12 Clamp-On Ground Resistance Tester | MODEL P81001 Clamp-On Ground Resistance Tester | MODEL P81001 13
Important notes for measuring earth resistance
There can be a considerable dierence when comparing
testing values measured by a meter versus a traditional
voltage and current method.
Whether unclasped (grounding body to measure is separated
from grounding system) has been done when measuring
resistance by traditional voltage and current method. If not,
the earth resistance that is measured refers to the parallel
connection value of earth resistance of all grounding bodies.
It is not benecial to measure parallel connection value of
earth resistance of all grounding bodies. Measuring earth
resistance is making a comparison between the earth
resistance and a permitted value regulated by relevant
standards to decide whether earth resistance is qualied.
For example, earth resistance per radix tower refers to
the resistance measured when a grounding body cuts o
electric connection with a ground wire. If the grounding body
doesn’t cut o electric connection with a ground wire, earth
resistance measured refers to the parallel connection value of
earth resistance of multi-radix towers.
ON-SITE APPLICATION
Application in power systems
(1) Measurement for earth resistance of power transmission
line tower
The grounding of power transmission line tower forms
a multi-point grounding system. To measure of earth
resistance, clamp grounding rods with the meter.
(2) Measurement for earth resistance of neutral point of
transformer
There are two cases in neutral point grounding of
transformers. If multiple grounding is applied, it is a multi-
point grounding system. All other cases are single-point
grounding.
For measurement, if the meter shows L0,01 Q it may mean
that the same pole and tower or transformer has more than
two grounding rods linked together underground. Unveil
other grounding rods and keep one rod remaining.
(3) Application in substation of power plant
The meter can check the status of touch and link in circuits.
With assistance from a line, it can measure link status
between equipment’s in-station and earth grid. Earth
resistance is measured according to single-point grounding.
Application in telecommunication systems
(1) Measurement of earth resistance of machinery room in
telecom building
The machinery rooms for telecommunication systems are
often placed on a high oor of the building, which can make
it diicult to measure. It can be measured with the meter by
linking a re hydrant and grounding electrode to measure
with a test line (re hydrant is equipped in the machinery
room). Measure the test line with the meter.
Reading of resistance = earth resistance of machinery
room + resistance of testing line + earth resistance of
re hydrant
(2) Measurement of earth resistance of machinery room and
transmitter tower
Grounding of machinery room and transmitter tower usually
forms a two-point grounding system as shown in Figure 21.
• If the measured value of the meter is lower than the
permitted value of earth resistance, earth resistance of the
machinery room and transmitter tower is qualied.
• If the measured value of the meter is higher than the
permitted value of earth resistance, apply measurement
of single-point grounding.
Figure 21
