TDK Electronics · TDK Europe

October 16, 2018

ThermoFuse varistors: Compact overvoltage protection with an integrated fuse


TDK Corporation (TSE:6762) has extended its EPCOS ThermoFuse™ family of fuse protected varistors with the new compact NT14 and NT20 series. The new ThermoFuse components feature a footprint that fits into existing circuit board layouts. The NT14 series (disk diameter 14 mm) is designed to absorb maximum surge currents with an 8/20-μs pulse of 6 kA at rated voltages of between 130 VRMS and 680 VRMS, while the NT20 series (disk diameter 20 mm) has a surge current capability with an 8/20-μs pulse of 10 kA at rated voltages of between 130 VRMS and 750 VRMS. The NT14 and NT20 series offer a maximum energy absorption of up to 220 J and 480 J for 2 ms, respectively. Both series are available in 2-leaded and 3-leaded types, with the third lead used to monitor whether the fuse has been activated.

ThermoFuse varistors are uniquely designed disk varistors that are connected in series with a thermally coupled fuse and are therefore intrinsically safe. If the varistor overheats, the patented thermal fuse trips and isolates the varistor from the grid with unrivalled dependability. This prevents any potential damage on the PCB or to components located near the varistor and increases the reliability of the equipment to be protected. Thanks to their thermal resistance and flame-retardant design of the epoxy coating, the ThermoFuse NT series meet UL 94 V-0 requirements, and are also listed as Type 4CA in UL 1449, 4th edition 

With their compact dimensions and excellent surge current capability over a broad range of voltages, the NT types are suitable for use in a wide range of applications, such as ballasts for lighting, home appliances, power supplies, inverters for solar installations, frequency converters for drives, and smart meters. They can also be used for the general protection of electrical wiring and installations

Main applications

  • Ballasts for lighting, home appliances, power supplies, inverters for solar installations, frequency converters for drives, smart meters
  • General protection of electrical wiring and installations

Main features and benefits

  • Compact size
  • Wide range of voltages from 130 VRMS to 750 VRMS
  • High surge current capability of up to 10 kA
  • UL 1449 listed

Key data 

Surge current
Max. energy 
NT14, 2 leadsB72214R*14130 to 680650 to 220
NT14, 3 leadsB72214W*14130 to 680650 to 220
NT20, 2 leadsB72220R*20130 to 75010100 to 480
NT20, 3 leadsB72220W*20130 to 75010100 to 480

Further information on the products can be found under  



About TDK Corporation

TDK Corporation is a leading electronics company based in Tokyo, Japan. It was established in 1935 to commercialize ferrite, a key material in electronic and magnetic products. TDK's comprehensive portfolio features passive components such as ceramic, aluminum electrolytic and film capacitors, as well as magnetics, high-frequency, and piezo and protection devices. The product spectrum also includes sensors and sensor systems such as temperature and pressure, magnetic, and MEMS sensors. In addition, TDK provides power supplies and energy devices, magnetic heads and more. These products are marketed under the product brands TDK, EPCOS, InvenSense, Micronas, Tronics and TDK-Lambda. TDK focuses on demanding markets in the areas of information and communication technology and automotive, industrial and consumer electronics. The company has a network of design and manufacturing locations and sales offices in Asia, Europe, and in North and South America. In fiscal 2018, TDK posted total sales of USD 12 billion and employed about 103,000 people worldwide.

Media Contact

Christoph Jehle TDK Electronics AG Munich/Germany Phone +49 89 54020-2441 Get in contact
Debbie Martin TDK Electronics Inc. Fountain Hills, AZ/USA Phone +1 480 836-4104 Get in contact
Candido Dall'Agnoll TDK Electronics do Brasil Ltda. São Paulo/Brazil Phone +55 51 3484-7007 Get in contact
Himalaya Baghel TDK India Private Limited Mumbai/India Phone +91 12 04 50 58 42 Get in contact
Stella Suen TDK Electronics Hong Kong Limited Phone +852 3669-8224 Get in contact
Vincent Gaff Tronic's Microsystems SA Phone +33 4 76 97 29 60 Get in contact

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