Fluke 1625-2 Site Application

Earth ground testing

for mine sites with

Fluke 1625

All mine sites have grounded
electrical systems, so that in
the event of a lightning strike
or utility overvoltage or ground
fault, the current would be able
to find a safe path to earth or
the neutral of the transformer.
To ensure a reliable connec­tion to earth, electrical codes,
engineering standards, and
local standards often specify
a minimum resistance for the
ground electrodes. This appli­cation note looks at how one of
the world’s leading mining and
exploration companies uses
Fluke’s earth ground testers to
maintain a safe working site.

Application Note

Rio Tinto is one of the world’s
leading mining and explora­tion companies. They find, mine
and process the earth’s mineral
resources—metals and minerals
essential for making thousands
of everyday products that meet
society’s needs and contribute to
improved living standards.

Products include aluminium,
copper, diamonds, energy prod­ucts, gold, industrial minerals
and iron ore.

The company’s activities span
the world but are strongly rep­resented in Australia and North
America with significant busi­nesses in South America, Asia,
Europe and southern Africa.

The Pilbara region

Rio Tinto has been at the fore­front of sustained innovation
and growth in the Pilbara region
for more than forty years.

Rio Tinto’s iron ore operations
in the Pilbara have expanded
to an annual capacity of 220
million tonnes, with advanced
plans to further expand. With a
network of 12 mines, three ship­ping terminals and the largest
privately owned heavy freight
rail network in Australia, the
company’s Pilbara operations
make up a major part of iron ore
activities globally. Its opera­tions began in 1966 and have

expanded to meet the growing
needs of the world’s iron and
steel industry.

Rio Tinto is a world-class
asset manager, operating and
maintaining all mining, rail,
power and port facilities in
the Pilbara on behalf of asset
owners Hamersley Iron and
Robe River.

Grounding systems

Regular earth testing is a very
important practice for mining
companies such as Rio Tinto.
The purpose of a ground,
besides the protection of people
and equipment, is to provide a

F r o m t h e F l u k e D i g i t a l L i b r a r y @ w w w . f l u k e . c o m / l i b r a r y

safe path for the dissipation of
fault currents, lightning strikes,
transient over-voltages, static
discharges, EMI and RFI signals
and interference.

A ground is a conducting con­nection, whether intentional or
accidental between an electri­cal circuit or equipment and the
earth, or to some conducting
body that serves in place of the
earth. It helps by stabilising the
voltage to earth during normal
operation, and limits the voltage
rise created by lightning, line
surges or unintentional contact
with higher-voltage lines.

In the event of an electrical
fault or lightning strike any­where in the vicinity of the
mining area, a low-impedance
ground electrode will help carry
the energy into the earth. By
keeping the potential gradient
low, damage is minimised.

Without an effective ground­ing system, workers could be
exposed to the risk of electric
shock, not to mention instru­mentation errors, harmonic
distortion issues, power factor
problems and a host of pos­sible intermittent dilemmas.
If fault currents have no path
to the ground through a prop­erly designed and maintained
grounding system, they will find
unintended paths that could
include people.

Poor grounding not only
contributes to unnecessary
downtime, but a lack of good

grounding is very dangerous
and increases the risk of equip­ment failure. A good grounding
system will improve the reli­ability of equipment and reduce
the likelihood of damage due to
lightning or fault currents.

The need for earth
testing

Over time, corrosive soils with
high moisture content, high salt
content, and high temperatures
can degrade ground rods and
their connections. Previous
faults may have melted connec­tions that aren’t easily visible.
So although the ground system
when initially installed had low
earth ground resistance values,
the resistance of the ground­ing system can increase if the
ground rods are eaten away
from causes due to corrosion of
ground rods, breaks in intercon­necting wires and water table
changes.

Earth resistance is the resis­tance of the earth to the passage
of electric current, and test
results show the resistance
offered by the earthing rods
with the connection leads,
which should be less than 1
Ohms in the case of Rio Tinto’s
installation. Resistivity defines
a material’s ability to conduct
current, which is a complex
property to measure within
the earth as it is affected by
several factors, including soil
composition, mineral content,
temperature and depth.

Intermittent electrical prob­lems at a mine site could be
attributed to poor grounding or
poor power quality.

That is why it is highly recom­mended that all grounds and
ground connections be checked
upon installation and on an
annual basis. During these
periodic checks, if an increase
in resistance of more than 20
per cent is detected, the tech­nician should investigate the
source of the problem, and
lower the resistance by replac­ing or adding ground rods to the
ground system.

Rio Tinto conducts regular
earth ground tests to ensure the
operational safety of a mine.
This is the first line of defense.
The ability to detect and monitor
ground connections can provide
valuable data for undertaking
appropriate risk assessments for
mining operations.

Ground beds provide safety
grounding of electrical equip­ments in mines. The goal in
ground resistance is to achieve
the lowest ground resistance
value possible that makes sense
economically and physically.
Ideally a ground should be of
zero ohms resistance.

David Oxley, electrical super­visor at the reliability assurance
department at Rio Tinto’s
Cape Lambert site in the Pil­bara region, oversees these
inspections.

David said, “We need to
ensure that earth grounding
at all substations is at its peak
performance, and that we are
comply with statutory rules
onsite.”

David and his team perform
checkups at their substations
regularly.

The process

Special instruments make it
simple and easy for maintenance
and safety teams to measure
earth-resistance and trouble­shoot problems.

For Rio Tinto, the Fluke 1625
is used to measure the capabil­ity of the earth ground system at
the substations.

Earth resistance
measurement: the
Fall-of-Potential
measurement

The classic Fall-of-Potential test
method is used at Rio Tinto’s
Cape Lambert facility to measure
the ability of an earth ground
system or an individual elec­trode to dissipate energy from a
site.

2 Fluke Corporation Earth ground testing for mine sites with Fluke 1625