An operating modes selector is for an earthing switch that includes power contacts and a motor for moving the power contacts. The selector includes a plurality of positions corresponding respectively to various operating modes of the earthing switch, and includes cams whose positions are defined by the selector position. The selector contains a first cam which pulls a first locking organ designed to mechanically block the motor of the earthing switch when the selector is in a position corresponding to a locked closed mode wherein the earthing switch is closed.