BEYOND THE GREEN WIRE
Is grounding science, art or black
magic?
Science – having the data and
knowledge to competently design a
system
 Art – always possible to manipulate a
design for a more elegant solution
based on factors such as budget or the
environment
 Black magic – the perception created
with gaps in knowledge / understanding

We must choose a perspective
BYNUM’S 5 LAWS OF ENGINEERS
 An engineer is empirically oriented
 An engineer is data driven
 An engineer in one way or another sells
his/her time and expertise
 Liability concerns
 Due diligence issues

Grounding, bonding, surge,
lightning
Cannot be treated discretely
 Each is an element of a coherent whole
 All may not be necessary but none can
be manipulated separately

Why grounding / earthing?
References a structure to the
environment – potentials rise and fall
together
 Set points for circuit breakers
 Fuse selection
 Defines and identifies ground reference
for ground fault and arc flash relays
 Coordination of the system

Where to start?
Whether in design, forensics or rehab
take a line from medical ethics
 “First do no harm”

Using the first two points of
Bynum’s Law
Engineers are compelled by training and
discipline to design TO something
 Anything else may be an educated
guess, informed guess or lucky guess…
but still a guess
 With grounding we design between what
we want or need and what the
environment allows

Point #2 of Bynum’s Law

When the required data is not available
the tendency becomes using a formerly
successful “boilerplate” design or to
“overdesign” effectively becoming a
guess
Standards
IEEE Std. 80 (1986)
 IEEE Std. 142-2007 (Green Book for
Commercial / Industrial Facilities)
 IEEE Std. 1100-2007 (Emerald Book for
Electronics)

The perfect world
The engineer will have a certified “start
point” in the form of results from a soil
resistivity test
 Fairly reliable predictor of grounding
electrode performance

Soil Resistivity Tests
4 Point Wenner Method Test developed
in 1915 by Dr. Frank Wenner of NIST for
U.S. Bureau of Land Management
 Most accurate test
 Used by civil engineers to locate water
table but CE test protocol may be
problematic for the electrical engineer

Soil Resistivity Tests
Schlumberger Array developed by
Conrad Schlumberger of France in the
2nd decade of the 20th century
 These are typically “green field” tests

Factors affecting resistivity
Moisture
 Temperature (Sandy loam with a 15.2%
moisture content @ 32 deg. F [ice] has
almost 3 times the resistivity of the same
sample @ 32 deg. F [water])
 Soil type – it has been reported the
Metroplex has over 250 separately
identifiable soil types

Factors affecting resistivity
Depth – varies with soil type, moisture
content and freeze line
 NOTE! There is a very real
correspondence between resistivity and
corrosion issues
 Electrolytes in the soil (active, pH
issues)
 Pollution issues

Rules of thumb
Most useful when talking about thumbs
 Designs generally specify 18” deep and
18”-24” outside of slab (drip line)
 At 18” the conductor merely connects
the electrodes
 30” and below (due to moisture content
and freeze line) the conductor begins to
act as an electrode in and of itself

Design Considerations
Types of Grounding Systems
 Facility Layout
 Conductor & Electrode Materials
 Special Considerations

Types of Grounding Systems
Solidly Grounded
 Low Resistance Grounding
 High Resistance Grounding
 Ungrounded

System Layout
Grid
 Counterpoise
 Instrumentation – Dedicated System

Conductor Materials
Copper or Tinned Copper
 Aluminum

Braided
 Concentric

Insulated
 Bare

Electrode Materials
Galvanized Steel
 Copperclad Steel
 Zinc or Magnesium Solid Shapes
 Graphite
 Chemically Enhanced Ground Rod
 Ufer

Special Considerations
Risk of Copper Theft
 Soil Reactivity
 Raw and Finished Products of Facility
 Depth of Conductors
 Cathodic Protection Systems
 Other Utilities

Acceptance & Maintenance
Grounding is not an “Install & Forget”
 Acceptance Testing & Documentation
 Scheduled Testing & Maintenance

Why establishing a baseline
is important.
We have a problem.
Summary
Grounding is a fundamental
Infrastructure system
 Yes, it can be expensive to get right.
 It is more expensive to correct problems
after construction.
 It is most expensive when a ground
system failure causes injury, equipment
damage or loss of product.
