A Fuse Box
A fuse box is an important electrical safety device designed to serve as a first point of failure in an electrical system. Fuses are intentionally designed to fail at electrical loads below the capacity of the circuit, ensuring that any overload damages a replaceable fuse instead of causing wiring damage.
Any given circuit's wiring can handle a specific amount of current without problems. But when current exceeds the normal wiring load, it will extremely heat up because of the electrical resistance. During that circumstance, if your circuit has no fuse, then overloaded current may cause a fire or damage. A fuse is designed to fail before this point to protect both the wiring and the more valuable equipment on the circuit.
Fuses are rated for their maximum amp, and should only be installed in circuits rated for that amount of current. For example, if a fuse rated for 40 amps is plugged into a 15 amp circuit, it can allow the circuit to overload before failing, potentially causing damage to the wiring.