DET4TC Presentation

1

New Earth Testers from Megger

Paul Swinerd

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Megger - Earth Testing Pioneer

Dr George Tagg pioneered earth testing at Megger

Designing, manufacturing and selling for well over 50 years

3

Days gone by

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Existing products

Direct 2 terminal & 3 terminal earth electrode testing• DET3TA• DET3TD• DET3TC• DET3/2

2 & 3 terminal and 4 terminal soil resistivity testing• DET5/4D• DET5/4R• DET2/2

Stakeless testers• DET10C-EU and DET20C-EU

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Products being replaced

DET5/4DDET5/4R

• Last orders plan to be maximum 6 months from release of new products, so June 2007

• This is for sales of products – not support and repair of the products which we plan to continue for a further five years

Why?• DET5/4 has been around for many years, now dated• Although sound design, has basic user interface and

feature set

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The new family New family to replace DET5/4D and DET5/4R

• DET4TC– 2, 3 and 4 pole ground tester digital display–Selective (ART) and Stakeless test capability

• DET4TCR– As DET4TC but rechargeable

• DET4TC + KIT–Fully kitted with ICLAMP and VCLAMP

• DET4TCR + KIT–Fully kitted with ICLAMP and VCLAMP

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DET4TC/RExcellent user interfaceFull diagnosticsNew case design

(as DET3TD/TC)Backlit displayARTStakeless testing

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DET4TC/R + KIT

Fully Kitted optionICLAMPVCLAMPStakeless test calibration loopInstrument calibration check boxRight angle adaptor kit

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Earth Testing theory

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Two Basic Test Types

Soil resistivity• Choose location and design for earth system

Earth system resistance• Check resistance low enough

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Soil Resistivity

Theory

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Soil Resistivity

Purpose of this test:• Find lowest possible resistance in an area• Obtain the values needed to design the earth system

Factors affecting soil resistivity• Soil composition• Moisture in the ground• Temperature

Consider• Resistivity will vary through the year• Moisture more constant at water table• Stable temperature below the frost line

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Soil Resistivity test methods

Purpose: Survey a site for the lowest resistance connections for Earth.

Methods: 4-pole (Wenner method).

A A A <A/20

C1 (E) C2 (H)P1 (ES) P2 (S)

Imeas

Emeas

Soil resistivity, ρ = 2πAR (Ωcm)

R = Emeas/Imeas

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Soil Resistivity test terms

Average soil resistivity, ρ = 2πAR (Ωcm)Variables

• ρ is average soil resistivity to depth A in ohm-cm • A is the distance between the spikes• R is the resistance read from the earth tester

For example• Planning to install 3m long electrodes?• Then measure soil resistivity with spacing, A, between

spikes at 3m• The depth of test probes should be less than 3/20 = <15cm

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Soil Resistivity test terms

Soil resistivity is of interest because by rearranging the formula and knowing its value from tables we can calculate the resistance of the earth electrode required.

ρ = 2πAR (Ωcm) therefore electrode resistance R = ρ / 2πA

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Earth System Resistance

Theory

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But First

Earth system definitionsWhy test?Component parts of earth electrode resistance

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Earth system definitions

Simple• Generally consists of a single ground electrode driven into

the ground

Complex• Multiple ground rods connected, mesh or grid networks

– More common in sub stations, cell sites etc

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Why test earth system?

Why a low earth resistance is required:• Enable protective devices to operate in good time• Reduce ground potential rises (GPR)• Danger of shock from GPR (during fault)

– Step potential– Touch potential– Adjacent conductors

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Step and touch voltages

V V

Step Touch

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Resistance and GPR from earth electrode

0.0

0.4

0.8

1.2

1.6

2.0R

esis

tanc

e (O

hms)

0

200

400

600

800

1000

Volta

ge (V

)

Resistance GPR

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Component parts of earth electrode resistance

1 – Resistance of the electrode and the connections to it 2 – Contact resistance of the surrounding soil to the electrode 3 – Resistance of the surrounding body of earth around the electrode – these can be thought of as “shells” and create a sphere of influencesphere of influence

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Earthing System Resistance - theory

Purpose: Measure resistance of earthing system to Earth - ascertain that prospective fault current can be conducted safely to Earth and thus limit “touch voltage”.Methods:

• 2-pole: Direct measurement.• 3-pole: Fall of Potential – Full method• 3-pole: Fall of Potential – short method• 3-pole: Slope Method.• Selective measurements: ART• Stakeless measurements: Earth Clamp.

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2-pole: Direct measurement

Measure “coupling” between two earth points; measure resistance of earth electrode to Earth.

C1 (E)C2 (H)P1 (ES)P2 (S)Imeas

Emeas

Earth electrode under test

Second earth electrode or other low resistance, conductive connection to Earth.

Measures resistance of the two Earth electrodes in series.

R = Emeas/Imeas

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2-pole: Direct measurement disadvantages

A series measurement of a resistance loop.Accuracy depends on assumption that all other elements in loop are of low resistance.Must disconnect individual ground electrodes to measure them.

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3-pole: Fall of Potential (full method)

Classic method for measuring resistance of a single earthing electrode, or of a system of electrodes to Earth.

A

B

C2 (H)P2 (S)

C1 (E)P1 (ES)

Imeas

Emeas

Earth electrode under test

Auxiliary test electrodes

R = Emeas/Imeas

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Fall of Potential - Full Method

Vary location of P2 (Potential) spike by regular steps along a straight line between the electrode under test and the C2 (Current) electrode.Plot graph of resistance measurements to distance of PResistance of system taken where slope is flat.Note: The C spike must be outside the sphere of influence to achieve a viable reading

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Fall of potential - Current Probe Sphere of Influence

AuxiliaryCurrent

Probe (C)

AuxiliaryPotentialProbe (P)

GroundElectrode

Under Test (X)

P probe must be outside of both spheres of influence for correct measurement

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Fall of potential – test and result

CurrentProbe

Position

Distance of Potential Probe from X (dp)Ground

ElectrodePosition

X C

Res

ista

nce

in O

hms

CurrentProbe (C)

PotentialProbe (P)Positions

GroundElectrode

Under Test (X)

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CurrentProbe

Position


ElectrodePosition

X C

Res

ista

nce

in O

hms

CurrentProbe (C)


GroundElectrode

Under Test (X)

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CurrentProbe

Position


ElectrodePosition

X C

Res

ista

nce

in O

hms

CurrentProbe (C)


GroundElectrode

Under Test (X)

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CurrentProbe

Position


ElectrodePosition

X C

Res

ista

nce

in O

hms

CurrentProbe (C)


GroundElectrode

Under Test (X)

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CurrentProbe

Position


ElectrodePosition

X C

Res

ista

nce

in O

hms

CurrentProbe (C)


GroundElectrode

Under Test (X)

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CurrentProbe

Position


ElectrodePosition

X C

Res

ista

nce

in O

hms

CurrentProbe (C)


GroundElectrode

Under Test (X)

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CurrentProbe

Position


ElectrodePosition

X C

Res

ista

nce

in O

hms

CurrentProbe (C)


GroundElectrode

Under Test (X)

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CurrentProbe

Position


ElectrodePosition

X C

Res

ista

nce

in O

hms

CurrentProbe (C)


GroundElectrode

Under Test (X)

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CurrentProbe

Position


ElectrodePosition

X C

Res

ista

nce

in O

hms

CurrentProbe (C)


GroundElectrode

Under Test (X)

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CurrentProbe

Position


ElectrodePosition

X C

Res

ista

nce

in O

hms

CurrentProbe (C)


GroundElectrode

Under Test (X)

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CurrentProbe

Position


ElectrodePosition

X C

Res

ista

nce

in O

hms

CurrentProbe (C)


GroundElectrode

Under Test (X)

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CurrentProbe

Position


ElectrodePosition

X C

Res

ista

nce

in O

hms

CurrentProbe (C)


GroundElectrode

Under Test (X)

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CurrentProbe

Position


ElectrodePosition

X C

Res

ista

nce

in O

hms

CurrentProbe (C)

PotentialProbe (P)Position

GroundElectrode

Under Test (X)

True system resistance measured here

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CurrentProbe

Position


ElectrodePosition

X C

Res

ista

nce

in O

hms

CurrentProbe (C)

PotentialProbe (P)Position

GroundElectrode

Under Test (X)

True system resistance measured here

Usually approx 62% of X to C distance

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Typical Probe Spacing

Single electrode• C probe 15m away• P probe 9.5m away

Large system, several electrodes or plates• C probe 60m away• P probe 38m away

Above only rough guide – look up tables available

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Fall of Potential Method – Disadvantages

Extremely time consuming and labour intensive.- Temporary probes must be placed.- Cables must be run to make connections.

Space constraints can make it hard to place remote probes. (probes usually many meters away)Must disconnect individual ground electrodes to measure them.

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3-pole: Fall of Potential (short method)

Reduced method based on fewer measurements, saving time

Earth electrode

under test

B

C2 (H)P2 (S)

Emeas

C1 (E)

P1 (ES)

Imeas

0.62B


R = Emeas/Imeas

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3-pole: Fall of Potential (short method)

Site P2 (Potential) spike at 62% of B and take resistance measurement.Locate P2 ± 0.1B around the 62% point and take additional resistance readings, Rb and Rc.If the three readings are within an agreed accuracy limit, the system resistance is the average

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Fall of Potential Method (short method)–Disadvantages

Not as accurate as less measurements are madeSpace constraints can make it hard to place remote probes.Must disconnect individual ground electrodes to measure them

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3-pole: Slope Method

Alternative method applicable for physically constrained sites.

B

C1 (E) C2 (H)

P1 (ES)

P2 (S)

Imeas

Emeas

Earth electrode

under test

0.4B

0.6B

0.2B


R = Emeas/Imeas

Distance to C probe (B) Now 2 to 3 times the maximum dimension of earth system.

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3-Pole: slope method

Distance of Potential Probe from X (dp)

Res

ista

nce

in O

hms

CurrentProbe (C)

PotentialProbe (P)

GroundElectrode

Under Test (X)

No flat area

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Vary location of P2 (Potential) spike by regular steps along a straight line between the electrode under test and the C2 (Current) electrodeMeasure resistance at each step and plot a graph of R versus distance.Measure resistance at 0.2B, 0.4B and 0.6B: R1, R2 and R3.Slope coefficient, m=(R3-R2)/(R2-R1) relates distance B and ideal distance of the voltage spike (P2) for measuring the resistance.

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Measure R1 at 20% distance to C2

C2 (H)

Earth electrode

under test

B

C1 (E)

P1 (ES)

Imeas

Emeas

0.2B

R1

C2 (H)

μ=(R3-R2)/(R2-R1)

R1= 9.3 ohm

R = Emeas/Imeasμ = (R3-R2) / (R2 – 9.3)

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C2 (H)

Earth electrode

under test

B

C1 (E)

P1 (ES)

Imeas

Emeas

0.4BR2

C2 (H)

μ=(R3-R2)/(R2-R1)

R1= 9.3 ohmR2= 16 ohm

R = Emeas/Imeasμ = (R3– 16) / (16 – 9.3)

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C2 (H)

Earth electrode

under test

B

C1 (E)

P1 (ES)

Imeas

Emeas

R30.6B

C2 (H)

μ=(R3-R2)/(R2-R1)

μ = (19.2 – 16) / (16 – 9.3)

R1= 9.3 ohmR2= 16 ohmR3= 19.2 ohm

R = Emeas/Imeas

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Calculate value of μ

C2 (H)

Earth electrode

under test

B

P2 (S)C1 (E)

P1 (ES)

Imeas

Emeas

0.4B

0.6B

0.2B

Auxiliary test electrodesR3R2R1

C2 (H)C2 (H)

μ=(R3-R2)/(R2-R1)

R = Emeas/Imeasμ = (19.2 – 16) / (16 – 9.3)

μ =0.478

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Tables of values for the co-efficient of slope against actual P spike distance is published in the instrument user guide.Take calculated value of m and look up ideal distance of the voltage spike (P2) for measuring the electrode resistance

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3-pole: Slope Methodμ =0.478

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Measure electrode resistance at 0.632B

Earth electrode

under test

C2 (H)

B

C1 (E)

P1 (ES)

P2 (S)

Imeas

Emeas

0.632B


C2 (H)C2 (H)

R = Emeas/Imeas

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3-pole: Slope Method - Disadvantages

Less accurate than the full fall of potentialRequires mathsMust disconnect individual ground electrodes to measure them

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Selective Measurements ‘ART’

Attached Rod Technique No need for the earth electrode to be disconnectedUses current clamp ‘ICLAMP’ to measure current flowing in electrode under test.

60

Application of ART

Potential Probe (P) CurrentProbe (C)

GroundElectrodes

Building earthconnection/s I Total

I System

Ie1

Ie 2Ie 3 Ie test Test

Ie Test > I Total20

X Connection

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ART with 4 pole measurement

Potential Probe (P) CurrentProbe (C)

GroundElectrodes

Under Test (X)

Building earth connection/s

I TotalI System

Ie 1 Ie 2Ie 3Ie Test

C1 and P1 connections

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Effects of Earth Coupling

X Test point

C P P

X Test point

C

Result – Clamp low symbol or unexpected high reading

Answer use 3 pole method – disconnect electrode

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Misuses – Telecom Guy Lines

Current CPotential P

X Connection

We MUST fully understand the test current path

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The Best Application of ART

Field of earth / Earth FarmsPole mounted transformersDomestic TT (earth electrode) systemsSingle guy lines on towers (isolated)Lightning protection electrodes

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Measuring Earth Leakage Current


System leakage current

Ie 1 Ie 2Ie 3 Ie 4 leakage (mA)DET4TC set to A range

Using ICLAMP to measure electrode leakage current

66

“Stakeless” MeasurementsNo need for the earth electrode to be disconnectedNo need for test spikes to be used

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Clamp-On / Stakeless Methodology

Inject a voltage and measure the resultant current produced in a ground loop.Requires a complete electrical circuit to measure.Measures the complete resistance of the path (loop) the signal is taking.In a multiple ground system the circuit can be considered a loop comprising:- The individual ground electrode.- A return path via all other electrodes.- The mass of earth.

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In a multiple ground system the circuit can be considered a loop comprising:- The individual ground electrode.- A return path via all other electrodes.- The mass of earth.The single electrode will have a higher resistance than the remainder of grounds connected in parallel.Inject a voltage and measure the resultant current produced in a “single turn” ground loop.

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GroundElectrode

Under Test


ICLAMP

VCLAMP

70


ICLAMP

VCLAMP

R testR1R2R3R425 Ohms 22 Ohms 19 Ohms 25 Ohms 45 Ohms

R Meas.= 50.6 Ohms

R Meas. = R test + 1 / (1/R1 + 1/R2 + 1/R3 + 1/R4)

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Clamp-On/Stakeless Methodology

For 6 similar electrodes each with a resistance of 10Ω

• Rloop = 10Ω + 2Ω = 12Ω reading on DET4TC/R

For 60 similar electrodes with a resistance of 10Ω• Rloop = 10Ω + 0.17Ω = 10.17Ω reading on DET4TC/R

The more electrodes the more accurate the reading

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Clamp-On /Stakeless Method - Advantages

Test is quick and easy• No disconnecting the ground rod from the system.• No probes need to be driven/cables connected.

Includes the bonding and overall connection resistance• Not available with Fall of Potential

Can measure the leakage current flowing through the system.

.

73

Clamp-On /Stakeless Method - Disadvantages

Effective only in situations with multiple grounds in parallel (pole grounds).Cannot be used on isolated grounds (no return path)

• Not applicable for installation checks/commissioning new sitesCannot be used if an alternate lower resistance return exists not involving the soil

• Cellular towers• Substations

Subject to influence if another part of the ground system is in “resistance area”

• Result will be lower than true resistance.Test is carried out at a high frequency (enables the transformers to be small)

• Less representative of a fault at power frequency but easier to filter out noise

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Requires a good return path• Poor return path may give high readings.

Connection must be on the correct part of the loop for the electrode under test

• Requires thorough understanding of the system• Wrong connection can give a faulty result.

Susceptible to noise from nearby substations and transformers (no reading).No basis for the test in standards – no objective reference for the test resultsLess effective for very “low” grounds• Extraneous elements in reading become comparatively large.

Clamp-On /Stakeless Method - Disadvantages

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Applications – Service Entrance/Meter

GroundRods

ServiceBox

Pole-MountedTransformer

ServiceMeter

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Applications – Lightning Protection

Removable links(Jug handles)

Link removed for2 pole measurement

Lightning protection tape

Normal 2 Pole method

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Applications – Lightning Protection

Removable links(Jug handles)

ICLAMP and VCLAMP


Using ‘Stakeless’ method no need to remove link

78

SubstationGrounded Perimeter

Fence

E

Clamp-OnGroundTester

Substation Ground System

TestCurrent

Misuses – Substations

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Misuses – Lightning ProtectionTest current flowing around loopOf lighting protection tape.


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The Best Application of “Stakeless” Testing

Field of earth / earth farmsPole Mounted transformer electrodesPole mounted transformer guy line when connected to earth systemEarthing in Sub-station cable cellars

• It is often impossible to drive in test spikes so this is an ideal application for stakeless measurements

Single guy lines on towersLightning protection electrodes

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DET4TC/R

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New product common philosophy

Intuitive to useOne button operationAutomatic checking to avoid mistakes and poor connections, indicated on displayComplete and ready to start testing kit, including calibration certificateCompetitively priced to sell, including distributionCombination of features, benefits and price makes these ground testers the most attractive on the market

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New product common features

Like DET3TD, based on building wiring housing Delivered in plastic carry caseIncludes stake and wire kit with each modelHigh quality large and easy to read backlit LCDIncludes batteriesHas quick start guide on the lidEasy to use wearing glovesComes with calibration certificate as standardThree year warrantyAvoids language variants for easy stock holding

84

Basic specification – DET4TC/R2 terminal test, no links required 3 terminal earth electrode test, no link required4 terminal Resistivity test to 20k OhmsART (Attached Rod Technique)‘Stakeless’ measurementsEarth voltage measurementEarth leakage current measurement (with ICLAMP)Automatic checking of

• Current spike resistance• Voltage spike resistance• Earth noise voltage• Blown fuse• Battery status

Rechargeable batteries on DET4TCR

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DET4TC/R specifications - electrical

Resistance range (2,3 & 4 pole): 0.01 to 20kΩMaximum P & C spike resistance: 100kΩ (50V output)ART range: 0.01 to 20kΩStakeless range: 0.01 to 200ΩEarth voltage range: 0 – 100VEarth current range (DET4TC/R + ICLAMP): 0.5mA to 19.9ATest frequency: 128 HzTest voltage: 25V or 50V selectable (Factory set 50V)Earth noise rejection: 40V peak to peakBattery type: 8 off AA cells or rechargeableApproximate battery life: 700 consecutive testsSafety: EN61010-1 CATIV 100VEMC: EN61326-1:1998 heavy industrial

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Common specifications - Mechanical

IP54Terminals: 4mm plug typeDimensions: 203 x 148 x 78mmWeight: 1kgOperating temperature range: -15 to 55°CStorage temperature range: -40 to 70°CHumidity: 95% RH non-condensing at 40°C

87

DET4TC/R Accessories

Standard• Hard carry case• Stake and wire kit (15m, 10m, 10m, and 3m)• External AC/DC adaptor – interchangeable plugs

Optional• ICLAMP• VCLAMP (includes calibration check pcb)• Calibration check box – 6220-824• Right angled terminal adaptor set – 6220-803• Black crocodile clip - 6220-850• Vehicle 12V charger lead – 6280-375

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DET4TC/R + KIT Accessories

Standard• Hard carry case• Stake and wire kit (15m, 10m, 10m, and 3m)• External AC/DC adaptor – interchangeable plugs• ICLAMP• VCLAMP (includes calibration check pcb)• Calibration check box – 6220-824• Right angled terminal adaptor set – 6220-803

Optional• Black crocodile clip - 6220-850• Vehicle 12V charger lead –

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Accessories – terminal adaptor set

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DET4TC/R Competitors

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4620/30 / CA 6460/2• Disadvantages

– 42V output only– P and C high ind. combined– No cal. Cert.– IP50– No leads or case etc. std.– Only 2kΩ range– Links required

• Advantages– However many lead kit

options

DET4TC/R• Advantages

– Superior noise rejection– CATIV 100V– Much lighter– ART and Selective

capability– Earth leakage current

range– Earth voltage range– Superior diagnostics

AEMC / Chauvin Arnoux

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AEMC / Chauvin Arnoux6470

• Advantages– 2 & 4 pole DC bond check– 0 – 100kΩ range– 16 or 32V output– Auto frequency control– 50Hz earth resistance test– Wenner method rho calc.– Schlumburger method rho

calc.– Memory for 512 tests– Software supplied

• Disadvantages– IP54 but only with lid closed– Rechargeable only


– ART & Stakeless capability

– 25 or 50V output– 128Hz only– Much lighter– Easy to use– Hard carry case

93

Fluke1623 (Saturn Geo Plus)

• advantages– Battery life 3000 tests– 125 or 128Hz– 2 years warranty– ART noise current

rejection better at 3A– Stakeless noise current

rejection better at 10A <20Ω

• Disadvantages– IP54 but battery door IP40– Only CAT II, 300V rated– Only supplied with 2 leads


– Full diagnostics– Superior temp specs.– Superior noise rejection– 25 and 50V output– No links required– Ground voltage range– Ground current range– Better ART accuracy– 12V charging– Much easier to use– Competitive price

94

Fluke1625 (Saturn Geo X)

• Advantages– ART noise current

rejection better at 3A– Stakeless noise current

rejection better at 10A <20Ω

– Battery life 3000 tests– Automatic frequency

control– DC continuity with buzzer– Test lead compensation– Display resolution 0.001Ω

• Disadvantages– IP54 but battery door IP40


– CATIV 100V– Superior temp specs.– Superior noise rejection– Much easier to use– Free cal. Cert.– Competitive price

95

MetrelM2124C

• Advantages– 2 pole DC bond check– Wenner method rho

calc.– 125 or 128Hz– Result memory– Output to PC

• Disadvantages– Large 30cm required

between clamps– Many accuracies not

specified


– Better quality– Accuracy– 25 and 50V output– Back lit display– Superior noise rejection– Superior temp specs.– Ground voltage range

96

Features and Benefits

Tough rubber armoured IP54 rated instrument case• Instrument will last a long time, and will be ready to test

when required

Supplied in tough blow moulded carry case• Helps prevent loss of accessories, also makes ideal ‘tray’

to put the instrument on when testing. Saves having to lay the instrument directly onto muddy ground.

Supplied with calibration certificate, test leads and spike kit

• Saves time having to source separate leads and spikes. No waiting for calibration to be carried out. No hidden costs. Convenient.

97


‘Attached Rod Technique’ capability, ART• Saves both time and aggravation having to undo rusted

connections. No need to shut down supply to ensure safety

‘Stakeless’ testing capability• Allows testing in areas when driving test spike is

impossible. E.g. Sub station cable cellars, or when testing lightning protection in concreted locations

One button operation with automatic noise check and automatic P and C spike resistance check

• Little time required learning operation, and time saved not having to spend considerable time troubleshooting poor connections etc.

98


User selectable output voltage – 25V or 50V• The ability to test in agricultural locations as per

IEC61557-5. 25V will not harm livestock

40V Pk to Pk Noise rejection• Can be used in most locations with ground noise such as

sub-stations, near transformers etc.

Back light• Easier to operate when not having to use a torch to be

able to read the display

99

Potential Customers

Existing DET5/4 customersPetro-chemical companiesUtilities, MaintenanceRailwaysRepair Organisations (Industrials), Telecoms and Datacoms installers Specialist grounding/earthing companies and consultantsService providersInsurance companies

100

Available?

New family in stock Dover from January LaunchDET5/4

• Declare intention to be made obsolete June 2007• Last orders accepted June 2007• Repaired and calibrated for a further 5 years.

DET4TC Presentation

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