SEFUSE Thermal Fuses

Thermal cut-outs are generally used in appliances that expected to frequently reach high temperatures, where the temperature needs to be carefully controlled up to a specific limit. The re-settable nature of thermal cut-outs make them ideal for repeated use in devices with cyclic thermal loading.

A prime example of this is kettles, but they are also frequently used air conditioners, motors, and an array of other kitchen appliances.

As they rely on bimetal elements, their thermal cut out temperature can vary significantly depending on the metals used and shape of the element. This results in thermal protection of devices over significant temperature ranges. The ASAHI US-622, for example, has an impressive operational temperature range of 0°C to +185°C.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

There are 2 types of thermal cut-outs that we sell here at ATC Semitec:

Snap Action Disc Thermal Cut-Outs, supplied by either ASAHI or EAW, which use a bimetallic disc.

Probe Thermal Cut-Outs, supplied by PEPI, which contain a bimetallic strip element.

PEPI’s JS Self-Hold Thermal Cutout includes an integral “self-hold” thermal and current sensitive cut-out allowing the protector latches to open after tripping and then reset remotely. This offers the same benefit as fitting a manual-reset cut-out but without the disadvantage of having to access it.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Bimetallic elements (or Bimetals) are comprised of 2 metals with differing thermal expansion coefficients, that are fixed together. As the element is heated, one side will expand at a faster rate than the other, resulting in unidirectional bending.

By altering the shape of the element at ambient temperature, the shape change can be made instantaneous, hence bimetals are often found as either curved discs or strips, which will ‘snap’ into shape.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Thermal cut-outs (or thermal switches) are a re-settable, temperature-sensitive device, which open at high temperatures, stopping current flow, and the re-close as the temperature decreases.

The opening and closing of the device is due to a bi-metallic element, which changes shape instantaneously with a change in temperature. They can either reset automatically, or manual reset options are available when an automatic and unattended restart could create a hazardous condition.

Thermal cut-outs are therefore used as fail-safe devices, preventing temperature from rising to dangerous levels, whilst their ability to reset makes them ideal for applications where high temperatures are reached frequently, without the need to replace the appliance.

We offer a range of products from world leading manufacturers, PEPI and Asahi in either probe or disc formats

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Circuit protectors offer circuit protection in devices in a manner that is far superior to using fuses.

This makes them ideal for applications containing:

Relay circuits

Motors

Heaters

Transformers

Solenoids

Semiconductors

Our CRD‘s from Semitec have a wide range of operating voltages that they can steady current over, and their small size makes them a neat solution in tight spaces.

PTC or Polymer PTC (PPTC) fuses carry current up to a threshold temperature. At this point, the crystalline polymer structure will change to an amorphous state, leading to a massive increase in resistance, preventing charge from being carried across the device.

The device will then remain in this high resistance state until the applied voltage is removed and they have cooled down, allowing the polymer structure inside to return to its original crystalline form. Hence, they are considered re-settable.

At ATC Semitec, we have a range of different PTC resettable fuses for use over many currents and operating temperatures.

To have a look at our current range of devices, click here.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

There are many different types of circuit protection devices due to the multiple different ways that current can be limited in a circuit. At ATC Semitec, we have a range of different circuit protects to suit your appliance.

From our repeat use Inrush Current Limiters from Thinking TKS, designed to protect front-end mains voltage supplies against current spikes at switch-on, to our SEFUSE Thermal Fuses from SCHOTT which offer one-shot ultimate thermal protection from 70°C to 240°C, our range can tailor to your requirements.

For more information, and to see our full range of devices, click here.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Circuit protection devices protect the circuit from excessive temperatures, currents or short circuit in an electrical conductor. They are essentially ‘weak links’ within the circuit that are designed to fail when a fault in the system is encountered. By breaking at low currents, they limit the amount of energy that is released during electrical failure, leading to safer devices.

From PTC resettable fuses, to CRDs, to MOV’s, we have an array of different devices to that can be implemented.

To see our full range of Circuit Protection Devices, click here.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

PEPI H series bi-metal fuses use a snap-action bi-metal temperature-sensing element instead of a melting solder or organic pellet.

At its set-point, the specially designed bi-metal element inverts (i.e. “snaps” from concave to convex) and opens a set of contacts, thus breaking the electric circuit.

Bi-metal fuses do not suffer from ageing (e.g. shrinking of pellet fuses or sagging in solder fuses) and so are more reliable, especially at temperature settings above 200°C.  These bi-metal fuses will not reset even at ambient temperatures as low as -35°C.

Also available in ½”disc (button) thermostat housings such as our Asahi US-622 series.

To view our full range of thermal fuses  click here

Have a question or need a sample ? Call one of our engineers today on 01606 871680 or complete our contact form

SEFUSE SM series solder-based thermal fuses are housed in a ceramic case.  The solder alloy inside responds to external high temperatures and at its set-point, will start to melt.  As the solder melts, it separates to either end of the case (helped by the surrounding flux) and thus breaks the electrical circuit.  See diagram below;

In the SM type, leads are connected by a fusible alloy. The current flows directly from one lead to the other. The fusible alloy is coated with a special flux.

When ambient temperature rises to the SEFUSE operating temperature, the fusible allow melts and condenses into a drop around the end of each lead because of the surface tension and the coating of special flux. The electrical circuit then opens.

To view our full range of Eutectic Solder Alloy Thermal Fuses click here

Have a question or need a sample ? Call one of our engineers today on 01606 871680

SEFUSE SF  series pellet thermal fuses are housed in a metal casing.  The organic thermal pellet inside responds to external high temperatures and close to its set-point, will start to melt.  As the pellet melts, it triggers a spring-loaded contact mechanism which breaks the electrical circuit as shown in the diagram below;

The SF-R thermal fuse contains a sliding contact, springs, and a thermal pellet inside a metal case. When spring B is compressed, contact between lead A and the sliding contact is maintained. At normal temperatures, current flows from lead A to the sliding contact and then through the metal case to lead B.

When the ambient temperature rises to the SEFUSE operating temperature, the heat transferred through the metal case melts the thermal pellet. When the thermal pellet melts, spring A and B expand, moving the sliding contact away from lead A. The electrical circuit is opened by breaking contact between the sliding contact and lead A.

To view our full range of Organic Pellet Thermal Fuses click here

Have a question or need a sample ? Call one of our engineers today on 01606 871680

ATC Semitec stock a number of different types of thermal fuse:

Organic pellet – see SEFUSE SF/R types for details

Eutectic solder alloy –  see SEFUSE SM/A types for details

Bimetal element –  see PEPI H types for details

Have a question or need a sample ? Call one of our engineers today on 01606 871680

Thermal fuses are generally used to protect electric heaters, household electrical appliances and electrical products used in hazardous areas.

Specific examples include

• • washing machines
  • tumble dryers
  • convector heaters
  • coffee makers
  • hair dryers
  • laser printers
  • rechargeable battery packs..

When designing with a thermal fuse, you need to consider the operating current, applied voltage and the duty hours of the appliance that it will protect.  The normal running temperature needs to be a minimum of 25°C below the fuse opening temperature not including any self-heating due to I²R/ current self-heating. The Th (holding temperature) and Tm (maximum temperature) values stated for the fuse should also be taken into account. This is to ensure reliable operation over the required product life, and that any IEC/EN standards they are approved to, are complied with.

Have a question or need a sample ? Call one of our engineers today on 01606 871680

A thermal fuse (or thermal cut-off or “tco”) is a one-shot/one-time, non- re settable, temperature-sensitive device that provides ultimate overheat temperature protection in small appliances, electric heaters and electronic circuits.

Thermal fuses are fail-safe devices which activate when other safety measures fail to operate. They help  prevent temperatures rising to dangerous levels, and  thus stop product fires from occurring. The original fault in the appliance could have been caused by either control malfunction or customer misuse.      

Thermal fuses therefore offer the ultimate thermal protection.

They are single use protection devices that cannot be reset or repaired. They have to be replaced once the original fault which caused the product failure has been identified and rectified. In the case of many consumer products, this would mean replacing the complete appliance.

Have a question or need a sample ? Call one of our engineers today on 01606 871680