Uchihashi Estec – Manufacturer of the Elcut brand of Thermal Cutoff Fuses

thermal cutoff fusesUchihashi Estec manufactures thermal cutoff fuses (Elcut brand) and solder products (solder bars, solder wires, flux cored solder wires, solder paste, solder fibers, solder ribbons and fluxes). Uchihashi Estec is fully committed to quality products and environmentally safe manufacturing processes. The company employs approximately 100 employees and has ISO 9001 certified manufacturing sites in Japan and Vietnam.

thermalcutofffuses1Uchihashi Estec began manufacturing and marketing solder products in 1918. For nearly a century, the company has been leading the development of the most advanced alloy technologies – including the successful commercialization of the world’s first small alloy thermal cutoffs. Uchihashi’s thermal cutoffs and solders may not always be visible to consumers, but they ensure the safe and reliable operation of a wide range of electrical products in which they are incorporated.

Key Milestones

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Rated Load Temperature Rise in Thermal Links — Design Considerations

Thermal cutoff links (TCO’s) are designed into electrical circuits to protect electrical devices from overheating. Since the TCO is part of the electrical circuit, current passes through it. Because of electrical resistance, there is a small amount of heat that is produced as electrical current passes through the thermal fuse.

Although the rise in temperature is normally well below the cutoff temperature when the current is within the stated electrical ratings, this self-heating contributes to the surrounding heat generated by the device itself and should be taken into consideration when designing electrical devices containing a thermal link. Manufacturers of high quality thermal links, such as NEC/SCHOTT can provide rated load temperature rise data for their TCO’s. As always, the manufacturer’s installation guidelines and cautions must always be adhered to.

Generally speaking, the higher the current, the higher the electrical resistance and heat produced. When selecting a TCO, the approved electrical ratings must be considered in addition to the cutoff temperature.

The temperature rise or self-heating under electrical loading can be measured and is provided by the manufacturer. For example, NEC/SCHOTT, the manufacturer of the SEFUSE brand of thermal links, provides charts of the Rated Load Temperature Rise. The data is generated by mounting the TCO in a measuring stand (Figure 1) located in a controlled environment at 25 plus or minus 5 degrees Celsius. An electrical current is then passed through the stand/TCO measuring device.

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Figure 1. Testing stand to measure the temperature rise of a thermal link under electrical load.

The temperature is measured with a thermocouple after the thermal link body’s temperature stabilizes. The rise in temperature is then calculated from the difference between the surrounding temperature and the thermal cutoffs’ body temperature. In the case of the SF-R series, the test is repeated five times. Result are show in Figure 2 showing the Temperature rise versus Current Load (A).

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Figure 2. Chart of temperature rise (Degrees Celsius) versus Loaded Current (A) for the NEC/SCHOTT SEFUSE BRAND SF-R series of high current thermal links. Error bars represent the standard deviation.

Results show that as the loaded current increases, the temperature rise above the surrounding temperature increases and can exceed 20 degrees Celsius at a current of 20 amperes.

Don’t Get Fooled Into Buying Counterfeit Thermal Cutoff Fuses

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As we begin a new year it’s important to always be aware of the possibility of counterfeit electronic components — even inexpensive thermal cutoff fuses. Some of the largest and most trusted thermal cutoff fuse makers discovered that cheap counterfeit fuses were being illegally sold. The counterfeits being distributed have not met Safety Standards and may not operate properly.

These problems could largely be avoided by only dealing with authorized distributors, but there is a growing pressure for smaller manufacturers to cut costs.

As of November 2015, the U.S. Bureau of Labor Statistics found that 7,791 electrical manufacturing establishments employed 371,700 people. One of the biggest issues that U.S. manufacturers have faced in recent years is the average 20% structural cost burden they face compared to overseas competitors, and many companies are looking for ways to lower operational costs. While there are ways manufacturers and electrical engineers can cut costs, thermal cutoffs shouldn’t be one of those ways.

NEC SCHOTT (maker of SEFUSE brand thermal fuses) confirmed that counterfeit thermal cutoff fuses were being sold in the Chinese market. These SEFUSE thermal fuses were sold with the official NEC SCHOTT logo and other familiar branding, but came with a “high risk that [they] can lead to serious accident.”

Before purchasing thermal cutoff fuses for use in your products, make sure you’re working with an authorized distributor, otherwise you could end up working with counterfeit thermal fuse suppliers.

We have also been informed that counterfeit thermal cutoffs using the Elcut brand have been found in the Chinese marketplace. This time, counterfeiters weren’t just using the official Elcut logo, they were also posing as official distributors to Chinese buyers.

Always purchase safety equipment and fuses from official authorized distributors, and never from overseas or bulk auction websites. Counterfeit thermal fuses might look the same at first glance, but may be of poor quality and may not operate as expected.

Thermal fuses for manufacturers have to work as designed and at the rated cutoff temperature. While we haven’t yet received any reports of counterfeit fuses here in the United States, anyone who plans to use thermal fuses in 2016 should take care to work with only a legitimate thermal fuse company and trusted, authorized suppliers.

Do Consumers Need To Understand How Thermal Fuses Work?

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While these small yet crucial devices are familiar to electrical engineers, the average consumer is largely ignorant of the important role thermal cutoff fuses play in keeping them safe on a daily basis. When a thermal fuse functions correctly, nothing may be immediately obvious to the consumer, except for example, their dryer will suddenly stop working.

As any electrical engineer knows, a thermal cutoff fuse is a single use device, sometimes known as thermal fuse, TCOs, thermal link or a thermal cutoff. When the temperature in an electrical component exceeds the designed thermal cutoff temperature of the thermal fuse, the thermal element in the fuse melts, interrupting the electrical flow. The thermal fuse functions as an extra line of protection, preventing overheating. But once the TCO is triggered, the device is permanently disabled. That leaves some consumers wondering if it’s possible to safely replace these devices on their own. So is it possible, and more importantly, is it advisable?

Short answer? No – Leave it to the professionals. Trying to tamper with an electronic device is more likely to do harm than good. It’s crucial that end users understand that only trained professionals should try and repair electronic equipment that use thermal fuses. In many cases it is not possible to replace a thermal fuse since it may be enclosed and sealed in the device.

Understanding Thermal Fuse Functions and Electrical Manufacturing
As of November 2015, the U.S. Electrical Manufacturing industry includes 7,791 enterprises that employ a combined 371,000 workers, according to the Bureau of Labor Statistics. The industry includes a number of sub sectors covering a wide range of fields. By revenue, the major sectors of the electrical manufacturing industry include household appliances (15%); communication and energy wires/cables (15%); batteries (10%); lighting equipment (10%); industrial controls (10%), generators and motors (10%); switchboard equipment (10%); wiring devices (10%); and transformers (5%).

If a home or building contains any kind of appliance, electronic, or temperature sensitive device, then it is likely to contain a thermal fuse. , For example, thermal cutoffs can be found in hair dryers, motors, microwaves, toasters, refrigerators, electronic chargers, appliances, coffee machines, automobiles, and more. Whether they realize it or not, the average consumer owns dozens of appliances that use thermal fuses.

But while most Americans have at least a surface level knowledge of their fuse box, most people have no idea how a thermal fuse protects their home and how it differs from a typical line fuse. However, most consumers also lack the electrical knowledge needed to safely install or replace thermal cutoffs, which is why the repair of appliances with TCOs should always be left to a professional or the manufacturer of the device.

Of course, if a thermal fuse is installed correctly, most people will never even know it’s there. Electrical engineers looking to replace or order thermal fuses for use in upcoming projects should always contact authorized distributors like Chatham Components for more information.

Bending Lead Wires – Cautions

Improper bending of the lead wires on a thermal cutoff could result in improper functioning of the TCO. Both Uchihashi and NEC/SCHOTT, the manufacturers of the Elcut and SUFFUSE brand of thermal cutoffs provide detailed cautions on lead wire bending and should be strictly followed.

Since the SEFUSE SF thermal fuses operate differently than the Elcut brand, the lead wires bending cautions are slightly different.

Improper lead bending/handling include

  1. Cracked or broken seals on the lead wire/body junction
  2. Broken lead wire-to-thermal element welds
  3. Damaged fuse bodies

NEC/SCHOTT SEFUSE brand (Cautions from NEC/SCHOTT):
When bending the lead wire, it is important not to apply excessive pressure to the root of the lead wire. The lead wire should be secured close to the case and bent (not twisted) at a distance 3 mm or more from the body of the fuse. It is important to secure the lead during bending so as to prevent excessive forces on the TCO body and lead-wire to body connection. The fuse body should never be exposed to crushing forces,

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The tensile strength applied to the lead wire should be 49N or less for SF types.

The force applied to the body of the thermal cutoff should be 98N or less for SF-type. With regards to the SF-type, deformation of the case may change the location of the sliding contact during operation and could lead to the thermal cutoff operating only at temperatures lower than the normal operating temperature range. The thermal cutoff may also not operate even if the thermal cutoff’s operating temperature is exceeded.

If using SF-type thermal fuses, the lead on the resin-sealed side must not be allowed to touch the case since the case is electrically conductive. This would cause the current to flow from the lead on the resin-sealed side to the opposite lead resulting in a non-functioning thermal cutoff.

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Note that the body of the SF-type is the same in potential as the circuit. Therefore, it must be electrically isolated from other metallic parts.

Uchihashi Elcut brand Thermal Cutoff Installation
Caution to be observed when installing thermal cutoffs

  • Do not twist the body or lead wires (i.e. do not turn or rotate lead wires respect to the body). This could result in breaking the lead wire-to-thermal element weld or may compromise the epoxy seal.
  • Do not push lead wired toward, or pull them away from the thermal cutoff body at axial stresses exceeding those shown in Table 1 (room-temperature reference values). Values in Table 1 were calculated from lead wire diameter according to IEC60691.
  • Tangential forces on the leads must be avoided (i.e. pushing or pulling on the leads at an angle to the thermal cutoff body) as such forces may damage the thermal cutoff’s seals.
  • When bending a lead wire for installation, fix the part of the lead between the body and the lead section to be bent using a tool, and gently bend the lead section that is at least 3 mm from the body. Never hold the body with a tool.
  • Do not damage lead wires by holding with a sharp instrument, and do not bend at a sharp angle.
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  • After a thermal cutoff has been connected, do not apply excessive force that will crush the thermal cutoff body, sealant, or lead wires, and ensure that leads are not subjected to tension, pressing, or twisting forces with respect to the thermal cutoff body
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How To Read Thermal Cutoff Fuse Markings and Ratings on SEFUSE and Elcut Brands

If you use thermal fuses in your work, then you’re no doubt familiar with the series of letters, numbers, and symbols printed on the sides of the fuse body. If you know how to read these markings you can learn a wealth of information about that particular thermal cutoff fuse. In this quick guide, we’ll show you how to read the markings on SEFUSE and Elcut thermal cutoffs.

Understanding the Markings on SEFUSE Brand Thermal Cutoffs…
use thermal fusesLet’s start with SEFUSE’s axial fuses, the SF/E and SF/R series manufactured by NEC/SCHOTT. Unlike Elcut brand thermal fuses, the SEFUSE cutoffs begin with the full brand name at the top followed by a series of letters, numbers, and symbols.
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In descending order on the SF/E and SF/R thermal cutoffs, these markings tell you:

  • Brand name
  • Part number
  • Rated functioning temperature. On the E series, the rated functioning temperature is preceded with the JET marking.
  • Rated current, sometimes preceded by the letters PSE (mark of Electrical Appliance and Material safety law in Japan), but only on the E series. On the SF/R, PSE markings are removed and the rated voltage can be found on the packaging.
  • On the E series, the CCC mark followed by the rated voltage. On the R series, the rated current.
  • A black line followed by the factory code and lot number (the first two digits of the lot number are the year, followed by the month, followed by a sub-lot number)

Reading the Markings on Elcut brand TCOs
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On Elcut’s line of radial and axial TCOs manufactured by Uchihashi Estec, you’ll find the following information in descending order:

  • Type number followed by an abbreviation of the company name
  • The rated current followed by the rated functioning temperature
  • The rated voltage followed by an AC mark and two capital letters that represent the date code
  • PSE mark and any third party approval

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Final Thoughts on TCO Markings, Ratings, and Safety: Why It’s Crucial To Always Use Thermal Fuses Properly
Here in the U.S., foreign-headquartered corporations like Uchihashi Estec and NEC/SCHOTT invest $750 billion in the manufacturing industry each year and employ more than 1.6 million people. Even though U.S. manufacturing companies still produce almost half of the nation’s exports, the industry has been stifled in recent decades. That’s because these companies face 20% higher structural costs (taxes, employee benefits, tort litigation, etc.) compared to other trading partners. Despite this, U.S. manufacturers still have a reputation for producing reliable, high-quality goods and parts.

Thermal fuses provide a crucial safeguard in many of these items, but only if used properly. Before you use thermal fuses, always double check the markings on the fuse body and/or packaging and follow the manufacturer’s installation instructions and cautions.

Remember: All of the electrical ratings, rating agency approvals, and technical specifications may not be listed on the TCO body because of space limitations. For complete specifications, always refer to the manufacturer’s catalog.

What’s The Best Design For Thermal Fuses? Choosing Radial or Axial TCOs

Whether you call them thermal cutoffs, TCOs, thermal links, or thermal fuses, this electrical component is used to prevent electrical devices from overheating. They accomplish this by cutting off the electrical current if the temperature within the thermal fuse ever reaches a set cutoff temperature. They can be found in many types of electrical devices that generate heat, like motors, heaters, teakettles, toasters, and even some dryers. Unlike re-settable thermal switches or thermostats, which automatically reset themselves when the temperature drops, the one-shot thermal fuse is a single-use device. It works by permanently cutting off the electrical current once the thermal element within the fuse melts.

Choosing Between Radial and Axial Thermal Cutoffs…
The difference between radial and axial TCOs is a frequent topic of discussion among some electrical engineers. Although, we should note here that the popular Elcut brand of thermal cutoff fuses from Uchihashi Estec makes TCOs in both an axial and a radial design. You can check out design drawings and animations illustrating the exact differences here.
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In short, both types involve a fusible thermal element that is composed of a eutectic alloy welded across a pair of lead wires. When the cutoff temperature is reached, that thermal element melts and liquefies the wire, severing the electrical current. In the axial design, the thermal element is enclosed in a ceramic tube. In the radial design, the thermal element is enclosed in a phenolic body. The lead wires are secured into the body with an epoxy based sealant in both designs, and both the ceramic tube and phenolic body are non-electrically conductive.

So which TCO is the right choice for your designs? That mostly depends on your space and mounting considerations. Also, the precise electrical and thermal specifications required may dictate which design is used, since not all electrical ratings or cutoff temperatures are available in each design. It’s not that either radial or axial TCO designs are superior to each other in some way, but about determining which fuse meets the specifications required for your device.

When used correctly, they can both be highly efficient design elements.