Fuses work on a simple principal. When a there is a current overload the result is heat. This is because all materials, including the wire that the circuit is made of, have resistance. Resistance is the natural opposition that materials have to electric current. As electrical energy is conducted through a circuit some of the energy is consumed in the process of pushing the electrons through the material. The consumed energy is converted into heat. When a fuse blows it is because too much current was passing through it. Too much current results in an even greater amount of heat and can damage a circuit. Fuses are rated for how much current they can conduct. If more current passes through a fuse than it is rated for the fuse will heat up until the thin filament in its center blows and disconnects the circuit form the power source.