Abstract: A generator circuitry for connecting a generator to or disconnecting the same from a bus connected to a power supply. The circuitry comprising a first disconnector, a breaker and a second disconnector connected in series with one another between the bus and the generator further includes a detecting circuit to detect the generator output and an operating circuit to prohibit an action of opening the second disconnector during detection of the generator output by the detecting circuit. Since the disconnector is opened in the state where the generator output is not detected, the disconnector is released from the duty to interrupt the charge current flowing to the interelectrode capacitance of the breaker, whereby the use of a small-sized disconnector is rendered possible.