It is a short length of wire made of lead /tin/alloy of lead and tin-zinc having a low melting point and low ohmic losses under normal operating conditions it is designed to carry the full load current.
If the current increases beyond this designed value do any of the reasons motioned above, the fuse melts [said to be blown ] isolating the power supply from the load.
The electrical equipment is designed to carry a particular rated value of the current under normal circumstance. Under abnormal condition such as short circuit, overload or any fault the current rise above this value, damaging the equipment and sometimes resulting in fire hazards.
Fuses are passed into operation under such situations.
Re-wearable OR kit Kat fuse
These fuses are simple in construction, cheap and variable up to a current rating of 200A. they erratic in operation and their performance deteriorates with time.
HCR cartridge fuse
The high rupturing capacity OR[HRC]fuse consists of a heat resistance ceramic body then silver OR bimetallic fuse element is welded to the end brass caps.