DESIGNING A LIGHTING, POWER AND PROTECTION SYSTEM...

UNIVERSITY OF NAIROBI

FACULTY OF ENGINEERING

DEPARTMENT OF ELECTRICAL AND INFORMATION

ENGINEERING.

DESIGNING A LIGHTING, POWER AND PROTECTION

SYSTEM OF A RESIDENTIAL ESTATE.

PROJECT INDEX: PRJ 059

BY

MIRANG’A VALENTINE MOKEIRA

F17/40230/2011

SUPERVISOR: PROF. N. O. ABUNGU

EXAMINER: MR. C. OMBURA

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

SUBMITTED ON: 16TH MAY 2016

DEDICATION

I dedicate this report to my parents and my brothers for the support and love they have

given me.

DECLARATION AND CERTIFICATION

COLLEGE OF ARCHITECTURE AND ENGINEERING

FACULTY/SCHOOL/INSTITUTE: ENGINEERING

DEPARTMENT: ELECTRICAL AND INFORMATION ENGINEERING

NAME OF STUDENT: MIRANG’A VALENTINE MOKEIRA

REGISTRATION NUMBER: F17/40230/2011

TITLE OF THE WORK: DESIGNING A LIGHTING, POWER AND PROTECTION SYSTEM

OF A RESIDENTIAL ESTATE.

DECLARATION

1. I understand what Plagiarism is and I am aware of the University’s policy in this regard

2. I declare that this assignment is my original work and has not been submitted elsewhere for

examination, award of a degree or publication. Where other people’s work, or my own work has

been used, this has properly been acknowledged and referenced in accordance with the University

of Nairobi’s requirements.

3. I have not sought or used the services of any professional agencies to produce this work

4. I have not allowed, and shall not allow anyone to copy my work with the intention of passing it

off as his/her own work

5. I understand that any false claim in respect of this work shall result in disciplinary action, in

accordance with University Plagiarism Policy.

Signature:

……………………………………………………………………………………….

Date:

……………………………………………………………………………………….

ACKNOWLEDGEMENT

I thank God for the continued strength, knowledge, understanding and good health and for seeing

me this far through my undergraduate degree.

I want to sincerely appreciate my supervisor Prof. Nicodemus Abungu Odero for the guidance and

constructive criticism that he had offered all through development of my project up to its completion.

To my friends, my sincere gratitude for both moral and technical support you extended with

respect to resources shared, time and words of encouragement.

To my family, from whom I have received the usual warm support without which this report

wouldn’t have been written.

And finally I would like to thank the Department of Electrical and Electronics Engineering

at the University of Nairobi, which has instilled in me the knowledge and discipline to pursue

a career in electrical engineering.

34

TABLE OF CONTENTS

CONTENTS

DEDICATION ........................................................................................................................... 2

DECLARATION AND CERTIFICATION ........................................................................... 3

ACKNOWLEDGEMENT ........................................................................................................ 4

TABLE OF CONTENTS ........................................................................................................... i

LIST OF TABLES .................................................................................................................... v

LIST OF FIGURES ................................................................................................................. vi

LIST OF ABBREVIATIONS ................................................................................................. vii

ABSTRACT ............................................................................................................................ viii

Chapter 1 ....................................................................................................................................... 1

1.1 INTRODUCTION ............................................................................................................... 1

1.2 OBJECTIVES ..................................................................................................................... 2

Chapter 2 ....................................................................................................................................... 3

2.1 LIGHT .................................................................................................................................. 3

2.1.1 PHOTOMERTIC QUANTITIES ............................................................................... 4

2.2 LIGHTING .......................................................................................................................... 4

2.2.1 LIGHTING SCHEMES ............................................................................................... 5

2.2.2 CALCULATING NUMBER OF FIXTURES ............................................................ 6

Chapter 3 ....................................................................................................................................... 8

3.1 POWER DISTRIBUTION ................................................................................................. 8

3.1.1 POWER DISTRIBUTION BETWEEN BUILDINGS .............................................. 8

3.1.2 POWER DISTRIBUTION WITHIN LARGE BUILDINGS ................................... 9

3.1.3 POWER DISTRIBUTION IN DOMESTIC BUILDINGS ....................................... 9

3.2 DISTRIBUTION BOARD (D.B) ........................................................................................ 9

3.3 CONSUMER UNIT (C.U) .................................................................................................. 9

3.4 SWITCHES ....................................................................................................................... 10

3.5 SOCKETS .......................................................................................................................... 10

3.6 CIRCUITS ......................................................................................................................... 11

3.6.1 SOCKET CIRCUITS ................................................................................................. 11

3.6.2 LIGHTING CIRCUITS ............................................................................................. 13

3.7 CABLE SIZING ................................................................................................................ 14

Chapter 4 ..................................................................................................................................... 15

4.1 PROTECTION .................................................................................................................. 15

4.1.1 PROTECTION AGAINST OVERCURRENT. ....................................................... 15

4.1.2 PROTECTION AGAINST LIGHTNING. .............................................................. 15

4.2 DISCRIMINATION.......................................................................................................... 16

4.3 POWER FACTOR CORRECTION ............................................................................... 17

4.4 GENERATORS ................................................................................................................. 17

Chapter 5 ..................................................................................................................................... 19

5.1 DESIGN SPECIFICATIONS. ......................................................................................... 19

5.1.1 LIGHT FITTINGS. .................................................................................................... 19

5.1.2 SWITCHES ................................................................................................................. 20

5.1.3 SOCKET OUTLETS .................................................................................................. 20

5.1.4 TELEVISION AND DATA POINTS ........................................................................ 20

5.1.5 SINGLE PHASE LOADS .......................................................................................... 21

5.2 DESIGN.............................................................................................................................. 21

5.2.1 LIGHT DESIGN IN HOUSING UNITS .................................................................. 21

5.2.2 ROAD LIGHTING DESIGN .................................................................................... 25

5.3 LOAD CALCULATION IN HOUSING UNITS ............................................................ 27

5.3.1 LOAD CALCULATION IN UNIT A2 ..................................................................... 27

5.4 SUMMERY OF LOAD IN THE ESTATE ..................................................................... 28

5.4.1 HOUSING UNIT A2 .................................................................................................. 29

5.4.2 HOUSING UNIT B2 ................................................................................................... 29

5.4.2 HOUSING UNIT C2 .................................................................................................. 31

5.4.3 TOTAL LOAD IN THE WHOLE ESTATE ........................................................... 32

5.4 CIRCUIT BREAKERS AND CONSUMER UNITS ..................................................... 32

5.4.1 CIRCUIT BREAKERS IN HOUSING UNITS ....................................................... 32

5.4.2 CONSUMER UNITS .................................................................................................. 34

5.5 SERVICE TURRETS ....................................................................................................... 35

5.6 CONSUMER UNIT CABLE SIZING. ............................................................................ 36

5.6.1 CABLE SIZING FOR CU-A2-1 ................................................................................ 37

5.7 SERVICE TURRET CABLE SIZING ............................................................................ 40

5.7.1 CABLES FEEDING SERVICE TURRET 1. .......................................................... 40

Chapter 6 ..................................................................................................................................... 41

6.1 TRANSFORMER SIZE ................................................................................................... 41

6.1.1 TRANSFORMER 1 TOTAL LOAD ........................................................................ 41

6.1.2 TRANSFORMER 2 TOTAL LOAD ........................................................................ 42

6.2 BACKUP GENERATOR ................................................................................................. 42

6.2.1 CAPACITY OF THE STANDBY GENERATOR .................................................. 42

6.2.2 CABLE SIZE OF THE STANDBY GENERATOR ............................................... 43

6.3 ELECTRICAL DISTRIBUTION SYSTEM RETICULATION. ................................. 45

6.4 POWER FACTOR CORRECTION ............................................................................... 46

6.5 DETERMINATION OF PROSPECTIVE FAULT CURRENTS ................................ 46

6.5.1 FAULT CURRENT AT THE SWITCHBOARD LEVEL ..................................... 46

6.5.2 FAULT CURRENT AT THE BEGINNING OF THE FINAL CIRCUITS ......... 48

6.6 DISCRIMINATION.......................................................................................................... 51

6.6.1 DISCRIMINATION BETWEEN CONSUMER UNITS AND SERVICE

TURRETS ........................................................................................................................... .51

6.6.2DISCRIMINATION BETWEEN SERVICE TURRETS AND LV SWITCH

BOARD….. ........................................................................................................................... 54

6.6.3DISCRIMINATION BETWEEN GENERATOR MCCB AND LV

SWITCHBOARD…. ........................................................................................................... 54

6.7 LIGHTNING PROTECTION ......................................................................................... 56

Chapter 7 ..................................................................................................................................... 57

7.1 RECOMMENDATIONS FOR FUTURE WORK ......................................................... 57

7.2 CONCLUSION .................................................................................................................. 57

APPENDIX 1: LIGHT DESIGN ........................................................................................... 59

APPENDIX 2: LOAD CALCULATIONS ............................................................................ 63

APPENDIX 3: CATALOGUES ............................................................................................. 67

REFERENCES ........................................................................................................................ 73

LIST OF TABLES

TABLE 2-1 COLOUR RENDERING INDEX. .......................................................................... 3

TABLE 3-1 RECOMMENDED NUMBER OF SOCKETS IN A ROOM ............................ 11

TABLE 5-1. TYPES OF LUMINAIRES USED....................................................................... 19

TABLE 5-2. CALCULATION OF MAXIMUM DEMAND IN UNIT A2 ............................ 28

TABLE 5-3 SUMMERY OF LOADS IN UNIT A2 ................................................................. 29

TABLE 5-4 SUMMERY OF LOADS IN UNIT B2 ................................................................. 29

TABLE 5-5 SUMMERY OF LOADS IN UNIT C2 ................................................................. 31

TABLE 5-6 SUMMERY OF LOADS IN THE ESTATE ....................................................... 32

TABLE 5-7 : MCBS IN DB-A2-1 .............................................................................................. 34

TABLE 5-8 CABLE SIZES USED FOR CONSUMER UNITS ............................................. 38

TABLE 5-9 CABLE SIZES FOR SERVICE TURRETS ....................................................... 40

TABLE 6-1 DISTRIBUTION OF LOADS IN TRANSFORMER 1 ...................................... 41

TABLE 6-2 DISTRIBUTION OF LOADS IN TRANSFORMER 2 ...................................... 42

TABLE 6-3 PROSPECTIVE FAULT LEVELS FOR THE CONSUMER UNITS ............. 49

TABLE 6-4 DISCRIMINATION BETWEEN CUS AND THEIR RESPECTIVE SERVICE

TURRETS .................................................................................................................................... 52

TABLE 6-5 DISCRIMINATION BETWEEN SERVICE TURRETS AND THE LOW

VOLTAGE SWITCHBOARD. .................................................................................................. 54

TABLE 6-6 GENERATOR 1 PHASE CURRENTS ............................................................... 54

TABLE 6-7 GENERATOR 2 PHASE CURRENTS ............................................................... 55

LIST OF FIGURES

FIGURE 2-1 POINT BY POINT METHOD ON VERTICAL SCALE .................................. 7

FIGURE 3-1. CONSUMER UNIT ............................................................................................ 10

FIGURE 3-2. RING CIRCUIT CONNECTION ..................................................................... 12

FIGURE 3-3. RADIAL CIRCUIT CONNECTION ................................................................ 13

FIGURE 3-4 LOOP-IN SYSTEM OF WIRING...................................................................... 14

FIGURE 5-1. LUMINAIRE ARRANGEMENT IN LOUNGE .............................................. 23

FIGURE 5-2. POINT BY POINT METHOD FOR A PAINTING ON A WALL ................ 24

FIGURE 5-3 CONSUMER UNIT ARRANGEMENT FOR CU-A2-1 .................................. 35

FIGURE 6-1 CABLES FEEDING THE GENERATOR ........................................................ 44

FIGURE 6-2 ELECTRICAL DISTRIBUTION SYSTEM RETICULATION FOR

TRANSFORMER 1 .................................................................................................................... 45

FIGURE 6-3 ELECTRICAL DISTRIBUTION SYSTEM RETICULATION FOR

TRANSFORMER 2 .................................................................................................................... 45

FIGURE 6-4 POWER FACTOR CORRECTION DIAGRAM ............................................. 46

FIGURE 6-5 LAYOUT FOR FAULT CALCULATION ....................................................... 48

FIGURE 6-6 LIGHTNING PROTECTION LAYOUT FOR UNIT A2 ................................ 56

LIST OF ABBREVIATIONS

KV: Kilovolts

A: Amperes

IEE: Institute of Electrical Engineers

KVA: Kilovolt amperes

KW: Kilowatts

CU: Consumer unit

DB : Distribution board

CB: Circuit breaker

PVC: Polyvinyl Chloride

IES: Illuminating Engineering Society

E: Illuminance

I: Luminous intensity

LCW: Wall luminance coefficient

W: Watts

KPLC: Kenya Power and Lighting Company

Ω: Unit of measurement of resistance

Z: Impedance

X: Reactance

mm: Millimeter

m: Meter

MCB: Miniature circuit breaker

MCCB: Moulded case circuit breaker

SP: Single pole

DP: Double pole

TX: Transformer

SPN: Single phase neutral

TPN: Three phase neutral

p.u: Per unit

kA: kilo ampere

ABSTRACT

This project was aimed at designing an efficient lighting, distribution and protection system for a

residential estate in Juja. The estate had 3 types of houses namely type A2, B2 and C2. The total

number of units in the estate was 75. Literature review on lighting, distribution and protection was

first done. Next, lighting design was done using the lumen method which was used to find the

number of luminaires required and the point-by-point method was used to calculate the illuminance

at a point. Street lighting was also done using IESNA [4] guidelines and the distance between each

luminaire was found to be 31m.

Power outlets design was according to the IEE regulations. The design covered socket outlets and

single phase load outlets. The load in each area was determined and assigned to the respective

consumer units and service turrets. Diversity was taken into account in load calculations and future

load growth catered for by including spare ways.

Sizes of breakers that protect final circuits were determined and the details of consumer units

drawn.

The total load of the estate was 1701.38 kVA the load was split into two load 1 with a total load

of 908.95 kVA and load 2 with a total load of 792.43 kVA. Two pad mounted transformers rated

1000 kVA with a reactance of 4.75% per unit to be used to supply the estate.

Using the load currents in each consumer unit, load balancing was achieved. The load current in

transformer 1 was 3219A and for transformer 2 was 2806.31A. Service turrets were assigned. 10

service turrets were used to cater for the loads in the estate. The sizes of cables that feed consumer

units, service turrets, the switch board and generator were determined using the Bahra Cables

Company catalogue. Voltage drop of 6% was set as the maximum limit.

An electrical distribution reticulation layout was designed showing distribution in the whole

building. Two 1000 KVA generator were used for back-up. Protection was tackled by calculation

of fault currents at various levels in the distribution to the houses. Discrimination was tackled using

the fault currents and the breaker ratings. Using the values of the breaker ratings obtained, a

distribution layout was designed from the consumer level (downstream) to the transformer level

(upstream). Lightning protection was done by the use of lightning arrestors. Power factor

correction was done. Finally, recommendations for future work were detailed and a conclusion

written. A list of references was also outlined. The appendix was put in place for reference.

1

Chapter 1

1.1 INTRODUCTION

Light plays a vital role in the quality of our daily lives. Light is basically radiation that is capable

of producing visual sensation. Every day activities require light. At work, in offices, good lighting

brings employee satisfaction, good performance, comfort and safety thus improving the economy

by extending working hours and enables continued activity in various areas. In shops, galleries

and public places, good lighting accentuates the architectural environment. At home, it brings

comfort, provides a safe welcoming environment and lights the day to day tasks. This calls for

attention to ensuring that efficient lighting is achieved.

Daylight was the main source of light in the earlier days but due to the advancement of artificial

light, daylight is constantly being phased out since artificial lighting is more efficient, has variety

of uses and is very reliable. Advanced artificial light sources and luminaires are currently available

as provided by manufacturers catalogues hence the need to incorporate them in lighting.

Distribution aims at ensuring supply of electricity to the necessary areas. The main purpose of an

electrical distribution system is to meet the customer’s demand of energy after receiving the bulk

supply of electrical energy from the transmission or sub-transmission station. Factors considered

while determining a distribution system include the type of demand, the load characteristics, type

of area and the load factor. The distribution system should be placed and sized carefully so as to

serve the maximum load possible. An efficient distribution system can be costly thus it is important

that a beneficial yet economical distribution system is achieved.

Electricity can be dangerous hence safety is a key factor. Proper protective measures, for the

building and its users, have to be put in place. Electrical protection is installed to isolate the faulty

part of the electric system hence preventing further damage of equipment and accidents for the

personnel handling the equipment. Some of the factors to be taken into account while selecting

protection equipment are speed, selectivity, reliability and also cost.

2

1.2 OBJECTIVES

The objectives of this project hence included:

i. Coming up with efficient lighting schemes for each housing unit in the residential estate

and also outdoor areas within the estate.

ii. Power distribution: this included the placement of the lighting points, electrical power

points, data points and consumer units, and their electrical connection and also sizing of

the various cables that fed the final circuits.

iii. Protection: this included protection of loads and cables from short circuit and overload and

lightning protection.

iv. Sizing of the various cables that were used in the electrical system.

v. Provision of a backup system for the area.

vi. Power factor correction

vii. Discrimination between various load centers.

Since this project focuses on a residential estate, the comfort, safety and security of the people and

are had to be focused on. The method of investigation applied is research. Sources of information

include books, the internet and people.

3

Chapter 2

2.1 LIGHT

Light is the part of the electromagnetic spectrum that can be perceived by the human eye. It is

closely related to other forms of electromagnetic radiation such as radio waves, micro waves, infra-

red, ultra-violet radiation and x-rays. The difference between the various forms of electromagnetic

radiation is in their wave lengths. Radiation with wavelengths between 380-780 nanometers forms

the visible part of the electromagnetic spectrum referred to as light. Light may be characterized in

terms of behavior and color. [1]

i. Behavior: The behavioral characteristics of light include; reflection, absorption,

transmission, refraction and interference.

ii. Colour: Colour is what distinguishes different wavelengths of light. It involves the spectral

characteristics of light itself, the spectral reflectance of the illuminated surface as well as

the perception of the observer. The properties of colour used in lighting include, colour

rendering ability and colour temperature.[1]

Table 2-1 Colour rendering index.

Colour rendering index Ra Colour rendering Properties

90-100 Excellent colour rendering properties

80-90 Good colour rendering properties

60-80 Moderate colour rendering properties

< 60 Poor colour rendering properties

4

2.1.1 PHOTOMERTIC QUANTITIES

These are the photometric units used for quantitative measurement of light.

i. Luminous flux Ф - This expresses the total quantity of light radiated per second by a light

source. SI units of luminous flux is lumen. (lm)

ii. Luminous Intensity I – Defined as flux of light emitted in a certain direction. The SI unit

of luminous intensity is candela. (cd)

iii. Illuminance E – Quantity of light falling on a unit area of a surface. SI unit is lumen/squared

meter lm/m2 or lux (lx). [1]

iv. Luminance L- Describes the light emitted from a unit area in a specific direction. SI unit is

candela/ squared meter cd/m2.

v. Luminous efficacy- Total luminous flux of a light source for each watt of power supplied

to the source. Measured in lumen/watt.[1]

2.2 LIGHTING

Lighting basically refers to the application of light. Types of lighting include:

Day lighting

It is mainly direct sunlight. Daylight illuminances are significantly higher than the illuminances

produced by artificial lighting. Entire buildings and individual rooms were inclined to the

incidence of the sun’s rays so as to get maximum illumination in the room. The disadvantage was

that there was unreliability as some areas had too much sunshine while others very little sunshine.

[3]

Artificial Lighting

Lamps and luminaires are the main sources of artificial lighting. Artificial lighting also provides

aesthetic value apart from meeting visual needs.

Good quality lighting is an important as is affects our ability to perform tasks. In order to design

an effective lighting system the following factors have to be considered; lighting level, luminous

contrasts, glare, spatial distribution of the light and colour. [1]

5

2.2.1 LIGHTING SCHEMES

Lighting schemes are ways in which a place can be lit. To design an efficient lighting scheme, we

have to consider the use of the room, duration of light usage, location of the area to be lit e.g.

indoors or outdoors and the mood to be created.

2.2.1.1 INTERIOR LIGHTING SCHEMES

This aims at providing general lighting, task lighting and decoration. Indoor lighting can use

battens (fluorescents), down lights, recessed lights, spotlights and track lights, surface mounted

and suspended luminaires and wall mounted luminaires.

2.2.1.2 EXTERIOR LIGHTING SCHEMES.

Outdoor lighting design can use spotlights, strip lights, backlights, floodlights, wall-mounted

luminaires, recessed architectural floodlights, surface mounted architectural floodlights among

others. It is applied on street lights, security lights, entry lights, signage and advertisement.

Road Lighting Design

The main aim of road lighting design is to provide patterns and sufficient levels of horizontal

pavement luminance and horizontal and vertical illuminance of objects. Factors to take into

consideration include; pedestrian conflict, luminaire arrangement style and roadway classification.

[5]

The method used to calculate average illuminance is known as the illuminance method and is given

by the equation below

x WS

LL MFUFEav

Where: Eav = average horizontal Illuminance in lux

LL = Lumen per fixture in lumens

MF = maintenance factor

UF = utilisation factor

S = luminaire spacing

W = Road width. [4]

6

2.2.2 CALCULATING NUMBER OF FIXTURES

The methods employed in finding the level of light in interior and exterior spaces include:

The lumen method

The point-to-point method.

2.2.2.1 THE LUMEN METHOD

It is a simplified method used in interior lighting design to calculate the light level in a room. This

enables us to estimate the costs. The steps involved are:

The room index (K) of the space has to be calculated using:

)WL(H

WLK

m

Where: K = room index (describes the influence of room geometry)

Hm = mounting height in meters

L = length of the room in meters

W = width of the room in meters [15].

The number of fixtures can be given by: A

LN

MFUFE

Where: E = Illuminance in lux

N = number of fittings

L = Lumen per fixture in lumens

MF = maintenance factor

UF = utilisation factor

A = area in mm2

Illuminance is the total flux per area. It measure the concentration of light on a surface

Maintenance factor (also called the light loss factor) refers to the reduction of luminous flux for

a source. Lamp output declines with time. Dirt is a major cause of this reduction.

Utilisation factor is a calculated ratio of the lumens effectively lighting an area to the total

available lumens from the lamp. Light is absorbed by surfaces causing a reduction in the lumens.

[4]

7

2.2.2.2 THE POINT-BY-POINT METHOD

The point-by-point is used to calculate the effect of individual luminaires at particular points. The

luminaire photometric data has to be known. The inverse square method is used to calculate

illuminance at a point. [4]

Inverse Square Method

This method is used when the distance from the source is at least 5 times the maximum dimension

of the source. In this method illuminance is directly proportional to the candle power of the source

in a given direction (luminous intensity) and inversely proportional to the square of the distance

from the source. [4]

E= I

D2

For a vertical plane, shown in figure 2-2 below,

H

R

D

Figure 2-1 point by point method on vertical scale

E = I x sin 𝜃 since, sin θ = cos β. Since D2 = H2

D2 Cos2 θ

E = I x sin θ x cos2 θ

H2

Where D - The actual distance from the light source to the point.

R - The horizontal distance from light source to the point

H – The mounting height from the point to the source. [4]

8

Chapter 3

3.1 POWER DISTRIBUTION

Electricity is supplied to a building by a supply authority. In Kenya, KPLC is in charge of

supplying electricity to all buildings. Power is generated at the generating stations in ranges of 11

kV to 25 kV using three-phase alternators. Energy sources include geothermal, hydro reservoirs,

fossil fuels, solar, wind and tides. [6]

The generated voltage is stepped up to ranges of 220 kV to 400 kV for transmission. At the

transmission substations, power is stepped down to voltages in the range of 11kV to 132 kV. For

distribution to high and medium consumers such as heavy industries, voltages of 66 kV or 33 kV

is supplied. For some medium and low industries voltages of 33 kV or 11 kV are supplied. For

distribution to domestic consumers, power is stepped down at the distribution substation to 415 V

(three-phase). Three-phase four-wire and single phase distribution can be achieved here due to the

use of star transformers. The mode of transmission commonly used is overhead transmission.

Underground transmission finds use in heavily populated areas. [6]

3.1.1 POWER DISTRIBUTION BETWEEN BUILDINGS

While distributing power from one building to another, ring or radial distribution systems are used.

Ring or loop system: Underground cable is laid from the substation to loops to each building then

taken back to the substation. Current flows in both directions from the intake. If the cable on the

ring is damaged at any point, it can be isolated for repair without loss of supply to any of the

buildings.

Radial system: Separate underground cables are laid from the substation to each building. It uses

more cable than the ring but only one fused switch is required below the distribution board in each

building.

9

3.1.2 POWER DISTRIBUTION WITHIN LARGE BUILDINGS

In large industries space can be allocated for an 11kV to 415kV step-down transformer. It should

be sited as near as possible to the heaviest loads so as to avoid long runs of expensive low-voltage

cables. Power from the transformer goes to a switchboard first. The switchboard has panels each

of which contains switches that allow electricity to be redirected to load areas. From the

switchboard, power then goes to distribution board then fed to various loads. [8]

3.1.3 POWER DISTRIBUTION IN DOMESTIC BUILDINGS

Power is mostly supplied to buildings through underground cabling (underground service entry)

to a suitable point in the building referred to as the main intake. The position of the entry of the

supply cable should be convenient, safe and secure. The length of the service cable should be

minimized to reduce heating and to ensure less reactive power. Single phase supply is used unless

a three-phase equipment is to be used. Protection at the incoming service cable position is with a

service fuse (high breaking capacity (HBC) fuse). Other equipment at this position are the

energy meter and the consumer’s distribution unit. [8]

3.2 DISTRIBUTION BOARD (D.B)

The distribution board (or a panel board) is a unit which ensures the distribution and comprises

one or more protective devices in an enclosure. Distribution board can be supplied by the

switchboard or another distribution board. They have an incoming integral isolator for protection.

[8]

3.3 CONSUMER UNIT (C.U)

The consumer unit CU or consumer control unit CCU can be described as the consumer’s power

supply control unit. They are incorporated with a double pole isolating switch on the incoming

side. CUs are available with 60A or 100A isolators and up to 12 fuse ways or CBs. Each way is

connected to a single circuit and individual circuit protection is used. Breaker rating is in

accordance with the circuit function. Consumer units can be fed from the distribution board or

other consumer units. Figure 2 shows various circuits in a C.U, together with the main isolator and

10

a spare way. Consumer units have protection against residual currents in addition to miniature

circuit breakers MCBs for each individual circuit. [6]

Figure 3-1. Consumer unit

3.4 SWITCHES

A switch is a device used to make or break a circuit. There is a maximum current which the contacts

of a 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 greater current than the switch can break. The

standard capacities by most manufacturers are 5A, 15A, 20A and a higher rating of 45A. [8]

3.5 SOCKETS

Socket outlets are the major outlets for power services. Great Britain standards use sockets that are

designed to accept 13A plugs. Sockets are available with or without switches. Sockets without

switches have their contacts permanently connected to the wiring and thus are permanently live.

Those with switches must be switched on for the contacts to close. Special sockets installed in

domestic houses include, shaving outlets, cooker control units, television and telephone outlets.

[8]

IEE wiring regulations BS 7671 recommends usage of 13A plugs and socket outlets for low

voltage applications. The mounting height of the sockets 150mm above finished floor or work

11

surface as a minimum. Sufficient number of socket outlets should be provided so that long flexible

cords are avoided. [9]

Modern Wiring Practice [7] chapter on design and arrangement of final circuits shows the

recommended minimum number of 13A twin socket outlets that should be installed in a domestic

premises according to The Electrical Installation Industry Liaison Committee. Table 3-1 below

shows the minimum number of twin socket outlets to be provided in homes as recommended by

the committee.

Table 3-1 Recommended number of sockets in a room

ROOM TYPE MINIMUM NUMBER OF TWIN SOCKETS

Main living room 6

Dining room 3

Single bedroom 3

Double bedroom 4

Study room 3

Kitchen 4

Hallway 1

3.6 CIRCUITS

3.6.1 SOCKET CIRCUITS

Final outlets of an electric system in a building are lighting points, sockets and fixed equipment.

A fuse or circuit breaker can serve several outlets. For socket outlets, ring or radial circuit

arrangements are used. [8]

Ring Circuit.

A ring circuit is one that forms a closed loop. It starts at one of the fuse ways in the distribution

board runs to a number of outlets one after another and returns to the distribution board. According

12

to ONSITE GUIDE BS 7671 [9] Appendix 8 IEE regulations recommend an unlimited number of

socket outlets connected to a ring final circuit serving a floor area not exceeding 100 m2 wired with

2.5 mm2 PVC insulated cables and protected by a 30 A or 32 A overcurrent protective device. The

diagram in figure 3 illustrates a ring circuit.

The advantage of this arrangement is that current can flow from the fuse way to the outlets along

both halves of the rings so that at any one point the cable carries only part of the total current being

taken by the whole circuit. This is the feature that makes it possible for the fuse rating to be greater

than the cable current rating the fuse carries the sum of the currents in the two halves and will

blow when the current is about half the current rating of the fuse.

Radial Circuit.

In the radial circuit, the wiring starts at the distribution boards fuse ways, connects each device in

turn and terminates at the last available socket as shown in figure 4. Radial circuits are more

economical than the ring circuit since they use less length of cables. According to ONSITE

GUIDE BS 7671 [9] Appendix 8 IEE regulations recommend an unlimited number of socket

outlets connected to a radial final circuit serving a floor area not exceeding 50 m2 wired with 4

mm2 PVC insulated cables and protected by a 30 A or 32 A overcurrent protective device.

Figure 3-2. Ring circuit connection

13

3.6.2 LIGHTING CIRCUITS

These are circuits that show how light fittings are connected. They are categorized into two:

Junction box circuit

This is where there is a junction box for each light. A cable runs from the consumer unit to the first

junction box, then to the next until it terminates at the last junction box. Another cable runs from

each junction box to its light and another wire from the junction box to the light switch. [6]

Loop-in circuit

This is where a cable runs from light to light terminating at the last light (as in radial), then a single

cable runs from the lights to the light switches. Figure 3-4 illustrates the loop in system of wiring.

[6]

Figure 3-3. Radial circuit connection

14

3.7 CABLE SIZING

The size of the cables to be used in a given circuit is governed by the current which the circuit has

to carry. A conductor carrying a current is bound to have some losses due to its own resistance.

These losses appear as heat and will raise the temperature of the insulation. The current the cable

can carry is limited by the temperature by which it is safe to raise the insulation. [8]

IEE regulations concerning the maximum allowable current for each type and size of cable is given

in ON SITE GUIDE BS 7671 [9The resistance of the conductor also results in a drop of voltage

along its length thus the voltage at the receiving end is less than that at the sending end. Since all

electric equipment used in the building is designed to operate on the nominal supply voltage, it is

necessary to limit the amount by which the voltage drops between the point of entry into the

building and the outlet serving an appliance. IEE guide limits the voltage drop to 3% of the nominal

voltage for lighting circuits and 5 % of nominal voltage for socket outlets. [9]

Figure 3-4 Loop-in system of wiring

15

Chapter 4

4.1 PROTECTION

In the designing of an electrical system, a large part is concerned with ensuring that accidents do

not happen and if they do, their effects will be limited. The general principal of protection is that

a faulty circuit should be cut-off from the supply and isolated until the fault can be found and

repaired. The protective device is the tool that detects and isolates the fault. Two damages to

prevent are fire and electric shock.

4.1.1 PROTECTION AGAINST OVERCURRENT.

Overcurrent is a condition in an electrical circuit where the current exceeds the rated current

capacity of that circuit. IEE wiring regulations require that every consumer unit contains devices

that protects the final circuits from short circuit faults, overload faults and earth faults. A short

circuit fault is one that occurs when the line or phase and the neutral conductors come into contact

with each other. An overload fault can be described as one that occurs when a circuit is carrying a

current much larger than the maximum current that the circuit can safely handle. An earth fault

occurs when a line conductor comes into contact with the earth metalwork. [8]

The various protective devices used include; rewirable fuses, High Breaking Capacity Fuses

(HBC), Circuit Breakers (CB) and Residual Current Devices (RCD).

4.1.2 PROTECTION AGAINST LIGHTNING.

Lightning is a natural phenomenon caused by separation of electrical positive and negative charges

by atmospheric processes. Lightning produces a great amount of energy that can cause damage. A

lightning protection system is used to prevent damage caused by lightning. The system comprises

of;

i. Air terminal which intercepts lightning flashes and connects them to a path to ground.

They include air terminals, metal masts and permanent metal parts of structures.

ii. Down conductors which link the strike termination device to the ground terminal and

provide a low resistance path to earth.

iii. An earth terminal is installed to provide electrical contact with the earth. [10]

Surge protectors are also used both at the main building entrance and on equipment.

16

Materials that are commonly used for lightning protection system are aluminum and copper. The

Zone of protection is the space within which a lightning conductor provides protection by

attracting the lightning stroke to itself. [10]

4.2 DISCRIMINATION

Many fuses or circuit breakers are incorporated to protect a circuit from the incoming supply to

the final outlet. Ideally, protective devices should be graded so that when a fault occurs, only the

device nearest to the fault operates. The discrimination of the CB’s can be based on either

magnitude of the fault current (current discrimination) or the duration of the time during which

the circuit breaker “sees” the fault current (time discrimination). [8]

CURRENT DISCRIMINATION

This requires a circuit breaker to have a lower continuous current rating and a lower instantaneous

pick-up value than the next upstream circuit breakers. Current discrimination increases as the

difference between continuous current ratings increases and as the pick-up settings increase

between the upstream and the downstream breakers. Current discrimination at short circuit levels

is necessary where high prospective faults levels exist at the circuit breaker distribution point.

TIME DISCRIMINATION

“The total clearing time of the downstream breaker must be less than the time delay setting of the

upstream breaker”. The upstream circuit breaker must have a sufficient withstand capability for

the thermal and electrodynamic effects of the full prospective short circuit.

In a distribution board, this requires the use, upstream, of circuit breakers with adjustable time

delay settings. The upstream breaker must be capable of withstanding the thermal and

electrodynamic effects of the full prospective fault current during the time delay.

17

4.3 POWER FACTOR CORRECTION

Power factor in ac circuits is the ratio of real power (kW) that is used by electric loads to that of

apparent power (kVA) that is supplied to the circuit. KVAR is the reactive or idle component of

power. . The kilo-watt-hour meter does not record the wattless current, so when current is charged

on the basis of units consumed, the distributor is not paid for this current. A load with a low power

factor draws more current than a load with a high power factor for the same amount of useful

power transferred. The high currents increase the energy lost in the distribution system and require

large conductors and equipment. Keeping the power factor close to 1 is a considerable economic

advantage to the utility company and to the consumer.

Power factor correction is the act of increasing the power factor. The power factor should be kept

as close to 1 as possible. Adjusting the power factor will reduce the reactive power in the circuit.

Capacitors are commonly used in correction. The capacitor can be connected in parallel with

individual items or a bank of capacitors can be connected to the main bus. Factors considered

during selection of a capacitor are the capacity, the working voltage and the leakage current.

4.4 GENERATORS

An electrical generator converts mechanical energy to electrical energy. They can be powered by

diesel or gas.

Generators can be classified as standby or portable.

Standby generators are used as permanently set up systems that turn on automatically

when a power failure is detected. They are larger in size and wattage and have a long run

time.

Portable generators are smaller in size and wattage. They are used for outdoor events and

other utilities that require a short run time.

Silent generators are designed to reduce the noise output of generators. Materials that absorb

sound are used in the casing of the generator.

Automatic generators have an auto-transfer switch that can sense power outage and start the

generator. When power is restored, the system connects itself back to the utility lines and turns

itself off. The standby generator connects to the house wiring via the transfer switch. This switch

18

provides protection too. The change-over panel ensures automatic transfer of power from the

mains power supply to the generator power supply within a few seconds interval.

In sizing generators, first the amount of load that will be used under backup has to be determined.

Next, the starting and running wattages of the respective items are determined. These are found on

the identification plate of the items. The total power is then calculated in watts or KVA by

multiplying the current by the voltage.

19

Chapter 5

This chapter is aimed at implementing all the issues discussed in the previous chapters in a

residential estate. During the implementation the various tasks to be carried out in individual units

of the estate, safety factors and also guidelines given by IEE and IES were taken into consideration.

Catalogues such as Searchlight and Thorn were used for luminaires. The residential estate

comprises of 75 housing units. There are 3 different designs of housing units in the residential

estate.

5.1 DESIGN SPECIFICATIONS.

5.1.1 LIGHT FITTINGS.

The types of luminaires used in the design implementation are shown in the table 5-1 below.

Table 5-1. Types of luminaires used

TYPE OF LIGHT FITTING NAMING CONVENTION

1 × 16W POLISHED BRASS flush ceiling mounting as search

light no LE1836-11CW

Type F

26 W LED downlight as THORN CRUZ 160 LED Type G

1 x 28W wall mounted up light as THORN CORACLE Type W

11.5 W THORN BASE JUNIOR LED recessed down lights Type D

1 × 28W THORN SUPER CLUB ceiling mounting. Type B

Ceiling rose complete with lamp holder with 20W compact

fluorescent lamp and decorative with lamp shade.

Type C

1 x 28W wall mounted up light as THORN CORACLE Type S

2 x 9W Outdoor 2-light modern porch wall light as searchlight

no LE3065GY

Type K

1 x 18 W outdoor light as searchlight 280BK Type N

1 x 18W outdoor porch light as searchlight 2942BK Type P

Wall mounted light fitting with shaver unit as thorn BK Type 2D

20

In the lighting circuits the lamp wattage and the voltage were used to calculate the current in each

lighting circuit and the current was used in selecting the size of the switches to be used.

E.g. for luminaire type C, the total wattage of the luminaire was 20 W. The voltage in the circuit

was 240 V. Hence using the formula P=IV

Curre𝑛𝑡 𝐼 = (𝑃𝑜𝑤𝑒𝑟(𝑃))/(𝑉𝑜𝑙𝑡𝑎𝑔𝑒 (𝑉))

= 20 𝑊240𝑉⁄ = 0.083 𝐴

5.1.2 SWITCHES

Using the current calculated for the lighting circuits, single pole switches rated 10 Amps were

used. The main types of switches used were the one-way and the two-way switches. One-way

switches were used for the areas that were accessible via one entrance such as washrooms. Two

way switches were used in areas which could be accessed via two entrances such as kitchen and

also rooms whose lighting needed to be accessed from different parts of the room such as

bedrooms. A switch was placed at each entrance for an area at a mounting height of 1200mm

above finished floor.

5.1.3 SOCKET OUTLETS

The number of socket outlets and the mounting height was in line with the IEE wiring

recommendations. 13 A socket outlets were used mounted at a height of 450mm above finished

floor. The number of sockets in each room was in accordance with the minimum number of twin

socket outlets to be provided in homes as given in Modern Wiring Practice [7] chapter on design

and arrangement of final circuits according to The Electrical Installation Industry Liaison

Committee.

5.1.4 TELEVISION AND DATA POINTS

These ports were installed in areas where data access and telephone services were needed. The

lounge, dining room area and master bedroom had both the television and data points. Other

bedrooms and kitchen were fitted with data points only.

21

5.1.5 SINGLE PHASE LOADS

These included the cooker unit and water heater. Their maximum rated wattages were used to

calculate the load in the circuit. For cooker units, diversity used was 10A plus 30% full load for

appliances in excess of 10 A plus 5 A for cooker units incorporating 13A socket outlets. For water

heaters, the diversity used was 100% full load of the largest appliance plus 100% of the second

largest plus 25% of the remaining appliances as given in IEE ONSITE GUIDE BS 7671 [9]

5.2 DESIGN

Lighting designs for each residential unit type A2, B2 and C2 was done taking one unit from each

type to demonstrate the design. The residential lighting design guide by Contech Lighting [11] was

used to obtain various parameters needed. The guide contains tables from The IES Lighting

handbook 8th edition. The lumen method was used in calculating the number of light fittings of the

various rooms in each housing unit. The IES lighting handbook application volume [4] was also

used to obtain the various parameters that were needed. The THORN catalogue [13],

SEARCHLIGHT catalogue [14] and the PHILLIPS LAMP catalogue [12] were used to give the

various types of luminaires and lamps used and their parameters.

5.2.1 LIGHT DESIGN IN HOUSING UNITS

The lounge in house A2 was used to illustrate how the lumen method was used in calculating

required number of light fittings and the arrangement of the light fittings in the room.

5.2.1.1 CALCULATING NUMBER OF LUMINAIRES

The following steps were used to calculate the number of luminaires;

i. Determination of recommended illuminance.

From the IES handbook application volume, areas devoted to relaxation require a low level of

general lighting to create a pleasant atmosphere for comfort and relaxation. From IES tables, the

recommended illumination is 100 lux.

22

ii. Determination of room dimensions.

The lounge had the following dimensions; Length= 5.54m, Width=5.39m, Height=2.7m.

Taking the height of a table in the lounge as 0.6m, the mounting height Hm= 2.7-0.6= 2.1

iii. Calculating room index.

The room index was calculated using the formula;

K = )WL(H

WL

m

=

)39.554.5(1.2

39.554.5

=1.3

iv. Obtaining the utilization factor (U.F).

The utilization factor was obtained from the utilization factor table in the Technical-lighting design

guide [15] using the room index, ceiling, wall and floor reflectance. The ceiling reflectance was

taken to be to be 70%, the wall reflectance to be 50% and the floor reflectance to be 20% as per

IES lighting handbook application volume [4]. It is not possible to read the room index of 1.3

directly from the tables hence interpolation was used.

For K = 1.25, the UF = 0.55

For K = 1.5, the UF = 0.59.

By interpolation, U.F. = 0.55 + (0.59 – 0.55) ×25.15.1

25.13.1

= 0.558

v. Selection of luminaire

The light fittings selected to be used in the lounge was a 26 W LED downlight as THORN CRUZ

160. With lumen output 2000 lumens, color rendition Ra = 80 and color temperature 3000K.

vi. Obtaining the maintenance factor.

A maintenance factor M.F of 0.7 was used.

vii. Calculation of flux

From the lumen method,

Illuminance, E = Area

M.F U.Fflux Installed

Installed flux = F..MF..U

AE

= lumens 7645 7.0558.0

86.29100

23

viii. Calculating number of fittings

From the Thorn catalogue the lumen output of CRUZ 160 is 2000 lumens per lamp.

Number of fittings = lampper output Lumen

flux Installed

= fittings 5 2000

7645

Five fittings were decided upon since they gave an average illuminance of 140 lux.

ix. Showing arrangement of luminaires.

Luminaires were arranged in order to ensure that all areas of the lounge were well lit and especially

areas with furniture and also ensure uniformity of illumination. In this lighting scheme, the rule

used was that the distance between the ends of adjacent luminaires should be twice the distance

from the luminaire to the wall. The arrangement of luminaires was as shown in fig 5-1 below.

Figure 5-1. Luminaire arrangement in lounge

24

The above concept was applied to all other rooms in all three housing units and the results

summarized in tables in APPENDIX 1.

5.2.1.2 CALCULATING ILLUMINANCE AT A POINT

The point-by- point method was also used to determine the illuminance on a painting on the wall

of lounge in unit A2. The paints’ dimensions were 0.5m x 0.76m and was mounted 1.6m above

the finished floor level. Taking a point P on the painting 1.85m from finished floor, the horizontal

distance from light source to the point whose illuminance is being computed, R was 2.3m, the

vertical mounting height H of the light source above R was 0.48m. The actual distance D from the

light source to the point was 2.77m.The angle between the light ray and the perpendicular to the

plane β= Tan -1 (0.48

2.73) =11.08 0. θ = 78.910. Figure 5-2 below illustrates this.

Figure 5-2. Point by point method for a painting on a wall

The following steps were followed in order to determine the illuminance at point P.

i. Calculating luminous intensity of the lamp

Luminous intensity is given by the equation; I =luminous flux 𝜙

𝛺

25

Where Ω is the solid angle into which the luminous flux is emitted.

Ω= 2𝜋(1 − cos𝛼

2) where α is the apex angle = 850.

Ω= 2𝜋(1 − cos85

2) = 1.65

I = 2000 lumens

1.65 = 1,211 cd

ii. Calculating illuminance

Illuminance is given by the formula

E = I x sin θ x cos2 θ

H2

E =1211 x sin 78.91 x cos2 78.91 = 190 lux

0.482

5.2.2 ROAD LIGHTING DESIGN

Road lighting design specifications were based on IES lighting handbook application volume. The

recommended illuminance values were from Roadway Lighting Design Guide- SaskPower [5]

with tables from IESNA [4].

i. Determination of recommended illuminance.

For local roads with low pedestrian conflict, using IESNA tables [4], the recommended average

maintained illuminance is 8 lux.

ii. Road width

The width of the road from curb to curb is 9m

iii. Selection of luminaire

The luminaire selected was Thorn JET 1 with a mounting height of 6m, using 57 W TC-TEL lamp

with lumen output of 4200 lumens, CRI= 80, and overhang distance (from pavement curb to

projection of luminaire) = 0.4m.

iv. Arrangement of luminaire.

The luminaire arrangement chosen was the one-sided arrangement.

26

v. Obtaining the utilization factor (U.F).

To calculate the utilization factor, for street lighting using IES tables,

Ratio = height mounting Luminaire

side) houseor (road width Transverse

For road side, Ratio =height mounting Luminaire

overhang - widthroad

= 43.16

0.4 -9 UF for road side= 0.35

For house side, Ratio =height mounting Luminaire

widthroad

= 5.16

9 UF for house side= 0.28

Total utilization factor = road side UF + house side UF

= 0.35 + 0.28 = 0.63

vi. Maintenance factor

The maintenance factor of the luminaire is 0.86

vii. Finding the spacing between two luminaires

Using the average illuminance method where

Average illuminance Eav = x WSS

M.F U.F LL

Where, LL- Initial lamp lumens

UF - utilization factor W – Road width

MF - Maintenance factor

SS - Luminaire spacing

The luminaire spacing was given as SS = 9 x 8

0.86 0.63 4200 = 31 meters.

27

5.3 LOAD CALCULATION IN HOUSING UNITS

For every housing unit, a count of the number of fittings, number of socket outlets and single phase

loads was done and grouped into the final circuits that would be used in the consumer unit. This

was then used to calculate the load current in the consumer units while putting diversity and load

growth into consideration.

5.3.1 LOAD CALCULATION IN UNIT A2

Housing unit A2 was used to show how the various loads were calculated. In this housing unit

several light fittings were used in the house. The lighting circuits were grouped into 4 final circuits,

2 circuits serving upstairs and two downstairs. This is to avoid total blackouts incase the circuit

breaker trips. A diversity factor of 66% was used in calculating the loads. The wattage of the

individual circuits was 176.88 W, 298.98 W, 237 W and 217.43 W. The voltage drop per meter

was also considered when selecting the number of light fittings in one circuit according to IEE the

voltage drop for lighting circuits should not exceed 3% of the nominal voltage. The calculation of

lighting final circuits was summarized in table in appendix 2.

Ring circuits were used in the final circuits of the socket outlets. 32 A ring circuits were used and

the maximum floor area to be covered by the ring circuits is 100m2. The ground floor area was

more than 100m2 hence a total of 2 ring circuits were used in unit A2. A diversity factor of 100%

was used for the largest point of utilization and 40% for every other points of utilization. The total

wattage for the most utilized ring circuit was 32A x 240V= 7680W. The other ring circuit had a

wattage of 7680 x 0.4 = 3072 W.

The cooker unit and water heater were the single phase loads in the housing units hence were

allocated their individual circuits. Cooker units rated 45 A was used hence applying diversity factor

= 10A+ 10.5A +5A = 25.5A. This gives a wattage of 6120 W.

Provision was also made for a 60 gallon solar water heater with electric heating element rated 1500

watts used for back-up to heat water further when there is not enough sunshine such as ASSOS

and SECUterm solar water heaters. Current rating of the water heater was 1500/240 = 6.25 A. The

above implementation is summarized in table 5-2. The loads in units B2 and C2 were calculated

in a similar manner and the results shown in table 2-5 and 2-6 in appendix 2.

28

Table 5-2. Calculation of maximum demand in unit A2

LOAD Diversity factor Total load(Watts) Total load current(A)

Lighting circuit 1 0.66 176.88 W 0.74A

Lighting circuit 2 0.66 298.98W 1.25A

Lighting circuit 3 0.66 237 W 0.99A


Circuit .T 0.66 130.68W 0.54A

Ring circuit 1 1 7680 W 32A

Ring circuit 2 0.4 3072 W 13A

Cooker unit

10A+30%for

appliances in excess

of 10A + 5A for

socket incorporation

6120 W

25.5A

Water heater 1 1500 W 6.25 A

TOTAL 19,433 W 80.97 A

5.4 SUMMERY OF LOAD IN THE ESTATE

The estate had 75 housing units. The housing unit A2 had a total of 11 houses, unit B2 had a total

of 40 houses and unit C2 had a total of 24 houses. The end gain of this part of the project was to

ensure that the load on the three phases of the incoming cable of the service turret was balanced.

The load on each consumer unit was tabulated and then individual loads were spread on all phases

to achieve balance.

29

5.4.1 HOUSING UNIT A2

There were a total of 11 houses of type A2 each having a total load of 19,433 W and a total load

current of 80.97 A. The load currents of the consumer units were tabulated and spread across the

phases as shown in table 5-3

Table 5-3 Summery of loads in unit A2

NAME Load

(watts)

Load

current

(Amps)

Consumer

Unit

RED

PHASE

LOAD

(Amps)

YELLOW

PHASE

LOAD

(Amps)

BLUE

PHASE

LOAD

(Amps) House 1 19,433 80.97 CU-A2- 1 80.97

House 2 19,433 80.97 CU-A2-2 80.97

House 3 19,433 80.97 CU-A2-3 80.97

House 4 19,433 80.97 CU-A2-4 80.97

House 5 19,433 80.97 CU-A2-5 80.97

House 6 19,433 80.97 CU-A2-6 80.97

House 7 19,433 80.97 CU-A2-7 80.97

House 8 19,433 80.97 CU-A2-8 80.97

House 9 19,433 80.97 CU-A2-9 80.97

House 10 19,433 80.97 CU-A2-10 80.97

House 26 19,433 80.97 CU-A2-26 80.97

TOTAL

LOAD

213,763 323.88 242.91 323.88

5.4.2 HOUSING UNIT B2

Type B2 had a total of 40 houses each having a total load of 19,310 W and a load current of

80.45A. The consumer load units were tabulated and spread across the phases as shown.

Table 5-4 Summery of loads in unit B2

NAME Load

(watts)

Load

current

(Amps)

Consumer

Unit

RED

PHASE

LOAD

(Amps)

YELLOW

PHASE

LOAD

(Amps)

BLUE

PHASE

LOAD

(Amps)

House 11 19,310 82.74 CU-B2-11 80.45

House 12 19,310 82.74 CU-B2-12 80.45

House 13 19,310 82.74 CU-B2-13 80.45

House 14 19,310 82.74 CU-B2-14 80.45

House 15 19,310 82.74 CU-B2-15 80.45

House 16 19,310 82.74 CU-B2-16 80.45

30

NAME Load

(watts)

Load

current

(Amps)

Consumer

Unit

RED

PHASE

LOAD

(Amps)

YELLOW

PHASE

LOAD

(Amps)

BLUE

PHASE

LOAD

(Amps)

House 17 19,310 82.74 CU-B2-17 80.45

House 18 19,310 82.74 CU-B2-18 80.45

House 19 19,310 82.74 CU-B2-19 80.45

House 20 19,310 82.74 CU-B2-20 80.45 House 21 19,310 82.74 CU-B2-21 80.45

House 22 19,310 82.74 CU-B2-22 80.45

House 23 19,310 82.74 CU-B2-23 80.45

House 24 19,310 82.74 CU-B2-24 80.45

House 25 19,310 82.74 CU-B2-25 80.45

House 27 19,310 82.74 CU-B2-27 80.45

House 28 19,310 82.74 CU-B2-28 80.45

House 29 19,310 82.74 CU-B2-29 80.45

House 30 19,310 82.74 CU-B2-30 80.45

House 31 19,310 82.74 CU-B2-31 80.45

House 32 19,310 82.74 CU-B2-32 80.45

House 33 19,310 82.74 CU-B2-33 80.45

House 34 19,310 82.74 CU-B2-34 80.45

House 35 19,310 82.74 CU-B2-35 80.45

House 36 19,310 82.74 CU-B2-36 80.45

House 37 19,310 82.74 CU-B2-37 80.45

House 38 19,310 82.74 CU-B2-38 80.45

House 39

19,310 82.74 CU-B2-39 80.45

House 40 19,310 82.74 CU-B2-40 80.45

House 41 19,310 82.74 CU-B2-41 80.45

House 42 19,310 82.74 CU-B2-42 80.45

House 43 19,310 82.74 CU-B2-43 80.45

House 44 19,310 82.74 CU-B2-44 80.45

House 45 19,310 82.74 CU-B2-45 80.45

House 46 19,310 82.74 CU-B2-46 80.45

House 47 19,310 82.74 CU-B2-47 80.45 House 48 19,310 82.74 CU-B2-48 80.45 House 49 19,310 82.74 CU-B2-49 80.45 House 50 19,310 82.74 CU-B2-50 80.45 House 51 19,310 82.74 CU-B2-51 80.45

TOTAL

LOAD

772,400

1045.85 1045.85 1126.

3

31

5.4.2 HOUSING UNIT C2

Type C2 had a total of 24 houses each having a total load of 19,167W and a load current of 79.86A.

The consumer load units were tabulated and spread across the phases as shown.

Table 5-5 Summery of loads in unit C2

NAME Load

(watts)

Load

current

(Amps)

Consumer

Unit

RED

PHASE

LOAD

(Amps)

YELLOW

PHASE

LOAD

(Amps)

BLUE

PHASE

LOAD

(Amps) House 52 19,167 79.86 CU-C2-52 79.86

House 53 19,167 79.86 CU-C2-53 79.86

House 54 19,167 79.86 CU-C2-54 79.86

House 55 19,167 79.86 CU-C2-55 79.86

House 56 19,167 79.86 CU-C2-56 79.86

House 57 19,167 79.86 CU-C2-57 79.86

House 58 19,167 79.86 CU-C2-58 79.86

House 59 19,167 79.86 CU-C2-59 79.86

House 60 19,167 79.86 CU-C2-60 79.86

House 61 19,167 79.86 CU-C2-61 79.86

House 62 19,167 79.86 CU-C2-62 79.86

House 63 19,167 79.86 CU-C2-63 79.86

House 64 19,167 79.86 CU-C2-64 79.86

House 65 19,167 79.86 CU-C2-65 79.86

House 66 19,167 79.86 CU-C2-66 79.86

House 67 19,167 79.86 CU-C2-67 79.86

House 68 19,167 79.86 CU-C2-68 79.86

House 69 19,167 79.86 CU-C2-69 79.86

House 70 19,167 79.86 CU-C2-70 79.86

House 71 19,167 79.86 CU-C2-71 79.86

House 72 19,167 79.86 CU-C2-72 79.86

House 73 19,167 79.86 CU-C2-73 79.86

House 74 19,167 79.86 CU-C2-74 79.86

House 75 19,167 79.86 CU-C2-75 79.86

TOTAL

LOAD

460,008

638.88 638.88 638.88

32

5.4.3 TOTAL LOAD IN THE WHOLE ESTATE

The total load in the whole estate across the phases is as shown in table 5-6.

Table 5-6 Summery of loads in the estate

NAME Load

(watts)

Load

current

(A)

Number of

consumer

Units

RED

PHASE

LOAD (A)

YELLOW

PHASE

LOAD (A)

BLUE

PHASE

LOAD (A)

UNIT A2 213763

890.6

11 323.88 323.88 242.91

UNIT B2 772,400

3218.3

40 1045.85 1045.85 1126.3

UNIT C2 460,008 1916.7 24 638.88 638.88 638.88

TOTALS 1446171 75 2008.6 2008.6 2008.1

The overall load currents were 2008.6A on the red phase, 2000.6A on the yellow phase and

2008.1A on the blue phase. Balance was hence achieved. The total current for all the phases was

6025.3A.

5.4 CIRCUIT BREAKERS AND CONSUMER UNITS

From the Eaton MEM catalogue [15] in appendix 3, the standard ratings for Miniature Circuit

Breakers (MCBs) are 1A, 2A, 4A, 6A, 8A, 10A, 13A, 16A, 20A, 25A, 32A, 40A, 50A, and 63A.

The standard consumer unit (CU) sizes are 4-way, 6-way, 8-way, 10-way, 12-way, 16-way, 18-

way and 24-way. Sizing of the MCB was done by calculating the load current then checking for

the rating of the MCB just above it.

5.4.1 CIRCUIT BREAKERS IN HOUSING UNITS

Housing unit A2 was used to show how the size of the circuit breaker and cables were selected.

The naming convention used for the distribution boards in housing units A2 was DB-A2-house

number this represented the distribution board, the type of housing unit it was in and the house

number.

33

The lighting loads were 194.04 W, 279.18 W, 296.67 W and 268.95 W. The current by each

lighting load was calculated as shown below;

Current in CIR.L1 = 176.88

240= 0.74 A


240= 1.25 A

Current in CIR.L3 = 237

240= 0.99 A


240= 0.91 A

Current in CIR.T =130.68

240= 0.54 A

A 4A, 10 kA, trip type B, SP MCB from Eaton MEM catalogue was therefore chosen as protection

for each lighting load. 1mm2 2-core PVC insulated cables were used.

Ring circuits were protected by a 32A, 10 kA, trip type B, DP MCB. 2.5 mm2 3-core PVC

insulated cables were used.

The cooker had a total load of 6120W and a current of 6120

240 = 25.5 A. The MCB chosen for

cooker protection was a 32A, 10 kA, trip type B, DP MCB. 6 mm2 3-core PVC insulated cables

were used.

The water heater load was 1500W and the current given was 1500

240= 6.25 A. The MCB chosen for

the water heater protection was a 10A, 10 kA, trip type B, DP MCB. 2.5 mm2 3-core PVC insulated

cables were used.

RCDs (residual current devices) rated 30 mA were used to protect circuits that are in wet areas

such as bathrooms and socket outlets.

A summary of the MCB ratings is given in table 5-7. Taking the hose number to be 1. The

distribution board label was DB-A2-1

34

Table 5-7 : MCBs in DB-A2-1

Type of load Total load

(Watts)

Total

Current

load (A)

MCB

size

Cable size (mm2)

Lighting CIR.LI 194.04W 0.74A 4A 1mm2

Lighting CIR.L2 298.98W 1.25A 4A 1mm2

Lighting CIR.L3 237 W 0.99A 4A 1mm2


Circuit .T 130.68W 0.54A 4A 1mm2

Ring circuit CIR.R1 7680W 32A 32A 2.5 mm2


Cooker CIR.DI 6120W 25.5A 32A 6 mm2

Water heater 1500W 6.25A 10A 2.5 mm2

The same procedure above was applied to the other housing units B2 and C2 and the results were

as shown in table 2-7 and 2-8 in appendix 2.

5.4.2 CONSUMER UNITS

The total load for housing unit A2, B2 and C2 as calculated was 19,433 W, 19,310 W and 19,167W

respectively. The currents by each load was given as 80.97A, 80.45A, 79.86A respectively.

Given the current on each load, consumer units with integral isolator of 100A and 14 circuit

breaker ways were used in each housing unit. The naming convention used for the distribution

boards in unit A2 was CU-A2 then followed by the house number. Consumer units for units B2

and C2 were labeled CU-B2 and CU-C2 respectively. The location of the consumer units had to

be taken into consideration so as to reduce the voltage drops and cost of cables. A total number of

75 consumer units was installed in the estate to cater for each house.

35

From the AutoCAD drawings attached, the consumer units were located in the store room of each

room of the housing unit. . A diagram depicting the arrangement of consumer unit for house

number 1 house type A2 is shown in figure 5-3. The consumer units for the other houses were

similar to that of house A2-1.

Figure 5-3 consumer unit arrangement for CU-A2-1

5.5 SERVICE TURRETS

Distribution of power to the houses was done using underground cables. Underground cables were

preferred due to the low maintenance costs because they rarely get damaged, improved reliability

since power interruptions are minimal as the risk of getting damaged due to severe weather such

as wind and storm surges is reduced. Underground cables also improve the property value as they

improve the aesthetics of the estate by removal of poles and structures that impact sidewalks.

Service turrets are used to distribute power throughout the estate. Each low voltage turret was

provided with a manhole and a service conduit from the manhole of each residential estate.

36

According to KPLC, service turrets feeding low voltage distribution systems and made for outdoor

use have the following specifications;

The service turret is designed to have 18 single phase circuits of 100A rating (outgoing circuits in

a 6x3- phase configuration) with cut-outs arranged with fuses in accordance to BS1361.

The rated voltage of the service turrets was 0.6/1kV and the rated current was 600A.

The total number of consumer units was 75 as seen in section 5.4. In selecting the number of

service turrets and determining their positions, the location of the consumer units had to be taken

into consideration. A longer cable between the service turret and the consumer unit could lead to

large voltage drops and greater cost of cables; which was undesirable in design.

From the AutoCAD drawings attached, the consumer units were located in the store of each

housing unit. The distance from the consumer unit to the power manhole which was located at a

corner outside the yard wall was approximately 8m. In order to avoid large voltage drops,

consumer units were grouped and lumped in such a way that the consumer units were served with

the turret closest to them.

The arrangement as shown in the AutoCAD drawing was such that the maximum number of houses

allowed on each phase of the turret was 3. The total number of turrets was 10.

5.6 CONSUMER UNIT CABLE SIZING.

The current in each housing unit was as 80.97A, 80.45A and 79.86A for unit A2, B2 and C2

respectively. The consumer units were lumped as follows;

Consumer units for houses 1,2,3,4 were fed by turret number 1

Consumer units for houses 5,6,7,8,9,10 were fed by turret number 2

Consumer units for houses 11,12,26,27,28 were fed by turret number 3

Consumer units for houses 13,14,15,16,29,30,31,32 were fed by turret number 4



Consumer units for houses 48,49,50,51,62,63,64,65,66 were fed by turret number 7


37

Consumer units for houses number 17,18,19,20,33,34,35,36,37 were fed by service turret

number 9


The above was shown in the AutoCAD drawings provided.

The distances between the consumer units and the respective service turrets were measured. In

order to cater for future load growth, the actual growth was increased by 20%. This gave the

revised load. Since the installation was underground, PVC insulated, PVC sheathed cables were

used. A maximum voltage drop of 1.5 % was allowed for cables feeding consumer units from the

distribution boards. Using the Bahra Cables Company catalogue in appendix 4, the voltage drop

rate was obtained using the design current. The values obtained were used to calculate the voltage

drop as follows:

240

100

1000

m)rate(mV/A/ drop voltagecurrent load revised length(m) drop voltage%

5.6.1 CABLE SIZING FOR CU-A2-1

The total load current for houses in unit A2 was 80.97A. The revised load was thus 120% of

80.97A which was 97A. The distance from the service turret to the house was 41m. A 70 mm2 core

copper conductor with a voltage drop of 0.61 mV/A/m and a current carrying capability of 154 A

was selected. The voltage drop was given as;

240V

100

1000

0.61mV/A/m A 97 41m drop voltage%

= 1.00 %

The % voltage drop was less than 1.5 % hence the conductor was selected.

The same concept was applied to the remaining CUs in the estate and the results summarized in

table 5-8.

38

Table 5-8 Cable sizes used for consumer units

CU Load

current

(A)

Design

current

(A)

Cable

length

(m)

Cable

size

(mm2)

Current

carrying

capability

(A)

Voltage

drop rate

(mV/A/m)

Voltage

drop (V)

% voltage

drop

CU-A2-1 80.97 97 41 70 154 0.61 2.42 1.00

CU-A2-2 80.97 97 48 70 154 0.61 2.84 1.18

CU-A2-3 80.97 97 40 70 154 0.61 2.36 0.98

CU-A2-4 80.97 97 41 70 154 0.61 2.42 1.00

CU-A2-5 80.97 97 43 70 154 0.61 2.54 1.06

CU-A2-6 80.97 97 33 70 154 0.61 1.95 0.81

CU-A2-7 80.97 97 29 70 154 0.61 1.71 0.71

CU-A2-8 80.97 97 38 70 154 0.61 2.24 0.93

CU-A2-9 80.97 97 46 70 154 0.61 2.72 1.13

3 CU-A2-10 80.97 97 63 70 154 0.61 3.72 1.50

CU-A2-26 80.97 97 30 70 154 0.61 1.78 0.74

CU-B2-11 80.45 97 34 70 154 0.61 1.95 0.81

CU-B2-12 80.45 97 26 70 154 0.61 1.53 0.64

CU-B2-13 80.45 97 42 70 154 0.61 2.48 1.03

CU-B2-14 80.45 97 30 70 154 0.61 1.83 0.76

CU-B2-15 80.45 97 36 70 154 0.61 2.13 0.88 CU-B2-16 80.45 97 58 70 154 0.61 3.43 1.43

CU-B2-17 80.45 97 58 70 154 0.61 3.43 1.43

CU-B2-18 80.45 97 38 70 154 0.61 2.24 0.93

CU-B2-19 80.45 97 28 70 154 0.61 1.66 0.69

CU-B2-20 80.45 97 38 70 154 0.61 2.24 0.93

CU-B2-21 80.45 97 50 70 154 0.61 2.96 1.23

CU-B2-22 80.45 97 33 70 154 0.61 1.95

0.81 CU-B2-23 80.45 97 25 70 154 0.61 1.48 0.62

CU-B2-24 80.45 97 43 70 154 0.61 2.54 1.06

CU-B2-25 80.45 97 34 70 154 0.61 1.95 0.81

CU-B2-27 80.45 97 25 70 154 0.61 1.48 0.62

CU-B2-28 80.45 97 35 70 154 0.61 2.07 0.86

CU-B2-29 80.45 97 36 70 154 0.61 2.13 0.88

CU-B2-30 80.45 97 24 70 154 0.61 1.42 0.59

CU-B2-31 80.45 97 33 70 154 0.61 1.95 0.81

CU-B2-32 80.45 97 50 70 154 0.61 2.95 1.23

CU-B2-33 80.45 97 58 70 154 0.61 3.43 1.43

CU-B2-34 80.45 97 39 70 154 0.61 2.30 0.96

CU-B2-35 80.45 97 31 70 154 0.61 1.83 0.76

CU-B2-36 80.45 97 26 70 154 0.61 1.53 0.64

CU-B2-37 80.45 97 36 70 154 0.61 2.13 0.88

CU-B2-38 80.45 97 34 70 154 0.61 1.95 0.81

CU-B2-39 80.45 97 25 70 154 0.61 1.48 0.62

39

CU Load

current

(A)

Design

current

(A)

Cable

length

(m)

Cable

size

(mm2)

Current

carrying

capability

(A)

Voltage

drop rate

(mV/A/m)

Voltage

drop (V)

%

voltage

drop

CU-B2-40 80.45 97 38 70 154 0.61 2.24 0.93

CU-B2-41 80.45 97 29 70 154 0.61 1.71 0.71

CU-B2-42 80.45 97 29 70 154 0.61 1.71 0.71

CU-B2-43 80.45 97 46 70 154 0.61 2.72 1.13

CU-B2-44 80.45 97 31 70 154 0.61 1.83 0.76

CU-B2-45 80.45 97 29 70 154 0.61 1.71 0.71

CU-B2-46 80.45 97 31 70 154 0.61 1.83 0.76

CU-B2-47 80.45 97 45 70 154 0.61 2.66 1.11

CU-B2-48 80.45 97 33 70 154 0.61 1.95 0.81

CU-B2-49 80.45 97 23 70 154 0.61 1.36 0.56

CU-B2-50 80.45 97 29 70 154 0.61 1.71 0.71

CU-B2-51 80.45 97 40 70 154 0.61 2.36 0.98

CU-C2-52 79.86 96 34 70 154 0.61 1.99 0.82

CU-C2-53 79.86 96 26 70 154 0.61 1.52 0.63

CU-C2-54 79.86 96 42 70 154 0.61 2.45 1.02

CU-C2-55 79.86 96 34 70 154 0.61 1.99 0.83

CU-C2-56 79.86 96 26 70 154 0.61 1.52 0.63

CU-C2-57 79.86 96 35 70 154 0.61 2.04 0.85

CU-C2-58 79.86 96 50 70 154 0.61 2.92 1.22

CU-C2-59 79.86 96 45 70 154 0.61 2.63 1.09

CU-C2-60 79.86 96 31 70 154 0.61 1.82 0.76

CU-C2-61 79.86 96 31 70 154 0.61 1.82 0.76

CU-C2-62 79.86 96 57 70 154 0.61 3.34 1.40

CU-C2-63 79.86 96 42 70 154 0.61 2.45 1.02

CU-C2-64 79.86 96 33 70 154 0.61 1.93 0.80

CU-C2-65 79.86 96 27 70 154 0.61 1.58 0.66

CU-C2-66 79.86 96 34 70 154 0.61 1.99 0.83

CU-C2-67 79.86 96 42 70 154 0.61 2.45 1.02

CU-C2-68 79.86 96 38 70 154 0.61 2.23 0.92

CU-C2-69 79.86 96 30 70 154 0.61 1.76 0.73

CU-C2-70 79.86 96 36 70 154 0.61 2.11 0.87

CU-C2-71 79.86 96 46 70 154 0.61 2.69 1.12

CU-C2-72 79.86 96 44 70 154 0.61 2.58 1.07

CU-C2-73 79.86 96 34 70 154 0.61 1.99 0.83

CU-C2-74 79.86 96 35 70 154 0.61 2.04 0.85

CU-C2-75 79.86 96 48 70 154 0.61 2.81 1.17

40

5.7 SERVICE TURRET CABLE SIZING

5.7.1 CABLES FEEDING SERVICE TURRET 1.

Service turret 1 fed CU-B2-17, CU-B2-18, CU-B2-19, CU-B2-20, CU-B2-33, CU-B2-34, CU-B2-

35, CU-B2-36 and CU-B2-37. The total phase load was found by summing up the currents on each

phase. Load current on the red phase was 162A, the yellow phase was 80.97 and blue phase was

80.97 A. Current of the red phase was used to size the cables as it was the largest. This current was

increased by 20% to cater for future load growth. The design current was therefore: 162 × 1.2 =

194A. The length of the cable connecting this service turret to the switch room was found to be

33m. A maximum voltage drop of 2 % was allowed. A 240 mm2 PVC insulated, PVC sheathed

conductor with a current carrying capacity of 301A and a voltage drop of 0.23 mV/A/m was

selected. The percentage voltage drop was thus calculated as

415V

100

1000

mV/A/m 0.23 A 194 m 33 drop voltage%

= 0.35 %

Since the percentage voltage drop was less than 2 % then the conductor was suitable. The cable

sizes of the other service turrets was selected and summarized in table 5-9.

Table 5-9 Cable sizes for service turrets

Service

turret

Largest

Load

current

(A)

Design

current

(A)

Cable

length

(m)

Cable

size

(mm2)

Current

carrying

capability

(A)

Voltage

drop rate

(mV/A/m)

Voltage

drop (V)

%

voltage

drop

ST.1 162.00 194 33 240 301 0.23 1.47 0.35

ST.2 162.00 194 53 240 301 0.23 2.36 0.98

ST.3 161.00 194 70 240 301 0.23 3.12 0.75 ST.4 241.35 290 125 300 339 0.20 7.25 1.75

ST.5 241.35 290 50 300 339 0.20 2.9 0.69

ST.6 241.35 290 123 300 339 0.20 7.13 1.72

ST.7 241.35 290 100 300 339 0.20 5.80 1.39

ST.8 241.35 290 62 300 339 0.20 3.60 0.87

ST.9 241.35 290 86 300 339 0.20 5.00 1.20

ST.10 241.35 290 15 300 339 0.20 6.03 0.15

41

Chapter 6

6.1 TRANSFORMER SIZE

The total line current of the entire estate was calculated as 2366.97A 0.85 415 3

1446171 IL

The total load of the estate in kVA was thus given by = √3 × IL × VL

=√3 × 2366.97 ×415

=1701.38 kVA

It was proposed that 2 pad mounted transformers rated 1000 kVA with a reactance of 4.75% per

unit to be used to supply the estate. The load of the estate was thus split into 2. Transformer 1

would be used to supply a load 1 with a total load of 908.95 kVA and transformer 2 used to supply

load 2 with a total load of 792.43 kVA.

6.1.1 TRANSFORMER 1 TOTAL LOAD

Table 6-1 shows how loads from various houses were distributed to the transformers and how load

balancing was to be achieved in each phase.

Table 6-1 distribution of loads in transformer 1

Housing

unit

Total

load

(watts)

Number

of

houses

Load

current

(Amps)

RED PHASE

LOAD(Amps)

YELLOW

PHASE

LOAD(Amps)

BLUE

PHASE

LOAD(Amps)

A2 213,763 11 80.97 323.9 242.91 323.9

B2 405,510 21 80.45 402.25 563.15 724.05

C2 153,336 8 79.86 399.3 159.72 79.86

TOTAL 772,609 1125.45 965.78 1127.8

The total load on transformer 1(TX 1) was 772,609 watts which was equal to 908.95 kVA.

42

6.1.2 TRANSFORMER 2 TOTAL LOAD

Table 6-2 Distribution of loads in transformer 2

Housing

unit

Total

load

(watts)

Number

of

houses

Load

current

(Amps)

RED PHASE

LOAD(Amps)

YELLOW

PHASE

LOAD(Amps)

BLUE

PHASE

LOAD(Amps)

B2 366,890 19 80.45 643.60 482.7 402.25

C2 306,672 16 79.86 239.58 479.16 559.02

TOTAL 673,562 883.18 961.86 961.27

The total load on transformer 2(TX 2) was 673,572 watts which was equal to 792.43 kVA.

6.2 BACKUP GENERATOR

Back-up generators in residential areas are becoming increasingly common providing backup

when the supply from KPLC is cut-out. It was therefore proposed that the power supply in the

residential estate be backed up by a standby generator. Backing up the whole estate seemed like

an expensive idea since the capacity of the generator would be large; but for continuity of house-

hold activities such as lighting, use of socket outlets and water heating, the back-up plan would be

of great advantage. This also attracted potential clients to purchase houses since the area was under

continuous power supply.

6.2.1 CAPACITY OF THE STANDBY GENERATOR

Two separate generators were selected to act as a stand-by power supply for loads served by

transformer 1 and 2.

In order to determine the size of generator required, the total load of the estate was considered.

The total load served by transformer 1 was 908.95 kVA. The load served by transformer 2 was

43

792.43 kVA. The optimal load of the generator was assumed to be 80% of the full load hence the

total load was found as: For load 1

80% = 908.95 kVA

100% = kVA19.113680

10095.908

For load 2

80% = 792.43 kVA

100% = kVA54.99080

10043.792

A standard 1250 kVA, 50Hz Cummins generator was found appropriate for load 1 and 1000 kVA

for load 2 since it could easily accommodate the load. Diesel was the selected source of fuel as it

is readily available. In order to deal with the noise challenges, a muffler was included to reduce

the noise produced by the generator.

6.2.2 CABLE SIZE OF THE STANDBY GENERATOR

Standby generator for load 1 supplied 1250 kVA of power at 50Hz, 1500 rpm. The line current

(IL) was:

A 1739 415 3

KVA 1250 IL

For load 2 a 1000 kVA generator supplied power. The line current was given by

1391.2A 415 3

KVA 1000 IL

44

From the standard cable sizes tables in appendix 3, no cable had a current carrying capability that

matched 1739A or 1391.2A. The current was therefore divided into three so that three parallel

cables were used in supply. Design current for generator 1 was hence 579.67A and for generator

2 was 463.7A. This is illustrated in figure 6-1.

The length of the cable from the generator 1 to the switch board was 7m. A maximum of 2%

voltage drop was allowed on this cable. Therefore:

415

100

1000

0.15mV/A/m 579.67A 7m drop voltage%

= 0.15%.

0.15 % is less than 2%, thus 500mm2 XLPE insulated and PVC sheathed 3-core copper

conductor with a voltage drop rate of 0.15mV/A/m and a current carrying capacity of 597A was

selected.

For generator 2 the length to the switch board was 3m. The voltage drop was given as;

415

100

1000

0.19mV/A/m 463.7A 7m drop voltage%

= 0.15 %.

A 400mm2 XLPE insulated and PVC sheathed 3-core copper conductor with a voltage drop of

0.19 mV/A/m and a current carrying capacity of 478A was selected

BUS BARS

RED YELLOW BLUE

FROM GENERATOR: 3 -

THREE PHASE CABLES

IN PARALLEL

Figure 6-1 Cables feeding the generator

45

6.3 ELECTRICAL DISTRIBUTION SYSTEM RETICULATION.

Figure 6-2 Electrical distribution system reticulation for transformer 1

Figure 6-3 Electrical distribution system reticulation for transformer 2

46

6.4 POWER FACTOR CORRECTION

Capacitor banks were used in the correction of the power factor. They were installed at the switch

board. Load 1 was 908.95kVA. A power factor of 0.85 is assumed before correction and a power

factor of 0.9 after correction, as required by KPLC. The power factor before and after correction

is as shown in figure 6-4.

Since a 104.47kVAR capacitor bank was not available in the market, a 150kVAR ABB 300series

capacitor bank electronically switched in 3 steps of 50kVAR each was selected.

The distance of the capacitor bank from the switch board was 5m. The maximum current drawn

by the capacitor bank = 3 415V

1000 104.47kVAR

= 145.34A

The 4-core PVC copper non-armoured 50mm2 cable with a current carrying capacity of 149A and

a voltage drop rate of 0.8mV/A/m was found appropriate. The voltage drop was 0.14%. Load 2

used the same capacitor bank rating.

6.5 DETERMINATION OF PROSPECTIVE FAULT CURRENTS

6.5.1 FAULT CURRENT AT THE SWITCHBOARD LEVEL

The fault current that was likely to occur at the switchboard level was calculated. The worst fault

that would occur was a 3 phase fault.

For both transformer 1 and 2 the transformer size was 1000kVA (KPLC provided). This gave the

base kVA (kVAB).

KVAR after power factor

correction

Capacitor bank

= 478.66 – 374.19

= 104.47kVAR

KVAR after power factor

correction

= 772.61kW tan 25.84°

= 374.19kVAR

KVAR before power factor

correction

= 772.61KW tan31.78°

= 478.66kVAR

908.95KVA

772.61KW

Cos-1 0.9

Cos-1 0.85

Figure 6-4 Power factor correction diagram

47

Base kV (kVB) was the transformer’s secondary voltage = 415V

MVA

)(kV impedane Base

B

B2

= 0.1722 1

415.0 2

The per unit (p.u) reactance for a 1000kVA transformer = 0.0475 p.u

The length of the cable from the transformer to the switch room = 10m = 0.01km

The series impedance of the feeder = 0.12 + j0.48 Ω/phase/km.

The actual feeder impedance was hence given by (0.12 + j0.48) Ω/phase/km × 0.01km = 0.0012+

j0.0048 Ω/phase

p.u impedance of feeder = impedance Base

impedance Actual

= p.u 0.028 j 0.007 0.1722

j0.0048 0.0012

The most severe fault was a three phase fault; therefore there was need to determine the three phase

fault at the bus bars.

impedancep.u

ep.u voltag current fault .u p

p.u IFimpedancefeeder impedancep.u r transforme

ep.u voltag

p.u 84.7- 13.19 j0.028 0.007 j0.0475

1

The base current (IB) = 0.415 3

1000

KV Base 3

KVA Base

= 1391.2A

The actual current I = Base current IB × p.u IF

= 84.7- 13.19 A 1391.2

= 18.4 kA (This is the 3-phase fault current at the switchboard level). This

was the same for transformer 2.

48

6.5.2 FAULT CURRENT AT THE BEGINNING OF THE FINAL CIRCUITS

Figure 6-5 Layout for fault calculation

Figure 6-4 shows the layout for the fault calculation for a fault occurring a final circuit.

In CU-A2-1, the largest MCB on this CU was rated 32A and it protected the kitchen unit. The total

load current drawn by this CU was 80.97A. In order to maintain discrimination between the

consumer unit and the service turret and also to protect the consumer unit, if a fault occurs in the

kitchen ring final circuit, the MCB protecting it should trip. If it does not, the fuse in service turret

5 will break to clear the fault. The fault current is calculated as follows;

Let X Ω: impedance of one phase winding of the transformer

Z1 Ω: impedance of one phase and neutral of the KPLC incomer

Z2 Ω: impedance of one phase and neutral of the cable between the switchboard and the service

turret.

Z3 Ω: impedance of the phase and neutral of the cable between the service turret and the

consumer unit

The p.u transformer impedance = j0.0475 Ω since the base impedance is 0.1722 Ω as calculated

in section 6.5.1, the actual impedance Z = base impedance × p.u impedance

= 0.1722 × j0.0475

X = j0.0081 Ω

In order to take into account the live and the neutral conductors, the impedances were multiplied

by 2.

Impedance of the KPLC incomer Z1= (0.12 + j0.48) Ω/phase/km × 0.01 km × 2

= 0.0024+ j0.0096

49

Impedance of the cable between lv switchboard and service turret Z2,

= 0.0764 x 0.033 x 2 = 0.005

Impedance of the cable between service turret and consumer unit Z3,

= 0.321 x 0.041 x 2 = 0.026

The fault current was therefore, IF = 321 Z Z Z

240

X

= 0.026 0.005 0.0096 j 0.0024 0081.0

240

j

IF = A 9.276349

The above implementation was applied to the rest of the consumer units and the results

summarized in table 6-3. Fault current levels for the service turrets was summarized in table 2-9,

appendix 2.

Table 6-3 Prospective fault levels for the consumer units

CU

NAME

CABLE SIZE

(mm2)

CABLE LENGTH

(m)

IMPEDANCE

(Ω)

FAULT

CURRENT (A)

CU-A2-1 70 41 0.033+0.0177j 6349

CU-A2-2 70 48 0.037+0.0177j 5800

CU-A2-3 70 40 0.033+0.0177j 6349

CU-A2-4 70 41 0.033+0.0177j 6349

CU-A2-5 70 43 0.040+0.0177j 5441

CU-A2-6 70 33 0.033+0.0177j 6349

CU-A2-7 70 29 0.030+0.0177j 6822

CU-A2-8 70 38 0.036+0.0177j 5929

CU-A2-9 70 46 0.033+0.0177j 6349

CU-A2-10 70 63 0.052+0.0177j 4339

CU-A2-26 70 30 0.032+0.0177j 6500

CU-B2-11

CU-

B2-11

70 34 0.035+0.0177j 6064

CU-B2-12 70 26 0.029+0.0177j 6993

CU-B2-13 70 42 0.039+0.0177j 5556

CU-B2-14 70 30 0.026+0.0177j 7550

CU-B2-15 70 36 0.035+0.0177j 6064

CU-B2-16 70 58 0.052+0.0177j 4339

CU-B2-17 70 58 0.052+0.0177j 4339

CU-B2-18 70 38 0.036+0.0177j 5929

CU-B2-19 70 28 0.030+0.0177j 6822

CU-B2-20 70 38 0.036+0.0177j 5929

50

CU NAME CABLE SIZE

(mm2)

CABLE LENGTH

(m)

IMPEDANCE

(Ω)

FAULT

CURRENT (A)

CU-B2-21 70 50 0.038+0.0177j 5676

CU-B2-22 70 33 0.025+0.0177j 7752

CU-B2-23 70 25 0.020+0.0177j 8886

CU-B2-24 70 43 0.030+0.0177j 6822

CU-B2-25 70 34 0.026+0.0177j 7550

CU-B2-27 70 25 0.029+0.0177j 6993

CU-B2-28 70 35 0.035+0.0177j 6064

CU-B2-29 70 36 0.035+0.0177j 6064

CU-B2-30 70 24 0.033+0.0177j 6409

CU-B2-31 70 33 0.052+0.0177j 4339

CU-B2-32 70 50 0.052+0.0177j 4339

CU-B2-33 70 58 0.052+0.0177j 4339

CU-B2-34 70 39 0.036+0.0177j 5929

CU-B2-35 70 31 0.025+0.0177j 7752

CU-B2-36 70 26 0.030+0.0177j 6822

CU-B2-37 70 36 0.036+0.0177j 5929

CU-B2-38 70 34 0.026+0.0177j 7550

CU-B2-39 70 25 0.020+0.0177j 8886

CU-B2-40 70 38 0.035+0.0177j 6064

CU-B2-41 70 29 0.031+0.0177j 6658

CU-B2-42 70 29 0.031+0.0177j 6658

CU-B2-43 70 46 0.050+0.0177j 4493

CU-B2-44 70 31 0.040+0.0177j 4492

CU-B2-45 70 29 0.039+0.0177j 5556

CU-B2-46 70 31 0.040+0.0177j 4492

CU-B2-47 70 45 0.050+0.0177j 4493

CU-B2-48 70 33 0.043+0.0177j 5120

CU-B2-49 70 23 0.037+0.0177j 5800

CU-B2-50 70 29 0.037+0.0177j 5800

CU-B2-51 70 40 0.048+0.0177j 4657

CU-C2-52 70 34 0.033+0.0177j 6349

CU-C2-53 70 26 0.030+0.0177j 6822

CU-C2-54 70 42 0.039+0.0177j 5556

CU-C2-55 70 34 0.034+0.0177j 6203

CU-C2-56 70 26 0.029+0.0177j 6993

CU-C2-57 70 35 0.034+0.0177j 6203

CU-C2-58 70 50 0.046+0.0177j 4832

CU-C2-59 70 45 0.050+0.0177j 4493

CU-C2-60 70 31 0.040+0.0177j 4492

CU-C2-61 70 31 0.040+0.0177j 4492

CU-C2-62 70 57 0.057+0.0177j 3995

CU-C2-63 70 42 0.047+0.0177j 4743

51

CU NAME CABLE SIZE

(mm2)

CABLE LENGTH

(m)

IMPEDANCE

(Ω)

FAULT

CURRENT (A)

CU-C2-64 70 33 0.041+0.0177j 5330

CU-C2-65 70 27 0.037+0.0177j 5800

CU-C2-66 70 34 0.041+0.0177j 5330

CU-C2-67 70 42 0.039+0.0177j 5556

CU-C2-68 70 38 0.036+0.0177j 5929

CU-C2-69 70 30 0.031+0.0177j 6658

CU-C2-70 70 36 0.035+0.0177j 6064

CU-C2-71 70 46 0.035+0.0177j 6064

CU-C2-72 70 44 0.039+0.0177j 5556

CU-C2-73 70 34 0.033+0.0177j 6349

CU-C2-74 70 35 0.033+0.0177j 6349

CU-C2-75 70 48 0.043+0.0177j 5120

6.6 DISCRIMINATION

6.6.1 DISCRIMINATION BETWEEN CONSUMER UNITS AND SERVICE TURRETS

This section would show how the protection devices used would ensure discrimination between

the consumer units and service turrets. CU-A2-1 was used to illustrate.

The load current was 80.97A as obtained in section 5.3.1.

The cable sizes used was 70mm2 with a current carrying capacity of 154A as shown in

section 5.6.1.

From table 6-3, the fault current arrived at was 6349A. The highest rated MCB as seen in section

5.4.1 was 32 A with a short circuit rating of 10kA. Cut-outs arranged with high rating capacity

fuses rated 100 Amps according to BS1361 were used in the service turrets to achieve

discrimination between the consumer unit and service turret as shown from the MEM Catalogue

Table in the Appendix 3. This was applied to the rest of the CUs and the results summarized in

table 6-4.

52

Table 6-4 Discrimination between CUs and their respective service turrets

CU NAME LOAD

CURRENT

(A)

CABLE

SIZE

(MM2)

CURRENT

CARRYING

CAPACITY

(A)

RATING OF

THE

LARGEST

MCB IN CU

(A)

FAULT

CURRENT

(A)

SERVICE

TURRET

FEEDING

CU

RATING OF

HRC FUSE

IN

SERVICE

TURRET(A)

CU-A2-1 80.97 70 154 32 6349 ST.5 100

CU-A2-2 80.97 70 154 32 5800 ST.5 100

CU-A2-3 80.97 70 154 32 6349 ST.5 100

CU-A2-4 80.97 70 154 32 6349 ST.5 100

CU-A2-5 80.97 70 154 32 5441 ST.6 100

CU-A2-6 80.97 70 154 32 6349 ST.6 100

CU-A2-7 80.97 70 154 32 6822 ST.6 100

CU-A2-8 80.97 70 154 32 5929 ST.6 100

CU-A2-9 80.97 70 154 32 6349 ST.6 100

CU-A2-10 80.97 70 154 32 4339 ST.6 100

CU-A2-26 80.97 70 154 32 6500 ST.4 100

CU-B2-11 80.45 70 154 32 6064 ST.4 100

CU-B2-12 80.45 70 154 32 6993 ST.4 100

CU-B2-13 80.45 70 154 32 5556 ST.2 100

CU-B2-14 80.45 70 154 32 7550 ST.2 100

CU-B2-15 80.45 70 154 32 6064 ST.2 100

CU-B2-16 80.45 70 154 32 4339 ST.2 100

CU-B2-17 80.45 70 154 32 4339 ST.1

100

CU-B2-18 80.45 70 154 32 5929 ST.1 100

CU-B2-19 80.45 70 154 32 6822 ST.1 100

CU-B2-20 80.45 70 154 32 5929 ST.1 100

CU-B2-21 80.45 70 154 32 5676 ST.3 100

CU-B2-22 80.45 70 154 32 7752 ST.3 100

CU-B2-23 80.45 70 154 32 8886 ST.3 100

CU-B2-24 80.45 70 154 32 6822 ST.3

100

CU-B2-25 80.45 70 154 32 7550 ST.3 100

CU-B2-27 80.45 70 154 32 6993 ST.4 100

CU-B2-28 80.45 70 154 32 6064 ST.4 100

CU-B2-29 80.45 70 154 32 6064 ST.2 100

CU-B2-30 80.45 70 154 32 6409 ST.2 100

CU-B2-31 80.45 70 154 32 4339 ST.2 100

CU-B2-32 80.45 70 154 32 4339 ST.2 100

CU-B2-33 80.45 70 154 32 4339 ST.1 100

CU-B2-34 80.45 70 154 32 5929 ST.1 100

CU-B2-35 80.45 70 154 32 7752 ST.1 100

CU-B2-36 80.45 70 154 32 6822 ST.1 100

CU-B2-37 80.45 70 154 32 5929 ST.1 100

CU-B2-38 80.45 70 154 32 7550 ST.3 100

CU-B2-39 80.45 70 154 32 8886 ST.3 100

53

CU NAME LOAD

CURRENT

(A)

CABLE

SIZE

(MM2)

CURRENT

CARRYING

CAPACITY

(A)

RATING

OF THE

LARGEST

MCB IN CU

(A)

FAULT

CURRENT

(A)

SERVICE

TURRETFE

EDING CU

RATING

OF HRC

FUSE IN

SERVICE

TURRET(A

)

CU-B2-40 80.45 70 154 32 6064 ST.10

100

CU-B2-41 80.45 70 154 32 6658 ST.10

100

CU-B2-42 80.45 70 154 32 6658 ST.10

100

CU-B2-43 80.45 70 154 32 4493 ST.9

100

CU-B2-44 80.45 70 154 32 4492 ST.9

100

CU-B2-45 80.45 70 154 32 5556 ST.9

100

CU-B2-46 80.45 70 154 32 4492 ST.9

100

CU-B2-47 80.45 70 154 32 4493 ST.9

100

CU-B2-48 80.45 70 154 32 5120 ST.8 100

CU-B2-49 80.45 70 154 32 5800 ST.8 100

CU-B2-50 80.45 70 154 32 5800 ST.8 100

CU-B2-51 80.45 70 154 32 4657 ST.8 100

CU-C2-52 79.86 70 154 32 6349 ST.7 100

CU-C2-53 79.86 70 154 32 6822 ST.7 100

CU-C2-54 79.86 70 154 32 5556 ST.10 100

CU-C2-55 79.86 70 154 32 6203 ST.10 100

CU-C2-56 79.86 70 154 32 6993 ST.10 100

CU-C2-57 79.86 70 154 32 6203 ST.10 100

CU-C2-58 79.86 70 154 32 4832 ST.10 100

CU-C2-59 79.86 70 154 32 4493 ST.9

100

CU-C2-60 79.86 70 154 32 4492 ST.9

ST.9

100

CU-C2-61 79.86 70 154 32 4492 ST.9

100

CU-C2-62 79.86 70 154 32 3995 ST.8 100

CU-C2-63 79.86 70 154 32 4743 ST.8 100

CU-C2-64 79.86 70 154 32 5330 ST.8 100

CU-C2-65 79.86 70 154 32 5800 ST.8 100

CU-C2-66 79.86 70 154 32 5330 ST.8 100

CU-C2-67 79.86 70 154 32 5556 ST.7 100

CU-C2-68 79.86 70 154 32 5929 ST.7 100

CU-C2-69 79.86 70 154 32 6658 ST.7 100

CU-C2-70 79.86 70 154 32 6064 ST.3 100

CU-C2-71 79.86 70 154 32 6064 ST.3 100

CU-C2-72 79.86 70 154 32 5556 ST.7 100

CU-C2-73 79.86 70 154 32 6349 ST.7 100

CU-C2-74 79.86 70 154 32 6349 ST.7 100

CU-C2-75 79.86 70 154 32 5120 ST.7 100

54

6.6.2 DISCRIMINATION BETWEEN SERVICE TURRETS AND LV SWITCH BOARD

Table 6-5 Discrimination between service turrets and the low voltage switchboard.

SERVICE

TURRET

NAME

LOAD

CURRENT

(A)

CABLE

SIZE

(mm2)

CURRENT

CARRYING

CAPACITY (A)

RATING OF

THE SERVICE

TURRET

FUSES(A)

FAULT

CURRENT

(A)

RATING OF TP/N

FRAME MCCB

UPSTREAM IN

SWITCHBOARD (A)

ST-1 162 240 301 100 12,510 320

ST-2 162 240 301 100 11,105 320

ST-3 161 240 301 100 10,810 320

ST-4 241.35 300 301 100 8,886 320

ST-5 241.35 300 301 100 11,105 320

ST-6 241.35 300 301 100 8,886 320

ST-7 241.35 300 339 100 8,406 320

ST-8 239.58 300 339 100 11,105 320

ST-9 241.35 300 339 100 10,229 320

ST-10 241.35 300 339 100 13,159 320

6.6.3 DISCRIMINATION BETWEEN GENERATOR MCCB AND LV SWITCHBOARD

The whole estate was under backup hence the generator phase currents were found by summing

up the phase currents in the service turrets. This was shown in table 6-6.

Table 6-6 Generator 1 phase currents

Service turret RED PHASE (A) YELLOW PHASE

(A)

BLUE PHASE

(A)

ST.1 161.94 80.97 80.97

ST.2 161.94 161.94 161.94

ST.3 160.9 160.9 80.97

ST.4 241.35 241.35

241.35

ST.5 239.58 159.72 241.35

ST.6 159.87 240.76 241.35

TOTALS 1125.58 1045.64 1047.93

55

Table 6-7 Generator 2 phase currents

Service turret RED PHASE (A) YELLOW PHASE

(A)

BLUE PHASE

(A)

ST.7 241.35 239.58 240.17

ST.8 239.58 239.58 239.58

ST.9 241.35 241.35 241.35

ST.10 160.90 241.35

240.17

TOTALS 883.18 961.86 961.27

Assuming 15% generator 1 reactance, the fault current was found to be:

= A593,1115.04153

10001250

A three phase fault would produce the largest fault current; this was therefore used as the basis to

select the short-circuit capabilities. The largest MCCB on switch board 1 was rated 320A. An

MCCB was hence required, that would allow a load current of 1125A to pass through, withstanding

a fault current of 11593 Amps, and discriminating 320 Amps MCCB at the switchboard in case of

fault at the service turrets. The appropriate MCCB is a 1250 Amps TP/N MEM M FRAME MCCB.

For generator 2 and lv switch board 2, fault current was found to be;

A927515.04153

10001000

The largest MCCB on switch board 2 was rated 320A. An MCCB was hence required, that would

allow a load current of 962A to pass through, withstanding a fault current of 9275 Amps, and

discriminating 320 Amps MCCB at the switchboard in case of fault at the service turrets. The

appropriate MCCB is a 1000 Amps TP/N MEM M FRAME MCCB.

56

6.7 LIGHTNING PROTECTION

Lightning arrestors were used. Air terminals were installed at the sharp points on the roof to

intercept lightning diverting it from people and equipment. The air terminals were then

interconnected via copper strips which ran along the roof ridges, then to the ground. The

conductors had to be straight to offer a direct path to the ground and gave a maximum resistance

of 10 ohms as per BS 6651. [10] Considering the value of the property, AC and signal surge

protectors were installed at the buildings main power entrance. This is shown in figure 6.5.

Figure 6-6 Lightning Protection Layout for unit A2

57

Chapter 7

7.1 RECOMMENDATIONS FOR FUTURE WORK

The areas of improvement in the project include:

Design of a program that would perform the calculations, for example, in cable sizing

and fault current calculations.

Preparing a bill of quantities. This is a document gives details of the materials, parts,

labour and their costs. The terms of implementation and repair contact are itemised. It

serves in helping to source contractual services.

Using an alternative source of energy for backup power supply; solar energy would be a

good option since it is economical.

7.2 CONCLUSION

This project aimed at designing a lighting, power distribution system protection scheme for a

residential estate. In lighting design, the number and placement of light fittings was determined

by use of the lumen method and the point-by-point method used to determine the illuminance at a

point. Road lighting was also done and the spacing calculated between each luminaire was found

to be 31m.

Circuiting was also done with switches being allocated too. Power points were placed in

accordance with the recommendations given by The Electrical Installation Industry Liaison

Committee.

Under power distribution, the total load in the estate was 1606.5 kVA. Due to the location of the

houses, the total load of the estate was split into two, load 1 being 908.95 kVA and load 2 was

792.43 kVA the loads fed by two 1000 kVA transformers. This was done to reduce the voltage

drop that was is caused by long distances between the transformers and the final power outlet.

From the KPLC feeder power was feed to the transformers. From the transformers, power was

supplied to the low voltage switch board which had two bus bars. The maintained and the essential

bus bar. The low voltage switchboard fed the service turrets and the service turret distributed power

to the individual consumer units. Consumer units with integral isolator of 100A and 14 circuit

58

breaker ways were used in each housing unit to supply power to the single phase loads. The total

number of consumer units was 75. A total of 10 service turrets were used in the estate.

1250kVA and 1000kVA capacity backup generators were used to supply power to the estate. An

electrical reticulation diagram was designed to show the major distribution points and their

interconnection.

Cable sizing was done in accordance with the IEE regulations. For the consumer unit a 70 mm2

core copper conductor with a voltage drop of 0.61 mV/A/m and a current carrying capability of

154 A was selected as the incoming cable. For the service turrets a 300 mm2 PVC insulated, PVC

sheathed conductor with a current carrying capacity of 339A and a voltage drop of 0.20 mV/A/m

was selected.

Consumer loads and cable protection was achieved using MCBs and MCCBs. Fault currents were

calculated and a magnitude of 18.4 kA was arrived at as the three phase fault current at the

switchboard level. Discrimination was achieved by using the fault currents at various levels.

Lightning protection was also achieved using a lightning protection system and surge protectors.

Power factor correction was also done using 104.47kVAR capacitors at the switchboard.

A great challenge was encountered in load balancing as the design of the estate used the consumer

unit load in balancing. This made it very difficult to split the load so as to ensure proper load

balance in the 3 phases.

The objectives of the project were hence fully met.

59

APPENDIX 1: LIGHT DESIGN

Table 1-1 Number of fittings in housing A2

Name of the

area

Area m2 Required

Illuminance

(lux)

Type of fitting(by

naming convention)

Number of

fittings

Lounge 29.86m2 100 TYPE G 5

Dining

7.83 m2 100 TYPE C 1

Family room

7.76 m2 145 TYPE C 1

Study room 7.88 m2

200 TYPE G 4

Kitchen

14.80 m2 200 TYPE G 5

Guest room

12.38 m2 100 TYPE C

TYPE W(for accentuation)

1

Master

bedroom

23.91 m2 120 TYPEG


5

Bedroom 2

11.71 m2 100 TYPE C


1

Bedroom 3

10.60 m2 100 TYPE C


1

Lobby and

passage

100 TYPE F 2

Closet

6.01 m2 100 TYPE D 2

Store

0.71 m2 100 TYPE D 1

Bathrooms

100 TYPE B 1

Exterior

entrances

100 TYPE N 4

Outdoor lights

100 TYPE K 9

Porch TYPE P 1

60

Name of the

area

Area m2 Required

Illuminance

(lux)

Type of fitting(by

naming convention)

Number of

fittings

Stairs

100 TYPE S 3

DSQ

7.24 m2 100 TYPE C


1

Table 1-2 Number of fittings in housing B2

Name of the area Area m2 Required

Illuminance

(lux)

Type of fitting(by naming

convention)

Number of

fittings

Lounge 23.49 m2 100 TYPE G

5

Dining

6.74 m2 100 TYPE CH 1

Kitchen

14.14 m2 200 TYPE G

5

Guest room

11.16 m2 100 TYPE C


1

Master bedroom

25.41 m2 100 TYPE G

TYPEW(for accentuation)

5

Bedroom 1

10.29 m2 100 TYPE C


1

Bedroom 2

11.03 m2 100 TYPE C


1

Lobby and passage 100 TYPE F 2

Closet

5.20 m2 100 TYPE D 2

Store

0.35 m2 100 TYPE D 1

Bathrooms

100 TYPE B 1

Exterior entrances

TYPE N 3

61

Outdoor lights

TYPE K 7


Illuminance

(lux)

Type of fitting(by naming

convention)

Number of

fittings

Porch

TYPE P 1

Stairs

TYPE S 3

DSQ

6.75 m2 100 TYPE C


1

Table 1-3 Number of fittings in housing C2


Illuminance

(lux)

Type of fitting(by

naming convention)

Number of

fittings

Lounge 24.77m2 100 TYPE G

5

Dining

6.77 m2 100 TYPE CH 1

Kitchen

14.37 m2 200 TYPE G

5

Guest room

11.52 m2 100 TYPE C


1

Master bedroom

19.59 m2 100 TYPE G


5

Bedroom 1

9.93 m2 100 TYPE C


1

Lobby and passage 100 TYPE F 2

Closet

5.41 m2 100 TYPE D 1

Store

0.43 m2 100 TYPE D 1

Bathrooms

100 TYPE B 1

Exterior entrances

TYPE N 4

62

Outdoor lights

TYPE K 7


Illuminance

(lux)

Type of fitting(by

naming convention)

Number of

fittings

Porch

TYPE P 1

Stairs

100 TYPE S 3

DSQ

7.40 m2 100 TYPE C


1

63

APPENDIX 2: LOAD CALCULATIONS

Table 2-1lighting final circuit 1(CIR.L1)

Fitting Number

of

fittings

Diversity

factor

Lamp

wattage

(Watts)

Total

load(Watts)(applying

diversity factor)

Type C 1 0.66 20W 13.2

Type W 3 0.66 28W 55.44

Type F 2 0.66 16W 21.12

Type G 4 0.66 26W 68.64

Type B 1 0.66 28W 18.48

TOTAL 176.88W

Table 2-2 lighting final circuit 2(CIR.L2)

Fitting Number

of

fittings

Diversity

factor

Lamp

wattage

(Watts)

Total


diversity factor)

Type C 1 0.66 20W 13.2 W

Type W 5 0.66 28W 92.4W

Type G 5 0.66 26W 85.8W

Type D 2 0.66 11.5W 15.18 W

Type B 2 0.66 28W 36.96 W

Type S 3 0.66 28W 55.44W

TOTAL 298.98 W


Fitting Number

of

fittings

Diversity

factor

Lamp

wattage

(Watts)

Total


diversity factor)

Type C 2 0.66 20W 26.4W

Type W 3 0.66 28W 55.44W

Type G 5 0.66 26W 85.8W

Type B 2 0.66 28W 36.96W

Type F 2 0.66 16W 21.12W

Type P 1 0.66 18W 11.88W

TOTAL 237W

64


Fitting Number

of

fittings

Diversity

factor

Lamp

wattage

(Watts)

Total


diversity factor)

Type G 5 0.66 26W 85.8W

Type D 1 0.66 11.5W 7.59W

Type K 2 0.66 18W 23.76W

Type C 2 0.66 20W 26.4W

Type W 3 0.66 28W 55.44W

Type B 1 0.66 28W 18.48W

TOTAL 217.43W

Table 2-5 Calculation of maximum demand in unit B2

LOAD Diversity factor Total Load(Watts) Total load current(A)



Lighting circuit 3 0.66 231 W 0.96A


CIR.T(outdoor lighting) 0.66 83.16 W 0.35A

Ring circuit 1 1 7680 32A

Ring circuit 2 0.4 3072 13A

Cooker unit

10A+30%for

appliances in

excess of 10A +

5A for socket

incorporation

6120

25.5A

Water heater 1 1500 6.25A

TOTAL 19,310 W 80.45A

65

Table 2-6 Calculation of maximum demand in unit C2

LOAD Diversity factor Total load(Watts) Total load current(A)





CIR.T 0.66 95.04W 0.40

Ring circuit 1 1 7680 W 32A

Ring circuit 2 0.4 3072 W 13A

Cooker unit 10A+30%for appliances

in excess of 10A + 5A

for socket incorporation

6120 W 25.5A

Water heater 1 1500 W 6.25A

TOTAL 19,167W 79.86A

Table 2-7 MCBs in DB-B2-1

Type of load Total load (Watts) Total

Current load (A)

MCB

size

Cable size

(mm2)

Lighting CIR.LI 163.68W 0.68A 4A 1mm2


Lighting CIR.L3 231 W 0.96A 4A 1mm2


CIR.T(outdoor

lighting)

83.16W 0.35 A 4A 1mm2



Cooker CIR.DI 6120W 25.5A 32A 6 mm2

Water heater 1500W 6.25A 13A 2.5 mm2

66

Table 2-8 MCBs in DB-C2-1

Type of load Total

load

(Watts)

Total

Current load

(A)

MCB

size

Cable size (mm2)

Lighting CIR.LI 122.1 W 0.51A 4A 1mm2




CIR.T(outdoor light) 95.04W 0.40 4A 1mm2

Ring circuit CIR.R1 7680 W 32A 32A 2.5 mm2

Ring circuit CIR.R2 3072 W 13A 32A 2.5 mm2

Cooker CIR.DI 6120 W 25.5A 32A 6 mm2

Water heater 1500 W 6.25A 13A 2.5 mm2

Table 2-9 Fault current levels for the service turrets

SERVICE

TURRET

NAME

CABLE SIZE

(mm2)

CABLE LENGTH

(m)

IMPEDANCE

(Ω)

FAULT

CURRENT (A)

ST-1 240 33 0.007+0.0177j 12,510

ST-2 240 53 0.012+0.0177j 11,105

ST-3 240 70 0.013+0.0177j 10,810

ST-4 300 125 0.020+0.0177j 8,886

ST-5 300 50 0.012+0.0177j 11,105

ST-6 300 123 0.020+0.0177j 8,886

ST-7 300 100 0.022+0.0177j 8,406

ST-8 300 62 0.012+0.0177j 11,105

ST-9

300 86 0.015+0.0177j 10,229

ST-10 300 15 0.004+0.0177j 13,159

67

APPENDIX 3: CATALOGUES

68

69

70

71

72

73

REFERENCES

[1] Basics of Light and Lighting: PHILLIPS

[2] Zumtobel: The Lighting Handbook: 1nd Edition, printed by Zumtobel Lighting GmbH

Schweizer Strasse 30 Postfach 72 6851 Dornbirn, AUSTRIA 2004.

[3] Harald Hofman and Rudiger Ganslant: Handbook of interior lighting design, ERCO edition,

published by Druckhaus Maack, Lüdenscheid in 1992.

[4] Illuminating Engineering Society of North America: IESNA Lighting handbook, reference and

application, 9TH edition

[5] SaskPower: Roadway lighting Design Handbook, Standard engineering practice section 4,

2013

[6] Fred Hall and Roger Greeno: Building services handbook, 5th Edition, printed by Elsevier

Limited Linacre House, Jordan Hill Oxford OX2 8DP 30 Corporate Road, Burlington, 2009.

[7] W E Steward and T A Stubbs with technical contributions by Trevor Marks and Steve Clarke

(Burlington) Elsevier: Modern Wiring Practice: Design and installation; Revised Edition printed

by Elsevier Limited Linacre House, Jordan Hill Oxford OX2 8DP 30 Corporate Road, Burlington,

2005.

[8] Barrie Rigby: Design for Electrical Services for Buildings 4th Edition, published by Spon press

2 Park, Milton park, Abingdon, Oxon 0X14 4RN 2005.

[9] IEE Wiring Regulations: ONSITE GUIDE BS 7671:2008 17TH Edition, published by The

Institution of Engineering and Technology, London, United Kingdom.

[10] IEEE Guide for Surge Protection of Equipment, published by standards information network

IEEE press.

[11] Contech Residential Lighting Design Guide. Copyright by Conservation Technology of

Illinois

[12] Philips lamps catalogue 2010

[13] The Thorn lighting catalogue

[14] The searchlight catalogue

[15] Technical-lighting design guide, the society of light and lighting.

74

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