A high or medium voltage electrical switch, particularly a GIS type isolating switch with three switching positions and a grounding position, includes a switching element in a closed and sealed enclosure that can be filled with a dielectrically insulating gas, containing a mobile switching element free to move along an axial direction to electrically connect two conducting bars at intervals from each other, and also including a fixed ground contact to be electrically connected to one of the two conducting bars through the switching element when the switch is in the grounding position. The fixed ground contact is offset from the path of the switching element along the axial direction and the switching element forms a Y with a contact pin such that the contact pin and the fixed ground contact engage in each other through displacement of the switching element along the axial direction.