Page 15 - Electrical Safety of Low Voltage Systems

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Dr. Massimo A. G. Mitolo

Preface

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