Megger DET2/2 Manuale utente

DET2/2

Digital Earth Tester

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 ‘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

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.

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

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

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.

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

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

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.

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