Abstract: A protective device includes a circuit breaker with an operating means connected to a fault current sensing control circuit. A small line current and/or a small fault current sensing current transformer means is conductively connected through individual rectifiers and series sensing resistors as a current source to charge a common power supply capacitor. A voltage limiting means across the capacitor maintains the current source. A high impedance signal processing amplifier includes a sensing transistor connected to the sensing resistor which establishes a minimum trip level and driving coupling transistors connected to the capacitor and including voltage sensitive means to positively inhibit full amplifier turn-on before the power supply capacitor is charged to an operating voltage level.