IET Wiring Regulations: Design and Verification of Electrical Installations

Brian Scaddan

• Publisher: Routledge
• Year: 2018
• Print ISBN: 9781138606012
• eBook ISBN: 9780429883118
• Edition: 9
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

This popular guide provides an understanding of basic design criteria and calculations, along with current inspection and testing requirements and explains how to meet the requirements of the IET Wiring Regulations. The book explains in clear language those parts of the regulations that most need simplifying. There are common misconceptions regarding bonding, voltages, disconnection times and sizes of earthing conductors. This book clarifies the requirements and outlines the correct procedures to follow.

This provides an affordable reference for all electrical contractors, technicians and other workers involved in designing and testing electrical installations. The content covers the requirements for both City & Guilds and EAL courses, and contains sample exam questions and answers. It also makes an ideal revision guide.

• Fully up to date with the 18th Edition of IET Wiring Regulations.
• Simplifies the advice found in the Wiring Regulations, explaining what they mean in actual working practice for design and testing.
• Expert advice from an engineering training consultant, supported with colour diagrams, examples and key data.

CHAPTER 1
Design

Important terms/topics covered in this chapter:

▪ Assessment of general characteristics

▪ Basic protection

▪ Fault protection

▪ IP and IK codes

▪ The earth fault loop path

▪ Supplementary equipotential bonding

▪ Overcurrent

▪ Let-through-energy

▪ Selectivity

▪ Undervoltage

▪ Overvoltage

▪ Isolation and switching

▪ Design current

▪ Diversity

▪ Nominal rating of protection

▪ Rating factors

▪ Current carrying capacity of conductors

▪ Voltage drop

▪ Shock risk and thermal constraints.

At the end of this chapter the reader should,

▪ understand the need to assess all relevant characteristics of the installation,

▪ have reinforced their knowledge of Basic and Fault protection and how such protection is achieved,

▪ understand how ‘let-through-energy’ can cause damage to cables,

▪ be able to distinguish between ‘Isolation’ and ‘Switching’,

▪ be able to determine suitable wiring systems for particular applications,

▪ be able to carry out basic design calculations to determine cable sizes,

▪ recognize various types of installation diagram.

Any design to the 18th Edition of the IET Wiring Regulations BS 7671 must be primarily concerned with the safety of persons, property and livestock. All other considerations such as operation, maintenance, aesthetics, etc., while forming an essential part of the design, should never compromise the safety of the installation.

The selection of appropriate systems and associated equipment and accessories is an integral part of the design procedure, and as such cannot be addressed in isolation. For example, the choice of a particular type of protective device may have a considerable effect on the calculation of cable size or shock risk, or the integrity of conductor insulation under fault conditions.

Perhaps the most difficult installations to design are those involving additions and/or alterations to existing systems, especially where no original details are available, and those where there is a change of usage or a refurbishment of a premises, together with a requirement to utilize as much of the existing wiring system as possible.

So, let us investigate those parts of the Wiring Regulations that need to be considered in the early stages of the design procedure.

ASSESSMENT OF GENERAL CHARACTERISTICS

Regardless of whether the installation is a whole one, an addition, or an alteration, there will always be certain design criteria to be considered before calculations are carried out. Part 3 of the 18th Edition, Assessment of General Characteristics’, indicates six main headings under which these considerations should be addressed. These are:

1. Purpose, supplies and structure

2. External influences

3. Compatibility

4. Maintainability

5. Recognized safety services

6. Assessment of continuity of service.

Let us look at these headings in a little more detail.

Purpose, supplies and structure

▪ For a new design, will the installation be suitable for its intended purpose?

▪ For a change of usage, is the installation being used for its intended purpose?

▪ If not, can it be used safely and effectively for any other purpose?

▪ Has the maximum demand been evaluated?

▪ Can diversity be taken into account?

▪ Are the supply and earthing characteristics suitable?

▪ Are the methods for protection for safety appropriate?

▪ If standby or safety supplies are used, are they reliable?

▪ Are the installation circuits arranged to avoid danger and facilitate safe operation?

External influences

Appendix 5 of the IET Regulations classifies external influences which may affect an installation. This classification is divided into three sections, the environment (A), how that environment is utilized (B) and construction of buildings (C). The nature of any influence within each section is also represented by a number. Table 1.1 gives examples of the classification.

With external influences included on drawings and in ...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Table of Contents
• Preface
• Chapter 1 Design
• Chapter 2 Inspection and Testing
• Chapter 3 Special Locations IET Regulations Part 7
• Appendix 1 BS 7671 Appendices
• Appendix 2 Sample Questions
• Appendix 3 Suggested Solutions to Sample Questions
• Appendix 4 MIMS and SWA CPC sizes and corrected Zs values
• Index