An electric circuit device and method is for recognizing a closed switch contact as well as a protective ground conductor interruption in a one- or multiphase electric supply line. A control of a residual current monitoring device (RCMB control) includes one fault current control unit for generating a control signal pattern including a series of switching-on impulses forwarded to a first electronic switch unit to activate a possible artificial passive fault current on one or more active conductors and the protective ground conductor (as a return conductor), this fault current actually flowing, being recognized, and evaluated in a closed circuit in a closed switch contact to be tested and an intact protective conductor. Owing to control signal patterns varying during monitoring, a reliable detection of the artificial passive fault current is ensured even in large dynamic disturbance levels while the electric installation (supply line) to be monitored is in operation.