soil resistivity and grounding system testing - roy whitten - lyncole xit grounding

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 manufacturer’s 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)

ρρ

= = 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

ohm

s)

125135145

y

ista

nce

(o

758595

105115125

Res

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

– Req’d 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