The deexcitation of a synchronous machine has been used for the protection of the power supply based on a diode rectifier in marine dc power distribution networks. The fault current from the generator can be eliminated with the protection method utilizing the deexcitation. This allows for removing generator circuit breakers. In this method, the rectifier should be designed to manage the peak fault current and energy limited by the deexcitation. Hence, this paper presents the fault current characteristics with the generator deexcitation by analytical and experimental approaches. The fault behaviours under the deexcitation are theoretically described and the rectifier sizing is discussed for the peak fault current and the overloading capability of the diodes. The deexcitation characteristics are calculated by the analytical expression and investigated in a test setup for different subtransient reactance, fault resistance, exciter response, and time delay.