critical facility grounding - john howard - lyncole xit grounding
TRANSCRIPT
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Critical Facility Groundingy g
XIT GROUNDINGXIT GROUNDING
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Agenda
Common Ground Importance / PyramidCommon Ground Importance / Pyramid
Grounding Resistance Defined
Site Specific Design Achieving 5 Ohms?
Electrode Choices Pros / Cons
Ground System Testing Why 95% is Invalid
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Why Ground?
Equipment Protectionq p
Satisfy Warranty Requirements
Service Protection
System Performance
Personnel Safety (NEC)
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Electrical Protection Systems
Protection Pyramid
Surge C ll t
RFCollectorsAC Surge
Telco / Data
LightningGroundingGrounding
Surge Dissipater
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Typical Performance Reqs
National Electrical Code (NEC) < 25 OHMS a o a ec ca Code ( C) 5 O S
IEEE Standard 142 Equipment D d t
Practical Safeguarding of..
Dependent IEEE Standard 1100 < 5 OHMS
Motorola Standard R-56 < 10 OHMS
Verizon Wireless 8501 < 5 OHMS
Typical Telecom Switch < 2 OHMSTypical Telecom Switch 2 OHMS
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Ground System Resistance
Defined!!Ground System Resistance?
Finite Resistance between the Ground System and Remote EarthGround System and Remote Earth
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Ground System Resistance
What Two Factors Determine Ground System Resistance??
Soil Resistivity ( P )
Size of the Grounding System ( A )
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Ground System Resistance
How Are They Related? The Relationship
R P / A
y p/ Simple Formula
R = P / AR = Ground System ResistanceR = Ground System Resistance
P = Soil ResistivityP Soil ResistivityA = Effective Cross Sectional
Area of The Ground System
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Ground System Resistance
With Only Two Elements, Why is
P
y yResistance Difficult to Design/Predict?
P - Varies with Depth/Location Of SoilOf Soil
A - Determined by Size / ConfigurationOf The Grounding System
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T fTypes ofGrounding ElectrodesGrounding Electrodes
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Types of Grounding Systems
Driven Rods Ground Enhancement Materials
Copper Platespp Chemical Wells Ufer GroundsUfer Grounds Building Steel
Ground Ring Ground Ring Water Pipes
XIT El t l ti S t XIT Electrolytic Systems++
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S il R i i iSoil ResistivityTestingTesting
(Determining P)
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Soil Resistivity Testing
4-Pt. WENNER METHOD
R=E/I
METHOD
4-Pole Digital
R=E/Ig
Ground Tester
Voltage Drop
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= 1 915 ARSoil Resistivity Testing
5 52 00 497 90
= 1.915 ARProbe Spacing Meter Reading Resistivity
5 52.00 497.90
10 19.68 370.87
15 10 16 292 0015 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
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Soil Resistivity Testing
Site Area
Direction of Test
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Grounding System Design
Grounding Calculationsg
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Grounding System Design
The Simple Formula:
R = P / Ap
R = Ground System Resistance P = Soil ResistivityA = Effective Cross Sectional
Area of The Ground SystemArea of The Ground System
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Grounding System Design
The Simple Formula:
R = P / Ap
R Is Known (Required Ohms, 5?)P P Is Known (Soil Resistivity)P & R A U d T D t i A
A P / R P & R Are Used To Determine A
A = P / R
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Grounding System Design
Design Alternatives?
NomographIEEE T bl
g
IEEE Table Software Programs
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Grounding System Design
Properly Designed System Benefits? Predictable Results
p y g y
Improved Personnel Safety
Improved Equipment ReliabilityImproved Equipment Reliability
Improved Equipment Performance
Improved Power Quality
Meet Mfgs Warranty RequirementsMeet Mfg s Warranty Requirements
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Grounding System Resistance Testing
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Ground System Testing
Why Test Grounds?y
Determine Baseline
Confirm Design Spec Validate Construction
Satisfied Satisfy Warranty Reqs Ensure Equip Protection & Performance
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Ground System Testing
Two Test Methods
Fall Of Potential Test - Inserting Current / Measuring Voltage
Clamp-On Test - Inducing Voltage / Measuring Current
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Fall of Potential Test
Advantageg Recognized As Accurate Most Commonly Utilized (IEEE Std 81)
DisadvantagesR lt F tl I lid (75 %)X
(95+%)
y ( )
Results are Frequently Invalid (75+%)X Requires Isolated Ground System Requires Large Area
Time Consuming Access To Soil
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Fall of Potential Test
Required Equipment
3 / 4 Pole TesterAEMC / Megger
q q p
AEMC / Megger
Test Kit Probes
Conductor Conductor Tape Measure
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Fall of Potential Test
3 Pole MeterCurrent Flow
R=E/I
Voltage
RemoteCurrentEl t d
Drop
Earth
Neutral Electrode
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Fall of Potential Test
195
155165 175
G d R i t (Pl t )
185 195
Resistance
115125 135 145 155 Ground Resistance (Plateau)
7585 95
105 115
Voltage Probe Spacing (%)
55 65 75
0 10 20 30 40 50 60 70 80 90 100
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Fall of Potential Test
You are testing every
d i
Neutral Connected
Currentground in parallel.
Connected
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Fall Of Potential TestNeutral Connected
Ohms
Neutral Connected
Invalid
Test With Neutral Connected20
Test GraphPlot For
5 Oh G dPlot For
25 Oh G dPlot For
100 Oh G dPlot For
1000 Oh G d
15
5 Ohm Ground25 Ohm Ground100 Ohm Ground1000 Ohm Ground
5
10
Distance (Ground-Probe)
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Clamp-On Resistance Test
Advantages Quick and Easy
No Disconnecting Neutral No Disconnecting Neutral
No Long Leads, Property
Disadvantage Ground Configuration Ground Configuration
Finding Proper Location To Test
Invalid Most Of The Time
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Clamp-On Resistance Test
??? ohms 2 Control Xformers
R = E / IR = E / I 2 Control Xformers
One Induces 4 mvOne Induces .4 mv
One Measures Current Flow
Current Flow
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Clamp-On Resistance Test
Neutral-Ground
Utility Neutral LineParallel Paths
Bond
Grounding G ou d gConductor
Series Loop
???Current Flow R = E/I???Current Flow R = E/I
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Clamp-On Resistance Test
Neutral-Ground
Utility Neutral LineInvalid Ground
Bond
Grounding
Clamp-On Test
Grounding Conductor
Additional Grounding Conductor
???R = E/I
Current Flow
???R = E/I
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Clamp-On Resistance Test
Main Reasons For Invalid Testingg
Fall Of Potential Test - Must Isolate Ground from Neutral
Clamp-On Test - Must have Single Point Ground
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Ground Resistance Testing
Contributing Reasons For Invalid Testing
Grounding / Testing Not Taught
g g
IEEE G id / P d W k
Not Many Good Courses Available
IEEE Guidance / Procedures Weak
Mfgs Procedures Weak / WrongMfg s Procedures Weak / Wrong
Old Habits / Bad Assumptions / Pressure
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Ground Resistance Testing
How To Improve Testing Results? Insist On Training
p g
Dont Insist On Results
Test Prior To Connecting Power
Design Facility For Testing
Dont Depend On Mfgs Procedures
Test Prior To Connecting Power
p g
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Lyncole XIT GroundingPhone 1-800-962-2610
Fax 1-310-214-1114Fax 1-310-214-1114www.Lyncole.com