A fuse protects an electrical circuit or device from excessive current when a metal element inside it melts to create an open circuit. In this post, we will look in to the construction and working of Fuse and the properties of fuse material.
With the exception of resettable fuses, a fuse must be discarded and replaced after it has fulfilled its function.
When high current melts a fuse, it is said to blow or trip the fuse. (In the case of a resettable fuse, only the word trip is used.)
A fuse can work with either AC or DC voltage and can be designed for almost any current. In residential and commercial buildings, circuit breakers have become common, but a large cartridge fuse may still be used to protect the whole system from short-circuits or from overcurrent caused by lightning strikes on exposed power lines.
In electronic devices, the power supply is almost always fused.
Schematic symbols for a fuse are shown in the figure. Those at the right and second from right are most frequently used. The one in the center is approved by ANSI, IEC, and IEEE but is seldom seen.
To the left of that is the fuse symbol understood by electrical contractors in architectural plans. The symbol at far left used to be common but has fallen into disuse.
How a FUSE Works?
If I is the current surge in amps and t is its duration in seconds, the surge sensitivity of a fuse—which is often referred to verbally or in printed format as I2t—is given by the formula:
I2t = I² * t
Manufacturer datasheets list the voltage drop that the internal resistance of a fuse is likely to introduce into a circuit.