A circuit breaker arrangement in supply of electric power has advantageous applications especially in power distribution units which supply DC power to electrical devices. Electromechanical circuit breakers are commonly used for circuit protection. They have a disadvantage of fixed tripping conditions, which can only be changed by changing the circuit breaker component. This is solved by providing a circuit breaker arrangement which has an electromechanical circuit breaker with a first, fixed tripping condition, and an additional circuit, which monitors the output current and mechanically trips the circuit breaker if the current exceeds a second tripping condition. This way, it is possible to use the first tripping condition of the electromechanical circuit breaker and/or a second, controllable tripping condition.