[ELECTRICAL WORKS FOR PROJECTS]
Eng.M.Tharwat
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Introduction
This course covers three main areas of the Electrical Contracting Process:
1. Basics of Electrical Works Design.
2. Shop drawing and Site Works.
3. Tendering of Electrical Projects.
The Course requires pre-knowledge of
[AutoCAD].
A project naturally progresses from design to the actual building going through the
following stages:
Project as an idea
Planning
Electrical Works
Design
Civil & Architecture Design
Electro-Mechanical Works Design
HVAC works Design
Plumping works Design
To
B.O.Q Preparation
Tendering & Analysis
Contractors
Tender selection
Consultant
Implementation Process
Shop Drawing
Approval
(Contractor)
So on
As the previous chart suggests, the electrical design is the first step of any electrical project, this
step has two major concerns besides the basic knowledge of electrical engineering which are
basic knowledge of Electrical Safety and Economical Design.
Where the design aspect of this course covers areas like: Interior Lighting design, Socket
distribution, panel Boards design, cables selection, etc.
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The second phase of the course addresses electrical site works supported with figures and videos
that introduces the student to real world experience of Sites Electrical Works and how to prepare
shop drawings for a given project.
Then the third phase, introduces the student to the basics of tendering and preparing a project bill
of quantity (B.O.Q).
At the end of this course, the student will have a head start extensive knowledge of how the
electrical contracting process works and will able to use this knowledge whenever facing an
electrical project.
With all respect …
Eng .Mohammed Tharwat
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Part One
Interior Lightning Design
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Interior lighting Design
While the most important aspect of this area of design is determining the
desirable lux according to Egyptian, international codes and standards to match
your project needs, whether your project is a bank, school or even a hospital
there are some basic rules to go by while determining the lux value of a given
area.
Lumen (lm):
The unit of luminous flux used to describe the quantity of light emitted by a source or received by a
Surface.
Illuminance (lux):
The luminous flux density at a surface, indicated in lm/m².
To have a better understanding of the role of lux in lighting designs consider the
following example:
A lamp connected to a power source, the lamp will emit many lighting lines as
shown in the figure:
Lighting lines
“Lumen”
The lighting lines that illuminates 1 m2 is a simple definition of Lux
Lux =
lumen/m2
So if we say that an office needs 300 lux to be illuminated.
This simply means each 1 m2 requires 300 lumen.
The required lux depends on the application or usage of this area.
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Some Lighting Parameters:
Colour Rendering Index (CRI):
A measure of the degree to which the appearance of a surface colour under a given light source
Compares to the same surface under a CIE reference source. The index has a maximum value of 100.
Colour Temperature (°K):
All materials emit light when heated (e.g. metal glows red through to white as the temperature
increase). The temperature to which a full radiator (or ‘black body’) would be heated to achieve the
Same chromaticity (colour quality) of the light source being considered, defines the correlated colour
temperature of the lamp, quoted in degrees Kelvin.
Luminous Efficacy (lm/W):
The ratio of light emitted, to the power consumed by a lamp.
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The following tables show required lux for many applications:
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Types of lamps:
Low
High
Low
High
Pressure
Pressure
Pressure
Pressure
Mercury
Mercury
Sodium
Sodium
Lamp
Lamp
Lamps
Lamps
Black Body
Quantum
Quantum
Quantum
Quantum
Quantum
Radiation
Radiation
Theory
Theory
Theory
Theory
Theory
100%
100%
50-95%
15-50%
65-90%
0
25-85%
8-17
13-25
60-95
40-60
70-95
125-200
40-90
1000-2000 hr
2000-4000 hr
8000 hr
5000-24000 hr
5000-20000 hr
6000-24000 hr
Can be
Can be
Can`t be
Can be
Can be
Can`t be
Can be
Dimmed
Dimmed
Dimmed
Dimmed
Dimmed
Dimmed
Dimmed
Indoor
Indoor
Indoor
Outdoor
Outdoor
Outdoor
Outdoor
Normal
Tungsten
Incident
Halogen
Lamp
Lamp
Theory Of
Black Body
Operation
Metal
Halide
Lamp
Color
Rendering
Luminous
Efficacy
Life Time
Dimming
Application
3000-12000
hr
In order to reach a satisfactory lux value for a given area, It`s required to use number of
lighting fixtures.
While the number of lighting fixture is dependent on a set of parameters which can be illustrated
in the following equation:
N=
Where:
N… number of lighting fixtures.
E … required lux.
A…. Area of room.
F… clearance factor.
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Q… lumen for lighting unit.
n… number of lamps per unit.
…utilization factor.
K…. Maintenance Factor [0.8].
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L
A) Area of room (A):
W
A = L.W
B) Clearance factor (F):
It is the factor that affect of num. lighting fixture according to
room clean degree.
For an open lighting fixture in a computer lap room and under a clean room condition,
clearance factor is 1.27
C) Number of lamps (n):
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4 x 18
n=4
2 x 36
n=2
Spot light:
100
n=1
60
n=1
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D) Utilization factor (
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):
For a certain lux value to be reached in a given room (area) there are some
parameters that affect the quantity of lumen per lamp, those parameters are
better illustrated as follows:
1. Room index:
Hf
Where:
Hm2
Kr…Room index w…Room width
L….Room length Hm…distance between the
lighting fixture & working
plan.
Hm1 = Ht – Hw ,
2. Reflection factors: (
Hm1
Hw
Hm2 = Ht - (Hw + Hf)
)
Depending on wall, ceiling, ground colors and materials, Reflection factor can be
determined by using the following tables:
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Utilization factor can be one from the following tables by using both of Room index and
Reflection factors.
Now that we have reached this point, we know all the required parameters to get the desired
number of lighting fixtures in a specified room.
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Lumen per lighting lamp:
Can be determined by the following table according to lamp type:
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Design lighting for the following project:
L = 15 m
L
W=8m
W
H=4m
Work plan = 85 cm
The above data is for a Conference room, with a white colored ceiling, it’s required that you
determine the number of lighting fixtures that achieves the desired Lux.
Solution
A = L.w = 15 x 8 = 120 m2
From tables: conference room has an E = 500 lux
The owner choose fixture (E). so, lamps = 2 x 36 watt , n = 2
From application: for a clean room, F = 1.33 (clearance factor = 1.33)
From lumen table: Q = 3250 lumen
From wall and ceiling color:
Hm = Ht – (Hs + Hw) lighting fixture will be on false ceiling (Hw = 0.7 m)
Hm = 4 – (0.85 + 0.7) = 2.45 m
Hm = 2.45 m
Kr =
Kr = 2.12
From tables:
(Uf = 0.52)
N=
N = 23.6 units ≈ 24 units
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Arrangement of lighting fixture
From the previous example the required number of lighting fixtures is 24 unit, now
the question is how they can be arranged?
(4x6) or (3x8) or (12x2) or ….etc
√
√
√
√
So we will arrange those as (4x6) units
As shown in the fig. below, The distance between each lighting fixture and the
other is double the distances between the lighting fixture and the wall to avoid a
blind spots.
12X = 10
8y = 8
x=
y=1m
m
X 2X
2X
2X
10 m
2X 2X
2X 2X 2X X y
2y
2y
2y
y
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Control of lighting circuits
Lighting circuits can be controlled by lighting switches.
Lighting switches can be classified into:
One way, one gang.
One way, two gang.
One way, three gang.
Two ways, one gang.
Two ways, two gang.
Two ways, three gang.
The difference between one way & two way switches is that the one way switch controls the
circuit from one location. However, two way switches controls the circuit from two locations.
Two way switches used in bed rooms, corridors….etc.
One way switch:
Two way switch:
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Part Two
Basics of Street lighting Design
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Street Lighting Design
Lighting is a vital rule to describe the importance of major
and minor roads, which constitute the lifelines of
communication in the motorized world today.
Good street lighting is aiming to:
 Reduce traffic accidents
 Combat crime
 Respect the environment
For good street lighting design there are some parameters
must be taken:




Area Classification.
Road way Classification.
Street Width.
Poles height.
A) Area Classifications:
 Commercial
 Intermediate
 Residential
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B/Roadway Classifications:
 Freeway
 Expressway
 Arterial
 Collector
 Local
 Alleys
Poles height and street width affect lighting arrangement
Street Lighting Arrangement:
1/Single sided:
This type of arrangement, in which all luminaries are
located on one side of the road, is used only when the width
of the road is equal to, or less than the mounting height of
the luminaries.
W<=H
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2/Staggered:
This type of arrangement in which the luminaries are
located on both sides of the road in a staggered, or zigzag,
arrangement is used mainly when the width of the road is
between 1 to 1.5 times the mounting height of the
luminaries.
W=1~1.5 H
3/Opposite:
This type of arrangement, with the luminaries located on
both sides of the road opposite to one another, is used
mainly when the width of the
road is greater than 1.5 times
the mounting height of the
luminaries.
W>1.5H
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4- Span wire
This type of arrangement, with the luminaries suspended along
the axis of the road, is normally used for narrow roads that have
buildings on both sides.
If Road is curved:
Single Sided:
If the radius is Small & The length is 300 m.
Opposite:
If the radius is Large & The length > 300 m.
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Types of lamps used in Street lighting
1- High pressure sodium lamps (Highway Streets):
It is suitable for such kinds of lighting even in cloudy weather.
2- Low pressure sodium lamps (Tunnels):
This type of lamp is used in tunnels and closed public places. They also have
relatively long life.
3- Metal halide lamps.
4- Mercury lamps (Internal Streets):
It gives a bright white light thus it could be used in illumination of open places
such as large stadiums since this type of lamps have strong glass.
Methods of switching of lamps
There are various methods, some of which are:
- Photo cell.
- Control switch.
- Timer.
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Street Lighting System
The distribution lighting network consists of:
- Lighting distribution box
- Poles
- Lighting luminaries
- Cables
Design of the street lighting scheme:
Where:
F: is lamp flux in lumens.
C.F: is the clearing factor, taken about 0.6.
M.F: is the maintenance factor, taken about 0.7.
S: is the space between the poles in meter.
W: is the street width in meter.
E: is the illumination level of street in lux.
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Part Three
Electrical Sockets & Power Calculations
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Electric sockets
Types of Electrical Sockets:
Single Socket
Duplex Socket
Power Socket
Fuse Switch or
Disconnect Switch
f
HD
Hand Drier
Single & Duplex Sockets are used for low current applications, as in TVs, DVDs, computers, laptops,
mobile chargers, cassettes, videos, and home instruments….etc.
Power sockets are used for heavy loads as Boilers – small motor pumps – water heaters…etc
Fuse Switch
Applications
Used for [A/C-W.H…ETC] as a isolator
switch & protective switch against over
current by using rapture fuse
Poles Number
Double Poles Only
Current Rating
26A-32A
Disconnect Switch
Used for [FCU-AHU-Pumps-Elevators…..ETC] as isolator switch only.
Double & Three Poles
16A – 20A – 32A – 40A – 60A – 80A – 100A
– 125A – 150A – 200A – 250A
All previous socket types are available with high IP for protection against water and dust in wet
and open or landscape areas.
Sockets distribution:
Socket distribution for a given room is dependent on the following factors:
1- Room application
2- Room furniture
3- Each 3 meters put a single or duplex socket (in case of no furniture DWG)
4- For kitchens, there must be at least one power socket.
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Power calculations
A) For lighting:
-
Incident lamps or spots
P = 20≈ 200 watts.
-
For florescent lamps
2 x 36 watt
4 x 18 watt
2 x 55 watt
-
For chandeliers
P= 400≈500 watt
B) For sockets:
-
Single socket........................200 VA
-
Duplex socket ......................400VA
-
Power socket……………….2000-2500VA
-
Hand driver …………………1500VA
-
Fuse switches
A.C
W.H
1 HP....... ...…...1000 VA
1500 VA
1.5HP………... 1500 VA
Up to 2000 VA
2.25 HP……….2250 VA
3 HP ………….3000 VA
4 HP………..…4000 VA
5 HP…………..5000 VA
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Power Factor:
It`s a percentage of used active power.
Where:
P ==== Active Power
S==== Apparent Power
For all cables and C.Bs calculations, power must be in (VA)
For lighting, power must be in VA but its data is given by watt so:
For fluorescent lamps
PF = 0.45 = 0.6
For halogen or spots
PF = 1
For current calculations:
Single phase loads
I (Amp) = 4.5 Skva
Three phase loads
I (Amp) = 1.5 Skva
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Capacitance Calculations:
Current Calculations:
For Single Phase Capacitors
√
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For Three Phase Capacitors
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Electric lines calculations
After Distributing lighting fixtures and sockets, it must be fed from a main panel board.
Each group of lighting fixtures or group of sockets has one line to the main panel board.
For lighting lines:
No more
Each line
With cable
1500 VA
Than
2.5 mm2
Size
With
16 Amp
MCB
For socket lines:
No more
Each line
With cable
2000 VA
Than
3 mm2
Size
With
20 Amp
MCB
For power socket lines:
Each line
No more
With cable
2000 VA
Than
4 mm2
Size
With
25 Amp
MCB
For hand drier:
Each unit
takes a
separate line
No more
With cable
1500 VA
Than
Size
4 mm2
With
25 Amp
MCB
For air conditioners:
Each unit takes a separate line:
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1, 2.25, 3 HP
4 mm2
25 Amp
4 - 5 HP
6 mm2
32 Amp
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Load schedules
Project Name:
Panel Name:
Breaking cap.:
Circuit
Cable
Type
Number
size
R1
Lighting 2.5 mm2
Y1
Lighting 2.5 mm2
B1
Lighting 2.5 mm2
R2
Socket
3 mm2
Y2
Socket
3 mm2
B2
A.C
4 mm2
R3
Spare
Y3
Spare
B3
Spare
MCB:
cable: size:
MCCB
16A
16A
16A
20A
20A
25A
16A
20A
32A
Total connected load
Three phase
Y
R
1000
B
Notes
820
990
1400
1600
1500
2400 2420 2490
Load balancing:
Given that the network is featuring a star connection.
It’s important to achieve I1 ≈ I2 ≈ I3 to reach an IN of nearly equal zero.
R
I1
R
N
IN
Y
Y
B
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B
I2
I3
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Balance Check:
For any panel board, there is a balance check for three phase loads due to reducing nuteral
current & unbalanced stresses on circuit breakers.
Unbalance ratio can be calculated by:
Unbalance Ratio mustn’t exceed a value of 5%.
For above panel bard unbalance ration will be:
Unbalance Ratio (%) = 3.61% so it’s balanced panel board.
Diversity factor:
It`s the percentage of expected on line loads connected at the same time.
 For lighting ……….. …………………… 0.7 ≈ 0.9
 For normal sockets……..............................0.6 ≈ 0.85
 For Air conditioners ……………..……..……..1
 For heaters and hand drier ……….………..….1
 For Power Socket ………………….………… 1
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Circuit breaker capacity calculations:
After conducting load and diversity factor calculations, now we consider C.B capacity
calculations which are as follows:
IC.B =
=
√
Circuit breaker standard:
10 – 16 – 20 – 25 – 32 – 40 – 50 – 60 – 63 – 75 – 80 – 100 – 125 – 160 – 200 – 250 – 320 – 400
– 630 Amp……Etc.
For pervious load, there will be a panel board to feed these circuits, Single line diagramme
for panel board required to represent panel specifications and component as following:
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[4x10]+10 mm CU/PVC
40A
380V,50HZ,Isc
32A
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20A
16A
32A
20A
16A
X1
X1
X1
X1
X2
X3
Spare
Spare
Spare
A.C
Socket
Lighting
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Part Four
Cables Selection
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Cable selection
Power cables are used to feed circuits with the required power.
So, cables selection must be according to transfer a full power to certain load, that mean the
cables must transfer the full current with no or limited voltage drop to ensure full power transfer.
Cables can be classified as following below:
Operating & Meggered Voltages
600/1000
450/750
Conductor Type
Copper
Aluminum
Insulation Material
PVC
XLPE
Number of cores
Single
Multi core
Armored
Armored
[STA – SWA]
Neutral Size
Reduced Neutral
NonArmored
NonReduced
Neutral
To select a cable for a certain load like below:
AC Source
380 V, 50HZ
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ELECTRICAL
LOAD
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The above mentioned cable should transfer full power from
source to load, so it must stand full load current with limited
voltage drop.
To ensure carrying full load current [Derating Factors] must be
taken in consideration.
Derating factor:
Derating factors are the factors that affect cables’ life time
and their standing current and its dependant on cable laying
methods.
From Cables catalogue we can obtain the Derating factors
ratings
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Df = D1 x D2 x D3 x D4 x D5 x D6 x…..Dy
Icable =
Voltage Drop:
A long distance cable and its internal impedance may
cause a voltage drop more than the allowed percentage.
Voltage Drop Percentage mustn’t more than 5%.
Voltage drop calculations:
VD% =
Where:
VD%
Voltage Drop Percentage
Voltage Drop for a certain cable
[Obtained from cables catalogues]
Circuit Breaker Current
Cables Length
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Part Five
Emergency Loads
Generators & UPS
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Generators and UPS
In some projects, power continuity is required for many different reasons
like:
(1) Data loss as in banks
(2) Emergency as in hospitals
(3) Production quantity as in factories…etc
So the important loads must be fed by a stand by source.
In case of power interruptions, another source will feed these loads
There are two devices that ensure power continuity:
(A)
(B)
Generators
UPS
Difference between Generators and UPS:
Generators are used as a standby power source with a delay time
between current interruption and continuity.
On the other hand, UPS are used as a power source without any
time delay between current interruption and current continuity.
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Theory of operation:
G
1
3
2
UPS
L5
Main power source is on:
S1 is on
S2 is on
S3 is off
Power interruption:
S1 is off
S2 is on
S3 is on
For load (5): Power continuity is needed without time delay so a UPS is
used to feed the load till the Generator starts up.
UPS is connected before load.
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A controller of three switches called (ATS)
ATS panels:
G
ATS
Main source
Load
It’s a panel that consists of three switches one is connected to the main
source, the second one is connected to the Generator and the third one is
connected to the load through a controller “Microcontroller, PLC…Etc”
Generator selection:
Generators are selected according to emergency loads’ power rating (KVA).
UPS selection:
A UPS is selected according to emergency load power rating (KVA) and discharging
time of back up batteries.
Co-ordination between Generator starting up time and backup battery discharging time is
crucial as to assure the continuity of power.
The UPS discharging time must be selected to cover the delay time between current
interruption and continuity.
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Part Six
Short Circuit Current
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Short circuit current
In case of short circuit, there is a large current value passing through protective devices.
If these protective devices fail to stand the current value, damage occurs in circuit
components which might cause fire or complete damage of the electrical system.
The power systems must be designed to stand short circuit currents for a short period of
time before the trip process takes place.
While the types of trips performed by a circuit breaker are:
Thermal trip: Responsible for protection against over load currents.
Magnetic trip: Responsible for protection against short circuit currents.
Thermal trip
Mag. trip
Im
Isc
Ik is the maximum current capacity that a device stands before damaging.
Short circuit current calculations:
Z Cab
It = ISC + IL
Z Load
At short circuit (IL = Zero):
IS.C =
Vph …………phase voltage
It
Zt ……………total circuit impedance
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Z Cab
Z Load
I sc
IL
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For the following circuit:
a
b
A) For part a:
IS.C =
=
B)For part b:
IS.C =
=
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Impedances Calculations:
1/Ring Main Units:
Power Rating
Reactance Value
250 KVA
0.633 m
500 KVA
0.316 m
1000 KVA
0.158 m
2/Transformers:
Power Rating
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Reactance Value
25 KVA
256 m
50 KVA
128 m
100 KVA
64 m
160 KVA
40 m
200 KVA
32 m
250 KVA
25.6 m
315 KVA
20.3 m
400 KVA
16 m
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500 KVA
12.8 m
630 KVA
10.16 m
800 KVA
9m
1000 KVA
8m
1600 KVA
7.35 m
3/Circuit breaker:
XC.B = 0.15 m
4/Bus Way:
Xb.w= 0.15L m
Cables:
XCable = 0.08L m
Resistances are negligible.
Short circuit current can be calculated by another method
“Up and Down Stream Tables”
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Part Seven
Earthing Systems
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Earthing systems
There are two types of ear thing systems:
(1) Function earthing
(2) Protection earthing
(1) Function earthing:
This is the earthing of neutral points.
A neutral point is connected to the earth point to get the potential of the neutral point to be zero.
(2) Protection earthing:
This is the earthing of the electrical equipment body for human protection.
Earthing system design:
The following shape shows electrical equipment having a current leakage problem while a human is
touching the equipment body.
The above circuit can be represented by:
Rh….. Human Resistance.
It
Re….. Earthing Resistance.
I1
The sole purpose of any earthing system is to protect humans from (I 1)
So for I1<<< I2 or (I1
zero)
So it’s required Re <<< Rh
For power systems: Rearthing = 2
It
4
For light current systems: Rearthing = 0.5
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I1
I2
Rh
Re
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Earthing Systems Resistance Calculation:
Re =
Where:
Re ……. Electrode Resistance
……Soil Resistivity
L
L…..Earth Electrode Length
Soil resistivity depends on soil type as show in table (1)
Rv =
Where:
Rv ……Total earth resistance
Re……Earth resistance for each electrode
L…..Electrode length
L
S……Distance between electrodes
N…….Number of electrodes
S
S
……..Utilization factor which calculated by tables (2), (3), (4).
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Also there is the resistance of wire that’s connected between electrodes (R h)
Rh =
Where:
….soil resistivity
L….wire length
….utilization factor.
Total Earth Resistance
Rt =
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