-15-
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 Grounding
rods. Meanwhile, oxidation layer on measured Grounding body must be
removed when measuring.
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
