Megger DET5/4R User manual

M
DET5/4R & DET5/4D
Digital Earth Testers
USER GUIDE
GUIDE DE L’UTILISATEUR
GEBRAUCHSANLEITUNG
GUÍA DEL USUARIO

SAFETY WARNINGS
•Special precautions are necessary when ‘live’ earths may be encountered, and isolation switches and fuses
are needed in this situation. See page 9.
•The earth spikes, test leads and their terminations must not be touched while the instrument is switched ‘On’.
•When working near high tension systems rubber gloves and shoes should be worn.
•The DET5/4D must be disconnected from any external circuit while its battery cells are changed.
•Replacement fuses must be of the correct type and rating
•Before charging the DET5/4R 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
THIS INSTRUMENT MUST ONLY BE USED BY SUITABLY TRAINED AND COMPETENT PERSONS.
2

Safety Warnings 2
Contents 3
Illustrations 4
General Description 5
Applications 7
Features and Controls 8
Live Earth Safety Precautions 9
OPERATION
General Testing Procedure 10
Display symbols 10
Setting-up the test spikes etc. 12
Basic test procedure 13
Battery charging (DET5/4R)14
Fitting or replacing the battery cells
(DET 5/4D)14
MEASURING TECHNIQUES
Testing earth electrodes
Fall-of-Potential method 15
The 61,8% Rule 16
The Slope method 18
Method using ‘Dead’ earth 21
BS7671 (16th Edition IEE Wiring
Regulations) Requirements 22
Other methods 22
Determining ‘Touch’ potential 23
Determining ‘Step’ potential 24
Measuring soil resistivity -
Typical variations in soil resistivity 25
Line traverse 26
Calculation of Resistivity 27
Continuity Testing 28
Circuit Description 29
Specifications 30
Accessories 34
Chart for use with Slope method 35
Repair and Warranty 40
Guide de l’utilisateur 42
Gebrauchsanleitung 52
Guía del usuario 62
Symbols used on the instrument
Caution: Refer to accompanying notes.
Equipment complies with EU Directives
CONTENTS
3

Fig.1 DET5/4 Features and controls 8
Fig.2 A method of connection where fault
conditions may occur 9
Fig.3 Low battery voltage indication 10
Fig.4 High Current spike resistance warning 11
Fig.5 Excessive ‘Noise’ warning 11
Fig.6 Reverse polarity indication 12
Fig.7 Fall-of-Potential method for measuring
resistance of an earth electrode 15
Fig.8 Fall-of-Potential method using single
lead to the earth electrode 16
Fig.9 Resistance areas associated with
electrode and Current spike 17
Fig.10 The 61,8% Rule method 17
Fig.11 Connection for Slope method
Fig.12 Resistance curve from Slope method
tests 19
Fig.13 Possible results from several Slope
method tests 20
Fig.14 ‘Dead’ earth testing 21
Fig.15 Test spike positions for BS7671
(16th Edition IEE Wiring Regulations 22
Fig.16 Determining ‘Touch’ potential 23
Fig.17 Determining ‘Step’ potential 24
Fig.18 Soil resistivity measurement 26
Fig.19 Resistivity calculation Nomogram 27
Fig.20 Continuity testing 28
Fig.21 Block diagram of instrument circuit 29
Fig.22 Instrument Accessories 34
Illustrations
4
DET 5/4R Battery Charger Power cord
If the power cord plug is not suitable for your type of socket outlets, do not use an adaptor. You should use a
suitable alternative power cord, or if necessary change the plug by cutting the cord and fitting a suitable plug.
The colour code of the cord is: Earth (Ground) Yellow / Green
Neutral Blue
Phase (Line) Brown
If using a fused plug, a 3 Amp fuse to BS 1362 should be fitted.
Note: Aplug severed from the power cord should be destroyed, as a plug with bare conductors is hazardous in
alive socket outlet.

The DET5/4R and DET5/4D Megger Digital Earth
Testers are compact portable instruments designed to
measure earth electrode resistance and perform four
terminal continuity tests. They may also make earth
resistance tests which lead to the measurement of soil
resistivity. The DET5/4R has an internal rechargeable
battery, with an integral charger unit. The DET5/4D is
powered from six internal, replacement alkaline cells.
TEST METHOD
The instruments use the well known four-terminal
method of measurement in which the resistance of the
current circuit test leads does not affect the result.
In the DET5/4R and DET5/4D the resistance of the
Potential circuit test leads can also be ignored because
abuffer stage is incorporated to prevent the measuring
circuit from loading the earth resistance under test.
Operation of the instrument is extremely simple. Two
modes of operation are selected by means of two push
buttons; one for a three terminal test and one for a four
terminal test. All other functions of the instrument are
automatic.
Areversing d.c. test current, generated electronically
from a “floating” constant current source within the
instrument, is passed via the ‘C1‘and ‘C2’terminals
through the earth being tested. The potential
developed across the earth is compared with the
current and, after filtering and phase sensitive
detection the resistance is given directly on the digital
display.
Test frequency is 128 Hz and in the interests of safety
the maximum test voltage is limited to 50 V (peak)
between C1 and C2 terminals. Short circuit current is a
maximum of 10 mA.
INSTRUMENT DESIGN
The instruments are very robust and have tough cases
moulded in ABS plastic. 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.
Mounted on the front panel are two push-button
switches for testing using either 3 or 4 terminal
measurement. The instrument’s 31⁄2digit liquid crystal
display shows the test result, warns of problems with
the test conditions and also indicates low battery
voltage. LEDs show high current circuit resistance, a
high Potential circuit resistance, (both usually caused
by a high test spike resistance) and a ‘Noisy’ earth
environment. As these factors can influence the
measurement being made, noise and current circuit
resistance are continuously monitored during a test,
while a check of the Potential circuit resistance is made
at the start of each test. The display shows all
measurements directly in ohms or kilohms with the
GENERAL DESCRIPTION
5

decimal point automatically positioned. It also gives an
over-range indication if the resistance under test
exceeds 20 kΩ.
This instruments has been designed to comply with the
performance specifications of BS7430 (formerly CP
1013 from BSI), BS7671 (IEE Wiring Regulations) IEC
364, NFC 15-100 French Specification and VDE 0413
Part 7 (1982) German specification.
The terminal ‘C1’ (‘E’) is for the Current connection to
the earth electrode to be tested.
The terminal ‘P1’(‘ES’) is for the Potential connection
to the earth electrode to be tested.
The terminal ‘P2’(‘S’) is for the connection to the
remote Potential test spike.
The terminal ‘C2’(‘H’) is for the connection to the
remote Current test spike.
6
GENERAL DESCRIPTION

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 DET5/4R and
DET5/4D 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
these instruments 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 archeological 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.
Afurther application is in continuity testing, for example
checking the resistance of conductors used in an
earthing circuit.
Resistances between 0,01 Ω and 19,99 kΩ can be
measured with a basic accuracy of ±2% of reading
±3digits. Individual test spike resistances of up to 4 kΩ
for the Current loop or 75 kΩ for the Potential circuit
can be tolerated on the lowest range, and on the higher
ranges greater Current loop values can exist.
7
APPLICATIONS

8Figure 1. DET5/4 Features
FEATURES AND CONTROLS
31⁄2digit L.C.D.
4terminal push button
To electrode under test
(3 terminal test)
To electrode under test
(4 terminal test)
Battery compartment
(and charger socket
cover DET5/4R)
Condition
Warning l.e.d.s 3terminal push button
Low Battery indicator point
Ωand kΩ range indicator points
To Potential test spike To Current test spike
Low Battery and
Range indicator
Condition
Warning
Alert

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. The
following safety precautions are essential when
working near high tension systems where any
unintentional ‘Live' earths may be encountered
between the site earth and remote earths established
for test purposes. A 'Live' earth is one that carries
current from the mains supply, or could do so under
fault conditions.
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 they wear
appropriate rubber gloves, rubber soled shoes,
and stand on a rubber mat.
2. The 'P'and 'C'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.
Fig.2 A method of disconnection where fault
conditions may occur.
Note: If a fault occurs while a test is being made the
instrument may be damaged. Incorporating fuses at the
isolation switch, rated at 100 mA, and able to cope with
the maximum fault voltage will provide some protection
for the instrument.
Live Earth Safety Precautions
9
Fault
current Isolation
switches
Fuses
C1 P2 C2
ESH
4POLE3POLE
MEASURER
E
P1
ES
MEGGERMEGGER
®
DET5/4DDET5/4D
EARTHEARTH
TESTERTESTER



Earth
resistance
Voltage rise of
earthing system
under fault
conditions
True earth
Remote
test spikes

10
GENERAL TESTING PROCEDURE
Firmly connect the instrument terminals to the
respective earth electrode and test spikes. See ‘Basic
Test Procedure’.
1. Press and hold the appropriate push button for
approximately 2 seconds. This starts the test
sequence including display test; circuit condition
and 'Noise' monitoring. DET5/4 remains on for 30
seconds, or until a push button is pressed to turn Off.
2. Check the circuit condition warning LEDs. If any
adverse conditions are indicated, the cause should
be rectified (to prevent a false reading), before the
test continues. Note:- If the Current spike
resistance is too high for the required
measurement range, the DET5/4 will autorange
to a range which can tolerate a higher Current
spike resistance. This results in a loss of
resolution.
3. If conditions for the test are satisfactory, the display
will stabilise, and the reading given may be
accepted.
4. It is advisable that the battery of the DET5/4R is
fully charged before embarking on a test
sequence. It can be extremely inconvenient if the
battery becomes too low while a field test is in
progress. Similarly, with the DET5/4D new
batteries should always be available.
DISPLAY SYMBOLS
The 31⁄2digit display shows the reading directly in Ωor
kΩ adjacent to the range indicator, with the decimal
point automatically positioned. If the resistance under
test exceeds 19,99kΩ, an over-range symbol appears
(‘1’as left hand digit).
Low battery voltage
Ifthe battery voltage is too low the segment of the display
alongside the battery symbol will flash. In this case the
batteries hold only enough charge for one or two more
measurements and must be recharged (DET5/4R)or
replaced (DET5/4D)before further testing.
Fig. 3 Low battery voltage indication
CIRCUIT CONDITION WARNING INDICATORS
Warning LED’s to the left of the display will indicate any
excessive resistance in the Current circuit or Potential
circuit, and any excessive electrical ‘Noise’ in the
circuit. The illumination of any of these LED’s will
always be accompanied by a warning alert indicator at
the top left of the display screen.
OPERATION