17
®
®
18
6. 3-Wires Earth Resistance Measurement :
3-wires measurement :
As shown below, short-circuit ES and S
interface, which is 3-wires measurement. The operation of meter is
the same with 4-wires measurement. The 3-wires method can’t
eliminate influence of line resistance, also can’t eliminate influence
of contact resistance between meter and testing wires, testing
wires and auxiliary earthing rods. Meanwhile, oxidation layer on
measured earthing body must be removed when measuring.
H.i65
07 i
EARTH-
TESTER
0
10
20
30
40
C
MEM
AL
CLR
SET
START
FUNCTION
OFF
EARTH
R
EARTH
EARTH
VOLTAGE
OFF
C
(H)
E
P
ES
(S)
AC 600V Max
Rs232
ES-E
P
(S)
Yellow
.
Measured earthing body
Red
C
(H)
Black
d
>5d
ES-E
>5d
7. 2-Wires Simple Measurement :
When select commercial use power supply system
earth as auxiliary earth electrode, it must use detector
to confirm that is it the earth ground electrode for
commercial use power supply system, otherwise the
breaker may start, it is dangerous.
Using 2-wires simple method for measuring earth
resistance, try to choose a earthing body which has a
small re value as auxiliary earthing electrode, so that
the reading value is more close to the real value. The
metal pipes, metal fire hydrant have priority in
choosing auxiliary earthing electrodes.
2-wires method :
This method is a simple method for
measurement that does not use auxiliary earthing rod, taking the
earth electrode with the minimal existing earth ground resistance
value as auxiliary earth electrode, and connecting by two simple
testing wires (in which
C
(H)
-
P
(S)
,
E-ES
interfaces are in short circuit).
It can make use of metal pipes, fire hydrants and other metal buried
objects, common earthing of commercial electric power system or
lightning protection earth ground electrode and others to replace
auxiliary earthing rods
C
(H)
,
P
(S)
, and pay attention to remove oxide
layer on the connection point of the selected metal auxiliary earthing
object when making measurement.
Wire connection is as following figure, and refer to 4-wires
measurement for other operations.
000
EARTH-
TESTER
0
10
20
30
40
C
MEM
AL
CLR
SET
START
FUNCTION
OFF
EARTH
R
EARTH
EARTH
VOLTAGE
OFF
C
(H)
E
P
ES
(S)
AC 600V Max
Rs232
E-ES
C
(H)
-
P
(S)
Red
Black
.
C
(H)
-
P
(S)
E-ES
RX
Measured earthing body
Take metal pipe or building lighting proof earth as the auxiliary earth electrodes
000
EARTH-
TESTER
0
10
20
30
40
C
MEM
AL
CLR
SET
START
FUNCTION
OFF
EARTH
R
EARTH
EARTH
VOLTAGE
OFF
C
(H)
E
P
ES
(S)
AC 600V Max
Rs232
E-ES
C
(H)
-
P
(S)
Red
Black
.
Secondary
circuit
Transformer
First
circuit
Commercial earthing body
Measured
earthing body
C
(H)
-
P
(S)
E-ES
RX
re
