Page 71 - Electrical Safety of Low Voltage Systems
P. 71
54 Chapter Four
FIGURE 4.10 Earth
resistance’s
equivalent circuit.
their electric potentials are not significantly affected by their recipro-
cal influence (Fig. 4.11).
Equation (4.9) can be generalized to the case of two dissimilar
electrodes, buried at different depths and leaking different currents I 1
and I 2 , by writing the following system of equations [Eq. (4.13)]:
⎧
V GTOT = R 11 I 1 + R 12 I 2
⎪
⎨
V GTOT = R 12 I 1 + R 22 I 2
⎪
⎩
I GTOT = I 1 + I 2 (4.13)
R 11 (R 22 ) is the earth resistance of the first (second) electrode, ob-
tained by disconnecting the second (first) one; R 12 (R 21 ) is the ratio of
the ground potential attained by the first (second) electrode, not con-
nected to the grounding system, to the current flowing through the
second (first) one. R 12 and R 21 are referred to as mutual resistances.
FIGURE 4.11 Potentials due to two independent electrodes.
