ELECTRICAL DESIGN
& INSTALLATIONS
Begad Kishk
begadkishk@gmail.com
Contents
List of figures .......................................................................................................................................................... 5
List of tables ............................................................................................................................................................ 7
Chapter 1 ................................................................................................................................................................. 8
1
Introduction to lighting ................................................................................................................................... 8
1.1
Types of luminaires ................................................................................................................................. 8
1.1.1
Surface mounted luminaires ........................................................................................................... 8
1.1.2
Recessed mounted luminaires ......................................................................................................... 8
1.1.3
Suspended luminaires ..................................................................................................................... 9
1.2
Ceiling types ........................................................................................................................................... 9
1.3
Luminaire construction ......................................................................................................................... 10
1.3.1
Wiring ........................................................................................................................................... 10
1.3.2
Junction Box ................................................................................................................................. 10
1.3.3
Lamp Holder ................................................................................................................................. 10
1.3.4
Lamp ............................................................................................................................................. 10
1.3.5
Reflector ........................................................................................................................................ 10
1.3.6
Lens ............................................................................................................................................... 10
1.3.7
Trim ............................................................................................................................................... 10
1.4
IP rating (Ingress protection) .................................................................................................................11
1.5
CRI (Color rendering index) ................................................................................................................. 12
1.6
Color temperature ................................................................................................................................. 13
1.7
Polar curves ........................................................................................................................................... 14
1.8
Uniformity factor .................................................................................................................................. 14
Chapter 2 ............................................................................................................................................................... 15
2
Lightning design and calculations ................................................................................................................ 15
2.1
Luminous flux (∅) ................................................................................................................................. 15
2.2
Luminous intensity (I)........................................................................................................................... 15
2.3
Illuminance (E) ..................................................................................................................................... 15
2.4
Luminance (L) ...................................................................................................................................... 15
2.5
Luminous efficacy ................................................................................................................................ 16
2.6
Calculating lumens and number of luminaires ..................................................................................... 16
2.6.1
utilization factor ............................................................................................................................ 17
2.6.2
Maintenance factor........................................................................................................................ 17
1
Electrical Design – DK_R_21
Begad Wesam Kishk
2.7
Manual calculations problem ................................................................................................................ 18
2.8
Lighting design using dialux software .................................................................................................. 18
2.9
How to change lux in dialux ................................................................................................................. 18
2.10
Reading the luminaire code .................................................................................................................. 19
2.11
Lighting design using AutoCAD .......................................................................................................... 19
2.11.1
Steps for design ............................................................................................................................. 19
2.11.2
What to avoid ................................................................................................................................ 20
2.11.3
Some standards from the Egyptian code ....................................................................................... 20
2.12
Explaining the different types of loads ................................................................................................. 20
2.12.1
Normal Loads................................................................................................................................ 20
2.12.2
Emergency loads ........................................................................................................................... 21
2.12.3
Critical loads ................................................................................................................................. 21
2.13
Switching methods for lighting control ................................................................................................ 21
2.13.1
Manual control methods ............................................................................................................... 21
2.13.2
Automatic control switches........................................................................................................... 23
2.13.3
LCP control (lighting control panel) ............................................................................................. 23
Chapter 3 ............................................................................................................................................................... 24
3
Power and MEP design ................................................................................................................................. 24
3.1
Introduction ........................................................................................................................................... 24
3.2
Sockets design ....................................................................................................................................... 24
3.3
Types of sockets .................................................................................................................................... 24
3.3.1
For mounting type ......................................................................................................................... 24
3.3.2
For socket itself type ..................................................................................................................... 26
3.4
Sockets and power distribution and AutoCAD applications................................................................. 29
3.5
MEP equipment..................................................................................................................................... 29
3.5.1
What are Mechanical Loads? ........................................................................................................ 29
3.5.2
Key Mechanical Equipment in MEP Design ................................................................................ 29
3.5.3
Importance of MEP design ........................................................................................................... 30
Chapter 4 ............................................................................................................................................................... 31
4
Electric Panels Scheduling ............................................................................................................................ 31
4.1
Introduction ........................................................................................................................................... 31
4.2
Mounting types ..................................................................................................................................... 31
4.2.1
Wall Mounted ................................................................................................................................ 31
2
Electrical Design – DK_R_21
Begad Wesam Kishk
4.2.2
4.3
Embedded ..................................................................................................................................... 32
Components .......................................................................................................................................... 32
4.3.1
Miniature Circuit Breakers (MCB) ............................................................................................... 32
4.3.2
Molded Case Circuit Breaker (MCCB) ........................................................................................ 32
4.3.3
Isolators ......................................................................................................................................... 33
4.3.4
Busbars.......................................................................................................................................... 33
4.3.5
Identification Labels ..................................................................................................................... 33
4.4
Types of busbars ................................................................................................................................... 34
4.4.1
Phase Busbars (Hot Busbars) ........................................................................................................ 34
4.4.2
Neutral Busbar .............................................................................................................................. 34
4.4.3
Ground Busbar (Earth Bar) ........................................................................................................... 34
4.4.4
Fishbone Busbars .......................................................................................................................... 35
4.5
Spare and space ..................................................................................................................................... 36
4.6
Types of electric panels in terms of applications .................................................................................. 36
4.6.1
MDB Panel.................................................................................................................................... 36
4.6.2
SMDB Panel ................................................................................................................................. 37
4.6.3
FDB ............................................................................................................................................... 37
4.6.4
MCC.............................................................................................................................................. 38
4.7
Conditions to Take Care of While Installing the Panel ......................................................................... 38
4.8
Panel Scheduling ................................................................................................................................... 39
4.8.1
Naming the DB ............................................................................................................................. 39
4.9
Electric room and busbar standards ...................................................................................................... 39
4.10
Unbalance rule ...................................................................................................................................... 40
4.11
Electrical factors ................................................................................................................................... 40
4.11.1
Connected load.............................................................................................................................. 40
4.11.2
Demand factor ............................................................................................................................... 40
4.11.3
Diversity factor ............................................................................................................................. 40
4.12
Cables.................................................................................................................................................... 41
4.12.1
Construction: ................................................................................................................................. 41
4.12.2
Factors Affecting Performance: .................................................................................................... 41
4.12.3
Naming the cable .......................................................................................................................... 41
4.12.4
For sizing ...................................................................................................................................... 43
Chapter 5 ............................................................................................................................................................... 44
3
Electrical Design – DK_R_21
Begad Wesam Kishk
5
Bulk and SLD ............................................................................................................................................... 44
5.1
Introduction ........................................................................................................................................... 44
5.2
Transformers ......................................................................................................................................... 45
5.3
Diesel engine generators ....................................................................................................................... 46
5.4
UPS ....................................................................................................................................................... 47
5.5
ATS ....................................................................................................................................................... 48
5.6
RMUs and distributors .......................................................................................................................... 49
5.6.1
RMUs ............................................................................................................................................ 49
5.6.2
distributors .................................................................................................................................... 49
5.7
SLD ....................................................................................................................................................... 50
Chapter 6 ............................................................................................................................................................... 51
6
Some important calculations ......................................................................................................................... 51
6.1
Introduction ........................................................................................................................................... 51
6.2
Calculating derating factors .................................................................................................................. 52
6.3
Voltage-drop calculations ...................................................................................................................... 54
6.4
Short circuit calculations....................................................................................................................... 55
References ............................................................................................................................................................. 58
4
Electrical Design – DK_R_21
Begad Wesam Kishk
List of figures
Figure 1-1 Surface mounted luminaires .................................................................................................................. 8
Figure 1-2 Recessed mounted luminaires ............................................................................................................... 9
Figure 1-3 Suspended luminaires............................................................................................................................ 9
Figure 1-4 Luminaires construction ...................................................................................................................... 10
Figure 1-5 IP ratings ..............................................................................................................................................11
Figure 1-6 Luminaires CRI ................................................................................................................................... 12
Figure 1-7 Color temperature comparison ............................................................................................................ 13
Figure 1-8 Luminaire polar curves ....................................................................................................................... 14
Figure 1-9 Uniformity factor ................................................................................................................................ 14
Figure 2-1 Luminous flux ..................................................................................................................................... 15
Figure 2-2 Luminous intensity .............................................................................................................................. 15
Figure 2-3 Illustrative representation of different lighting quantities ................................................................... 16
Figure 2-4 Calculating room index ....................................................................................................................... 17
Figure 2-5 The X,2X rule...................................................................................................................................... 18
Figure 2-6 Example for luminaire code ................................................................................................................ 19
Figure 2-7 Wrong Vs. Correct curves drawing ..................................................................................................... 20
Figure 2-8 Difference between electrical loads .................................................................................................... 21
Figure 2-9 Switches .............................................................................................................................................. 21
Figure 2-10 Deviator switch ................................................................................................................................. 22
Figure 2-11 Intermediate switch ........................................................................................................................... 22
Figure 2-12 Dimmer switch .................................................................................................................................. 22
Figure 2-13 Timer switch wiring .......................................................................................................................... 23
Figure 2-14 Basic LCP construction ..................................................................................................................... 23
Figure 3-1 Flush mounted socket .......................................................................................................................... 24
Figure 3-2 Wall mounted socket ........................................................................................................................... 25
Figure 3-3 Floor box ............................................................................................................................................. 25
Figure 3-4 2P socket ............................................................................................................................................. 26
Figure 3-5 2P+E socket ......................................................................................................................................... 26
Figure 3-6 Tamper resistant outlet ........................................................................................................................ 27
Figure 3-7 WP socket ............................................................................................................................................ 27
Figure 3-8 High Power & Industrial Sockets ........................................................................................................ 28
Figure 3-9 Disconnect switch ............................................................................................................................... 28
Figure 4-1 Wall mounted panel ............................................................................................................................. 31
Figure 4-2 Embedded DB ..................................................................................................................................... 32
Figure 4-3 Miniature CB ....................................................................................................................................... 32
Figure 4-4 MCCB ................................................................................................................................................. 33
Figure 4-5 Busbars ................................................................................................................................................ 33
Figure 4-6 Identification labels ............................................................................................................................. 33
Figure 4-7 Phase busbars ...................................................................................................................................... 34
Figure 4-8 Neutral busbars.................................................................................................................................... 34
Figure 4-9 Fishbone busbar .................................................................................................................................. 35
5
Electrical Design – DK_R_21
Begad Wesam Kishk
Figure 4-10 Fishbone type connections ................................................................................................................ 35
Figure 4-11 Difference between spare and space ................................................................................................. 36
Figure 4-12 MDB .................................................................................................................................................. 36
Figure 4-13 SMDB ............................................................................................................................................... 37
Figure 4-14 FDB ................................................................................................................................................... 37
Figure 4-15 MCC panel ........................................................................................................................................ 38
Figure 4-16 Naming the DB ................................................................................................................................. 39
Figure 4-17 Y-connected power system ................................................................................................................ 40
Figure 4-18 Cables construction ........................................................................................................................... 41
Figure 4-19 Example of cable naming .................................................................................................................. 41
Figure 4-20 Cable catalog from Elsewedy cables................................................................................................. 42
Figure 4-21 CB ratings.......................................................................................................................................... 43
Figure 5-1 Power system components .................................................................................................................. 44
Figure 5-2 Transformer ......................................................................................................................................... 45
Figure 5-3 Emergency generator........................................................................................................................... 46
Figure 5-4 UPS ..................................................................................................................................................... 47
Figure 5-5 UPS construction ................................................................................................................................. 48
Figure 5-6 ATS ...................................................................................................................................................... 48
Figure 5-7 RMU.................................................................................................................................................... 49
Figure 5-8 Distributers diagram ............................................................................................................................ 49
Figure 5-9 Example for SLD ................................................................................................................................ 50
Figure 6-1 SLD example ....................................................................................................................................... 51
Figure 6-2 Calculate the accumulated VD ............................................................................................................ 54
Figure 6-3 Types of short circuits ......................................................................................................................... 55
Figure 6-4 A simple fault problem ........................................................................................................................ 55
Figure 6-5 Percentage of faults occurrence .......................................................................................................... 56
Figure 6-6 SLD SC calculations ........................................................................................................................... 57
6
Electrical Design – DK_R_21
Begad Wesam Kishk
List of tables
Table 1-1 Color temperature ................................................................................................................................. 13
Table 2-1 Luminous efficacy of different lamps. Source ...................................................................................... 16
Table 2-2 Determining U.F ................................................................................................................................... 17
Table 3-1 General sockets rating........................................................................................................................... 26
Table 5-1 Typical power transformers ratings ...................................................................................................... 45
Table 5-2 Typical distribution transformers ratings .............................................................................................. 46
Table 5-3 Typical generator ratings....................................................................................................................... 47
Table 6-1 Air Temp. DF ........................................................................................................................................ 52
Table 6-2 Burial depth DF .................................................................................................................................... 52
Table 6-3 H&V formation DF ............................................................................................................................... 53
Table 6-4 Touching DF ......................................................................................................................................... 53
Table 6-5 Four core cables datasheets .................................................................................................................. 56
Table 6-6 SC capacity ........................................................................................................................................... 57
7
Electrical Design – DK_R_21
Begad Wesam Kishk
Chapter 1
1 Introduction to lighting
Lighting in any room needs these three elements:
1. Luminaire type
2. Illumination
3. Room type & dimensions
1.1 Types of luminaires
1. Surface mounted luminaires
2. Recessed mounted luminaires
3. suspended luminaires
1.1.1 Surface mounted luminaires
Surface-mounted luminaires are versatile lighting fixtures that are directly attached to the surface of a ceiling or
wall, rather than being recessed or embedded. They are a popular choice in modern architectural spaces due to
their ease of installation, diverse illumination offerings, and aesthetic versatility.
Figure 1-1 Surface mounted luminaires
1.1.2 Recessed mounted luminaires
Recessed mounted luminaires, also known as downlights, pot lights, or can lights, are lighting fixtures installed
into hollow openings in a ceiling, appearing flush with the surface. This design provides a clean, minimalist, and
unobtrusive look, making them a popular choice in modern interior design.
highly versatile and are used in a wide range of residential and commercial settings, including living rooms,
kitchens, hallways, bathrooms, offices, retail stores, and hospitality venues.
8
Electrical Design – DK_R_21
Begad Wesam Kishk
Figure 1-2 Recessed mounted luminaires
1.1.3 Suspended luminaires
Suspended luminaires, often referred to as pendant lights or hanging lights, are lighting fixtures that are hung
from the ceiling by a rod, chain, or cord. Unlike surface-mounted or recessed lights, they drop down into the
space, making them a prominent design element as well as a source of illumination.
Figure 1-3 Suspended luminaires
1.2 Ceiling types
ceiling type determines the type of the luminaire that will be used, so that it’s an important condition.
•
Types are:
1. Recessed mounted ceiling.
2. Surface mounted ceiling.
3. Gipson board mounted ceiling.
4. Trusses (in factories).
9
Electrical Design – DK_R_21
Begad Wesam Kishk
1.3 Luminaire construction
The diagram below identifies the components of a light fixture, also known as a luminaire. The diagram shows a
recessed can fixture, but the components apply to all light fixtures. Keep in mind that some of the components
are optional and will not be found on every luminaire. Descriptions of the components can be found below the
diagram.
1.3.1 Wiring
Electrical wiring, which provides power to the luminaire.
Depicted here is flexible conduit, but it can also be hard
piped based on electrical codes.
1.3.2 Junction Box
The junction box provides a location to connect the wiring
that comes from the power source with the internal wiring
for the light fixture. Shown is a box attached to the top of
the fixture; however, this is sometimes a separate box and
sometimes the connection is made inside the fixture.
1.3.3 Lamp Holder
The lamp holder or light socket is the receptacle that the
lamp screws into.
1.3.4 Lamp
Figure 1-4 Luminaires construction
The lamp, often referred to as the light bulb, emits light when connected to a power source. The lamp is often
sold separately from the fixture. It is important to use lamps in a wattage that are recommended for the fixture to
prevent damage or possible fire.
1.3.5 Reflector
The reflector provides a reflective surface to direct or spread the light from the lamp out into the space. Parabolic
reflectors focus light toward a point, while elliptical reflectors spread light.
1.3.6 Lens
The lens is a transparent or translucent material used to direct or diffuse light. In addition, the lens protects the
lamp; however, it can also trap heat, which can be problematic.
The lens, reflector, and lamp all contribute to lighting levels and the light distribution in a space.
1.3.7 Trim
The trim or flange is a decorative element that is detachable. This piece is installed after the finished wall or
ceiling material is installed. Since ceiling materials require a space between the fixture and the material, the trim
piece is used to cover this space and provide a clean finish.
10
Electrical Design – DK_R_21
Begad Wesam Kishk
1.4 IP rating (Ingress protection)
Ingress protection determines if an electrical product’s exterior case or enclosure will protect the working parts
from water, dust or solid object intrusion, keeping the product electrically safe and lasting longer. Ingress
protection testing, or IP testing, provides a repeatable test standard to compare the enclosure protection; IP testing
should always be performed at an accredited test laboratory.
Figure 1-5 IP ratings
11
Electrical Design – DK_R_21
Begad Wesam Kishk
1.5 CRI (Color rendering index)
It is a quantitative measure of how accurately a light source reveals the true colors of various objects compared
to a natural or standard light source (like natural daylight or incandescent light).
CRI is measured on a scale from 0 to 100.
Which CRI Ranges to Use?
When purchasing and installing white LED lights, we recommend a CRI for over 90 but also say in some projects,
a minimum of 85 can be acceptable.
Figure 1-6 Luminaires CRI
12
Electrical Design – DK_R_21
Begad Wesam Kishk
1.6 Color temperature
•
•
•
•
•
Color temperature is a way to describe the light appearance provided by a light bulb. It is measured in Kelvin
(K) degrees on a scale from 1,000 to 10,000.
Typically, Kelvin temperatures for commercial and residential lighting applications fall somewhere on a scale
from 2000K to 6500K.
A light bulb’s color temperature lets us know what the look and feel of the light produced will be.
The color temperature of a light bulb is assigned using the basis of correlated color temperature (CCT).
For example, if you heat up a metal object, the object appears to glow. Depending on the Kelvin temperature
that the metal object is being heated at, the glow will be various colors, such as orange, yellow or blue. The
color temperature of light bulbs is meant to replicate the Kelvin temperature of the metal object.
Figure 1-7 Color temperature comparison
Table 1-1 Color temperature
13
Electrical Design – DK_R_21
Begad Wesam Kishk
1.7 Polar curves
The light distribution curve drawn in a polar diagram denotes the luminaire’s luminous intensity in different
directions as a function of viewing angle in one or more planes. It is usually represented by an unbroken line that
indicates the light distribution perpendicular to the light source’s longitudinal axis and with a dashed line that
indicates the light distribution in direction of the longitudinal axis.
Figure 1-8 Luminaire polar curves
1.8 Uniformity factor
In lighting, uniformity refers to how evenly light is distributed across the surface. It's a measure of the variation
between the brightest and darkest areas, with higher uniformity indicating a more balanced and consistent lighting
experience.
The uniformity factor should be higher than 40%.
Figure 1-9 Uniformity factor
14
Electrical Design – DK_R_21
Begad Wesam Kishk
Chapter 2
2 Lightning design and calculations
2.1 Luminous flux (∅)
Is the total amount of light energy radiated from a light source in all directions per unit time.
Figure 2-1 Luminous flux
2.2 Luminous intensity (I)
Is the luminous flux per unit solid angle in each direction.
Figure 2-2 Luminous intensity
2.3 Illuminance (E)
It is the total luminous flux incident on a surface, per unit area.
2.4 Luminance (L)
Is the luminous intensity per unit area of light travelling in a given direction
15
Electrical Design – DK_R_21
Begad Wesam Kishk
Figure 2-3 Illustrative representation of different lighting quantities
2.5 Luminous efficacy
is the ration of the luminous flux emitted by a light source (in lumen) and against the power that it demands (in
watts). It measures the efficiency with which the source provides visible light from electricity. The luminous
efficacies (lm/W) of typical lamps are displayed on the table below.
Table 2-1 Luminous efficacy of different lamps. Source
2.6 Calculating lumens and number of luminaires
The main equation to calculate is the following:
𝐸=
𝑁 ∗ ∅ ∗ 𝑈. 𝐹 ∗ 𝑀. 𝐹
𝐿∗𝑊
And from this equation, the number of luminaires could be calculated:
𝑁=
Electrical Design – DK_R_21
𝐸∗𝐿∗𝑊
∅ ∗ 𝑈. 𝐹 ∗ 𝑀. 𝐹
16
Begad Wesam Kishk
Where:
•
•
•
•
•
•
N is the number of luminaires
L, W are the room dimensions
U.F is the utilization factor
MF is the maintenance factor
E is the illuminance
∅ is the luminous flux
2.6.1 utilization factor
U.F is calculated from room dimensions and reflectivity
of wall and ceiling and floor.
For first, room index is calculated
𝑘=
𝐿∗𝑊
ℎ𝑅𝐶 (𝐿 + 𝑊)
Then the utilization factor can be calculated or determined
from the table below.
Figure 2-4 Calculating room index
Table 2-2 Determining U.F
2.6.2 Maintenance factor
It is a crucial value in lighting design that accounts for the reduction in light output over time due to factors like
dirt accumulation, lamp aging, and other environmental conditions.
17
Electrical Design – DK_R_21
Begad Wesam Kishk
2.7 Manual calculations problem
After calculating the number of luminaires, the light sources are distributed over the required room manually
using the (X, 2X) rule.
Figure 2-5 The X,2X rule
Then, if the number of luminaires is fractional, we will choose the higher number and calculate the new value of
E again.
The maximum allowable tolerance is 10% of lux above and below so that it may be necessary to recalculate and
distribute manually again.
The Dialux software solves this problem as will be shown.
2.8 Lighting design using dialux software
1.
2.
3.
4.
5.
6.
7.
8.
Start a New Project & Import Plan.
Define Room/Building Geometry.
Determine the room standard and working plan, etc....
Select & Place Luminaires.
Adjust their mounting heights and orientations.
Perform Calculations.
Analyze & Optimize Results.
Generate Documentation & Reports.
2.9 How to change lux in dialux
There are two methods to change the lux and recalculate the results:
1. Changing the number of luminaires with constant luminaires.
2. changing the luminaire type with constant number of luminaires.
18
Electrical Design – DK_R_21
Begad Wesam Kishk
For uniformity factor: a new downlights or the movement of luminaires position can change and improve the
value of uniformity factor, remember it should be higher than 40%.
2.10 Reading the luminaire code
For example, check the figure below
28 S 830
2800 Lumen
80 CRI
3000 K
Figure 2-6 Example for luminaire code
2.11 Lighting design using AutoCAD
Designing and applying the lighting system in AutoCAD has specified steps and some conditions to avoid.
2.11.1 Steps for design
1.
2.
3.
4.
5.
6.
7.
8.
9.
Extract the CAD file from dialux.
Move the designed system into the original CAD plan.
Numerate each luminaire type in the legend table.
Divide the loads (in this case the luminaires) into three types:
a. Normal loads.
b. Emergency loads.
c. Critical loads.
Create a block for each luminaire type.
Put every load type in a single layer.
Replace the old dialux layer with the new luminaire layers.
Connect the luminaires by lines with each other (every type alone).
Distribute the exit sign along the plan as the standards.
19
Electrical Design – DK_R_21
Begad Wesam Kishk
2.11.2 What to avoid
1. Don’t connect the normal loads with emergencies or critical loads.
2. Don’t connect the lighting system with sockets with the same connections.
3. The line path shouldn’t be sharp at the curves.
Figure 2-7 Wrong Vs. Correct curves drawing
4.
5.
6.
7.
8.
Don’t connect more than 15 luminaires in one line.
Don’t connect more than 3 rooms with the same line.
Wires must not pass through the concrete.
Line length should not exceed 60-70 meters due to voltage drop.
Don’t connect the normal and emergency loads with the same DB.
Remember that the good design should be achieved by:
•
•
•
Good reliability.
Low cost.
Code standards.
2.11.3 Some standards from the Egyptian code
1. Emergency loads should be 25% of normal loads and the critical loads should be 25% of emergency loads.
2. All stair loads, paths and electrical rooms are emergency or critical loads.
3. For a given length of exit sign, this length is multiplied by 200 which gives the distance between every
two adjacent signs (if the signal is 10 cm tall then this distance should be 20 meters).
2.12 Explaining the different types of loads
2.12.1 Normal Loads
Are your everyday lights, powered by the standard utility supply. Think of all the general lighting in an office, a
classroom, or a retail store. They're essential for daily operations and comfort during regular hours. If they go out,
it's an inconvenience, but not a life-threatening emergency, assuming other systems are in place. They're
controlled by typical switches and dimmers.
20
Electrical Design – DK_R_21
Begad Wesam Kishk
2.12.2 Emergency loads
are all about life safety. These lights automatically kick in when the main power fails, specifically to help people
safely exit a building. This includes exit signs and dedicated emergency lights in corridors and stairwells. They're
powered by backup systems like batteries or generators and must meet strict building codes for illumination levels
and how long they stay on. Their failure could lead to panic and injuries during an evacuation.
2.12.3 Critical loads
are the lights that simply cannot fail because they support essential, high-priority operations. Imagine the lighting
in a hospital operating room, a data center, or a security control room. Losing power to these lights would have
severe consequences, like patient harm, data loss, or major operational disruptions. They're backed up by the most
reliable power sources, often including Uninterruptible Power Supplies (UPS) for seamless transitions, ensuring
continuous function even during an outage.
The diagram below explains the difference between these loads:
Normal
Emergency
Critical
A
T
S
UPS
Figure 2-8 Difference between electrical loads
2.13 Switching methods for lighting control
This topic is divided into manual and automatic control and LCP control.
2.13.1 Manual control methods
1.
2.
3.
4.
5.
One switch.
Deviator switch.
Intermediate switch.
Dimmer switches.
Timer switches.
2.13.1.1 One switch method
The classic method which controls the light system by switching
on and off.
Figure 2-9 Switches
21
Electrical Design – DK_R_21
Begad Wesam Kishk
2.13.1.2 Deviator switches
An electrical switch that allows you to control a light source from two different locations.
The operation of this switch is shown in the figure 2-10.
Used in corridors and medium to large rooms.
Figure 2-10 Deviator switch
2.13.1.3 Intermediate switch
used in lighting circuits with three or more switches controlling the same light. It allows you to control a light
from multiple locations, typically on staircases, hallways, or rooms with multiple entrances. The intermediate
switch sits between two-way switches in the circuit.
Figure 2-11 Intermediate switch
2.13.1.4 Dimmer switch
an electrical device that regulates the amount of electricity flowing to a light bulb, allowing you to adjust the
brightness of the light.
Figure 2-12 Dimmer switch
22
Electrical Design – DK_R_21
Begad Wesam Kishk
2.13.1.5 Timer switches
an electronic device that automatically controls the on/off times of electrical equipment or circuits. It acts as a
programmable switch, allowing you to set specific times for devices to turn on and off, rather than relying on
manual operation. This can be used for various purposes, such as controlling lighting.
Figure 2-13 Timer switch wiring
2.13.2 Automatic control switches
Used for automatic turning on-off for light systems, such as:
1. Motion sensors.
2. Occupancy sensors.
2.13.3 LCP control (lighting control panel)
A system used to control and operate lighting devices using various methods like Digital Addressable Lighting
Interface (DALI) and low-voltage analog signals. Uses contactor as the power switch and can be controlled with
it.
Panel
LCP
CB
Control cable
Contactor
Figure 2-14 Basic LCP construction
23
Electrical Design – DK_R_21
Begad Wesam Kishk
Chapter 3
3 Power and MEP design
3.1 Introduction
Power and MEP (Mechanical, Electrical, and Plumbing) design are essential for modern buildings, forming the
backbone of their functionality, comfort, safety, and efficiency. Power design focuses on the safe and reliable
generation, transmission, and distribution of electricity. MEP design covers a broader range of systems, including
HVAC, fire suppression, lighting, communication networks, and plumbing. The two are interdependent: a strong
power infrastructure is vital for MEP systems, and MEP demands significantly influence power requirements. As
buildings become more complex and sustainability gains importance, skilled power and MEP engineers are crucial
for creating functional, responsible, and economically viable environments.
For the first part of this chapter, the power design will be explained.
3.2 Sockets design
Sockets design depends on some factors such as:
•
•
•
Installing type.
Socket type.
Load and C.B rating.
3.3 Types of sockets
3.3.1 For mounting type
1. Flush mounted type.
A flush mount power outlet is installed directly into the
walls, so the surface is flush, level with wall. This
eliminates the need for cover plates.
Installing a flush mount requires professionally trained
tradespeople. Flush mount outlets can only be installed as
part of the drywall installation process, meaning it’s only
an option for remodelers or while rooms are under
Figure 3-1 Flush mounted socket
construction. An electrician and a drywall installer place
the electric box, or the piece of machinery that powers the outlet, inside the drywall, and then "mud" it in using
construction methods.
24
Electrical Design – DK_R_21
Begad Wesam Kishk
2. Surface mounted sockets.
Surface-mounted outlets use the same general set-up as flush-mount or recessed electrical outlets, except the
housing sits on the wall rather than in it. They’re a common choice when you don’t have access to the inside of
the wall and can’t run wire through it. Like all home system components, there are positives and negatives to this
type of outlet. Read on to learn more about surface-mounted electrical outlets.
Figure 3-2 Wall mounted socket
3. Floor box.
A floor box is an electrical box designed to be installed on a floor, providing accessible power and data
connections in locations where wall outlets might be inconvenient or unavailable. They are commonly used in
commercial and residential settings, particularly in open spaces like offices or kitchens.
Floor boxes offer a convenient way to bring power and data connections to the floor level, allowing for easy
access to outlets in areas where wall space is limited or where a more central location for connections is needed.
Usually used in Conference rooms, open-plan offices, and retail spaces often utilize floor boxes to power
workstations, computers, and other equipment.
Figure 3-3 Floor box
25
Electrical Design – DK_R_21
Begad Wesam Kishk
3.3.2 For socket itself type
1. General purpose socket
These are the most common types found in residential and commercial settings for everyday appliances.
Used for low-power appliances that do not require an earth connection for safety (e.g., phone chargers, small
lamps, radios, small kitchen appliances, electric razors). Common in older installations or for double-insulated
devices.
Less safe than grounded sockets, as they lack protection against electrical shock if an insulation fault occurs.
These sockets can be two or three poles. Used in applications up to 1kW.
Figure 3-4 2P socket
Figure 3-5 2P+E socket
The table below explains the rating of each type (both are the same)
Table 3-1 General sockets rating
2. Power sockets.
In case of connecting a Single socket to a Single branch circuit, it is called a Single socket in this case. But when
connecting more than one Power socket to a single branch circuit, it is called General sockets in this case, where
up to 10 outlets can be connected to the single branch circuit. Therefore, the description of a power socket is the
same as the description of a normal socket, but it is preferable to differentiate between them in color (preferably
a power socket in black or a different color).
Note: More than one power socket can be connected to a single branch circuit, provided that more than one outlet
is not used at the same time
These sockets can be used in kitchens and for applications from 1kW to 2.5kW (check the Egyptian code).
26
Electrical Design – DK_R_21
Begad Wesam Kishk
3. Tamper-Resistant Outlets.
Feature internal shutters that prevent foreign objects (like paper clips or keys) from being inserted into the slots,
greatly enhancing safety, especially in homes with children. They only open when a proper plug is inserted
simultaneously into both slots.
Figure 3-6 Tamper resistant outlet
4. Weather-Resistant Outlets
Designed for outdoor use (e.g., patios, decks, gardens, near pools). They are constructed with UV-stabilized,
corrosion-resistant materials and often come with protective covers to shield them from rain, snow, and extreme
temperatures. They are often also GFCI.
Used in medical facilities where extreme reliability and durability are critical. They are subject to stricter testing
for secure ground connections and resistance to impact, often identifiable by a green dot.
Figure 3-7 WP socket
27
Electrical Design – DK_R_21
Begad Wesam Kishk
5. High Power & Industrial Sockets
These are designed to handle higher voltages and currents for specific equipment.
Figure 3-8 High Power & Industrial Sockets
6. Disconnect switch
Used in normal areas such as houses or hospitals for power applications higher than 2.5kW.
Standards for it are: 16,20,25,32,40,50,63,80,100,125,150 Amperes
Description for it: 25A, 3ph, 12.5kVA, for operation unit. In AutoCAD.
𝑃
𝑟
The current rating is calculated by: 𝐼𝑟 = 𝑝.𝑓∗√3𝑉
for three phases.
𝐿𝐿
𝑃
𝑟
And 𝐼𝑟 = 𝑝.𝑓∗𝑉
for single phase.
𝐿𝐿
The current is multiplied by 1.25 for soft starters (VFD) and by 2.5 for DOL if a motor existed. Then the nearest
upper standard is chosen.
Figure 3-9 Disconnect switch
28
Electrical Design – DK_R_21
Begad Wesam Kishk
3.4 Sockets and power distribution and AutoCAD applications
Distribution rules depend on the furniture which is determined by the architecture engineer.
And then the Egyptian code determines the placement rules of the sockets which depends on the room size,
application and so on.
For example, these are some of the code rules:
1. Sockets are placed in 30-40 cm height from the ground but for kitchens and bathrooms become 120-135
cm.
2. Usually, the sockets are classified into normal + critical (UPS) only type.
3. Maximum sockets per line is 10 normal sockets since the socket is rated at 200 VA usually.
4. Power sockets are connected individually with lines into the DB due to the high rating.
In AutoCAD drawing, make sure for the following:
1.
2.
3.
4.
Check the legend and description of each socket.
Change the symbol for the change of height or type.
Normal wiring and critical wiring are in different layers.
Make sure to follow the rules of distribution from the code and the owner.
3.5 MEP equipment
In the realm of Mechanical, Electrical, and Plumbing (MEP) design, mechanical systems are pivotal to a building's
comfort, functionality, and safety. These systems primarily encompass Heating, Ventilation, and Air Conditioning
(HVAC), as well as various plumbing and fire protection components. A core aspect of designing these systems
involves understanding and calculating the "mechanical loads" that the equipment must manage.
3.5.1 What are Mechanical Loads?
In MEP design, "mechanical loads" refer to the heating, cooling, and fluid flow requirements that mechanical
systems must meet to maintain desired indoor environmental conditions, provide essential services, and ensure
safety. These are not structural mechanical loads (like the weight of a beam) but rather energy transfer or fluid
movement requirements.
3.5.2 Key Mechanical Equipment in MEP Design
The "mechanical" aspect of MEP primarily revolves around HVAC systems but also includes crucial elements of
plumbing and fire protection.
•
HVAC Equipment:
1. Chillers: Produce chilled water for cooling, often used in large commercial or industrial buildings.
2. Air Handling Units (AHUs): Condition and distribute air throughout a building via ductwork. They
typically contain fans, coils (heating/cooling), filters, and humidifiers/dehumidifiers.
3. Fan Coil Units (FCUs): Smaller, localized units that provide heating and cooling to individual zones
or rooms.
4. Fans: Used for ventilation, exhaust, and air circulation within various systems.
5. Pumps: Circulate water in chilled water, hot water, and condenser water loops.
29
Electrical Design – DK_R_21
Begad Wesam Kishk
•
Plumbing Equipment:
1. Water Heaters (Calorifiers): Provide hot water for domestic use.
2. Pumps: Used for water supply (boosting pressure), wastewater removal (sewage ejector pumps), and
circulating hot water.
3. Water Storage Tanks: Store potable water.
4. Piping Systems: For hot water, cold water, drainage, waste, vent, and sometimes fuel gas.
3.5.3 Importance of MEP design
The accurate calculation of mechanical loads in MEP design is crucial because it ensures:
1. Optimal Equipment Sizing: Prevents both under- and oversizing, avoiding discomfort/failure or wasted
costs/inefficiency.
2. Energy Efficiency: Leads to reduced energy consumption and lower operating costs.
3. Occupant Comfort & Health: Guarantees proper thermal comfort, indoor air quality, and humidity
control.
4. Code Compliance: Ensures adherence to building codes and safety standards.
5. Cost Management: Avoids unnecessary expenses and costly retrofits.
6. System Reliability & Longevity: Results in less equipment stress, fewer breakdowns, and a longer
operational lifespan.
30
Electrical Design – DK_R_21
Begad Wesam Kishk
Chapter 4
4 Electric Panels Scheduling
4.1 Introduction
Electric panels are crucial for managing and distributing electricity safely in various settings, from homes to
industrial facilities. Understanding their mounting types, internal components, and installation precautions is
essential for their efficient and secure operation.
also known as breaker boxes, distribution boards, or switchboards, serve as the central control point for an
electrical system. They house protective devices and control mechanisms, ensuring reliable power delivery and
safeguarding against electrical hazards.
4.2 Mounting types
The method of mounting an electric panel depends largely on the available space, environmental conditions, and
aesthetic considerations. Common mounting types include:
4.2.1 Wall Mounted
This is the most common type, where the entire panel enclosure is mounted directly onto the surface of a wall.
Surface-mounted panels are easy to install and access for maintenance. They are often used in garages, utility
rooms, or industrial settings where the panel's appearance is less critical.
Figure 4-1 Wall mounted panel
31
Electrical Design – DK_R_21
Begad Wesam Kishk
4.2.2 Embedded
designed to be installed within a cavity, with only the door and outer trim visible. This provides a clean, seamless
appearance, making them popular for residential and commercial interiors where aesthetics are important.
Installation is more involved as it requires cutting into the wall.
Figure 4-2 Embedded DB
Note that the type of DB depends on wall type, thickness and the application.
4.3 Components
The distribution board houses several electromechanical devices
4.3.1 Miniature Circuit Breakers (MCB)
A miniature circuit breaker controls the supply to various miniature circuits on the main circuit. They switch off
if they detect an overcurrent i.e. current that supersedes the circuit’s current rating. They can be single-pole,
double-pole, triple-pole, and four-pole, based on the capacity of each circuit and the required energy input of the
appliances connected.
Figure 4-3 Miniature CB
4.3.2 Molded Case Circuit Breaker (MCCB)
These devices have the same function as MCBs, except with a far higher current rating. This means it has more
versatility and can interrupt larger current ranges, allowing it to be used in both residential and industrial
applications.
32
Electrical Design – DK_R_21
Begad Wesam Kishk
Figure 4-4 MCCB
4.3.3 Isolators
These are manually controlled electromechanical devices for isolating a part of the circuit for maintenance. They
are often used in series with MCBs when an MCB fails. Electricians use this to cut off the current in a circuit so
that they can repair the circuit without getting shocked.
4.3.4 Busbars
Busbars are copper or aluminum conducting strips that carry a large amount of current from the incoming meter
line to the various circuit breakers in the distribution board.
Figure 4-5 Busbars
4.3.5 Identification Labels
These stickers help name the different miniature circuits based on the rooms they control, so that end users can
understand which switch they have to flip to turn off or turn on a specific section of the house/unit.
Figure 4-6 Identification labels
33
Electrical Design – DK_R_21
Begad Wesam Kishk
4.4 Types of busbars
4.4.1 Phase Busbars (Hot Busbars)
These are the primary current-carrying busbars that distribute the live (phase) current from the main incoming
supply to the individual circuit breakers. In a three-phase system, there will be three distinct phase busbars (e.g.,
L1, L2, L3 or R, Y, B).
Figure 4-7 Phase busbars
4.4.2 Neutral Busbar
This is a separate terminal bar where all the neutral wires from the various circuits are terminated. It provides a
common return path for the current to the source. The neutral busbar is typically insulated from the panel's metal
enclosure, except at the main service entrance where it is bonded to the ground bar. Also, the number of busbar
points depends on the panel design and the number of circuits.
Figure 4-8 Neutral busbars
4.4.3 Ground Busbar (Earth Bar)
This is a dedicated terminal bar for all the grounding (earth) wires from the circuits, as well as the main grounding
electrode conductor (connected to an earth rod or other grounding electrode). The ground busbar is always directly
bonded (connected) to the metal enclosure of the panel, ensuring a safe path for fault currents to dissipate into the
earth, protecting against electric shock.
34
Electrical Design – DK_R_21
Begad Wesam Kishk
4.4.4 Fishbone Busbars
refers to a specific design or arrangement of busbars within an electrical panel, particularly common in
distribution boards (DBs). The name comes from its resemblance to the skeleton of a fish, with a central
"backbone" busbar and smaller "ribs" branching off to connect to individual circuit breakers or outgoing circuits.
Figure 4-9 Fishbone busbar
The figure below shows the connection of this type in the electric panels:
Figure 4-10 Fishbone type connections
35
Electrical Design – DK_R_21
Begad Wesam Kishk
4.5 Spare and space
A "space" in an electrical panel refers to an empty physical slot on the busbar where a circuit breaker can be
installed. Each slot is typically designed to accommodate a standard single-pole breaker.
A "spare" in an electrical panel refers to a circuit breaker that is already installed in a "space" but is not currently
connected to any active load. It's a pre-installed, ready-to-use breaker that is simply waiting for a circuit to be
wired to it.
Figure 4-11 Difference between spare and space
4.6 Types of electric panels in terms of applications
4.6.1 MDB Panel
It is the central hub of an electrical system within a building or facility. It's typically the first point of distribution
after the main power source, such as a utility transformer or a generator.
The MDB receives the primary incoming electrical power and then efficiently and safely distributes it to various
sub-main distribution boards (SMDBs), final distribution boards (DBs), and large, critical loads throughout the
premises.
Figure 4-12 MDB
36
Electrical Design – DK_R_21
Begad Wesam Kishk
It houses the main incoming circuit breaker (often a large Air Circuit Breaker - ACB or Molded Case Circuit
Breaker - MCCB), robust busbar systems (usually copper or aluminum), and outgoing protective devices (like
MCCBs) for each major feeder circuit. It also includes neutral and earth (ground) busbars. Metering and
monitoring devices are frequently integrated.
4.6.2 SMDB Panel
acts as an intermediate electrical distribution point in larger buildings or facilities. It sits hierarchically between
the main distribution board (MDB) and the final distribution boards (DBs).
An SMDB receives power from the MDB and further distributes it to specific sections, floors, or zones of a
building. It essentially breaks down the large power supply from the MDB into more manageable sub-sections,
which then feed individual smaller distribution boards or direct large-area loads.
Figure 4-13 SMDB
The income and outcomes of SMDB are MCCBs.
4.6.3 FDB
A Final Distribution Board (FDB), often simply referred to as a Distribution Board (DB) or a consumer unit (in
residential contexts), is the last point of power distribution before electricity reaches individual circuits and
appliances within a building.
Figure 4-14 FDB
37
Electrical Design – DK_R_21
Begad Wesam Kishk
The FDB receives power from an SMDB (or directly from an MDB in smaller installations) and then distributes
it to individual, smaller circuits that directly supply power to lights, power outlets, appliances, and other specific
loads within a defined area (e.g., a room, a floor section, or a small apartment).
4.6.4 MCC
It is a centralized assembly of one or more enclosed sections, with a common busbar, containing motor control
units. It's specifically designed for the organized control and protection of multiple electric motors from a single
location.
The primary purpose of an MCC is to provide a central point for starting, stopping, controlling the speed (if VFDs
are included), and protecting a group of electric motors. This consolidates motor control functions, improving
operational efficiency and safety.
Figure 4-15 MCC panel
4.7 Conditions to Take Care of While Installing the Panel
Proper installation of an electric panel is paramount for safety and long-term reliability. Here are some critical
conditions to observe:
1. Safety First: Always ensure the main power supply to the building is turned off before commencing any
work on the electrical panel. Use appropriate personal protective equipment (PPE) such as insulated
gloves, safety glasses, and non-conductive tools.
2. Compliance with Codes: Adhere strictly to local electrical codes (e.g., NEC in the USA, IEE Wiring
Regulations in the UK, or equivalent national standards). These codes dictate clearances, wire sizing,
grounding requirements, and overall installation practices.
3. Proper Location: Choose a location that is easily accessible for maintenance and emergencies, free from
obstructions, and not exposed to excessive moisture, dust, or extreme temperatures. Ensure sufficient
working space around the panel as per code requirements.
4. Adequate Grounding and Bonding: Establish a robust grounding electrode system and ensure all
metallic parts of the panel and associated electrical equipment are properly bonded to the grounding
system. This is crucial for safety and fault protection.
38
Electrical Design – DK_R_21
Begad Wesam Kishk
5. Correct Wire Sizing and Termination: Use the correct gauge of wire for each circuit as specified by the
load requirements and code. Ensure all wire connections are tight and secure, with no frayed strands.
Overtightening or under tightening can lead to issues.
6. Clear Labeling: Clearly label each circuit breaker with its corresponding circuit (e.g., "Kitchen Lights,"
"Bedroom Outlets"). This is vital for safety, troubleshooting, and future maintenance.
7. Environmental Protection: If installed outdoors or in a damp environment, ensure the panel has an
appropriate NEMA or IP rating to protect against water, dust, and other contaminants.
8. Professional Installation: If you are not a qualified electrician, it is strongly recommended to hire a
licensed professional for electric panel installation. Electrical work can be dangerous if not performed
correctly.
By understanding these aspects, one can ensure the safe, efficient, and compliant installation and operation of
electric panels, forming the backbone of a reliable electrical system.
4.8 Panel Scheduling
4.8.1 Naming the DB
Naming the DB depends on the application, floor, number and the feeding source
Load Type
EMG
UPS
Feeding
L
E
P
U
AC
Placement
Number
P FLOOR
No.
Panel
D
ELP-G-03
ACP-01-02
DP-05-04
Figure 4-16 Naming the DB
The figure above describes briefly how to name any DB.
4.9 Electric room and busbar standards
•
•
•
The electric room must cover a circle with a radius of 50m so that the voltage drop at an acceptable level.
The line length should not exceed 60m long at any placement.
Panel busbar has a standard number of lines (6 multipliers): 6, 12, 18, … ,48 and any number not in the
range will be a higher cost.
• RST phases are in red, blue and yellow colors.
• The neutral is black.
• Earth is yellow and green.
39
Electrical Design – DK_R_21
Begad Wesam Kishk
4.10 Unbalance rule
Usually in Y-connected loads, the neutral current is zero at the balanced three phase loading.
This is a hard case to achieve so that the unbalance shouldn’t be higher than 10%.
The unbalance can be calculated by: 𝑈𝑛𝑏𝑎𝑙𝑎𝑛𝑐𝑒% =
𝑀𝑎𝑥 𝐿𝑜𝑎𝑑−𝑀𝑖𝑛 𝐿𝑜𝑎𝑑
𝑀𝑎𝑥 𝐿𝑜𝑎𝑑
∗ 100%.
The load is measured in VA.
Figure 4-17 Y-connected power system
4.11 Electrical factors
4.11.1 Connected load
It is defined as the sum of ratings of all electrical equipment that are connected at the supply point regardless of
their status of operation.
4.11.2 Demand factor
The ratio between the maximum load demand on the system and the connected load.
𝐷𝐹 =
𝑀𝑎𝑥 𝐷𝑒𝑚𝑎𝑛𝑑
𝐶𝑜𝑛𝑛𝑒𝑐𝑡𝑒𝑑 𝐿𝑜𝑎𝑑
4.11.3 Diversity factor
The ratio of the sum of individual maximum demands of all customers to the maximum demand for a specific
station is known as the diversity factor.
𝐷𝑖𝑣 𝐹 =
𝑠𝑢𝑚 𝑜𝑓 𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑑𝑒𝑚𝑎𝑛𝑑𝑠
𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑑𝑒𝑚𝑎𝑛𝑑 𝑜𝑓 𝑡ℎ𝑒 𝑝𝑎𝑛𝑒𝑙
All these factors are used to reduce the overall cost, CB, cables and transformer ratings.
40
Electrical Design – DK_R_21
Begad Wesam Kishk
4.12 Cables
Power cables are vital components in electrical systems, enabling the transmission of electrical energy across
various applications, from household wiring to high-voltage power grids. These cables typically consist of
conductors, insulation, and protective sheathing, all designed for efficient and safe power delivery.
Our study case is the low voltage cables.
Figure 4-18 Cables construction
4.12.1 Construction:
1. Conductor: Usually made of highly conductive metals like copper or aluminum, facilitating electricity
flow. Aluminum is a more affordable and recyclable alternative to copper.
2. Insulation: Crucial for preventing short circuits and ensuring safety. Materials like oil-impregnated paper,
PVC, XLPE, and Ethylene Propylene Rubber (EPR) are used, with stronger insulation required for higher
voltages. Insulation also provides resistance against heat, electrical stress, and environmental factors.
3. Sheath/Outer Covering: Provides external protection against environmental damage, fire, and chemical
reactions. PVC is a common material for sheathing.
4.12.2 Factors Affecting Performance:
1.
2.
3.
4.
5.
Section Area: Larger conductor area leads to higher current-carrying capacity.
Temperature: Hotter environments can degrade insulation faster.
Conductors: More bundled conductors can reduce heat dissipation.
Installation: Methods like ducts, trays, conduits, and raceways can impact heat dissipation.
Degradation: Natural aging, oxidation, and conductor fatigue can increase resistance and lead to failure.
4.12.3 Naming the cable
Can be named as the example below to understand easier:
Figure 4-19 Example of cable naming
41
Electrical Design – DK_R_21
Begad Wesam Kishk
Note that sometimes the neutral wire is half the CSA of normal wires to reduce cost.
The figure below shows a cable catalog for example.
Figure 4-20 Cable catalog from Elsewedy cables
42
Electrical Design – DK_R_21
Begad Wesam Kishk
4.12.4 For sizing
The Cable rating should be higher than CB rating by 1.25 times.
You can choose the CB rating from the figure below.
Figure 4-21 CB ratings
Remember to consider the motor loads starting method in calculations.
43
Electrical Design – DK_R_21
Begad Wesam Kishk
Chapter 5
5 Bulk and SLD
5.1 Introduction
An electrical power system is a complex network designed to generate, transmit, and distribute electrical energy
to consumers. At its heart lies a collection of bulk equipment, large-scale components that are fundamental to
the system's operation, reliability, and efficiency. This bulk equipment forms the backbone of the power grid,
enabling the massive flow of electricity from power plants to distant load centers and ensuring a stable and
continuous supply. Understanding these critical components is essential to comprehending the intricate workings
and formidable challenges of modern electrical power systems.
•
This equipment is:
1. Transformers.
2. Diesel engine generators.
3. UPS.
4. Transfer switch (ATS, MTS).
5. RMUs and distributors.
Figure 5-1 Power system components
44
Electrical Design – DK_R_21
Begad Wesam Kishk
5.2 Transformers
In the vast and interconnected world of electrical power systems, transformers stand as indispensable workhorses,
silently enabling the efficient and reliable flow of electricity across immense distances and diverse applications.
These static electrical devices, based on the fundamental principles of electromagnetic induction, possess the
remarkable ability to change alternating current (AC) voltage levels without altering the frequency. From stepping
up voltages at power generation sites for long-distance transmission, minimizing energy losses, to stepping them
down for safe distribution to homes and industries, transformers are critical links in the power delivery chain.
Their widespread application underscores their pivotal role in shaping the modern electrical grid, ensuring that
electrical energy, generated perhaps hundreds of kilometers away, arrives at our fingertips at the precise voltage
required.
Figure 5-2 Transformer
Transformers are mainly classified into power transformers and distribution transformers.
For power transformers rating, see the table below which shows the power ranges and voltage.
Table 5-1 Typical power transformers ratings
Also, for distribution transformers rating:
45
Electrical Design – DK_R_21
Begad Wesam Kishk
For sizing transformers:
Table 5-2 Typical distribution transformers ratings
Find the total load current and power in (VA), then use the maximum loading rule which that the maximum
transformer loading is 80%.
𝑅𝑎𝑡𝑖𝑛𝑔 =
𝐿𝑜𝑎𝑑 𝑖𝑛 𝑉𝐴
0.8
Then choose the nearest upper standard.
Also, the CB should be higher than or equal the transformer rated current.
5.3 Diesel engine generators
In the realm of power generation, particularly for standalone, backup, or remote applications, diesel engine
generators play a pivotal role. These robust machines combine a diesel engine with an electrical generator
(alternator) to convert the chemical energy stored in diesel fuel into usable electrical energy. They are essential
for providing reliable power in situations where grid electricity is unavailable, unstable, or insufficient, making
them a cornerstone for critical infrastructure like hospitals, data centers, and telecommunication towers, as well
as for construction sites, mining operations, and even remote homes. The inherent efficiency, durability, and
immediate power-on-demand capabilities of diesel engine generators solidify their position as a crucial
component in ensuring continuous and stable power supply across a vast spectrum of industries and settings.
Figure 5-3 Emergency generator
46
Electrical Design – DK_R_21
Begad Wesam Kishk
Sizing of the generators have the same rule as the transformers with maximum loading of 80%.
Table 5-3 Typical generator ratings
5.4 UPS
Uninterruptible Power Supplies: The Silent Guardians of critical loads in our system.
A UPS is an electrical apparatus that provides emergency power to a load when the input power source, typically
the utility grid, fails or deviates from acceptable parameters. Unlike traditional backup generators that require a
brief startup period, a UPS offers near-instantaneous protection by drawing on stored energy, usually in batteries,
supercapacitors, or flywheels. This immediate response is what fundamentally differentiates a UPS and makes it
crucial for sensitive and mission-critical applications.
Figure 5-4 UPS
47
Electrical Design – DK_R_21
Begad Wesam Kishk
While its primary function is to provide short-term power during outages, the role of a UPS extends far beyond
simple backup. It acts as a comprehensive power conditioning device, addressing a multitude of power quality
issues that can plague an electrical system.
Figure 5-5 UPS construction
UPS is sized by its maximum current and how much time it can feed it.
5.5 ATS
An Automatic Transfer Switch is an electrical device that automatically switches the power supply from its
primary source (typically the utility grid) to a backup source (such as a diesel generator, a secondary utility feed,
or even a solar array with battery storage) when the primary source experiences an outage or significant deviation
from acceptable voltage and frequency parameters. Its core purpose is to ensure the continuous supply of
electricity to critical loads, preventing the costly and potentially dangerous consequences of power interruptions.
Figure 5-6 ATS
ATS can be converted into manual control method (MTS).
Used to feed emergency load and has the same EMG generators rating.
48
Electrical Design – DK_R_21
Begad Wesam Kishk
5.6 RMUs and distributors
5.6.1 RMUs
An RMU is designed to be installed at load connection points in a "ring-type" distribution network. This ring
configuration is key to its effectiveness, allowing electricity to flow in multiple directions. If a fault occurs in one
section of the ring, the RMU can quickly isolate that faulty section and reroute power through an alternative path,
thus preventing widespread outages and ensuring a continuous supply to consumers.
Figure 5-7 RMU
The significance of RMUs stems from their ability to combine multiple critical functions within a single, spacesaving unit, fundamentally enhancing the stability and reliability of the distribution grid.
5.6.2 distributors
The distribution system takes medium voltage (MV) electricity from primary substations and, through a series of
transformers and lines, reduces it to the low voltages required by consumers. It is the segment of the power system
that directly interacts with and serves individual loads, representing the "last mile" of electrical delivery.
Figure 5-8 Distributers diagram
49
Electrical Design – DK_R_21
Begad Wesam Kishk
The primary function of the distribution system is to bridge the gap between the high-voltage transmission
network and the diverse demands of individual consumers. Its multifaceted roles are crucial for a functional and
accessible electrical supply.
The distribution system branches out extensively, forming a localized network that physically connects to every
consumer. This intricate web of feeders and service lines ensures that every premise requiring electricity can be
reached and supplied.
A key objective of distribution is to provide a continuous and stable power supply to end-users. This involves
designing the network with redundancy where possible (e.g., using ring main units, as previously discussed),
implementing protective devices to isolate faults quickly, and maintaining infrastructure to minimize outages.
5.7 SLD
An SLD is a simplified, symbolic representation of an electrical power system that shows the major components
and their interconnections using single lines, rather than representing each phase of a multi-phase system. Despite
its simplified appearance, it provides a wealth of critical information about the system's configuration, operation,
and protection.
Figure 5-9 Example for SLD
These specialized diagrams zoom in on the final stage of electricity distribution, illustrating how power is
distributed and protected within a specific building, facility, or even a particular floor. They represent the "last
leg" of the electrical journey, detailing the circuits that feed individual loads and ensure safe, localized power
delivery.
50
Electrical Design – DK_R_21
Begad Wesam Kishk
Chapter 6
6 Some important calculations
6.1 Introduction
Calculating derating factors, voltage drop and short-circuit currents are crucial in cable design and panel building
to ensure the safety, efficiency, and reliability of electrical systems.
•
Derating factors account for real-world conditions (like ambient temperature, cable grouping, and
installation methods) that can reduce a cable's current-carrying capacity. Ignoring these can lead to
overheating, insulation damage, reduced cable lifespan, and even fire hazards.
•
Voltage drop calculations are vital to ensure that electrical equipment receives sufficient voltage to
operate correctly. Excessive voltage drop can result in reduced performance, malfunctions, increased
energy losses, and even damage to sensitive equipment.
•
Short-circuit calculations determine the maximum fault current an electrical system can experience. This
is essential for selecting appropriately rated protective devices (like circuit breakers and fuses) and
ensuring that all components within the panel and cabling can safely withstand these high currents,
preventing extensive equipment damage, serious injury, or fire during a fault.
In essence, these calculations are indispensable for designing a robust electrical infrastructure that complies with
safety standards, minimizes energy waste, and provides consistent power to connected loads.
From MV
TRANS
2500 KVA
Busduct 5000A
MDB 1700 KVA
SMDB1
SMDB2
Both same
ratings
SMDB3
ATS
Cables
FDB1
EMDB
G
EMG Loads
UMDB
FDB_n
FDB2
Critical Loads
Figure 6-1 SLD example
51
Electrical Design – DK_R_21
Begad Wesam Kishk
6.2 Calculating derating factors
Cable derating factors are multipliers (typically less than 1) applied to a cable's standard current-carrying
capacity (ampacity) to account for real-world conditions that can limit its ability to safely dissipate heat and carry
current. These factors are crucial because if a cable is used beyond its safe operating temperature, its insulation
can degrade, leading to premature failure, fire hazards, and reduced system reliability.
The primary reasons for applying derating factors are:
1. Ambient Temperature: Cables are typically rated for a specific ambient temperature (e.g., 30∘C or
40∘C). If the actual operating temperature is higher, the cable's ability to dissipate heat is reduced, so its
ampacity must be derated.
2. Grouping/Bundling of Cables: When multiple cables are installed close together (e.g., in a conduit, cable
tray, or bundle), they mutually generate and trap heat. This cumulative heating effect reduces the
individual ampacity of each cable within the group. The more cables in a group, the lower the derating
factor.
3. Installation Method: How a cable is installed significantly impacts its heat dissipation. For example, a
cable installed in free air will dissipate heat more effectively than one buried directly in the ground, in a
conduit, or encased in thermal insulation. Different installation methods have different inherent derating
factors.
4. Soil Thermal Resistivity (for buried cables): For direct-buried cables, the type and moisture content of
the surrounding soil affect how well heat can dissipate. Soils with higher thermal resistivity (poorer heat
conduction) will require greater derating.
Table 6-1 Air Temp. DF
Table 6-2 Burial depth DF
52
Electrical Design – DK_R_21
Begad Wesam Kishk
Table 6-3 H&V formation DF
Table 6-4 Touching DF
53
Electrical Design – DK_R_21
Begad Wesam Kishk
From all these factors above, which can be obtained from the cable catalog as shown, the derating factor of the
cable can be calculated as follows:
𝐷𝐹 = 𝐷𝐹1 ∗ 𝐷𝐹2 ∗ … ∗ 𝐷𝐹𝑛
Then the new rating of the cable will be: 𝐼𝑐𝑎𝑏𝑙𝑒𝑛𝑒𝑤 = 𝐼𝑐𝑎𝑏𝑙𝑒𝑏𝑎𝑠𝑒 ∗ 𝐷𝐹 which will be lower than the base value.
𝑆
Where: 𝐼𝑐𝑎𝑏𝑙𝑒𝑏𝑎𝑠𝑒 = 𝐿𝑜𝑎𝑑
𝑖𝑛 𝑉𝐴
√3∗380
If the new value is lower than the C.B rating, the cable CSA must be increased to the next standard.
6.3 Voltage-drop calculations
Voltage drop refers to the reduction in electrical potential (voltage) along the length of a conductor due to its
resistance and reactance, as current flows through it. It's a critical calculation in cable design because excessive
voltage drop can lead to:
•
Reduced Performance: Equipment operating below its rated voltage may perform inefficiently, suffer a
reduced lifespan, or fail to operate at all. For example, motors can overheat and burn out, and lighting can
dim.
•
Increased Energy Losses: The "lost" voltage means dissipated power as heat in the cables, leading to
wasted energy and higher electricity bills.
To calculate the voltage-drop, refer to the following equations:
𝑉𝐷 =
𝑚𝑣|𝐴|𝑚 ∗ 𝐼𝑏𝑎𝑠𝑒 (𝐴) ∗ 𝐿(𝑚)
1000
𝑉𝐷% =
𝑉𝐷
∗ 100%
380
Maximum allowed voltage drop percentage is 2.5%
Note that the voltage-drop is accumulated value, start from the source and accumulate the drops until the required
point or board, the figure below shows how to calculate the accumulated value.
From MV
TRANS
2500 KVA
MDB 1700 KVA
Busduct 5000A
1 = 0% due to busducts
1 =
SMDB
1
=
1 +
3 =
+
1
1
1
1000
=
FDB1
1000
Figure 6-2 Calculate the accumulated VD
54
Electrical Design – DK_R_21
Begad Wesam Kishk
6.4 Short circuit calculations
Short-circuit calculations are essential in cable design and panel building to determine the maximum current
that would flow in an electrical system during a fault condition (e.g., when a live wire accidentally touches a
neutral wire or ground). This is critical for selecting protective devices (circuit breakers, fuses) with adequate
interrupting ratings and ensuring that all components (cables, busbars, switchgear, panel enclosures) can safely
withstand the immense thermal and mechanical stresses caused by these high currents without damage or
catastrophic failure.
Ignoring short-circuit calculations can lead to:
•
Equipment Damage: Components not rated for the fault current can explode, melt, or be permanently
damaged.
•
Fire Hazards: Excessive heat generated during a short circuit can ignite surrounding materials.
•
Personnel Injury: Arcs and explosions during a short circuit can cause severe burns or other injuries.
The figure below shows the different types of SCs.
Figure 6-3 Types of short circuits
How to calculate short circuit current?
𝑉𝑝𝑟𝑒
This can be obtained by the equation: 𝐼𝑠𝑐 = 𝑍
𝑡𝑜𝑡
Where the 𝑉𝑝𝑟𝑒 is the pre-fault voltage, 𝑍𝑡𝑜𝑡 is the total impedance from the source to the faulty point.
The figure below shows a simple example to how to calculate the SC.
E
1
F
Figure 6-4 A simple fault problem
55
Electrical Design – DK_R_21
Begad Wesam Kishk
From the figure above, the fault current at point F can be calculated as:
𝐼𝑓 =
𝐸
𝑍𝐸 + 𝑍1 + 𝑍2 + 𝑍𝑓
And for solid fault the 𝑍𝑓 becomes zero.
Usually faults calculations are performed in the three phase faults, which is the worst case.
Figure 6-5 Percentage of faults occurrence
Then how can the fault equivalent impedance be obtained? Especially the cables
Cables impedance can be obtained from the catalog, observe the table below.
Table 6-5 Four core cables datasheets
56
Electrical Design – DK_R_21
Begad Wesam Kishk
From the table above the cable resistance and reactance can be obtained, then multiplied by the cable length in
km, then the cable impedance will be:
2
2
𝑍𝑐𝑎𝑏𝑙𝑒 = √𝑅𝑐𝑎𝑏𝑙𝑒
+ 𝑥𝑐𝑎𝑏𝑙𝑒
Also, from the figure below the fault current can be calculated.
From MV
TRANS
2500 KVA
MDB 1700 KVA
.
Busduct 5000A
from TR nameplate
=0
1
Calculated from catalog
SMDB
FDB1
F
Figure 6-6 SLD SC calculations
And thus:
𝐼𝑓 =
𝑉𝑝𝑟𝑒
𝑍𝑡𝑟 + 𝑍𝑐1 + 𝑍𝑐2
From the fault current you can determine the SC capacity for each cable to choose and adjust your C.B.
Table 6-6 SC capacity
57
Electrical Design – DK_R_21
Begad Wesam Kishk
References
(2025, July 9). Retrieved from https://waldmannlighting.com/surface-mounted-lights-an-architects-guide/
(2025, July 9). Retrieved from https://www.archtoolbox.com/light-fixture-components/
(2025, July 9). Retrieved from https://integral-led.com/en/content/what-is-ip-rating-ingress-protection
(2025, July 9). Retrieved from https://www.westinghouselighting.com/color-temperature.aspx
(2025, July 9). Retrieved from https://en.wikipedia.org/wiki/Recessed_light
(2025, July 9). Retrieved from https://www.fagerhult.com/knowledge-hub/planning-and-calculationtips/measurement/#:~:text=The%20light%20distribution%20curve%20drawn%20in%20a,distribution%
20in%20direction%20of%20the%20longitudinal%20axis.
(2025, July 13). Retrieved from https://lyntec.com/lcp-lighting-control-panelboards/
(2025, July 17). Retrieved from https://cassonhardware.com/blogs/stories/flush-mount-outlets-and-where-toplace-them-wall-poweroutlets#:~:text=An%20electrician%20and%20a%20drywall,then%20%22mud%22%20it%20in%20usin
g
(2025, July 17). Retrieved from https://expresselectricalservices.com/what-are-surface-mounted-electricaloutlets/#:~:text=Surface%2Dmounted%20wiring%20accessories%20and,dimmer%20switch%20or%20
USB%20receptacle.
(2025, July 18). Retrieved from https://precisionelectricals.com/everything-about-distribution-boards-usestypes-safety-tips/
(2025, July 20). Retrieved from https://gobridgit.com/blog/role-of-mep-in-construction/
(2025, July 20). Retrieved from https://www.ggs-interior.com/en/news/studies/understanding-the-vital-role-ofmep-systems-in-building-construction/
(2025, July 20). Retrieved from https://en.wikipedia.org/wiki/Motor_control_center
(2025, July 20). Retrieved from https://kdmfab.com/distribution-board-types/
(2025, July 22). Retrieved from https://woodstockpower.com/blog/common-diesel-generator-uses-applications/
(2025, July 22). Retrieved from https://www.monolithicpower.com/en/learning/mpscholar/ac-power/the-powergrid/power-distribution-systems
(2025, July 22). Retrieved from https://en.wikipedia.org/wiki/Uninterruptible_power_supply
(2025, July 28). Retrieved from https://elek.com/articles/cable-rating-derating-factors/
(2025, July 28). Retrieved from https://digital-library.theiet.org/doi/10.1049/jiee-1.1934.0184?doi=10.1049/jiee1.1934.0184#:~:text=C.,the%20rating%20of%20the%20cable.
(2025, July 28). Retrieved from https://www.jadelearning.com/blog/derating-current-carrying-conductors-forconditions-of-use/
58
Electrical Design – DK_R_21
Begad Wesam Kishk
(2025, July 28). Retrieved from https://www.geeksforgeeks.org/electrical-engineering/how-to-calculate-shortcircuit-current/
Dar Alkahrabaa. (2025, 6 24). Retrieved from YouTube: https://www.youtube.com/@daralkahrbaa
Gilany, D. M. (2013). Electrical design and installations. Cairo.
Gilany, D. M. (2013). Electrical power engineering. Cairo.
Shaban, D. A. (2022). Electrical sockets design guide. Cairo.
59
Electrical Design – DK_R_21
Begad Wesam Kishk