Fuses are usually made of a low melting point lead-tin alloy, zinc, copper, silver wire or sheet material. When the current in a circuit is too high, the wire or piece of metal in it becomes hot and blows, interrupting the current and protecting the circuit from harm. When a fuse blows, it must be replaced manually to restore the circuit to operation.

Types and Labeling

Fuses are usually labeled with rated current, rated voltage, brand, safety standards, speed, and interrupting capacity, etc.In order to match the characteristics of the circuit, fuses can be categorized into several types according to their blowing rate. The type of blowing rate of small fuses is usually indicated by an alphabetical designation.The common ones are
T (Time-lag) for slow blow type
F (Fast) for fast-melting type
M (Medium time-lag) for medium speed
There are also TT for slower melting than T and FF for faster melting than F, etc.
Meaning of specifications
Rated current: The current at which the fuse can allow continuous flow without blowing (not the current at which the fuse will blow).
Rated voltage: The voltage that the fuse can handle when it blows. If the voltage that the fuse can withstand is not enough, arcing may occur between the two end points of the fuse and it will not be able to completely break the circuit.
Let-through energy : Also known as the I²t, the energy passed from the overcurrent to the fuse when it blows.
Breaking capacity or interrupting capacity: The maximum current that can be safely handled by a fuse before it breaks. The interrupting capacity of the fuse must be less than the maximum short-circuit current that may flow through the circuit, otherwise the short-circuit moment is not yet blown before the risk of danger, is one of the important safety parameters of the power fuse. BS 88 fuse interrupting capacity of 80kA; small electronic fuse interrupting capacity is small, generally no labeling of this parameter.
Temperature derating: A fuse with a rated capacity of 1 ampere at 25°C may be allowed to pass 10 to 20% more current at low temperatures (e.g., minus 40°C), and only 80% of its original capacity at high temperatures (e.g., 100°C). Temperature reductions vary among fuses and should be checked in the specifications.
Cut-off current: If the fault current is high, the fuse will blow before the peak of the fault current, and the reduced peak is called the cut-off current.
Appearance
Wire: Early primitive type of fuse, directly screw-locked, used in old switches and sockets of various sizes.
Chip (bare): Easier to use than the old filament type.
Glass: Available in several different sizes, commonly used in electronics.
6.3 x 32 mm (diameter x length)
5 x 20 mm
Ceramic : Available in several different shapes and sizes, prevents glass from bursting.
Plastic sheet shape with sheet metal pins: automotive fuses.
Surface Mount Device (SMD) type
Cylindrical, plug-in type: Soldered directly to the circuit board for use inside the product.