Chauvin Arnoux C.A 6115N User Manual Download Page 25

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5.7 Measuring earth resistance R

and

(since Software version 2.8)

The instrument must be connected to the live network and the earth to be measured must not be
disconnected. A single auxiliary earth testing rod (probe) is needed, saving a great deal of time compared
to the traditional 2 auxiliary earth testing rod method.
The test is carried out by measuring the potential difference between the probe (earth testing rod),
serving as a reference point, and the earth to be measured. As a function of the current injected, the
earth resistance (going up to 10 k

Ω)

is calculated

The instrument tolerates and measures parasite voltages of up to 20 V. If these voltages are higher,
measurement is not possible. In this case, the probe has to be moved.
An automatic test of the probe’s resistance takes place before measurement. The instrument tolerates
probe resistances of up to 15 k

Ω

If, during measurement, fault voltages > 50 V in relation to the earth are experienced, the measurement
stops automatically within 200 ms.
In some cases, inductive components may be essential (long tower line in TT systems, or poor earth
conditions in TN systems). In these cases the CA 6115N with Version 2.8 has the ability to show the Z

impedance. Normally this function is inhibited, but combined with the Utility Software 3.2, this function
can be set valid in the set up panel. See also chapter 5.8.
For measurements on RCD-protected installations, make sure to use the "R

"measurement

function. This function enables measurement of the earth resistance without tripping 30 mA
RCD’s.
Furthermore, it is also possible to selectively measure a single earth among several, without having
to disconnect the earth from the installation. A current clamp (optional) must be connected to the
C.A 6115N (See also chapter 5.8).
NOTE: unstable measurements, caused by heavy disturbances in the mains supply can be reduced by
making a long press on the “TEST” button (available since Version 2.8).

5.7.1 Description of the function
During the test, the current source is connected to the conductor with the highest voltage in relation to
the “PE”. The network is then charged with a current that varies according to the earth resistance and
the drop in voltage on the earth connection is measured in relation to the reference earth (probe). The
earth resistance is calculated from the two values I and U. If using a current clamp, only the current
measured by the clamp is used in the calculation.

NOTE: in case of very low parallel earth resistances, the contact resistance and the lead resistance of
the PE connection influences greatly the measurement result. Therefore it is advisable to compensate
the lead resistances at the point of connection before the measurement is carried out. Please place the
clamp very close to the PE connection.

Earth resistance (with probe), as per EN 61557–5 (Ed. 97).
Measurement method: Measurement of the potential difference with a probe and current

(DIN VDE 0413 part 7 - 7/82)

Nominal voltage:

95 . . . 145 V, 175 ... 300 V

Frequency ranges:

15.3 ... 17.5 Hz, 45 ... 65 Hz

Permissible overload: U

rms

max. = 500 V (measurements are not started beyond 300 V)

function: R

, Za (since Version 2.8)

Measurement range