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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.