The actual methods for analyzing the starting point of any event are unable to define correctly this kind of phenomena with enough accuracy. Methods based on RMS calculation often have substantial errors in time and highly depend on the phase of the voltage waveform. In spite of this previous disadvantage, these methods are being used in most of the PQ analyzers. This paper develops a novel method to characterize accurately the parameters that define each event (dips, swells and interruptions), mainly the duration, start and end instant by the calculation of the root mean square value during the disturbance. The wavelet theory will be used in the development of the method