Index: WMGBMRU120
Earthing resistance and soil resistivity meter
Technical Specification
  • Description

    Multifunctional earthing resistance meter

    With the use of the presented earth resistance and soil resistivity meter Sonel MRU-120 it is possible to carry out earth resistance measurements using 3-pole and 4-wire method, measurements with the use of additional clamps (multiple earthing - without the necessity of unfastening the monitoring connections), as well as measurements using two-clamp method - in some cases it is possible to carry out the measurement without the necessity of using auxiliary probes driven into the ground. Sonel MRU-120 is a device designed to meet the needs of the power industry and used for earthing measurements - measuring range (measurements in accordance with EN 61557 standard) from 0.30 Ω. The functionality of the device is completed by the possibility to measure the resistivity of soil and the continuity of protective and equalising connections.

    Measurement methods

    • 3-pole and 4-wire method – measurement of earthing systems using auxiliary probes
    • 3-pole method with clamp – measurement of earthing systems with multiple earth electrodes
    • Two-clamp method – measurement of earthing system when the auxiliary probes cannot be used
    • Soil resistivity – Wenner method
    • Resistance of earth connection and equipotential bonding measured using current ≥200 mA with auto-zero function – meets the requirements of EN 61557-4

    Additional features

    • Measurement current of 200 mA – facilitates earth resistance measurements in difficult areas (sand, stony soil)
    • Measurement of resistance of auxiliary electrodes RS and RH
    • Measurement of interference voltage
    • Measurement in the presence of interference voltage generated by power networks with frequency of 50 Hz and 60 Hz
    • Selection of maximum measuring voltage (25 V and 50 V)
    • Automatic calculation of soil resistivity in ohm-meters (Ωm) and ohm-feet (Ωft)
    • Memory of 990 measurement results (10 banks of 99 cells each)
    • Calibration of clamp used
    • Real time clock (RTC)
    • Data transmission to the computer
    • Battery indication


    MRU-120 meter was created for the most difficult working conditions. It generates a measuring current exceeding 200 mA, which provides effective measurements of grounding of energy objects such as transformer stations and power stations.

    Thanks to the methods using clamps, it is not necessary to disconnect the control connectors, which is sometimes a very tedious operation. This plays a special role when performing works on objects exposed to weather conditions, where the connecting elements are sometimes corroded or tarnished. The graphical user interface provides clear readings and explicit messages. This translates into quick, trouble-free service.

    Protection and equipment

    Housing of MRU-120 ensures safe operation in field conditions and inside buildings. Ingress protection rating of IP54 protects the device against water and solids in case of splashes or dusty conditions. Moreover, the design of the device provides very good protection during transport and handling. Extensive standard equipment allows user to perform most measurements without the need to purchase additional accessories. MRU-120 is a versatile solution that offers comprehensive testing of earthing systems.


    The measuring methods available in the device allow for comprehensive control of working and protective grounding. The calibration function of the test leads eliminates the influence of their resistance on the result. However, this is just the beginning.

    • The four-lead method provides very accurate measurement of the expected small values of resistance – eliminates the resistance of the test leads connecting the meter to grounding.
    • Measurement of the continuity of protective connections and equipotential bondings with a current exceeding 200 mA meets the requirements of EN 61557-4 standard.
    • Before performing the measurement, the meter checks whether the tested object is a subject to excessive interference voltage, which may indicate additional problems.

    Memory and results

    The results can be saved to the device’s memory. It is divided into 10 banks of 99 cells, each corresponding to one measurement. These results can be easily transferred to the Sonel Reader software for archiving or subsequent analysis and research.

    Other useful functions

    Built-in help function – auxiliary illustrations demonstrate how to properly perform the measurement for each method.

    Correctness of connections – if the meter detects an error, which prevents a correct measurement, it will indicate this in the top of the screen using the appropriate test socket symbol.

    Complete measurement data – in addition to earth resistance measurement, the device performs additional measurements on interference voltages and resistance of auxiliary probes. Their results are provided with information about the date and time of testing, which facilitates preparing test documentation.

  • Technical Specification
    Measurement functions Measurement range Display range Resolution Accuracy
    Interference voltage 0 V…100 V 0 V…100 V 1 V ±(2% m.v. + 3 digits)
    Resistance of earth connection and equipotential bonding 0.24 Ω…19.9 kΩ acc. to EN 61557-4 0.00 Ω…19.9 kΩ from 0.01 Ω from ±(2% m.v. + 2 digits)
    Earth resistance
    3-pole and 4-wire method 0.30 Ω…19.9 kΩ acc. to EN 61557-5 0.00 Ω…19.9 kΩ from 0.01 Ω from ±(2% m.v. + 2 digits)
    3-pole + clamp method 0.44 Ω…1999 Ω acc. to EN 61557-5 0.00 Ω…1999 Ω from 0.01 Ω ±(8% m.v. + 3 digits)
    two-clamp method 0.00 Ω…149.9 Ω 0.00 Ω…149.9 Ω from 0.01 Ω from ±(10% m.v. + 3 digits)
    auxiliary electrodes resistance 0 Ω…19.9 kΩ 0 Ω…19.9 kΩ from 1 Ω ±(5% (RE +RH+RS) + 8 digits), but ≥10% RE
    Earth resistivity 0.0 Ωm…999 kΩm 0.0 Ωm…999 kΩm from0.1 Ωm Depends on the accuracy of the RE 4p measurement, but not less than ±1 digit

    “m.v.” - measured value

  • Files

Optional accessories

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