Page 282 - Electrical Safety of Low Voltage Systems

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

Electrical currents, physiological responses to (Cont.):
permissible body current, 81, 81f
tetanization, 77–78, 78f
thermal shock, 79–80, 80f
threshold of reaction, 77
ventricular fibrillation, 78–79, 79f
Electrical safety
applications of, 243–262
basic protection, 9
definition of, 9
direct contact protection
barriers, 11–14
IP2X and, 13, 13f
IPXXB and, 13
enclosures, 11–14
IP2X and, 13, 13f
IPXXB and, 13
mechanical impacts and, 14, 14t
live parts insulation, 10–11, 11f
obstacles, protection by, 14–15, 15f
residual current devices, 15–18
Earth resistance measurement, 226–228, 227f, 228f
industrial facilities and, 228–230, 229f
in TT systems, 230–232, 230f
electrical separation, 245, 246f
in external lighting installations, 253–254, 254f
fall of potential method, 226
fault-loop impedance, TN systems, 232–234, 232f, 233f, 234f
fault protection, 9
fundamental measurements, IT systems, 238–239, 239f
fundamentals of, 9–26
for high protective conductor current equipment, 246–248, 246f, 247f
indirect contact protection
automatic disconnection
Class II equipment, 20–21, 21f
disconnection times, 19
Earth-free local equipotential bonding, 22–23, 23f
electrical separation, 23–25, 24f, 25f
nonconducting locations, 21–22, 22f
nuisance trippings and, 20
reinforced insulation, 21
insulation resistance test, 240–242, 241f, 241t, 242f
in marinas, 244–246, 244f, 246f
mathematical principles of, 29–42
acceptable residual risk, 33–36, 34f, 35f, 36f
basic insulation, 36–37, 37f
Class 0 equipment, 37–38
Class I equipment, 38–39, 38f
Class II equipment, 39–41, 40f
definition of, 29–32, 30f, 31f
direct contact, risk of, 32–33
electrical separation, 41–42, 41f
indirect contact, risk of, 32–33
in medical locations
electrical separation, 257–259, 258f, 259f
leakage currents, 255–256, 256f
local equipotential earthing connection, 256–257, 257f
microshock, 254–255
patient leakage current, 256, 256f