An electrical fuse is a safety device placed in an electric circuit to prevent overloading. It usually comprises a wire of low-melting-point metal mounted in or on an insulated frame. Current passing through the wire heats it (see electrical resistance); and excess current heats it to the point where it melts, so breaking the circuit. In most domestic plugs, the fuse consists of a cylinder of glass, capped at each end by metal, with a wire running between the metal caps. Similar, but larger, cartridge fuses are used in industry. Resettable circuit breakers offer an alternative to fuses.