This paper presents a generalized model of the arcing fault circuit in a.c. extendable to d.c., that consents to identify the arc resistance operating in the fault. This model allows to describe completely the trend of all the prospected parameters of interest in a normalized form in relation to the bolted short circuit current and the apparent power related to it. The adoption of the arc fault current, the incident energy and the arc flash boundary, calculated adopting the IEEE 1584 guide, as reference values in the equations of the proposed model, allows an interesting insight into the analysis of the arc flash phenomenon. The IEEE guide allows to calculate the arc fault current interpolating the intermediate average values, adopting as input the bolted short circuit current of the fault circuit, but without a direct correlation to its power factor and without the definition of the power factor of the arc fault current. This paper proposes to evaluate the arc resistance of each single event in a deductive way from the analysis of the complete fault circuit considering the prospected variations due to the incidence of the power factor of the bolted short circuit current in an assigned identified range.