What device acts to prevent excessive current from damaging circuits?

A fuse serves as a protective device in electrical circuits, designed to prevent excessive current flow which can lead to overheating and potential damage. When current exceeds a certain level, the fuse will 'blow' or melt, interrupting the circuit and stopping the flow of electricity. This safety feature helps protect electrical equipment and wiring from failure by ensuring that they operate within safe limits.

In contrast, a lightning arrester is used to divert surge currents caused by lightning strikes away from delicate electrical systems, rather than regulating current flow during normal operation. A voltage regulator maintains consistent voltage levels to ensure stable operation of electrical devices but does not directly address current overload situations. A relay is a switch operated by an electric current but does not serve as a protective device against excessive current; rather, it is used to control circuits. Thus, the function of preventing excessive current damage is uniquely fulfilled by a fuse.