Page 12 - Electrical Safety of Low Voltage Systems

ix
Dr. Massimo A. G. Mitolo

9 IT Grounding System 155
9.1 Introduction 155

9.1.1 Insulation Monitoring Device 158
9.1.2 Equipotential Bonding 159

9.2 Overvoltages Due to Faults in IT Systems 159
9.3 Resonant Faults in IT Systems 161

9.4 Protection Against Direct and Indirect Contact by Using RCDs in IT Systems 163
9.5 Protection Against Indirect Contact in the Event of a Second Fault to Ground 164

9.5.1 ECPs Earthed Individually or in Groups 164
9.5.2 ECPs Earthed Collectively to a Single Grounding System 165

9.6 Role of the Fault Resistance in TT and IT Systems 167
FAQ 170

Endnote 170
10 Extra-Low-Voltage Systems 171

10.1 Introduction 171
10.2 Separated Extra-Low-Voltage (SELV) Systems 172
10.2.1 Protection Against Indirect Contact 172

10.2.2 Protection Against Direct Contact 174

10.3 Protective Extra-Low-Voltage (PELV) Systems 175
10.3.1 Application of PELV Systems to Control Circuits 176
10.4 Functional Extra-Low-Voltage (FELV) Systems 178

Endnotes 180

11 Earth Electrodes, Protective Conductors, and Equipotential Bonding Conductors 181
11.1 Introduction 181
11.2 Earth Electrodes 182

11.2.1 Corrosion Phenomena 183

11.3 Protective Conductors 185
11.3.1 Analytical Calculation of the Minimum Cross-Sectional Area of PEs 186
11.3.2 Metallic Layers of Cables as Protective Conductor 192

11.4 Equipotential Bonding Conductors 193

11.4.1 Where Should We Use Equipotential Bonding Conductors? 195
11.5 Earthing Conductors and Main Earthing Terminal 196