A switch-fuse module and a ring main unit. The switch-fuse module includes: at least one fuse; and at least one fuse canister having the fuse inside; the security device including: at least one slider configured to linearly move between an open slider position and a closed slider position; at least one earthing switch that i) is galvanically connected to an end of the fuse, ii) is operable between an open and a closed state, iii) is designed to earth the end of the fuse in the closed state, and iv) is coupled to the slider in such a manner that the open slider position effects the open state of the earthing switch and the closed slider position effects the closed state of the earthing switch; an energy-storing propulsion element configured to move the earthing switch from the open to the closed state when discharging; and a locking mechanism adapted for blocking access to the fuse in a locked state and for releasing access to the fuse in an unlocked state, wherein the slider is coupled to the locking mechanism in such a manner that the slider is in the closed slider position while the locking mechanism is in the unlocked state, so that the fuse may only be accessed if it is ensured that the fuse is earthed.