An improved discriminating circuit breaker system for use with an electrically grounded direct current power distribution system. A three-tier safeguard system is provided to insure proper operation of the breaker should a fault occur. The basic components include the electrically operated circuit breaker and a control circuit therefor. The control circuit sends a control signal to the breaker to operate it depending on whether a illegitimate load is detected on the power distribution system. This detection process utilizes: a pilot wire through which any control signal flows; an alternating current (a.c) signal generator to superimpose such a signal on the transmission line; a current detector to sense the a.c. level and produce a control signal if its current value exceeds a maximum level; a voltage detector to sense the voltage level of the a.c. signal and to produce a control signal if the value falls below a minimum level; and a switch system responsive to the control signals and in series with the pilot wire to activate the opening of the circuit breaker when the wire is open or when a control signal is produced.