Preface to the Fourth Edition
There are many books on electrical installation practice where the focus is on calculations and regulations. Electrical Installation Designs has been written from a different viewpoint. Typical projects are examined to produce designs that will fit current standards. Most electrical contractors have an understanding of requirements related to their own regular everyday activities, where work is carried out using rule-of-thumb methods.
Repetitive designs are used. Many installers claim that they are not designers and show concern that they are now required to certify the adequacy of an installation design. In practice, problems only arise when an unusual project is undertaken or there is a change in regulations. There is no harm in using a standardised design, rather in the way that an experienced cook uses a published recipe for a cake. Electrical Installation Designs is a book of recipes.
The installer may select a design that corresponds as near as possible to the contract in hand and take up such technical and regulatory advice as is required. This will reduce the need for lengthy calculations and detailed study of BS 7671, Requirements for Electrical Installations (IET Wiring Regulations). Most basic electrical installations may be completed by a competent person, with appropriate guidance to avoid serious problems and hazards. Project chapters illustrate methods that could be used for particular types of installation ranging from a house to an industrial workshop. The ideas are by no means exclusive.
Alternative solutions are always possible. In many instances carrying out detailed calculations and utilising different circuitry will be more profitable. By their very nature, simplified examples of fictional projects can only produce generalised results. The book contains special chapters on earthing, isolation and switching and overcurrent protection, which give a down to earth interpretation of the regulations. Electrical installation students and non-electrical associates in the construction industry will appreciate the user-friendly approach. Nevertheless, this is not a do-it-yourself book for the untrained person.
Warnings are therefore given where more specialised study is necessary. For example, readers are advised not to embark on installations in hazardous areas (such as petrol filling stations) without further training. Apart from moral implications and contractual risks, statutory requirements are such that incompetent work may carry criminal penalties. Although the emphasis is on tried and tested methods, some new techniques are introduced. The most significant is the option for tree circuitry as an alternative to the ring final circuit. This is the first book to give designers the opportunity to compare the advantages of the tree system for both domestic and commercial installations. In recent years, consumer requirements have changed.
It is essential that the industry keeps an open mind on changes in traditional wiring practice. Introduced in this fourth edition are new chapters on Residual Current Devices and, for those readers who require a basic understanding of circuit design, a chapter explaining the process for carrying out simple cable design calculations. This book takes account of all amendments published since the 17th edition of the Wiring Regulations was first issued in 2008, including those introduced by Amendment 1, which was first issued in 2011 and which came into effect on 1 January 2012.