I indicated that the Earthing Systems Design Steps process has (3) main steps:
Earthing Systems Design
Steps

And I explained the first step: Data Collection in the following Articles:
I explained the second step: Data Analysis in the following Articles:
And I explained What we are going to design for grounding system in any building in the following Articles:
And, in Article " Grounding Design Calculations – Part One ", I indicated the following:
In this Article, I explained the first method of grounding design calculations: Equations Method.
Also, in Article " Grounding Design Calculations – Part Two ", I explain Some solved examples for grounding design calculations using the Equations Method.
Today, I will explain the Other Methods for Performing of Grounding System Design Calculations.
You can preview the following Articles for more info:
In the next Article, I will explain Other Methods of Grounding Design Calculations. Please, keep following.
And, in Article " Grounding Design Calculations – Part One ", I indicated the following:
Grounding System Design
Calculations according to type of the building
The procedures for performing the Grounding System Design
Calculations can differ slightly according to the type of the building
as follows:

First: Domestic,
commercial and industrial premises
We mean by domestic, commercial and
industrial premises, all installations up to 1,000 V ac and 1,500 V dc 
between phases, with some minor exceptions.

Methods of Grounding Design
Calculations
There are many methods can be used for
performing Grounding System Design Calculations But the common methods
are:

In this Article, I explained the first method of grounding design calculations: Equations Method.
Also, in Article " Grounding Design Calculations – Part Two ", I explain Some solved examples for grounding design calculations using the Equations Method.
Today, I will explain the Other Methods for Performing of Grounding System Design Calculations.
You can preview the following Articles for more info:
Second: Nomographs
Method

Definition:
A Nomograph
is a mathematical tool consisting of several nonlinear scales (see fig.1)
on which known values can be plotted and the desired unknown value can be
derived by simply connecting the points with a straightedge and finding the
resultant by reading the intersecting point on the desired scale.

Factors That Affect Earth Resistance Of The Electrode
The
resistance of a rod Rr in ohms (Ω) may be calculated from:
Where:
ρ is
the resistivity of soil, in ohm metres (Ωm);
L is
the length of the electrode, in metres (m);
d is
the diameter of the rod, in metres (m).
From
the above equation, the factors that affect earth resistance of the electrode
are:

Uses of Nomographs
The
Nomographs can be a helpful guide in meeting the established standard for a
minimum earth resistance as follows:
The Nomograph using is severely
limited in several aspects as follows:

Application Of Nomographs Method
The
Nomographs method is applied for two cases of rod electrodes as follows:

Case#1: For A Single Earth Rod
For a
single earth rod, two types of Nomographs are existing:

Second: Nomograph relating
the basic factors affecting the earth resistance of a single earth rod
2.1
Nomograph Structure: (see fig.2)
The
Nomographs in this case will consist of the (5) scales:
2.2
Methods Steps:
We
have two methods for applying the Nomograph relating the basic factors
affecting the earth resistance of a single earth rod as follows:
A finding
the depth needed to achieve the desired resistance,
B Finding the resistance of a single earth rod
2.2.A Finding The Depth Needed To Achieve The Desired Resistance
2.2.A.1 Prerequisites:
Knowing of the following data:
2.2.A.2 Method Steps:
Example#2:
Find
the rod depth needed to achieve a desired resistance of 10 ohms, if the soil
resistivity 6515 ohmcentimeters and the rod diameter is 5/8 inches.
Solution:
Note
to Example#2:
2.2.B Finding The Resistance Of A Single Earth Rod
2.2.B.1 Prerequisites:
Knowing of the following data:
2.2.B.2 Method Steps:
Example#3:
Find a
resistance of 5/8 inch rod diameter, 10 feet long, if earth resistivity is 4020
ohmcm.
Solution:
Example#4:
If using a largerdiameter
electrode at a deeper depth with respect to example#3, what will be grounding
electrode resistance improvement? Noting that the new rod diameter is 3/4
inch and the new depth will be 20 feet. (Same earth resistivity)
Solution:
Example#5:
A 5/8in. rod driven 10 ft into
the soil and The Megger instrument indicates an earth resistance of 6.6 ohm
but the desired resistance is 4 ohm. Find the required depth to give a 4 ohm
earth resistance.
Solution:
Step#1: determine the earth
resistivity
Step#2: determine the required
rod depth for a 4 ohm earth resistance
Notes for Example#5:

Case#2: For Multiple Rod Electrode System
Monograph for Multiple Rod Electrode System is a means of calculating the
resistance of an electrode system in respect of a number of electrodes driven
in line, around the perimeter of a square site or forming a solid square when
the electrodes are spaced their length apart ( space between each two
electrodes = length of one electrode).
1.1
Nomograph Structure: (see fig.3)
This monograph consists of (5) scales as follows:
1.2 Prerequisites:
Knowing of the following data:
1.3 Method Steps:
Note:
Example#6:
For two 5 meter rods, each 10
ohm individual resistance, spaced 5 meter apart, what is the combined earth
resistance?
Solution:
Example#7:
an earthing electrode system of A holow square
configuration consisting of 20 rod electodes ( each side has 6 rods) what is the combined earth resistance of these electrodes knowing
that the
soil resistivity is 10,000 ohmcm, Rod electrode depth is 10 feet and rod
diameter is 3/4 inch.
Solution:
Step#1: Determine the resistance of one of the ground rods from
Figure2 in above.
Step#2: Combined Earth
Resistance

Other Nomographs for Multiple Rod Electrode System
Example#8:
Find the combined earth resistance for 26 rods distrbuted
on the perimeter of a 100 ft x 160 ft rectangular building as shown in
Figure4 , notingthat the soil resistivity measurements 10,000 ohmcm and
10foot ground rods length is used.
Solution:
Step#1:Determine the resistance of one of the ground rods
from Figure2 .
Same as in Step#1 of example#7
Step#2: Assume spacing of 20 feet or twice the rod length
between rods.
Notes:

In the next Article, I will explain Other Methods of Grounding Design Calculations. Please, keep following.
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