A circuit breaker for high and medium tension including insulation by means of a dielectric gas and puffer arc blasting, the circuit breaker comprising a gastight insulating casing, containing:a fixed assembly comprising, in particular, a fixed main contact and a fixed arcing contact;a moving assembly driven by a drive rod and including, in particular, a moving main contact and a moving arcing contact;a first blast volume extended by a blast nozzle;a blast piston; andfirst and second secondary contacts disposed inside a second volume and designed to strike a secondary arc;wherein the first secondary contact is fixed relative to the fixed assembly, the second secondary contact being semi-moving relative to the moving assembly, possessing its own source of energy for displacing it during a circuit breaker disengagement operation, and being provided with means for conferring a shorter stroke thereto than the stroke of the moving assembly.