Grounding Rods Oh but Why?
Electrical circuits may be connected to ground (earth) for several
reasons. In mains powered equipment, exposed metal parts are
connected to ground to prevent contact with a dangerous voltage
if electrical insulation fails. Connections to ground limit the build-
up of static electricity when handling flammable products or
when repairing electronic devices.
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• If you’re reading this, chances are you have enjoyed the
sense of accomplishment that comes from driving an 8-foot
long, mostly steel rod into the earth and connecting a
ground wire to it. It’s tough work. At the end of the day, you
know that your effort was justified because you have
installed a system that will protect people from electrical
shock, help safeguard expensive electronic equipment,
limit neutral-to-ground voltage and satisfy the NEC along
the way. There is an increasing awareness in the electrical
industry of the benefits of a low-resistance, high-quality
grounding system. This article takes a nuts-and-bolts
approach to examining one the most commonly installed
components: the ground rod.
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What is a ground rod?...
•
A ground rod is a metal shaft used for grounding. With plastic pipe now
being used for water systems these rods are being used for services and
other devices to be grounded. These rods are to be driven in the ground at
least 8 ft. These rods when made of iron or steel shall be at least 5/8
inches thick. Non ferrous rods should be free of paint or any other non
conductive material should be listed and not less than 1/2 inches thick.
Most codes call for a ground system of 25 ohms or less. While, as a
practical matter, you can't get to zero ohms, you certainly can get to 25
ohms if the ground rods are properly installed. A single electrode
consisting of rod, pipe, or plate that does not have a resistance to ground
of 25 ohms or less shall be augmented by one additional electrode of any
of the types specified above. Where multiple rod, pipe, or plate electrodes
are installed to meet these requirements, they shall not be less than 6 feet
apart.
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Copper
• Copper-bonded, galvanized, and stainless steel ground rods are
available in many different sizes. We will not focus on stainless steel
rods as their high cost prohibits widespread use. More commonly
used are copper-bonded and galvanized steel ground rods. Besides
price, what really makes these rods different? Both rods are
composed of a steel core with a tensile strength ranging from
58,000 psi for galvanized rods to >90,000 psi for copper-bonded
steel rods. From a theoretical standpoint, the higher the tensile
strength, the less likely the rod is to “mushroom” or spread when
being driven. This is a concern when rods are being coupled or
when connections are being made to the top of the rod. Practically
speaking, we all know that any ground rod will mushroom if you hit
it without using a drive sleeve specifically designed to prevent this.
So, the steel used in a copper-bonded rod may give it a slight edge
in “driveability,” but not enough to classify it as a superior
electrode.
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Galvanized ground rods
• Recently, UL-listed galvanized ground rods have shown up in the market. You may
have wondered why now and what does this mean? Underwriters Laboratories
had never listed galvanized ground rods in the past and there are no listing
requirements for galvanized rods in the existing UL 467 Standard, unlike copper-
bonded and stainless steel rods which have clear listing requirements. These rods
use the higher tensile strength steel found in copper-bonded rods, which is a plus,
but we’ve already established that as a minor benefit. These galvanized rods have
a smaller diameter than non-UL listed galvanized rods requiring special accessories
and different exothermic welding equipment.
• Most importantly, these rods are coated with the same amount of zinc as their
non-UL listed cousins (3.9 mils). Since the coating is the same, there is no increase
in service life. So what makes them better? It has been suggested that the UL
listing will make the inspector’s job easier by allowing them to visually inspect for
the UL mark. Inspectors that had trouble qualifying galvanized rods in the past may
appreciate this, but I believe this to be a small minority of the dedicated
individuals in this profession.
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Effective
• Effective earth grounding is essential for
grounded AC and DC electrical equipment and
distribution systems. Effective grounding
provides the level of safety required to protect
personnel and equipment from shock and fire
hazard. The understanding and evaluation of a
facility ground system should be part of any
power quality assurance program
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Time vs. Nature. Vs. Chemicals
Over time, corrosive soils with high moisture
content, high salt content, and high
temperatures can degrade ground rods and
their connections. 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.
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Shake and Bake Values
First, the NEC code (1987, 250-83-3) requires a
minimum ground electrode length of 2.5 meters
(8.0 feet) to be in contact with soil. But, there
are four variables that affect the ground resistance
of a ground system:
1. Length/depth of the ground electrode
2. Diameter of the ground electrode
3. Number of ground electrodes
4 . Ground system design
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It is not for life
• The main difference between the two rods is the
thickness and type of material used to cover the steel
core. Galvanized ground rods are coated with zinc to a
thickness of 3.9 mils or .0039 inches. Copper-bonded
ground rods are coated with copper to a thickness of
10 mils or .010 inches. It is the thickness and type of
material coating that primarily determines the rod’s
corrosion resistance and service life. In essence, we are
comparing zinc to copper and 3.9 mils to 10.0 mils. I
think everyone would agree that, regardless of the
material, a thicker coating would provide better
corrosion protection and, therefore, longer service life.
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Think what do I need
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It is about this simple
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Grounding Eliminates
• limits voltage in a electrical distribution system to definite fixed values
• limits voltage to within insulation ratings
• provides a more stable system with a minimum of transient over voltage
and electrical noise
• provides a path to ground in fault conditions for quick isolation of
equipment with operation of ground fault protection
• provides grounding of all conductive enclosures that may be touched by
personnel, thereby eliminating shock hazards
• reduces static electricity that may be generated within facilities
• provides protection from large electrical disturbances (such as lightning)
by creating a low resistive path to earth
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It Prevents the Incident
• No matter the cause of the ground fault, the path of the electricity
does not flow through the circuit as normal. When working
properly the electricity is fed through the positive wire into a load,
such as an appliance, then it returns to the electrical panel via the
neutral wire. When a ground fault happens, the current bypasses
the load and if wired correctly pass through to the grounding wire.
Because the circuit now has a direct path to the ground, it causes
what is known as a short or short circuit. This short in turn causes
the circuit to use overflowing power, this extra power consumption
then results in the breaker inside your electrical panel to trip
shutting off the power to the circuit.
• Because grounding is so terribly important, the connections that
connect your electrical panel to the earth must be made using
specific connections.
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We use them everywhere
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Remember
• Often an issue of great confusion, static
electricity can cause catastrophic damage if
not controlled properly, especially when
transferring flammable materials
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Size does matter
Length/depth of the ground electrode
One very effective way of lowering ground resistance is to drive ground
electrodes deeper.
Soil is not consistent in its resistivity and can be highly unpredictable. It
is critical when installing the ground electrode, that it is below the
frost line. This is done so that the resistance to ground will not be
greatly influenced by the freezing of the surrounding soil.
Generally, by doubling the length of the ground electrode you can
reduce the resistance level by an additional 40 %. There are occasions
where it is physically impossible to drive ground rods deeper—areas
that are composed of rock, granite, etc. In these instances, alternative
methods including grounding cement are viable.
Diameter of the ground electrode
Increasing the diameter of the ground electrode has very little effect in
lowering the resistance. For example, you could double the diameter
of
a ground electrode and your resistance would only decrease by 10 %.
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You are at risk
Poor grounding not only contributes to unnecessary
downtime, but a lack of good grounding is also dangerous
and increases the risk of equipment failure.
Without an effective grounding system, we 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.
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Your safety too
• Electric current can be
described as the flow of
microscopic particles called
electrons through wires and
electrical appliances. Materials
like metal and water through
which electric current
(electricity) travels easily are
called conducting materials or
conductors. The body is an
excellent conductor, and
electric current from any
source passing through the
body produces electric shock
injuries.
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It comes with instructions
To create a proper ground, you need to drive the rod into the ground. Be aware that pounding
the top of the rod may make it impossible to fit the coupler and/ or the wire clamp over the
top of the rod. Make sure you put the coupler and wire clamp onto the rod before you begin
pounding. You can secure the ground wires to the rod after you’ve driven the rod into the
ground.
The height of the grounding rod, when fully assembled, may make it difficult to pound the top.
You might want to stand on a ladder when pounding or you might want to place the coupler
onto the bottom rod (flat side into the coupler) and pound the top of the coupler to drive the
rod into the ground a little way.
Then place the second rod into the coupler (point side into the coupler) and continue driving
the assembled rod into the ground as described below. You may simply place the rod, point
side down, in the desired location and drive it into the ground until only 4-5 inches (10-12 cm)
of the rod remains visible.
Or, you may dig a hole about 6” (15 cm) deep and 6“ (15 cm) wide into which you will drive the
rod. Place the rod, point side down, in the desired location (inside the hole) and drive it into
the ground until only 4-5 inches (10- 12 cm) of the rod remains visible. Attach ground wires to
the rod at this point.
The advantage of digging the hole is that you may partially fill in the hole once you have
attached ground wires to the rod, thus making less of the rod visible above ground. However,
P bar Y of the rod visible above
you should always leave some portionSafety Consultants Alberta Canadaground.
There is a distance used
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ATTACHING GROUND WIRES
• To attach ground
wires to the rod,
strip away 1 inch (3
cm) of insulation,
insert
• the wires between
the wire clamp and
the rod, and secure
the wires in place by
• tightening the wire
clamp
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A rule of thumb
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Earth grounding
There are four types of earth ground testing
methods available:
• • Soil Resistivity (using stakes)
• • Fall-of-Potential (using stakes)
• • Selective (using 1 clamp and stakes)
• • Stakeless (using 2 clamps only)
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Soil resistivity
The formula is as follows:
ρ=2pAR
(ρ = the average soil resistivity to depth A in
ohm—cm)
p = 3.1416
A = the distance between the electrodes in cm
R = the measured resistance value in ohms from
the test instrument
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Place it here please
The soil composition, moisture content, and temperature
all impact the soil resistivity. Soil is rarely homogenous
and the resistivity of the soil will vary geographically and
at different soil depths. Moisture content changes
seasonally, varies according to the nature of the sub
layers of earth, and the depth of the permanent water
table. Since soil and water are generally more stable at
deeper strata, it is recommended that the ground rods be
placed as deep as possible into the earth, at the water
table if possible. Also, ground rods should be installed
where there is a stable temperature, i.e. below the frost
line.
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Put it in the ground
The first method.
• I call the barbarian method. Please let me explain.
• We take ground rod in hand and place it in the location of are picking and then with are free hand
we strike it with a hammer or other blunt instrument. Results? Well usually you never get that
ground clamp on. Secondly you probably have several banged up parts all over your upper
appendages. And finally you'll get disgusted and saw it off long before you have it deep enough to
do any real benefit. This is the hard and wrong method.
The second method.
• is simply an improved version of the above where we fashion a covering device such as section of
iron pipe with a cap screw on. And pound it in the same fashion. End result about same as above.
The third method.
• Now this will get you all wet that I promise you. But here we go. We construct are own piece of
machinery here folks. So get ready to visit your local hardware store. You will need a piece of ¾ inch
steel conduit 10 feet long if you doing an 8-foot rod add 3 feet for 12-foot rods. You'll need 1 bronze
hose adapter and lastly a garden hose. Now to assemble are parts. You need to have the conduit
thread with national standard pipe thread on one end. This is where you screw the bronze adapter
on.
• Connect water hose and insert rod in to conduit. Place the unit over where you want the rod and
turn on the water. You may want to install a ball cock valve on conduit between bronze adapter and
conduit to start and stop water flow. Now you simply what the water rushing out the pipe dig your
hole for you. I like this method it is not fast and don't work in rocks. But hey you have the tool left
for whom ever May want use it. And they think your pretty darned smart to have made this gizmo.
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For me
• MOST OF US HAVE OVER THE YEARS SIMPLY POUNDED THE GROUND RODS WE
USE DIRECTLY INTO THE GROUND AND THEN MADE OUR CONNECTIONS. I HAVE
LEARNED THAT THIS IS NOT THE BEST WAY TO INSTALL A GOOD GROUND ROD. IN
FACT, POUNDING THE GROUND ROD ALL THE WAY IN DAMAGES THE GROUND ROD
AND WILL REDUCE THE LIFE OF THE ROD. WHEN YOU POUND IN THE ROD, THE
ROCKS IN THE GROUND SCRATCH OFF THE COPPER PLATING EXPOSING THE
UNDERLYING STEEL. THE STEEL CORRODES AND THUS YOUR ROD STARTS TO
DETERIORATE.
• LOCATION CONSIDERATIONS: CHOOSE A LOCATION AS CLOSE TO THE CONTROLLER
AS POSSIBLE. ALSO LOOK FOR ROUTES FOR YOUR GROUND WIRE WHICH WILL BE
AS STRAIGHT AS POSSIBLE. KEEP IN MIND THAT ELECTRICITY, LIKE WATER, WILL
TRAVEL THROUGH THE PATH OF LEAST RESISTANCE. BENDS, CURVES, AND
DISTANCE CHANGE CONDUCTIVE CHARACTORISTICS. IF USING A MULTIPLE ROD
CONFIGURATION, AND IF YOU HAVE THE REAL ESTATE TO ACCOMODATE, INSTALL
THE RODS 2 TIMES THEIR LENTH FROM EACH OTHER. THE GEOMETRIC SHAPE IS
NOT AS IMPORTANT AS THE SPACE BETWEEN THE RODS. IF THE ROD IS 10 FEET
LONG, SPACE THE RODS 20 FEET APART EITHER IN A STRAIGHT LINE OR IN A
TRIANGLE.
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Rod measurements
• The length and diameter of the ground rod not only affect its resistance but also its
driving characteristics. Although larger diameter ground rods do not have an
appreciably lower ground resistance value, they do have a larger steel core that
makes them easier to drive in harder soil by providing extra rigidity. It's probably
no coincidence that most rods driven in Canada, with its harder soil, are 3/4 inch in
diameter as opposed to 5/8-inch rods which dominate in the United States.
• The length of a ground rod plays a much bigger role in its final ground resistance
measurement, and it goes without saying that it takes longer to drive a longer
ground rod. The NEC and UL require a ground rod to be at least 8 feet in length.
This specification was obviously created by engineers that had never driven a
ground rod or noticed that most people are not 8’ tall. Longer rods are more
dangerous to install and bow more when being driven. The more a rod bows or
shudders, the less efficient the driving process is. Shorter rods are safer and easier
to drive. In fact, I would love to see the industry standardize on using two 4-foot
rods and a coupler to achieve the required 8 feet total length. Installations would
be faster, easier, and safer not to mention that the logistics of transporting and
storing a 4-foot rod are much simpler than longer 8- or 10-foot rods.
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Not all ground rods are created equal
• Not all ground rods are created equal nor are the
techniques used to install them. Installing a
grounding system is best-done right the first time
as it is every expensive to rework, and failure of
the grounding system puts people and expensive
electronic equipment jeopardy. Understanding
the functions of a grounding system and the
characteristics of the various components used to
implement it will allow the electrical contractor
to make educated buying decisions.
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Ground resistance
Another way to lower ground resistance is to use multiple ground
electrodes. In this design, more than one electrode is driven into the
ground and connected in parallel to lower the resistance. For
additional electrodes to be effective, the spacing of additional rods
need to be at least equal to the depth of the driven rod. Without
proper spacing of the ground electrodes, their spheres of influence will
intersect and the resistance will not be lowered.
To assist you in installing a ground rod that will meet your specific
resistance requirements, you can use the table of ground resistances,
below. Remember, this is to only be used as a rule of thumb, because
soil is in layers and is rarely homogenous. The resistance values
will vary greatly.
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Assurance of an Incident
However, good grounding isn’t only for safety; it is
also used to prevent damage to industrial plants
and equipment. A good grounding system will
improve the reliability of equipment and reduce the
likelihood of damage due to lightning or fault
currents.
Billions are lost each year in the workplace due to
electrical fires. This does not account for related
litigation costs and loss of personal and corporate
productivity
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Last Page the test of your work
• ALWAYS MEASURE AND RECORD THE
GROUND RESISTENCE OF YOUR WORK WITH A
METER
• Measure electrical ground rod
and grid resistance
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