Simple Guide to Fuses: Fuses 101
Fuses are an essential safety feature used in all modern electronics and are designed to fail when too much electrical current is passed through. This provides reliable current sensitive protection for discrete components or circuits against excessive current. Fuses contain a piece of wire which melts easily when the rated current is reached.
An excess in current flow can be caused by several factors; these include overload of the circuit (the connection of equipment that draws too much current from the circuit), circuit damage (wear over time, loose connections or shortage) or incorrect wiring.
Fuse ratings
Fuses have both a continuous rating and a blow rating.
The continuous rating is the rating at which a current will continuously pass through without blowing. Due to surges in the current it is important that the continuous current does not exceed ~75% of the fuses blow rating, otherwise the fuse may blow needlessly.
The blow rating is the current that the fuse will blow at. Needless to say, the blow rating should be higher than the continuous rating and a factor of two is often applied. Therefore, a fuse with a 10A continuous rating would have a 20A blow rating.
Fuses should always be replaced like for like. Replacing a fuse with a higher blow rating can seriously compromise a circuit and can lead to a high risk of electrical fire due to component failure. Therefore care should always be taken when replacing fuses within a circuit.
Common Types of Fuses:
The most common types of fuses are detailed below; these include glass cartridge fuses, blade fuses, link and continental fuses. Others are available on the market for various purposes however we would consider these to be the most common and popular fuse.
Glass cartridge fuses are fully enclosed body fuses with metal contacts at either end joined to the interior fuse link. 20mm, 30mm and 32mm length glass fuses are most common and have a 5mm and 6.35mm diameter respectively. These fuses are generally used for older appliances and low current applications. Glass fuses have the advantage that the metal melting strip is easily visible for inspection to determine whether the fuse has blown. Several types and variations of fuse holder are able to accommodate glass cartridge fuses.
Blade fuses are the most common automotive fuse with most modern cars utilising blade fuses with their fuseboxes. They are used for a variety of automotive purposes and are a plastic casing with two metal prongs for push fit application into holders or fuse boxes. The most common sizes are micro blade fuses (APS or ATT), mini blade fuses (APM or ATM), standard blade fuses (APR, ATC or ATO) and Maxi blade fuses (APX).
It is important to check which size fuse is necessary as car models can use a mixture of mini or standard fuses, however micro and maxi fuses are also available. Blade fuses are particularly suited for automotive purposes as many can fit into a standard car fuse box and many fuses are required to protect the different electrical components on modern vehicles.
Maxi blade fuses (APX) are used for higher current power applications and have a higher rating than micro, mini and standard blade fuses.
Link and strip type fuses are used for higher current applications. Strip, Midi Link and Mega Link fuses are available, Mega link fuses are used for very high currents, 100-500A. Link fuses have mounting holes in order to bolt down the fuses into position.
Continental fuses are primarily use in older vehicles before blade fuses were introduced. Otherwise known as Torpedo fuses because of their shape and appearance, Bosch Fuses, GBC or ATS fuses. Continental fuses, as with blade fuses are coloured coded as to their amperage.
This is intended as a general guide to Fuses - every application is different so it is important to consider all factors above when picking the correct fuse for your job. For any assistance please get in touch!
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