A self-extinguishing expansion switch or circuit breaker, including an extinguishing chamber and an expansion chamber connected by a duct. The extinguishing chamber is positioned above the expansion chamber. An axially movable tube supports a movable arcing contact which is cooperable with a stationary arcing contact. The axially movable tube separates axially from a conducting tube supported by an operating rod such that the circuit breaker is in an isolated position beyond an open position.