80
Ground Resistance Tester Model 6471
Reference earth
The area of earth (especially at the surface) which is outside the range of influ-
ence of the earth electrode or earthing system.
Resistivity of the earth
(
ρ
)
Resistivity is defined as the resistance from wall to opposite wall of a cubic
meter of soil. It is measured in ohm-meters (
Ω
m).
Selective earth resistance
The parallel partial resistance of an earth connection or earthing system. It
is measured by selective measurements of current in the corresponding re
-
sistance branch. A selective earth resistance is always greater than the total
earth resistance (parallel connection).
Step voltage
The potential difference bridged by a person who takes a step of 1m (approx.
3 ft), with the resulting current flowing through the body from one foot to the
other (cf. touch voltage).
Supplementary electrode
An additional earth electrode (earth stake, earth rod).
Touch voltage
The potential difference which a person is able to bridge with his or her body,
the resulting current being limited by the body and the local earth resistance
(cf. step voltage).
The general term earth measurement can refer to measurements of individual
earth electrodes, earth connections or entire earthing systems, depending on the
object of interest.
Glossary
This glossary lists the terms and abbreviations used on the instrument and the
digital display.
3-Poles
: measurement of earth resistance with 2 auxiliary stakes (3-
Pole method)
4-Poles
: 4-Pole measurement of low earth resistance with 2 auxiliary
stakes (4-Pole method)
C
1
: earth coupling coefficient R
A
with earth R
b
(C
1
= R
C
/ R
1
)
C
2
: earth coupling coefficient R
b
with earth R
A
(C
2
= R
C
/ R
2
)
d, A
: distances to be programmed to calculate resistivity according
to the measuring method used
m
Ω
: measurement of low resistance /continuity
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