, usable up to 1,500 °C, not resistant to alkali vapours. Cheaper; JUMO puts it at about a fifth of the price of KER 710 (C 799). Keep it out of reducing atmospheres.
- C 530 (porous). WIKA: not gas-tight, fine-pored, highly resistant to changes in temperature, usable up to 1,600 °C. Used as an outer tube around a gas-tight inner tube, where thermal shock would crack a dense one.
What the class numbers mean in detail, and why C 799 isn't the same as 99.7%, is in C 799, C 610 and C 530 grades. Our standard grade is 99.5% Al₂O₃, which we benchmark against C 799 and call C799-class; 99.7%, 99% and 95% are available too. We confirm the grade in each quotation.
Types S, R and B: why the tube material matters
Platinum-rhodium wires are poisoned by contamination, and WIKA says the risk rises with temperature. Two rules come up in every maker's literature:
- Above 1,200 °C, use gas-tight ceramic, preferably high-purity C 799 (WIKA). JUMO says both the insulating rod and the protection tube should be KER 710, the old name for C 799.
- Watch silica in reducing atmospheres. JUMO notes that 0.2% SiO₂ in the tube or insulator is already enough to form brittle platinum silicides there.
Gas-tight doesn't mean sealed forever. WIKA points out that ceramic tubes count as gas-tight under DIN EN 50446, but gas can still diffuse into the sensor at high temperature, so the wire itself has to tolerate the atmosphere.
If your thermocouple is type S, R or B, tell us the atmosphere and the working temperature when you ask for a quotation. 99.7% is available if you need it, and our yearly lab reports are available on request.
Tube and insulator sizes by type
WIKA fits types K, N and J with Ø1 or Ø3 mm wire in C 610 insulating tubes, and types S, R and B with Ø0.35 or Ø0.5 mm wire in C 799 insulating rods. Rössel lists 1.0, 1.38, 2.0 and 3.0 mm for base-metal wire and 0.5 or 0.35 mm for platinum. Which of our twin- and four-bore insulators each wire passes through is tabled in insulator sizes by wire diameter.
For the protection tube, European buyers mostly order the C 799 series sizes 10×6 mm, 15×10 mm and 24×18 mm; all three are among our standard sizes. The full list, with the C 610 series and the standard lengths, is in thermocouple protection tube sizes, and every size we make is on the protection tubes page.
Standard sizes usually ship from stock: about 3 days for a small order, about 7 for a bulk one. For a quotation, send the thermocouple type, OD × ID × length, the grade and the quantity.
Questions buyers ask
- What is the maximum temperature of a type K thermocouple?
- IEC 60584-1 gives type K −40 to 1,200 °C in tolerance class 2 and −40 to 1,000 °C in class 1. ASTM E230 gives 0 to 1,260 °C. In a closed-end protection tube, ASTM E230 suggests 1,260 °C for 8 AWG (3.25 mm) wire but only 760 °C for 30 AWG (0.25 mm) wire.
- Which thermocouple should I use above 1,200 °C?
- A precious-metal type: R or S (0 to 1,600 °C in IEC 60584-1) or B (600 to 1,700 °C). WIKA states that above 1,200 °C only precious-metal thermocouples can be used.
- How hot can a metal thermocouple protection tube go?
- Up to about 1,200 °C, depending on the steel. In WIKA's table, 1.0305 carbon steel is rated to 550 °C in air, 316Ti to 800 °C, 446 and 310 to 1,150 °C and 1.4762 to 1,200 °C. Above that, use a ceramic tube.
- Why do platinum thermocouples need high-purity alumina?
- Platinum wires are poisoned by contamination, and the risk rises with temperature. WIKA recommends gas-tight ceramics, preferably high-purity C 799, above 1,200 °C. JUMO notes that in a reducing atmosphere 0.2% SiO₂ in the tube or insulator is enough to form brittle platinum silicides.
- Is a ceramic protection tube completely gas-tight?
- C 610 and C 799 tubes count as gas-tight under DIN EN 50446, but WIKA notes that process gas can still diffuse into the sensor at high temperatures, so the thermocouple wire must also suit the atmosphere.
Sources
- WIKA data sheet TE 65.80, thermocouples with ceramic protection tube
- Tempco catalog page 14-103: ASTM E230 suggested upper temperature limits for protected thermocouples, by wire gauge
- JUMO data sheet 90.1000 (German), KER 710 and KER 610
- Rössel-Messtechnik, Praxis der Thermoelemente (German), Table 9 and insulating rods
- Our own figures: the factory's standard-size list, 2026 orders and test report, as recorded in our product catalog.