Sonel Mru-30 User manual

MRU-30 –USER MANUAL

USER MANUAL

EARTH GROUND RESISTANCE METER

MRU-30

SONEL S. A.

Świdnica, Poland

SONEL TEST & MEASUREMENT

Santa Clara, CA 95054

Version 1.05 26.07.2021

MRU-30 –USER MANUAL

The Sonel MRU-30 meter is an easy-to-use instrument that is designed for the safe measurement of

earth ground resistance.

The MRU-30 uses established methods of earth ground resistance measurements such as 3-pole, 4-

pole, and 3-pole with auxiliary clamp. Additionally the MRU-30 employs the two clamp method of

measurement without the use of auxiliary test rods when rods can't be used in some situations.

MRU-30 measurements include: soil resistivity, continuity measurement of protective and equipotential

conductors, leakage currents, and interference voltages.

An integral screen clearly displays results. For safety, and to ensure successful studies, software will

alert the user of possible dangers and irregularities.

The MRU-30 is highly portable, and engineered with a lightweight and compact case. The enclosure

is robust andweatherproof (IP65)to prevent ingress of dust andmoisture, makingit idealfor all outdoor

field work.

It contains a built-in rechargeable battery that can be recharged from a power adapter, or from a stand-

ard 12V vehicle socket.

Please acquaint yourself with this manual to avoid measuring errors and prevent possible problems

related to operation of the meter.

This device complies with part 15 of the FCC Rules. Operation is subject to the following two

conditions: (1) This device may not cause harmful interference, and (2) this device must accept

any interference received, including interference that may cause undesired operation.

This equipment has been tested and found to comply with the limits for a Class B digital device,

pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection

against harmful interference in a residential installation. This equipment generates, uses and

can radiate radio frequencyenergyand, if not installed and used in accordance with the instruc-

tions, may cause harmful interference to radio communications. However, there is no guarantee

that interference will not occur in a particular installation. If this equipment does cause harmful

interference to radio or television reception, which can be determined by turning the equipment

off and on, the user is encouraged to try to correct the interference by one or more of the fol-

lowing measures:

- Reorient or relocate the receiving antenna.

- Increase the separation between the equipment and receiver.

- Connect the equipment into an outlet on a circuit different from that to which the receiver is

connected.

- Consult the dealer or an experienced radio/TV technician for help.

CAUTION:

Equipment changes or modifications not expressly approved by SONEL TEST &

MEASUREMENT Inc., the party responsible for FCC compliance, could void the user’s author-

ity to operate the equipment, and could create a hazardous condition.

MRU-30 –USER MANUAL

TABLE OF CONTENTS

1Safety ................................................................................................................5

2Turning the meter ON and activating the screen backlight. .......................6

3Meter configuration .........................................................................................6

4Measurements..................................................................................................9

4.1 Measurement of AC+DC interfering (noise) voltages...............................................9

4.2Earth resistance measurement with 2-pole method (RE2P) ................................... 10

4.3 Earth resistance measurement with 3-pole method (RE3P) ................................... 11

4.4 Earth resistance measurement with 4-wire method (RE4P..................................... 15

4.5 Earth resistance measurement with 3-pole method with additional clamp (RE3P+C)... 18

4.6 Earth resistance measurement with two-clamp method (2C)................................. 22

4.7 Calibration of the measurement clamp C-3............................................................ 24

4.8 Measurement of resistance of protective conductors and equipotential bonding

(RCONT) ................................................................................................................... 26

4.9 Calibration of the test leads for RCONT measurement ............................................. 28

4.10 Earth resistivity measurement (ρ)........................................................................... 29

5Memory of measurement results .................................................................33

5.1 Storing the measurement results in the memory.................................................... 33

5.2 Viewing memory data............................................................................................. 35

5.3 Deleting memory data............................................................................................ 36

5.3.1 Deleting cell data .........................................................................................................36

5.3.2 Deleting bank data.......................................................................................................37

5.3.3 Deleting the whole memory..........................................................................................39

6Data transmission..........................................................................................40

6.1 Computer connection accessories......................................................................... 40

6.2 Data transmission through USB port...................................................................... 40

7Firmware update ............................................................................................41

8Power supply of the meter............................................................................41

8.1 Monitoring the power supply voltage...................................................................... 41

8.2 Charging the rechargeable battery pack ................................................................ 42

8.3 General principles of using Ni-MH batteries........................................................... 43

9Cleaning and maintenance ...........................................................................43

10 Storage............................................................................................................43

11 Dismantling and disposal .............................................................................44

12 Technical specifications ...............................................................................44

12.1 Basic data .............................................................................................................. 44

12.2 Additional data ....................................................................................................... 47

12.2.1 Influence of the serial interference voltage UZon earth resistance measurements for

methods RE3P, RE4P, RE3P+C, ρ.................................................................................47

12.2.2 Influence of the auxiliary electrodes on earth resistance measurements for methods

RE3P, RE4P, RE3P+C, ρ...............................................................................................47

MRU-30 –USER MANUAL

12.2.3 Influence of the interference current IZon the result of the earth resistance for method

RE3P+C....................................................................................................................... 47

12.2.4 Influence of interference current on the result of the earth resistance measurement for

two-clamp method (2C)...............................................................................................48

12.2.5 Influence of the relation of the resistance measured with clamp for the multiple earthing

branch to the resultant resistance (RE3P+C)................................................................48

12.2.6 Additional uncertainties in accordance with IEC 61557-5 (RE3P, RE4P).......................48

13 Accessories ................................................................................................... 49

13.1 Standard accessories.............................................................................................49

13.2 Optional accessories ..............................................................................................49

14 Manufacturer.................................................................................................. 50

15 Laboratory services ...................................................................................... 51

MRU-30 –USER MANUAL

1 Safety

Electrical safety depends on the correct design and function of earth/ground systems. The MRU-

30 meter has been designed to measure earth/ground installations. For correct operation and correct

results, understand and follow these recommendations:

Before you proceed to operate the meter acquaint yourself thoroughly with this manual and observe

all safety regulations.

The MRU-30 meter has been designed for measurements of earth/ground connections, equipoten-

tial bonding, and ground resistivity. Any application or use of the MRU-30 that differs from those

specified in this manual may result in damage to the meter and constitute a source of danger to the

user.

The device must be operated by appropriately qualified personnel with relevant certification to carry

out measurements of electric installations. Operation of the meter by unauthorized personnel may

result in damage to the device and constitute a source of danger to the user.

Using this manual does not exclude the need to comply with occupational health and safety regu-

lations and other relevant fire regulations required during the execution of a particular type of work.

Before starting work with the device in special environments, e.g. those with potential fire-risk or

explosive environments, consult with the individual responsible for health and safety.

Do not operate the meter in the following situations:

A meter that is damaged or completely or partially malfunctioning.

A meter with damaged test leads or insulation.

A meter stored for long periods in unfavorable conditions (e.g. excessive humidity or tempera-

ture extremes). If the meter is transferred from a cold to a warm environment with a high

level of relative humidity internal condensation can occur. Do not operate until the meter

has reached the new ambient temperature (approximately 30 minutes).

Before operation make sure the test leads are securely connected to the appropriate measurement

sockets.

Do not power the meter from sources other than those described in this manual.

The meter’s inputs are electronically protected from power surges in case of accidental connection

to live conductors: up to 276 V for 30 seconds.

Manufacturer’s calibration does not include test leads resistance. The displayed result is the sum

of the measured object and the test leads resistance. The procedure for calibrating for test lead

resistance is described in section 4.9.

The device complies with the following standards: EN 61010-1 and EN 61557-1, -4, -5.

Note:

Due to continuous development the manufacturer reserves the right to change appearance,

the accessories, and technical parameters of the meter. The display, in case of some of the

functions, may also slightly differ from the display presented in this manual.

MRU-30 –USER MANUAL

2 Turning the meter ON and activating the screen backlight.

Turn on the meter with the button.

Short press the button to turn the

screen backlight on; press the button

again to turn the backlight off.

Switch off the meter by pressing and

and holding the button for approx.

2 sec.

Emer-

gency si-

tuations.

Pressing the button for approx. 7

seconds will turn off the meter in case

of emergency.

3 Meter configuration

Turn on the meter by pressing the

button and the SET/SEL button simulta-

neously.

When the Fn screen is displayed use the

and buttons to set the local mains

frequency –50 Hz or 60 Hz (50 Hz is set

as default).

MRU-30 –USER MANUAL

Use the and buttons to show bEEP

on the screen to allow turning audio sound

on or off.

Use the and buttons to turn the au-

dio sound ON ( ) or OFF ( ).

Press the and buttons to show the

oFF screen to allow the setting of the

auto-power off time (Auto-OFF):

Use the and buttons to set the

time to turn the meter off automatically

(Auto-OFF): The choices are 300 s, 600 s,

900 s or none (dashes - Auto-OFF is disa-

bled).

MRU-30 –USER MANUAL

Use the and buttons to show the

diSt screen to allow the unit of length to be

selected:

Use the and buttons to set the unit

of length: ‘m’(meters) or ‘ft’(feet) (‘m’is

set as default).

Use and buttons to show the UPdt

screen to install new firmware updates.

Press ENTER to enter firmware update mode.

The update process is described in section 7.

After changing the parameters, to exit the SETUP menu, either:

Press the ENTER button to memorize set-

tings (not applicable for the Update screen)

Or: press the ESC button to go to the meas-

urement screen without confirming changes.

MRU-30 –USER MANUAL

4 Measurements

Note:

During measurements the status bar is displayed.

4.1 Measurement of AC+DC interfering (noise) voltages

Note:

This measurement is active only when the meter is set for the following measure-

ments, before starting them with the START button: RE2P, RE3P, RE4P, RE3P+C,

RCONT, ρ.

Before starting the measurement in these modes: RE2P, RE3P, RE4P, RE3P+C, RCONT

and ρ, and before pressing the START button the MRU-30 monitors the voltage pre-

sent on the measurement terminals (between Eand other sockets) and displays the

value of the interfering voltage on the screen.

Additional information displayed by the meter

VN>100V,>100V and

a continuous tone ,

‘NOISE!’and

The voltage on the measurement terminals is > 100 V.

The measurement cannot proceed.

VNxxV,>40V and a

continuous tone ,

‘NOISE!’and

Where xx is the value of the interfering voltage. The volt-

age on the measurement terminals is > 40 V. The meas-

urement cannot proceed.

VNxxV,>24V,

‘NOISE!’and

Where xx is the value of the interfering voltage. The volt-

age on the measurement terminals is > 24 V, but < 40 V.

The measurement cannot proceed.

‘NOISE!’

The value of the interfering voltage is < 24 V, but has a

high value. Results may be affected by additional uncer-

tainty.

MRU-30 –USER MANUAL

4.2 Earth resistance measurement with 2-pole method (RE2P)

Use the << or >> buttons to select the measurement

mode: 2P. The LED is illuminated. The meter is

now in the state of measuring interfering noise volt-

age between the measurement terminals.

Press the SET/SEL button to select the measurement

voltage.

Use the and buttons to set the measurement

voltage value to 25 V

or 50 V.

Press ENTER to save the setting or press

ESC to exit without saving.

The meter is ready for

measurement.

Press START to begin measurement.

Connect the test leads according to the drawing.

MRU-30 –USER MANUAL

After the measurement

completes view the results

on the screen.

The result is displayed for 20 seconds. Press ENTER to display again.

Additional information displayed by the meter

VN>100V,>100V and

a continuous tone ,

‘NOISE!’ and

The voltage on the measurement terminals is > 100 V.

The measurement cannot proceed.

VNxxV, >40V and a

continuous tone ,

‘NOISE!’ and

Where xx is the value of the interfering voltage. The volt-

age on the measurement terminals is > 40 V. The meas-

urement cannot proceed.

VNxxV,>24V,

‘NOISE!’ and

Where xx is the value of the interfering voltage. The volt-

age on the measurement terminals is > 24 V, but < 40 V.

The measurement cannot proceed.

‘NOISE!’

The value of the interfering voltage is < 24 V, but has a

high value. Results may be affected by additional uncer-

tainty.

4.3 Earth resistance measurement with 3-pole method (RE3P)

The basic type of earth ground resistance measurement is the 3-pole measurement.

Disconnect the earth electrode object of test.

MRU-30 –USER MANUAL

Use the << or >> buttons to select the

measurement mode: 3P.The LED is

illuminated. The meter is now in the state of

measuring the interfering noise voltage

seen on the measurement terminals.

Press the SET/SEL button to select the

measurement voltage.

Use the and button to set the meas-

urement voltage value to 25 V or 50 V.

Press ENTER to save the setting or

press ESC to exit without saving.

Drive the current electrode into the ground and connect it to the Hterminal of the

meter.

Drive the voltage electrode into the ground and connect it to the Sterminal of the

meter.

Connect the earth electrode object of test to the Eterminal of the meter.

All 3 electrodes should be aligned in a straight line.

The meter is ready for

measurement.

Connect the test leads according to this diagram:

MRU-30 –USER MANUAL

Press START to begin measurement.

After the measurement

completes view the results

on the screen.

Use the and buttons to toggle between

the measurement results:

RH –resistance of current electrode

RS - resistance of voltage electrode

ER –additional uncertainty caused by the re-

sistance of the auxiliary electrodes

VN –interfering (noise) voltage

The result is displayed for 20 seconds. Press ENTER to display again.

Repeat the test two or more times by moving the

voltage electrode a couple of meters or yards, alter-

nately towards and away from the earth electrode

object of test (E) and repeat steps 7, 8 and 9.

If the REtest results differ bymore than 3% it is nec-

essary to significantly increase the distance be-

tween the current electrode and the earth electrode

object of test (E) and repeat the measurements.

Note:

Earth resistance measurements are usually good if the interference voltage is

< 24 V. The meter can measure in the presence of interference voltage up to

100 V. Over 40 V it is indicated as hazardous. Do not connect the meter to a volt-

age exceeding 100 V.

Pay attention to the quality of the connection to the electrode object of test with the test

leads –the contact area must be cleaned of paint, rust, corrosion etc.

If the resistance of the auxiliary electrodes is too high, then the measurement of the REearth

electrode will be distorted by additional uncertainty. A particularly high measurement

uncertainty is generated if we measure a low value of the earth resistance with electrodes of

a loose contact with the soil (such a situation occurs often if the earth electrode is properly

made and the upper layer of the ground is dry and characterized by alow conductivity). Then

the relation between the electrode resistance and the resistance of the measured earthing is

MRU-30 –USER MANUAL

very high, andso is the case of the measurement uncertainty which depends on it. Whatmay

be done then is to perform, in accordance with the formulae specified in point 12.2,

calculations, which will permit to evaluate the influence of the measurement conditions. It is

also possible to improve the contact of the electrode with the ground, for example by means

of moistening of the place when the electrode is driven, its driving into the ground in another

place or using a 80 cm electrode. Check also the test leads and make sure the insulation is

not damaged and the contacts: test lead –banana plug –electrode are not corroded or

loosened. In most cases the achieved resolution of the measurement is sufficient, but it is

necessary to be conscious of the uncertainty the measurement is burdened with.

Additional information displayed by the meter

RE>9999Ω

Measurement range exceeded.

VN>100V,>100V

and a continuous

tone , ‘NOISE!’

and

The voltage on the measurement terminals is > 100 V.

The measurement cannot proceed.

VNxxV,>40V and a

continuous tone ,

‘NOISE!’ and

Where xx is the value of the interfering voltage. The volt-

age on the measurement terminals is > 40 V. The meas-

urement cannot proceed.

VNxxV, >24V,

‘NOISE!’ and

Where xx is the value of the interfering voltage. The volt-

age on the measurement terminals is > 24 V, but < 40 V.

The measurement cannot proceed.

‘NOISE!’

The value of the interfering voltage is < 24 V, but has a

high value. Results may be affected by additional uncer-

tainty.

and ER along with %

value

The uncertainty caused by resistance of the electrodes is >

30%. (Uncertainties calculated on the basis of the meas-

ured values.)

and RHor RSalong

with Ωvalue

The resistance of H and S electrodes, or one of them ex-

ceeds 19.9 kΩ. The measurement is subject to error.

Flashing symbols:

, ,

Flashing symbols E, H, S, indicate a test lead is discon-

nected from the measurement terminals.

MRU-30 –USER MANUAL

4.4 Earth resistance measurement with 4-wire method (RE4P

The 4-wire method is recommended in the case of measurements of earth ground resistance of

very low values. It eliminates the influence of the test lead resistances. To evaluate the resistivity of the

ground it is recommended to use the dedicated measurement function in section 4.9.

Disconnect the earth electrode object of test.

Use the << or >> buttons to select the

measurement mode: 4P. The LED is

illuminated. The meter is now in the state of

measuring interfering noise voltage be-

tween the measurement terminals.

Press the SET/SEL button to select the

measurement voltage.

Use the and buttons to select the

measurement voltage of 25 V or 50 V.

Press ENTER to save the setting or

press ESC to exit without saving.

Drive the current electrode into the ground and connect it to the Hterminal of the meter.

Drive the voltage electrode into the ground and connect it to the Sterminal of the meter,

Connect the earth electrode object of test to the Eterminal of the meter.

Connect the ES terminal to the earth electrode object of test below the E connection.

All 3 electrodes should be aligned in a straight line.

Connect the test leads according to this diagram:

MRU-30 –USER MANUAL

The meter is ready for

measurement.

Press START to begin measurement.

After the measurement

completes view the results

on the screen.

Use the and buttons to toggle between

the measurement results:

RH –resistance of current electrode

RS - resistance of voltage electrode

ER –additional uncertainty caused by the re-

sistance of the electrodes

VN –interfering (noise) voltage.

The result is displayed for 20 seconds. Press ENTER to display again.

Repeat the test two or more times by moving the

voltage electrode a couple of meters or yards, alter-

nately towards and away from the earth electrode

object of test (E) and repeat steps 7, 8 and 9.

If the REtest results differ by more than 3% it is

necessary to significantly increase the distance be-

tween the current electrode and the earth elec-

trode object of test (E) and repeat the measure-

ments.