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Critical Facility Groundingy g
XIT GROUNDINGXIT GROUNDING
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
Why Ground?
– Equipment Protectionq p
– Satisfy Warranty Requirements
– Service Protection
– System Performance
– Personnel Safety (NEC)
Electrical Protection Systems
Protection Pyramid®
Surge C ll t
RFCollectorsAC Surge
Telco / Data
LightningGroundingGrounding
Surge Dissipater
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
Ground System Resistance
Defined!!Ground System Resistance?
Finite Resistance between the Ground System and Remote EarthGround System and Remote Earth
Ground System Resistance
– What Two Factors Determine Ground System Resistance??
– Soil Resistivity ( P )
– Size of the Grounding System ( A )
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 Resistivity
A = Effective Cross Sectional Area of The Ground System
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 / Configuration
Of The Grounding System
T fTypes ofGrounding ElectrodesGrounding Electrodes
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++
S il R i i iSoil ResistivityTestingTesting
(Determining P)
Soil Resistivity Testing
4-Pt. WENNER METHOD
R=E/I
METHOD
4-Pole Digital
R=E/Ig
Ground Tester
Voltage Drop
ρ= 1 915 ARSoil Resistivity Testing
5 52 00 497 90
ρ= 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
Soil Resistivity Testing
Site Area
Direction of Test
Grounding System Design
Grounding Calculationsg
Grounding System Design
– The Simple Formula:
R = P / Ap
R = Ground System Resistance
P = Soil Resistivity
A = Effective Cross Sectional Area of The Ground SystemArea of The Ground System
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
Grounding System Design
– Design Alternatives?
– NomographIEEE T bl
g
– IEEE Table– Software Programs
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 Mfg’s Warranty RequirementsMeet Mfg s Warranty Requirements
Grounding System Resistance Testing
Ground System Testing
– Why Test Grounds?y
– Determine Baseline
– Confirm Design Spec – Validate Construction
Satisfied– Satisfy Warranty Reqs– Ensure Equip Protection & Performance
Ground System Testing
– Two Test Methods
– Fall Of Potential Test - Inserting Current / Measuring Voltage
– Clamp-On Test - Inducing Voltage / Measuring Current
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
Fall of Potential Test
– Required Equipment
– 3 / 4 Pole TesterAEMC / Megger
q q p
– AEMC / Megger
– Test Kit– Probes
Conductor– Conductor– Tape Measure
Fall of Potential Test
3 Pole MeterCurrent Flow
R=E/I
Voltage
RemoteCurrentEl t d
Drop
Earth
Neutral Electrode
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
Fall of Potential Test
You are testing every
d i
Neutral Connected
Currentground in parallel.
Connected
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)
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
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
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
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
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
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
– Mfg’s Procedures Weak / WrongMfg s Procedures Weak / Wrong
– Old Habits / Bad Assumptions / Pressure
Ground Resistance Testing
– How To Improve Testing Results? – Insist On Training
p g
– Don’t Insist On Results
Test Prior To Connecting Power
– Design Facility For Testing
– Don’t Depend On Mfg’s Procedures
– Test Prior To Connecting Power
p g
Lyncole XIT GroundingPhone 1-800-962-2610
Fax 1-310-214-1114Fax 1-310-214-1114www.Lyncole.com
S @Support@Lyncole.com
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