Chauvin Arnoux C.A 6115N, User Manual

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TT system: This is the ideal diagram for quick and easy measurement of the ground earth: no earth
connection to disconnect and just one extra earth testing rod to plant!
IT system: It is also easy on a TT system but BEWARE:
The supply transformer must be connected to the earth by an impedance. It must not
be totally isolated from this, otherwise the measurement current cannot flow.
The ground earth R
A
” and the transformer earth must also be distinct, otherwise the
measurement current will not go through the earth.
The network must not be in a state of single fault that has not been rectified, since the
measurement creates a second fault at the earth! Check the indication given on your
CPI.
TN system: You can easily measure each earth in parallel with the PEN using the current clamp
(selective measurement).
Without using the clamp, the measurement gives the value of the entire earthing system
connected to the network, which is of little use or significance. In fact, on a TN system,
the fault currents do not flow, or flow very little, in what is a purely “functional” earth.
The fault currents loop back, mainly by the neutral, and, except in the presence of
RCD’s, the low impedance of the fault loop makes these currents very high. They are
then cut by fuses or RCD’s.
It is therefore much more useful to measure the fault voltage according to the RCD’s in
place (protection of persons against indirect contact), as well as the fault loop impedance
to calibrate the fuses and circuit-breakers.
2. Set the selector switch to the R
A
position. If the " " symbol flashes, then the probe necessary for the
measurement is not connected to the “S / “ terminal.
3. To start a measurement, press the “TEST” button.
Read off the Ra or Za (since Version 2.8) or that of R
A
sel.
NOTE: the Za function is accessible with the Utility Version 3.2 (Default setup is Za inhibited)
4. Read off the R
A
measurement or that of R
A
SEL
5. If you want to, save the measurements with the “MEM” button, or print them out with the “PRINT”
button.
To start a new measurement, press the “TEST” button once more.
To return to the display of the network voltage U
L-N
, turn the selector switch or press CHANGE or SELECT.
CAUTION! To avoid any influence, make sure to position the probe in a potential-free zone – at a
distance of approximately 20 m from the active earths (see connection diagrams). Carry out the
measurement, reposition the probe and repeat the measurement. If the measurement remains unchanged,
this means that the distance is sufficient. If not, relocate the probe until the value stabilises.
Measuring without the probe
If it is impossible to use the probe, the probe lead can be connected to the earthed neutral conductor
(conductor N). Since the earth resistance of the transformer neutral (R
B
) is included in the calculation,
the measurement is therefore of an excessive earth value.
Evaluating measurement values
The table below gives the maximum values that should be displayed, accounting for measurement
errors, to be sure of having a maximum earth resistance (see standards).
Theoretical maximum earth resistance (Ra) Maximum values displayed
0.1
Ω
0.06
Ω
0.3
Ω
0.24
Ω
0.5
Ω
0.42
Ω
0.7
Ω
0.60
Ω
1.0
Ω
0.88
Ω
3.0
Ω
2.70
Ω
5.0
Ω
4.52
Ω
10.0
Ω
9.06
Ω