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Soil Resistivity and GroundingSoil Resistivity and Grounding Systems Testing

Roy “Chip” Whitten/Senior Applications Engineer/Education Specialist

Lyncole Grounding Systems, LLCIn lieu of paper evaluations for each session at the Winter Conference, all evaluations may now be taken digitally from your laptop, tablet or smartphone.

D l d h Wi C f A bi i /Download the Winter Conference App at www.bicsi.org/apps or go to www.bicsi.org/surveys to provide your feedback for each of the sessions you attend.

For your safety please note that emergency exits are located to the left or right ofFor your safety, please note that emergency exits are located to the left or right of this room.

What Is Grounding?

An 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 earth.

Reasons For GroundingReasons For Grounding

P l f d i i b– Personnel safety and equipment protection by providing a path to safely dissipate any unwanted charges or potentialscharges or potentials.

– Ensure equipment performance and protection

– Satisfy manufacturer’s warranty

Electrical Protection PyramidElectrical Protection Pyramid®®

RFRFAC SurgeAC SurgeAC SurgeAC Surge

Telco / DataTelco / Data

LightningLightning

GroundingGroundingGroundingGroundinggggg

Resistance To EarthResistance To Earth

25 Ohms

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

SoilSoilResistivity

Basics

Soil Resistivity

Key Variable in System Design

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

– Soil typeM i t– Moisture

– Electrolytes– Temperaturep

Soil Resistivity Comparison

Soil Type Resistivity (ohm-cm)

Surface Soils 100 - 5,000Clay 200 - 10,000Sand and Gravel 5,000 - 100,000Sand and Gravel 5,000 100,000Surface Limestone 10,000 - 1,000,000Limestone 500 - 400,000Sh l 500 10 000Shale 500 - 10,000Sandstone 2,000 - 200,000Granites, Basalts, etc 100,000Decomposed Gneisses 5,000 - 50,000Slates, etc 1,000 - 10,000

SoilSoilResistivity

Testing

Soil Resistivity Testing

– Key Variable in System Design– 4 Point Wenner Method

– Most Accurate– Multiple Depth Testingp p g

4-Pt. Wenner Method

– Visually Survey Lease Area to Determine Location and Direction For Test– 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 C1P1P1P2P2C2C2

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

AA

4-Pt. Wenner Method

Site Area

Direction of Test

4-Pt. Wenner Method

Probe Spacing Meter Reading Calculated Resistivity(Feet) (Ohms) (Ohm-Meter)

ρρ

= 1.915 AR

(Feet) (Ohms) (Ohm-Meter)

5 52.00 497.90

10 19 68 370 8710 19.68 370.87

15 10.16 292.00

20 6.53 250.10

30 4.30 247.04

40 10.80 827.28

60 7.40 850.26

80 5.58 855.60

100 4.44 850.26

Typical ypGrounding Electrode System

R i t R i tResistance Requirements

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

18,000A Potential Rise will be

~450KV at the site~450KV at the site

5 Ohm Grounding System

Lightning

StrikeStrike

18,000A Potential Rise will be

~90KV at the site~90KV at the site

Gro nding S stemGrounding System Resistance Testingg

Grounding System Testing

– Why Test Grounds?Why Test Grounds?

– Determine Baseline

– Confirm Design Spec

– Validate Construction

Confirm Design Spec Satisfied

– Satisfy Warranty ReqsSatisfy Warranty Reqs

– Ensure Equip Protection & Performance

Testing Methods

– Two Test Methods

− Fall of Potential (Three Point) Test

− Clamp-on TestClamp on Test

Fall-of-Potential Method

RemoteRemoteCurrentCurrentC1C1

C2C2

CurrentCurrentElectrodeElectrode

C1C1P1P1

P2P2 Auxiliary Voltage ElectrodeAuxiliary Voltage ElectrodeGround Ground RodRod

UnderUnder

EarthEarth11 ftft 110%0%220%0% 330%0% 440%0% 550%0%660%0%770%0%880%0% 990%0%

Under Under TestTest 1010 x depth of electrodex depth of electrode

Fall of Potential

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

– Visual Plateau– Confirms Test Validity

145

y

(ohm

s)

105115125135145

Res

ista

nce

65758595

105

R

5565

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

Fall Of Potential Test

– #1 Reason

Why Invalid?

#1 Reason– Not Isolating System Under Test

– Meter is a constant amperage meterp g– 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?

– #2 Reason– Insufficient Probe Spacing

R ’d A id h S h f I fl– Req’d to Avoid the Spheres of Influence

Fall of Potential Test

– Spacing For Current Probe? p g– Single Electrode

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

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

Ground Resistance Testing

Clamp-on Resistance Testing Cl G d R i t M tClamp-on Ground Resistance Meter– Convenient, Quick, Easy

Does Not Req ire Disconnecting– Does Not Require Disconnecting Equipment

– Measures Current on the GroundMeasures Current on the Ground

May Read Ground Loops vs. Ground ResistanceMay Read Ground Loops vs. Ground Resistance

Clamp-on Meter Operation

2 Control Xformers

Current Flow

R = E / IR = E / I

??? ohms

Current Flow

??? ohms

Clamp-On Resistance Testing Example

3 Phase Utility 3 Phase Utility LineLine

Service MeterService Meter

Induced Current FlowInduced Current Flow

Ground ConductorGround Conductor

Ground RodsGround RodsCurrent From Other GroundsCurrent From Other Grounds Current From Other GroundsCurrent From Other Grounds

Invalid Clamp-on Reading

Reading: < 1 Ohm

InvalidCurrent Path

Invalid

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

2014 BICSI Winter ConferenceRoy “Chip” Whitten

Senior Applications Engineer/Education SpecialistLyncole Grounding Solutions, LLC

800-962-2610800 962 2610

Soil Resistivity and GroundingSoil Resistivity and Grounding Systems Testing

Roy “Chip” Whitten/Senior Applications Engineer/Education Specialist

Lyncole Grounding Systems, LLCIn lieu of paper evaluations for each session at the Winter Conference, all evaluations may now be taken digitally from your laptop, tablet or smartphone.

D l d h Wi C f A bi i /Download the Winter Conference App at www.bicsi.org/apps or go to www.bicsi.org/surveys to provide your feedback for each of the sessions you attend.

For your safety please note that emergency exits are located to the left or right ofFor your safety, please note that emergency exits are located to the left or right of this room.