Essential low-voltage grounding and bonding methodologies
Minimize voltage exposures and mitigate shock risk using expert, life-safety measures and design solutions from an engineering professional. Through comprehensive explanations, mathematical analysis, and circuit diagrams, Electrical Safety of Low-Voltage Systems provides the latest bonding and grounding strategies. Identify and quantify hazards, prevent faults and overvoltages, properly size conductors, and develop sound earthing systems. This comprehensive guide includes details on complying with current codes, working in high-risk locations, and testing system components.
Electrical Safety of Low-Voltage Systems offers electricians and electrical engineers a comprehensive safety regimen, based on the fundamental characteristics of low-voltage electrical systems. Fully explaining the grounding and bonding of low-voltage systems as they relate to Article 250 of the National Electrical Code, this essential safety tool provides an analytical approach to accident control to replace the haphazard rules of thumb currently in use.
- Calculate IEC and IEEE permissible body currents and touch voltages.
- Employ residual current devices and ground-fault circuit interrupters.
- Design reliable TT, TN, PME and IT grounding systems.
- Determine optimal makeup and size of protective conductors subject to earth faults.
- Handle ground faults, overvoltages, and excessive stress voltages.
- Mitigate fire risks due to static charges and residual voltages.
- Accurately test fault-loop impedances, soil resistivity, and earth resistance.
- Build circuits using nondangerous currents and extra-low voltages.
From the Preface
- Readers will find relevant IEEE and IEC standards, low-voltage fault loops in different types of grounding systems, and many other topics designed to minimize accident rates and ensure low-voltage system safety.
Electrical safety may be perceived only as a list of prudent actions to or not to undertake in the presence of energized objects, constituting the defense against direct contact with live parts. However, the safety of persons also depends on their exposure to indirect contact, that is, contact with parts normally not in tension, but likely to become energized due to faults. Thus, the attitude toward live parts is not the only key in preventing accidents.
This book, prompted by this concept, is an attempt, from the academic point of view, to bridge the existing gap between life-safety electrical issues in low-voltage systems (i.e., not exceeding 1 kV) and their proper comprehension and design solution, in light of applicable IEC and IEEE standards. We assume, in fact, that we can analytically quantify the hazards caused by indirect contact, thereby promoting a proper design for the electrical system and minimizing the related risk.
The book, based on my 20-year-long experience as a professor and as a professional engineer, provides an explanation of the fault-loops in different types of grounding systems (i.e., TT, TN, and IT) and of the faults occurring on both sides of the supply (i.e., the primary and secondary of substation transformers). The crucial role played by the state of the neutral is deeply examined, thereby allowing the comprehension of the reasons behind the methodologies of protection against electric shock, which are required by current standards and codes.
The book's audience consists of electrical engineering students who need to know the principles of electrical safety as well as professional engineers who are involved in the bonding and grounding of power systems. Background requirements include a knowledge of a.c. electric circuits, algebra, complex numbers, and basic calculus.
Each chapter is arranged in a format that is aimed at promoting the reader's understanding by providing many figures and equivalent circuits to clarify, both visually and analytically, the concepts discussed, such as the determination of fault currents and touch voltages. Several chapters also have a section of frequently asked questions at the end, with relative answers based on the actual inputs of students and professionals.
The first three chapters explain the fundamental principles of electrical safety, providing the basic concepts of protection against direct contact and indirect contact as well as the mathematical interpretation of safety and risk of standard protective measures.
Chapter 4 discusses the role of the earth as an available return path to the supply source of fault currents, thus analyzing the theory of ground potentials and ground resistances of electrodes.
Chapter 5 describes the effects of currents passing through the human body as interfering with the body's own electricity as well as causing thermal stress to its tissues. This chapter also explains the concepts of permissible body current and permissible touch voltage as used in IEC and IEEE technical standards.
Chapters 6 through 9 explain the protection against indirect contact in different grounding systems, such as TT, TN, PME, and IT, and detail voltage exposures and protective issues in each of them.
Chapter 10 is devoted to the extra-low-voltage systems and describes the safety issues arising under fault conditions.
Chapter 11 describes the fundamental components of earthing arrangements, explains their functions, and provides minimum acceptable sizes following applicable technical standards. An analytical method to determine the minimum cross-sectional area of protective conductors, assuming an adiabatic thermal process during faults, is also offered.
Chapter 12 discusses the effects of overvoltages, in particular the temporary ones, within different types of grounding systems as well as the stress voltages that may arise under fault conditions, possibly causing the breakdown of the basic insulation of equipment.
Chapter 13 examines the safety issues caused by static electricity and residual voltages, eventually present on de-energized items. The energy stored in charged objects is calculated and the mitigation strategies to reduce it are described.
Chapter 14 discusses the methodologies of measurement employed during the design phase (e.g., soil resistivity test) and after the installation of the electrical system as well as prior to putting it into service (e.g., earth resistance test).
The final chapter analyzes the safety requirements against indirect contact employed in special installations or locations, where environmental conditions may increase the risk of indirect contact (i.e., marinas, train stations, swimming pools, surgery rooms, etc.).
The three appendices discuss the basic concepts of sinusoids and phasors, the fundamental conventions, and the network theorems that are extensively used throughout the text. Their purpose is to give the reader a basic theoretical support for the comprehension of the technical methodologies profusely applied in the book.
Writing this book has been a formidable journey through the core of the bonding and grounding of electrical systems, and I do hope that it will shed some light on some of the concepts commonly accepted by the community of the practitioner engineers, but perhaps not completely understood.
About the Author
Massimo A G Mitolo, educated in Italy, received his doctoral degree in electrical engineering from the University of Naples "Federico II." His field of research is the analysis and grounding of power systems. Dr. Mitolo has been a registered Professional Engineer in Italy since 1991 and is currently working as an Associate Electrical Engineer at Chu & Gassman Consulting Engineers in New York. He is an IEEE Senior Member and is very active within the IEEE IAS Industrial & Commercial Power Systems Department, where he is currently the Vice Chair of the Power Systems Engineering Main Technical Committee, the Chair of the Papers Review Subcommittee, the Chair of the Power Systems Analysis Subcommittee, and the Vice Chair of the Power Systems Grounding Subcommittee. Dr. Mitolo is also an Associate Editor of the IEEE Manuscript Central.
Table of Contents
Preface . Chapter 1: Basic Definitions and Nomenclature. Chapter 2: Fundamentals of Electrical Safety. Chapter 3: Mathematical Principles of Electrical Safety. Chapter 4: The Earth. Chapter 5: Effects of Electric Currents Passing through the Human Body, and Safety Requirements. Chapter 6: TT Grounding System. Chapter 7: TN Grounding System. Chapter 8: Protective Multiple Earthing (TN-C-S Grounding System). Chapter 9: IT Grounding System. Chapter 10: Extra-Low-Voltage Systems. Chapter 11: Earth Electrodes, Protective Conductors, and Equipotential Bonding Conductors. Chapter 12: Safety against Overvoltages. Chapter 13: Safety against Static Electricity. Chapter 14: Testing the Electrical Safety. Chapter 15: Applications of Electrical Safety in Special Locations and Installations. Appendix A: Sinusoids and Phasors. Appendix B: Fundamental Conventions and Electric Circuit Theorems. Appendix C: Fundamental Units, Symbols, and Correct Spellings. Index.