Electrical circuit breaker with arc extinguishing compressed fluid

Electrical circuit breaker of the type using an arc extinguishing compressed fluid, in particular a gas, such as sulphur hexafluoride, comprising within a tightly sealed casing filled with the extinguishing fluid, a current bearing connector with a stationary contact, a current bearing connector in which a movable contact actuated by a driving mechanism is guided, a fluid blasting device formed by a piston solid with the movable contact and defining a compression zone, and by a fluid blasting nozzle of insulating material brought by the movable contact to an advanced position relatively to the stationary contact with an opening communicating with said compression zone, as well as a body of insulating material for the closure of the blasting nozzle, slidingly mounted for a stroke limited by a stop element on the stationary contact and under the action of elastic means, said movable body being suitable to be moved, so as to go away from said stop element by means of said nozzle during the movable contact closure stroke, characterized in that said movable body is provided with a cavity forming a chamber open towards said blasting nozzle, said chamber of the movable body being placed in communication with said compression zone through said blasting nozzle in that part of the stroke of movable contacts in which the blasting nozzle holds the movable body away from said stop element, whilst the opening of said chamber is facing the opening of the nozzle during the residual part of the stroke of movable contacts.