This paper proposes a new approach capable of locating the voltage sag source side in the power grid based on power-flow behavior at the common coupling point. Measuring the phase voltages and the phase currents flowing at the interested systems interconnection point, the proposed approach is a suitable solution to locate the side of symmetrical and asymmetrical voltage sag source using a set of Boolean logics. A comparative analysis is performed between the best distance relay fault locator method and the proposed approach after being assessed through a simulated case study in a Brazilian utility and industrial systems. Each simulated system has a distributed generation, active loads and power flowing at any directions. The novelty proposal is justified by the simplicity and robustness. Theoretical analysis and simulation have verified its effectiveness.