Page 185 - Electrical Safety of Low Voltage Systems
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168 Chapter Nine
FIGURE 9.12 Fault-loop impedance Z including the neutral conductor.
S
the ground resistance, in the determination of the prospective touch
voltage V ST .
With reference to Fig. 6.2, in TT systems the prospective touch
voltage, taking into account R F , becomes
1
TT
V = V ph × (9.27)
ST
1 + [R N /(R G + R F )]
200
160
V ST 120 TT (V)
IT (mV)
80
40
0
0 5 10 15 20 25 30 35 40 45 50
R
G
FIGURE 9.13 V ST in TT and IT systems as a function of R G .
