This paper presents a simplified model of arc fault that allows to analyze the dynamic behavior and to evaluate the RMS value of arcing fault current and the incident energy released by the electric arc. The study confirms previous results carried out in low voltage and medium voltage systems in different configurations, where the values of arcing fault current estimated by the simplified model are in accordance with the corresponding values determined by the equations described by IEEE standard 1584. The dynamic behavior of the electric arc depends on a lot of factors. As improvement the simplified model allows to analyze and to determine basic parameters such as conduction angle, peak value, reduction factor of arc current, power and energy supporting the understanding of the phenomenon of the arc flash. The behavior of the arc current conduction is predicted by knowledge of the phase angle of fault circuit impedance and the phase angle of the ignition voltage; the reduction factor of arc current is variable depending on whether the conduction is continuous or pulsating.