Fuse FAQs

How do I select a fuse?

Fuses are overcurrent protection devices, meaning they are intended to operate during undesired overcurrent conditions. Therefore, during normal load conditions, a fuse should carry the normal operating current of the circuit without opening, which is also called a nuisance opening. However, when an overcurrent occurs, the fuse must interrupt the overcurrent as designed and withstand the voltage across the fuse after internal arcing and opening for full interruption. To properly select a fuse, criteria such as the voltage rating current rating, overload conditions and opening times and other factors should be considered. Please visit our fuse technology web page for help with proper fuse selection. Additionally, please visit Eaton’s parametric search tool for assistance with selecting a fuse provided some basic inputs.

What is the amp or ampere rating?

An amp or an ampere rating is the current rating for a specific fuse. The current rating of a fuse identifies the allowable current that the fuse can carry without opening under specified test conditions.  Each fuse is marked with its current rating. This rating can be identified with a numeric, alpha or color code mark. Marking codes can be found in each product’s data sheet.

What is the interrupting rating?

The interrupting rating commonly referred to and is also known as the “breaking capacity” or sometimes mentioned as the “short circuit rating.” The interrupting rating is the maximum available current, at rated voltage, that the device can safely open without rupturing. The interrupting rating of a fuse must be equal to or greater than the available short circuit current of the circuit to provide its intended protection.

What is the difference between a one-time fuse and a resettable fuse?

Both a one-time fuse and a resettable PTC fuse can be used for overcurrent protection of circuits. One-time fuses provide protection from an overload situation by opening only once, creating a one-time positive disconnect. A resettable fuse can provide overcurrent protection for multiple excessive current situations without requiring replacement after each event. The PTC shifts from a low to high resistance state during the overcurrent but allows some residual current still passing through the device. For more information and visuals on resettable devices please, click here.

Can I replace a one-time fuse with a PTC or resettable fuse? Are they interchangeable?

A PTC resettable fuse might be able to replace a one-time fuse, but they are not immediately interchangeable. While they are similar and offer protection against overcurrent events, they provide different protection characteristics and behave differently in various environmental conditions.  Given these differences, each technology is recommended to be evaluated independently to ensure proper protection is provided.  For more information  on Eaton’s PTC resettable fuses please, click here.

What is a ferrule fuse?

A cylindrical fuse with a glass or ceramic body with metal end caps which serve as termination points to facilitate inser­tion and removal. Ferrule fuses are often called cartridge fuses.

How do I mount a ferrule fuse on a printed circuit board?

Most of Eaton’s ferrule fuses come with an axial leaded option that allows the fuse to be mounted on a PCB. Eaton also offers a complete line of fuse holders and fuse clips that are recommended to mount a ferrule fuse to a PCB. Please find the full line of products here.

What are the standards that govern fuses?

UL and IEC are two of the main standard bodies that write the standards that govern fuses. Additionally, there are other standards agencies that are country specific and leverage IEC standards with additional country specific requirements, such as VDE, CCC, Semko, PSE.

What is IEC?

The International Electrotechnical Commission is the world’s leading organization for the preparation and publication of international standards for all electrical, electronic and related technologies. This organization is an independent agency that is comprised of technical and national committees that develop numerous standards.   However, they do not approval or certification to their standards.  Multiple different national organizations or 3^rd parties often provide approval to the IEC published standards.

What is UL?

UL is a global certification company that sets safety standards for electrical commercial, industrial and consumer products. They are a 3^rd party standards organization that also evaluates, can test and provide their approval for product that meet their standards.

What is CSA and how is it different than a cURus rating?

The CSA Group (Canadian Standards Association) coordinates with businesses, organizations and code authorities for product standards and codes development CSA is a governing body with standards creation for Canada.  A CSA mark can be applied after testing, certifying and receiving approval from CSA. The cURus is similar in that the product is still tested and evaluated to the CSA standard, however certification is provided via UL. 

I’ve selected the fuse to protect my circuit, what are the options to mount it?

Eaton has an extensive line of fuse holders and accessories that can be used to mount a fuse in a circuit. Please visit Eaton’s fuse accessory selection guide for the full list of in-line fuse holders, panel mount fuse holders, Fuse blocks, PCB fuse clips and PCB mount fuse holders that support each fuse type.

My fuse has a Vac rating, can I place it in a Vdc circuit?

Fuses have their Vac or Vdc rating explicitly defined on their datasheet. Some fuses do have both Vac and Vdc ratings. Fuses without a Vdc rating should not be applied in Vdc circuits.   Please refer to the respective datasheet located at www.eaton.com/fuses. Eaton can provide application specific testing and internal validation or external certification for volume production if the specific application conditions are not covered in the datasheet. 

What is the difference between interrupting rating and breaking capacity?

Breaking capacity and interrupting rating are often used interchangeably. A fuse must be able to safely open the circuit under a short circuit condition without rupturing endangering its surroundings. The interrupting rating of a protective device is the maximum available current, at rated voltage, that the device can safely open without rupturing. The interrupt­ing rating of a fuse must be equal to or greater than the available short circuit current of the circuit.

Why is the interrupting rating important?

Fuses are inherently safety devices against overcurrents. Protecting against the highest possible overcurrent condition helps ensures the equipment and human safety. Interrupting rating is important as devices with low interrupting ratings that are used in circuits with higher available fault currents have the potential to fail causing a safety issue.

Do fuses need to be derated at higher or lower temperatures?

Yes. Ambient temperature is the temperature of the air immediately surrounding the fuse and is not necessarily room temperature. Most electrical characteristics of a fuse generally stated at standardized conditions, which is  at an ambient temperature of 25 °C. Both higher and lower ambient temperatures will affect a fuse’s opening and current carrying characteristics. This effect is demonstrated in temperature derat­ing curves found on the fuse datasheets. Additionally, the single element de-rating curve is available as well. It is an overall governing de-rating curve for single element fuses that can be found here. Click here, for further information if de-rating curve is not readily available. 

What is the Mean Time Between Failure (MTBF) or Failure in Time (FIT)?

There is no FIT/MTBF data for fuses. When an overcurrent event occurs, the fuse opens as designed and interrupts the flow of current. This is not a “fuse failure,” but a proper function of the fuse design. What are perceived as fuse and/or fuse holder “failures” are mostly reactions to excess heat produced by loose or corroded connections, improper component sizing or application outside the device’s operating temperature range. These are not device failures, but rather inappropriate device selection. Fuses do not require maintenance until an overcurrent event causes them to open – then they need replacing after properly addressing the cause of the overcurrent event.

What is the terminal finish or terminal material?

Most datasheets reference this information. If it is not listed, please contact technical support. 

What is the MSL rating of the fuse?

Please contact technical support.

Is my fuse RoHS compliant?

As Eaton conducts business around the world, we are committed to enhancing our products to meet global governmental environmental mandates now in effect. Eaton has pledged to eliminate hazardous materials in our products regardless of application or market. We’ve initiated a comprehensive review of Bussmann® series products to substitute non-hazardous materials into their construction wherever possible.

For applicable fuses, RoHS compliance can be found listed on the fuse datasheet. Compliance status is also kept up to date in a database and available online using our RoHS compliance product search tool. Additionally please reach Eaton via the product stewardship webpage.

Are 3D models available for fuses?

Some 3D models (.STEP) are available upon request. Please contact technical support.

How do I find a cross for competitors’ products?

Please visit Eaton’s on-line cross reference search, or contact technical support.

What amperage fuse should I select?

There are a variety of variables that need to be accounted for when selecting the amperage of a fuse for a specific application. This would include normal operating current, any inrush current or regular pulse currents, desired opening performance and ambient temperature.   Please visit Eaton’s detailed fuse selection page that illustrates fuse selection criteria.

Can a time delay fuse be used to replace a fast-acting fuse?

This depends on the opening performance and protection desired.  Fast acting fuses help quickly limit fault currents from damaging downstream components during short circuit events. However, harmless inrush or temporary surge currents may cause nuisance openings unless these fuses are oversized.  Time-delay fuses allow for some higher withstand capability during these harmless inrush or surge currents and allow for closer overcurrent protection for short circuit events. Replacing a fast-acting fuse with a time-delay fuse ultimately requires analysis of the normal operating conditions, possible inrush or surge currents and desired opening performance. For technical support regarding your specific application, please contact technical support.

Does Eaton offer automotive circuit protection devices?

Eaton provides a variety of circuit protection devices ideal for automotive applications.  These products are tested and conform to AEC-Q200 test programs to ensure their suitability in automotive applications.  Along with fuses, Eaton also provides ultra-low capacitance PolySurg ESD Suppressors as well as a suite of inductors for automotive. Visit the automotive selector tool.