Abstract: A current-interrupting chamber is filled with a dielectric fluid and includes a moving assembly. The moving assembly is mounted to move axially between a position at the start of a circuit-breaker opening operation and a position at the end of a circuit-breaker opening operation. The moving assembly has a first compression chamber whose volume decreases between the start position and a position in which the first chamber is open; a first arcing contact designed to co-operate with a second arcing contact; and a second compression chamber communicating with the first compression chamber. The volume of the second compression chamber decreases between the start position and the end position. The second compression chamber is designed to inject fluid into the first compression chamber, between the open position and the end position, when the pressure in the first chamber is lower than the pressure in the second chamber.