For initiating a control function based on a real time available fault current measurement, a measurement module measures an operating voltage, a short voltage, and a ring parameter of alternating current power lines. A processor calculates an impedance of the power lines as a function of the operating voltage, the short voltage, and the ring parameter. The processor further calculates a dynamic available fault current as a function of the impedance. In addition, the processor initiates a control function based on the available fault current.