Electrical Grounding Group (CADWELD)

Grounding & Bonding
The Foundation For Effective Electrical Protection
January 24, 2006
Tuesday 2:15-3:00 PM
Curtis R. Stidham
Harger Lightning & Grounding

Objectives
• Define the difference between grounding & bonding and to
describe the roles they play in providing protection for
personnel and equipment.
• Define the role of grounding & bonding as the key element
for an effective electrical protection and power quality
system.
• Present the different types of equipment & products used to
implement an effective grounding and bonding system.

Outline
• Grounding & Bonding
– What is Grounding & Bonding?
– Why do we Ground?
– Different types of Ground Systems
– Hazards & Safety
– Relevant Standards
• Ground Electrode System
– What makes up the system?
– Results from NFPA - NEGRP
– Connections (Critical Element)

Outline
• Grounding and Bonding Applications
– Power Systems
– Lightning Protection
– Computer Installations

Foundation of Protection
Lightning
Protection
Surge
Suppression
Bonding
Grounding

Key to Systems Approach
• Protection systems are not independent.
• Lightning Protection and Surge Suppression Systems rely on a good
grounding & proper bonding for effective performance.
• Grounding & bonding are not always well understood in their application.
• Improper grounding & bonding is commonly the root cause of Power
Quality Problems.

Risks of Not Providing Protection
• Human safety
• Equipment damage
• Downtime and loss of operations
• Customer dissatisfaction about reliability
• Loss of revenue and service

What is Grounding?
• Definition: (IEEE 100)
A conducting connection, whether intentional or
accidental, by which an electric circuit or
equipment is connected to the Earth, or to some
conducting body of relatively large extent that
serves in place of the Earth.

What is Grounding?
• Purpose:
– Used for establishing and maintaining the
potential of the Earth or approximately that
potential, on conductors connected to it.
– Conduct ground current to and from the Earth.

Why Ground?
Required by CODE (NFPA 70 - NEC Article 250)
• The National Electrical Code, NFPA-70, addresses
proper electrical systems and equipment installation
to protect people and property from hazards arising
from the use of electricity in buildings and structures.

Why Ground?
Personnel Safety
Reduce Potential Differences
Between enclosures
Between enclosures and Earth

Why Ground? Personnel Safety
Current Ranges
• 1-6 mA, (often referred to as let-go currents)
– unpleasant
– Does not impair control of muscles
• 9-25 mA
– may be painful
– difficult or impossible to release energized objects grasped by the hand
• 60-100 mA
– ventricular fibrillation
– stoppage of the heart
– inhibition of respiration might occur

Why Ground? Personnel Safety
ANSI/IEEE Std. 80-2000
• Step Potential: Difference in surface potential
experienced by a person’s feet bridging a
distance of 1m without contacting any other
grounded surface.
• Touch Potential: Potential difference between
GPR and the surface potential at the point
where a person is standing, while at the same
time having hands in contact with a grounded
structure.
MOST DANGEROUS

Why Ground? Personnel Safety
• Step Potential: Controlled by
properly designed ground electrode
system (grid) or the use of wire mesh.
• Touch Potential: Controlled by
proper bonding and protective
systems such as personnel safety
mats.
Bonding Conductor
Safety Mat
Flexible Braid
Switch Handle Bond

Why Ground?
• Equipment Protection
– Operate over-current devices during a ground fault.
– Provide over-voltage control.

Why Ground?
• Lightning Protection Systems (Dissipate Energy)
NFPA 780

Why Ground?
• ESD (Electrostatic Discharge)

Why Ground?
• Signal Reference Grounding – Noise Control
IEEE Std 1100 (Emerald Book)
Powering and Grounding Electronic Equipment

Summary:
Why Ground?
• Human Safety
• Protect Equipment
• Lightning Protection
• Electrostatic Discharge
• Signal Reference Grounding

Relevant Standards & Codes
• NFPA 70 National Electric Code
• IEEE Std C2 National Electric Safety Code
• NFPA 780 Standard for the Installation of Lightning Protection Systems
• ANSI/J-STD-607-A-2002 Commercial Building Grounding (Earthing) and
Bonding Requirements for Telecommunications
• ANSI T1.313-2003 Electrical Protection for Telecommunications Central
Offices and Similar Type Facilities

Relevant Standards & Codes
• IEEE Std 80 Guide for Safety in AC Substation Grounding
• IEEE Std 142 (Green Book): Recommended Practice for
Grounding of Industrial and Commercial Power Systems
• IEEE Std 602 (White Book): Recommended Practice for
Electric Systems in Health Care Facilities
• IEEE Std 1100 (Emerald Book): Recommended Practice for
Powering and Grounding Electronic Equipment

Equipment Grounding
• Purpose:
• Provide Personnel Safety
• Means:
• Interconnecting all non-current carrying metal
components to eliminate potential differences between
them. (raceways, cabinets, frames, cable armor,
building steel, etc…)
• Connecting the equipment grounding conductor to
Earth will eliminate potential differences between metal
components and Earth.

Equipment Grounding
(Personnel Safety)

System Grounding
• Purpose:
• Provide equipment protection by operating over-current
devices to clear fault current and providing a potential
reference.
• Means:
• An intentional connection to equipment ground from
one of the current carrying conductors of an electrical
distribution system.

System Grounding
(Equipment Protection)

Effective Grounding Path
NEC 250
• The path to ground from circuits, equipment, and metal
enclosures for conductors shall (1) be permanent and electrically
continuous, (2) have capacity to conduct safely any fault current
likely to be imposed on it, and (3) have sufficiently low
impedance to limit voltage to ground and to facilitate the
operation of the circuit protective devices.
• The Earth shall not be used as the sole equipment grounding
conductor.

Earth as Equipment Grounding Electrode
Unacceptable / Code Violation

What is Bonding?
• Definition: (NEC 250)
The permanent joining of metallic parts to form an
electrically conductive path that will assure
electrical continuity and the capacity to conduct
safely any current likely to be imposed.

Bonding
• Interconnect ALL Ground Electrode Systems
– Electrical Grounding System
– Lightning Grounding System
– Telecommunications Grounding System
– Cable Grounding System
• Interconnect ALL conductive objects together both internal
and external to the facility
• Provides near zero voltage difference during GPR

Bonding
• Poor bonding is often the principle cause of many
hazardous and noise-producing situations.
• Leading to:
– Unacceptable Voltage Drops
– Heat Generation
– Intermittent Operation
– Electrical Noise
– High Resistance Grounds

Bonding Components:
• Conductors
• Connectors/Clamps/Lugs
• Ground Bars

Bonding Components:
• Equipment Ground Plates
• Fence Clamps and Gate Jumpers
• Equipotential Mesh and Mats

Bonding Components:
• Signal Reference Grids
• Coaxial Ground Kits

Ground Electrode System
• Soil
• Ground Electrode Conductors
• Connectors
• Electrodes

Soils
• Soil Resistivity - Some soils, (such as sandy soils), have such high
resistivities that conventional ground rods or ground electrode systems
may be unable to attain the desired ground resistance requirement.
Enhanced ground electrodes or ground enhancement materials may be
required to meet the grounding specification.
• Soil PH/type - PH a factor in choosing. Some ground rod types work
better in different soils.
• Soil Characteristics - Some sites may have only a few inches of soil (or
none) sitting on top of bedrock. In this case, ground mesh is the preferred
electrode. (Never drill into bedrock).

Soil Conditions
• Soil Resistivity Must Be Carefully Considered, Including
Moisture Content and Temperature.

Grounding Electrode System
NEC 250.52
Formed by bonding all of the following:
• Metal underground water pipe (soil contact at least 10’)
• Building steel
• Concrete encased electrode (Ufer Ground)
• Ground ring
• Made and other electrodes
• Local underground systems or structures, piping, tanks, well
casings
• Rod & Pipe electrodes
• Plates electrodes

Ground Electrodes
• Electrodes must be of proper material and cross section to
provide a low impedance path to fault current without fusing.
• Many Types of Electrodes are Available
• Driven Ground Rods
• Pole Butt Plates (Distribution Poles)
• Ground Plates
• Counterpoise Wires
• Foundations (UFER GROUNDS)
• Electrolytic (Enhanced) Ground Rods

NEC 250: Resistance of Made Electrode
• Single Electrode
– R = 25 ohms or less
– R > 25 ohm, a second electrode is installed
• Electrodes at least 6 feet apart

Electrode Considerations Cont..
Ground Rod Diameter - Doubling
diameter reduces resistance only 10%.
Ground Rod Length - Doubling length
reduces resistance 40%, actual
reduction depends on soil resistivities
encountered in multi-layered soils.
Ground Rod Spacing - Approximately
twice the length. (in good soil).
RESISTANCE, %
RESISTANCE, OHMS
600
500
400
300
200
100
120%
100%
0
80%
60%
40%
20%
RESISTANCE VS ROD DIAMETER
RESISTANCE %
0%
0.500 0.625 0.750 0.875 1.000 1.125 1.250 1.375 1.500
ROD DIAMETER, INCHES
RESISTANCE VS ROD DEPTH
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
ROD DEPTH, FT
1/2 ROD OHMS
1" ROD OHMS

Ground Rod Spacing
¾” x 10’ Rod
• One Ground Rod
R = 32 Ω
ρ= 100 Ωm
• Two Ground Rods
• Spacing = 20’
R = 17.4 Ω

Electrode Considerations
Ufer Grounds - Concrete encased electrode.
For example, tying into the tower footing
rebar or building pad rebar provides a Ufer
ground. Ufer grounds should never be used
as the sole ground electrode.
Copper Ground Mesh - Used to augment the
grounding system. The mesh can be
strategically placed to protect personnel
against step and touch potentials.

Conductive Backfill
Vertical Application Horizontal Application

Enhanced Ground Rods
Contain electrolytic salts that lower soil resistivity over time

Galvanized Ground Rod (5/8”x10’)
NFPA - NEGRP Pawnee Site
10 years in the ground

Copper Clad Steel Ground Rod (5/8”x8’)
NFPA - NEGRP Pawnee Site
10 years in the ground

Horizontal Cu-Clad Steel Ground Rod in GEM ®
NFPA - NEGRP Pawnee Site
• This electrode (5/8”x8’) and the connections were completely enclosed in GEM.
• The 1’ long bent portion of the ground rod was completely corroded away up to
the exothermic connection. The remaining ½” long portion of the ground rod and
the exothermic weld was connected with less than one strand of wire.
• The mechanical connection was also very corroded.
• Only small sections of the rod were found within the GEM due to significant
corrosion of the ground rod.

Leads
Bent Portion of
Rod Missing
Only Copper
Coating Remains
at this Point
Remaining
Portion of Rod
Horizontal Cu-Clad Steel Ground Rod in GEM ®
NFPA - NEGRP Pawnee Site
10 years in the ground

Horizontal Cu-Clad Steel Ground Rod in GEM®
NFPA - NEGRP Pawnee Site

Ground Conductor Considerations
Sizing - withstand maximum fault current for the maximum clearing time.
Inductance - Flat strap conductors have less inductance than their
similarly sized round conductor counterparts.
Strength/Durability - Round conductors are much stronger than thin flat
strap conductor. This should be a consideration when backfilling
trenches.
Exothermic Connections - Preferred type of connection.

Effect of Inductance
For 1 meter of 4/0 conductor:
L = 1.02 µH R = 0.16
mW
Voltage Rise:
dI
V = ( L × ) + ( R × I )
dt
R L
Conductor Model
For a strike of Imax = 18,000 A in 1µsec
−6
18000
−3
V = ( 1.
02 × 10 × ) + ( 0.
16 × 10 × 18000)
−6
1×
10
= 18,360 + 3 Volts/meter of conductor
Inductive Term Greatly Dominates Resistive Term

Connectors
• Connections must be of proper material and mass, and be
able to resist corrosion to maintain original low resistance
for the life of the system.
• Types
• Exothermic
• Mechanical
• Compression

What is Lightning?
Consider Lightning a Gigantic Electrical Spark traveling between Cloud to Cloud
or Cloud to Earth containing an average Charge of 30 to 50 Million Million
Volts and a
Current of 18,000 Amps.

Basic Principles of Lightning Protection
• Intercept the Lightning Discharge
• Safely Conduct the Lightning Currents
• Minimize the Effects of Lightning Currents
• Dissipate the Lightning Currents in the Earth

Lightning Surface Arcing

NFPA 780 Lightning Protection Standard
• Scope - This document shall
cover traditional lightning
protection system installation
requirements for ordinary
structures, misc. structures,
special occupancies, etc.

Risks Posed from a Direct Strike

Risks Posed from an Indirect Strike

Basic LP Components
• Air Terminals
• Lightning Conductors
• Ground Terminals
• Connectors/Fittings
• Surge Suppression Devices

Lightning Characteristics
Lightning - High frequency (approx. 1 megahertz) electrical
discharge carrying on average 18,000 amps and 30 million
volts. Time duration of event is measured in microseconds.
Lightning Conductors - Multiple, parallel low
impedance paths sufficient enough to carry lightning
currents safely to ground terminal system. Minimum
standard requirements set by UL96A & NFPA 780.
* Due to its high frequency & voltage, lightning does not
like to stay on one conductor. Therefore, multiple parallel
paths are critical!!!

Characteristics of Electricity
Electricity - low frequency (60 Hz) low voltage (

In other words…..
A lightning ground does not equal a “green wire” ground!!!!!

Lightning
• Lightning Travels on the outside surface of a conductor, the
so called “skin affect”. Therefore, the larger the surface area
of a conductor and not necessarily the cross sectional area, the
better path it makes.
• Remember, multiple parallel paths are very important. The
fewer paths you have the larger the surface area or diameter
the conductor needs to have.

Lightning Conductor Types
Solid conductors -
Difficult to work with
Concentric strand - Next
easiest to work with
Rope Lay LP - Easiest to
work with
Flat strap - least
inductance; hardest to
work with

Lightning Conductor Routing & Placement
General rules of Thumb for Routing:
• Maintain downward sloping path to ground
(equipotential bonds exception)
• Do not run conductors uphill (1/4 rise
acceptable to a point)
• Maintain at least an 8” radius of bend

To Comm.
Equipment
Drain Pipe
Ground
From
Antenna
• Uphill path to
ground
• Radius of bend less
than 8”
• Bonding issue
• Water pipe?

Lightning Surface Arcing

Lightning Ground Systems
• Provide multiple ground paths for lightning energy
• Radials effectively lower impedance (R & X L)
• Divert lightning energy away from equipment shelter
• Maximum Radial Length of 90’ for Lightning Effectiveness
• Use Radials of different lengths

Computer Installations
Grounding System – Four
Distinct Subsystems
• NEC Compliant Fault/Personnel
Protection Power System Ground
(including surge suppression)
• Lightning Protection subsystem
(per NFPA 780)
• Telecom, data transmission, and signaling circuit surge protection
grounding subsystem.
• Signal Reference Structure

High Frequency Grounding System
• Reduces or eliminates high
frequency transients by
achieving a common ground
reference for all equipment
within a contiguous area.
• Consists of a Signal Reference
Grid, low-impedance bonding
straps, transient suppression
plates and bare copper bonding
conductors.

Why a High Frequency Grounding System?
• Most computer systems today run on
roughly a 3 volt operating system. A
transient of just one volt can cause
serious data errors. (Transient Over-
Voltages).
• It is imperative to tie all equipment
together with a low impedance
“signal reference” bonding system to
keep any voltage differences at a
minimum.

Sources of Transient Over-voltages
• Lightning Induced Surges
• Power Systems Operations
• Power System Faults
• Reactive Load Switching
• Harmonics
• Ground Potential Rise

Transients May be Induced onto:
• Power Lines
• Telephone Lines
• Data Signaling Lines
• RF Feeders
• Building Structural Members (lightning)
• Differential Grounds

Signal Reference Grid (SRG)
• Function: Minimize voltage differences between
interconnected equipment by providing a low
impedance equipotential ground plane for high
frequency low voltage noise.

SRG Types
• Round Conductor
– Easier to install when retrofitting an
existing raised floor system.
• Flat Strip
– Superior system. (Less impedance than
round conductors; very important at
high frequencies).
– Less labor to install.

Grounding & Bonding
The Foundation For Effective Electrical Protection
January 24, 2006
Tuesday 2:15-3:00 PM
Curtis R. Stidham
Harger Lightning & Grounding