National Electrical Grounding
Research Project
Technical Report
August 30, 2007
Prepared by: Travis Lindsey
Travis Lindsey Consulting Services Inc.
Prepared for:
The Fire Protection Research Foundation
1 Batterymarch Park
Quincy, MA 02169-7471
Foreword
The use of electricity has long been recognized as a potential hazard to people and
property. When an electrical system fails, the result can cause accidental electrocution,
fire, causality, and equipment damage.
The concept of circuit grounding for electrical systems was one of the more hotly
contested topics in the early history of electrification. In the early 1890’s, the New York
Board of Fire Underwriters had condemned the practice of grounding the neutral as a
dangerous practice. The Edison utility companies, on the other hand, found just cause to
ground their supply systems, even as others thought the utilities were doing this just to
save copper and money at the cost of an increased fire risk. The great debate continued
for over a decade, but in 1903 the National Electrical Code (NEC®) was revised to
recommend that certain circuits be grounded, and finally in the 1913 NEC® a mandatory
circuit grounding requirement was included for these circuits. [1]
One of the most common ways to ground a wiring system has been to use the building’s
metal water piping as a grounding electrode. The early Codes permitted water-piping
systems of 3 ohms or less to ground to be used as an electrode, which was usually the
case if the metal water pipe extended several feet into the ground. In 1923, the NEC®
first mentioned driven rod or pipe electrodes. The 1925 NEC® further referred to these
driven electrodes as “artificial” electrodes, and required them to be at least 8 feet long,
with minimum diameters of ½ in. for a rod and ¾ in. for pipe. It also noted that if only
one of these artificial electrodes had a resistance of greater than 25 ohms to ground, then
two artificial electrodes had to be provided, spaced at least six feet apart. In subsequent
years, and in recognition of the increased use of non-metallic water pipe, requirements
were added to the NEC® to supplement the water-pipe electrode with an additional
electrode or electrodes. [1]
The practice of grounding (earthing) electrical systems to buried electrodes has been
recognized for decades by the National Fire Protection Association (NFPA) and other
safety standards development organizations as the recommended method to safeguard
against people and property becoming the accidental electrical connection to the earth.
There is ample evidence that accidental contact with earth can cause stray voltages, and
dangerous errant current flows. The electrical system’s grounding electrode provides the
system with a predetermined, and calculable path, to channel away dangerous currents,
and reduce electrical hazards. In the absence of an effective grounding electrode, the
stray voltages or path of any ground currents often must be determined forensically after
an accident has occurred, by site survey, computations, and subjective opinion.
Today, the NEC® recognizes electrical system grounding as an effective means to limit
the voltage imposed by lighting, line surges, or unintentional contact with higher-voltage
lines, as that will stabilize the voltage to earth during normal operation. The NEC does
not include requirements for or the instruments to be used in testing the performance of
the grounding electrode, thus, many default conditions could exist with simply two
electrodes. In some soil conditions, two electrodes may produce a resistance to earth far
in excess of 25 ohms, and that would still be acceptable.
ii
There are many unknowns in predicting how each of the many types of electrodes may
perform their intended purpose of providing proper electrical grounding. Factors which
may relate to performance of the electrode include: earth resistivity, earth chemistry,
earth moisture, earth temperature, electrode resistance, weather or seasonal changes in the
moisture of the earth, the current carrying capability of the electrode in earth, corrosion,
material comprising the electrode, and mass of the electrode. The repeatability and
reproducibility of the measurement of several of these factors can often not be accounted
for to any great extent.
The longevity of an electrode is another issue that cannot be easily addressed in
installation codes or performance standards. Electrodes are rarely re-tested after
installation, and rarely replaced or augmented. Electrodes may be damaged by lightning,
direct impressed currents, corrosion or mechanical means.
This report includes basic information which can be used by professionals who design,
construct and install grounding systems and components, and for those who develop
codes, standards or specifications. Those who work with grounding should understand
that the grounding electrode resistance to earth can fluctuate. The resistance can fluctuate
with the seasonal variations of soil temperature and moisture. In addition, the inherent
conductivity of the soil can vary between different locations due to the natural chemical
makeup and physical characteristics. This report documents the variation of grounding
electrode earth resistance at different geographic locations and explores the effects of
several of the dominant variables over a period of ten years. The data in this report
including the electrode resistance, ancillary experiment results, soil characteristics and
the corrosion data shown in Appendix 11.3, provides important information for designers,
manufacturers and regulatory officials on the performance of grounding electrodes and
components.
iii
TABLE OF CONTENTS
1. INTRODUCTION
1.1. Background/Chronology
1.2. Objectives
1.3. Scope
2. TEST SITES
3. ELECTRODE TEST SAMPLES
3.1. Electrode Legend
3.2. Electrode Details
4. EXPERIMENTS and METHOD
4.1. Sample Preparation
4.2. Installation and Exhumation
4.3. Electrode Resistance
4.4. DC Active Experiments
4.5. Dissimilar Metals Passive Experiments
4.6. Earth Resistivity
4.7. Soil Moisture
4.8. Soil Temperature
4.9. Passive Metal Corrosion
5. INSTRUMENTATION
5.1. Earth Testers
5.2. Multi-Meters
5.3. DC Current Probe
5.4. Thermocouple Thermometer
5.5. Moisture Meter
6. RESULTS
6.1. Electrode Resistance
6.1.1. Percentage of Readings Exceeding Certain Values
6.1.2. Resistance of Individual Electrodes at all Sites
6.1.3. Vertical and Horizontal Electrode Resistance- Las Vegas Sites
6.1.4. Vertical and Horizontal Electrode Resistance- National Sites
6.1.5. Comparison of Electrode Resistance
6.2. Ancillary Experiments
6.2.1. DC1 and DC2 Results
6.2.2. Dissimilar Metals Results
6.2.3. Benign Corrosion Experiments
6.3. Soil Characteristics
6.3.1. Earth Resistivity
6.3.2. Earth Resistivity versus Resistance for Selected Electrodes
6.3.3. Soil Temperature
6.3.4. Earth Resistivity and Soil Temperature
6.3.5. Soil Moisture
6.4. Corrosion Results
7. SUMMARY
8. AREAS of FURTHER STUDY
9. LIST OF FIGURES
10. CITATIONS
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pg. 1
pg. 2
pg. 4
pg. 4
pg. 5
pg. 6
pg. 6
pg. 10
pg. 18
pg. 18
pg. 18
pg. 19
pg. 19
pg. 20
pg. 20
pg. 20
pg. 20
pg. 20
pg. 22
pg. 22
pg. 22
pg. 22
pg. 22
pg. 22
pg. 24
pg. 25
pg. 25
pg. 29
pg. 34
pg. 47
pg. 56
pg. 83
pg. 83
pg. 92
pg. 96
pg. 97
pg. 97
pg. 98
pg. 100
pg. 105
pg. 109
pg. 114
pg. 117
pg. 120
pg. 122
pg. 125
11. APPENDICES (on CD)
11.1 Electrode Graphs Las Vegas
11.2 Electrode Graphs National
11.3 Corrosion Report
11.4 Exhumation Reports
11.5 Soils Reports
11.6 National Sites Construction Plans
11.7 Las Vegas Sites Construction Plans
v
1 INTRODUCTION
The practice of connecting electrical systems to earth using grounding electrodes has
historically been the preferred means to safeguard against results of accidental contact of
electrical power to earth.
Previous research by the National Association of Corrosion Engineers Task Group T-4A3, “Methods and Materials for Grounding” (1966) and Naval Civil Engineering
Laboratory, Technical Report R660, “Field Testing of Electrical Grounding Rods”
(1970) indicated some degree of variability in the performance of commonly used types
of grounding electrodes.
In 1995, the National Electrical Grounding Research Project (NEGRP) was created by
the Fire Protection Research Foundation (FPRF) to study this issue, and a technical
advisory committee (TAC) was formed. The purpose of the TAC was to develop the
scope, implement the site installations, make critical decisions during the term of the
project, and insure that annual and final reports were issued.
The project, which was managed by FPRF, evaluated many types of grounding electrodes
in differing geographies to provide comparative results for a broad range of conditions,
and to study electrodes over extended periods of time. This involved recording periodic
measurements of electrode performances, and recording of soil conditions over the period
of the study.
Some features of the project included electrode resistance, earth resistivity, earth
temperature, earth moisture, and effects of direct current on electrodes. After being
buried for extended periods, some electrodes at selected sites were exhumed for corrosion
analysis, and observation.
Throughout the term of the project, the FPRF issued ten annual data collection reports
beginning in 1995. (Available from FPRF)
This report and its appendices includes background, data, results, summaries, and areas
for further study.
1
1.1 Background/Chronology
The research project was initiated as an effort to identify, and provide resolution for issues
related to electrical grounding. In 1990, the Southern Nevada Chapter of the International
Association of Electrical Inspectors (IAEI /SNC) initiated a study of buried grounding
electrodes.
Materials, labor, instrumentation, and maintenance needed for the IAEI study were donated
by individuals, members at large, and by manufacturer participants whose products were
included in the study.
The scope of the study initially encompassed five test sites in the Las Vegas Valley, the last
of these being installed in 1992. Each site contained sets of approximately 18 different
types of buried grounding electrodes. Layout and electrode selection was similar for each
site to facilitate direct comparison of data. Measurements were taken bi-monthly.
The program included grounding electrodes which were not connected to a power source
(passive electrodes), electrodes connected to a DC supply (active electrodes), and evaluation
of bare conductor electrodes to evaluate the effects of dissimilar metals (passive electrodes),
located in close proximity, in the same soil. One of each electrode type was installed in the
Las Vegas sites. Some sample electrodes were encased in concrete and other materials
during installation. Stranded copper 6 AWG conductors were installed from the electrodes
to a terminal junction box, where data was collected. To test the effectiveness of
connections, most of the electrodes were equipped with ERICO® Cadweld tm
exothermically welded connectors, Burndy ® bolted type connectors, and some were
additionally equipped with Burndy ® Hyground tm compression type connectors.
In an effort to provide consistency of results, permanent test pins for electrode resistance and
soil resistivity measurements were installed at predetermined locations on each site.
In the following years, (1993- 1994) data were collected and reviewed for unusual
characteristics. Some of these data from the study showed that there was a large diversity
in results when comparing similar electrodes in different test site locations. These data
were the subject of papers presented at IEEE conferences, [2] and articles presented to
industry. Industry professionals interested in advancing the study including the Copper
Development Association (CDA®), and the International Facility Management
Association, recommended an expansion of the project to include other geographic
locations around the country, noting that the diversity of performance seen in the Nevada
study may not be isolated to the Las Vegas geography.
During 1994, the governing committee (IAEI/SNC) for the Nevada study predicted
difficulty in the prospective management for a proposed larger study and recognized a
need to select a proctor for governance to maintain propriety. To provide independent
oversight and review for the study, the Committee sought assistance from several
university and research institutions.
Initial contact was made with the Fire Protection Research Foundation in 1994. In 1995,
FPRF formulated the first phase of the National Electrical Grounding Research Project
(NEGRP). This project began by soliciting potential sponsors interested in funding a
more comprehensive project with the objective of addressing the noted diversity by
2
installing electrodes in a number of test sites around the U.S. (termed the National sites
in this report).
Because soil temperature and moisture sensors were planned for the National sites, in
1995, sensors were also installed in the Las Vegas sites, in an effort to provide for data
collection with consistency,
Several sponsors elected to participate, which initiated Phase 1 of the NEGRP. A
Technical Advisory Committee (TAC) was created, and during 1996 the planning of the
expansion of Phase two was underway.
During the Phase 1 deliberations, the original IAEI/ SNC Las Vegas sites were
incorporated into the project by the TAC.
Sites were selected from lands made available by the sponsors. Chief among the
selection process was the requirement for data collection, and availability of site
management.
Phase two of this project which began in 1995, was originally planned to span five and
one- half years, including start-up, and demobilization. Phase two of the project included
the construction of five National sites at various locations in the U.S. including Illinois,
Texas, California, Virginia and New York.
3
1.2 Objectives
The primary objectives of the National Electrical Grounding Research Project were to:
•
•
•
•
•
Evaluate the performance, over time, of buried grounding electrodes.
Provide information to regulators to use in enforcement of existing regulations.
Provide information to standards development organizations for use in improving
codes and standards.
Provide information to industry that could be used to improve grounding system
design and installation.
Provide information to industry that could be used to develop new types of
grounding electrodes.
1.3 Scope
The scope of this project included ten test sites, five of which were in the Las Vegas Valley
and five of which were in the National test sites. The test sites are shown in Table 1.
Included in the project were 15 to 18 different types of passive and active direct current
(DC) electrodes per site. Measurements included electrode resistance, soil temperature, soil
moisture and earth resistivity. The project began in 1992 and ended in 2007.
Some limitations of the project included the following.
•
•
•
•
•
Adequate funding to perform all initially desired scientific analyses of the
samples.
Personnel changes in management, staff, TAC membership, and within the ranks
of the site managers.
Some sites, specifically in Las Vegas, experienced encroachment of building
construction. This resulted in earlier than anticipated exhumation.
Funding prevented the TAC from hiring an archeologist to exhume the samples.
Several of the TAC members personally did the exhumation and made every
effort to ensure the samples were not damaged.
Several limitations occurred during the DC experiments, including interruption of
power, and required changes in instrumentation.
4
2 TEST SITES
Test sites for this project included plots of land, representing different soil conditions
which were selected in various locations to install buried grounding electrodes and
conduct the specified experiments. The following sites shown in Table 1 were selected.
Sites 1-5 were in the Las Vegas, Nevada area, and sites 6-10 were considered the
National sites.
Table 1 - Sites Legend
SITE
PA-1
LM-2
BA-3
PE-4
CH-5
LOCATION
Pawnee
Las Vegas, NV
Central
Lone Mountain
Las Vegas, NV
North
Balboa
Henderson, NV
(LV) South
Pecos
Las Vegas, NV
North
Charleston
Las Vegas, NV
East
INSTALL
DATE
REMOVE
DATE
SOIL CONDITIONS
May-92
03
Water table ranging from 10 to 20 ft. generally
clayey silt
Jun-92
04
Normally dry, silty, sandy clays
Aug-92
01
Normally dry, rock and gravel
Dec-92
04
Normally dry , silt and sand to 6 ft., silty clays 6
to 11 ft.
Dec-92
NA
Normally dry, sand, and gravel, surface froth
VA-6
Staunton, VA
Jun-97
NA
Sand, and silt to a depth of approximately 6 feet,
silty clays 6 to 11 ft.
TX-7
Dallas, TX
Jun-98
NA
Normally dry, sandy soil to a depth of 5 to 6
ft. increasingly stiff sandstone to 11 ft.
NY-8
Hibernia, NY
Sep-98
06
Water table at 10 ft to 11 ft. gravel, sand and
clays with occasional cobbles to 11 ft. depth
IL-9
Northbrook, IL
Illinois
Sep-98
NA
Periodically covered with rainwater runoff,
contains silts and clays to a depth of 11 ft.
CA-10
Moffet Field,
Mountain View,
CA
Jan-02
NA
Normally dry, sand, silt with inorganic and
organic clays
5
3 ELECTRODE TEST SAMPLES
3.1 Electrode Legend
Tables 2 through 5 identify the electrode by material, installation parameters, length, fill
surrounding the electrode, and orientation in the test site.
Table 2 - Electrode Types A through K
Electrode
ID
Material
A
No. 2
AWG
stranded
copper
wire
No. 4
uncoated
steel
reinforcing
bar
Centered in 12 in. of sand at 36 in. below grade
measured to the conductor.
50 ft
Orientation *
H
Fill
or
V
Sand
H
Within, and near the bottom of a concrete foundation
consisting of 12 in. by 12in. of 2500 psi concrete. The
top of the concrete was located 6 in. below grade.
20 ft.
Concrete
H
C
No. 4 solid
copper
wire
Centered in 6 in. by 6 in. of ERICO ® Ground
Enhancement Material, (GEM tm) located at 20 in., to
the bottom of the concrete.
25 ft
GEM tm
H
D
No. 4 solid
copper
wire
Centered in 6 in. by 6in. of 2500 psi concrete. located
at 20 in. to the bottom of the concrete. This electrode
is designed to represent the thickened edge of post
tensioned concrete construction.
25 ft
Concrete
H
E
Copper
Bonded
Steel Rod
5/8 in. diameter, centered in a 9 in. diameter, 9 ft. deep
boring in earth, encased in ERICO ®
(GEM tm ) backfill.
8 ft.
GEM tm
V
F
Copper
Bonded
Steel Rod
5/8 in. diameter, installed horizontally centered in a
trench, encased in ERICO® (GEM tm) backfill, 24 in.
to the bottom of the (GEM tm ) backfill material.
8 ft.
GEM tm
H
G
Copper
Bonded
Steel Rod
5/8 in. diameter, directly buried in a trench 36 in deep.
8 ft.
None
H
H
Copper
bonded
steel rod
5/8 in. diameter, driven vertically in earth.
8 ft.,
None
V
I
galvanized
steel rod
3/4 in. diameter, driven vertically in earth.
10 ft.,
None
V
J
galvanized
steel rod
3/4 in. diameter 10 ft. directly buried at a depth of 36
in.
10 ft
Soil
H
K
Copper
grounding
“pole”
plate
For Las Vegas sites 30 in. depth., T&B® Blackburntm
Model PBH, .025 in. thickness 7 in. wide by 7 3/8 in.
long, with connection capable of up to No.4 AWG
Stranded wire For National sites, 36in. depth, T&B®
Blackburntm GP-114, 14 in. diameter, .025 in.
thickness.
NA
Soil
na.
B
ELECTRODE LEGEND
Installation Parameters
* Orientation H- Horizontal V- Vertical
6
Length
ft.
Table 3 - Electrode Types L through V
Electrode
ID Material
L
M
Lyncole®
XITtm,
copper Tube
Steel, and
Concrete
N
No. 4 AWG
solid copper
wire
O
No. 4 AWG
solid copper
wire
P
Wood pole
with copper
grounding
pole plate to
6 AWG
solid copper
wire
Copper
Bonded
Steel Rod
Q
ELECTRODE LEGEND
Installation Parameters
Length
ft.
Orientation
Fill
H
o
r
V
V
Vertical chemically charged electrode assembly in
an 11 ft. deep, 9 in. diameter boring.
10
Lynconite II
Arrangement designed to represent a light pole base
with six ea., 2 ft. long No. 4 reinforcing steel
vertical, tied with 3 ea., No. 2 steel horizontal hoops
separated 12 in., vertically in a 2 ft., deep 36 in.
diameter excavation, encased in 2500 psi concrete,
20 ft. of wire rolled into a coil approximately 18 in.
diameter, installed in a 2 ft. round by 2 ft. deep
excavation in concrete 2500 psi.
NA
Concrete
20 Coil
Concrete
20 Coil
GEM tm
20 ft. of wire rolled into a coil approximately 18 in.
in diameter, installed in a 2 ft., round by 2 ft., deep
excavation encased in ERICO Ground Enhancement
Material ™.
Approximately 18 in. diameter, with Blackburn GP114 copper grounding pole plate attached at bottom
using No. 6 AWG solid copper wire wrapped in a
spiral for 6 ft., at approximately 6 in. spacing
between wraps.
n
a.
8
Soil
1/2 in. diameter, rod installed horizontally, directly
buried at 30 in. depth.
8
Soil
H
R
LEC®
Chemrod
Vertically charged electrode assembly in an 11 ft.
deep 9 in. diameter boring encased in Ground
Augmentation Fill (GAF tm).
10
GAF tm With
Earth
V
S
Lyncole®
XITtm
Horizontal chemically charged electrode assembly
installed at a depth of 36 in.
10
Lynconite II
H
T
Galvanized
steel water
pipe
3/4 in. diameter galvanized (water) pipe, driven
vertically in earth.
8
None
V
V
4/0 AWG- 7
strand
copper wire
4/0 AWG- 7 strand bare copper cable, directly
buried horizontally 36 in. deep.
20
Soil
H
* Orientation H- Horizontal V- Vertical
7
Table 4 - Electrode Types W through AE
Electrode
ID
Material
ELECTRODE LEGEND
Installation Parameters
Length
ft.
Orientation
Fill
Mortar
H
or
V
V
8
None
V
LEC® Chemrod tm charged electrode assembly
installed at a depth of 36 in., encased in GAFtm
backfill.
Wire Mesh consisting of No. 6 copper plated steel
on 4 in. centers measuring 2 ft. wide.
10
GAF tm With
Earth
H
8
Soil
H
Copper
Tube
ERICO® Horizontal Model Chemical Electrode.
10
GEM tm
H
AB
Copper
Tube
Harger® Vertical Model Chemical Electrode.
11
Ultrafilltm
V
AC
Copper
Tube
ERICO® Vertical Model Chemical Electrode.
10
GEM tm
V
AD
Copper
Tube
Lyncole® Vertical Model Sectional Chemical.
Electrode
10
Lynconite II
V
AE
Copper
Tube
Lyncole® Horizontal Model Sectional Chemical
Electrode.
10
Lynconite II
H
DC1
Rod
DC1A,B, and C are 5/8 in. copper bonded steel rod.
8
None
V
DC2
Pipe
DC2A, B, and C are ¾ in. by 8 ft. galvanized steel
pipe.
8
None
V
DM
Rod and
Pipe
DM1A, 2A,and 3A are 5/8 in. copper bonded steel
rods.
DM1B, 2B,and 3B are ¾ in.Galvanized Steel pipe.
8
None
V
W
Assembly
of copper
bonded
rods
Dominion Virginia Power Co., ground cage,
(proprietary)using multiple 8 ft. long, 5/8 in.
diameter copper bonded rods installed in a mortar
backfill.
NA
X
Stainless
steel rod
5/8 in. diameter stainless steel ground rod driven
vertically in earth.
Y
LEC®
Chemrod
Z
Copper
plated
steel mesh
AA
* Orientation H- Horizontal V- Vertical
8
8
V
For the benign corrosion experiments, the following electrodes in Table 5, were installed
without connections or conductors for resistance measurements. A limited corrosion
analysis was done on these samples.
Table 5 - Electrode Types 1A through 2C
Electrode
ID
Material
ELECTRODE LEGEND
Installation Parameters
1A
Copper Wire
4/0 AWG, 7 strand bare copper wire,
installed at a depth of 36 in.
20
Orientation
Fill
H
or
V
GEM tm
H
2A
Copper Wire
500 kcmil copper wire, installed at a depth
of 36 in.
20
GEM tm
H
1B
Copper Wire
4/0 AWG, 7 strand bare copper wire,
installed at a depth of 36 in.
20
Soil
H
2B
Copper Wire
500 kcmil copper wire, installed at a depth
of 36 in.
20
Soil
H
1C
Copper Wire
4/0 AWG, 7 strand bare copper wire,
installed at a depth of 36 in.
20
Lynconite II
(Bentonite)
H
2C
Copper Wire
500 kcmil copper wire, installed at a depth
of 36 in.
20
Lynconite II
(Bentonite)
H
Orientation H- Horizontal V- Vertical
9
Length
ft.
3.2 Electrode Details
Figures 1 through 12 are included to provide a visual representation for informational
purposes, and may not be a complete representation of installed conditions.
CAD drawings of these illustrations are provided in Appendix 11.6 and 11.7.
Figure 1 – Las Vegas Pullbox , Type M, N and R Electrodes
Figure 2 - Types A, F and Q Electrodes
10
Figure 3 - Electrode Types E, H, L, S, K and P
Figure 4 - Electrode Type B Concrete Encased Electrode
The electrode in Figure 4 is representative of the electrode specified in NEC 250.52
(A)(3) [3].
11
Figure 5 - Electrode Types H, T and X
Figure 6 - Electrode Type V
12
Figure 7 - Electrode Type W
Figure 8 - Electrode Type Y
13
Figure 9 - Electrode Type Z
Figure 10 - Electrode Type AA
14
Figure 11 - Electrode Type AB
Figure 12 - Electrode Type AC
15
Figure 13 - Direct Current Experiment DC2 (DC1 Similar)
Figure 14 - Dissimilar Metals Experiment DM
16
Figure 15 – Electrodes, CDA- 1A, 1B, 2A, 2B, 3A and 3B
17
4 EXPERIMENTS AND METHOD
The testing conducted on the static electrodes included electrode resistance, earth
resistivity, soil moisture, and soil temperature.
4.1 Sample Preparation
Prior to installation, the electrode samples were given a distinct sample number that was
stamped directly into the sample. In some cases, the samples were also identified with a
polymeric tag. All connectors used in the experiment were initially weighed using a
calibrated scale. It was anticipated during the planning stage of the project that the
weight of each connector would be compared before installation and after exhumation in
an effort to determine the effects of corrosion by loss of material to the soil on each of the
connectors used. Due to site limitations, weighing of the connectors was not carried out
at the end of the experiment.
The bolt-on, crimp type, and welded connectors were installed on the electrodes using the
manufacturers recommended installation procedures. The recommended torque, crimp
tool and die, and welding procedures were used.
A site plan was developed by the TAC. The plan included trenching details, sample
layouts, sample numbering, junction box location, and other detail and specifications.
The plans are shown in Appendix 11.6, and 11.7. It should be noted that some
differences occur between the plans and actual installation. Since every site had different
conditions for installations (ie. size, terrain) the plan shown in the appendix varied from
site to site based on installation decisions made by the site manager. No as-built site
drawings were prepared.
4.2 Installation and Exhumation
The electrodes were installed using earth moving equipment including backhoe,
trenching machines, and hydraulic augers. Other chief equipment used included cement
mixers, electrical generators, pneumatic hammers and selected hand tools. Installation
was accomplished by firstly opening the trenching, digging holes for samples, positioning
the samples, installing 6 AWG conductors in plastic conduits, laying conduits in trenches
with termination at the electrode samples, and at junction box connections where
resistance readings were taken. Driven rods and pipes were installed using pneumatic
hammers. Conductors terminated at a connector on the electrode and at the junction box.
The conductors were protected in the plastic conduit.
Specific samples were then backfilled with their required backfill material including
mortar, concrete, GEM tm, GAF tm, Ultrafill tm, Lynconite II, bentonite, or natural earth.
Once this was done, all other samples and trenches were backfilled with native soil.
None of the chemically charged electrodes in any of the sites were re-charged during the
term of the project.
All of the Las Vegas sites and the New York site were exhumed. Exhumation was done
generally with a backhoe. Care was taken in every case to exhume a sample without
destroying the electrode or the connection. Once a sample was exhumed, the bulk of the
backfill material was removed by hand. Mortar and concrete were removed mechanically
using hammers and jackhammers. Short lengths of 6 AWG conductors were left intact in
18
the connectors. Following this, the samples were cleaned with nylon brushes, clearly
identified, and wrapped in plastic for storage.
4.3 Electrode Resistance
The value of resistance to earth for each connection to each electrode was recorded
during data collection, using the IEEE 81-1983 [4], Fall of Potential Method.
Each electrode had an additional length of conductor from the junction box to the
electrode under test. Various distances for test pin spacing were evaluated for the
optimum distances for testing. Each electrode under test had a 6 AWG conductor
permanently attached to it from the terminal box to allow for periodic measurements, the
additional resistance was considered insignificant. This additional lead length was no
more than 100 feet long. For the Fall of Potential resistance measurements, various
distances for test pin spacing were evaluated for the optimum spacing, contributing to a
small degree of variability in readings.
For the five Las Vegas sites, a remote test pin distance of 100 ft. was used with the
electrical current pin at 62 ft. from the termination box. The remote pin location of
100 ft. was determined to be sufficient to eliminate variability in readings due to location
of the electrode. For the National sites, because of the larger footprint of the sites, the
remote current electrode was located a distance of 200ft. with the potential electrode
located 124 ft. from the terminal box.
4.4 DC Active Experiments
The direct current experiments (DC1 and DC2) were developed as a method to evaluate
the properties associated with damage to existing rod and pipe electrodes. In the National
sites, there were two DC pods; DC1, and DC2. These experiments consisted of three
driven rods in the DC1 pod, or pipes DC2 pod. Each pod was in a triangular formation
with a rod or pipe located in the center of the pod that served as the negative terminal
conductor. As shown in Figure 11, the surrounding electrodes were connected together
using 6 AWG stranded copper conductors, and to the positive terminal conductor of a
12V@ 20 mA, DC power supply. The center rod or pipe was then connected to the
negative terminal of the power supply across a standard (corrosion process 0.1 ohm)
resistor. This method of connection has the effect of applying most of the (destructive
force) current across the earth, and on the center rod or pipe. Permanent power was
provided by means of a 120V power supply, and in two cases a solar photovoltaic array
supplied the DC power. Time was recorded from hour meters located within test
terminal enclosures.
The design utilized three grounding rods or pipes spaced equally apart with a 5-milliamp
DC current flowing through each of them. The fourth ground rod or pipe served as the
negative (center rod in the pod) initially having 15 milliamps DC current flowing though
it. The initial design was based on the concept that the negative would carry the
summation of the currents flowing in each of the three outer electrodes. The current
flowing in any of the outer electrodes should change based upon change of resistance
mainly due to corrosion.
Measuring DC currents for the DC and the dissimilar metals experiments was
accomplished using either the direct connection to a portable meter capable of displaying
19
current in milliamperes, or by using a clamp-on style DC current probe in conjunction
with a voltmeter.
4.5 Dissimilar Metals
The Dissimilar Metals Experiment included six electrodes arranged in three sets of two.
The purpose of this experiment was to develop data that could show changes of
resistance, mainly caused by dissimilar metals in an earth coupled cell, which could
possibly produce current flow. Figure 12 illustrates the experiment and shows the
grounding electrode samples used.
This experiment in the National sites was designed to identify electrical currents, and
resulting corrosion of electrodes consistent with the currents measured across an earth
coupled cell (galvanic corrosion). The cell consisted of a single 8 ft. long copper bonded
steel ground rod, and a single ¾ in. diameter galvanized steel pipe spaced 6-1/2 ft. apart,
in the earth and connected together using a standard (corrosion process .01 ohm) resistor.
The resulting DC current between the two electrodes was measured.
The test samples DM1A, DM2A and DM3A were 5/8” x 8’ copper bonded ground rod
and the DM1B, DM2B and DM3B samples were ¾” x 8’ galvanized steel pipe. The
descriptions of the electrodes are shown in Figure 12. There is 6 1/2 ft. between the
copper bonded ground rod and the paired galvanized steel pipe ground rod. The
experiment included the measurement of current flow through each paired grounding
electrode circuit. A precision 0.01 ohm resistor was used in the circuit to standardize
current measurement.
4.6 Earth Resistivity
Earth resistivity was established for 10 ft. and 20 ft. test pin spacing using the IEEE 811983, Four Point Method for each data collection exercise. [2] The resulting ohm-meter
resistance values were converted and recorded in ohm-cm. Per IEEE 81-1983 this method
gives approximately the average resistivity of the soil to the depth represented by the
probe spacing.
4.7 Soil Moisture
Soil moisture was recorded using a specialized moisture meter with buried sensor blocks
at depths of 126 in. 78 in., and 30 in. for each site. In this report, soil moisture is shown
in Delmhorst ® units. These units are defined by the Delmhorst® KS-D1 instrument.
4.8 Soil Temperature
Soil temperature was recorded using thermocouple thermometers connected to Type K
thermocouple sensors buried at depths of 126 in., 78 in., and 30 in. at each site.
4.9 Passive Metal Corrosion
Adjunct to this research project was a corrosion experiment with six grounding
electrodes. These grounding electrodes were not connected to a power supply or any
termination.
20
The experiment is shown in Figure 13. Samples 1A, 2A, and 3A consisted of 20 ft. of 4/0
stranded bare copper conductor and Sample 1B, 2B, and 3B consisted of 20 ft. of
500KCMIL stranded bare copper conductor. Samples 1A and 1B were backfilled with
GEM tm, Samples 2A, 2B were backfilled in earth, and Samples 3A and 3B were
backfilled in Bentonite. This was a long-term corrosion experiment of copper grounding
electrodes in various backfills. There were no monthly resistance measurements
conducted. Any corrosion observed after exhumation was assumed to be caused by the
corrosive effects of the backfill and surrounding earth.
21
5 INSTRUMENTATION
The following calibrated instruments were used for data collection.
5.1 Earth Testers
Models used include:
AVO / Megger- Det 2/2
AEMC- 4500
LEM - GEO
Biddle Null Balance
AEMC 3720 Clamp Earth Tester - Used in conjunction with the AEMC 4500 as a
verification for the site manager.
A standard four terminal instrument [2] was used to perform tests for resistance to earth,
fall of potential testing, and earth resistivity testing.
5.2 Multi-Meters
Fluke 87 or equal
AC/DC volts, ohm, milliamps
Multi-meters were used as a means to perform various routine tests such as continuity,
current, and voltage measurements for portable equipment requiring the temporary
connection of test leads, and general maintenance of wire, and terminations associated
with experiments.
5.3 DC Current Probe
AEMC K110
The DC current probe is a clamp-on style sensor. When connected to a volt-meter, and
clamped around a wire carrying small DC currents, it is capable of producing measurable
voltages which are then converted to a value of DC current.
5.4 Thermocouple Thermometer
Omega HH-25KF or similar
Used for measuring earth temperature requiring direct connection using a standard plug
for Type K thermocouples.
5.5 Moisture Meter
Delmhorst KSD1
22
Soil moisture measurements were made at each of the Las Vegas and National sites using
the Delmhorst moisture measuring system. The system consisted of two chief parts:
gypsum soil block sensors, and the measuring instrument - Model KS-D1 moisture meter.
The gypsum served as a buffer against the effects that salts may have on the soils
conductivity. The blocks were buried at soil depths of 30, 78, and 128 in. The blocks
absorb or release moisture into the soil, until their moisture content reaches equilibrium
with the moisture content of the surrounding soil. When the meter is connected to the
block, current flows between two current probes and the electrical resistance of the block
is measure. The meter is calibrated to relate moisture content with electrical resistance.
23
6 RESULTS
Information in this section was derived from the specific data shown in the appendices.
Some data include readings for each of the three connector types (bolt-on, crimp type,
welded), but most data includes the results for only one connector type when the data
were similar.
The data is organized as follows.
•
•
•
•
Electrode Resistance
o Percentage of Readings Exceeding Resistance of Certain Values
o Resistance of Individual Electrodes at All Sites
o Vertical and Horizontal Electrode Resistance
o Comparison of Electrode Resistance
Ancillary Experiments
o DC1 and DC2 Results
o Dissimilar Metals Results
o Benign Corrosion Experiments
Soil Characteristics
o Earth Resistivity
o Soil Temperature
o Soil Moisture
Corrosion Results
24
6.1
Electrode Resistance
6.1.1
Percentage of Readings Exceeding Resistance of Certain Values
Tables 6 through 9 are based on average resistance values over the term of the project.
The Tables indicate percentage of readings which exceeded the specified values of 25,
50, 100, and 250 ohms respectively.
Table 6 - Percentage of Readings Exceeding 25 ohms
Of the 18 electrodes in the Balboa test site, 14 of these exceeded 25 ohms for 90% or
more of the readings; electrode Types E, L and R were the exception. Similarly, for
electrodes in the New York test site, 100% of the readings exceeded 25 ohms for 13 of
the 15 electrodes in the site; the exceptions being electrodes Type L and R.
It is noted that the percentage of readings for electrode Type B, (NEC Section 250.52) [2]
exceeded 25 ohms for 74% or more of the readings in four of the 10 test sites.
Electrode Type K readings exceeded 25 ohms for 75% or more of the readings at nine of
the 10 test sites with Texas readings exceeding 25 ohms for 21% of the readings.
25
The Illinois site had the least number of electrodes with readings exceeding 25 ohms.
Electrodes H and K having 11% and 79% respectively that exceeded 25 ohms. This
could be due to generally wet soil conditions based upon site location in a drainage field.
Table 7 - Percentage of Electrodes Exceeding 50 ohms
In the New York, site 10 of 15 electrodes exceeded 50 ohms more than 50% of the time.
In the Balboa site, nine of 16 electrodes exceeded 50 ohms 50% of the time, as compared
to the Illinois site where no electrodes exceed 50 ohms except for the K electrode (18%).
Although the Las Vegas Pecos and Balboa sites, were in the same geographical area the
results differed greatly. In the Balboa site, nine of 18 electrodes exceeded 50 ohms more
than 50% of the time, whereas, in the Pecos site only the K electrode exceeded 50 ohms
50% of the time.
Any electrode which exceeded 50 ohms exceeded the NEC 25 ohm requirement by a
factor of two.
26
Table 8 - Percentage of Electrodes Exceeding 100 ohms
As expected, there were fewer electrodes exceeding the 100 ohm value than those shown
in the previous tables.
The results showed that only one electrode in each of the Illinois and Texas sites
exceeded 100 ohms. In Illinois, 3% of the readings for the K electrode exceeded 100
ohms and in Texas, 7% of the readings for the X electrode exceeded 100 ohms.
In the Las Vegas sites, only the B, I, L, and S electrodes had readings less than 100 ohms.
The K electrode for all sites had the worst results.
Over the term of the project in the New York site, three of the 15 electrode readings
measured 100 ohms or greater for at least 95% of the readings. In the Balboa site, two of
the electrodes exceeded 100 ohms for at least 95% of the readings.
Any electrode exceeding 100 ohms, also exceeded the NEC 25 ohm requirement by a
factor of four.
27
Table 9 - Percentage of Electrodes Exceeding 250 ohms
As with the results for readings exceeding 25, 50, and 100 ohms, the K electrode also
exhibited the worst performance when evaluated against 250 ohms. If the data for the K
electrode in the above Table was eliminated, then none of the electrodes in the Las Vegas
Pecos, or Charleston sites would have any values exceeding 250 ohms.
Any electrode which exceeded 250 ohms exceeded the NEC 25 ohms requirement by a
factor of ten.
28
6.1.2
Resistance of Individual Electrodes at All Sites
6.1.2.3 Illinois Site Resistance Experiments
In the Illinois site, there were 15 different electrodes evaluated for resistance, with three
samples of each buried in the site. Of the 15 types, there were five electrodes that had a
trend of decreasing resistance over time. Ten of the 15 electrodes had an increasing
trend. For the Illinois as well as other sites, the slope of the trendlines was not calculated,
nonetheless, inferences can be made by the reader regarding this trend continuing over
time beyond the conclusion of this experiment. It is assumed that those electrodes that
had decreasing trendlines would not actually reach a zero resistance value. For those
electrodes with increasing trendlines, it is not known whether or not any specific trend
would continue at the same slope for the service life beyond the period of this
experiment, however, this trendline could be used for predicting performance, and also
for comparing one electrode to another.
Northbrook, IL
All Electrodes
100
B1
E1
F1
G1
H1
K1
L1
R1
S1
T1
V1
W1
X1
Y1
Z1
Ohms
75
50
25
10/25/06
6/14/06
2/15/06
6/22/05
10/19/05
2/22/05
10/29/04
6/23/04
2/18/04
10/8/03
6/13/03
2/19/03
10/17/02
6/17/02
2/18/02
6/26/01
10/22/01
2/19/01
6/19/00
10/11/00
2/15/00
10/15/99
6/18/99
2/18/99
10/8/98
0
Figure 16- Illinois Electrodes Resistance
The data for all electrodes in the Illinois site is shown in the above Figure 16. All
electrodes except for the K1 and H1 had resistance readings for the tenure of the
experiment less than 25 ohms.
29
6.1.2.3 Texas Site Resistance Experiments
In the Texas site, there were 15 different electrodes evaluated for resistance, with three
samples of each buried in the site. Of the 15 types, there were three electrodes that had a
trend of decreasing resistance over time. Twelve of the 15 electrodes had an increasing
trend.
Dallas, TX
All Electrodes
100
B1
E1
F1
G1
H1
K1
L1
R1
S1
T1
V1
W1
X3
Y1
Z1
Ohms
75
50
25
11/22/06
5//06
8/29/06
2//06
8/29/05
11/28/05
5/31/05
2/28/05
8//2004
11//2004
5//2004
2//2004
8/19/03
11/25/03
5/22/03
2/18/03
8/26/02
11/25/02
5/28/02
2/25/02
8/28/01
11/26/01
5/31/01
2/26/01
8/28/00
11/20/00
5/31/00
2/24/00
8//1999
11/22/99
5/21/99
1/29/99
7/30/98
10/30/98
0
Figure 17– Texas Electrodes Resistance
The data for all electrodes in the Texas site is shown in Figure 15. All electrodes except
for the type B, F, G, K, and V electrodes had resistance readings for the period of the
experiment less than 25 ohms. It is noted that the type V electrode, exceeded 25 ohms
only over a narrow period of approximately three months over the tenure of the
experiment.
30
6.1.2.3 California Site Resistance Experiments
In the California site, there were 18 different electrodes evaluated for resistance, with
three samples of each buried in the site. Of the 18 types, all electrode types showed
increasing resistance over time. Of all the National sites, the California site had the
shortest period of time from which resistance readings were taken. In addition, the
California site included additional electrodes not present in the other National sites.
These electrodes were types AA, AB, AC, AD and AE and there were three of each
present in the site.
Moffett Field, CA
All Electrodes
175.0
B1
E1
F1
G1
H1
K1
L1
S1
T1
V1
W1
X1
Z1
AA1
AB1
AC1
AD1
AE1
150.0
125.0
Ohms
100.0
75.0
50.0
25.0
12/26/06
9//06
11/16/06
5//06
7/7/06
3//06
1//06
9/1/2005
11/4/2005
5//2005
7/6/2005
3//2005
1//2005
9//2004
11//2004
7//2004
5//2004
3//2004
1//2004
9//2003
11//2003
7//2003
5//2003
3//2003
1//2003
9/1/2002
11/1/2002
7/1/2002
3//2002
5/1/2002
1/30/2002
0.0
Figure 18 - California Electrodes Resistance
The data for all electrodes in the California site is shown in Figure 18. All electrodes
except for the type B, F, G, K, T, V, Z and AB electrodes had resistance readings for the
tenure of the experiment less than 25 ohms. Even though some electrodes for the tenure
of the test had readings less than 25 ohms, all electrodes showed an increasing trend of
resistance.
31
6.1.2.4 Virginia Site Resistance Experiments
In the Virginia, site there were 15 different electrodes evaluated for resistance, with three
samples of each buried in the site. Of the 15 types, there were four electrodes that had a
trend of decreasing resistance over time. Eleven of the 15 electrodes had an increasing
trend.
Staunton, VA
All Electrodes
450
400
B1
E1
F1
G1
H1
K1
L1
R1
S1
T1
V1
W1
X1
Y1
Z1
350
Ohms
300
250
200
150
100
50
7//06
11/28/06
3/3/06
7/28/05
11/18/05
3/24/05
10/28/04
7/29/04
11//04
3/19/04
3//03
7/3/03
7/12/02
11/26/02
3/29/02
11/7/01
7/23/01
3/29/01
11/14/00
3/9/00
7/11/00
11/30/99
7/29/99
11//99
3/25/99
7/10/98
3/26/98
11/24/97
0
Figure 19 - Virginia Electrodes Resistance
The data for all electrodes in the Virginia site is shown in Figure 19. The type E and R
electrodes had resistance readings for the tenure of the experiment less than 25 ohms.
32
6.1.2.5 New York Site Resistance Experiments
In the New York site, there were 15 different electrodes evaluated for resistance, with
three samples of each buried in the site. Of the 15 types, there was only one electrode,
the B electrode, that had a trend of decreasing resistance over time.
Cenhud Hibernia NY
All Electrodes
900
800
B1
E1
F1
G1
H1
K1
L1
R1
S1
T1
V1
W1
X1
Y1
Z1
700
Ohms
600
500
400
300
200
100
5/1406
3//2006
12//2005
9/1/2005
3//2005
6/9/2005
9//2004
12//2004
6//2004
3//2004
9//2003
12//2003
6//2003
3//2003
9//2002
12//2002
6//2002
3//2002
9//2001
12//2001
3//2001
6/20/2001
9/20/2000
12/13/2000
6/15/2000
9//99
03/22/00
9/27/1999
6/18/1999
3/19/1999
9/24/1998
12/29/1998
0
Figure 20 - New York Electrodes Resistance
In most cases, the electrodes resistance greatly exceeded 25 ohms. As was expected the
K electrodes had high resistance readings. The best results were with the L and R
electrodes, however, some of their readings exceeded 25 ohms with an increasing trend
line.
33
6.1.3 Vertical and Horizontal Electrodes - Las Vegas Sites
The following Figures 19 through 28 and their associated data in Tables 10 through 19,
show the relationship between resistance and time of the vertical and horizontal rod
electrodes. The vertical electrodes (H) shown in red exhibited lower resistance values
than did the horizontal electrodes (G) shown in blue for every Las Vegas site. The
horizontal electrodes were installed at 36 in. depth to evaluate installations where rock
bottom is encountered, as referenced in NEC Section 250 53(G). Vertical electrodes
were driven to a depth of approximately 8 ft.
Las Vegas, NV
Balboa
G vs. H
600
500
G
H
Linear (G)
Linear (H)
300
200
100
9/1/2002
4/19/2001
12/6/1999
7/24/1998
3/11/1997
10/28/1995
6/15/1994
1/31/1993
0
9/19/1991
Ohms
400
Figure 21 - Balboa Test Site Graph Electrode Type G and H
34
Table 10 - Balboa Test Site Data for Electrode Type G and H
The vertical electrode Type H, exhibited consistently lower resistance levels than Type
G, horizontal. Additionally the data showed that the average resistance over time of the
vertical electrodes was much less than the horizontal electrodes. It is noted, however,
that none of the vertical electrodes met the NEC requirement of 25 ohms.
35
Las Vegas, NV
Charleston
G vs. H
500
450
400
350
Ohms
300
G
H
Linear (G)
Linear (H)
250
200
150
100
50
12/6/1999
7/24/1998
3/11/1997
10/28/1995
6/15/1994
1/31/1993
9/19/1991
0
Figure 22 - Charleston Test Site Graph for Electrode Type G and H
Table 11 - Charleston Test Site Data for Electrode Type G and H
The vertical electrode Type H exhibited consistently lower resistance levels than Type G,
horizontal. Additionally the data showed that the average resistance over time of the
vertical electrodes was much less than the horizontal electrodes. Three of the average
resistance readings for the Type H electrode exceeded the NEC requirement of a
maximum 25 ohms.
36
Las Vegas, NV
Lone Mountain
G vs. H
280
240
200
160
Ohms
G
H
Linear (G)
Linear (H)
120
80
40
9/1/2002
4/19/2001
12/6/1999
7/24/1998
3/11/1997
10/28/1995
6/15/1994
1/31/1993
9/19/1991
0
Figure 23 - Lone Mountain Test Site Graph for Electrode Type G and H
Table 12 - Lone Mountain Test Site Data for Electrode Type G and H
Lone Mountain had similar results to the Balboa and Charleston sites. In all cases, the
vertical rods met the NEC requirement of 25 ohms. In all cases except one, the
horizontal rods did not meet the requirement.
37
Las Vegas, NV
Pecos
G vs. H
140
120
100
80
Ohms
G
H
Linear (G)
Linear (H)
60
40
20
9/1/2002
4/19/2001
12/6/1999
7/24/1998
3/11/1997
10/28/1995
6/15/1994
1/31/1993
9/19/1991
0
Figure 24 - Pecos Test Site Graph for Electrode Type G and H
Table 13 - Pecos Test Site Data for Electrode Type G and H
Some Type G electrode readings were not included due to damage during excavation.
Once again, the data showed that the vertical rods had lower average resistance than the
horizontal rods. All of the vertical rods meet the NEC 25 ohm requirement, but this
cannot be said for the horizontal rods. Seventy percent of the average resistance readings
for horizontal electrodes did not meet the NEC 25 ohm requirement.
38
Las Vegas, NV
Pawnee
G vs. H
25
20
15
Ohms
G
H
Linear (G)
Linear (H)
10
5
1/14/2004
9/1/2002
4/19/2001
12/6/1999
7/24/1998
3/11/1997
10/28/1995
6/15/1994
1/31/1993
9/19/1991
0
Figure 25 - Pawnee Test Site Graph for Electrode Type G and H
Table 14 - Pawnee Test Site Data for Electrode Type G and H
The results showed that for both types of rods, the NEC requirement of 25 ohms was met.
These results could be attributed to lower earth resistivity than is present at Balboa,
Charleston, Lone Mountain and Pecos sites.
39
Las Vegas, NV
Balboa
I vs. J
400
350
300
Ohms
250
I
J
Linear (J)
Linear (I)
200
150
100
50
9/1/2002
4/19/2001
12/6/1999
7/24/1998
3/11/1997
10/28/1995
6/15/1994
1/31/1993
9/19/1991
0
Figure 26 - Balboa Test Site Graph for Electrode Type I and J
Table 15 - Balboa Test Site Data for Electrode Type I and J
The vertical electrode Type I exhibited consistently lower resistance levels than Type J,
horizontal. Additionally, the data showed that the average resistance over time of the
vertical electrodes was much less than the horizontal electrodes. Regarding the average
resistance readings, in all cases except for one, all electrodes either vertical or horizontal
did not meet the NEC 25 ohm requirement.
40
Las Vegas, NV
Charleston
I vs. J
140
120
100
80
Ohms
I
J
Linear (J)
Linear (I)
60
40
20
12/6/1999
7/24/1998
3/11/1997
10/28/1995
6/15/1994
1/31/1993
9/19/1991
0
Figure 27 - Charleston Test Site Graph for Electrode Type I and J
Table 16 - Charleston Test Site Data for Electrode Type I and J
Some of vertical electrodes showed low average resistance readings, whereas others
exceeded the NEC requirement. In all cases the average resistance readings for the
horizontal electrodes exceeded those of the vertical electrodes. This data clearly showed
once again, that resistance readings are dependent upon positioning in soil. This could be
due to a number of factors including soil moisture, soil compaction and possibly
temperature.
41
Las Vegas, NV
Lone Mountain
I vs J
25
20
15
Ohms
I1
J1
Linear (J1)
Linear (I1)
10
5
9/1/2002
4/19/2001
12/6/1999
7/24/1998
3/11/1997
10/28/1995
6/15/1994
1/31/1993
9/19/1991
0
Figure 28 - Lone Mountain Test Site Graph for Electrode Type I and J
Table 17 - Lone Mountain Test Site Data for Electrode Type I and J
The results showed that for both types of rods, the NEC 25 ohm requirement was met.
For the average resistance readings, in all cases the vertical electrodes had average
resistances less than or equal to resistances of horizontal electrodes.
42
Las Vegas, NV
Pecos
I vs J
25
20
15
Ohms
I1
J1
Linear (J1)
Linear (I1)
10
5
9/1/2002
4/19/2001
12/6/1999
7/24/1998
3/11/1997
10/28/1995
6/15/1994
1/31/1993
9/19/1991
0
Figure 29 - Pecos Test Site Graph for Electrode Type I and J
The results showed that for both types of rods, the NEC 25 ohm requirement was met.
For the average resistance readings, in 18 of 20 cases the vertical electrodes had average
resistances less than or equal to resistances of horizontal electrodes.
43
Table 18 - Pecos Test Site Data for Electrode Type I and J
44
Las Vegas, NV
Pawnee
I vs J
14
12
8
I
J
Linear (J)
Linear (I)
6
4
2
1/14/2004
9/1/2002
4/19/2001
12/6/1999
7/24/1998
3/11/1997
10/28/1995
6/15/1994
1/31/1993
0
9/19/1991
Resistance (Ohms)
10
Figure 30 - Pawnee Test Site Graph for Electrode Type I and J
45
Table 19 - Pawnee Test Site Data for Electrode Type I and J
As compared to other Las Vegas sites, the Pawnee site exhibited resistance readings well
below the NEC requirement in all cases. Unlike other sites, Pawnee soil consistency was
mostly clayey sand, which could explain the low level of earth resistivity.
46
6.1.4 Vertical and Horizontal Electrodes – National Sites
The following Figures 31 through 35 and their associated data in Tables 20 through 24
show the relationship between resistance and time for the vertical and horizontal rod
electrodes in the National sites. The variant results for the Illinois site could be attributed
to the relatively high water table and standing water occurring many weeks during the
year. This is the only National site where average resistance values were less for the
horizontal electrodes than for vertical electrodes. Unlike the vertical electrodes, there
were no specific readings exceeding 25 ohms for their horizontal counterpart. For the
horizontal electrode, the average resistance values met the 25 ohm requirement.
The vertical electrode (H) shown in red exhibited lower resistance values than did the
horizontal electrode (G) shown in blue. For the National sites, the horizontal electrodes
were installed at a 36 in. depth to evaluate installations where rock bottom is
encountered, as referenced in NEC Section 250 53(G). Vertical electrodes were driven to
a depth of approximately 8 ft.
Northbrook, IL
G- Horizontal vs
H- Vertical
40
35
30
G1
H1
Linear (G1)
Linear (H1)
20
15
10
5
8/23/06
12/12/06
4/18/06
12/22/05
8/16/05
4/18/05
12/29/04
8/16/04
4/28/04
8/18/03
12/18/03
4/23/03
8/16/02
12/12/02
4/15/02
12/18/01
6/26/01
2/19/01
6/19/00
10/11/00
2/15/00
6/18/99
10/15/99
2/18/99
0
10/8/98
Ohms
25
Figure 31 – Illinois Test Site Graph for Electrode Type G and H
47
Table 20 – Illinois Test Site Data for Electrode Type G and H
National Electrical Grounding Research Project
Location: Northbrook, IL
Test Site: UL
Read Date
10/8/98
11/6/98
1/18/99
2/18/99
3/17/99
4/13/99
5/21/99
6/18/99
7/16/99
8/11/99
9/30/99
10/15/99
11/10/99
12/20/99
1/18/00
2/15/00
3/8/00
4/14/00
5/15/00
6/19/00
7/17/00
8/16/00
9/13/00
10/11/00
11/22/00
12/20/00
1/10/01
2/19/01
3/20/01
4/18/01
5/16/01
6/26/01
9/27/01
10/22/01
11/7/01
12/18/01
1/22/02
2/18/02
3/12/02
4/15/02
5/15/02
6/17/02
7/15/02
8/16/02
9/17/02
10/17/02
11/13/02
12/12/02
1/28/03
2/19/03
3/14/03
4/23/03
5/19/03
6/13/03
7/18/03
8/18/03
9/16/03
10/8/03
11/20/03
12/18/03
1/14/04
2/18/04
Resistance (Ohms)
Horizontal Rods
Vertical Rods
G1
G2
G3
H1
H2
7
7
6
8
9
7
7
6
7
7
9
9
9
9
10
9
8
8
9
9
9
9
8
9
9
7
7
7
8
9
7
6
7
7
8
6
5
6
7
9
7
7
7
9
17
12
9
9
9
11
6
6
6
8
9
6
6
6
8
9
10
9
8
9
10
7
8
8
8
9
8
8
9
9
10
8
8
9
10
10
7
7
8
9
9
7
7
8
9
9
6
6
7
9
9
6
6
6
8
8
5
6
6
8
11
6
6
6
13
17
5
6
6
13
10
6
7
7
9
8
7
8
8
9
8
7
9
8
9
9
7
8
8
9
9
8
7
8
10
10
7
7
8
10
10
6
6
7
9
9
6
6
6
9
9
5
6
6
9
16
5
7
6
10
9
5
7
7
9
9
6
7
7
9
10
6
7
8
10
11
7
8
9
17
22
6
7
8
11
12
6
6
8
10
12
5
6
7
10
11
5
6
7
9
11
5
5
6
9
13
5
6
7
22
26
5
6
7
21
27
5
5
7
20
21
5
6
7
14
21
6
7
8
23
23
5
6
8
10
14
6
8
11
14
18
6
7
9
14
22
5
6
9
13
22
4
5
6
11
14
4
5
6
9
12
4
5
6
9
20
3
4
5
13
18
4
5
6
23
26
4
5
6
28
31
5
6
7
32
28
4
6
7
12
13
6
7
8
11
12
5
6
8
11
12
5
6
8
12
15
48
Soil Resistivity
(Ohm-cm at 10 ft.)
H3
9
7
10
9
10
9
9
12
18
26
10
9
10
9
9
9
9
9
8
7
7
7
7
7
8
8
8
9
9
8
8
8
7
7
8
8
9
9
9
9
8
8
8
9
8
7
8
9
10
11
23
9
8
8
7
8
9
9
8
9
9
6
Read Date
2938
2505
2647
3152
3164
3168
2953
2719
2490
2562
2566
2589
2601
2804
3068
3210
3275
3083
2984
2712
2455
2321
2375
2313
2432
2681
2934
3007
3202
3171
2984
2662
2509
2358
2482
2597
2815
3175
3187
3175
3018
2777
2570
2601
2811
2348
2478
2696
2991
3298
3451
3497
3087
2842
2693
2436
2543
2670
2746
2762
3141
3305
3294
10/8/98
11/6/98
1/18/99
2/18/99
3/17/99
4/13/99
5/21/99
6/18/99
7/16/99
8/11/99
9/30/99
10/15/99
11/10/99
12/20/99
1/18/00
2/15/00
3/8/00
4/14/00
5/15/00
6/19/00
7/17/00
8/16/00
9/13/00
10/11/00
11/22/00
12/20/00
1/10/01
2/19/01
3/20/01
4/18/01
5/16/01
6/26/01
9/27/01
10/22/01
11/7/01
12/18/01
1/22/02
2/18/02
3/12/02
4/15/02
5/15/02
6/17/02
7/15/02
8/16/02
9/17/02
10/17/02
11/13/02
12/12/02
1/28/03
2/19/03
3/14/03
4/23/03
5/19/03
6/13/03
7/18/03
8/18/03
9/16/03
10/8/03
11/20/03
12/18/03
1/14/04
2/18/04
Average Resistance
(Ohms)
G
H
6
9
7
7
9
9
8
9
9
9
7
9
7
8
6
9
7
15
10
15
6
9
6
9
9
10
8
9
8
9
8
10
7
9
7
9
6
9
6
8
6
9
6
12
6
10
7
8
8
8
8
9
8
9
8
10
7
10
6
9
6
9
6
11
6
9
6
8
7
9
7
10
8
16
7
11
7
10
6
10
6
9
5
10
6
19
6
19
6
16
6
14
7
18
6
11
8
14
7
16
7
19
5
11
5
10
5
12
4
13
5
19
5
23
6
23
6
11
7
11
6
11
6
11
Dallas, TX
G- Horizontal vs
H- Vertical
75
50
Ohms
G1
H1
Linear (G1)
Linear (H1)
25
7/30/2006
7/30/2005
7/30/2004
7/30/2003
7/30/2002
7/30/2001
7/30/2000
7/30/1999
7/30/1998
0
Figure 32 – Texas Test Site Graph for Electrode Type G and H
At the Texas site, in every case, the average resistance values of the horizontal and
vertical electrodes met the 25 ohm requirement of NEC Section 250.52(G). For the
horizontal electrodes there were many specific readings that exceeded 25 ohms. No
readings exceeded 25 ohms for the duration of the test for the vertical electrodes.
49
Table 21 – Texas Test Site Data for Electrode Type G and H
National Electrical Grounding Research Project
Location:
Test Site:
Dallas,Texas
Megger
Read Date
7/30/1998
8/17/1998
9/30/1998
10/30/1998
11/30/1998
12/16/1998
1/29/1999
3/23/1999
4/26/1999
5/21/1999
6/29/1999
7/30/1999
9/20/1999
10/25/1999
11/22/1999
12/22/1999
1/24/2000
2/24/2000
03/28/00
4/18/2000
5/31/2000
6/26/2000
7/30/1999
8/28/2000
9/29/2000
10/26/2000
11/20/2000
12/28/2000
1/26/2001
2/26/2001
3/13/2001
5/31/2001
6/20/2001
7/31/2001
8/28/2001
9/20/2001
10/16/2001
11/26/2001
12/28/2001
1/28/2002
2/25/2002
3/28/2002
4/25/2002
5/28/2002
6/24/2002
7/30/2002
8/26/2002
9/23/2002
11/25/2002
12/18/2002
1/29/2003
2/18/2003
3/24/2003
4/28/2003
5/22/2003
6/30/2003
8/19/2003
9/22/2003
10/28/2003
11/25/2003
12/15/2003
2/28/2005
3/22/2005
4/25/2005
5/31/2005
6/28/2005
G1
46
64
50
6
6
6
62
8
9
12
17
20
29
36
39
15
5
14
12
10
17
12
20
29
34
36
15
14
12
10
8
16
19
26
26
16
22
29
17
19
16
15
13
16
21
24
25
27
5
15
15
15
13
15
17
14
23
22
29
31
35
12
13
15
18
21
Resistance (Ohms)
Horizontal Rods
G2
G3
H1
77
94
8
66
102
8
53
97
7
7
6
5
7
6
5
7
7
5
69
79
8
9
9
5
14
11
6
19
13
5
18
18
6
25
24
8
50
38
10
65
46
11
76
48
11
16
15
7
17
16
7
18
18
6
11
15
6
11
14
5
14
14
5
11
12
5
25
24
8
34
31
12
41
36
13
49
35
9
14
15
7
14
17
7
13
15
7
12
14
7
9
12
7
16
17
6
19
18
6
26
21
9
25
19
8
9
9
5
15
13
6
21
15
7
17
15
7
19
18
7
17
17
7
16
16
7
15
15
6
18
16
7
21
18
9
22
21
9
25
22
10
28
24
10
16
16
8
16
16
7
17
17
6
16
17
6
15
16
6
18
21
7
19
23
7
14
13
5
23
22
8
22
19
7
30
24
8
33
25
7
39
28
7
14
12
5
15
12
5
16
13
6
20
15
7
22
17
10
Vertical Rods
H2
8
8
6
5
5
5
8
5
6
5
6
9
11
12
12
6
6
6
5
5
5
5
9
16
16
12
6
6
6
6
5
6
7
9
8
5
6
6
6
7
6
6
6
7
8
9
9
9
6
6
7
7
7
8
7
6
9
8
9
9
9
7
8
9
9
14
50
Soil Resistivity
(Ohm-cm at 10 ft.)
H3
10
9
7
5
5
5
10
5
6
5
6
9
11
12
12
6
6
6
6
5
5
5
9
11
12
10
6
6
6
6
5
6
7
10
9
5
5
6
6
6
6
6
6
6
8
9
9
10
6
6
6
6
6
7
7
5
10
8
9
8
8
5
6
7
7
11
3983
4021
3926
3753
3677
2739
2857
2819
3014
3661
3646
4079
4079
4577
3221
3252
3037
2746
2585
3106
2309
3646
3868
4175
3849
2758
3081
3026
2945
2781
3244
3631
3673
3661
2237
1735
3386
2869
3024
3079
2907
3083
3321
3849
3926
3887
3926
2804
2754
2972
2915
2934
3799
3577
2819
2662
2815
3707
3359
3416
1563
3018
3700
3148
3887
Read Date
7/30/98
8/17/98
9/30/98
10/30/98
11/30/98
12/16/98
1/29/99
3/23/99
4/26/99
5/21/99
6/29/99
7/30/99
9/20/99
10/25/99
11/22/99
12/22/99
1/24/00
02/24/00
03/28/00
04/18/00
05/31/00
06/26/00
07/30/99
08/28/00
09/29/00
10/26/00
11/20/00
12/28/00
1/26/01
2/26/01
3/13/01
5/31/01
6/20/01
7/31/01
8/28/01
9/20/01
10/16/01
11/26/01
12/28/01
1/28/02
2/25/02
3/28/02
4/25/02
5/28/02
6/24/02
7/30/02
8/26/02
9/23/02
11/25/02
12/18/02
1/29/03
2/18/03
3/24/03
4/28/03
5/22/03
6/30/03
8/19/03
9/22/03
10/28/03
11/25/03
12/15/03
2/28/05
3/22/05
4/25/05
5/31/05
6/28/05
Average Resistance
(Ohms)
G
H
72
8
77
8
67
7
6
5
6
5
7
5
70
8
8
5
11
6
15
5
18
6
23
9
39
11
49
12
54
12
16
7
13
6
16
6
13
6
12
5
15
5
12
5
23
9
31
13
37
14
40
10
15
6
15
6
13
6
12
6
10
6
16
6
19
7
24
9
23
8
11
5
17
5
22
6
16
6
19
7
17
6
16
6
14
6
17
7
20
8
22
9
24
9
27
10
12
7
15
6
16
6
16
6
15
6
18
7
20
7
14
5
22
9
21
8
28
9
30
8
34
8
13
6
14
6
15
7
18
8
20
12
Figure 33 – California Test Site Graph for Electrode Type G and H
Figure 31 California test site graph for electrode type G and H was purposely omitted to
due lack of data.
Table 22 – California Test Site Data for Electrode Type G and H
National Electrical Grounding Research Project
Location:
Test Site:
Moffett Field, CA.
NASA
Read Date
6/13/2003
2/5/2005
7/6/2005
8/4/2005
9/1/2005
11/4/2005
6/2/2006
7/7/2006
10/2/2006
11/16/2006
12/4/2006
12/26/2006
G1
27
33.4
30
33.7
39.5
57.9
31
30.5
48.3
64.7
73.3
80.9
Resistance (Ohms)
Horizontal Rods
Vertical Rods
G2
G3
H1
H2
3.8
3.5
14.1
14.2
4.09
4.02
12.61
14.33
4.39
4.48
20.2
23
4.39
4.67
20.8
23
4.4
4.6
22.1
23.3
4.69
5
23.7
24.3
4.29
4.48
19.8
23.1
4.31
4.41
20.4
23.4
4.46
4.89
22
20
4.72
5.28
22
20.5
4.81
5.89
20.6
20.1
4.96
5.91
19.53
19.77
51
H3
22.7
25.4
31.8
32.3
32.6
31.9
31.9
31.6
30.9
32
31.6
33.1
Soil Resistivity
(Ohm-cm at 10 ft.)
Read Date
517
781
3677
3868
4577
3160
3621
3753
3037
3374
1792
1666
6/5/1993
12/29/1993
6/23/1994
12/27/1994
6/10/1995
12/21/1995
6/29/1996
12/29/1996
6/28/1997
12/13/1997
12/4/2006
6/28/1998
Average Resistance
(Ohms)
G
H
11
17
14
17
13
25
14
25
16
26
23
27
13
25
13
25
19
24
25
25
28
10
31
24
Staunton, VA
G- Horizontal vs
H- Vertical
200
175
150
Ohms
125
G1
H1
Linear (G1)
Linear (H1)
100
75
50
25
8/6/06
1/18/06
9/28/05
5/20/05
12/4/04
7/29/04
3/19/04
9/11/03
5/8/03
12/16/02
9/23/02
4/22/02
8/15/01
12/20/01
3/29/01
11/14/00
3/9/00
7/11/00
7/29/99
11/30/99
3/25/99
10/23/98
5/15/98
11/24/97
0
Figure 34 – Virginia Test Site Graph for Electrode Type G and H
At the Virginia site, only one electrode of types G and H met the NEC requirement, and
that electrode was H3. The average resistance for the horizontal electrodes was more
than 100 percent greater than the average resistance for all vertical electrodes. The
average resistance values over time for the vertical rods, was relatively consistent for the
duration of the test. The trendline shows decreasing values for both types of electrodes
during the term of the experiment.
52
Table 23 – Virginia Test Site Data for Electrode Type G and H
National Electrical Grounding Research Project
Location: Staunton, VA
Test Site: Dominion Virginia Power Co.
Read Date
11/24/97
12/19/97
1/26/98
3/26/98
5/15/98
7/10/98
8/14/98
9/11/98
10/23/98
12/4/99
1/12/99
2/10/99
3/25/99
4/22/99
5/27/99
6/30/99
7/29/99
8/26/99
10/7/99
10/26/99
11/30/99
12/1/99
2/8/00
3/9/00
4/5/00
5/31/00
6/8/00
7/11/00
8/15/00
9/12/00
10/4/00
11/14/00
12/27/00
1/9/01
2/7/01
3/29/01
4/24/01
6/12/01
7/23/01
8/15/01
9/19/01
10/3/01
11/7/01
12/20/01
1/25/02
2/18/02
3/29/02
4/22/02
5/16/02
6/13/02
7/12/02
9/23/02
9/23/02
10/23/02
11/26/02
12/16/02
1/16/03
2/25/03
4/3/03
5/8/03
6/4/03
7/3/03
8/31/03
9/11/03
10/30/03
12/4/03
G1
30.2
34.9
14.2
41.1
35.2
65.3
120.8
138.0
161.3
186.2
61.1
50.7
41.9
53.6
111
168
170
140
38
47
70
55
65
57
52
44
94
79
91
42
42
88
73
77
66
60
55
73
122
71
146
162
190
186
194
192
77
47
51
97
155
177
195
123
52
50
66
56
55
56
34
50
74
65
62
59
Resistance (Ohms)
Horizontal Rods
G2
G3
H1
35.5
31.6
24.7
45.2
35.5
27.1
14.8
14.1
28.8
54.0
42.2
29.9
47.1
39.5
28.5
71.3
52.9
31.1
104.0
69.7
34.2
110.0
71.8
29.9
120.4
80.0
28.5
156.2
98.6
34.7
98.4
68.9
29.7
86.4
60.2
30.8
73.7
53.1
28.9
81.5
59.2
29.7
108
67
31
134
85
34
129
80
31
104
79
35
59
40
23
71
49
23
88
61
24
78
57
26
88
66
28
77
57
28
71
52
26
63
44
25
94
64
28
86
58
29
90
59
25
64
43
29
64
43
27
103
67
26
93
67
28
98
72
29
92
66
28
85
60
28
76
53
28
84
54
25
107
72
28
99
67
26
135
82
27
146
88
27
166
98
28
175
104
28
188
111
30
176
106
29
101
63
26
61
39
24
75
49
23
96
63
26
135
80
27
145
85
28
154
88
26
111
72
23
69
50
23
72
50
24
97
65
26
77
58
28
81
54
27
77
51
26
46
32
25
62
42
26
83
55
27
80
56
27
87
65
26
87
62
26
Vertical Rods
H2
25.5
27.9
29.1
31.1
30.4
33.6
38.9
37.5
39.7
49.0
40.9
38.3
35.3
35.7
36
44
45
49
28
28
29
31
34
34
32
30
33
37
34
35
32
31
34
36
36
35
34
31
39
38
43
45
49
51
55
55
45
36
34
34
40
46
46
44
33
34
36
38
35
34
31
31
30
29
31
32
53
H3
21.6
23.5
24.6
26.7
26.4
28.6
31.7
27.9
26.6
32.2
25.1
27.0
25.2
26.2
27
31
30
34
20
20
21
22
24
24
23
22
24
26
22
27
25
23
23
24
24
24
24
21
25
22
25
25
26
27
28
28
24
21
21
22
25
27
26
24
20
22
24
25
24
24
23
23
22
22
22
22
Soil Resistivity
(Ohm-cm at 10 ft.)
Read Date
9,958
10,437
10,073
9,728
19,533
10,207
11701
11,701
10,647
10,647
10,647
10,667
11,145
11,318
11,222
8,464
8,675
9,020
9,518
10302.7
10168.65
9766.5
9421.8
9747.35
9651.6
10647.4
9192
9038.8
9287.75
9900.55
10302.7
10436.75
10206.95
9881.4
9249.45
9575
9268.6
9517.55
9785.65
9938.85
10743.15
11758.1
11490
10360.15
9172.85
8923.9
8847.3
10149.5
9670.75
9651.6
9709.05
8617.5
9172.85
9747.35
10436.75
9919.7
9881.4
9230.3
9096.25
8847.3
8560.05
8962.2
9383.5
10838.9
11/24/97
12/19/97
1/26/98
3/26/98
5/15/98
7/10/98
8/14/98
9/11/98
10/23/98
12/4/99
1/12/99
2/10/99
3/25/99
4/22/99
5/27/99
6/30/99
7/29/99
8/26/99
10/7/99
10/26/99
11/30/99
12/1/99
2/8/00
3/9/00
4/5/00
5/31/00
6/8/00
7/11/00
8/15/00
9/12/00
10/4/00
11/14/00
12/27/00
1/9/01
2/7/01
3/29/01
4/24/01
6/12/01
7/23/01
8/15/01
9/19/01
10/3/01
11/7/01
12/20/01
1/25/02
2/18/02
3/29/02
4/22/02
5/16/02
6/13/02
7/12/02
9/23/02
9/23/02
10/23/02
11/26/02
12/16/02
1/16/03
2/25/03
4/3/03
5/8/03
6/4/03
7/3/03
8/31/03
9/11/03
10/30/03
12/4/03
Average Resistance
(Ohms)
G
H
32
24
39
26
14
28
46
29
41
28
63
31
98
35
107
32
121
32
147
39
76
32
66
32
56
30
65
31
95
31
129
36
126
35
108
40
46
23
55
24
73
25
64
26
73
29
63
28
58
27
50
26
84
29
75
30
80
27
50
30
50
28
86
27
78
28
82
29
75
30
68
29
61
29
71
26
100
31
79
29
121
32
132
32
152
34
155
36
164
38
158
37
81
31
49
27
58
26
86
27
123
31
136
34
146
33
102
31
57
25
57
27
76
29
63
30
63
28
61
28
37
26
52
27
71
26
67
26
71
26
70
27
/99
54
5/1406
3/23/2006
6/9/2005
6/20/2001
4/19/2001
1//2001
11/16/2000
9/20/2000
7/19/2000
5/26/2000
03/22/00
9/
10/19/1999
8/16/1999
6/18/1999
4/15/1999
2/19/1999
12/29/1998
10/23/1998
Ohms
Hibernia, NY
G- Horizontal vs
H- Vertical
400
350
300
250
200
G1
H1
Linear (G1)
Linear (H1)
150
100
50
0
Figure 35 – New York Test Site Graph for Electrode Type G and H
Table 24 – New York Test Site Data for Electrode Type G and H
National Electrical Grounding Research Project
Location:
Test Site:
Hibernia, NY
CENHUD
Read Date
9/24/1998
10/23/1998
11/20/1998
12/29/1998
1/21/1999
2/19/1999
3/19/1999
4/15/1999
5/27/1999
6/18/1999
7/16/1999
8/16/1999
9/27/1999
10/19/1999
11/19/1999
9/ /99
2/15/2000
03/22/00
4/19/2000
5/26/2000
6/15/2000
7/19/2000
8/18/2000
9/20/2000
10/17/2000
11/16/2000
12/13/2000
1//2001
2/15/2001
4/19/2001
5/16/2001
6/20/2001
7/19/2001
6/9/2005
1/20/2006
3/23/2006
4/28/2006
5/1406
G1
681
95
138
173
136
133
111
143
104
164
164
265
83
112
154
124
173
139
155
114
108
216
103
114
190
165
261
256
213
180
228
194
234
250
164
240
135
152
Resistance (Ohms)
Horizontal Rods
G2
G3
443
291
81
80
116
104
141
129
109
102
107
100
96
98
126
135
89
99
128
147
125
130
173
167
68
64
104
110
135
144
114
138
145
146
120
122
142
147
97
97
93
93
161
173
88
88
97
95
166
162
136
127
222
223
215
207
172
180
163
171
197
216
151
156
162
169
187
178
142
140
214
224
148
152
135
141
H1
111
102
118
134
140
137
142
136
114
122
116
118
108
115
130
139
157
155
143
124
119
123
109
110
125
130
151
162
162
156
151
130
124
140
155
171
155
144
Vertical Rods
H2
118
104
119
136
143
137
142
139
115
121
113
116
105
113
126
134
150
151
142
123
117
122
109
108
122
127
145
157
156
153
152
132
125
152
158
81
530
153
Soil Resistivity
(Ohm-cm at 10 ft.)
H3
124
109
124
142
147
141
147
143
118
126
116
123
110
117
133
140
156
154
145
124
119
125
110
109
126
130
151
161
162
157
154
131
125
155
160
184
405
155
Read Date
19916
18575
21237
22407
22349
23229
23172
21831
18575
17427
17158
18288
16086
17235
19093
19686
22406
21142
20222
17503
16948
16737
15378
16086
18020
18729
21237
23037
24014
21574
20299
18193
17081
17886
18499
29491
19035
20108
9/24/1998
10/23/1998
11/20/1998
12/29/1998
1/21/1999
2/19/1999
3/19/1999
4/15/1999
5/27/1999
6/18/1999
7/16/1999
8/16/1999
9/27/1999
10/19/1999
11/19/1999
9/ /99
2/15/2000
03/22/00
4/19/2000
5/26/2000
6/15/2000
7/19/2000
8/18/2000
9/20/2000
10/17/2000
11/16/2000
12/13/2000
1//2001
2/15/2001
4/19/2001
5/16/2001
6/20/2001
7/19/2001
6/9/2005
1/20/2006
3/23/2006
4/28/2006
5/1406
Average Resistance
(Ohms)
G
H
472
118
85
105
119
120
148
137
116
143
114
138
101
144
135
139
97
116
146
123
140
115
202
119
72
108
109
115
144
130
125
138
155
154
127
154
148
143
103
124
98
118
184
123
93
109
102
109
173
124
142
129
235
149
226
160
188
160
171
155
214
152
167
131
188
125
205
149
149
158
226
145
145
363
143
151
As compared to earth resistivity readings in other sites, Hibernia, NY, was consistently
greater on average than any of the other sites. Neither the horizontal nor the vertical rods
had average resistance values that met the NEC Section 250.53(G), 25 ohm requirement.
The average resistance values for the vertical rods over time were relatively consistent for
the duration of the test. The trendlines for the both vertical and horizontal electrodes
showed an increasing trend.
55
6.1.5
Comparison of Electrode Resistance
Table 25 shows the electrode comparisons that were made at the Las Vegas, National,
and at all sites combined. The Type K (plate) electrode differs in diameter for the
National sites and Las Vegas Sites, thus graphs for each are shown. The objective of this
section was to show how the electrode resistance varied from site to site. By charting the
yearly mean of the electrode resistance with one data point, ignoring the monthly
variations, the average trend or influence each test location has on an electrode can be
more easily evaluated.
Site Location
Las Vegas
All
Las Vegas
Las Vegas
All
All
All
All
Las Vegas
Las Vegas
National
Las Vegas
All
Table 25 - Electrode Comparison Legend
Electrode Type
Site Location
A
Las Vegas
B
Las Vegas
C
Las Vegas
D
Las Vegas
E
Las Vegas
F
All
G
National
H
National
I
National
J
National
K
National
K
National
L
National
56
Electrode Type
M
N
O
P
Q
R
S
T
V
W
X
Y
Z
LAS VEGAS SITES
A- ELECTRODES
COMPARISON
80
70
60
Ohms
50
BA-A1
PA-A1
LM-A1
PE-A1
CH-A1
40
30
20
10
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 36 - Type A Electrode Comparison
The comparison shows that the Pawnee A electrode had lower yearly mean resistance
over time than other type A electrodes.
57
All Sites
B- Electrodes
Comparison
80
70
60
IL-B1
VA-B1
TX-B1
NY-B1
CA-B1
BA-B1
PA-B1
LM-B1
PE-B1
CH-B1
Ohms
50
40
30
20
10
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 37 - Type B Electrode Comparison
The B electrode was installed in all sites. B electrodes in the Illinois, Pawnee, Lone
Mountain, Pecos and Charleston all had resistance readings less than 20 ohms when
evaluated with their yearly mean resistance calculated for the term of the project.
58
LAS VEGAS SITES
C- ELECTRODES
COMPARISON
200
180
160
140
Ohms
120
BA-C1
PA-C1
LM-C1
PE-C1
CH-C1
100
80
60
40
20
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 38 - Type C Electrode Comparison
The data showed a spike in mean resistance during the fourth and sixth year at the
Pawnee site, and there was also a spike in resistance during the seventh year at the
Balboa site. This could be caused by loose connections or corroded conductor. The C
electrodes in the Lone Mountain and Pecos sites had resistance readings less than 20
ohms when evaluated with their yearly mean resistance calculated for the term of the
project.
59
LAS VEGAS SITES
D- ELECTRODES
COMPARISON
140
120
100
BA-D1
PA-D1
LM-D1
PE-D1
CH-D1
Ohms
80
60
40
20
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 39 - Type D Electrode Comparison
Three sites had resistance readings that were relatively flat during the term of the
experiment; those were Balboa, Lone Mountain and Pawnee. Greater variability with
higher resistance readings occurred at the Charleston site. The D electrodes in the Lone
Mountain and Pawnee sites had resistance readings less than 20 ohms when evaluated
with their yearly mean resistance calculated for the term of the project.
60
All Sites
E- Electrodes
Comparison
60
50
IL-E1
VA-E1
TX-E1
NY-E1
CA-E1
BA-E1
PA-E1
LM-E1
PE-E1
CH-E1
Ohms
40
30
20
10
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 40- Type E Electrode Comparison
The E electrode in all sites except in New York, had relatively consistent yearly mean
resistance readings for the term of the experiment. Except for New York, all mean yearly
data points for this electrode were less than 25 ohms.
61
All Sites
F- Electrodes
Comparison
200
180
160
IL-F1
VA-F1
TX-F1
NY-F1
CA-F1
BA-F1
PA-F1
LM-F1
PE-F1
CH-F1
140
Ohms
120
100
80
60
40
20
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 41 - Type F Electrode Comparison
Very few readings were made at the California site to make any inferences on that data.
In addition, there was nearly a four-year break in data collection for the F electrode in the
New York site. The data showed that the majority of F electrodes had relative consistent
yearly mean resistance plots during the term of the experiment.
62
All Sites
G- Electrodes
Comparison
450
400
350
IL-G1
VA-G1
TX-G1
NY-G1
CA-G1
BA-G1
PA-G1
LM-G1
PE-G1
CH-G1
Ohms
300
250
200
150
100
50
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 42 - Type G Electrode Comparison
The graphs showing the highest resistance yearly mean readings were the New York and
Balboa sites. The lowest resistance readings for these sites occurred in the second year at
about 140 ohms. The variability of the electrodes in the Virginia and Lone Mountain
sites were similar, and were mostly above 50 ohms. All other electrodes, except for those
at the Charleston site, had mean yearly resistance readings below 50 ohms for the term of
the experiment.
63
All Sites
H- Electrodes
Comparison
180
160
140
IL-H1
VA-H1
TX-H1
NY-H1
CA-H1
BA-H1
PA-H1
LM-H1
PE-H1
CH-H1
Ohms
120
100
80
60
40
20
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 43 - Type H Electrode Comparison
Once again, there was a break in the data collection for the New York site. Nonetheless,
the highest mean yearly resistance readings were at the New York site. The H electrode
in the Balboa site showed an increasing trend during the experiment. Other electrodes
showed this trend, but were not so pronounced. Except for the H electrode in the Balboa
and New York sites, all other electrodes during the term of the project were below yearly
mean readings of approximately 30 ohms.
64
LAS VEGAS SITES
I- ELECTRODES
COMPARISON
50
40
30
Ohms
BA-I1
PA-I1
LM-I1
PE-I1
CH-I1
20
10
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 44 - Type I Electrode Comparison
The I electrodes in every Las Vegas site showed relatively little variability in mean yearly
readings during the term of the experiment. Only the electrode in Balboa was greater
than 10 ohms, but it was less than 40 ohms during the term of the experiment.
65
LAS VEGAS SITES
J- ELECTRODES
COMPARISON
275
250
225
200
Ohms
175
BA-J1
PA-J1
LM-J1
PE-J1
CH-J1
150
125
100
75
50
25
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 45 - Type J Electrode Comparison
The graph clearly showed that the J electrode in the Balboa site had the highest mean
yearly resistance readings and the greatest variability. All other electrodes showed a
decreasing or relatively flat trend over time.
66
National Sites
K- Electrodes
Comparison
700
600
500
IL-K1
VA-K1
TX-K1
NY-K1
CA-K1
Ohms
400
300
200
100
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 46 - Type K Electrode Comparison National Sites
The K electrodes in all sites had the highest resistance readings. Based on this, the
graphs also showed high mean yearly readings through the term of the experiment. This
is especially so with the K electrodes in the Virginia, New York, and California sites.
67
LAS VEGAS SITES
K- ELECTRODES
COMPARISON
600
550
500
450
400
BA-K2
PA-K2
LM-K2
PE-K2
CH-K2
Ohms
350
300
250
200
150
100
50
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 47 - Type K Electrode Comparison Las Vegas Sites
The K electrodes in all Las Vegas sites had the highest resistance readings. Based on
this, the graphs also show high mean yearly readings through the term of the experiment,
except for the Pawnee site. The Pawnee K electrode, however, does show an increasing
trend in resistance over time.
68
All Sites
L- Electrodes
Comparison
70
60
IL-L1
VA-L1
TX-L1
NY-L1
CA-L1
BA-L1
PA-L1
LM-L1
PE-L1
CH-L1
50
Ohms
40
30
20
10
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 48 - Type L Electrode Comparison
In all sites except for Virginia, the L electrode had resistance readings of less than
approximately 40 ohms for the term of the experiment, averaging below 25 ohms for nine
out of ten years. The L electrode in the Virginia site had a steep positive slope for the
mean yearly resistance reading from year 9-10. As compared to other L electrodes, the
electrodes in the Illinois, Texas, California, Pawnee, and Pecos sites had low mean yearly
resistance readings.
69
LAS VEGAS SITES
M- ELECTRODES
COMPARISON
110
100
90
80
Ohms
70
BA-M1
PA-M1
LM-M1
PE-M1
CH-M1
60
50
40
30
20
10
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 49 - Type M Electrode Comparison
The M electrode in the Balboa site clearly had the highest mean yearly readings during
the term of the experiment. The best results were with the Pawnee site. Most electrodes
showed an increasing trend in resistance.
70
LAS VEGAS SITES
N- ELECTRODES
COMPARISON
100
90
80
70
Ohms
60
BA-N1
PA-N1
LM-N1
PE-N1
CH-N1
50
40
30
20
10
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 50 - Type N Electrode Comparison
The N electrode in the Balboa site had the highest mean yearly readings during the
experiment. The best results were with the electrode in the Lone Mountain, Pawnee and
Charleston sites.
71
LAS VEGAS SITES
O- ELECTRODES
COMPARISON
80
70
60
Ohms
50
BA-O1
PA-O1
LM-O2
PE-O1
CH-O1
40
30
20
10
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 51 - Type O Electrode Comparison
Once again, the electrode in the Balboa site had the highest mean yearly readings.
Somewhat similar results for the N electrode were obtained for the O electrodes - the
worst case was in the Balboa site, and the best cases were with the Lone Mountain,
Pawnee and Charleston sites.
72
LAS VEGAS SITES
P- ELECTRODES
COMPARISON
100
90
80
70
Ohms
60
BA-P1
PA-P1
LM-P1
PE-P1
CH-P1
50
40
30
20
10
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 52 - Type P Electrode Comparison
Again, for the electrodes in the Las Vegas sites, the P electrode in the Balboa site was the
worst case. All other sites had resistance readings less than 40 ohms through the term of
the experiment.
73
LAS VEGAS SITES
Q- ELECTRODES
COMPARISON
300
275
250
225
200
BA-Q1
PA-Q1
LM-Q1
PE-Q1
CH-Q1
Ohms
175
150
125
100
75
50
25
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 53 - Type Q Electrode Comparison
For the Q electrode, the Balboa site had the highest resistance readings. The Lone
Mountain, Pecos and Pawnee sites showed a sharp decrease in mean resistance from year
one to year two. In contrast, the Q electrode in the Charleston site showed a sharp
increase during that same time period.
74
All Sites
R- Electrodes
Comparison
40
35
30
Ohms
25
IL-R1
VA-R1
TX-R1
NY-R1
CA-R1
BA-R1
20
15
10
5
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 54 - Type R Electrode Comparison
The R electrode was present only in the sites shown in the graph legend. There was
approximately a four-year break in data collection from the New York site. Nonetheless,
the limited data shows that the mean yearly resistance readings were greatest at the New
York site. The R electrodes in the Texas and Illinois sites had very low mean yearly
resistance readings.
75
All Sites
S- Electrodes
Comparison
120
100
Ohms
80
IL-S1
VA-S1
TX-S1
NY-S1
CA-S1
PA-S1
PE-S1
60
40
20
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 55 - Type S Electrode Comparison
Except for the New York site, the S electrodes in all other sites showed relatively low and
consistent mean yearly readings for the term of the experiment.
76
National Sites
T- Electrodes
Comparison
120
100
Ohms
80
IL-T1
VA-T1
TX-T1
NY-T1
CA-T1
60
40
20
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 56 - Type T Electrode Comparison
The results for the T electrode were very similar to the results for the S electrodes in the
National sites. The chief difference was that the T electrode had slightly higher readings
than the S electrode.
77
National Sites
V- Electrodes
Comparison
160
140
120
Ohms
100
IL-V1
VA-V1
TX-V1
NY-V1
CA-V1
80
60
40
20
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 57 - Type V Electrode Comparison
Once again, for the National sites, the highest mean yearly resistance readings were with
the New York site. The lowest readings were with the Illinois site, which showed
consistency throughout the term of the experiment.
78
National Sites
W- Electrodes
Comparison
45
40
35
Ohms
30
IL-W1
VA-W1
TX-W1
NY-W1
CA-W1
25
20
15
10
5
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 58 - Type W Electrode Comparison
Once again, for the National sites, the highest mean yearly resistance readings were with
the New York site. The lowest readings were with the Illinois site, which showed
consistency throughout the term of the experiment.
79
National Sites
X- Electrodes
Comparison
For Year 7 and 8,
TX- X1and X2 Exceed 3000 Ohms
120
100
Ohms
80
IL-X1
VA-X1
TX-X3
NY-X1
CA-X1
60
40
20
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 59 - Type X Electrode Comparison
The X1 and the X2 electrodes in the Texas site readings exceeded 3000 ohms in year
seven and eight of the experiment. The Figure above plots electrode X3 which remained
low for the term of the experiment. The X1 electrode in the California and Illinois sites
were less than 20 ohms for the mean yearly resistance readings.
80
National Sites
Y- Electrodes
Comparison
100
80
60
Ohms
IL-Y1
VA-Y1
TX-Y1
NY-Y1
40
20
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 60 - Type Y Electrode Comparison
The Y electrode was not installed in the California site. Again, the New York site had
the highest readings, followed by Virginia, Texas, and Illinois.
81
National Sites
Z- Electrodes
Comparison
90
80
70
Ohms
60
IL-Z1
VA-Z1
TX-Z1
NY-Z1
CA-Z1
50
40
30
20
10
0
Year
Year
Year
Year
Year
Year
Year
Year
Year
Year
1
2
3
4
5
6
7
8
9
10
Years of Service
Figure 61 - Type Z Electrode Comparison
The Z electrodes had similar results to other electrodes in the National sites. That is, the
highest mean yearly readings were with the New York site, followed by Virginia,
California, Texas, and Illinois.
6.2 Ancillary Experiments
82
The ancillary experiments included: a) DC Active, b) Dissimilar Metals, and c) Benign
Corrosion experiments.
6.2.1 DC1 and DC2 Results
Northbrook, IL
Direct Currrent Experiment
DC1
7
6
Milliamps
5
4
DC1A
DC1B
DC1C
3
2
1
12/12/06
7/26/06
10/25/06
4/18/06
1/19/06
7/15/05
10/19/05
4/18/05
1/25/05
8/16/04
11/23/04
5/26/04
2/18/04
10/8/03
7/18/03
4/23/03
1/28/03
7/15/02
10/17/02
4/15/02
1/22/02
7//01
10/22/01
4/18/01
1/10/01
7/17/00
10/11/00
4/14/00
1/18/00
7/16/99
10/15/99
4/13/99
1/18/99
10/8/98
0
Figure 62 - Illinois DC1 Experiment
The results for the DC1 pod showed that the current in all three electrodes were relatively
similar over the term of the experiment. All electrodes showed a decrease in current in
about the sixth year of the experiment, and a continuing progressive decrease through the
eighth year. The decrease in current is possibly due to either corrosion and/or a loosening
of the connection means and separation between the soil and the rod itself.
83
Northbrook, IL
Direct Currrent Experiment
DC2
40
35
30
Milliamps
25
DC2A
DC2B
DC2C
20
15
10
5
10/8/98
1/18/99
4/13/99
7/16/99
10/15/99
1/18/00
4/14/00
7/17/00
10/11/00
1/10/01
4/18/01
7//01
10/22/01
1/22/02
4/15/02
7/15/02
10/17/02
1/28/03
4/23/03
7/18/03
10/8/03
2/18/04
5/26/04
8/16/04
11/23/04
1/25/05
4/18/05
7/15/05
10/19/05
1/19/06
4/18/06
7/26/06
10/25/06
12/12/06
0
Figure 63 - Illinois DC2 Experiment
Unlike the results for the DC1 pod, the electrodes in the DC2 pod did not show a specific
decrease in DC current at a specific period in time. It was determined that at about the
second year of the experiment the polarity in the DC2 pod was reversed. This means that
electrode material was not being lost to the surrounding soil. Except for one abnormality
during the end of the third year, the current for the three electrodes in the DC2 pod were
similar.
84
Dallas, TX
Direct Current Experiment
DC1
12
10
Milliamps
8
DC1A
DC1B
DC1C
6
4
2
11/22/06
3//06
7/12/06
7/29/05
11/28/05
3/22/05
7/ /2004
11/ /2004
3/ /2004
7//03
11/25/03
3/24/03
7/30/02
11/25/02
3/28/02
7/31/01
11/26/01
3/13/01
11/20/00
07/30/99
03/28/00
11/22/99
7/30/99
3/23/99
7/30/98
11/30/98
0
Figure 64 - Texas DC1 Experiment
Except for some abnormalities, the results for the DC1 pod showed that the current in all
three electrodes were relatively similar over the term of the experiment. All electrodes
showed a decrease in current in about the fourth year of the experiment and remained at a
relatively low level for the remaining term of the experiment. As with the Illinois site,
the results for the DC1 pod showed that the current in all three electrodes were relatively
similar over the term of the experiment. The decrease in current is possibly due to one or
more of the following factors: corrosion; loosening of the connection means; and
separation between the soil and the rod itself.
85
Dallas TX
Direct Current Experiment
DC2
12
10
Milliamps
8
DC2A
DC2B
DC2C
6
4
2
11/22/06
3//06
7/12/06
7/29/05
11/28/05
3/22/05
7/ /2004
11/ /2004
3/ /2004
7//03
11/25/03
3/24/03
7/30/02
11/25/02
3/28/02
7/31/01
11/26/01
3/13/01
11/20/00
07/30/99
03/28/00
11/22/99
7/30/99
3/23/99
7/30/98
11/30/98
0
Figure 65 - Texas DC2 Experiment
The results showed that the three electrodes in the DC2 pod did not reach a low current
level until late 2005. Once again, the overall decrease in current indicated that there was
an increase in resistance due to a number of contributing factors, one of which could be
corrosion.
86
Moffett Field, CA
Direct Current Experiment
DC1
30
25
Milliamps
20
DC1A
DC1B
DC1C
15
10
5
12/26/06
10/2/06
7/7/06
4//06
1//06
10//05
7/6/05
4//05
1//05
10//2004
7//2004
4//2004
10//03
1//2004
7//03
4//03
1//03
10//02
7//02
4//02
1/28/02
0
Figure 66 - California DC1 Experiment
Unlike the other National sites, little data was collected from the California site. Based
on this it was difficult to draw any specific conclusion. The figures for both DC pods are
included for reference.
Moffett Field, CA
Direct Current Experiment
DC2
7
6
4
DC2A
DC2B
DC2C
3
2
1
Figure 67 - California DC2 Experiment
87
12/26/06
10/2/06
7/7/06
4//06
1//06
10//05
7/6/05
4//05
1//05
10//2004
7//2004
4//2004
1//2004
10//03
7//03
4//03
1//03
10//02
7//02
4//02
0
1/28/02
Milliamps
5
Staunton, VA
Direct Current Experiment
DC1
10
Milliamps
8
6
DC1A
DC1B
DC1C
4
2
12//06
9//06
5/24/06
1/18/06
9/28/05
5/20/05
9//04
1/ /2005
1//06
5/21/04
9/11/03
5/8/03
1/16/03
9/23/02
5/16/02
1/25/02
5//01
9/19/01
1/9/01
9/12/00
1//00
5/31/00
10/7/99
5/27/99
9//98
1/12/99
5/15/98
1/26/98
0
Figure 68 - Virginia DC1 Experiment
Except for one abnormality in mid 2000, the results for the DC1 pod showed that the
current in all three electrodes was relatively similar up until the sixth year of the
experiment. At this time the DC1 electrode measured little or no current. This indicated
that the DC1A electrode had a high resistance, which could be due to a number of factors,
including corrosion.
88
Staunton, VA
Direct Current Experiment
DC2
10
Milliamps
8
6
DC2A
DC2B
DC2C
4
2
12//06
9//06
5/24/06
1/18/06
9/28/05
5/20/05
9//06
1/ /2005
1//06
5/21/04
9/11/03
5/8/03
1/16/03
9/23/02
5/16/02
1/25/02
5//01
9/19/01
1/9/01
9/12/00
5/31/00
1//00
10/7/99
5/27/99
9//98
1/12/99
5/15/98
1/26/98
0
Figure 69 - Virginia DC2 Experiment
The results for the DC2 experiment showed very similar results for all electrodes in the
pod. These results were consistent during the term of the experiment. The graph seems
to show that this experiment needs to be conducted for a longer period of time to result in
a current drop due to an increase in resistance from corrosive effects.
89
Hibernia, NY
Direct Current Experiment
DC1
10
Milliamps
8
6
DC1A
DC1B
DC1C
4
2
4//06
8//05
12//05
4//05
8//04
12//04
4//04
8//03
12//03
4//03
8//02
12//02
4//02
8//01
12//01
5/16/01
1/15/01
09/20/00
1//00
05/26/00
9/27/1999
5/27/1999
1/21/1999
9/24/1998
0
Figure 70 - New York DC1 Experiment
The New York site experiment was active for the first two and one-half years, and
inactive for the following three and one-half years.
Except for DC1A, the results for the DC1 pod showed that the current in all three
electrodes was relatively similar up until mid 2000. All electrodes showed a decrease in
current at about the end of the second year of the experiment, and decreased through the
remaining term of the experiment. This was not true, however, for the DC1A electrode
which showed an increase in current after the second year.
90
Hibernia, NY
Direct Current Experiment
DC2
10
Milliamps
8
6
DC2A
DC2B
DC2C
4
2
4//06
8//05
12//05
4//05
8//04
12//04
4//04
8//03
12//03
4//03
8//02
12//02
4//02
8//01
12//01
5/16/01
1/15/01
09/20/00
1//00
05/26/00
9/27/1999
5/27/1999
1/21/1999
9/24/1998
0
Figure 71 - New York DC2 Experiment
The results for the DC2 pod had similar readings to the DC1 pod for the term of the
experiment. A marked decrease in current took place two years into the experiment, and
the data showed that all three electrodes had minimal current at about two and one-half
years into the experiment. The data indicated that the direct current had a pronounced
effect on the resistance of the electrode to earth.
91
6.2.2 Dissimilar Metals Results
6.2.2.1 Illinois DM Experiments
The Dissimilar Metals (DM) Experiment included six electrodes arranged in three sets of
two. The purpose of this experiment was to develop data that could show changes of
resistance, mainly caused by dissimilar metals in an earth coupled cell that could possibly
produce current flow and lead to corrosion.
Figure 70 illustrates the experiment and shows the grounding electrode samples used.
DM1A, DM2A, DM3A are 5/8” x 8’ copper bonded ground rod and DM1B, DM2B,
DM3B are ¾” x 8’ galvanized steel pipe. There is 6-1/2 ft. between the copper bonded
ground rod and the paired galvanized steel pipe ground rod. The experiment included the
measurement of current flow through each paired grounding electrode circuit. A
precision 0.01 ohm resistor was used in the circuit to standardize current measurement.
Northbrook, IL
Dissimilar Metals Experiment
6
5
Milliamps
4
DM1
DM2
DM3
Linear (DM1)
Linear (DM2)
Linear (DM3)
3
2
1
10/8/98
1/18/99
4/13/99
7/16/99
10/15/99
1/18/00
4/14/00
7/17/00
10/11/00
1/10/01
4/18/01
7//01
10/22/01
1/22/02
4/15/02
7/15/02
10/17/02
1/28/03
4/23/03
7/18/03
10/8/03
2/18/04
5/26/04
8/16/04
11/23/04
1/25/05
4/18/05
7/15/05
10/19/05
1/19/06
4/18/06
7/26/06
10/25/06
12/12/06
0
Figure 72 - Illinois Dissimilar Metals Experiments
Figure 69 shows the trendlines for the three sets of DM electrodes. In all cases, the trend
shows a decrease in current over time, which would indicate an increase of resistance
between the electrodes and earth.
92
Dallas TX
Dissimilar Metals Experiments
6
5
Milliamps
4
DM1
DM2
DM3
Linear (DM1)
Linear (DM2)
Linear (DM3)
3
2
1
11/22/06
3//06
7/12/06
7/29/05
11/28/05
3/22/05
7/ /2004
11/ /2004
3/ /2004
7//03
11/25/03
3/24/03
7/30/02
11/25/02
3/28/02
7/31/01
11/26/01
3/13/01
11/20/00
07/30/99
03/28/00
7/30/99
11/22/99
3/23/99
11/30/98
7/30/98
0
Figure 73 - Texas Dissimilar Metals Experiments
The current readings over time are relatively similar for each of the electrodes. The
trend, however, showed two electrodes decreasing with one electrode increasing. This
increase may be due to one relatively high reading measured in early 2006.
93
Moffett Field, CA
Dissimilar Metals Experiments
70
60
Milliamps
50
40
DM1
DM2
DM3
30
20
10
12/26/06
10/2/06
7/7/06
4//06
1//06
10//05
7/6/05
4//05
1//05
10//2004
7//2004
4//2004
10//03
1//2004
7//03
4//03
1//03
10//02
7//02
4//02
1/28/02
0
Figure 74 - California Dissimilar Metals Experiments
Relatively few data points for this experiment were taken at the California site. The
figure for the DM electrodes is included for reference.
94
Staunton, VA
Dissimilar Metals Experiments
10
8
DM1
DM2
DM3
Linear (DM1)
Linear (DM2)
Linear (DM3)
Milliamps
6
4
2
9//06
12//06
5/24/06
1/18/06
9/28/05
5/20/05
9//06
1/ /2005
1//06
5/21/04
5/8/03
9/11/03
1/16/03
9/23/02
5/16/02
1/25/02
5//01
9/19/01
1/9/01
9/12/00
1//00
5/31/00
10/7/99
5/27/99
9//98
1/12/99
5/15/98
1/26/98
0
Figure 75 - Virginia Dissimilar Metals Experiments
Figure 73 shows trendlines for the three sets of electrodes. In two of three cases, the
trend shows a decrease in current over time, which would indicate an increase of
resistance between the electrodes and earth. In the one case (DM1) the trend is nearly
flat.
95
Hibernia, NY
Dissimilar Metals Experiments
4
Milliamps
3
DM1
DM2
DM3
Linear (DM1)
Linear (DM2)
Linear (DM3)
2
1
4//06
8//05
12//05
4//05
12//04
8//04
4//04
12//03
8//03
4//03
12//02
8//02
4//02
8//01
12//01
5/16/01
1/15/01
09/20/00
1//00
05/26/00
9/27/1999
5/27/1999
1/21/1999
9/24/1998
0
Figure 76 - New York Dissimilar Metals Experiments
For the term of the experiment, the trendlines for all electrodes are decreasing.
This indicated a decrease in current which results in an increase in resistance between
earth and the electrode.
6.2.3
Benign Corrosion Experiments
The Copper Development Association (CDA®), sponsored an adjunct corrosion
experiment that consisted of using 4/0 AWG and 500 KCM bare copper conductors
installed directly in earth, Bentonite or GEM tm backfill materials. Samples of these
conductors from the New York site were exhumed for corrosion analysis, and these
results are shown in Section 5.5 of the, “Condition Report of Grounding Electrodes after
Underground Burial at Las Vegas Nevada and Poughkeepsie, NY”, (Corrosion Report).
See Appendix 11.3.
96
6.3 Soil Characteristics
6.3.1
Earth Resistivity
Earth resistivity (IEEE 81-1983 [4]) is a key factor that can determine the resistance of
grounding electrodes. A set of readings taken with various probe spacings gives a set of
resistivities which, when plotted against spacing, indicates whether there are distinct
layers of different soil or rock and gives an idea of their respective resistivities and depth.
Earth resistivity varied by location as shown in Table 26. Recorded resistivity values for
the National and the Las Vegas test sites ranged from 517 to 23,363 ohm-cm, and 77 to
31,597 ohm-cm respectively. To properly predict the performance of electrodes, earth
resistivity values must be obtained. Standardized testing methods, such as those
referenced in IEEE 81-1983 [4], should be used to determine these values.
Table 26 - Earth Resistivity for All Sites 10 Year Data
Earth Resistivity 10 ft. Spacing
MIN
AVE
MAX
2313
2821
3497
IL
1563
3319
4577
TX
517
2763
4577
CA
153
2527
9000
LM
77
1362
9575
PA
708
2084
9575
CH
766
1734
12868
PE
7603
9930
19533
VA
15378
19527
24014
NY
3217
8736
31597
BA
Earth Resistivity 20 ft. Spacing
MIN
AVE
MAX
1896
2098
2306
IL
1655
3242
8158
TX
460
2118
9000
CH
766
4638
9506
CA
613
3158
9958
LM
575
2079
13175
PE
306
1651
14056
PA
8235
10269
15090
VA
11011
20409
23363
NY
1915
11474
25278
BA
Data in Table 26 are arranged in ascending order using the maximum values.
97
6.3.2
Earth Resistivity versus Resistance for Selected Electrodes
Soil classification reports were provided for each of the Las Vegas sites, and are included
in Appendix 11.5. In tables 27 through 31, comparisons of electrode resistance were
made to earth resistivity. Pawnee represented a low value of earth resistivity and Balboa
represents the highest value.
A limited analysis was conducted to determine whether or not there would be significant
differences in resistance of horizontal versus vertical electrodes. This analysis included
electrodes in the Pawnee, Pecos, Lone Mountain, Charleston and Balboa Las Vegas sites.
The results showed that the average electrode resistance in all cases except for one, the
horizontal electrodes had higher average resistance readings than the vertical types.
Tables 27 through 31, show average electrode resistance values as compared to average
soils resistivity values.
Table 27 - Pawnee Resistance Compared to Earth Resistivity
Table 28 - Pecos Resistance Compared to Earth Resistivity
98
Table 29 - Lone Mountain Resistance Compared to Earth Resistivity
Table 30 - Charleston Resistance Compared to Earth Resistivity
Table 31 Balboa Resistance Compared to Earth Resistivity
99
6.3.3 Soil Temperature
With the exception of the Charleston site, all sites had soil temperatures taken at depths
of 30 in., 78 in., and 126 in.
Northbrook IL
Soil Temperature
80
70
60
Deg F.
50
T1 -126 Inches
T2 -78 Inches
T3 -30 Inches
40
30
20
10
10/8/98
1/18/99
4/13/99
7/16/99
10/15/99
1/18/00
4/14/00
7/17/00
10/11/00
1/10/01
4/18/01
7//01
10/22/01
1/22/02
4/15/02
7/15/02
10/17/02
1/28/03
4/23/03
7/18/03
10/8/03
2/18/04
5/26/04
8/16/04
11/23/04
1/25/05
4/18/05
7/15/05
10/19/05
1/19/06
4/18/06
7/26/06
10/25/06
12/12/06
0
Figure 77 - Illinois Soil Temperature
The greatest range of temperatures measured was with the T3 sensor, located at a 30 in.
depth. This range was approximately 35 to 71 degrees F. As expected, the smallest
range in temperature occurred with the T1 sensor at 126 in. below the surface. The range
was approximately 44 to 59 degrees F. As expected, there was less fluctuation in soil
temperature as soil depth increased. Also as expected, the graph shows a shift in the
maximum and minimum temperatures recorded by any specific sensor over time.
100
Dallas, TX
Soil Temperature
120
100
Deg F.
80
T1 -126 Inches
T2 -78 Inches
T3 -30 Inches
60
40
20
11/22/06
3//06
7/12/06
7/29/05
11/28/05
3/22/05
7/ /2004
11/ /2004
3/ /2004
7//03
11/25/03
3/24/03
7/30/02
11/25/02
3/28/02
7/31/01
11/26/01
3/13/01
11/20/00
07/30/99
03/28/00
7/30/99
11/22/99
3/23/99
7/30/98
11/30/98
0
Figure 78 - Texas Soil Temperature
The greatest range of temperatures measured was with the T3 sensor, located at a 30 in.
depth. This range was approximately 48 to 83 degrees F. As expected, the smallest range
in temperature occurred with the T1 sensor at 126 in. below the surface. Except for the
abnormality in mid 1998, the range was approximately 59 to 72 degrees F.
As expected, there was less fluctuation in soil temperature as soil depth increased. Also
as expected, the graph showed a shift in the maximum and minimum temperatures
recorded by any specific sensor over time. Also as expected, all three sensors recorded
the lowest temperatures during the winter months and the highest temperatures in the
summer months.
101
Moffett Field, CA
Soil Temperature
90
80
70
Deg F.
60
50
T1 -126 Inches
T2 -78 Inches
T3 -30 Inches
40
30
20
10
12/26/06
10/2/06
7/7/06
4//06
1//06
10//05
7/6/05
4//05
1//05
10//2004
7//2004
4//2004
1//2004
10//03
7//03
4//03
1//03
10//02
7//02
4//02
1/28/02
0
Figure 79 - California Soil Temperature
The greatest range of temperatures measured was with the T3 sensor, located at a 30 in.
depth. This range was approximately 55 to 78 degrees F. As expected, the smallest
range in temperature occurred with the T1 sensor at 126 in. below the surface. Also as
expected, there was less fluctuation in soil temperature as soil depth increased.
102
Staunton, VA
Soil Temperature
80
70
60
Deg F
50
T1 -126 Inches
T2 -78 Inches
T3 -30 Inches
40
30
20
10
10/23/02
7/12/02
4/22/02
1/25/02
10/3/01
7/23/01
4/24/01
1/9/01
10/4/00
7/11/00
4/5/00
1//00
7/29/99
10/26/99
4/22/99
1/12/99
10/23/98
7/10/98
04//98
1/26/98
0
Figure 80 - Virginia Soil Temperature
Reliable temperature data for the Virginia site was only captured through 2002.
The greatest range of temperatures measured was with the T3 sensor, located at a 30 in.
depth. This range was approximately 42 to 71 degrees F. The smallest overall range in
temperature occurred with the T1 sensor at 126 in. below the surface. As expected, there
was less fluctuation in soil temperature as soil depth increased.
103
Hibernia, NY
Soil Temperature
80
70
60
Deg F.
50
T1 -126 Inches
T2 -78 Inches
T3 -30 Inches
40
30
20
10
4//06
8//05
12//05
4//05
8//04
12//04
4//04
8//03
12//03
4//03
8//02
12//02
4//02
8//01
12//01
5/16/01
1/15/01
09/20/00
1//00
05/26/00
9/27/1999
5/27/1999
1/21/1999
9/24/1998
0
Figure 81 - New York Soil Temperature
The greatest range of temperatures measured was with the T3 sensor, located at a 30 in.
depth. This range was approximately 35 to 67 degrees F. As expected, the smallest
range in temperature occurred with the T1 sensor at 126 in. below the surface. The range
was approximately 43 to 59 degrees F. As expected, there was less fluctuation in soil
temperature as soil depth increased. Also as expected, the graph shows a shift in the
maximum and minimum temperatures recorded by any specific sensor over time.
104
6.3.4 Earth Resistivity and Soil Temperature
Northbrook, IL
Earth Resistivity
and Soil Temperature
3497
3298
2451
45.1 F
43 F
6/27/04
5/27/04
4/27/04
3/27/04
2/27/04
Soil Temp ° F
1/27/04
12/27/03
11/27/03
9/27/03
10/27/03
8/27/03
7/27/03
5/27/03
4/27/03
3/27/03
2/27/03
1/27/03
12/27/02
11/27/02
9/27/02
10/27/02
8/27/02
7/27/02
6/27/02
5/27/02
4/27/02
3/27/02
2/27/02
1/27/02
12/27/01
11/27/01
9/27/01
10/27/01
6/27/03
Resistivity Ohm-cm
41.4 F
Figure 82 - Illinois Earth Resistivity and Soils Temperature
The data compares the earth resistivity and soil temperature taken at the 126 in. depth.
As expected in most cases, the graph showed an inverse relationship between earth
resistivity and soil temperature.
105
Dallas TX
Earth Resistivity
and Soil Temperature
3925
3887 3926
69.2
70.1
67.7
11/22/06
3//06
7/12/06
7/29/05
11/28/05
3/22/05
7/ /2004
11/ /2004
3/ /2004
11/25/03
7//03
3/24/03
11/25/02
7/30/02
3/28/02
7/31/01
11/26/01
3/13/01
11/20/00
07/30/99
03/28/00
11/22/99
7/30/99
3/23/99
7/30/98
11/30/98
Ohm-cm
Temp ° F
Figure 83 - Texas Earth Resistivity and Soils Temperature
Unlike the Illinois site, there was not a clear inverse relationship between earth resistivity
and soil temperature for the Texas site. With some data over the term of the experiment
there was an inverse relationship, but at other times (e.g. 7/30/99) there was a direct
relationship between resistivity and temperature. It is speculated that these results were
based upon relatively large fluctuations in soil moisture content.
106
Staunton, VA
Earth Resistivity
and Soil Temperature
9//06
5/24/06
1/18/06
9/28/05
5/20/05
9//06
1/ /2005
5/21/04
1//06
9/11/03
5/8/03
1/16/03
9/23/02
5/16/02
1/25/02
5//01
Soil Temp ° F
9/19/01
1/9/01
9/12/00
5/31/00
1//00
10/7/99
5/27/99
9//98
1/12/99
5/15/98
1/26/98
Resistivity Ohm-cm
Figure 84 - Virginia Earth Resistivity and Soils Temperature
The data compares the earth resistivity and soil temperature taken at the 126 in. depth.
As expected in most cases, the graph showed an inverse relationship between earth
resistivity and soil temperature.
107
Hibernia, NY
Earth Resistivity
and Soil Temperature
24014
23037
21237
49.2
45.5
2//06
5/14/06
8//05
11//05
5//05
2//05
8//04
11//04
5//04
2//04
8//03
11//03
5//03
2//03
8//02
5//02
2//02
8//01
11//01
3//01
6/20/01
12/13/00
09/20/00
06/15/00
/99
9/
03/22/00
9/27/1999
6/18/1999
3/19/1999
9/24/1998
12/29/1998
11//02
Earth Resistivity ohm-cm
Soil Temp ° F
43.3
Figure 85 - New York Earth Resistivity and Soils Temperature
As was done with the data for other sites, the data compares the earth resistivity and soil
temperature taken at the 126 in. depth. As expected in most cases, the graph showed an
inverse relationship between earth resistivity and soil temperature.
108
6.3.5 Soil Moisture
A higher Delmhorst unit represents a greater moisture content and a lower resistance.
Northbrook IL
Soil Moisture
120
100
Delmhorst Units
80
M1 -126 Inches
M2 -78 Inches
M3 -30 Inches
60
40
20
6/14/06
10/25/06
2/15/06
10/19/05
6/22/05
2/22/05
7/12/04
11/23/04
3/19/04
10/8/03
6/13/03
2/19/03
6/17/02
10/17/02
2/18/02
6/26/01
10/22/01
2/19/01
6/19/00
10/11/00
2/15/00
6/18/99
10/15/99
2/18/99
10/8/98
0
Figure 86 - Illinois Soil Moisture
The data for all three sensors at each level showed relative consistency throughout the
term of the experiment regarding soil moisture. Some abnormalities in data exist, but this
was for relatively short periods of time.
109
Dallas, TX
Soil Moisture
140
120
Delmhorst Units
100
80
M1 -126 Inches
M2 -78 Inches
M3 -30 Inches
60
40
20
11/22/06
3//06
7/12/06
7/29/05
11/28/05
3/22/05
7/ /2004
11/ /2004
3/ /2004
7//03
11/25/03
3/24/03
7/30/02
11/25/02
3/28/02
7/31/01
11/26/01
3/13/01
11/20/00
07/30/99
03/28/00
7/30/99
11/22/99
3/23/99
7/30/98
11/30/98
0
Figure 87 - Texas Soil Moisture
The data for all three sensors at each level showed large swings in soil moisture content
during the term of the experiment. The range was approximately 1 to 118 Delmhorst
units. The M2 and M3 sensors recorded relative consistent soil moisture, beginning with
about the third year into the experiment.
110
Moffett Field, CA
Soil Moisture
120
100
Delmhorst Units
80
M1 -126 Inches
M2 -78 Inches
M3 -30 Inches
60
40
20
12/26/06
7/7/06
10/2/06
4//06
1//06
10//05
7/6/05
4//05
1//05
10//2004
7//2004
4//2004
1//2004
7//03
10//03
4//03
1//03
10//02
7//02
4//02
1/28/02
0
Figure 88 - California Soil Moisture
The limited data for all three sensors at each level showed at least one swing in soil
moisture content during the term of the experiment. Beginning in the last year of the
experiment, the three sensors began to show relatively constant soil moisture, with the
sensor at the deepest level, M1, showing the greatest Delmhorst units.
111
Staunton, VA
Soil Moisture
120
100
Delmhorst Units
80
M1 -126 Inches
M2 -78 Inches
M3 -30 Inches
60
40
20
10/23/02
7/12/02
4/22/02
1/25/02
10/3/01
7/23/01
4/24/01
1/9/01
10/4/00
7/11/00
4/5/00
1//00
10/26/99
7/29/99
4/22/99
1/12/99
10/23/98
7/10/98
04//98
1/26/98
0
Figure 89 - Virginia Soil Moisture
The results of the data showed periods of moist soil conditions at approximately 95
Delmhorst units, followed by periods of drier soil conditions. Fluctuations were recorded
with sensors at all depths. The greatest fluctuations were with the M2, and M3 sensors.
The smallest range in soil moisture fluctuation was with the M1 sensor at the 126 in.
level.
112
Hibernia, NY
Soil Moisture
120
100
Delmhorst Units
80
M1 -126 Inches
M2 -78 Inches
M3 -30 Inches
60
40
20
4//06
8//05
12//05
4//05
8//04
12//04
4//04
8//03
12//03
4//03
8//02
12//02
4//02
8//01
12//01
5/16/01
1/15/01
09/20/00
05/26/00
1//00
9/27/1999
5/27/1999
1/21/1999
9/24/1998
0
Figure 90 – New York Soil Moisture
Until one and one-half years into the experiment, the soil moisture readings at every
depth were relatively consistent. The M3 sensor showed a sharp decrease in Delmhorst
units in about April 2000, and remained relatively consistent through mid 2001. There
was a break in data collection from mid 2001 through mid 2005.
113
6.4 Corrosion Results
When this project began, it was anticipated that all sample electrodes in every site would
be exhumed and then evaluated for corrosion. Based upon this, the samples including
their three wire connectors were weighed prior to installation in the National sites.
Weight is an important physical characteristic of the sample electrodes and their
connectors, to be judged by a corrosion analysis. As the project progressed, it became
apparent that due to a number of reasons including lack of complete funding, full
exhumation and corrosion analysis of all electrodes in every National site would not be
possible. In addition, difficulty was encountered with some of the sites due to
unanticipated changes including the lack of site access authorization for exhumation.
Nonetheless, a corrosion analysis was conducted on selected exhumed electrodes from
New York and from three of the five Las Vegas sites; Balboa, Lone Mountain and Pecos.
Corrosion and Materials Consultancy Inc., was contracted by FPRF to conduct a
corrosion analysis on the exhumed samples. The complete report is shown in Appendix
11.3.
A summary of the corrosion report by Corrosion and Materials Consultancy Inc. follows.
Grounding electrodes were examined following underground soil exposure testing at sites
near Las Vegas, NV and Poughkeepsie, NY. Specifically, the test samples were
examined after about 9 to 11 years, (Las Vegas) and following 8 years and 8 months,
(Poughkeepsie). The Las Vegas samples were exhumed from four sites (Balboa, Lone
Mountain, Pecos, and Pawnee) between May, 2001 and April, 2004. The samples from
Poughkeepsie, were exhumed in May, 2006.
The corrosion report describes the general condition of the buried grounding electrodes,
notably the extent of corrosion degradation or damage following the approximately ten
year burial period. Given the geometry of electrode assemblies and the three connectors
installed thereon, it was not possible to fully quantify the material performance. Thus, the
majority of the findings were based upon visual appearances supported by selective
metallurgical testing.
The corrosion condition of the grounding electrode assemblies was reviewed according to
the visual appearance and metallurgical condition of the materials. The metallurgical
testing conducted in this program was performed to assess the extent of corrosion damage
confined to the metal substrate. This could include general or localized pitting, metal
thinning, cracked or fractured metals, internal pits, de-alloying and intergranular attack.
Conventional optical microscopy and selective electron microscopy were used to better
describe the nature and extent of corrosion displayed by representative grounding
electrodes after about 10 years burial in soil.
A corrosion rating (CR) was allocated in an attempt to better define the extent and nature
of the corrosion condition of the various grounding electrodes based upon the visual and
metallurgical assessments that were performed. This approach should be of value
regarding the potential for corrosion in any particular type of grounding electrode. The
CR rating shown in Table 32 was not intended as a ranking of one electrode type over
another.
114
Table 32 – Corrosion Ratings
Corrosion rating (CR )
0
none
1
slight
2
moderate
X
heavy
Features
No visible corrosion products or pitted metal
Superficial occurrences of corrosion - not over all
surfaces
Moderate build up of products; some protrusions;
local pitting
Significant build-up of products over all; metal section
loss
The three types of connectors were exposed to the same underground soil conditions as
the grounding electrodes for the same periods of time. The grounding electrodes were
connected using 6 AWG insulated stranded copper conductor to the pull box – the central
place for termination of connectors. Exothermic connections were connected to the top
end of the electrodes; compression and bolted connectors were generally connected
approximately 3-in. apart down from the exothermic connectors.
Most connections retained their integrity during the complete test period. Corrosion was
manifested as rust or green corrosion products on the exothermic connections and on the
steel or copper connectors, respectively. The connectors performed under static
conditions, and were not exposed to high-fault current.
The study demonstrated that many of the grounding electrodes tested at the Las Vegas,
NV sites performed well in the silt, sand, clay-like soils that can generally be regarded as
corrosive-to-highly corrosive. The effects of corrosion at the Poughkeepsie, NY site
were generally less extensive.
The copper-bonded grounding electrodes were generally better ranked from a corrosion
viewpoint by contrast to the galvanized rods (Las Vegas, NV) or pipes (Poughkeepsie,
NY) that displayed more extensive corrosion (rusting). The corrosion report includes a
discussion of the effect of the soil environment on corrosion. The report concludes that
soil properties are only guides and should be considered against other factors when
choosing appropriate grounding electrodes. For all National and Las Vegas sites, a soil
analysis was conducted on either a soil sampling from core boring or soil “grab” sample.
Based upon funding limitations for the corrosion analysis, the soil chemistry correlation
to electrode performance was not conducted.
In summary, the majority of the grounding electrode materials performed well over the
approximately ten year soil exposure tests. Notable exceptions included:
•
•
•
•
The loss of zinc on galvanized steel ground rods, which resulted in excessive
steel corrosion.
Copper-bonded steel ground rods showed minimal corrosion. The exposed
steel at the uncoated end of the copper-bonded ground rods showed evidence
of corrosion (rust) over a distance (typically) of about 1-1.5 inches.
Certain of the grounding electrodes filled with chlorides and encased in
Lynconite II or Bentonite clay corroded at the tip end and around the weep
holes, by contrast to others that displayed minimal corrosion.
Certain of the grounding electrodes – encased horizontally – in coke based
ground enhancement material (GEM tm) corroded along the entire length by
115
•
contrast to others – enclosed vertically – in coke based GEM tm that showed
minimal corrosion.
Failed connectors in general were damaged during the exhumation processes,
where connecting wires were occasionally pulled free of the connectors.
Exothermic connections placed at the ends of the ground rods were
particularly vulnerable to mechanical damage. There was generally
insignificant corrosion of the steel or copper fasteners.
116
7. SUMMARY
The data and observations documented under this research project support the following
findings.
7.1
In evaluating the data for all electrodes in all National sites, the electrodes as a
group in the Illinois site appeared to have the lowest resistance readings, whereas,
the New York site had the highest readings, with the majority of readings in New
York not meeting the 25 ohm requirement of NEC Section 250.52. In a comparison
of all electrodes in each National site, the best results were with the E, L and R
electrodes. Other electrodes that did relatively well were the, S, W and X
electrodes. For most sites, the K and G electrodes were poor performers.
7.2
A limited analysis of the horizontal versus the vertical rod type electrodes for the
Las Vegas sites showed that the vertical electrodes had lower resistance values than
their horizontal counterparts. This was also a similar case for all the National sites
except for Illinois. Variations in earth resistivity and other factors did not appear
alter this relationship.
7.3 Yearly mean electrode resistance readings were compared in the Las Vegas,
National, and all sites combined. For the Las Vegas sites, in almost every case for
every electrode, the Balboa site had the highest yearly mean readings, whereas the
Pawnee site had the lowest values. For the National sites, the yearly mean readings
for all electrodes were highest in the New York site, and lowest in the Illinois and
Texas sites. The B, E, F, G, H and L electrodes were included in all sites.
7.4
As expected, the worst case results were with the New York and Balboa sites,
whereas, the best-case results were generally with the Illinois, Pawnee, and Texas
sites. Electrode resistance values are required to be lower than 25 ohms for
individual rod, pipe and plate electrodes to meet NEC 250.56 [3] requirement.
Concrete encased electrodes per NEC 250.52 [3] are not required to be lower than
the 25 ohm value and may be installed without testing. The concrete encased
electrode, (Type B) exceeded the 25 ohm value in the Texas, Virginia and New
York sites, for the majority of readings.
7.5
Distinct patterns can be seen in data for many of the sites. These patterns appear to
be sympathetic to seasonal variations. It is apparent in comparisons of data from
many sites that an inverse relationship exists between earth resistivity and soil
temperature. According to the Soares Book on Grounding [5], soil temperatures
vary inversely with relative earth resistivity. Knowledge of this factor could be
useful in determining the suitability of an electrode.
7.6 The resistance reading for the National sites showed that Illinois had only two
electrodes that exceeded 25 ohms during the term of the study. This could be due to
the Illinois site being located in moist soil conditions. Most of the electrodes in the
Dallas site for the term of the study were less than 25 ohms. The difference in
resistance readings between the sites can be attributed to soil chemistry, moisture,
resistivity, and other mechanical conditions. The data can be used to make
inferences for appropriate electrodes for use in similar locations.
117
7.7
The DC experiments were designed to evaluate the effects of corrosion due to the
presence of direct currents. With many of the DC electrodes in the National sites,
the data showed a sharp decrease in current with time. It is assumed that this
decrease is due to the corrosive effects of the DC current possibly resulting in
progressively higher resistance levels between the electrode and earth ground.
7.8
The purpose of the dissimilar metals experiment was to evaluate the corrosion of
electrodes caused by different metals (Zn, Cu) installed in close proximity to one
another. Data was developed showing changes of resistance, mainly caused by
dissimilar metals in an earth-coupled cell that could possibly produce a direct
current flow and lead to accelerated corrosion. In most cases, the trendline showed
a decrease in current over time, which indicates an increase of resistance between
electrodes and earth due to corrosion caused by DC current from dissimilar metals
located in an electrolyte (earth).
7.9
The results for the CDA® sponsored benign corrosion experiment showed that the
4/0 AWG and 500 KCM bare copper conductors backfilled with earth, Bentonite or
GEM tm , received a CR of no worse than 0/1- slight superficial occurrences of
corrosion, not over all surfaces.
7.10 To properly predict the performance of electrodes, earth resistivity values were
obtained. Standardized testing methods such as those referenced in IEEE 81-1983
[4] were used to determine these values. Care was taken to ensure reliability and
reproducibility of readings. Even though this was done there were a few
abnormalities in the data. Nonetheless, the data for most sites show reliability
through the term of the project, except for California which showed some
variability. It is known that brackish water exists below the surface of the
California site. Earth resistivity varied by location. Resistivity values for the
National sites ranged from 517 to 24,014 ohm-cm. In the Las Vegas sites, the range
was 30 ohm-cm to 31,597 ohm-cm. Data support the concept that a direct
relationship exists between earth resistivity and electrode resistance.
7.11 Soil temperature measurements were taken at three different depths. Reliability
was shown by the data in all sites since there was less fluctuation in soil
temperature as depth increased. The purpose for the soil temperature measurements
was to compare this information to earth resistivity. As was expected in most cases,
the data showed an inverse relationship. This information could be used by
installers of grounding electrode systems to predict performance during seasonal
changes.
7.12 Project data indicated that moist soil does not necessarily ensure low earth
resistivity or low electrode resistance values. All National sites were in different
geographic locations, and, therefore, subjected to different local weather climates
and soils content. Soil moisture values for the Virginia and New York sites indicate
mostly wet soil for the majority of readings while average resistivity values were in
the range of 9,817 and 20,424 ohm-cm for 10 ft. spacing respectively. Electrode
resistance average values were in the range of 39.6 ohms in Virginia to 94.6 ohms
in New York.
7.13 An independent corrosion analysis of some exhumed grounding electrodes was
conducted. The analysis indicated that the majority of the grounding electrode
118
materials performed well over the approximately ten year exposure test except for
the following: a) loss of zinc on galvanized steel rods resulted in excessive
corrosion, b) copper-bonded steel ground rods showed minimal corrosion, however,
the exposed steel at the unplated end of the ground rod was particularly vulnerable
to corrosion although the average loss was minimal, c) some electrodes filled with
salts and encased in Bentonite corroded at the end of the electrode and around the
weep holes by contrast to others that displayed minimal corrosion, d) vertical
electrodes in GEM tm displayed minimal corrosion in contrast to their horizontal
counterparts, and e) there was generally insignificant corrosion of the three types of
connectors, mechanical, compression, and exothermic, during the term of the
study.
119
8. AREAS OF FURTHER STUDY
8.1 Comparison of Data to Theoretical Models - The data from this project could be
used to compare the values obtained using mathematical modeling found in other
published sources (IEEE and proprietary models).
8.2
Second Generations Study, DC and DM Re-examined - In the DC experiments, a
declining trend in current was present in much of the data. It was apparent that after
a period of time the current flow in many cases was reduced to zero, or near zero
levels. This reduction in current flow is assumed to be caused by corrosion deposits
at the electrode or connector, however, there may be other causes. One implication
of this decreasing current could be that corrosion, meaning loss of electrode
material to the soil due to ionic transport, will occur on rod or pipe grounding
electrodes as a result of being subjected to prolonged low level DC currents in the
grounding system, such as those produced by small household DC power supplies.
Further work could study the corrosive effects of DC current by providing needed
insight into the function and interaction of soils and electrodes relative to small DC
levels.
The DM experiments were passive (non-powered). The current for these
experiments had a tendency to become lower as time progressed in similar fashion
to the active DC experiments. Experiments could be designed to further examine
the corrosive effects due to dissimilar metals and current flow in soil. Electrode
resistance was typically not measured during DC or DM testing, and should be
considered for future experimentation.
8.3
Controlled Soils: Temperature versus Earth Resistivity - During the course of the
experiment, it was observed that the soils temperature affected the earth resistivity
inversely. When soil temperature decreased it caused earth resistivity to increase.
The degree of increase varied in all sites, possibly due to geographic location,
varying moisture levels and soil chemistry. A further study could seek to eliminate
some of the variables by controlling the moisture and soil chemistry while
examining only the effect of temperature.
8.4
Controlled Soils: Moisture versus Earth Resistivity - Similar to and in conjunction
with controlled temperature experiments, an evaluation of the effects of soil
moisture could be designed to examine the primary effect of soil moisture on earth
resistivity where the moisture levels are controlled and can be set to known
variables.
8.5 Controlled Soils Chemistry – Laboratory experiments which control and vary
temperature and moisture of soil could produce indicators for the performance of
grounding electrodes. Varying the chemistry of soils may similarly provide insight
into performance of electrodes, but in a broad scope the examination of soils
chemistry may provide a greater insight into their corrosive effects on various types
of electrodes and connectors. Further work could also seek to evaluate the soil
chemistry, and its effects on earth resistivity. Experiments which require measuring
the effects of corrosion require long-term exposure, and in many cases multiple
samples, some of which could remain for the duration of the experiment and some
which could be removed and examined during the course of the experiment.
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8.6
Horizontal versus Vertical Electrodes – In this report comparisons were made of
some vertical rod and pipe electrodes installed in vertical and horizontal
orientations. Further work on orientation could re-examine the performance
relationships of different orientations of electrodes in the study.
8.7
Data Analysis - The raw data could be further studied in a number of ways,
including further comparisons, statistical confidence and uncertainty.
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9. LIST OF FIGURES and TABLES
Table 1. Sites Legend
Table 2. Electrode Types A through K
Table 3. Electrode Types L through V
Table 4. Electrode e Types W through AE
Table 5. Electrode Types 1A through 2C
Figure 1. Las Vegas Pullbox , Type M, N and R Electrodes
Figure 2. Types A, F and Q Electrodes
Figure 3. Electrode Types E, H, L, K and P
Figure 4. Electrode Type B Concrete Encased Electrode
Figure 5. Electrode Types H, T and X
Figure 6. Electrode Type V
Figure 7. Electrode Type W
Figure 8. Electrode Type Y
Figure 9. Electrode Type Z
Figure 10. Electrode Type AA
Figure 11. Electrode Type AB
Figure 12. Electrode Type AC
Figure 13. Direct Current Experiment DC2 (DC1 Similar)
Figure 14. Dissimilar Metals Experiment DM
Figure 15. Electrodes CDA 1A, 1B, 2A, 2B, 3A and 3B
Table 6. Percentage of Readings Exceeding 25 ohms
Table 7. Percentage of Electrodes Exceeding 50 ohms
Table 8. Percentage of Electrodes Exceeding 100 ohms
Table 9. Percentage of Electrodes Exceeding 250 ohms
Figure 16. Illinois Electrodes Resistance
Figure 17.Texas Electrodes Resistance
Figure 18. California Electrodes Resistance
Figure 19. Virginia Electrodes Resistance
Figure 20. New York Electrodes Resistance
Figure 21.Balboa Test Site Graph Electrode Type G and H
Table 10. Balboa Test Site Data for Electrode Type G and H
Figure 22. Charleston Test Site Graph for Electrode Type G and H
Table 11. Charleston Test Site Data for Electrode Type G and H
Figure 23. Lone Mountain Test Site Graph for Electrode Type G and H
Table 12. Lone Mountain Test Site Data for Electrode Type G and H
Figure 24. Pecos Test Site Graph for Electrode Type G and H
Table 13. Pecos Test Site Data for Electrode Type G and H
Figure 25. Pawnee Test Site Graph for Electrode Type G and H
Table 14. Pawnee Test Site Data for Electrode Type G and H
Figure 26. Balboa Test Site Graph for Electrode Type I and J
Table 15. Balboa Test Site Data for Electrode Type I and J
Figure 27. Charleston Test Site Graph for Electrode Type I and J
Table 16. Charleston Test Site Data for Electrode Type I and J
Figure 28. Lone Mountain Test Site Graph for Electrode Type I and J
Table 17. Lone Mountain Test Site Data for Electrode Type I and J
Figure 29. Pecos Test Site Graph for Electrode Type I and J
Table 18. Pecos Test Site Data for Electrode Type I and J
Figure 30. Pawnee Test Site Graph for Electrode Type I and J
Table 19. Pawnee Test Site Data for Electrode Type I and J
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Figure 31. Illinois Test Site Graph for Electrode Type G and H
Table 20.Illinois Test Site Data for Electrode Type G and H
Figure 32. Texas Test Site Graph for Electrode Type G and H
Table 21. Texas Test Site Data for Electrode Type G and H
Figure 33. California Test Site Graph for Electrode Type G and H
Table 22. California Test Site Data for Electrode Type G and H
Figure 34. Virginia Test Site Graph for Electrode Type G and H
Table 23. Virginia Test Site Data for Electrode Type G and H
Figure 35. New York Test Site Graph for Electrode Type G and H
Table 24. New York Test Site Data for Electrode Type G and H
Table 25. Electrode Comparison Legend
Figure 36. Type A Electrode Comparison
Figure 37. Type B Electrode Comparison
Figure 38. Type C Electrode Comparison
Figure 39. Type D Electrode Comparison
Figure 40. Type E Electrode Comparison
Figure 41. Type F Electrode Comparison
Figure 42. Type G Electrode Comparison
Figure 43. Type H Electrode Comparison
Figure 44. Type I Electrode Comparison
Figure 45. Type J Electrode Comparison
Figure 46. Type K Electrode Comparison National Sites
Figure 47. Type K Electrode Comparison Las Vegas Sites
Figure 48. Type L Electrode Comparison
Figure 49. Type M Electrode Comparison
Figure 50. Type N Electrode Comparison
Figure 51. Type O Electrode Comparison
Figure 52. Type P Electrode Comparison
Figure 53. Type Q Electrode Comparison
Figure 54. Type R Electrode Comparison
Figure 55. Type S Electrode Comparison
Figure 56. Type T Electrode Comparison
Figure 57. Type V Electrode Comparison
Figure 58. Type W Electrode Comparison
Figure 59. Type X Electrode Comparison
Figure 60. Type Y Electrode Comparison
Figure 61. Type Z Electrode Comparison
Figure 62. Illinois DC1 Experiment
Figure 63. Illinois DC2 Experiment
Figure 64. Texas DC1 Experiment
Figure 65. Texas DC2 Experiment
Figure 66. California DC1 Experiment
Figure 67. California DC2 Experiment
Figure 68. Virginia DC1 Experiment
Figure 69. Virginia DC 2 Experiment
Figure 70. New York DC1 Experiment
Figure 71. New York DC2 Experiment
Figure 72. Illinois Dissimilar Metals Experiments
Figure 73. Texas Dissimilar Metals Experiments
Figure 74. California Dissimilar Metals Experiments
Figure 75. Virginia Dissimilar Metals Experiments
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Figure 76. New York Dissimilar Metals Experiments
Table 26. Earth Resistivity for All Sites
Table 27. Pawnee Resistance Compared to Earth Resistivity
Table 28. Pecos Resistance Compared to Earth Resistivity
Table 29. Lone Mountain Resistance Compared to Earth Resistivity
Table 30. Charleston Resistance Compared to Earth Resistivity
Table 31. Balboa Resistance Compared to Earth Resistivity
Figure 77. Illinois Soil Temperature
Figure 78. Texas Soil Temperature
Figure 79. California Soil Temperature
Figure 80. Virginia Soil Temperature
Figure 81. New York Soils Temperature
Figure 82. Illinois Earth Resistivity and Soils Temperature
Figure 83. Texas Earth Resistivity and Soils Temperature
Figure 84. Virginia Earth Resistivity and Soils Temperature
Figure 85. New York Earth Resistivity and Soils Temperature
Figure 86. Illinois Soil Moisture
Figure 87. Texas Soil Moisture
Figure 88. California Soil Moisture
Figure 89.Virginia Soil Moisture
Figure 90. New York Soil Moisture
Table 32. Corrosion Ratings
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10. CITATIONS
[1] D. A. Dini, “Some History of Residential Wiring Practices in the U.S.,” The Fire
Protection Research Foundation Aged Electrical Systems Research Application
Synposium, Chicago, Illinois, October 18-19, 2006, pp. 4-20.
[2] T. Lindsey, T. D.W. Zipse, T Krob, “Grounding/earthing electrode studies. I “,1994
IEEE Industrial, and Commercial Power Systems Technical Conference,
Conference Record, Papers Presented at the 1994 Annual Meeting, 1994 IEEE
Irvine, California, 1-5 May 1994 pp: 163 - 174
[3] National Fire Protection Association, Inc. National Electrical Code. 2005 Edition.
Quincy, MA.
[4] IEEE Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface
Potentials of a Ground System, IEEE Standard 81-1993.
[5] IAEI. Soares Book on Grounding, Eighth Edition. Richardson TX: IAEI, 2001.
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11. APPENDICES
11.1.
11.2.
11.3.
11.4.
11.5.
11.6.
11.7.
Electrode Graphs Las Vegas
Electrode Graphs National
Corrosion Report
Exhumation Reports
Soils Reports
National Construction Plans- Example
Las Vegas Construction Plans
126