The verb "fuse" means "to melt". A fuse is an overcurrent responsive safety device used to protect an electrical circuit from the effects of excessive current. It is placed in series with the electrical circuit it is intended to protect. Its essential component is a strip of metal that will melt when the electric current in the circuit exceeds the fuse's rated value. The element (link) in the fuse melts and opens the circuit.


When a problem exists, the fuse is called upon to open (melt its link). The opening of a fuse signifies that something is wrong with the circuit and should be corrected before the current is turned back on. The problem can be an accident, a defective component or a worn-out component.


Two types of fuses are commonly used, cylindrical and plug fuses. A cylindrical fuse consists of a ribbon of fusible metal enclosed in a ceramic or fiber cylinder. This type of fuse is placed in an electric circuit so that the current must flow through the metal strip to complete the circuit. If excess current surges through the circuit, the metal link will heat to its melting point and break. This action will open the circuit, stop the current flow, and thus protect the circuit. The cylindrical type of fuse is used mostly to protect electrical equipment and appliances. Plug fuses are commonly used to protect electric wiring in homes. This type also consists of a fusible metal strip through which the current must flow to complete the circuit. The strip is, however, enclosed in a plug that can be screwed into a fusible electric panel. Plug fuses usually have a window so that the condition of the metal strip can be seen at a glance.