Abstract: A pole-unit of a gas-blast electrical circuit breaker comprises a tranverse partition made of injected insulating plastic material which at the same time performs guiding of the movable contact which passes through it. The injected material part bears an O-ring ensuring tightness with the casing and a one-way check valve of gas flow orifices arranged in the transverse partition. The gas-blast piston securedly united to the movable contact is also made of injected material and it comprises housing and clipping means of the puffer nozzle securedly fixed to the piston. A scraper seal in the form of a split segment is housed in a circumferential groove arranged in the injected part of the piston. The electrical connection between the movable contact rod and a flexible current supply insert is achieved by a braided strip extending in the form of a half-loop in a transverse plane to the pole-unit.