Page 290 - Electrical Safety of Low Voltage Systems

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Electrical Safety of Low-Voltage Systems Dr. Massimo A. G. Mitolo

TN grounding system (Cont.):
touch voltage in, 13f, 135–139, 135f, 137t, 138f, 234–235, 235f
transferred potentials, 128f, 129–130, 129f
transformer earthing and, 118–120, 119f
voltage exposure in, 120–122, 120f, 121f
TN-C grounding system, 5, 5f
PEN conductor and, 132–134, 133f, 134f
TN-C-S grounding system, 5, 6f
definition of, 143
fault-loop impedance in, 146
fault loops in, 145
faults phase-to-PEN, 149–150, 149f, 150f
ground fault
low-voltage utility, 146–148, 147f
medium voltage utility, 147f, 148–149, 148f
PEN conductor and, 146, 150–151, 151f
stray currents, 151–152, 152f
stray voltages, 151–152, 152f, 153f
TN-S grounding system, 5, 6f
indirect contact protection
overcurrent devices, 123–126, 123f, 124t
RCDs and, 127–128, 128f
voltage exposure in, 120–121, 120f
Touch voltage, 59–62, 60f, 61f, 62f
in TN grounding system, 13f, 135–139, 135f, 137t, 138f
Touch voltage measurement, TN systems, 234–235, 235f
Touch voltage vs. step voltage, 140–141
Train stations, electrical safety in, 248–250, 249f, 250f
Transverse voltage, 201
TT grounding system, 5, 7f, 19
definition of, 95
earth resistance measurement in, 230–232, 230f
electrical interference in, 106–108, 107f
fault resistance in, 167–169, 168f, 169f
independently grounded ECPs in, 104–106, 105f, 106f
indirect contact protection
overcurrent devices, 99–102, 100f, 100t, 101f
residual current devices, 102–103, 103f
leaking-to-ground ECPs in, 106, 106f, 107f
main equipotential bonding, 110f
incoming pipes and, 112–113, 112f, 113f
plasticpipes and, 111–112, 111f, 112f
metal parts and, 113–115, 114f
neutral conductor in, 108–109, 108f, 109f
neutral-to-ground fault in, 103–104, 103f, 104f
resistance of the utility neutral, 109–110
supplementary equipotential bonding, 113, 114f
temporary overvoltage in, 204–206, 205f, 205t, 206f
usage of, 95
voltage exposure in, 96–99, 96f, 98f, 99f

U
Upper explosive limit (UEL), 214

V