In the years since the book was written there has been a great change in protection. Not in the principles, but in the relays which are now applied.
The development of electronic and microprocessor-based relays has been such that these are now a less expensive option than the electromechanical relay.
The problems which existed in the early days have been completely eliminated and the lower burden and greater accuracy of these types of relay means that they are now the usual type of relay to be selected.
This does not mean that electromechanical relays have disappeared. Far from it. They still feature in the vast majority of installed equipment and so are still discussed at length in this new edition.
It would not do for me to ignore the help I have been given in preparing this new edition.
Once again it has come from many sources, all of whom I thank, and once again I must record my thanks to Mr K. Preston for his technical advice, back-up and proof-reading