What Is A Fuse?

What is a fuse?

What is a fuse? Simply put, it’s your first line of defense against a short circuit.

When a circuit experiences an excessive amount of current flow, fuses heat up and blow to protect the circuit from damage, such as fires. Usually, fuses are found close to the battery in order to avoid battery damage from a direct short in the cables coming off the posts. Often times you’ll find one larger fuse block closer to the battery, and then have the circuit branch out further away with additional, smaller fuse blocks.

Fuses function similar to circuit breakers, except circuit breakers are often more accessible. Typically, engineering schematics will dictate when and where you’ll need to use fuses versus circuit breakers. 

Types of Fuses

There are a few main types of fuses. Most common are the blade and bolt down fuses. However, cartridge fuses and glass fuses have their place too. Let’s dive in:

Blade Fuses

One of the most common types of fuses are blade fuses, which typically have two flat terminals protruding from the fuse element housing. The housings are colored by amperage according to 78035_primary.jpgthe industry standards, and indicator fuse style housings appear clear. The clear housing of indicator fuses allows easy visibility to the indicator light showing a fuse is blown.

To begin, consider the most common type of blade fuse, ATO fuses. This basic type of fuse is widely used automotive and marine applications. With standard size, color, and varied mounting options, they are an easy choice. This style of blade fuse even has a Smart Glow fuse to indicate when a fuse is blown and makes it easy to find.

Another type of blade fuse you’ll see are the Mini fuses. Mini fuses were considered standard in newer vehicles for quite some time, being found in both domestic and foreign cars. There is also a Mini indicator fuse to show when your fuse has blown. A Low-profile mini fuse is a great choice for when there are numerous electrical circuits, especially due to their small size. However, there are some blade fuses even smaller than the Mini fuses!

Micro2 fuses and Micro3 fuses have now surpassed Mini fuses in being the new vehicle standard. Micro2 fuses are great for high temperature environments, and are RoHS compliant. On the other hand, Micro3 fuses are similar to Micro2 fuses except the Micro3s have a different footprint. Instead of just having 2 terminals, they have 3 terminals. The center terminal in Micro3 fuse is common to both of its fuse elements.

Last, but not least, are the Maxi blade fuses. These are the largest type of blade fuse, and are often found in older vehicles with high amperage circuits. Maxi fuses are found in both foreign and domestic cars. Maxi indicator fuses are also available.

Bolt Down Fuses

When more amperage is required, bolt-down fuses come into play. Plus, having a bolt-down design allows for easy installation and replacement.

MEGA fuses provide the best battery and alternator protection, with their ultra-high current protection. Similar to other fuses, MEGA fuses are an industry standard for high current automotive applications. Available in 100A-500A. BF2 MEGA fuses are now also available, which provide tin-plated contacts and clear housing for identifying blown fuses fast and easy.

On the other hand, MIDI fuses are not only a space saver for high current applications, but they are cost-effective. Plus, with tin-plated contacts there is a superior resistance to corrosion. 79210_alt.jpgAvailable 30A-300A. Now, also available is the BF1 MIDI fuse which has a clear housing for quick identification of a blown fuse.

For inductive circuits, there are ANL fuses. Designed as a low-voltage fuse with time-delay sizing, these fuses are an excellent choice for fork lifts, marine, aviation, and more. Plus,  the small footprint is a space saver! ANL fuses isolate equipment faults in battery operated systems. These fuses come standard with a visible indicator of a blown fuse, and have silver-plated contacts to resist corrosion.

ZCase fuses are great when a minimal footprint is required, and are similar to MEGA fuses in their time current characteristic. They can actually be used directly on a battery post!

For marine applications, the Marine Rated Battery Fuse offers high current protection, minimal space, and a clear view inspection window to see if it is blown. MRB fuses are commonly used in main and auxiliary circuit protection such as alternator outputs, start motor inputs, and accessory circuits.

Finally, we have the Class T fuses which are preferred when a high-degree of current-limitation is needed on short-circuits. With that, Class Ts are commonly used for load centers, disconnect switches, and meters. Easily install these fuses in panel boards and control centers due to their size. This is often times a safer option when the existing circuit breakers cannot be used.

Cartridge Fuses

Designed reverse to other fuses, cartridge fuses are a female version of a blade fuse in to avoid wear and tear. 79625_primary.jpg

Cartridge fuse styles include JCASE, MCASE, and PAL. The style you choose largely depends on the application demands. For example, if you need a time delay, MCASE is probably a good option to consider.

Glass Fuses

Glass fuses are often found in older vehicles, yet can still be found in electrical applications today. The AGC style fuses are a classic fuse and are the style you’ll find in the older 79885_primary.jpgvehicles. On the other hand, the MDL Slow Blow fuse is a time delay glass fuse that is found in a variety of applications. The one you choose largely depends on your application’s specs.

Like many things, the type of fuse you need to use depends on the application in which you’re using it. If you still have questions on the best fit for your application, give our Technical Support a call at 1.800.654.4757. 

To read more articles and how-to content, check out our blog, “The Current” here!

Posted in Fuses & Fuse Accessories.