41
Analysis:
The values read must never exceed a few ohms, or a few tens of ohms.
Higher values indicate the presence of a fault in the earth loop tested. Comparison with
nearby loop values will allow you to locate the common faulty link. This must be
subjected to further investigation: measurement of the continuity of the cable
connected to the earth, measurement of the resistance of local earths isolated from
the rest of the network, ...
Note
: With model C.A 6415 it is also possible to record each measurement during a
series of tests, and to trigger an alarm if the fixed threshold value put in by the operator
is exceeded.
TESTING THE EQUIPOTENTIAL OF GROUNDING SYSTEMS
In establishments equipped with sensitive
electronics, protection is reinforced by a mesh of
grounding conductors, connected to multiple
earths. An extended earth is thus obtained which
makes it possible to produce a grounding system
without equipotential defects.
To guarantee a perfect flow of loads to the earth,
the resistive values of the loops formed by these
means must be low, but also, practically identical.
A loop with a value different from the rest of the
grounding system would be likely to create a
difference in potential, for example, in case of
lightning. This excess voltage is likely to cause serious damage to sensitive equipment.
Your clamp allows you to easily check your earth meshes, and therefore to guarantee
the equipotential:
- Measure the resistive value of each loop.
- Compare all the measurements with one another.
Analysis:
See preceding analysis and note.
General remark on loop measurement
Note that for the measurements discussed up to this point, we mention "loop
resistance". Given the principle of the measurement clamp and the measurement
signal generated (2403 Hz), it would be more correct to speak of the measurement
of "loop impedance".
In fact, in practice the reactive values in series in the loop (in line choke) can be ignored
in relation to the loop resistance (Z
≈
R).
