The most commonly used protective measure against electric shock in the event of an earth fault is that termed "earthed equipotential bonding and automatic disconnection of supply". The requirements associated with this protective measure are determined by the touch voltages created by our earth fault. Although the term "touch voltage" has appeared in technical articles and in some books it is believed that there has been no detailed explanation of the touch voltage concerpt yet published. The book also introduces the reader to the impedance characterists of fuses and miniature circuit breakers (developed some years ago by the author) which are a very simple graphical approach to show the interrelationship between the operating characteristics of the fuses and m.c.b.s and the international touch voltage duration curve. Whilst the book is based on British practice and devices it will be of interest to other countries which are adopting the same international wiring rules on which the IEE Wiring Regulations have been based.