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Page 1: -Electrical Grounding Techiques-LEM Instruments

fromElectrical grounding techniques

Page 2: -Electrical Grounding Techiques-LEM Instruments

Why Ground ?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

What is a ground and what does it do ?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Ground Resistance Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Ground Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Types of Ground Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Ground Resistance Testing - Soil Resistivity . . . . . . . . . . . . . . . . . . . . . . . . . . .

Measuring Soil Resistivity 4 - Pole Method . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Ground Resisting Testing 3 - Pole Fall of Potential . . . . . . . . . . . . . . . . . . . . . .

Ground Resistance Testing Existing Systems Selective Clamp - On . . . . . . . .

Ground Resistance Testing Existing Systems "Stakeless" . . . . . . . . . . . . . . . .

Ground Resistance Testing 2 - Pole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Ground Impedance Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Measuring Ground Resistance at Substations . . . . . . . . . . . . . . . . . . . . . . . . . .

Measuring Ground Resistance at Central Offices . . . . . . . . . . . . . . . . . . . . . . .

Measuring Ground Resistance at Cellular Sites/Microwave and Radio Towers

Measuring Ground Resistance at Remote Switching Sights . . . . . . . . . . . . . .

Measuring Ground Resistance for Lightning Protection Commercial/Industrial

Ground Testing Instruments - UNILAP GEO / GEO X . . . . . . . . . . . . . . . . . . . .

Ground Testing Instruments - SATURN GEO / Handy GEO . . . . . . . . . . . . . . .

Ground Resistance -Principles, Testing,Techniques & Applications

Table of Contents

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LEM Instruments

Palmersstrasse 2

A-2351 Wr. Neudorf

Tel: +43/2236/691-0

Fax: +43/2236/691 415

email: [email protected]

http://www.lem.com

Publication A 99415 E

Printed in Austria

Page 3: -Electrical Grounding Techiques-LEM Instruments

1

Ground resistance values

hy Ground ?

There is a good deal of confusionas to what constitutes a good groundand what the ground resistance valueneeds to be. Ideally a ground shouldbe of zero ohms resistance. TheNEC has stated that "A singleelectrode consisting of a rod, pipe,or plate which does not have aresistance to ground of 25 ohms orless shall be augmented by oneadditional electrode...". Once youhave added the supplemental groundyou have met the requirement forthe NEC. This does not mean thatthe value of the ground now has tobe 25 ohms or less. The groundresistance values objectives varyfrom industry to industry.Telecommunications industry hasoften used 5 ohms or less as theirvalue for grounding and bonding.The goal in ground resistance valuesis to achieve the lowest groundresistance value possible that makessense economically and physically.

There are a number of good reasons to ground but primary among them

is to ensure personnel safety. The following agencies and organizations

all have recommendations and / or standards for grounding, to ensure

that personnel safety is being protected. The organizations that provide

guidelines/rules for grounding are: The International Electrotechnical

Commission (IEC), European Committee for Electrotechnical

Standardization (CENELEC), Underwriters Laboratories (UL), National

Fire Protection Association (NFPA), American National Standards Institute

(ANSI), Mine Safety Health Administration (MSHA), Occupational Safety

Health Administration (OSHA), Telecommunications Industry Standard

(TIA) and others.

Good grounding is not only for the safety of personnel but to provide for

the protection of plants and equipment. A good ground system will

improve the reliability of equipment and reduce the likelihood of damage

as a result of lightning or fault currents.

What is a ground and what does it do ?

The NEC, National Electrical Code defines a ground as: "a conducting

connection, whether intentional or accidental between an electrical circuit

or equipment and the earth, or to some conducting body that serves in

place of the earth." When talking about grounding it is actually two

different subjects, earth grounding and equipment grounding. Earth

grounding is an intentional connection from a circuit conductor usually

the neutral to a ground electrode placed in the earth. Equipment grounding

is to ensure that operating equipment within a structure is properly

grounded. These two grounding systems are required to be kept separate

except for a connection between the two systems to prevent differences

in potential from a possible flashover from a lightning strike. The purpose

of a ground besides the protection of people plants and equipment is to

provide a safe path for the dissipation of Fault Currents, Lightning Strikes,

Static Discharges, EMI and RFI signals and Interference.

Page 4: -Electrical Grounding Techiques-LEM Instruments

2

round Electrodes

1

2

Sphere of influence:

The resistance of a groundelectrode has 3 basiccomponents:

A) The resistance of the groundelectrode itself and the connectionsto the electrode.

B) The contact resistance of thesurrounding earth to the electrode.

C) The resistance of the surroundingbody of earth around the groundelectrode.

consist of three basic components:

ground conductor

the connection/bonding of the conductor

to the ground electrode

the ground electrode itself3

Page 5: -Electrical Grounding Techiques-LEM Instruments

A) The resistance of the groundelectrode and it's connection isgenerally very low, ground rods aregenerally made of highly conductive/low resistance material such ascopper of copper clad.

B) The contact resistance of the earthto the electrode: The Bureau ofStandards has shown this resistanceto be almost negligible providing thatthe ground electrode is free frompaint, grease etc. and that the groundelectrode is in firm contact with theearth.

C) The resistance of the surroundingearth: The ground electrode issurrounded by earth which is madeup of concentric shells all having thesame thickness. Those shells closestto the ground electrode have thesmallest amount of area resulting inthe greatest degree of resistance.Each subsequent shell incorporatesa greater area resulting in lowerresistance. This finally reaches a pointwhere the additional shells offer littleresistance to the ground surroundingthe ground electrode.

The NEC specifies that the groundelectrode shall be installed so that itis at least 2,4 m in length and incontact with the soil. There are 3variables that affect the resistance ofa ground electrode:

1. The ground Itself2. The length/depth of the ground electrode3. Diameter of the ground electrode.

Increasing the diameter of the groundelectrode has very little effect inlowering the resistance. For exampleyou could double the diameter of aground electrode and your resistancewould only decrease by as much as10 %.

One very effective way of loweringresistance is to drive groundelectrodes deeper. Because the earthis in layers resistivity changes andvaries considerably on the layer andthe depth within that layer. Soil is notconsistent in its resistivity but highlyunpredictable. With that in mind it isof critical importance that wheninstalling the ground electrode that itis below the frost line so that theresistance to ground will not be greatlyincreased by the freezing of thesurrounding soil. Generally speakingby doubling the length of the groundelectrode you can reduce theresistance level by an additional40 %. There are occasions where itis physically impossible to driveground rods deeper, areas that arecomposed of rock, granite etc. Inthese instances alternative methodssuch as grounding cement are aviable alternative.

3

To assist you in installing aground rod that will meet yourspecific resistance require-ments you can use the tableof ground resistances on page5. Remember this is to beused only as a rule of thumb,because soil is in layers andis rarely homogenous, so theresistance values will varygreatly.

Another system to loweringground resistance is throughthe use of multiple groundelectrodes. In this system morethan one electrode is driveninto the ground and connectedin parallel to lower the resi-stance. Each ground electrodehas it's own sphere of influenceand for additional electrodesto be effective the spacing ofadditional rods needs to be atleast equal to the depth of thedriven rod. Without proper spa-cing of the ground electrodesthe spheres of influence willintersect and the lowering ofthe resistance will be minimaland of little value.

Multiple ground electrodes - Interaction

Page 6: -Electrical Grounding Techiques-LEM Instruments

As shown in the table there can bea change in resistivity from top tobottom by a factor of 50.

4

ypes of Ground Systems

Why measure soil resistivity?

The reason for measuring soilresistivity when selecting a locationfor a sub-station or central office isto find a location that has the lowestpossible resistance. Once a site hasbeen selected, measuring the soilresistivity will give you the informationnecessary to design and build aground field that will meet your groundresistance requirements.There are a number of factorsaffect ing soi l resist ivi ty, soi lcomposition being one of them. Soilis rarely homogenous and theresistivity of the soil will varygeographically and at different depths.

The second factor affecting soil resi-stivity is moisture or the amount ofwater in the ground. Moisture contentchanges seasonally, varies accordingto the nature of the sub layers of earthand the depth of the permanent watertable. The table on page 5 showsdifferent types of soil and the affectsthat moisture has on their resistivity.

Since soil resistivity is so closelyrelated to moisture and moisture ispresent in the soil we can logicallyassume that as moisture increasesresistivity will decrease and vice versa.

There are two types of groundingsystems, simple and complex. Simpleconsist of a single ground electrodedriven into the ground. The use of asingle ground electrode is the mostcommon form of grounding and canbe found outside your home or placeof business. Complex groundingsystems consist of multiple groundrods connected, mesh or gridnetworks, ground plates and groundloops. These systems are typicallyinstalled at power generatingsubstations, central offices andcellsites.

Ground Resistance Testing- Soil Resistivity

Page 7: -Electrical Grounding Techiques-LEM Instruments

5

Ω m

Moist humus soil,moor soil, swamp 30Farming soilloamy and claysoils 100

Sandy clay soil 150

Moisty sandy soi 300

Dry sand soil 1000

Concrete 1: 5 400

Moist gravel 500

Dry gravel 1000

Stoney soil 30,000

Rock 10 7

Soil resistivity

3 6 10 5 10 20

10 5 3 12 6 3

33 17 10 40 20 10

50 25 15 60 30 15

66 33 20 80 40 20

330 165 100 400 200 100

- - - 160 80 40

160 80 48 200 100 50

330 165 100 400 200 100

1000 500 300 1200 600 300

- - - - - -

Earthing resistance (Ω)

Earthing rod m depth Earthing strip mREType of Soil

Ground Resistance Values

Soil resistivity depends on soil composition, moisture andtemperature. It stands to reason that soil resistivity willvary through out the year in those areas of the countrywhere seasonal changes bring about a change in themoisture and temperature content of the soil. For agrounding system to be effective it should be designed towithstand the worst possible conditions.

Since soil and water are generally more stable at deeperstrata it is recommended that the ground rods be placedas deep as possible into the earth, the water table ifpossible. Ground rods should also be installed wherethere is a stable temperature i.e. below the frost line.

Caution! Soil that is low in resistivity is often highly corrosivebecause of the presence of water and salts, and this soilcan eat away at ground rods and their connections. Thatis why it is highly recommended that grounds and groundfields be checked at least annually. Although resistanceto ground will change seasonally and over time anyincrease of resistance >20% or more should be investigatedand corrective action taken to lower the resistance.

Soil Resistivity

Measuring Soil Resistivity 4 - Pole MethodThe measuring procedure described below uses theuniversally accepted Wenner method developed by Dr.Frank Wenner of the US Bureau of Standards in 1915.(F. Wenner, A Method of Measuring Earth Resistivity;Bull,National Bureau of Standards, Bull 12(4) 258, p. 478-496;1915/16.

The formula is as follows:ρ = 2 π A R

Where: ρ = the average soil resistivity to depth A in ohm - cmπ = is the constant 3.1416A = the distance between the electrodes in cmR = the measured resistance value in ohms from the test instrument

The calculation of this measurement can besimplified by converting distance in cm to distancein feet giving you the following equation:

ρ = 191.5 A RWhere: ρ = the average soil resistivity to depth A

in ohm - cmA = the distance between electrodes in feetR = the measured resistance value in ohms from the test instrument

Note: Divide ohm - centimeters by 100 to convertto meter - ohms.For example, you have decided to install 3 m groundrods as part of your grounding system. To measurethe soil resistivity at a depth of 3 m requires thatthe spacing between the test electrodes is 3 m. Thedepth that the test electrodes is to be driven is A/20.To measure the soil resistivity start the GEO andread the resistance value in ohms. Now if yourresistance reading is 100 ohms the soil resistivityfor one cubic meter would be:

ρ = 2 x π x 3 x 100ρ = 1885 Ωm

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6

The ground stakes are positioned ina straight line equidistant from oneanother and at a distance betweenone another reflecting the depth tobe measured. The ground stakesshould be screwed in no deeper than1/3 the distance from one another. Aknown fixed current is generated bythe GEO between the two outerground stakes and a drop in potential(which is a result of the resistance)is then measured automaticallybetween the two inner ground stakes.The GEO then displays this resistancevalue in ohms.

Because measurement results areoften distorted and invalidated byunderground pieces of metal,underground aquifers etc. additionalmeasurements in which the stakesaxis is turned 90 degrees is alwaysrecommended. By changing the depthand distance several times a profileis produced that can determine asuitable ground resistance system.

Soil resistivity measurements are of-ten corrupted and/or prevented bythe existence of ground currents andtheir harmonics. To prevent this fromoccurring the GEO uses an AutomaticFrequency Control System (AFC),that automatically selects the testingfrequency with the least amount ofnoise enabling you to get a clearreading.

To test soil resistivity connect the groundtester as indicated.

oil Resistivity Testing

Page 9: -Electrical Grounding Techiques-LEM Instruments

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To achieve the highest degree ofaccuracy when performing a 3 - Poleground resistance it is essential thatthe probe is placed outside the sphereof influence of the ground electrodeunder test and the auxiliary earth.

If you do not get outside the sphereof influence the effective areas ofresistance will overlap and invalidateany measurements that you aretaking.

The following table is a guidelinefor setting probe (S/P2) and auxi-liary ground (H/C2).

To test the accuracy of theresults and to ensure that theground stakes are outside the'spheres of influence' repositionground stake P2 / S 3 ft in eitherdirection and take a freshmeasurement. If the measuredvalue remains fairly constantthe distance between theground stakes is sufficient. Ifthere is a significant change inthe reading (30 %) you need to increase the distance between theground rod under test and P2/S andC2/H until the measured valuesremain fai r ly constant whenrepositioning the P2/S ground stake.

Often the driving of a singleground rod into the earth doesnot result in a resistancereading low enough or desired,this is especially true insubstations and central officeswhere resistances of < 3 ohmsare required. In this case theguidelines for setting yourauxiliary ground stakes maynot get you outside the sphereof the influence. Take themaximum distance of theground field either straight lineor diagonal and the spacingfor the first reference stake tobe twice the distance. Thetable can be utilized as a guidefor setting reference stakes forcomplex ground systems.

Ground resistance measure-ments are often corruptedand / or prevented by the exi-stence of ground currents andtheir harmonics.

To prevent this from occurringthe GEO uses an AutomaticFrequency Control System(AFC), that automaticallyselects the testing frequencywith the least amount of noiseenabling you to get a clearreading.

3 - Pole Fall of PotentialTesting for ComplexGround Systems

The 3 - pole fall of potential methodis used to measure the dissipationcapabil ity of a single groundelectrode, ground grids, foundationgrounds and other groundingsystems.

Stake Setting

The potential difference is measuredwith a voltmeter and the current flowby an ammeter internally by the GEO.Using Ohm's law:

R = E/I we can calculate R

Connect the ground tester as shownin the picture below. Press START,and read out the RE, (resistance)value. This is the actual value of theground electrode under test. If thisground electrode is in parallel orseries with other ground rods the REvalue is the total value of allresistances.

Depth ofelectrode under

test C1/E

Distance toprobe P2/S

Distance toauxiliary probe

C2/H

2 15 25

3 20 30

6 25 40

10 30 50

Approximate distance to auxiliary probesusing the 62% method (in m)

Page 10: -Electrical Grounding Techiques-LEM Instruments

round Resistance TestingExisting Systems 'Selective' Clamp-on

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This unique exclusive LEM methodhas been created to measureresistances of individual groundelectrodes in all types of groundedsystems including ground grids andwired meshes as are common insubstations, high voltage pylons withground cabling, and commercialsettings with multiple grounds. Byusing a specialized clamp-on currenttransformer the effects of parallelresistances are

eliminated from the measuringprocess and therefore do notinfluence the measuring results. Aspecial rectification method is usedto isolate or 'digitally filter' out othercurrents to significantly increaseaccuracy. As with the standard 3-PoleFall of Potential testing the rules /guidelines for the setting of groundstakes apply for both simple andcomplex grounds.

NO DISCONNECTION REQUIRED!

The "Ground Under Test" does nothave to be disconnected!

Diameterof

Ground Grid, orField in m -

Distance toProbe P2/S

in m

30

50

70

100

130

50

80

100

170

200

Distance toProbe C2/H

in m

20

25

30

50

70

Connect the ground tester as shown in the picture above. Press START, andread out the RE value. This is the actual value of the ground electrode undertest.

Page 11: -Electrical Grounding Techiques-LEM Instruments

9

To test the accuracy of the resultsand to ensure that the ground stakesare outside the 'spheres of influence'reposition ground stake P2/S 1 m ineither direction and take a newmeasurement. If the measured valueremains fairly constant the distancebetween the ground stakes issufficient. If there is a significant chan-ge in the reading (30 %) you need toincrease the distance between theground rod under test and P2/S andC2/H until the measured valuesremain fai r ly constant whenrepositioning the P2/S ground stake1 m or so.Ground resistance measurementsare often corrupted and or preventedby the existence of ground currentsand their harmonics. To prevent thisfrom occurring the UNILAP GEOuses an Automatic Frequency ControlSystem (AFC), that automaticallyselects the testing frequency with theleast amount of noise enabling youto get a clear and accurate reading.

Testing individual ground electroderesistances of high voltagetransmission towers with overheadground or static wire requires thatthese wires be disconnected. If atower has more than one ground atit's base, these must also bedisconnected one by one and te-sted.The UNILAP GEO X with the31 cm diameter clamp-on currenttransformer can measure theindividual resistances of each legwithout disconnecting any groundleads or overhead static/ground wires.

'Selective' Measuring ofHigh Voltage TransmissionTowers

From the picture above we can see that the total resistance of anindividual tower is the parallel sum of all grounds. The tower has 4individual grounds you must measure all 4, generating the individualresistance and then calculate according to the formula above.

Page 12: -Electrical Grounding Techiques-LEM Instruments

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Clamp-on technology only measures individual groundrod resistances in parallel to earth grounding systems. Ifthe ground system is not straight parallel to earth thenyou will either have an open circuit or be measuringground loop resistance.

Ground Resistance Testing 2 - PoleIn situations where the driving of ground stakes is neitherpractical or possible the GEO does give you the ability todo 2 - pole ground resistance/continuity measurements.To perform this test requires a good known ground suchas an all metal water pipe. The water pipe should beextensive enough and be metallic throughout without anyinsulating couplings or flanges. Unlike many testers theGEO performs this test with relatively high voltage ACwith up to 250 mA of current.

The UNILAP GEO X measures individual groundresistances in multi-grounded systems using two clamp-on current transformers, eliminating the dangerous andtime consuming activity of disconnecting parallel groundsas well as the process of finding suitable locations forauxiliary ground stakes.

How it Works...

The GEO X works on the principle that in parallel /multigrounded systems the net resistance of all groundpaths will be extremely low as compared to any singlepath (the one under test).So the net resistance of all the parallel return pathresistances (R1...Rn) is effectively zero. It is reasonableto assume any resistance measured must be associatedwith the individual path to ground the clamp is around(Rx).

The first current transformer induces a voltage in thecircuit while the second current transformer measuresthe actual current flowing allowing the GEO X to calculatethe resistance of the ground path after synchronousrectification of current and voltage.

round Resistance TestingExisting Systems - 'Stakeless'

Page 13: -Electrical Grounding Techiques-LEM Instruments

There are 3 separatetypes o f g roundmeasurements thatare necessary toconduct when doinga grounding audit ofa substation.

Measur ing Ground Resistance atSubstations

First determine the nature of the ground system, i.e. mat,rods, water system, combination etc. Substations generallyconsist of high voltage transmission towers andtransformers that are connected and grounded to a groundgrid.Follow the rules / guidelines for stake setting to ensurethat the measurement is accurate and has not beeninfluenced by the effects of the grid. Reposition P2/S ayard or so and take a new measurement. If there is adeviation >30 % of measured value, reposition both P2and C2 further from the ground under test and repeat.This value should then be recorded. These measurementsshould be repeated at least annually to detect any changewithin the ground grid.

11

After having completed the 3-Pole test for the entire gridwe to measure individual ground rods and theirconnections in the grid using the selective clamp-onmethod. We measure each connection separately withouthaving to disconnect. The purpose of the selective clampon is to ensure that the resistances within the grid arefairly uniform.

To conduct a selective clamp-on test, keep in mindthat the spacing requirements for the referencestakes are the same as with a standard fall ofpotential test. Make sure that you leave enoughslack in your leads so you can move easily fromconnection to connection. The results of this testshould be recorded and the test repeated at leastannually.

Ground Impedance Measurements

When attempting to calculate possible short circuit currentsin power plants and other high voltage/current situations,determining the complex grounding impedance is importantsince both inductivity and resistivity are present. Becauseinductivity and resistivity are known in most cases actualimpedance can be determined using a complex compu-tation. Since impedance is frequency dependent, GEOuses a 55 Hz signal for this calculation to be close tomains as possible without corrupting the measurement.Accurate direct measurements of grounding impedanceare possible.

Power utilities testing high voltage transmission lines areinterested in two things. The ground resistance in caseof a lightning strike and the impedance of the entiresystem in case of a short circuit on a specific point in theline. Short circuit in this case means an active wire breaksloose and touches the metal grid of a tower.

The first measurement to be taken is a "Stakeless"measurement. Use the GEO X to clamp around allgrounding connections.

A measurement that showed a great deviation tothe other measurements is probably indicative ofa problem that should be investigated.

Depth ofelectrode

Approximate distance to auxiliary probes using the 62% method in m

2

3

6

10

25

30

40

50

15

20

25

30

Distance toprobe C1/E

Distance to auxilliaryprobe C2/H

Page 14: -Electrical Grounding Techiques-LEM Instruments

a ground lead going toth e MGN (Mu l t i -Grounded Neutral) orincoming service, a se-parate ground leadfrom the MGB to theground field,another ground leadfrom the MGBconnected to the waterpipe and a ground leadconnected to structuralor building steel.The first measurementto take is stakelessmeasurement of all the

by as much as a mile.

Record the measurement and thistest should be repeated at leastannually.

12

When conducting a grounding audit of a central office there are 3 or 4different measurements required. First locate the MGB (Master Ground Bar)within the central office to determine the type of ground. The MGB will have

easuring Ground Resistance At Central Offices ...

Measurements would be accurate butwould not show how the systembehaves as a network, because inreal life in the event of a lightningstrike or fault current everything isconnected. To prove this out you canmeasure each leg separatelydisconnected via the 3-pole methodand record each measurement. UsingOhm's law again these measure-ments should be equal to the resi-stance of the entire system. From thecalculations you will see that you arefrom 20 - 30 % off the total RE value.The final way to measure theresistances of the various legs of theMGB is the 'Selective StakelessMethod'. It works similat to theStakeless Method but it differs in theway we use the two separate CT's.We clamp the inducing voltage CTaround the cable going to the MGB,and since the MGB is connected tothe incoming power which is straightparallel to earth system we haveachieved that requirement.Take the sensing CT and clamp itaround the ground cable leading outto the ground field (see below). Whenwe measure the resistance this is theactual resistance of the ground fieldplus the parallel path of the MGBwhich because it should be very lowohmically should have no real effectonthe measured reading. This processcan be repeated for the other legs ofthe Ground Bar i.e. water pipe andstructural steel. To measure the MGBvia the Stakeless Selective method

individual grounds coming off of the MGB. The purpose is to ensure that allthe grounds are connected especially the MGN. It is important to note thatyou are not measuring the individual resistance rather the loop resistance ofwhat you are clamped around. Connect the GEO X and measure the loopresistance of the MGN, the ground field the water pipe and the building steel.

clamp the inducing CT around thelead going to the water pipe as thewater pipe should have very lowresistance, your reading will be forthe MGN only.

Page 15: -Electrical Grounding Techiques-LEM Instruments

There are 3 measurements required when conducting an audit at a cell site,microwave or radio tower. At most locations there is a 3 legged tower witheach leg individually grounded. These grounds are then connected with acopper cable. Next to the tower is the Cell site building housing all thetransmission equipment. Inside the building there is a halo ground and a MGBwith the halo ground connected to the MGB. The cell site building is groundedat all 4 corners connected to the MGB via a copper cable the 4 corners arealso interconnected via copper wire. There is also a connection between thebuilding ground ring and the tower ground ring.

13

... at Cellular Sites/Microwave and Radio Towers

the otherones, the reason for this should be determined.

This is mainly a continuity testto verify that we are groundedand do have an electricalconnection and can passcurrent.

Page 16: -Electrical Grounding Techiques-LEM Instruments

There are 3 key measurements when conducting tests at remote switchingsites also known as slick sites, digital line concentrators and probably more.The remote site is generally grounded at either end of the cabinet and thenwill have a series of ground stakes around the cabinet connected by copperwire.

14

easuring Ground Resistance at Remote Switching Sites ...

The second measurement to be

Page 17: -Electrical Grounding Techiques-LEM Instruments

15

... and for Lightning Protection Commercial / Industrial

There are 3 ground resistance measurements required when conducting an audit of a lightning/fault currentprotection system. Most lightning fault current protection systems follow the design of having all 4 corners ofthe building grounded and these are usually connected via a copper cable. Depending on the size of thebuilding and the resistance value that was tried to be obtained number of ground rods will vary.

Keep in mind the rules for stake setting. Thismeasurement should be recorded and measure-ments should take place at least semi-annually.

Page 18: -Electrical Grounding Techiques-LEM Instruments

16

300 kΩ , 2%1 mΩ20/48 V250 mA55...128Hz, autoüüüüü

üWinGEOü

UNILAP GEO

3-pole measurement and additional2-pole resistance measurements with AC.

Ground Testing Instruments

WinGEO

Application software for PCs usingWindows®, Windows® 95,Windows® NT.Suited for UNILAP GEO X (with RS232interface or DOCU-PACK), measureddata acquisition, remote control, logging,SETUP, DIAGNOSE.

Technical Data Handy GEO SATURN GEO UNILAP GEO UNILAP GEO X

Measuring rangeResolutionMeasuring voltageTest current max.Frequency4-pole2-pole3-poleSelektiveStakeless meas.

AccessoriesRS232 interfaceSoftwareDOCU-PACK

2000 Ω , 6%10 mΩ<25 V>50 mA128Hz-üü--

üWinVIEW-

300 kΩ , 2%1 mΩ20/48 V250 mA55...128Hz, autoüüü--

---

Universal ground testing instruments for testing installations and lightning protection. All instruments operate with abattery, have automatic an switch-off, a display illumination, adjustable limits, and display probe and auxiliary earthresistances. Auto-ranging and parasitic current suppression provide reliable measuring results. For standard 3-polemeasurements, many additional special functions are available.

UNILAP GEO X

Ground tester for measurements onsingle grounds or multi-loop systemswithout breaking into the circuits.

Selective ground measurementswithout influence from parallelgrounds,

stakeless ground measurements for quick testing,measurements of the specificground resistanceGround impedance of high voltagetowers.

2-pole and 4-pole resistance measurements with DC (>200 mA)

2-pole resistance measurements with AC

Measured value output via interface (to printer or PC)

Storage or direct printout of the values via optional DOCU-PACK (RS232 interface required)

Logging of measured values via optional Windows® software WinGEO

300 kΩ , 2%1 mΩ20/48 V250 mA55...128Hz, autoüüü--

---

Page 19: -Electrical Grounding Techiques-LEM Instruments

SATURN GEO

Universal earth tester 4-pole ground measurement 3-pole ground measurement 2-pole resistance measurements Resistance measurements with AC Specific earth resistance Digital display Earth impedance of high voltage

pylonsExtremely rugged housing thanks toprotective cover and carrying strap.

17

Handy GEO

Small, handy ground tester 3-pole ground measurement 2-pole resistance measurements Digital display, bar graph

Logging of the measured values viaan optional RS 232 interface and PCsoftware WinVIEW or directly via aprinter.

Ground Testing Instruments

Designation Order No.

Handy GEO base instrument A 1885 03110Handy GEO incl. ground measuring kit+ 2 ground stakes, 2cable reels (25m, 50m), carrying case A 1885 03111Handy GEO base instrument+ RS 232 interface and PC-software WinVIEW A 1885 03112Ground measuring kit2 stakes, 2 reels (25m, 50m), case A 6030 03100

SATURN GEO without accessories A 1885 06411

UNILAP GEO without accessories A 1885 06110UNILAP GEO incl. ground measuring set: A 1885 061114 ground stakes, 2 cable reels (25 m), 1 cable ree (50 m), case

UNILAP GEO X incl. ground measuring set A 1885 06211UNILAP GEO X incl. ground measuring set and RS232 A 1885 06212UNILAP GEO X incl. ground measuring set and stakeless kit A 1885 06213UNILAP GEOX with ground measuring set and DOCU-PACK A 1885 06215

WinGEO PC software for UNILAP GEO X with RS232/DOCU-PACK A 1885 0017212 1/2" split core transformer A 6805 06211Earth/Ground measuring kit: 2 stakes, 2 reels (25m, 50m) in carrying case A 6045 10301

Page 20: -Electrical Grounding Techiques-LEM Instruments

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