Relationship between pipeline source impedance and touch voltage hazards induced by power lines

Touch voltage rather than prospective touch voltage is a critical measure in assessing earthing safety particularly for third party assets such as pipelines. The touch (or `loaded') voltage is an expression of the actual hazard across a subject. It is a significant leveller because it is a consistent measure of hazard irrespective of soil resistivity, existence of surface impedances and other series impedances. A key component of the touch voltage circuit, and one largely ignored or misunderstood by the inexperienced, is the source impedance of a prospective touch voltage, which is discussed in detail herein. This paper analyses the importance of the touch voltage for electrical hazards on insulated metallic pipelines. It paves the way for further research in consideration of the change from Dalziel's fixed body resistance to Biegelmeier's voltage dependent body resistance distribution. It has important implications for design and safety verification of pipe earthing systems.