Frequently Asked Questions

Fault loop measurements – What type of meter should I choose for measurements on small fault loops in switchgears?

Use MZC-310S as this device applies the high-current method enabling its user to measure fault loop with the resolution of 0.0001Ω (standard meters 0.01Ω). The lowest value of the measurement range in this meter is 7.2mΩ (standard meters 0.13..0,30Ω).

MPI-520 – what is the difference between MPI-520START version and the full version of MPI-520?

The difference lies in the number of accessories. MPI-520 (full) set is equipped also with accessories for earthing measurements (test leads on reels, crocodile clips) and larger case.

MPI-520 and MPI-525 – What are the differences?

MPI-520 measures insulation resistance with the following voltages: 50, 100, 250, 500 and 1000V, whereas MPI-525 additionally uses 2500V.

MPI-520 provides (real-time) measurements of: voltage, current, power (apparent, active, reactive), cosφ.

MPI-525 is equipped (as standard) with rechargeable cell, AC power adaptor, car power adaptor for supplying the internal charging unit.

How to change the firmware in a meter?

Select and download required firmware from (menu, “download” – “firmware”). Do not connect your meter to PC before installing and starting the firmware. Then from the meter menu choose the firmware update mode as described in the manual and connect the meter to your PC.

Follow the displayed instructions.

Note! Batteries or rechargeable batteries must be fully charged.

SONEL PE 5 firmware – Is it provided with any meter as a standard?

Our meters are provided with Sonel Reader” software, which allows to send the results to a PC and save them as a text file or Excel file, compatible with Sonel PE.

Sonel PE software- Where can I download the demo versions of the software for creating the protocol?

At, on the product page of individual software types.

Webpage: – Where can I find manuals?

individually for each instrument in “Files” tab.

Laboratory services – How often should I check metering devices?

Applicable regulations (Act on Measures, PN-E 04700:1998 standard) require all instruments used for safety / electric shock measurements to have certificates confirming their technical efficiency. However, these regulations do not specify in details a document or its validity.
PN-ISO 10012-1 standard, Annex A provides, among others, that the manufacturer of a device may recommend the interval of metrological inspection for its instruments.

Therefore it is necessary to observe internal rules or standards, if they specifically state the manner of the metrological control of equipment used in a given place (especially in case of having ISO quality control system); otherwise you can rely on the manufacturer’s recommendations (see the manual of the instrument).

Laboratory services – Should I send my meter for calibration with the test leads?

Accessories don’t need to be provided with instruments sent to the laboratory for calibration. Cables and other accessories are not subject to calibration (they are considered as consumables) – it is up to user to inspect their quality (visually and e.g. their continuity).

The meters operating with user’s own clamps are calibrated together with them (at the same price); the calibration certificate will include additional note informing about this fact.

Laboratory services

All information on issuing calibration certificates (including delivery, prices, dates) are presented at in “Laboratory” tab.

Data transmission from meters – how to do that?

Data read-outs from Sonel meters are performed using a protocol of “Sonel Pomiary Elektryczne” software (Sonel Electrical Measurements), or “Sonel Reader” software (supplied free with the meter or downloaded from the website).

The results taken from “Sonel Reader” may be freely used – the software has the option to export results to a text file or MS Excel file.

In order to provide data read-outs the meter must be switched into the data transmission mode, detailed information for a given instrument type can be found in the manual.

MRU (series) – How to perform earth electrode measurements when the area is covered by concrete and probes cannot be entered into the ground?

If the earthing system is not interconnected underground (e.g. a ground ring), but is connected to other earthing elements (e.g. air terminals on the roof), then you can use the double clamp method available in MRU-120, MRU-200 and MPI-530 meters (no need to enter the probes into the ground). In case of a single earthing this method can be applied, when the earthing is connected to PE of network (results will be slightly overstated, but an error in this direction is acceptable). For single earthing, you can try the fault loop method – a loop in the circuit consisting of phase and tested earthing is measured, whereas the circuit is closed by the earth.

The results of earth resistance are overstated as they are increased by the values of the fault loop of the power supply circuit. However this method is susceptible to power network interferences and requires proper interpretation of results by the operator (too low value may indicate that the circuit was closed by a metal element).

When you want to apply the fault loop method for multiple ground ring, disconnect power supply to the tested object and then disconnect all control connections and equipotential connections.

MRU-120, MRU-200, MPI-530 – Can I use the double clamp method for every type of earthing?

Only for the multiple earthing measurements, but not connected underground, as the current flowing through the tested earthing must flow in a circuit closed by the earth.

The double clamp method cannot be used for single earthing, nor the ground rings.

This method is described in “Guide to PN-EN 62305 Standard. Measurement of earth resistance” (link).

MRU-200 – Should I disconnect the earth electrode during earth impedance measurements carried out with the current surge method?


MRU-200 – Can I apply the current surge method for current measurements on electric poles and stations without disconnecting their earthing?

Since this is a pulse method, it can be used for the measurement of multiple earthing, including objects such as power line poles, without the need to disconnect their earthing (and this requires switching the line off).

In addition, PN-EN 62305 standard requires the earthing impedance measurements, which are carried out with the current surge method.

During the measurement a lightning current flow (pulse current) is simulated. The largest part in grounding this current has the initial part of the earth electrode, where measurements take place.

PAT – What is the difference between two types of leakage current?

A Leakage current is a current that flows from live parts of a device, through isolation, to the ground. PAT meters provide the measurement of four types of leakage current:

Replacement leakage current: current is measured after applying voltage between shorted L and N and PE (Class I devices) or a probe in contact with the device housing (Class II);
Ground leakage current: only current flowing through PE conductor of the tested device is measured (the leakage through other routes is not measured);
Differential leakage current: the difference between current flowing through L conductor and the current flowing through N conductor is measured – taking into account all current leakage routes;
Touch leakage current: the leakage current is measured by taking into account human perception and response in accordance with PN-EN 60990 (internal resistance of the test probe = 2kΩ).
Detailed description of the above measurements is presented the guide entitled “Testing the safety of electrical equipment” available on our website.

Display range and measurement range – what is the difference?

The display range means all the features that may be displayed by the meter. However, every measurement may include some error caused by the measuring device. EN 61557 standard defines maximum error values for electrical measurements. Basing on this standard a measurement range of the instrument is defined to provide measurement results with an error lower than specified limits –this is called the measurement range. It should be noted that devices available in the European Union must have their measurement ranges specified on their cover casings, in accordance with EN-61 557.

LKZ-700 – Routing of a cable when only one end is available

When the cable is not damaged and the circuit is live, use the magnetic field method (receiver and transmitter in “M” or “I” mode). Then connect one transmitter conductor to the phase conductor and the second to the PE cable in the farthest location (PE cable in another room, earthing, grounded metal pipe for the heating system …). The receiver detects a signal in places where the cable is located.

In an undamaged circuit without voltage, connect the transmitter conductor to N wire, while the second to another, distant earthing, and select the current-voltage mode (transmitter in the “E + M” or “U + I” mode and the receiver in the “M” or “I” mode).

It is possible to connect both transmitter conductors to N and L conductors of one socket, but remember that signals flowing through L and N (depending on the arrangement of conductors) will more or less reduce each other, and the signal level indicated by the receiver may vary, misleading operators inexperienced in locating wires.

In case of damaged conductors in the cable see LKZ-700 – routing of a cable with a broken conductor.

LKZ-700 – Routing of a cable with a broken conductor

Set the transmitter and receiver at the voltage mode (“E” or “U” marking) and connect it to the tested conductor. Other conductors in the cable and the other end of the broken conductor (when you have an access to the other end of the cable) must be grounded to prevent the penetration of electric field. The receiver will show the signal level as long as you move it over the cable route – up to the point of damage.

Due to the applied electric field (susceptible to damping), the method is not recommended for locating cables (depth too large = significant distance from the cable generating the field).

LKZ-700 – Instruction video for the trace

The instruction video for LKZ-700 Wire Tracer is available on the subpage of the device – it may be watched under “product description” tab or downloaded from “download file” tab.

PQM-701, PQM-701Z, PQM-701Zr, PQM-702: Why is the value of asymmetry 327,67%?

The value is shown unbalance because of the faulty connection of analyzer to the network – switch off two voltage test leads.

Unbalance on the level of 327% is impossible in reality (maximum real value of unbalance can be 100% in theory). This is also visible in the value of opposite component of U2, which usually should be within single volts.

For correctly connected system, value of U1 should be about the nominal voltage.

PQM (series) – Should users update the software of these instruments?

Internal software of these devices (firmware) and PC software should be regularly updated, as updates help to remove discovered errors and introduce new functionalities. When the firmware is updated, check whether a new version of “Sonel Analiza” software is also available (and vice-versa). If yes, perform both updates.

PQM (series) – Data export from “Sonel Analiza” software to CSV or PDF file?

Choose a data block and select “User Report” from “Reports” in “Measurement” window.

PQM-701Z, PQM-701ZR – What is DC voltage measurement range?

0…1150V – as peak values of AC voltages

KT-384, KT-160, KT-160A, KT-150, KT-140 battery problems:

Batteries in KT series cameras charging without having to remove them from the camera – just plug in the AC adapter to the camera and turn off the camera. If the battery is completely discharged (for example, after a long period of inactivity), and every 5 charges (in order to extend their life – because of the series connection of the camera) it is recommended to carry out an external charger, charging each cell independently.

New batteries should be three-fold completely discharged, then charged in an external charger to form – it also provides the increased viability (after recharging can take place at any time).
If the camera is to be unused long time, it is recommended that every few weeks recharge the batteries. When not using the camera, batteries should be removed from the camera.

KT-140, KT-150, KT-160, KT-160A, KT-384: What is the maximum distance for temperature measurements with a thermal imaging camera?

Theoretically, the distance is infinite, but in Earth conditions the stratosphere is the limit (several kilometres), hence the cloudless blue sky is “colder” than the clouds.

However, other parameters must be also considered, e.g. minimum size of the object being measured in terms of measuring distance, the resolution of camera matrix and the lens used.

MIC-5000, MIC-5010 and MIC-5005 – Can I make measurements above 2500 m above mean sea level?

MIC-5000: the device performs the full range of measurements up to 2000m above mean sea level.

MIC-5005, MIC-5010: the device performs the full range of measurements up to 2000m above mean sea level.

MIC-5000: Is there an option for PI (Polarization Indicator) and DAR (Dielectric Absorption Ratio) measurements?


The time after which the measurements are taken may be set from 1 sec. to 600 sec., so when you set t1=60 sec. and t2=600 sec., insulation resistance values measured after these times will be recorded and displayed along with PI value (i.e. the calculated ratio of resistance after 10 minutes to the resistance measured after one minute).

If you set 30 and 60 seconds, Dielectric Absorption Ratio will be calculated.

If you set three intervals (30, 60, 600 seconds) the device will measure both coefficients.
Note – the meter does not display PI, DAR symbols – Ab1 (for calculations after t2, t1) or Ab2 (after t3, t2) are displayed.

MIC-2510: Is there an option for PI (Polarization Indicator) and DAR (Dielectric Absorption Ratio) measurements?


In the device settings define the type of absorption coefficient – depending on the choice the following symbols will be displayed: Ab1, Ab2, or DAR, PI.

In order to measure DAR you must also set the measurement time t1=30s, t2=60s.
In order to measure PI must also set time t3=600s.

MIC (series) Insulation Resistance Meters – how to start (maintain) a correct measurement?

MIC-2: Keep “Start” button pressed and simultaneously press “SEL” button. In order to end the measurement, press “Start” button again.

MIC-3: Keep “Start” button pressed and simultaneously press „UBAT/ACU”. In order to end the measurement, press „Start” button again.

MIC-10: Keep “Start” button pressed and simultaneously press „ENTER”. In order to end the measurement, press „Start” button again or press “Esc” button.

MIC-30, MIC-2505, MIC-2510: Keep “Start” button pressed and simultaneously press “ENTER”. The measurements ends automatically after the pre-set time; in order to end the measurement at any chosen moment press “Start” button again or press “Esc” button.

MIC-1000, MIC-2500, MIC-5000: Keep “Start” button pressed and simultaneously press “arrow-up” button. The measurements ends automatically after the pre-set time; in order to end the measurement at any chosen moment press “Start” button again.

RCD – How to perform measurements on type A switch?

Perform all the measurements applying alternating current (AC), unidirectional current and unidirectional current with a constant component of 6mA.

Measuring the effectiveness of electric shock protection in systems situated downstream of UPS and inverters.

UPS: measure impedance without emergency power equipment, e.g. after activating the bypass switch – obtained results will be increased (overstated) by the impedance of the power supply system up to the installed UPS device. While calculating short circuit current take the lowest voltage that occurs after a sudden increase in load. If the calculated fault current is greater than the limited fault current provided by a backup source in the worst operational condition, take the limited current for further calculations.

Motors powered from inverters:
In this case the unknown level of inverter settings may create a problem (resulting in changed fault loop impedance) during the shorting – this prevents determining the fault loop current. Another problem is changing input voltage which prevents correct measurements with instruments for system measurements. In such situation we recommend checking whether during an earth fault the touch voltage on the available conducting part decreases to a value that does not exceed permissible values of prolonged touch voltage in environmental conditions.

Problems during measurements on systems with inverters are described in details in the paper of Lech Danielski PhD Eng. and Ryszard Zacirka PhD Eng. Entitled “Analysing electric shock protection in systems powered by inverters or UPS with frequency converters”, 6th SONEL Technical Conference “Measurements on Protection Instruments and Diagnostics of Systems and Electric Equipment”, Zawiercie 2011.