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Index: WMGBMRU21
Earth Resistance Meter
Technical Specification
  • Description

    Basic measurements of earthing systems and continuity of connections

    The Sonel MRU-21 earth resistance meter is a simple meter which makes it possible to measure earthing with the use of the technical method and to measure the continuity of protective and equalising connections.

    Characteristic features of this model include very simple operation, excellent resistance to interference and high measurement precision. The meter allows for earth resistance measurements with auxiliary electrodes using the 3p method, as well as 2p resistance measurements. The device is also suitable for testing the continuity of equalising and protective connections. The Sonel MRU-21 meter is dedicated to employees of the power and electricity industry.

    Measurement methods

    • 3-wire method – measurement of earthing systems using auxiliary probes
    • 2-wire method – simplified measurement of resistance-to-earth
    • Resistance of earth and compensatory conductors measured using current ≥200 mA with auto-zero function – meets the requirements of EN 61557-4

    Additional features

    • Measurement of resistance of auxiliary electrodes RS and RH
    • Measurement of interference voltage
    • Selection of maximum measuring voltage (25 V and 50 V)
    • Auto-zero function for the resistance of measurement leads (RCONT zero)


    MRU-21 is designed as a reliable measuring instrument, which is both technically advanced and easy to use. It is suitable for tests in industrial plants and in companies providing electrical measurement services. MRU-21 allows user to test individual earth electrodes and systems with multiple earthing electrodes.


    Large and easy to read display shows the resistance values and supporting information in all weather conditions. Additional warnings inform the user about irregularities during the measurement.

    Housing with IP54 rating ensures safety in difficult weather conditions and protect the device against splashes.

    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.

  • 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)
    Connection and equipotential bonding resistance 0.13 Ω…199 Ω acc. to EN 61557-4 0.00 Ω…199 Ω from 0.01 Ω ±(2% m.v. + 3 digits)
    Earth resistance
    2-wire method 0.00 Ω…1.99 kΩ 0.00 Ω…1.99 kΩ from 0.01 Ω from ±(2% m.v. + 3 digits)
    3-wire method 0.50 Ω…1.99 kΩ acc. to EN 61557-5 0.00 Ω…1.99 kΩ from 0.01 Ω ±(2% m.v. + 3 digits)
    auxiliary electrodes resistance 0 Ω…50.0 kΩ 0 Ω…50.0 kΩ from 1 Ω ±(5% (RE +RH+RS) + 3 digits)

    “m.v.” - measured value

  • Files

Optional accessories

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