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UNIVERSITY OF NAIROBI
FACULTY OF ENGINEERING
DEPARTMENT OF ELECTRICAL AND INFORMATION ENGINEERING
BUILDING ELECTRICAL SERVICES DESIGN FOR HOSTEL
ALONG NYERERE ROAD
PROJECT NUMBER: PRJ 095
BY
OELE O. COLLINS ERICK
F17/1999/2005
SUPERVISOR: DR. N. O. ABUNGU
EXAMINER: MR. DHARMADHIKARY
PROJECT REPORT SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE AWARD OF THE DEGREE
OF
BACHELOR OF SCIENCE IN ELECTRICAL AND ELECTRONIC ENGINEERING OF THE UNIVERSITY OF NAIROBI 2010
Submitted on: 18th May, 2011
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DEDICATION
This project is dedicated to all my immediate family members. They have been my source of
inspiration all my life.
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ACKNOWLEDGEMENTS
I humbly do acknowledge the ALMIGHTY GOD for enabling me reach this far with this project.
I gratefully acknowledge the support of Dr. Nicodemus Abungu, my project supervisor. He has
been of immense help and motivation during this entire project process. I also acknowledge my
fellow colleagues who challenged me with their input and constructive criticism. I do extend
much sincere thanks and appreciation to all the aforementioned.
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DECLARATION AND CERTIFICATION
ND CERTI
This BSc. work is my original work and has not been presented for a degree award in this or any
other university.
………………………………………..
OELE O. COLLINS ERICK
F17/1999/2005
This report has been submitted to the Department of Electrical and Information Engineering,
University of Nairobi with my approval as supervisor:
………………………………
DR. NICODEMUS ODERO ABUNGU
Date: 18th May 2011
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ABSTRACT
The main objective of the project is to design the building electrical services for a hostel along
Nyerere road and located in Nairobi, Kenya. The site plan has one building with a total of six, (6)
floors. Due to the location, the most reliable source of electrical power is the mains national grid
power. In order to achieve the main objective and to specify the size and number of back-up
generators to be employed, the final circuits consisting of lighting and power sockets is designed
first. The lighting design is done using the lumen method which takes into consideration the size
and use of the room being lit. Power points layout design is done by considering the needs of the
final user of the premises in every room; this ensures that the need for electrical power is
fulfilled in the design. The final circuits are to be supplied by fifteen, (15) consumer units. These
consumer units are then all distributed on one, (1) distribution board, ensuring that all the single-
phase loads are balanced almost equally on each phase with 341.389 amperes on red phase,
333.472 amperes on the yellow phase and 335.972 amperes on the blue phase. This guaranteed
that cables and distribution equipment are utilized much more effectively due to small
differences in current on each phase. The load of the entire building is 308.6 kW or 385.75 kVA
and so the power back-up systems design has one hooded diesel generator rated 450 kVA. This
is located at a convenient area and caged within the site compound. To ensure co-ordinated
operation of the Miniature Circuit Breakers (MCB), and Moulded Case Circuit Breakers
(MCCB) when safeguarding against the effects of overloads and short circuits, discrimination
between the devices is observed. This has enabled the system to switch off only the breaker
closest to the fault without disruption of supply to other areas. Finally lightning protection is
done to safeguard against the effects of a lightning stroke. With this system the hostel will have
safe, reliable and expandable power supply.
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TABLE OF CONTENTS
DEDICATION ......................................................................................................................................... i
ACKNOWLEDGEMENTS ..................................................................................................................... ii
DECLARATION AND CERTIFICATION ............................................................................................ iii
ABSTRACT ........................................................................................................................................... iv
CHAPTER 1 ........................................................................................................................................... 1
1.0 INTRODUCTION ............................................................................................................................. 1
1.1 Objectives ...................................................................................................................................... 1
1.2 Prelude .......................................................................................................................................... 1
1.2.1 Building Electrical Services Design ......................................................................................... 2
1.2.2 Codes and Standards ............................................................................................................... 2
1.2.3 End – User Accessories ........................................................................................................... 2
CHAPTER 2 ........................................................................................................................................... 3
2.0 THEORY AND BACKGROUND ..................................................................................................... 3
2.1 Lighting Design ............................................................................................................................. 3
2.1.1 Hostel Lighting Design ........................................................................................................... 3
2.1.2 Illuminance Recommendations ................................................................................................ 4
2.1.3 Light Sources .......................................................................................................................... 4
2.1.4 Lumen Method of Lighting Design .......................................................................................... 5
2.1.5 Light Switches ........................................................................................................................ 6
2.2 Electrical Power Circuits ................................................................................................................ 6
2.2.1 Socket Outlets ......................................................................................................................... 6
2.2.2 Kitchen Unit ........................................................................................................................... 7
2.3 Electrical Service Network ............................................................................................................. 7
2.3.1 Diversity ................................................................................................................................. 7
2.3.2 Power Circuit Design .............................................................................................................. 7
2.3.3 Consumer Units ...................................................................................................................... 8
2.3.4 Distribution Board................................................................................................................... 9
2.3.5 Switch-Boards ......................................................................................................................... 9
2.3.6 Commercial Back-Up Diesel Power Generators..................................................................... 10
2.3.7 Wiring .................................................................................................................................. 11
2.3.8 Cable Sizing .......................................................................................................................... 11
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2.4 Protection Systems ....................................................................................................................... 11
2.4.1 Overload Protection .............................................................................................................. 12
2.4.2 Short Circuit Protection ......................................................................................................... 12
2.4.3 Protection System Equipment ................................................................................................ 13
2.4.4 Discrimination and Protection System Co-ordination ............................................................. 13
2.4.5 Lightning Protection.............................................................................................................. 14
CHAPTER 3 ......................................................................................................................................... 16
3.0 PROJECT WORK AND IMPLEMENTATION ............................................................................... 16
3.1 Site Location................................................................................................................................ 16
3.2 Site Plan and Introduction ............................................................................................................ 16
3.2.1 Sample Lumen Method of Lighting Design Calculation for One Hostel Room ....................... 16
3.2.2 Sample Power Points Layout Design for One Hostel Room ................................................... 19
3.3 Entire Hostel Lighting Fittings Design and Power Points Layout Designs .................................... 20
CHAPTER 4 ......................................................................................................................................... 21
4.0 DESIGN ANALYSIS AND DISCUSSIONS ................................................................................... 21
4.1 Design Analysis Based on Load Calculations and Circuits Arrangements ..................................... 21
4.1.1 Introduction .......................................................................................................................... 21
4.1.2 Lower Floor .......................................................................................................................... 22
4.1.3 Upper Ground Floor .............................................................................................................. 23
CHAPTER 5 ......................................................................................................................................... 28
5.0 DISTRIBUTION SYSTEM TOPOLOGY........................................................................................ 28
5.1 Consumer Unit, (CU) Design and Specifications .......................................................................... 28
5.1.1 Consumer Unit, CU UGF 1 ................................................................................................... 30
5.1.2 Consumer Unit Total Single-Phase load calculations, Total Load Currents Drawn, Cable Length and Cable Size Selection from the Distribution Board, (DB) feeding the CU. ..................... 31
5.2 Distribution Board, (DB) Design and Specifications ..................................................................... 33
5.2.1 Single-Phase Loads Distribution Board Design and Specifications......................................... 33
5.2.2 Three-Phase Loads Distribution Board Design and Specification ........................................... 37
5.3 Power Back-Up Generator ........................................................................................................... 41
5.3.1 Size of Back-Up Generator .................................................................................................... 41
5.3.2 Sizing of Cable of the Back-Up Generator ............................................................................. 42
5.4 Electrical Distribution Reticulation .............................................................................................. 43
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5.5 Electrical Distribution Protection System based on Fault Current Levels at Various Points in the Installation......................................................................................................................................... 44
5.5.1 Fault Current Level at the Switch-Board ................................................................................ 44
5.5.2 Fault Current Levels at the Beginning of Final Circuits ......................................................... 45
5.5.3 Discrimination between CUs and DBs ................................................................................... 48
5.5.4 Discrimination between DBs and the Switch-Board ............................................................... 49
5.5.5 Discrimination between Moulded Case Circuit Breaker, (MCCB 1) and Switchboard ............ 50
5.5.6 Discrimination between Generator Moulded Case Circuit Breaker, (MCCB 2) and Switch-Board............................................................................................................................................. 51
5.6 Lightning Protection Design ........................................................................................................ 52
5.7 Power Factor Correction .............................................................................................................. 53
CHAPTER 6 ......................................................................................................................................... 55
6.0 CONCLUSIONS ............................................................................................................................. 55
CHAPTER 7 ......................................................................................................................................... 56
7.0 RECOMMENDATION FOR FUTURE WORK .............................................................................. 56
7.1 Software for Building Electrical Services Design ......................................................................... 56
7.2 Bill of Quantities ......................................................................................................................... 56
7.3 Earth Faults ................................................................................................................................. 56
CHAPTER 8 ......................................................................................................................................... 57
8.0 REFERENCES ................................................................................................................................ 57
CHAPTER 9 ......................................................................................................................................... 59
9.0 APPENDICES ................................................................................................................................. 59
Appendix A-1: Auto Computer Aided Designs, (AUTOCAD) for Lighting Design and Power Points Layout Design ................................................................................................................................... 59
Appendix A-2: Lightning Protection Design ...................................................................................... 60
Appendix B: Consumer Units Designs and Specifications .................................................................. 61
Appendix C: IEE tables ..................................................................................................................... 62
Appendix D: MEM Catalogue Extracts .............................................................................................. 64
Appendix E: Power Back-Up Generator Data Sheet and Performance ................................................ 66
Appendix F: Utilization Factors ......................................................................................................... 67
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CHAPTER 1
1.0 INTRODUCTION
1.1 Objectives
The main objective of the project is to do a building electrical services design for a hostel along
Nyerere road. In order to achieve the main objective, the project work is split into other smaller
but related sections and scopes with specific targets to be met. The areas of utmost interest and
covered exhaustively and in detail in this project are thus:
Lighting design
Power points layout design
Cables sizing
Power back-up system
Protection system design
Discrimination and co-ordination system
Power factor correction
1.2 Prelude
Engineering specialization consists of various fields. One of these fields is the building design
and construction which has six different categories: civil, structural, mechanical, electrical,
environmental and materials engineering.1
This project will focus on the electrical category of building design and construction from the
electrical services design engineer’s perspective rather than that of the installation electrician or
architect. The main focus is to ensure that the electrical system meets the following criteria:
Reliability
Durability
Maintainability
1 Sidney M. Levy, “Construction Process Planning and Management, An Owners Guide to Successful Projects” 2007, Page 47
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Efficiency
Economy2
1.2.1 Building Electrical Services Design
Any electrical requirements are greatly influenced by the needs of the client or end-user of the
building. The end-user is more interested in the appearance and the function of the various
appliances whereas the design engineer is interested in the complete electrical design and
installation.
1.2.2 Codes and Standards
Every building must follow the laid down local, national or international codes and standards
that it is associated with its location and the acceptable codes and standards for that region.
The international codes and standards are developed by international standardization
organizations such as the Institute of Electrical and Electronics Engineers (IEEE). They prepare
standards that are adoptable and acceptable on a global scale.
National codes and standards are developed by associations within a particular country or region
which are then applied within local or national legislation in order to be enforceable by law.3
Such codes and standards have to be considered by the design engineer in order for the final
work to be acceptable to the client and the local authorities.
1.2.3 End – User Accessories
These are the various electrical equipments which are utilized by the end user in controlling the
function of the electrical installations made within the living or working space. They are called
accessories “because they are accessory to the wiring.” 4 These accessories include switches,
socket outlets, fused connection units, and the kitchen units.
2 U.S. Army Corps of Engineers, “Electrical Power Supply and Distribution” Technical Manual No. 5-811-1, Page 1-1
3 http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=70&cookie_test=1
4 Barrie Rigby, “Design of Electrical Services for Buildings” 4th Edition, Page 1
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CHAPTER 2
2.0 THEORY AND BACKGROUND
2.1 Lighting Design
This area covers all the literature reviewed for purposes of lighting design covered in the scope
of the project.
2.1.1 Hostel Lighting Design
The scope of lighting considered for this project is known as artificial lighting or more
intrinsically electrical light sources. This is the use of electric energy to produce “illuminance
levels similar to those of daylight and could technically now be produced in interior living and
working spaces or in exterior spaces, for example the lighting of streets and public spaces, or for
the floodlighting of buildings” 5
Definition of terms used in lighting design is important in order to avoid ambiguity:
Luminous Intensity represents the force that generates the light that we see.6 The SI Unit
is the candela (candle power) abbreviated cd.
Luminous Flux is a quantity of light with an SI unit lumen abbreviated lm.
Luminance is the density of luminous power, expressed in terms of lumens per unit area
and is abbreviated E.
Maintenance Factor is used in order to allow for the collection of dirt on a lamp and also
ageing, both of which cause loss of light. It has no unit and is abbreviated M.F
Utilization Factor is the ratio of the lumens received on the working plane to the total flux
output of lamps in the scheme. It has no unit and is abbreviated U.F
Luminous Efficacy describes the luminous flux of a lamp in relation to its power
consumption and is therefore expressed in lumen per watt (lm/W).
5 Rüdiger Ganslandt, Harald Hofmann, Handbook of Lighting Design, ERCO Edition, Page 22
6 Walter T. Grondzik, Alison G. Kwok, Benjamin Stein, John S. Reynolds, Mechanical and Electrical Equipment for Buildings, 11th Edition, Page 471
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2.1.2 Illuminance Recommendations
There are general recommendations arising from visual task studies which indicate that assuming
good contrast, the required luminance, categorized by type of task are shown in table 2.17
Furthermore, the chartered institute of building service engineers has published standards for
luminance recommendations in the Code for Lighting, 2006.
Table 2.1: General Luminance Recommendations
Category of Visual Task Required Luminance (cd/m2)
Casual 10 – 20
Ordinary 20 – 100
Moderate 100 – 200
Difficult 200 – 400
Severe 400 and above
.
They have used a method to determine the recommended average luminance level known as the
standard maintained luminance.
2.1.3 Light Sources
Discharge lamps produce light by a process where gases are heated within a controlled
enviroment in the lamp. This is done by applying voltage between two electrodes located in a
discharge tube filled with inert gases or metal vapors. A current is produced between the two
electrodes. Electrons in the discharge collide with gas atoms, which are in turn excited to radiate
light, when the electrons are travelling at a sufficiently high speed. For every type of gas there is
7 Walter T. Grondzik, Alison G. Kwok, Benjamin Stein, John S. Reynolds, Mechanical and Electrical Equipment for Buildings, 11th Edition, Page 492
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a certain wavelength i.e. light, is produced from one or several narrow frequency ranges. These
lamps include fluorescent lamps and opal spheres enclosed diffusing fluorescent luminaires
which have wide applications due to low power consumption and availability.
Fluorescent lamps are usually tubular in shape, whereby the length of the lamp is dependent on
the wattage and have a high luminous efficacy. They have a long lamp life, but this reduces
considerably with the higher the switching rate. Both igniters and ballasts are required for the
operation of fluorescent lamps. Fluorescent lamps ignite immediately and attain full power
within a short period of time. Instant reigniting is possible after an interruption of current.
Fluorescent lamps can be dimmed. There are no restrictions with regard to burning position.
For purposes of this report, the different types of fluorescent fittings utilized have the following
general specifications: 2× 58 Watts HPF Surface Mounted Fluorescent Batten with Mirror Brite
Lovres 2800 lumens (type 5 light fitting), 2× 58 Watts HPF Dust Proof Jet Proof and Corrosion
Resistant Fluorescent with Acrylic Differ 2800 lumens (type D light fitting), 1×36 Watts HPF
Fluorescent Batten 2800 lumens (type 4 light fitting) 8
The different types of opal spheres enclosed diffusing fluorescent luminaires utilized in this
project have the following general specifications: 100 Watts Ball Fitting 2800 lumens (type 2
light fitting), 23 Watts Single Angular Wall Bracket with PL lamp 2800 lumens (type W light
fitting), 12” 28 Watts Pendant set 2800 lumens (type B light fitting) 9
2.1.4 Lumen Method of Lighting Design
The lumen method of lighting design is used to determine a lighting layout that will provide a
design maintained luminance. The method uses the formula:
푁 =퐸 × 퐴
퐹 × 푈퐹 × 푀퐹
Equation 2.1
Where the letters carry the following meanings:
8 Rüdiger Ganslandt, Harald Hofmann, Handbook of Lighting Design, ERCO Edition, Page 62
9 Rüdiger Ganslandt, Harald Hofmann, Handbook of Lighting Design, ERCO Edition, Page 62
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N – Number of luminaires
E – Average luminance on the working plane in lux
A – Area of the working plane in m2
F – Flux from one lamp in lumens
UF – Utilization Factor
MF – Maintenance Factor
2.1.5 Light Switches
Light switches are used to make or interrupt a circuit. There is a maximum current which the
contacts of any particular switch can make or break, and a maximum voltage that the contact gap
can withstand. A switch must not be put in a circuit which carries a current greater than that
which the switch can break.
It is sometimes necessary to fully isolate power equipment such as heaters or fans. This means
disconnection of both the live and neutral contacts from the circuit. This is done with the use of
double pole switches.
2.2 Electrical Power Circuits
Electricity power circuits in a building consist of light switches, sockets, kitchen units and
similar outlets connected in a safe and balanced manner in order to ensure continuity of supply
and user satisfaction.
2.2.1 Socket Outlets
Socket outlets are electrical devices that allow the safe connection of appliances to the power
source. They typically have three pins. Two of the three pins are for the line and neutral cables,
and the third one is for a separate circuit protective conductor, earth cable.
The standard employed in this project is to connect a maximum of six, (6) twin sockets in a ring
circuit. This allows for a maximum load power of 1000W 240V on each twin socket within the
circuit if the diversity factor chosen is one, (1).Hence adequate protection can be applied using
the current drawn as:
=1000푊 × 6
240푉 = 25 퐴푚푝푠
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Equation 2.2
The ring circuit consists of live, neutral conductors and an exposed earth looped into each socket
outlet. This allows for supply from either direction hence ensuring continuity of supply even
when one of the sockets fails to operate.10
2.2.2 Kitchen Unit
Kitchen appliances such as microwaves and electric kettles draw higher electric current than
most other appliances. They therefore, require more durable and resistant sockets known as the
kitchen unit. The kitchen unit switch is double pole thus providing complete isolation of the
appliance to the wiring.
2.3 Electrical Service Network
2.3.1 Diversity
“Diversity occurs in an operating system because not all loads connected are operating
simultaneously or are not simultaneously operating at their maximum rating”11
For commercial buildings such as the hostel in this project, the diversity was assumed to be
100% for all the lighting loads. This ensures that the system is able to handle maximum load at
any given time in order to improve on the reliability of the system. A diversity factor of 67 % is
applied for the twin socket outlets in the hostel rooms and a diversity factor of 50% for the high
level twin socket outlets. A diversity factor of 100% is also applied for the kitchen unit.
2.3.2 Power Circuit Design
In order to design the power circuits, it is important to take note of the miniature circuit breaker,
(MCB) standard ratings that are available. The MCBs utilized for the purpose of this project are
6Amps, 10Amps, and 20Amps size ratings.
10 http://www.mkelectric.co.uk/Documents/English/EN%20Superswitch%20Catalogue/Superswitch%20Catalogue.pdf Page 5
11 http://www.davmark.co.uk/group/services/electric/diversity.html
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The lighting fittings are assigned to circuits such that they do not exceed the 5Amp switch rating
for each circuit. This would enable the use of the 6Amps MCB to protect the individual lighting
circuits.
Similarly, the socket outlets are assigned to circuits such that they can be assigned to the
standard MCB ratings. The 20 Amps MCB rating is found appropriate to protect a single ring
socket outlet.
2.3.3 Consumer Units
They are also known as consumer control units. These are single phase boards which are utilized
to house the miniature circuit breakers protecting all the power circuits within a given area. The
maximum rating of the consumer units, (CUs) utilized for this project is 100Amps and is
operated by the two-pole switch as shown in Figure 2.1
Figure 2.1: Consumer Unit, (CU)
The CU has ways which are the individual circuits within the area served by it. This ensures that
each circuit or way is protected by its individual miniature circuit breaker. It also provides a
simple way of balancing the loads equally amongst all the three phases of a three phase supply
system because each consumer unit is assigned one phase.
The CUs are designed to have a certain number of ways such as 12-way CU and 13-way CU for
this project. Each way is a circuit consisting of either lighting fittings or socket outlets or a
kitchen unit.
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2.3.4 Distribution Board
A distribution board, (DB) is a component utilized in a power supply system to divide the 3-
phase power into balanced loads while providing protection to each consumer unit connected to
it. The protection is provided using moulded case circuit breakers, (MCCB) for each way. A
typical DB is shown in figure 2.2
Figure 2.2: Distribution Board, (DB)
2.3.5 Switch-Boards
The main reason for using cubicle switch boards is to ensure that if there is any future load
growth the bus-bars within the cubicle would enable easy expansion of the distribution network.
They also provide a safe enclosure for all connections to meters and power isolators as well. A
typical cubicle switch board is shown in figure 2.312
12 Dr C. R. Bayliss and B. J. Hardy, “Transmission and Distribution Electrical Engineering” 3rd Edition, Page 139
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Figure 2.3: Cubicle Switch Board
2.3.6 Commercial Back-Up Diesel Power Generators
Diesel engines are more suited to continuous running for lengthy periods at higher load ratings
and are therefore used more widely for stationary applications.
The use of hooded diesel generators as shown in figure 2.4 is becoming increasingly important in
industries. These generators provide for low noise levels which reduce noise pollution. The hood
also ensures that the generator may be placed outdoors which lowers the cost of installation by
eliminating the need to build a generator room.
Figure 2.4: Diesel Generator
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2.3.7 Wiring
External wiring is done depending on the location of various consumer units. This is achieved
using underground or overhead cables. Underground cables are usually armoured poly vinyl
chloride, (PVC) insulated cables. They provide extra protection against mechanical damage due
to the armour that is wound over the insulated cables along its entire length. The armored cable is
run in a high-impact grade heavy gauge PVC conduit which is buried at least 600mm13 below
ground level and 750mm under a road.
Cable entries into a building have to be through a hole in the wall which has to be tight round the
cable. It has to be sealed to prevent dirt, vermin and moisture entering. This may be done using a
draw box above the ground level or using a duct built through the wall below ground level.
Internal wiring is done using PVC insulated copper wires which run in a PVC conduit fixed into
the concrete during construction or in a false ceiling for lighting.
2.3.8 Cable Sizing
The size of the cable is determined by the amount of current it has to carry as well as the length
which the cable has to be laid. This is done using recommended ampacity and voltage drop
values provided in the IEEE 835-1994 standard power cable ampacity tables which were used for
purposes of this project. Other recommended standards can be found in the Appendix C of this
document.
2.4 Protection Systems
No matter how well designed a power system is, there is always a likelihood of faults occurring.
These fault currents can cause a great deal of damage even over a very short period of time, tens
or hundreds of milliseconds. It is therefore essential to provide adequate protection to detect and
disconnect elements of the power system before irrepairable damage occurs.
Overcurrent is defined in the 16th Edition of the IEE Wiring Regulations as “a current exceeding
the rated value. For conductors the rated value is the current-carrying capacity.” Overcurrent
can be divided into two individual levels of fault these being overload current and short circuit
current.
13 Barrie Rigby, “Design of Electrical Services for Buildings” 4th Edition, Page 65
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2.4.1 Overload Protection
An overload is an overcurrent in a circuit that is electrically sound. This may be due to too many
appliances drawing current from a system, a faulty appliance, or a motor subjected to mechanical
overload. Regulation 433-01-01 of the 16th Edition of the IEE Wiring Regulations defines the
basic requirement for overload protection, “protective devices shall be provided to break an
overload current flowing in the circuit conductors before such a current could cause a
temperature rise detrimental to insulation, joints, terminations, or the surroundings of the
conductors. Circuits shall be so designed that a small overload of long duration is unlikely to
occur”.
The IEE Wiring Regulations specify the following current levels for coordinating overload
protection between cables and protective devices.
퐼 ≤ 퐼
퐼 ≤ 퐼
퐼 ≤ 1.45 퐼
Equation 2.3
Where the symbols carry the following meanings:
퐼 = design current of circuit
퐼 = nominal current of protective device
퐼 = current-carrying capacity of the cable
퐼 = minimum operating current of protective device
2.4.2 Short Circuit Protection
Short circuit is defined in the 16th Edition of the IEE Wiring Regulations as: “an overcurrent
resulting from a fault of negligible impedance between live conductors having a difference in
potential under normal operating conditions”.
Protection of cables against short circuit can be done by utilizing the adiabatic equation. “The
time ‘t’ in which a given short circuit current will raise the temperature of the conductors to the
limiting temperature, can be calculated from the formula”
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푡 = 푘 푠퐼
Equation 2.4
Where the symbols carry the following meanings:
t = duration in seconds
s = cable cross section (mm2)
I = effective short circuit current (Amps)
k = a factor taking into account various criteria of the conductor
Therefore, if the circuit breaker protecting the cable operates in less time than that required for
the cable to reach its temperature limit, the cable is protected.
2.4.3 Protection System Equipment
Moulded case circuit breaker, (MCCB) is a power switch with built-in protective functions used
on circuits requiring high current ratings. They operate as switches for normal load current
opening and closing functions. They also automatically disconnect excessive overloads and
interrupt short circuit currents as quickly as possible. They as well as provide indication status of
the MCCB if it is open, closed or tripped. They are normally utilized in distribution boards, (DB)
and switch boards.
Miniature circuit breakers, (MCBs) are similar to moulded case circuit breakers but as their name
implies, these are smaller in size and are mostly used for current ratings below 100 A. They are
mainly used to protect the final circuits and are housed in the consumer unit, (CU).
2.4.4 Discrimination and Protection System Co-ordination
Discrimination in power systems describes a hierarchy of circuit devices that are arranged such
that a single upstream circuit breaker can fan out to several downstream protective devices to act
in a co-ordinated fashion should a fault occur. Under fault conditions, only the upstream
protective device closest to the fault should operate to clear the fault, leaving all other healthy
circuits operational. In this project current discrimination and time discrimination will be
employed.
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2.4.5 Lightning Protection
In lightning protection design, the goal is to dissipate static charges around a given structure at a
rate sufficient to maintain the charge below the value at which a lightning flash will occur. The
typical duration of a lightning flash is approximately 0.5 seconds. A single flash is made up of
various discharge components, among which are typically three or four high-current pulses
called strokes. Each stroke lasts about one 1ms; the separation between strokes is typically
several tens of milliseconds.
Application of the point discharge theory is widely utilized in lightning protection. The theory
holds that discharge from the point of an electrode to a surrounding medium will follow
predictable rules of behavior. It has been proven that the sharper the point of the air conductor
then the greater the discharge. The greater the number of discharge points, the more efficient the
dissipation system. The air terminal provides a zone of protection which can be described as a
cone. This is shown in figure 2.5.The air terminal at the highest point offers the greatest
protection zone.
Figure 2.5: Lightning Protection Zones and Cones
Air termination is provided to intercept a lightning strike and no part of a roof should exceed 5 m
from part of a termination conductor, unless it is a lower level projection which falls within the
zone of protection. The air terminations are horizontal conductors running along the ridge of a
pitched roof or around the periphery of a flat roof
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The down conductor is that part of the external lighting protection system that conducts lightning
current from the air terminal system to the earth termination system. They provide a low
impedance route from the air terminations to the earth terminals. The down conductor must be
installed straight and vertically in order to provide the shortest and most direct path to earth thus
the formation of bends must be avoided.
The earth termination system is the part of the external lightning protection system that conducts
and disperses lightning current to earth and it is required to give the lightning discharge current a
low resistance path to earth.
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CHAPTER 3
3.0 PROJECT WORK AND IMPLEMENTATION
This chapter covers the scope of work carried out for the building electrical services design for a
hostel along Nyerere road located in Nairobi, Kenya.
3.1 Site Location
The site of the hostel is in Nairobi, the capital city of Kenya. Therefore, no issues are raised
about national power grid and mains connectivity and reliability of power supply.
3.2 Site Plan and Introduction
The project site plan has one building with a total of six floors. It is a proposed hostel along
Nyerere road with a total of six floors. These are lower floor, upper ground floor, first floor,
second floor, third floor and the attic floor as shown with the architectural floor plans drawings
attached in appendix A-1. The architectural floor plans drawings are then used to come up with
an appropriate lighting scheme through a lighting fittings design and power points layout design
on each hostel floor plan. A schedule of symbols and lighting luminaires settled for in the
lighting fittings design and power points layout design has been attached as drawing number E01
in appendix A-1 as an aid to understanding this project work.
3.2.1 Sample Lumen Method of Lighting Design Calculation for One Hostel Room
3.2.1.1 Lounge Area in One Hostel Room Located at the Upper Ground Floor Illuminance = 150 lux (IES Code recommendation for such an area).
The position of measurement was the desktop.
Floor area dimensions: Length = 5.8metres, Width = 2.821metres
Ceiling height = 2.5metres
Mounting height (floor): mH 2.5 m –0.85 m = 1.65 metres
m
LWRoom index KH L W
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17
푲 =5.8 × 2.821
1.65 ( 5.8 + 2.821 ) = ퟏ.ퟏퟓ
The utilization factor, (UF) is obtained from the table of utilization factors versus the room index
for a opal sphere enclosed diffusing single angular wall bracket and having a down light output
ratio, (DLOR) of 45%.This UF table is attached in appendix F of this project document. For a
room of K = 1.15 and ceiling and wall reflectances of 0.7 and 0.5 respectively, the utilization
factor, (UF) is by use of interpolation:
푼푭 = 0.36 +1.15 − 11.25 − 1
(0.41 − 0.36) = ퟎ.ퟑퟗ
The opal sphere enclosed diffusing single angular wall brackets complete with 23 W PL lamp
(type W light fitting) luminaires and the opal sphere enclosed diffusing pendant set complete
with 100 W lamp (type B light fitting) luminaire are used. Each luminaire has a known lighting
design lumen, (LDL) output of 2800 lumens.
The lumen method of lighting design, equation 2.1, in section 2.1.4 is now applied for the lounge
area in one hostel room in upper ground floor plan as shown in Table 3.1
From the previous analysis and discussions for the lounge area, the following parameters have
been achieved:
E = 150 lux A = (5.8m×2.821m) = 16.36m2 F = 2800 lumens UF = 0.39 MF =
0.8
푁푢푚푏푒푟 표푓 푙푖푔ℎ푡 푓푖푡푡푖푛푔푠 푓표푟 푡ℎ푒 풍풐풖풏품풆 푎푟푒푎 =150 × 16.36
2800 × 0.39 × 0.8 = ퟐ.ퟖ 푙푖푔ℎ푡 푓푖푡푡푖푛푔푠
This is approximated to three, (3) light fittings for lighting the lounge area or region in the hostel
room as shown in figure 3.1
The same lumen method of lighting design is done and repeated for the other regions or areas
within the hostel room. The results are summarized in table 3.1.
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18
Table 3.1: Summary of Lumen Method of Lighting Design for a Single Hostel Room
Region/area
in a Single
Hostel Room
Illuminance,
E (Lux)
Area,
A
(푴ퟐ)
Maintenance
Factor ,
MF
Utilization
factor ,
UF
Flux of one
light
fitting, F
(Lumens)
No. of
light
fittings,
N
Lounge
150 16.36 0.8 0.39 2800 3
Bedroom 300 12.00 0.8 0.54 2800 3
Bath 150 4.07 0.8 0.14 2800 2
Kitchen 500 6.50 0.8 1.45 2800 1
These details and results for the lumen method of lighting design for one hostel room are now
shown fully in figure 3.1
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Figure 3.1: Small Section of Upper Ground Floor Plan Comprising of One Hostel Room
illustrating the Lumen Method of Lighting Design
Similar calculations were applied to all the other rooms and the other regions or areas of the
entire project site plan.
3.2.2 Sample Power Points Layout Design for One Hostel Room
In domestic power socket design an unlimited number14 of sockets can be connected in a ring
circuit for a floor area of up to 100m2. This design problem is for a commercial hostel and thus
ring circuiting for the socket outlets is used to allow for supply from either direction hence
ensuring continuity of supply even when one of the sockets fails to operate. Therefore, the design
incorporated two, (2) normal-level twin sockets estimated to draw a power of 1000W each.
These are shown in the turquoise (faded blue) color located in the lounge and bedroom areas. 14 Building Services Handbook, 4th Edition, Page 390
Page 28
20
Power points layout design also has one, (1) high-level twin socket estimated to draw a power of
1000W also shown in turquoise color and located in the kitchen area. The same kitchen area has
one, (1) kitchen unit shown in red color. These are all illustrated in figure 3.2
Figure 3.2: Small Section of Upper Ground Floor Plan Comprising of One Hostel Room
illustrating Power Points Design Layout.
3.3 Entire Hostel Lighting Fittings Design and Power Points Layout Designs
An appropriate lighting scheme and power points layout as with factors discussed in section 3.2
is now adopted and applied to the entire hostel regions. The entire and complete lighting fittings
and power points layout designs on architectural A3 paper size drawings are attached in
appendix A-1 and labeled as appropriate.
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21
CHAPTER 4
4.0 DESIGN ANALYSIS AND DISCUSSIONS
4.1 Design Analysis Based on Load Calculations and Circuits Arrangements
4.1.1 Introduction
A count is done from the lighting and power points designs drawings on A3 paper sizes attached
in appendix A-1, to establish the number of light fittings and power points on each hostel floor.
The total load is then calculated to facilitate determination of the number of consumer units,
(CUs) and distribution boards, (DBs) to be used in supplying each hostel floor. The CUs and
DBs are located for safety, convenience of supplying the loads (that is, good spartial spread) and
so as to be near the centre of gravity of the loads they are to supply. Their distances from the
DBs supplying them are measured and so is the distance of the various DBs from the
switchboard determined. The fittings are then assigned to be supplied by the various CUs (that is,
‘circuiting’ is done). The factors taken into account when assigning fittings are:
1. Total current for a group of lights switched on by a single switch must not exceed
5 Amperes, this been the limiting value current that an ordinary switch’s contacts
can repeatedly make or break without risking excessive burning that would
shorten the service life of the switch. Putting a worst case that is the upper limit of
100W on each light fitting supplied at 240 V implies:
Current drawn =100 0.4167 /240
W Amps fittingV
Maximum number of fittings per switch = 5 120.4167
fittings
2. In this work the maximum load assigned per CU should not draw current more
than 100 amperes. For the hostel floors with heavy loads a CU load of 70Amps-
76Amps is adopted, while the hostel floors with light loads a CU load of 40Amps-
55Amps is adopted.
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22
A sample calculation on the lower floor plan loads being considered as the hostel floor with
light load is documented in section 4.1.2. From the architectural drawings provided the upper
ground floor, first floor, second floor and third floor plans depicted the same architectural design
and upper ground floor is settled for consideration as the hostel floor with heavy load and its
sample load calculations documented as shown in section 4.1.3.
4.1.2 Lower Floor
From the lighting fittings design in drawing number E02 in the appendix A-1, a count is done to
establish the number of lighting fittings on this floor and the results summarized in table 4.1 as:
Table 4.1: Summary for Lighting Fittings Loads on Lower Floor.
Fitting type No. of fittings Diversity factor Assumed rate (Watts) Total load (watts)
Type W 5 1 100 500
Type 4 12 1 100 1200
Type 5 2 1 100 200
Type N 8 1 100 800
Type B 1 1 100 100
Type D 9 1 100 900
Type 2 8 1 100 800
Type 2D 6 1 100 600
Total (watts) 5100
The assumption made here is this been a hostel all lights are likely to be on at the same time
hence a diversity factor of 1
From the power points layout design in drawing number E03 in appendix A-1, the same
procedure is repeated and the results are summarized in table 4.2
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23
Table 4.2: Summary for Power Points Loads on the Lower Floor.
Fitting type No. of fittings Diversity factor Assumed rate(watts) Total load(watts)
Twin sockets 18 23
1000 12000
Hand drier 2 23
1500 3000
Fan 2 23
1500 1000
Total(watts) 16000
The assumption made in the power points design analysis is not all sockets, toilet hand driers and
toilet fans are likely to go on at the same time hence a diversity factor of 2 3 is assumed.
Therefore, total load for lower floor = 5100 푊 + 16000 푊 = 21100 푊푎푡푡푠
Applying 20% future load growth the total load for lower floor is:
= 21100 ×120100 = 25320 푊푎푡푡푠
Therefore the total current drawn by lower floor loads is:
=25320 푊
240 푉 = 105.5 퐴푚푝푠
A standard consumer unit settled for in this project has a 100 Amps integral isolator and thus
allows a maximum load current of 100Amps.For a load current of 105.5 Amps, logically 2
consumer units (CUs) are required with each consumer unit drawing current of around 105.5
2 = 52.75 퐴푚푝푠/ 퐶푢. Hence a CU load of 40A-55A is adopted for hostel floors with
light loads that is the lower floor and the attic floor.
4.1.3 Upper Ground Floor
There are a total of twelve, (12) rooms on this floor. Therefore, for phase balance at the
distribution board, (DB) a working formula is:
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=12 푟표표푚푠3 푝ℎ푎푠푒푠 = 4 푟표표푚푠/푝ℎ푎푠푒
Looking at one hostel room and doing a load analysis of the overall lighting fittings as in table
4.3:
Table 4.3: Summary for Lighting Fittings Loads Design on One Hostel Room on Upper
Ground Floor.
Fitting type No. of fittings Diversity factor Assumed rate(watts) Total load(Watts)
Type B 2 1 100 200
Type W 3 1 100 300
Type N 1 1 100 100
Type 2D 1 1 100 100
Type 2 1 1 100 100
Type 4 1 1 100 100
Total(Watts) 900
Power points design
Looking at one hostel room and doing a load analysis of the overall power points as in table 4.4:
Table 4.4: Summary for Power Points Loads Design on One Hostel Room on Upper
Ground Floor.
Fitting type No. of
fittings
Diversity
factor
Assumed rate
(watts)
Total load
(watts)
Twin sockets 2 23
1000 1333.33
High level twin
sockets
1 12
1000 500.00
Kitchen unit 1 1 1500 1500
Page 33
25
Total (Watts) 3333.33
Therefore total load per room = 900 푊 + 3333.33 푊 = 4233.33 푊푎푡푡푠
Current drawn per room is:
=4233.33 푊
240 푉 = 17.639 퐴푚푝푠
Therefore, total current for 4 rooms is: = 17.639 × 4 = 70.556 퐴푚푝푠. Hence a CU load of 70
Amps-76 Amps is adopted for hostel floors with heavy loads. That is upper ground floor, first
floor, second floor and third floor.
Applying 20% future load growth the total current for 4 rooms is:
= 70.556 × 120100 = 84.6672 퐴푚푝푠
84.6672 퐴푚푝푠 is less than 100 퐴푚푝푠 where 100 퐴푚푝푠 is the maximum load current of a
standard CU with a 100 Amps integral isolator which is chosen in this project. Therefore a load
current of 84.6672 Amps will be comfortably handled with 1 CU, implying 1 CU will supply 4
hostel rooms on the upper ground floor.
Therefore, 12 rooms on the entire upper ground floor will be supplied by:
=12 푟표표푚푠4 푟표표푚푠 × 1 퐶푈 = 3 퐶푈푠
The 3 CUs will thus be arranged and distributed on the upper ground floor as:
Consumer Unit upper ground floor 1 (CU UGF1), Consumer Unit upper ground floor 2 (CU
UGF2), and Consumer Unit upper ground floor 3 (CU UGF3).
However, there are corridor and balcony light fittings with a load analysis of:
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26
Table 4.5: Summary for Corridor and Balcony Light Fittings Loads on Upper Ground
Floor
Type of fitting No. of fittings Diversity factor Assumed rate(watts ) Total load (watts)
Type N 14 1 100 1400
Total (watts ) 1400
The load current drawn by balcony and corridor light fittings is:
=1400 푊
240 푉 = 5.833 퐴푚푝푠
This current will be supplied by one of the three CUs arrived at in the design load analysis
earlier and consumer unit, CU UGF 2 is chosen for this supply.
Therefore, now evaluating the total single-phase load for upper ground floor with a total of 12
rooms is:
= (4233.33 × 12)푊 + 1400푊 = ퟓퟐퟐퟎퟎ 푾풂풕풕풔
The same analysis is done for the other hostel floors and the single-phase loads results
summarized in the table 4.6
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Table: 4.6: Summary for All Single-Phase Hostel Loads.
Floor Total
load(Watts)
20% future load
growth factored in
total load(Watts)
Total Current
drawn(Amps)
No.
of
CUs
CUs
Arrangement
Lower 21100 25320 105.5 2 CU LF1, CU LF2
Upper
ground
52200 62640 261 3 CU UGF1, CU
UGF2, CU UGF3
First 52200 62640 261 3 CU FF1, CU
FF2, CU FF3
Second 52200 62640 261 3 CU SF1, CU
SF2, CU SF3
Third 52200 62640 261 3 CU TF1, CU
TF2, CU TF3
Attic 12700 15240 63.5 1 CU AF1
TOTAL 242600 291120 15
CUs
From the summary table 4.6 the overall single-phase loads for the entire hostel will be supplied
by 15 CUs. The lifts and hose reel pumps are three-phase loads and will be supplied directly
from one distribution board, (DB) way.
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CHAPTER 5
5.0 DISTRIBUTION SYSTEM TOPOLOGY
5.1 Consumer Unit, (CU) Design and Specifications
Consumer Unit Design based On: Circuits Arrangement, Load Calculations, Miniature
Circuit Breaker, (MCB) size and Cables Selection.
From table 4.6, it is apparent that all the single-phase loads will be supplied with fifteen, (15)
CUs. In order to avoid redundancy, the first consumer unit at upper ground floor, (CU UGF1) is
chosen in this project document to explain the concept of consumer unit design and
specifications in details. The results for the other consumer units are then summarized.
Referring to the upper ground floor circuits arrangements design drawing number E04 and E05
attached in appendix A-1 where circuiting has been done; the various assignments of single-
phase loads are analyzed as follows:
Circuit CIR UGF 1.1
CIR UGF 1.1 means that the single-phase loads are assigned to consumer unit, CU UGF 1 and
the way assigned to them on this CU is also way 1.Thus the assignment of fittings on this CU
way is summarized in table 5.1
Table 5.1: Summary for Assignment of Fittings on Circuit CIR UGF 1.1
Fitting type No. of fitting Diversity factor Assumed rate(watts) Total load(watts)
Type W 3 1 100 300
Type B 2 1 100 200
Type 2D 1 1 100 100
Type N 1 1 100 100
Type 2 1 1 100 100
Type 4 1 1 100 100
Total(watts) 900
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29
Therefore, current drawn by the assignment of fittings on circuit CIR UGF 1.1 is:
=900 푊240 푉 = 3.75 퐴푚푝푠
The standard sizes for miniature circuit breakers, (MCBs) by MEM catalogue are 6A, 10A, 16A,
20A, 32A, 40A, 50A, 63A. Therefore, a 6 A MCB is used to protect the circuit UGF 1.1.
From the IEE tables attached in the appendix C for one twin cable single phase, 1푚푚 cable
which carries up to 14 Amps is appropriate. However, 1.5푚푚 cable which carries up to 18
Amps is settled for supplying this circuit.
Circuit CIR UGF 1.2
CIR UGF 1.2 means that the single-phase loads are assigned to consumer unit, CU UGF 1 and
the way assigned to them on this CU is way 2. Thus the assignment of fittings on this CU way
is summarized in table 5.2
Table 5.2: Summary for Assignment of Fittings on Circuit CIR UGF 1.2
Fitting type No. of fitting Diversity factor Assumed rate(watts) Total load(watts)
Type W 3 1 100 300
Type B 2 1 100 200
Type 2D 1 1 100 100
Type N 1 1 100 100
Type 2 1 1 100 100
Type 4 1 1 100 100
Total(watts) 900
Therefore current drawn by the assignment of fittings on circuit CIR UGF 1.2 is:
=900 푊240 푉 = 3.75 퐴푚푝푠
Therefore, a 6 A MCB is used to protect the circuit UGF 1.2. Again, a 1.5푚푚 cable which
carries up to 18 Amps is settled for supplying this circuit.
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30
The same design and specifications analysis is done for circuits CIR UGF 1.3, CIR UGF 1.4,
CIR UGF 1.5, CIR UGF 1.6, CIR UGF 1.7, CIR UGF 1.8, CIR UGF 1.9 and CIR UGF 1.10.
The overall consumer unit, CU UGF 1 design results and specifications are now summarized as
in section 5.1.1
5.1.1 Consumer Unit, CU UGF 1
Circuit and
way on CU
UGF
1.1
UGF
1.2
UGF
1.3
UGF
1.4
UGF
1.5
UGF
1.6
UGF
1.7
UGF
1.8
UGF
1.9
UGF
1.10
Total
load(watts)
900 900 1000 900 3666.67 3666.67 1500 1500 1500 1500
Total
current
(amps)
3.75 3.75 4.167 3.75 15.28 15.28 6.25 6.25 6.25 6.25
MCB size 6A 6A 6A 6A 20A 20A 10A 10A 10A 10A
Cable
size(풎풎ퟐ )
1.5 1.5 1.5 1.5 2.5 2.5 2.5 2.5 2.5 2.5
From section 5.1.1 specifications, the consumer unit, CU UGF 1 is now designed and specified
while incorporating the ten protected circuit ways and allowing for a minimum of two blank
spare ways for future use as shown in figure 5.1. The design and specification details for CU
UGF 1 are:
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Figure 5.1: 12-way Single-Phase and Neutral Consumer Unit, CU UGF1 on Upper Ground
Floor
The same design analysis is done for consumer unit, CU UGF 2 and consumer unit, CU UGF 3
located at the same upper ground floor. This is also done for all the other consumer units located
at the other hostel floors, which are CUs at the lower floor, CUs at first floor, CUs at second
floor, CUs at the third floor and a CU at the attic floor. The further design results for these CUs
and their specifications are attached in appendix B of this project document.
5.1.2 Consumer Unit Total Single-Phase load calculations, Total Load Currents Drawn,
Cable Length and Cable Size Selection from the Distribution Board, (DB) feeding the CU.
5.1.2.1 Consumer Unit, CU UGF1
From section 5.1.1, CU UGF1 will have a total overall single-phase load of:
Page 40
32
900+900+1000+900+3666.67+3666.67+1500+1500+1500+1500= 17033.34 푊푎푡푡푠
Therefore, current drawn by these single-phase loads is:
= 17033.34 푊
240 푉 = 70.98 퐴푚푝푠
Length of cable to feed this CU from the Distribution board, (DB A) located at the lower ground
floor is = 18m
From IEE tables for non-armoured one twin cable single-phase enclosed type, attached at the
appendix C, a 25푚푚 cable which carries up to 79 Amps is chosen. Its appropriateness is
chosen through a voltage drop calculation. Allowing up to a maximum of 1.5% voltage drop
(which is the maximum voltage drop allowed for in this design between a DB and CU) on this
cable chosen to supply this CU from the DB.
%voltage drop 70.98 18 1.8 / / 1 100% 0.958%1000 240
A m mV A m
0.958% is less than the maximum 1.5% design voltage drop allowed for. A 25푚푚 , non-
armoured one twin cable single-phase chosen from the enclosed category is hence very
appropriate and settled for.
The same analysis is done for all the other CUs on the same upper ground floor (CU UGF2 and
CU UGF3) and also the other floors. The results are then summarized are in section 5.1.2.2
5.1.2.2 Summary for All the 15 Consumer Units within the Hostel Consumer
unit
Total load
(watts)
Total current
(Amps)
Cable length
(Metres)
Cable
size(풎풎ퟐ)
Voltage
drop (%)
CU UGF1 17033.34 70.98 18 25 0.96
CU UGF2 18133.34 75.56 9 25 0.51
CU UGF3 17033.34 70.98 24 25 1.36
CU LF1 10800.00 45.00 4 10 0.56
CU LF2 10300.00 42.92 6 10 0.45
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33
CU FF1 17033.34 70.98 20 25 0.36
CU FF2 18133.34 75.56 12 25 0.56
CU FF3 17033.34 70.98 25 25 0.45
CU SF1 17033.34 70.98 23 25 0.46
CU SF2 18133.34 75.56 14 25 0.23
CU SF3 17033.34 70.98 29 25 1.33
CU TF1 17033.34 70.98 25 25 0.87
CU TF2 18133.34 75.56 17 25 0.54
CU TF3 17033.34 70.98 32 25 0.44
CU AF1 12700.00 52.92 19 16 0.38
5.2 Distribution Board, (DB) Design and Specifications
From the proposed hostel architectural drawings in Appendix A-1, the light fittings and power
points layouts were single-phase loads. The proposed hostel design also allowed for two
passenger lifts and two hose reels pumps as a fire fighting measure. The proposed hostel thus had
both single-phase loads and three-phase loads. The distribution board system design settled for is
to treat the single-phase loads separately and also the three-phase loads separately. Thus:
5.2.1 Single-Phase Loads Distribution Board Design and Specifications
From the 15 consumer units, (CUs) summary in section 5.1.2.2 and settling on a single or one
distribution board, (DB) to feed all of them. This is designated as DB ‘A’ and placed at the lower
floor within the hostel premises for safety as shown in drawing number E03, in the auto
computer aided designs in appendix A-1.
The distribution system topology in figure 5.2 is then adopted to feed all the 15 CUs with single-
phase loads of the proposed hostel.
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34
Fig 5.2: Distribution Topology to feed all the 15 CUs Supplying Single-Phase Loads.
5.2.1.1 Load Balancing at the Supply Phases of Distribution Board, (DB) ‘A’
The 15 CUs are then distributed amongst the red, yellow and blue phases of the DB ‘A’ so as to
result in as close balance as possible at the supply phases. The results are summarized in table
5.3
Table 5.3: Summary for Load Balancing at the DB ‘A’ Supply Phases
Floor
Phase load Consumer
unit
Red phase
(Watts)
Yellow phase
(watts )
Blue phase
(watts )
Lower ground 10800 CU LF1
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35
10300 CU LF2
Upper ground
17033.34 CU UGF1
18133.34 CU UGF2
17033.34 CU UGF3
First 17033.34 CU FF1
18133.34 CU FF2
17033.34 CU FF3
Second 17033.34 CU SF1
18133.34 CU SF2
17033.34 CUSF3
Third
17033.34 CU TF1
17033.34 CU TF3
18133.34 CU TF2
Attic 12700 CU AF1
Phase totals
(watts)
81933.36
(Red phase)
80033.36
(Yellow phase)
80633.36
(Blue phase)
Thus distribution board, DB ‘A’, distribution system topology to supply the various CUs and its
supply phases balanced as closely as possible is shown in figure 5.3
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36
Figure 5.3: Distribution Board, DB ‘A’ at the Lower Floor to Supply the 15 CUs at Various
Floors
5.2.1.2 Sizing of Cable Feeding Distribution Board ‘A’
DB ‘A’ supplies consumer units; CU LF1, CU LF2, CU UGF1, CU UGF2, CU UGF3, CU FF1,
CU FF2, CU FF3, CU SF1, CU SF2, CU SF3, CU TF1, CU TF2, CU TF3 and CU AF1.
Consumer units; CU UGF1, CU UGF2, CU UGF3, CU TF1 and CU AF1 have a total load of
81933.36W and are on the red phase as seen in section 5.2.1.1.
Therefore, DB current on red phase 81933.36 341.389240
W AmpsV
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37
CUs SF1, SF2, SF3, TF3 and LF1 have a total load of 80033.36W and are on the yellow phase as
seen in section 5.2.1.1.
Therefore, DB current on yellow phase 80033.36 333.472240
W AmpsV
CUs SFF1, FF2, FF3, TF2 and LF2 have a total load of 80633.36W and are on the blue phase as
seen in section 5.2.2.2.
Therefore, DB current on blue phase 80633.36 335.972240
W AmpsV
Length of cable connecting DB ‘A to the switchboard = 4m
Current used for sizing the cable = 341.389 Amps (the largest of 341.389, 333.472 and 335.972)
Allowing for a max of 1.5% voltage drop on this cable
341.389 4 0.2 / / 1% 100% 0.0658%1000 415
A m mV A mvoltagedrop
0.0658% Voltage drop is less than the maximum 1.5% design voltage drop allowed. This
means the 240mm2, non-armoured one 3 or 4 core cable three-phase is appropriate.
5.2.2 Three-Phase Loads Distribution Board Design and Specification
The three-phase loads within the proposed hostel are the two passenger lifts and two hose reel
pumps for fire-fighting measures that are allowed for .The power ratings settled for these three-
phase loads in the design are summarized as in table 5.4
Table 5.4: Power Ratings for the Three-Phase Loads
Three-phase load Power rating (watts)
Passenger lift 22000
Passenger lift 22000
Fire fighting hose reel pump 11000
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Fire fighting hose reel pump 11000
Total three-phase load (watts) 66000
Another distribution board, (DB) is settled for in the design to supply these three-phase loads
only. The reason is to avoid overloading DB ‘A’ already settled for in section 5.2.1 for supplying
the hostel single-phase loads. This is designated as distribution board, DB ‘B’ and it is placed at
the attic floor within the hostel premises for safety as shown in drawing number E13 in the auto
computer aided designs in appendix A-1.
The distribution system topology in figure 5.4 is then adopted to directly feed all the three-phase
loads for the proposed hostel.
Fig 5.4: Distribution Topology to Supply all the Hostel Three-Phase Loads Directly.
Thus in the next sections we proceed with three-phase loads power supply designs.
5.2.2.1 Lift Power Supply Design
The lift is intended to take a power of 22kW, 3-phase at a power factor of 0.8.
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39
3 . 22L LV I p f kW
Where:
415LV Lift line voltage
LI Line current drawn by the lift
.p f Lift power factor
22 22 1000 38.26. 3 415 0.8 3L
L
kWI AmpsV p f
Thus, a 60 Amps isolator is chosen for one passenger lift .Therefore, the two passenger lifts are
to be supplied with two 60 Amps isolators.
5.2.2.2 Hose Reel Pump Power Supply Design
The hose reel pump is intended to take a power of 11kW, 3-phase at a power factor of 0.8.
3 . 11L LV I p f kW
Where:
415LV Hose reel pump line voltage
LI Line current drawn by the hose reel pump
.p f Hose reel pump power factor
11 11 1000 19.13. 3 415 0.8 3L
L
kWI AmpsV p f
Thus, a 30 Amps isolator is chosen for one hose reel pump. Therefore, the two hose reel pumps
are to be supplied with two 30 Amps isolators.
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40
These been three-phase loads they will balance equally at the DB supply phases; that is red,
yellow and blue phases. Thus distribution board, DB ‘B’ and its distribution system topology to
supply three-phase power directly to all the three-phase loads is shown in figure 5.5
Figure 5.5: Distribution Board, DB ‘B’ at the Attic Floor to Supply all the Hostel Three-Phase
Loads
5.2.2.3 Sizing of Cable Feeding Distribution Board ‘B’
DB ‘B’ supplies two, three-phase lift isolators each of rating 60Amps and two, three-phase hose
reel pump isolators each of rating 30 Amps.
Therefore DB ‘B’ current (2 60) (2 30) 180Amps on every phase
Length of cable connecting DB ‘B’ at the attic floor to the switchboard = 20m
Current used for sizing the cable = 180 Amps.
Allowing for a maximum of 1.5% design voltage drop on this cable
180 20 0.42 / / 1% 100% 0.3643%1000 415
A m mV A mvoltagedrop
0.3643% Voltage drop is less than 1.5% design voltage drop, meaning the 95mm2 non-
armoured one 3 or 4 core cable three-phase is appropriate.
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41
5.3 Power Back-Up Generator
During the distribution design a standby generator for the entire establishment is also settled for
as part of the project objective. This been a commercial building the back-up generator is to be
able to ensure continuous power supply to the hostel incase of absence of Kenya Power and
Lighting Company, (KPLC) grid power. A proposed generator room or necessarily a cage for
this back-up generator is seen in drawing number E03 in the computer aided designs for lower
floor plan in appendix A-1.
5.3.1 Size of Back-Up Generator
From section 5.1.2.2, a summary for the hostel total single-phase loads is inferred. Section 5.2.2
also gives a summary for the total three-phase loads for the proposed hostel. The total load
capacity for the hostel is therefore summarized in table 5.5
Table 5.5: Summary for the Hostel Total Load Capacity
Floor/three-phase load Total load(watts)
Lower floor 21100.00
Upper ground floor 52200.02
First floor 52200.02
Second floor 52200.02
Third floor 52200.02
Attic floor 12700.00
2 lifts 44000.00
2 hose reel pumps 22000.00
Total hostel load (watts) 308600.08
Applying 15% future load growth for the possibility of an addition of another floor within the
establishment or air-conditioning of the hostel premises;
The total hostel load 308600.08 1.15 354890.092 354.89watts kW
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42
Total hostel load in 354.89 443.61250.8
kWkVA kVApowerfactor
Going by generator capacities currently available in Kenyan markets, a standard 450 kVA,
Volvo 50 Hz, hooded back-up generator is chosen. Its datasheet is attached in the appendix E of
this project document. Other alternatives settled for are the John- Deere and Caterpillar types
hooded diesel back-up generators of the same rating.
5.3.2 Sizing of Cable of the Back-Up Generator
The backup generator will supply 450 kVAat 50Hz frequency thus:
3 450L LV I kVA
Where:
415LV Generator line voltage
LI Line current drawn by the generator
450 450 1000 626.0423 415 3L
L
kVAI AmpsV
Length of generator cable (from the generator to switchboard) = 20m.
Current used for sizing the cable = 626.042 313.0212
Amps since no cable size exists for a line
current of 626.042 Amps. Thus we use two cable conductors in parallel, sized to accommodate
313.021 Amps each.
Allowing for a max of 3% voltage drop on this cable:
313.021 20 0.24 / / 1% 100% 0.3623%1000 415
A m mV A mvoltagedrop
0.3643% Voltage drop is less than the 3% maximum value allowed. This means the two
185mm2 armoured, one 3 or 4-core cable three-phase connected in parallel are appropriate.
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43
5.4 Electrical Distribution Reticulation
Combining all the distribution system topology discussions in section 5.0, section 5.1, section 5.2
and section 5.3, the comprehensive electrical distribution reticulation in figure 5.6 is arrived at
for the proposed hostel as:
Figure 5.6: Electrical Distribution Reticulation for the Hostel
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44
5.5 Electrical Distribution Protection System based on Fault Current Levels at Various
Points in the Installation
5.5.1 Fault Current Level at the Switch-Board
Base kVA = transformer kVA = kVAB = 1,000 kVA (KPLC provided)
Base kV = transformer secondary voltage = 415V, therefore kVB = 0.415 kV
Per unit reactance of transformer = j0.04 p.u
Length of feeder (from transformer at gate to Switch-board room) = 300 m = 0.3km
Series impedance of feeder =(0.12 + 푗0.48) / /phase km
Therefore actual feeder impedance = 0.3 0.12 0.48 0.036 0.144 /j j phase .
Therefore p.u. reactance of feeder = 2 1,000
B
B
kVAActual ImpedancekV
= 2
1,0000.036 0.1440.415 1,000
j
= 0.209 0.836 .j p u
A three-phase fault is the most severe fault that can occur; so a breaker capable of clearing this
magnitude of fault will have sufficient capacity to clear any other kind of fault occurring at the
same point. For a three-phase short-circuit at the Switch-board essential bus-bars,
p.u. fault current =
. . . .. . . .p u voltage transformer p u voltage
p u impedance p u impedance transformer feeder
= 10.209 0.836 0.04j j
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45
= 0.2577 1.08j
= 1.11 76.58 .p u
Base current, 1,000 1,391.203 3 0.415BBase kVAI Amps
Base kV
Fault current (for three-phase fault at Switch-board bus-bars)
= p.u. fault current Base current, BI
= 1.11 76.58 1,391.20 Amps â
= 1544.2 76.58 Amps
5.5.2 Fault Current Levels at the Beginning of Final Circuits
The consumer unit, (CU) is placed in relation to the distribution board (DB) as shown in Figure
5.7. Largest MCB on consumer unit CU UGF 1 is of 20A, protecting a ring circuit of socket
outlets. Total current drawn by CU UGF 1 is 70.98A. To be able to decide the ratings of the
MCBs to use to provide discrimination, the fault current for a fault at a point just after the CU
DB copper cable,
r = 18µΩm
DB CU
CU copper cable,
r = 18µΩm
final circuit conductor
Figure 5.7: Layout and parameters for fault current calculation
transformer secondary,
reactance = j0.04p.u,
base kV = 0.415,
KPLC incomer, length = 0.3km,
impedance = 0.12+j0.48Ω/phase/km
N Switc
hboa
rd
Page 54
46
must be determined. This would be the point at which the most severe fault the miniature circuit
breaker (MCB) in the CU would have to clear, failing which the moulded case circuit breaker
(MCCB) at the DB would have to clear. The fault is a phase to neutral one and so that particular
phase all the way back to the transformer plus the neutral would be involved. The transformer
voltage would have to push current through the impedance of:
1. One phase/winding of the transformer, X .
2. The phase and neutral of the KPLC incomer, 3Z
3. The phase and neutral of the DB cable between the switchboard and the DB, 2Z
4. The phase and neutral of the CU cable between the DB and the CU, 1Z
From section 5.5.1:
2 1,000, . . B
B
kVactual transformer impedance X p u transf impedance
KVA
20.415 1,0000.04
1,000j
0.006889j
The impedance of the KPLC incomer, 3 0.12 0.48 / / 0.3 2Z j phase km km
= 0.072 0.288j
Calculation of the impedances of the DB and CU cables can be done with via the use of the
resistivity of copper ( 81.72 10 m at 20 C ), e.g.
For the DB cable, the impedance of the KPLC incomer,
3 0.12 0.48 / / 0.3 2Z j phase km km
= 0.072 0.288j
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47
Calculation of the impedances of the DB and CU cables can be done via the use of the resistivity
of copper ( 81.72 10 m at 20 C ), for example:
For the DB cable, 8
2 6 2
1.72 10 42 1.38 2 1.38 0.00542535 10
copper l m mZA m
The factor of 2 been used to take into account the phase and neutral conductors. The factor 1.38
been used for PVC insulation.
So that for the for the CU cable,8
1 6 2
1.72 10 182 1.38 2 1.38 0.0244110 10
copper l m mZA m
The short circuit current, 1 2 3
240SCI
X Z Z Z
240
0.006889 0.02441 0.005425 0.072 0.288V
j j
769.29 70.95 Amps
A summary of results follow in sections 5.5.2.1, 5.5.2.2 and 5.5.2.3.
5.5.2.1 Fault Current Levels at Consumer Units at the Upper Ground Floor, Lower
Ground Floor and First Floor
Consumer unit UGF1 UGF2 UGF3 LF1 LF2 FF1 FF2 FF3
CU cable size(풎풎ퟐ) 25 25 25 10 10 25 25 25
CU cable length(m) 18 9 24 4 6 20 12 25
Impedance transfer
up to CU (phase-
neutral) (Ω)
0.312 0.308 0.315 0.306 0.307 0.312 0.309 0.315
Fault current (Amps) 769.29 778.69 762.56 783.53 781.63 767.08 775.65 761.41
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48
5.5.2.2 Fault Current Levels at Consumer Units at the Second Floor, Third Floor and the
Attic Floor
Consumer unit SF1 SF2 SF3 TF1 TF2 TF3 AF1
CU cable size(풎풎ퟐ) 25 25 25 25 25 25 16
CU cable length(m) 23 14 29 25 17 32 19
Impedance transfer up to CU
(phase-neutral) (Ω)
0.314 0.310 0.317 0.315 0.312 0.319 0.312
Fault current (Amps) 763.70 773.57 756.72 761.41 770.37 753.11 768.19
5.5.2.3 Fault Current Levels at the Distribution Boards
Distribution board A B
Distribution board cable size(풎풎ퟐ) 240 50
DB cable length(m) 4 20
Impedance transfer up to CU (phase-neutral) (Ω) 6.409 6.426
Fault current (Amps) 1538.249 1542.1452
5.5.3 Discrimination between CUs and DBs
Following results summarized under sections 5.5.2, protective devices that would ensure
discrimination between CUs and DBs are here tabulated.
As an aid to understanding the tables, an explanation is here given of how column 2 under
consumer unit UGF 1 has been filled in table 5.6:
a) 25 mm2 cable size was arrived at in Section 5.1.2.1
b) 79 Amps cable current capacity was arrived at in Section 5.1.2.1
c) 70.98 Amps cable current was arrived at in Section 5.1.2.1
d) 769.29 Amps fault current was arrived at in Section 5.5.2 and also section 5.5.2.1
e) 20 Amps MCB in CU was arrived at after considering ratings of protective devices for the
various ways in the CU.
f) 100 Amps SP/N G FRAME MCCB in DB for discrimination is arrived at from the MEM
Catalogue Table in the Appendix D.
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Table 5.6: Summary for Discrimination between CUs and DBs
Consumer unit UGF1 UGF2 UGF3 LF1 LF2 FF1 FF2 FF3
CU cable size(풎풎ퟐ) 25 25 25 10 10 25 25 25
Cable current
capacity(Amps)
79 79 79 53 53 79 79 79
Cable current(Amps) 70.98 75.56 70.98 45.00 42.92 70.98 75.56 70.98
Rating of largest MCB
in CU(Amps)
20 20 20 20 20 20 20 20
Fault current(Amps) 769.29 778.69 762.56 783.53 781.63 767.08 775.65 761.41
CU’ s DB A A A A A A A A
Rating of SP/N G
FRAME MCCB
Upstream in
DB(Amps)
100 100 100 63 63 100 100 100
Table 5.7: Summary for Discrimination between CUs and DBs
Consumer unit SF1 SF2 SF3 TF1 TF2 TF3 AF1
CU cable size((풎풎ퟐ) 25 25 25 25 25 25 16
Cable current capacity(Amps) 79 79 79 79 79 79 70
Cable current(Amps) 70.98 75.56 70.98 70.98 75.56 70.98 52.92
Rating of largest MCB in
CU(Amps)
20 20 20 20 20 20 20
Fault current(Amps) 763.70 773.57 756.72 761.41 770.37 753.11 768.19
CU’ s DB A A A A A A A
Rating of SP/N G FRAME
MCCB Upstream in DB(Amps)
100 100 100 100 100 100 80
5.5.4 Discrimination between DBs and the Switch-Board
Following results summarized under section 5.5.2.3, protective devices that would ensure
discrimination between DBs and the switchboard are here tabulated.
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As an aid to understanding the table 5.8, an explanation is given here of how column 2 under
Distribution Board ‘A’ has been filled:
a) 240 mm2 cable size was arrived at in Section 5.2.1.2
b) 392 Amps cable current capacity is from IEE Tables.
c) 341.389 Amps cable current was arrived at in Section 5.2.1.2
d) 1538.249 Amps fault current was arrived at in Section 5.5.2.3
e) 100 Amps MCCB in DB was arrived at Section 5.5.3
f) 200 Amps TP/N F FRAME MCCB in Switch-board for discrimination is arrived at from the
MEM Catalogue Table in the Appendix D; the 160 Amps being ruled out as it offers
discrimination up to 1600 Amps fault current which is considered to be too close to the
1538.84 Amps fault current expected at DB B1.
Table 5.8: Summary for Discrimination between DBs and the Switch-Board (MCCB 3 and
MCCB 4)
Distribution Board A B
DB cable size(mm2) 240 95
DB cable current capacity(Amps) 392 215
DB cable current (Amps) 341.389 180
Largest MCCB in DB(Amps) 100 50
Fault Current(Amps) 1538.249 1542.1452
Rating of TP/N F FRAME MCCB Upstream in
Switchboard(Amps)
200
(MCCB 3)
200
(MCCB 4)
5.5.5 Discrimination between Moulded Case Circuit Breaker, (MCCB 1) and Switchboard
From section 5.4 using figure 5.6, the essential copper bus-bars are supplying all DBs (DB ‘A’
and DB ‘B’) when KPLC power is available. Therefore:
Essential bus-bars, red phase current = Sum of red phase currents of DB ‘A’+ Sum of red phase
currents of DB ‘B’ = 341.389 38.26 38.26 19.13 19.13 456.169 Amps
In a similar manner the essential bus-bars yellow and blue phase currents can be calculated. The
results are summarized in table 5.9
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Table 5.9: Summary for Switch-Board Essential Bus-Bar Phase Currents
Item Red Phase
(Amps)
Yellow Phase
(Amps)
Blue Phase
(Amps)
DB ‘A’ 341.389 333.472 335.972
DB ‘B’ 114.78 114.78 114.78
Switchboard essential bus bar
currents(Amps)
456.169 448.252 450.752
From section 5.5.4, considering the MCCB’s feeding the DBs, the largest MCCB in the switch-
board is of 200 Amps rating. In section 5.5.1, the prospective fault current at the switch-board
bus-bars for a three-phase short circuit fault was found to be 1544.2 Amperes. At the essential
bus-bars of the switch-board, the largest current has just been calculated above to be 456.169
Amperes.
Therefore, a moulded case circuit breaker, (MCCB) is required that is capable of passing through
456.169 Amps normal load current and withstanding 1544.2 Amps fault current while
discriminating the 200 Amps largest MCCB feeding the DBs.
From the MEM catalogue in Appendix D, it is clear that the 250 Amps MCCB would be the
most appropriate. Hence MCCB 1 breaker rating from the electrical distribution reticulation (in
section 5.4) is 250 Amps.
5.5.6 Discrimination between Generator Moulded Case Circuit Breaker, (MCCB 2) and
Switch-Board
Since the entire proposed hostel establishment is on back-up, the generator phase currents are
obtained as the sum of phase currents supplied to DB ’A’ and DB ‘B’. In summary we get:
GENERATOR PHASE CURRENTS
Item Red Phase Yellow Phase Blue Phase
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52
(Amps) (Amps) (Amps)
DB ‘A’ 341.389 333.472 335.972
DB ‘B’ 114.78 114.78 114.78
Generator phase
currents(Amps)
456.169 448.252 450.752
Often, a 3-phase fault produces the largest short-circuit current magnitude; thus, this worst-case
result is then used as the basis to select the short-circuit capabilities of switchgear from
manufacturers' tables.
So the requirement now becomes one of picking an MCCB that can let load current of 456.169
Amps pass through, withstand a fault current of 1544.2 Amps, and discriminate a 200 Amps
MCCB at the switchboard in case of fault at DB ‘A’. The appropriate MCCB is a 250 Amps
TP/N MEM 2J FRAME MCCB.
Therefore, MCCB 2 shown in the electrical distribution reticulation in section 5.4 has a breaker
rating of 250 Amps
5.6 Lightning Protection Design
The lightning protection is shown in drawing number E14, attached at the appendix A-1
The lightning protection is done and achieved using air terminals (shown in the blue color)
which are mounted at the highest point of the roof thereby offering the greatest zone of
protection and interception of lightning strikes. Earth rods (also shown in blue color) are sunk
into the ground. The earth rods will conduct and disperse lightning current to the earth by giving
the lightning discharge current a low resistance path to the earth. Copper tape or down
conductors (shown in red color) are used to connect the air terminals to the earth rods thus
conducting lightning current from the air terminal system to the earth termination system.
Therefore, lightning strokes are discharged and directed to the ground as shown in figure 5.8
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Figure 5.8: Lightning Protection for the Hostel
5.7 Power Factor Correction The total load for the building = 443.6125 KVA, and assuming a worst case power factor of 0.65
and trying to bring it to 0.9 as per the regulations. In practice penalties are charged to a
consumer whenever the consumer’s system has lesser power factor. To begin with, most loads
are inductive in nature. Therefore, adding shunt capacitance can reduce the inductive reactance
as the capacitive reactance opposes the inductive reactance of the load.
Total building load:
=√3 × 415 푉 × 456.169 퐴푚푝푠
1000 = 327.89 푘푉퐴
Assuming a power factor of 0.65 before correction to the value of 0.9 required by Kenya Power
and Lighting Company, the analysis can be done using the power factor triangle as shown in
figure 5.9
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54
Figure 5.9: Power Factor Triangle
Hence the proposed Capacitor Bank Size = 150 kVAR electronically switched in steps of 50, 50,
and 50 kVAR each.
Cable length connecting capacitor bank to switchboard bus-bars = 4m
Maximum current drawn by capacitor bank:
=150 × 1000√3 × 415
= 208.68 퐴푚푝푠
Appropriate 3 or 4-core three-phase, non-armoured PVC cable size = 120 mm2
%푣표푙푡푎푔푒 푑푟표푝 =208.68 퐴 × 4푚 × 0.34푚푉/퐴/ 푚
1000×
1415
× 100% = 0.0684% < 3%
Therefore, the 120 mm2, cable is appropriate.
Cos-1 0.65 = 49.46˚
Cos-1 0.9 = 25.84˚
327.89 kVA
327.89 × 0.65= 213.1285 푘푊
= 213.1285푘푊 × tan 25.84
= 103.21 푘푉퐴푅
Reactive Power after power factor correction
= 249.18 − 103.21= 145.97 푘푉퐴푅
Capacitor Bank
= 249.18 푘푉퐴푅
= 294.5퐾푉퐴푅
kVAR before p.f correction
=327.89 × sin 49.46°
Page 63
55
CHAPTER 6
6.0 CONCLUSIONS
In this project, an attempt has been made to come up with an appropriate lighting scheme and
distribution system layout for a proposed hostel. Various sizing of cables have also been
discussed to supplying power to the entire hostel building. Overload, short-circuit and lightning
protections have also been included in the building electrical services design. A power back-up
generator capacity size of 450 kVA has also been settled on for the entire establishment.
These achievements are all in line with the main objectives of the project. Therefore, the laid
down objectives at the start of the project were successfully met during the entire project process.
Some challenges arose during the project process and appropriate solutions were considered. A
challenge such as load balancing for the hostel was not an easy and smooth task. However, a
solution was found by first assigning each of the overall loads of the first three similar hostel
floors to a single independent supply phase. Topping-up of the three supply phases with the
remaining deficit loads of the other hostel floors was done evenly and the end result was a close
as possible load balancing.
The other challenge was sizing the generator cable which has a line current of 626.042 Amps.
From the IEE tables no cable size exists for such a line current. This was solved as; Current used
for sizing the cable = 626.042 313.0212
Amps . Therefore, the solution was to use two cable
conductors connected in parallel and sized to accommodate 313.021 Amps each.
As a result of appropriate solutions to the challenges faced and achievement of the project main
objectives, the building electrical services design for a hostel along Nyerere road project was
indeed a success.
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CHAPTER 7
7.0 RECOMMENDATION FOR FUTURE WORK
7.1 Software for Building Electrical Services Design
Small computer programs and macros can be written and coded to be able to compute the load
calculations, currents drawn by various load circuits and voltage drops across the cable
conductors. The programs can further be developed to be able to pick appropriate cables from the
IEE tables for cable and conductors databases depending on the calculation results. Hence it will
do cable sizing for all the building electrical power systems. Further development of the
computer programs to display and give all the building electrical services power systems
parameters at strategic points is also necessary and recommended. These programs when
integrated leads to development of a comprehensive software for the building electrical services.
This will save the manual time and energy in this demanding project work due to its wider scope.
This will also enable computational implementation of the project in future
7.2 Bill of Quantities A bill of quantities can be prepared to give an estimate of the financial cost of the building
electrical services design for the hostel along Nyerere road. The bill of quantities will also help
in contract administration procedures as part of engineering practice in the real practical world.
7.3 Earth Faults Because of time, I was not able to cover the scope of earth faults, its analysis and effects during
the project process. I would therefore recommend a detailed study of earth faults along the
aforementioned areas in the future.
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57
CHAPTER 8
8.0 REFERENCES 1. Sidney M. Levy, “Construction Process Planning and Management, An Owners Guide to
Successful Projects” 2007, Page 47
2. U.S. Army Corps of Engineers, “Electrical Power Supply and Distribution” Technical
Manual No. 5-811-1, Page 1-1
3. http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=70&cookie_test=1
4. Barrie Rigby, “Design of Electrical Services for Buildings” 4th Edition, Page 1
5. Rüdiger Ganslandt, Harald Hofmann, Handbook of Lighting Design, ERCO Edition,
Page 22
6. Walter T. Grondzik, Alison G. Kwok, Benjamin Stein, John S. Reynolds, Mechanical and
Electrical Equipment for Buildings, 11th Edition, Page 471
7. Walter T. Grondzik, Alison G. Kwok, Benjamin Stein, John S. Reynolds, Mechanical and
Electrical Equipment for Buildings, 11th Edition, Page 492
8. Rüdiger Ganslandt, Harald Hofmann, Handbook of Lighting Design, ERCO Edition,
Page 62
9. Rüdiger Ganslandt, Harald Hofmann, Handbook of Lighting Design, ERCO Edition,
Page 62
10. http://www.mkelectric.co.uk/Documents/English/EN%20Superswitch%20Catalogue/Sup
erswitch%20Catalogue.pdf Page 5
11. http://www.pikosystem.hu/download/katalog_eng.pdf
12. http://www.oac.be/docs/nc.pdf
13. http://www.davmark.co.uk/group/services/electric/diversity.html
14. Dr C. R. Bayliss and B. J. Hardy, “Transmission and Distribution Electrical Engineering”
3rd Edition, Page 139
15. Turan Goren, “Guide to Electrical Power Distribution Systems”, 6th Edition, Page 57
16. Barrie Rigby, “Design of Electrical Services for Buildings” 4th Edition, Page 65
17. Riang Yer Zuor, http://www.sudantribune.com/spip.php?article19285
18. http://www.mbendi.com/indy/powr/af/su/p0005.htm#Directories
19. Building Services Handbook, 4th Edition, Page 390
Page 66
58
20. www.cumminspower.com
21. EATON MEM, MEM Circuit Protection & Control, 2003 Issue, Page 16
22. EATON MEM, MEM Circuit Protection & Control, 2003 Issue, Page 16
23. EATON MEM, MEM Circuit Protection & Control, 2003 Issue, Page 16
24. EATON MEM Memshield Air Circuit Breakers Specification, Page 1
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59
CHAPTER 9
9.0 APPENDICES
Appendix A-1: Auto Computer Aided Designs, (AUTOCAD) for Lighting Design and Power Points Layout Design
Table A.1: Guidance of AUTOCAD designs labeling
Drawing No. Floor plan Design description
E01 Schedule of symbols and lighting luminaires
E02 Lower floor Lighting fittings design and circuit arrangements
E03 Lower floor Power points layout design and circuit arrangements
E04 Upper ground floor Lighting fittings design and circuit arrangements
E05 Upper ground floor Power points layout design and circuit arrangements
E06 First floor Lighting fittings design and circuit arrangements
E07 First floor Power points layout design and circuit arrangements
E08 Second floor Lighting fittings design and circuit arrangements
E09 Second floor Power points layout design and circuit arrangements
E10 Third floor Lighting fittings design and circuit arrangements
E11 Third floor Power points layout design and circuit arrangements
E12 Attic floor Lighting fittings design and circuit arrangements
E13 Attic floor Power points layout design and circuit arrangements
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60
Appendix A-2: Lightning Protection Design
A detailed and clearer lightning protection design is shown in drawing number E14 attached in
this appendix A-2 section.
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61
Appendix B: Consumer Units Designs and Specifications
This appendix B shows more consumer units detailed schematics, designs and specifications
with the drawing number E15 attached here.
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62
Appendix C: IEE tables
NON-ARMOURED CABLE SIZES – PVC INSULATED COPPER CABLES
ENCLOSED
One twin cable Single phase
mm2 A mV/A/m 1 14 42
1.5 18 28 2.5 24 17
4 32 11 6 40 7.1
10 53 4.2 16 70 2.7 25 79 1.8 35 98 1.3 50 168 0.92 70 209 0.65 95 257 0.48
120 295 0.4 150 337 0.32 185 390 0.29 240 461 0.25 300 523 0.23 400 589 0.22
One 3 or 4 core cable three phase
mm2 A mV/A/m 1 13 37
1.5 17 24 2.5 24 15
4 32 9.2 6 40 6.2
10 54 3.7 16 71 2.3 25 90 1.6 35 115 1.1 50 140 0.81 70 176 0.57 95 215 0.42
120 251 0.34 150 287 0.29 185 330 0.24 240 392 0.2 300 450 0.18 400 520 0.17
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63
ARMOURED CABLE SIZES – PVC INSULATED COPPER CABLES
One 3 or 4 core cable three phase
mm2 A mV/A/m 1.5 18 25 2.5 24 16
4 31 9.6 6 41 6.3
10 56 3.8 16 73 2.3 25 97 1.6 35 119 1.1 50 147 0.81 70 180 0.57 95 219 0.42
120 257 0.34 150 295 0.29 185 333 0.24 240 399 0.2 300 451 0.18 400 523 0.17
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Appendix D: MEM Catalogue Extracts
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Appendix E: Power Back-Up Generator Data Sheet and Performance
450KVA VOLVO DIESEL GENERATOR 360KW, SDMO V450KSA DIESEL
GENERATOR SET
360Kw (450Kva) Standby, 320Kw (400Kva) Prime, 50Hz, 1500RPM, 3 Phase, 0.8PF
VOLVO TAD1242GE, Turbocharged heavy duty diesel engine, 4 stroke, 1500rpm,
Electronic governor
LEROY SOMER LSA472VS3, 12lead Alternator. IP23 drip-proof protection, Insulation
class H. Automatic voltage regulation.
MERLIN GERIN, Main line circuit breaker, 3 pole, output rated, UL listed
SDMO TELYS2, Advanced auto-start Digital control panel. All alarms, genset
parameters, control functions and indicators. CE and UL listed
50 HERTZ, 3 PHASES, 0.8PF, 1500 RPM
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Appendix F: Utilization Factors
