This paper presents a mathematical study along with the first preliminary results to correlate the equivalent impedance of a medium voltage cable-joint to its Tangent Delta value (i.e. its Dissipation Factor value). The failures of cable joints are a broad and current topic which is being investigated inside the electric engineering community. In the paper the results of both the study carried out to determine correlation between the joint impedance and its Tangent Delta value and the variation of this last one vs. temperature are presented.