A residual current protective circuit is integrated into a vehicle electrical system, in particular on the high-voltage side of a multiple-voltage vehicle electrical system, and operates without current measurement. The residual current is determined in an evaluation logic system by evaluating two voltages. These two voltages are voltages that drop at two high-impedance resistors, each of which being connected to ground between a connection between the battery and the generator. If the evaluation logic system detects a residual current, it opens both connections between the battery and the generator or the vehicle electrical system. In conjunction with a dual-voltage vehicle electrical system having two sub-systems connected by a DC voltage converter, a voltage-dependent circuit may be connected in parallel to the DC voltage converter, the parallel circuit grounding the high-voltage side in the event of a fault.