Megger DET5/4R Manual de usuario

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.

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

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

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

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.

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.

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

Fault

current Isolation

switches

Fuses

C1 P2 C2

ESH

4POLE3POLE

MEASURER

MEGGERMEGGER

DET5/4DDET5/4D

EARTHEARTH

TESTERTESTER







Earth

resistance

Voltage rise of

earthing system

under fault

conditions

True earth

Remote

test spikes

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

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