critical facilityyg grounding - bicsi · pdf fileagenda – common groundcommon ground...

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


– What Two Factors Determine Ground System Resistance??

– Soil Resistivity ( P )

– Size of the Grounding System ( A )


– 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


– 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


– 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


– 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


– Design Alternatives?

– NomographIEEE T bl

g

– IEEE Table– Software Programs


– 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


– Required Equipment

– 3 / 4 Pole TesterAEMC / Megger

q q p

– AEMC / Megger

– Test Kit– Probes

Conductor– Conductor– Tape Measure


3 Pole MeterCurrent Flow

R=E/I

Voltage

RemoteCurrentEl t d

Drop

Earth

Neutral Electrode


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


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


??? 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


Neutral-Ground

Utility Neutral LineParallel Paths

Bond

Grounding G ou d gConductor

Series Loop

???Current Flow R = E/I???Current Flow R = E/I


Neutral-Ground

Utility Neutral LineInvalid Ground

Bond

Grounding

Clamp-On Test

Grounding Conductor

Additional Grounding Conductor

???R = E/I

Current Flow

???R = E/I


– 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 @[email protected]

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