Protection grille comprising a grille made up of a series of parallel bars (4) having bushings (5, 18) of equal length at the ends and constrained by connecting rods (3); guides (6, 7) at least partially shaped as concentric arcs to an axis (24), the final sections (11) of said guides (6,7) being arranged so that the packing of the protection grille is allowed; wheels (10) shaped as equilateral polygon with even number of sides having recesses (12, 13) in each vertex at alternate distance from the centre which allow to engage the bushing (5, 18) relative to adjacent bars (4), characterized in that in the lifting step of the grille the shaped wheels (10) constrain the bushing (18) engaged in the recess (12) arranged at major distance from the centre to engage the outer guide (6), while the next bushing (5), engaged in the recess (13) arranged at minor distance from the centre is pushed by the dragging force exerted by the previous bushing (18) and by the weight of the grille to engage the inner guide (7).