A protective device breaks an electrical circuit when a stated electric current that passes through it is exceeded. A protective device may include both the tripping unit and the breaking unit or it may simply represent the breaking unit if the tripping unit is specified individually as a protective device tripping unit.
An earthing switch is protective device used to open or close a circuit when there is no current. Used to isolate a part of a circuit, a machine, a part of an overhead line or an underground line so that maintenance can be safely conducted.