Soil Resistivity and Grounding System Testing - Roy Whitten - Lyncole XIT Grounding

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  • Soil Resistivityandand

    Grounding System TestingGrounding System Testing

    Roy Chip WhittenSenior Applications Engineer/Education SpecialistLyncole Grounding Solutions, LLC

  • What Is Grounding ?What Is Grounding ?

    A l t i l ti h th i t ti l id t l b tAn electrical 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 earthbody that serves in place of the earth.

  • Reasons For GroundingReasons For Grounding

    Personnel safety and equipment protection by providing aPersonnel safety and equipment protection by providing apath to safely dissipate any unwanted charges or potentials.

    Ensure equipment performance and protection Ensure equipment performance and protection

    Satisfy manufacturers warrantySatisfy manufacturer s warranty

  • Electrical Protection PyramidElectrical Protection Pyramid

    RFRFAC SurgeAC Surge

    Telco / DataTelco / DataLightningLightning

    GroundingGroundingGroundingGrounding

  • Resistance To EarthResistance To Earth

    25 Ohms

    20v 12v 10.6v11v16v 10.18v10.5v 10.45v 0

  • SoilR i ti itResistivity

    BasicsBasics

  • Soil Resistivity

    Key Variable in System Design

    Determines grounding system resistance Changes from Site to Site Dependent on:

    Soil type Moisture Electrolytes Temperature

  • Soil Resistivity Comparison

    SurfaceSurface SoilsSoils 100100 -- 5,0005,000Soil TypeSoil Type Resistivity (ohmResistivity (ohm--cm)cm)

    SurfaceSurface SoilsSoils 100 100 5,0005,000ClayClay 200 200 -- 10,00010,000Sand and GravelSand and Gravel 5,000 5,000 -- 100,000100,000Surface LimestoneSurface Limestone 10,00010,000 -- 1,000,0001,000,000Surface LimestoneSurface Limestone 10,000 10,000 1,000,0001,000,000LimestoneLimestone 500 500 -- 400,000400,000ShaleShale 500 500 -- 10,00010,000SandstoneSandstone 2,000 2,000 -- 200,000200,000,, ,,Granites,Granites, Basalts, etcBasalts, etc 100,000100,000Decomposed Decomposed GneissesGneisses 5,000 5,000 -- 50,00050,000Slates, etcSlates, etc 1,000 1,000 -- 10,00010,000,, ,, ,,

  • SoilR i ti itResistivity

    TestingTesting

  • Soil Resistivity Testing

    Key Variable in System Design 4 Point Wenner Method

    Most Accurate Multiple Depth Testing

  • 4-Pt. Wenner Method

    Visually Survey Lease Area to Determine Location Visually Survey Lease Area to Determine Location and Direction For Test

    Not parallel to buried metallic objects Not parallel to buried metallic objects Not parallel overhead power lines

    Sufficient straight line distance to allow for test Sufficient straight line distance to allow for test

    Minimal distance 300 feet

  • 4-Pt. Wenner Method

    C1P1P1P2P2C2C2

    15 ft15 ft 10 ft10 ft 5 ft5 ft 0 ft0 ft15 ft15 ft 10 ft10 ft 5 ft5 ft 0 ft0 ft

    AA

  • 4-Pt. Wenner Method

    Site AreaSite Area

    Direction of TestDirection of Test

  • 44--Pt. Wenner MethodPt. Wenner Method

    Probe SpacingProbe Spacing Meter ReadingMeter Reading Calculated ResistivityCalculated Resistivity(Feet)(Feet) (Ohms)(Ohms) (Ohm(Ohm Meter)Meter)

    = = 1.915 1.915 ARAR

    (Feet)(Feet) (Ohms)(Ohms) (Ohm(Ohm--Meter)Meter)5 52.00 497.90

    10 19.68 370.87

    15 10.16 292.00

    20 6.53 250.10

    30 4 30 247 0430 4.30 247.04

    40 10.80 827.28

    60 7.40 850.26

    80 5.58 855.60

    100 4.44 850.26

  • T i lTypical Grounding Electrode SystemGrounding Electrode System

    Resistance Requirementsq

  • Typical Resistance Requirements

    NFPA 70 NEC 25 OHMS or Two Rods

    IEEE Standard 142 & 1100 Equipment Dependent

    Motorola Standard R-56 10 OHMS (Design Goal)

    Telecommunications 5 to 10 OHMS

    Emerson DeltaV 3 OHMS

    Essilor 3 OHMS

    GE Medical Systems 2 OHMS

  • 25 Ohm Grounding System

    Lightning

    StrikeStrike

    18,000APotential Rise will be

    ~450KV at the site

  • 5 Ohm Grounding System

    Lightning

    StrikeStrike

    18,000APotential Rise will be

    ~90KV at the site

  • Grounding System Resistance Testing

  • Grounding System Testing

    Why Test Grounds?y Determine Baseline

    Validate Construction Confirm Design Spec

    Satisfied

    Validate Construction

    Satisfy Warranty Reqs Ensure Equip Protection & Performance

  • Testing Methods

    Two Test Methods

    Fall of Potential (Three Point) TestFall of Potential (Three Point) Test Clamp-on Test

  • Fall-of-Potential Method

    RemoteRemoteCurrentCurrent

    ElectrodeElectrodeC1C1P1P1

    P2P2 Auxiliary Voltage ElectrodeAuxiliary Voltage ElectrodeGround Ground RodRod

    EarthEarth

    C2C2P1P1

    11 ftft 110%0%220%0% 330%0% 440%0% 550%0%660%0%770%0%880%0% 990%0%RodRodUnder Under

    TestTest

    11 ftft 110%0%220%0% 330%0% 440%0% 550%0%660%0%770%0%880%0% 990%0%

    1010 x depth of electrodex depth of electrode

  • Fall of Potential

    Why 10+ Samples? Single Point Could Be Misinterpreted Data Must Be Plotted

    Visual Plateau Confirms Test Validity

    o

    h

    m

    s

    )

    125135145

    y

    i

    s

    t

    a

    n

    c

    e

    (

    o

    758595

    105115125

    R

    e

    s

    556575

    0 10 20 30 40 50 60 70 80 90 100 P2 Probe Spacing

  • Fall Of Potential Test

    Why Invalid? #1 Reason

    l d

    Why Invalid?

    Not Isolating System Under Test Meter is a constant amperage meter Part of the current travels through the connection The ground system is part of a parallel network

    Test Is Invalid Unless Disconnected

  • Fall Of Potential Test

    Why Invalid?Why Invalid?

    #2 Reason Insufficient Probe Spacing

    Reqd to Avoid the Spheres of Influenceq p

  • Fall of Potential Test

    S i C b ? Spacing For Current Probe? Single ElectrodeS g e ect ode

    Minimum 5X Length of Rod Ideal, 10X Length of Rod

    10 Foot Rod, 50-100 Feet Away , y 200 Foot Well, 1000-2000 Feet Away

  • Ground Resistance Testing

    Clamp-on Resistance Testing Clamp on Ground Resistance MeterClamp-on Ground Resistance Meter Convenient, Quick, Easy

    i i i Does Not Require Disconnecting Equipment

    Measures Current on the Ground

    May Read Ground Loops vs. Ground ResistanceMay Read Ground Loops vs. Ground Resistancey py p

  • Clamp -on Meter Operation

    2 Control Xformers

    Current Flow

    R = E / I

    Current Flow??? ohms

  • ClampClamp--On Resistance Testing ExampleOn Resistance Testing Example3 Phase Utility 3 Phase Utility LineLine

    Service MeterService Meter

    Induced Current FlowInduced Current FlowInduced Current FlowInduced Current Flow

    Ground ConductorGround Conductor

    Ground RodsGround RodsCurrent From Other GroundsCurrent From Other Grounds C t F Oth G dC t F Oth G dGround RodsGround RodsCurrent From Other GroundsCurrent From Other Grounds Current From Other GroundsCurrent From Other Grounds

  • Invalid Clamp-on Reading

    Reading: < 1 Ohm

    Current Path

    gInvalid

  • THANK YOU FOR YOUR ATTENTION Please enjoy the rest of your time at thePlease enjoy the rest of your time at the

    2013 BICSI Fall Conference & ExhibitionRoy Chip Whitten

    Senior Applications Engineer/Education Specialistpp g / pLyncole Grounding Solutions, LLC

    800-962-2610

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