Page 10 - Electrical Safety of Low Voltage Systems

vii
Dr. Massimo A. G. Mitolo

5.3 Influence of Frequency on the Effects of Current 76
5.4 Physiological Response to Electrical Currents 77

5.4.1 Tetanization 77
5.4.2 Ventricular Fibrillation 78

5.4.3 Thermal Shock 79
5.5 Permissible Body Current and Person’s Body Mass 81

5.6 Permissible Body Current Independent of Human Size 82
5.6.1 Heart Current Factor 83

5.7 Human Body Impedance 84
5.8 Current Paths 86

87
5.9 Permissible Prospective Touch Voltage
5.10 Effects of Direct Currents 90

FAQs 93
Endnotes 93

6 TT Grounding System 95
6.1 Introduction 95

6.2 Voltage Exposure in TT Systems 96
6.3 Protection Against Indirect Contact in TT Systems by Using Overcurrent 99
Devices
6.4 Protection Against Indirect Contact by Using Residual Current Devices 102

6.5 Neutral-to-Ground Fault in TT Systems 103
6.6 Independently Grounded ECPs in TT Systems 104

6.7 Leaking-to-Ground ECPs in Three-Phase TT Systems 106
6.8 Electrical Interferences in TT Systems 106

6.9 The Neutral Conductor in TT Systems 108
6.9.1 Resistance of the Utility Neutral in TT Systems 109

6.10 Main Equipotential Bonding 110
6.10.1 Should We Bond Incoming Pipes Made of Plastic? 111

6.10.2 Should We Bond Incoming Pipes Electrically Separated by a Dielectric 112
Joint?

6.11 Supplementary Equipotential Bonding 113

6.12 Potential Differences Among Metal Parts in Fault Conditions in TT Systems 113
FAQs 115
Endnotes 115