Analysis of Touch Voltage in TN-S Earthing System

This paper presents touch voltage analysis in TN-S connected earth system. For this purpose, calculation of touch voltages and touch durations (as per IEEE and International Electrotechnical Committee (IEC) standards) with equivalent formulas is done for different sizes of cable and protective conductor (PE). Cable ampacity calculations for underground cable as well as thermal sizing of cable and PE are presented. Furthermore, in this paper a novel way of improving the safety in TN-S system that is by increasing the size of PE for same cable size is investigated. It is found that not only touch voltage and body current decreases but also touch duration increases which are desirable conditions from safety point of view. Also, effect of different seasons on touch duration and body current are evaluated. Especially, in raining season when soil resistivity becomes quite low, it is shown that with increase in size of PE system can become safer.