Deleting The Measured Value Memory; Ambient Conditions; Electrical Specifications - Benning CM E1 Bedienungsanleitung

5.3.4 Deleting the measured value memory

Delete the complete measured value memory by pressing the REC key 5 and by simultaneously switching
on the BENNING CM E1 from the switching position "OFF". The "CL" symbol being shown on the display
4 means that the measured value memory has been deleted.
5.4 Functional principle of earth loop resistance measurement
Earth loop resistance measurement is one of the methods of measuring the earth resistance without using
rods. It offers the advantage that no additional probes/auxiliary earth electrodes have to be installed and
the earth connection itself does not have to be disconnected. The method is used, among other things,
in electrical installations with several parallel earthing connections, such as overhead line networks with
pole-type earth electrodes, lightning protection and street lighting systems.
The BENNING CM E1 has a specially shielded measuring clamp 1 with integrated excitation winding and
sensor winding. The excitation winding induces a current flow in the clamped earthing conductor/earth
connection via a defined AC voltage E. The current flow I is measured via the sensor winding and the
resistance of the entire earth loop Rs is calculated and displayed via the BENNING CM E1.
Rs = E / I
with (R1 II R2 ...II Rn) << Rx and (Rb + Rl) < Rx
This means that the earth loop resistance Rs measured by the BENNING CM E1 is always higher than the
searched earth loop resistance Rx. The higher the number of parallel earth connections, the more accurate
the displayed value Rs corresponds to the searched earth resistance Rx. If the displayed resistance value
is too high, check the earth connection.
Rs: Earth loop resistance (entire earth loop)
Rx: Searched earth resistance
R1 ... RN: Parallel earth connections, negligible the higher the number
Rb: Resistance of the soil, usually <1 Ω
Rl: Resistance of the earthing lines, usually <1 Ω
see figure 3: Earth loop resistance measurement

6. Ambient conditions

- The BENNING CM E1 is intended for measurements under dry ambient conditions
- Maximum barometric height for measurements: 2000 m
- Overvoltage category / installation category: IEC 60664/ IEC 61010 → 300 V category III
- Contamination class: 2 according to EN 61010-1
- Protection class: IP 30 (DIN VDE 0470-1, IEC/ EN 60529)
IP 30 means: Protection against access to dangerous parts and protection against solid impurities of
a diameter > 2.5 mm, (3 - first index). No protection against water, (0 - second index).
- Operating temperature and relative humidity:
For operating temperatures from 0 °C to 50 °C: relative air humidity lower than 85 %, noncondensing.
- Storage temperature: The BENNING CM E1 can be stored at temperatures between - 20 °C and
+ 60 °C, at a relative air humidity lower than 75 % without batteries.

7. Electrical specifications

Note: The measuring accuracy is specified as the sum of:
- a relative part of the measured value and
- a number of digits (i.e. counting steps of the last digit).
This measuring accuracy applies to temperatures from 23 °C ± 5 °C and a relative air humidity lower than
80 %.
09/ 2019
provided that: Rs = Rx + (R1 II R2 ... II RN) + Rb + Rl
BENNING CM E1
results in Rs Rx
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