Our expert answers a question from a Voltimum user following a training session on Amendment 1 of BS 7671 18th Edition Wiring Regulations.
Question: Why 70v and not 50v (touch voltage) for 722.411.4.1(iii) ?
Answer: The 70 V value was chosen specifically for electric shock protection in an electric vehicle charging installation in the event of a discontinuity fault in the PEN conductor of the pulic low voltage electricity distribution network. Its based on information given in IEC Technical Report IEC TR 60479-5, Effects of current on human beings and livestock – Part 5: Touch voltage threshold values for physiological effects. The 50 V AC conventional touch voltage limit relates to the requirements of Section 411 of IET Wiring Regulations for protection against electric shock in a TN system in the event a fault between a line conductor and earthed exposed-conductive-parts or a protective, under healthy network conditions.
- John Bradley - Standards Manager and Chairman of JPEL/64, Schneider Electric