HT instruments MACROTEST 5035 - Manual (Page 79)

MACROTEST 5035
EN - 78
Curve 1: as
ρ decreases only in
depth, it’s possible to use only a
rod in depth.
Curve 2: as
ρ decreases only
until the depth A, it’s not useful to
increase the depth of the rod
beyond A.
Curve 3: even at a superior
depth,
ρ does not decrease,
therefore a ring rod must be
used.
APPROXIMATE EVALUATION OF INTENTIONAL RODS CONTRIBUTION (64-12 2.4.1)
The resistance of a rod Rd can be calculated with the following formulas (
ρ = medium
resistivity of the ground).
a) resistance of a vertical rod
Rd =
ρ / L
L= length of the element touching the ground
b) resistance of an horizontal rod
Rd = 2
ρ / L
L= length of the element touching the ground
c) resistance of linked elements
The resistance of a complex system with more elements in parallel is always higher
than the resistance which could result from a simple calculation of elements in
parallel, especially if those elements are close and therefore interactive. For this
reason, in case of a linked system the following formula is quicker and more effective
than the calculation of the single horizontal and vertical elements:
Rd =
ρ / 4r
r= radius of the circle which circumscribes the link
Distance between the rods a(m)
Sp
e
c
ifi
c
re
sis
tiv
ity
o
f t
he
g
ro
un
d
E
(
m
)
ρ
Ω
3
2
1