A switching device, in particular an electrical power circuit breaker, is disclosed for protecting an electrical circuit. The switching device includes two pole terminals, a switching mechanism for automatically interrupting the electrical connection of the two pole terminals in the event of an overload, electrical components for controlling the switching device and a pole cassette in which the switching mechanism is disposed in a switching chamber. The pole cassette includes at least one gas duct which is connected to the switching chamber in a gas-communicating manner and is designed to discharge gas from the pole cassette past the electrical components to the environment.