ProductsEarth Ground TesterSmart earth resistance tester
Smart earth resistance tester

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Smart earth resistance tester

  • Earth resistance measurement
  • Ground resistivity (Wenner´s method)
  • High spurious voltage rejection
  • Spurios voltage measurement
  • 0.01 Ω resolution
  • Up to 20 kΩ resistance range
  • Auto-range
  • Built-in memory
  • Built-in printer (optional)
  • USB interface
The EM-4055 earth tester is a digital, microprocessor controlled instrument that allows to measure the earth resistance and ground resistivity (using Wenner´s method), as well as to detect parasitic voltages present in the ground. This instrument is suitable to measure earth systems in power substations, industries, distribution networks, etc., according to IEC 61557-5.

It is also suitable for soil resistivity measurements, in order to optimise the earth systems project. It is a fully automatic and easy-to-operate equipment. Before starting each measurement, the equipment will check that conditions are within appropriate limits and will notify the operator in case any abnormality turns up (too high interference voltage, too much resistance in test spikes, very low test current, etc). Then, it will look for the most suitable range and show measurement results in an alphanumeric display.

In order to conveniently test the earth system, EM-4055 allows to perform measurements using the test current which frequency may be operator-selected (270 Hz or 1,470 Hz). On one hand, the lowest frequency will allow to analyse the earth system behaviour related to fault currents of industrial frequency, while on the other hand, the measurement performed with the highest frequency will best show the behaviour in connection with electrical currents caused by lightning and will offer a very high immunity related to interference voltages that are usually present in soils, specially near substations.

The instrument has four ranges that are automatically selected, covering measurements from 0.01 Ω up to 20 kΩ, which allows to obtain very accurate measurements for any kind of soils. During ground resistivity measurement, the operator may indicate the distance between spikes in order for the equipment to apply Wenner's formula and to show the resistivity value directly.

The EM-4055 has a built-in memory to store measurements and a built-in printer (optional), besides the USB interface that allows to communicate measured values to a computer or data logger for their later analysis. It is a portable, strong and lightweight equipment, suitable to be used out in the field and under severe weather conditions. It is powered by a rechargeable battery with a 110 V or 220 V charger and it is supplied with all the necessary accessories for measurements (test spikes, leads, etc) within an auxiliary case that makes it simple to carry.

Operation frequency

During R measurement, operator should select the following test frequencies: 270 Hz ± 1 Hz or 1470 Hz ± 1 Hz.


In the voltmeter function, the equipment operates as a CA conventional voltmeter, making it possible to measure voltages generated by parasitic currents.

Measurement ranges

Resistance: 0 - 20 kΩ (autoranging).
Resistivity: 0 - 50 kΩm (autoranging).
Voltage: 0 - 60 V~.


Resistance and Resistivity measurements: ± (2% of the measured value ± 2 digits).
Voltage measurement: ± (3% of the measured value ± 2 digits).

Reading resolution

0.01 Ω in the resistance measurement.
0.01 Ωm in the resistivity measurement.
0.1 V in the voltage measurement.

Output current

The short-circuit current is limited to less than 20.0 mA R.M.S. (according the IEC 61557-5 - 4.5).

Imunity to spurious voltage interference

During the R measurement, it allows the presence of spurious voltage up to 7 V~.

Earth resistance of auxiliary rods

In the R measurement it allows Raux up to 50 kΩ with error < 30%.

Battery status checking

The battery charge status is verified under normal using conditions.

Advanced features

Automated detection of abnormal conditions that may cause excessive errors (low battery, too high noise interference, too high test spikes resistance).

Soil resistivity computing

When performing soil resistivity measurements, the operator informs to the EM-4055 the distance between spikes and the equipment automatically computes soil resistivity using the Wenner full equation.



Built-in printer (optional)

For a printed register document of measured values.

Power supply

Internal rechargeable battery, 12 V - 2.3 Ah.

Battery charger

For 100-240 V~ mains supply.

Safety class

In accordance with IEC 61010-1:1990.


In accordance with IEC 61326-1.

Electrostatic immunity

In accordance with IEC 61000-4-2.

Electro magnetic irradiation immunity

In accordance with IEC 61000-4-3.

Environmental protection

IP54 with closed lid.

Operation temperature

-10°C to 50°C.

Storage temperature

-25°C to 65°C.


95% RH (without condensation).

Equipment weight

Approx. 3.6 kg (without printer).


274 x 250 x 124 mm.

Included accessories

4 Steel rods.
1 Rod extractor.
1 Charger power cord.
1 40 Meters cable.
2 20 Meters cable.
1 5 Meters cable.
1 5 Meters cable to connect to the grounding system to be measured.
1 USB cable.
1 Canvas bag.
1 User guide.

Images for illustration purposes only. Megabras reserves the right to change design and specifications without prior notice.

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