Megger DET2/2 User manual

M
DET2/2
Digital Earth Tester
USER GUIDE
GUIDE DE L’UTILISATEUR
GEBRAUCHSANLEITUNG
GUÍA DEL USUARIO

2
SAFETY WARNINGS
•Special precautions are necessary when ‘live’ earths may be encountered, and isolation switches and fuses
are needed in this situation. See ‘Operation - Earth Testing Safety Precautions’.
•The earth spikes, test leads and their terminationsmust not be touched while the instrument is switched ‘On’.
•When working near high tension systems, rubber gloves and shoes should be worn.
•The DET2/2 must be disconnected from any external circuit while its battery cells are being charged.
•A 12 V d.c. battery must not be used as an external supply while it is still connected to the vehicle.
•Replacement fuses must be of the correct type and rating
•Before charging the DET2/2 battery ensure that the correct supply fuse is fitted and the voltage selector is
set correctly.
•Warnings and precautions must be read and understood before the instrument is used. They must be
observed during use.
NOTE
THE INSTRUMENT MUSTONLY BE USED BYSUITABLY TRAINED AND COMPETENT PERSONS.

Safety Warnings 2
Contents 3
General Description 4
Applications 5
Features and Controls 6
Initial Configuration 7
Setting up Test spikes 8
Earth Testing Safety Precautions 9
Operation
General Testing Procedure 11
Test condition adjustments 11
Display messages 12
Error messages 13
Battery charging 15
Measuring Techniques
Testing earth electrodes
Fall-of-Potential method 17
The 61,8% Rule 18
The Slope method 20
Method using ‘Dead’ earth 22
BS7671 (16th Edition IEE Wiring
Regulations) Requirements 23
Other methods 23
Determining ‘Touch’ potential 24
Determining ‘Step’ potential 25
Measuring soil resistivity -
Typical variations in soil resistivity 26
Line traverse 27
Calculation of Resistivity 27
Continuity Testing 29
Specification 30
Accessories 33
Chart for use with Slope method 35
Repair and Warranty 40
Guide de l’utilisateur 43
Gebrauchsanleitung 67
Guía del Usuario 90
Symbols used on the instrument
Caution: Refer to accompanying notes.
Equipment protected throughout by
Double Insulation (Class II)
Equipment complies with EU Directives
Contents Guide de l’utilisateur p43 Gebrauchsanleitung s67 Guía del usuario p91
3

The Megger DET2/2 is a self contained compact
portable instrument designed to measure earth
electrode resistance and perform four terminal
continuity tests. It may also make earth resistance tests
which lead to the measurement of soil resistivity.
Powered by internal rechargeable battery with an
integral charger unit, the instrument design takes full
advantage of microprocessor technology and features
a large, clear liquid crystal display to provide digital
readings. Terminals on the instrument provide an
alternative power source connection to an external 12V
battery, e.g. motor vehicle battery.
Display language can be selected from English,
French, German, Portuguese or Spanish. A range of
frequencies can be selected. DET2/2 is auto ranging,
and will indicate earth resistance in the range - 0,010 Ω
to 19,99 kΩ, with a maximum resolution of 1 mΩ. The
display warns of problems with the test conditions and
also indicates low battery voltage. This enables the
earth spikes to be re-positioned or instrument settings
to be adjusted, to achieve optimum test conditions.
The red TEST push button is pressed to switch the
instrument on, and then turned clockwise to hold it in
the On position. To switch the instrument Off, the TEST
button is turned anti - clockwise and released.
To suit prevailing lighting conditions, the LCD display
can be adjusted by turning the contrast knob.
Four separate membrane switches (marked with ▲or
▼) control the measurement function and are used to
set the required language and test settings.
Test leads are not supplied with an instrument but form
part of an earth testing field accessory kit which is
available as an option. This kit also includes test spikes
(electrodes) for making temporary earth spikes.
The instrument is housed in a robust and tough case
moulded in ABS plastic. All the controls, the terminals
and the LCD display are mounted on the front panel.
DET2/2 is splash proof, and suitable for outdoor use
in most weather conditions.
Terminal ‘C2’ (‘H’) is for the connection to the remote
Current test spike.
Terminal ‘P2’ (‘S’) is for the connection to the remote
Potential test spike.
Terminal ‘P1’ (‘ES’) is for the Potential connection to
the earth electrode to be tested.
Terminal ‘C1’ (‘E’) is for the Current connection to the
earth electrode to be tested.
General Description
4

The installation of satisfactory earthing systems is an
essential part of electricity supply, wiring safety and
installation economics. It is also of great importance in
many communications systems.
The primary application of the DET2/2 is in the testing
of earth electrodes, whether these take the form of a
single electrode, multiple electrodes, mesh systems,
earth plates or earth strips. All earthing arrangements
should be tested immediately after installation and at
periodic intervals thereafter.
Choice of electrode site
For an earth electrode system to perform satisfactorily
it must always have a low total resistance to earth. This
value will be influenced by the specific resistance of
the surrounding soil. This in turn depends on the
nature of the soil and its moisture content. Before
sinking an electrode or electrode system it is often
helpful to survey the surrounding area before choosing
the final position for the electrode. It is possible with
DET2/2 to obtain the resistivity of the soil over an area
and at different levels beneath the surface of the
ground. These resistivity surveys may show whether
any advantage is to be gained by driving electrodes to
a greater depth, rather than increasing the cost by
having to add further electrodes and associated cables,
in order to obtain a specified total earth system
resistance.
Earthing Systems Maintenance
After installation, checks may be made on an earthing
system to see if there is any significant change in the
resistance over a period of time or under different soil
moisture conditions, (e.g. brought about by changing
weather conditions or different seasons of the year).
Such checks will indicate if the earth electrode
resistance to earth has been exceeded by changing
soil conditions or ageing of the system.
Other Applications
For archaeological and geological purposes, an
investigation of soil structure and building remains can
be carried out at varying measured depths, by the
resistivity survey technique.
In all cases the accuracy of the instrument readings
may be taken to be higher than the changes caused by
natural variables in soil characteristics.
A further application is in continuity testing, for example
checking the resistance of conductors used in an
earthing circuit.
Applications
5

6
Features and Controls
To electrode under test
(Potential connection)
To electrode under test
(Current connection)
Charger socket
External 12 V d.c.
supply Terminals
Display contrast
adjustment
To Potential test spike
To Current test spike
On / Off Test Button
(Rotate clockwise
to lock)
31⁄2digit L.C.D.
Test control
switches

Default Language Setting
Select and set the display language default as follows:
1. Press the left hand key ▲and the TEST button
together. Rotate the TEST button clockwise to the
lock position. The language options are displayed.
2. Adjust the display contrast as necessary.
3. Using the centre ▲key, scroll through the
language options. When the required language is
highlighted with a box surround, press the left
hand ▲key. The test frequency options are
displayed.
Default Frequency Setting
Default test frequencies are available as follows:-
108 Hz - For use when testing with interference
frequencies in the vicinity of 16 Hz.
128 Hz - For use when testing with interference
frequencies in the vicinity of 50 Hz.
135 Hz -
150 Hz - For use when testing with interference
frequencies in the vicinity of 60 Hz.
For each default value, the test frequency range can be
incremented in 0,5 Hz steps from 105 Hz to 160 Hz;
using the ▲ ▼ keys.
Select and set the default Frequency as follows:
1. Using the centre ▲key, scroll through the
Frequency options. When the required Frequency
is highlighted with a box surround, press the left
hand ▲key. The Test and Calibration mode
options are displayed. The message “Please
wait...” is displayed.
Saving the Test Parameter settings
The settings made for Test current and filtering options,
and the Frequency of the Test current may be saved for
use in subsequent tests as follows:
1. After making the settings, press and hold the ▲
Scroll key during the measuring mode. The
display lists the default selection.
2. Accept the settings and press the ▲Yes key, or
press the ▲No key to cancel.
Once accepted, further tests may, if desired be carried
out with different settings. The instrument will default to
the saved settings if switched Off and back On again.
7
Initial Configuration

For earth electrode testing and for earth resistivity
surveying, the instrument’s test leads are connected to
spikes inserted in the ground. The way the connections
are made depends on the type of test being undertaken
and details are given in ‘Measuring Techniques’.
Test spikes and long test leads are necessary for all
types of earth testing and the optional earth testing field
accessory kits contain the basic equipment. See
‘Accessories’.
1. Insert the Current test spike into the ground 30 to
50 metres away from the Earth electrode to to be
tested.
2. Connect this spike to the instrument terminal 'C2'
(‘H’).
3. Insert the Potential test spike into the ground
midway between the Current test spike and the
Earth electrode, and in direct line with them both.
4. Connect this spike to the instrument terminal 'P2'
(‘S’).
5. When running the test leads out to each remote
electrode, avoid laying the wires too close to each
other.
Setting up the Test spikes
8

9
Electrode Isolation or Duplication
It is preferable that the earth electrode to be tested is
first isolated from the circuit it is protecting, so that only
the earth is measured and not the complete system.
When this is done, the circuits and equipment must be
de-energised. If however this is not possible, the earth
electrode should be duplicated, so that when it is
disconnected for test purposes, the other one provides
the necessary circuit protection.
‘Live’ earth safety precautions
The DET2/2 allows earth testing to be done at a
relatively safe voltage using a maximum of a 50 V RMS
square wave at a frequency of nominally 128 Hz. In use
it is normally connected only to electrodes which are at
earth potential.
A 'Live' earth is one that carries current from the mains
supply, or could do so under fault conditions.
When working around power stations or sub stations
there is a danger that large potential gradients will
occur across the ground in the event of a phase to earth
fault. A wire which is connected to ground many metres
away will then no longer be at the same potential as
local ground, and in some cases could rise to above
1 kV. The following safety precautions are essential.
1. All persons involved must be trained and
competent in isolation and safety procedures for
the system to be worked on. They must be
clearly instructed not to touch the earth
electrode; test spikes; test leads, or their
terminations if any 'Live' earths may be
encountered. It is recommended that persons
involved wear appropriate rubber gloves, rubber
soled shoes, and stand on rubber mats.
2. The 'P2' and 'C2' terminals should be connected
through a double pole isolation switch, the rating
of which will cope with the maximum fault
voltage and current. The isolation switch must
be open whilst any personal contact is made
with the remote test spikes, or the connecting
leads, e.g. when changing their position.
A method of disconnection where fault conditions
may occur.
Earth Testing Safety Precautions
Earth
resistance
D.P. Isolation switch
True earth
Fuses Remote
spikes
Voltage rise of
earthing system
under fault
conditions
Fault
current

Earth Testing Safety Precautions
10
If isolation switches cannot be used, the leads should
be disconnected from the instrument before remote
spikes and leads are handled. When the remote
connections have been made, the final connections
should be made to the instrument using insulated
plugs, ensuring that the Operator takes adequate and
appropriate precautions such as insulating mats,
rubber gloves etc.
If a fault occurs while a test is being made the
instrument may be damaged. Incorporating fuses
(rated at 100 mA and able to cope with the maximum
fault voltage) at the isolation switch will provide some
protection for the instrument.
Caution: When working on live sites, do not use an
external battery to power the instrument, as this would
also become live under fault conditions.