The SCHOTT SEFUSE® SF type is a thermal cutoff based on a one-shot operation principle and prevents electrical appliances from catching fire due to overheating. It uses an organic thermo-sensitive material inside a metal case and is able to operate in electric circuits with large currents.

Product Description

SF type

The SF type contains a sliding contact, two springs and a thermal pellet inside a metal case. Under normal temperatures, the sliding contact touches the top of the lead. The current flows through the sliding contact and the metal case to the other lead and the electrical circuit is closed. When the ambient temperature reaches a critical point, the thermal pellet melts and the springs move the sliding contact away, resulting in an interruption of the electrical flow.

Product Advantages

The SF type thermal cutoff has the following advantages:
  • Remarkable sensitivity to temperature rise due to its shape and small size
  • High reliability and accuracy due to resin-seal
  • Appropriate for electric flows with large currents (6A-15A)
  • Environmentally-friendly product complying with the Directive on Waste Electrical and Electronic Equipment Directive (WEEE), and the Directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment (RoHS)


It is used for a great variety of applications such as:
  • Home Appliances (e.g. irons, coffee makers, rice cookers, bread makers, toasters, refrigerators)
  • Comfort Conditioning Appliances (e.g. air conditioners, fans, humidifiers, heaters)
  • Personal Care Appliances (e.g. hair dryers, hair curlers, hair setters, razors)
  • Business Appliances (copiers, laser printers, facsimiles, power strips)
  • Electrical Components (e.g. transformers, solenoids, AC adopters)


An organic thermo-sensitive material with a specific melting point is used as a thermal element in the SF type. Silver cuprate “AgCuO” has been used as the sliding contact material since April 2003 and replaced “AgCdO”, which was used prior to that time. Its patent has been registered in many countries worldwide.

For additional information about this technology, please click on this link to our technology page.

Features/ Specifications

The SF type uses an organic thermo-sensitive material as a thermal element; hence the SFH type has the most stable material. The operating temperature ranges from 73°C to 240°C. All SF types except the SF/K version have a ceramic pipe in order to protect the sealing resin from stress caused by possible bending of the leads.
Series Electrical Ratings Opening Temperature Standard
AC/DC Current Voltage
SF/K Series AC 6A 250V 73°C-216°C UL, cUL, VDE, BEAB, KTL, PSE
SF/Y Series AC 15A 250V 73°C-240°C PSE, (UL), CCC
Please refer to "Cautions" in the Thermal Cutoff catalog for our design guidelines.

Forms of Supply and Product Packaging

Standard forms of supply are available. Please contact our sales department if you have any special requests concerning supply and packaging.

Quality Assurance

The SF type is a reliable thermal protection device manufactured in a factory certified by the International Standards Organization (ISO9001/14001 quality standard).

All SF type thermal cutoffs undergo an automatic internal resistance check, in addition to the standard quality assurance processes of SCHOTT to ensure the consistent high quality of the product.

For further information, please review our quality assurance page. The Thermal Cutoff catalogs are also available from our download page.