Puffer switch having a two-volume break chamber

An electric switch comprising a first arcing contact surrounded by a puffer break chamber in which a gas is pressurized by a thermal effect, and a second arcing contact movable along an axial direction relative to the first arcing contact, said break chamber including an inner partition separating a first compartment of fixed volume from a second compartment of smaller volume, both compartments being filled with said gas under pressure and each possessing an orifice to blast the arc, said orifices being separate and placed in series along said axial direction, the second arcing contact initially releasing the orifice of the first compartment while still closing the orifice of the second compartment when the arcing contacts separate, wherein each compartment is connected to its own orifice via a respective blast channel, wherein the first compartment with its blast channel and its orifice are placed adjacent to said first arcing contact, wherein the second compartment is placed mainly between the ends of the first arcing contact and a permanent-current contact corresponding thereto, and wherein the compartments communicate with each other via a channel that is closed by an excess pressure vent device allowing gas at excess pressure to pass in one direction only from the smaller volume compartment to the larger volume compartment.