This paper presents a method to determine the impact of low-voltage direct current circuit breakers on the availability of the dc bus. Low-voltage direct current is gaining traction in industry, and protection is an important aspect. New circuit breaker technologies are extensively researched, but the impact of this speed of interruption on direct current bus availability has not yet been investigated. This paper demonstrates how to determine the fault clearance probability, which is used to set up the state transition diagrams for the feeder states. These state transition diagrams are solved using the semi-Markov process. The solutions of the semi-Markov process are used in a UGO method to determine the availability of the direct current bus. Furthermore, it is shown that the results depend on the length of the feeder and the capacitance of the direct current bus. For feeders with a fault clearance probability lower than 100percent, the number of feeders also influences the availability of the direct current bus.