Application Note

To prove this, you need to perform a few
additional tests on individual resistances.
First, perform the 3-pole Fall-of-Potential
test on each leg off the MGB and record each
measurement. Using Ohm’s Law again, these
measurements should be equal to the resistance
of the entire system. From the calculations you
will see that you are from 20 % to 30 % off the
total R
E
value.
Finally, measure the resistances of the
various legs of the MGB using the Selective
Stakeless method. It works like the Stakeless
method, but it differs in the way we use the
two separate clamps. We place the inducing
voltage clamp around the cable going to the
MGB, and since the MGB is connected to the
incoming power, which is parallel to the earth
system, we have achieved that requirement.
Take the sensing clamp and place it around the
ground cable leading out to the ground field.
When we measure the resistance, this is the
actual resistance of the ground field, plus the
parallel path of the MGB. And because it should
be very low ohmically, it should have no real
effect on the measured reading. This process can
be repeated for the other legs of the ground bar
i.e. water pipe and structural steel.
To measure the MGB via the Stakeless Selec-
tive method, place the inducing voltage clamp
around the line to the water pipe (since the
copper water pipe should have very low resis-
tance) and your reading will be the resistance
for only the MGN.
H/C2
OFF
3
POLE
4
POLE
4
POLE
2
POLE
S/P2
ES/P1
E/C1
START
TEST
DISPLAY
MENU
CHANGE
ITEM
SELECT
1625-2
ADVANCED EARTH / GROUND TESTER GEO
E S H
AC
Rresistance
300kΩEarth/Ground Resistance 300kΩ
DC
Resistance 3kΩ
RA
R
—
R
~
2
POLE
3
POLE
3
POLE
4
POLE
MGN
MGB
H/C2
OFF
3
POLE
4
POLE
4
POLE
2
POLE
S/P2
ES/P1
E/C1
START
TEST
DISPLAY
MENU
CHANGE
ITEM
SELECT
1625-2
ADVANCED EARTH / GROUND TESTER GEO
E S H
AC
Rresistance
300kΩEarth/Ground Resistance 300kΩ
DC
Resistance 3kΩ
RA
R
—
R
~
2
POLE
3
POLE
3
POLE
4
POLE
EI-162X
SENSING CURRENT
TRANSFORMER
MGN
MGB
EI-162AC
INDUCING CURRENT
TRANSFORMER
EI-162X
SENSING CURRENT
TRANSFORMER
Figure 1: Stakeless testing
of a central office.
Figure 2: Perform
the 3-Pole
Fall-of-Potential
test of the entire
ground system.
13
H/C2
OFF
3
POLE
4
POLE
4
POLE
2
POLE
S/P2
ES/P1
E/C1
START
TEST
DISPLAY
MENU
CHANGE
ITEM
SELECT
1625-2
ADVANCED EARTH / GROUND TESTER GEO
E S H
AC
Rresistance
300kΩEarth/Ground Resistance 300kΩ
DC
Resistance 3kΩ
RA
R
—
R
~
2
POLE
3
POLE
3
POLE
4
POLE
MGN
MGB
EI-162AC
INDUCING CURRENT
TRANSFORMER
EI-16
2AC
I
NDUC
I
N
G
CURRENT
TRANS
FO
RMER
EI-162AC
IN
DU
CING CURR
ENT
TRANSFORMER
EI-162AC
INDUCING CURRENT
TR
ANSFORMER
Figure 3:
Measure the
individual
resistances of
the ground
system using the
Selective test.