1

A

RESEARCH DISSERTATION

ON

MODELLING THE COSTS OF FINAL SUB-CIRCUITS IN

RESIDENTIAL ELECTRICAL INSTALLATIONS

BY

OLAWUMI TIMOTHY OLUWATOSINQSV/08/4275

SUBMITTED TO:

THE DEPARTMENT OF QUANTITY SURVEYING

SCHOOL OF ENVIRONMENTAL TECHNOLOGY

FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE

ONDO STATE, NIGERIA

IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE AWARD OF

BACHELOR OF TECHNOLOGY DEGREE (B.TECH) IN QUANTITY SURVEYING

FEBRUARY, 2014

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CERTIFICATION

This is to certify that this research work was carried out by OLAWUMI, TIMOTHY

OLUWATOSIN, matriculation number QSV/08/4275, of the department of Quantity

Surveying, School of Environmental Technology, Federal University of Technology, Akure,

Ondo state.

Professor D.R. Ogunsemi Dr. I.O. Aje

Supervisor Head of Department

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DEDICATION

This research work is dedicated to GOD Almighty, the giver of all knowledge and the

embodiment of all wisdom for his showers of blessing, love, mercy and protection over me in

particular and my family in general.

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ACKNOWLEDGEMENT

All glory, honour, adoration in heaven and on earth goes to Almighty God, the creator of

heaven and earth who has made it possible for me to start this research work in good health

and finish strong.

I specially thank my project supervisor, Professor D.R. Ogunsemi for his unflinching support.

The guidance, suggestions and kind disposition of Mr O. Ogunsina towards the success of

this research work is highly commendable.

Also to other lecturers in the department of Quantity Surveying for imparting in me the basic

rudiments of Quantity Surveying profession, I confess that you all are the best set one could

ever wish to have as lecturers and on that note I say ‘thank you sirs’ - Dr. I.O. Aje, Dr.

Awodele, Dr. Ayeitan, Mr. Makanjuola, Mr. Akinola, Mr. Ibironke, Mr. A.E. Oke, Mr I.O.

Famakin, Mr. Adeniyi Onaopepo and Mr. T.O. Oladirin, Sirs, I am extremely grateful.

Also, to my wonderful family, I sincerely take a perfect but humble bow to you all in total

respect, greetings, submission, acknowledgement and appreciation for your support, love,

encouragement and prayers thus far. Dad and Mum; Dr. & Mrs. S.O Olawumi, you are

inestimable, and my wonderful siblings; Isaac and Stephen Olawumi for their love, care and

support throughout this project and majorly throughout my five (5) year career pursuit in

FUTA

My warmest regards also goes to Mr. Awosika Seyi for his unflinching assistance in the

course of this research, also to Prof. J.O. Afolayan, Prof. M. Arogunjo, Pastor Ogundele

Kayode, and their wives for their love, prayers, interest and support. Also to all the members

of the Deeper Life Campus Fellowship for their prayers and words of encouragement

during my research and my friends; Akinnagbe Femi, Ojo Stephen, Adebusoye Busayo,

Babatunde Olufemi, Oladejo John, Adebanjo Damilola, Akpan Glory and other colleagues

for contributing to the success of this research work. I appreciate you all. God bless you all.

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ABSTRACT

Previous researchers have developed models for determining building durations in Nigeria

and Hong Kong respectively; however little forage has been made in the area of electrical

services, a recent research work deals with the measurement of electrical services in

buildings; but there is yet not a model to determine the probable cost of electrical services in

residential buildings. Therefore, the aim of this study is to develop a cost model for

predicting the costs of final sub-circuits in residential electrical installations using multiple

regression techniques and linear regression techniques, based on data generated from 33 sets

of drawings- Architectural and Electrical drawings of Bungalows (17 bungalows) and

Duplexes (16 drawings) from which also, priced bill of quantities were generated. Also the

current market prices of electrical items as well as site-observation of electrical technician’s

productivity were also carried out with interviews which were used in calculation of unit

rates. In achieving the aim of this research work, six (6) cost models were developed; of

which 5 of the 6 models will fit in real life cost prediction works. The first two (2) models

was developed using multiple regression analysis to determine the final sub-circuit cost of

electrical installation with Coefficient of Determination, R2 of 0.968 and 0.980 respectively.

The other models were developed using linear regression analysis technique. The third

model assesses the influence of GFA on final circuit cost with R2 of 0.172. The fourth model

uses the number of lighting points to determine the length of cable with R2 of 0.823. The

fifth and sixth models use the length of cable to determine the length of conduits with R2 of

0.559 and 0.947 respectively. In assessing the predictive power of the cost models, model

validation was carried out using seven (7) floors of 3 bungalows and 2 duplexes. The model

validations/comparison further confirmed the validity of the models earlier generated as

valid enough to be used as a basis in cost prediction of residential electrical installation.

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TABLE OF CONTENTS

Title page i

Certification ii

Dedication iii

Acknowledgement iv

Abstract v

Table of Contents vi

List of Tables x

List of Figures xii

CHAPTER ONE

Introduction

1.1 Background of the Study 1

1.2 Statement of Research Problem 5

1.3 Research Questions 5

1.4 Aim and Objectives of the Study 6

1.5 Justification of the Study 6

1.6 Scope and Limitation of the Study 7

CHAPTER TWO

Literature Review

2.1 Building Services 8

2.1.1 The Construction Industry 10

2.1.2 The Nigerian Construction Industry 10

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2.2 The Building Team 11

2.3 Requirements for Electrical Installations 14

2.3.1 Notifiable Electrical Work 16

2.3.2 Non-notifiable Electrical work. 16

2.4 Electrical Accessories Installations 17

2.4.1 PVC Insulated and sheathed cables 17

2.4.2 Conduit Installations 18

2.4.3 Trunking Installations 21

2.5 Wiring 21

2.6 Electrical switches 23

2.6.1 Types of electrical switches 24

2.7 Essentials Tools for electrical institutions 26

2.8 Principles of Electrical Installation 30

2.8.1 Internal Distribution 31

2.8.2 Wiring Circuits for lighting 31

2.8.3 Water Heating Circuits 32

2.8.4 Cooker Circuits 32

2.8.5 Wiring Systems 33

2.8.6 Fixing the Conduits 35

2.8.7 Wiring Accessories 35

2.8.8 Earthing Systems 36

2.8.9 Choice of Wiring Systems 37

2.8.10 Circuits and Sub-Circuits 38

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2.9 Measurement of Electrical Services 41

2.9.1 Information required for effective measurement of Electrical

Installations 42

2.9.2 Electrical Installation Items for measurement 44

2.9.3 Concise Measurement Procedure 44

2.10 Cost Significant Models 45

2.10.1 Cost Estimation for Electrical Services 46

2.10.2 Applying Cost-estimating methods 47

CHAPTER THREE

Research Methodology

3.1 Introduction 51

3.2 Research Design 51

3.3 Study Population 51

3.4 Sampling Frame 51

3.5 Sampling Size 52

3.6 Sampling Techniques 52

3.7 Data Collection Instrument 52

3.4 Data Collection Procedure 52

3.5 Method of Data Analysis 53

CHAPTER FOUR

Data Presentation and Analysis of Results

4.1 Introduction 55

4.2 Data Analysis 55

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4.2.1 Identification of the Cost Significant Items 56

4.2.2 Model of Final Sub-Circuit Cost as a Function of The Cost Significant

Items. 59

4.2.3 Multiple Correlation and Determination 63

4.2.4 Model of Final Sub-circuit cost as a function of Gross Floor Area 64

4.2.5 Model of the Length of Cables as a function of the Number ofLuminaries 66

4.2.6 Model of the Length of Conduits as a function of the Length of Cables

674.2.7 Productivity Constant of Electrical Technicians 69

4.3 Model Validation 70

4.3.1 Model Validation of the Final Sub-circuit Cost as a Function of the

Cost Significant Items 70

4.3.2 Model Validation of the Length of Cables as a Function of the Number

of Luminaries. 73

4.3.3 Model Validation of the Length of Conduits as a Function of the

Length of Cables. 74

4.4 Discussion of Result 76

CHAPTER FIVE

Conclusion and Recommendations

5.1 Conclusion 79

5.2 Recommendations 82

5.3 Areas of Further Research 82

REFERENCES 83

APPENDIX 86

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LIST OF TABLES

Table 1.1 Electrical Accessories in main groups 4

Table 2.1 Comparison between various systems of Wiring 39

Table 4.1 Based on Building Type 55

Table 4.2 Based on Floor Classification 56

Table 4.3 Cross-Tabulation: Building Type to Number of Bedrooms 56

Table 4.4: Table Showing the Cost Significant Items for the Forty-Nine Floors 57

Table 4.5 Multiple Regression Results among the Final Sub-Circuit Costs & Cost

Significant Items 60

Table 4.6 Multiple Regression Results among the Final Sub-Circuit Costs & Cost

Significant Items 61

Table 4.7 Determination Coefficients among Items of Work and Final Sub-Circuit Cost

63

Table 4.8 Determination Coefficients among Items of Work and Final Sub-Circuit Cost

64

Table 4.9 Linear Regression Model f = c + b4x4 65

Table 4.10 Linear Regression Model cl = c + b5x 66

Table 4.11 Linear Regression Model dc= c + b6x6 67

Table 4.12 Linear Regression Model dc= c + b6x6 68

Table 4.13 Productivity Constant of Electrical Technicians` 69

Table 4.14 Cost Significant Items to Test Model Validity (CT) 70

Table 4.15 Final Sub-Circuit Costs Derived from Model (CM) 71

Table 4.16 Showing the Comparison between CT and CM 71

Table 4.17 Cost Significant Items to Test Model Validity (CT) 72

Table 4.18 Final Sub-Circuit Costs Derived from Model (CM) 72

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Table 4.19 Showing the Comparison between CT and CM 72

Table 4.20 Data needed to Test Model Validity (CT) 73

Table 4.21 Lengths of Cables Costs derived from Model (CM) 73

Table 4.22 Showing the Comparison between CT and CM 74

Table 4.23 Data needed to Test Model Validity (CT) 74

Table 4.24 Lengths of Conduits derived from Model (CM) 75

Table 4.25 Showing the Comparison between CT and CM 75

Table 4.26 Data needed to Test Model Validity (CT) 75

Table 4.27 Lengths of Conduits derived from Model (CM) 76

Table 4.28 Showing the Comparison between CT and CM 76

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LIST OF FIGURES

Figure 1: A twin and earth PVC insulated and sheathed cable. 17

Figure 2: Conduit fittings and saddles 19

Figure 3: Loop-in wiring 22

Figure 4: Radial (or junction box) wiring 22

Figure 5: A Switch 24

Figure 6: Single pole switch 24

Figure 7: Double pole switch 25

Figure 8: Three-way Electrical Switch Wiring 25

Figure 9: Four-way Electrical Switch Wiring 26

Figure 10: Electrical Distribution 30

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CHAPTER ONE

INTRODUCTION

1.1 BACKGROUND OF THE STUDY

Electricity was a luxury for houses in the past, but it is a necessity for each and every house,

irrespective of the scale or the category of the household. Within the Nigerian construction

industry, the installation cost of an electrical system in a building is significant.

Building services installations typically account for 20-30% of the total value of a project -

and sometimes a great deal more, (Simon and Andy, 2012). The complexity of building

services installations has increased in recent years as demand has grown for intelligently

operated environments, driving innovation to improve occupier comfort and extend building

performance.

Meanwhile, building services contracting is distinct from most other trades in terms of the

role of direct labour, the relevance of the job undertaken by sub-contractors, the extent of co-

ordination required between trades and the extent of design work that can be shared between

consultants and specialists.

Electrical installation in a general term means any fixed appliances, wires, fittings, apparatus

or other electrical equipment used for (or for purposes incidental to) the conveyance, control

and use of electricity in a particular place, but does not include any of the following; subject

to any regulation made under Electricity (Consumer Safety) Act 2004 subsection (4) – any

electrical equipment used, or intended for use, in the generation, transmission or distribution

of electricity that is: (owned or used by an electricity supply authority, or located in a place

that is owned or occupied by such an authority); Any electrical article connected to, and

extending or situated beyond, any electrical outlet socket; Any electrical equipment in or

about a mine; Any electrical equipment operating at not more than 50 volts alternating

current or 120 volts ripple-free direct current; Any other electrical equipment, or class of

electrical equipment, prescribed by the regulations.

Electrical wiring work means the actual physical work of installing, repairing, altering,

removing or adding to an electrical installation or the supervising of that work. Also,

Electrical wiring needs to be made of two main materials: a good conductor of electricity,

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usually copper, and; to prevent the wires inside a cable from connecting to one another - a

very good insulator, usually PVC (poly-vinyl-chloride) or special rubber.

Electrical wiring composes of electrical equipment such as cables, switch boards, main

switches, and miniature circuit breakers (MCB) or fuses, residual current devices (RCD),

lighting points, power points, lightning arrestors, etc.

The electrical work in residential houses must be made, taking into account the particular

interior design. In some cases, cables can be laid under the ceilings, while in others you will

need to drill walls and floor. That is why execution of electrical works here requires an

integrated professional approach that takes into account the requirements of operation, safety

and aesthetic perfection as well.

Part P of the building regulations limit what electrical work may be carried out by anyone

other than a professional electrician who is a competent person registered with an electrical

self-certification scheme. An electrical licence is required before any electrical wiring work

can be undertaken, regardless of the cost of the work and regardless of whether the work is

residential, commercial or industrial. When work is carried out by a professional electrician,

they will deal with the necessary paperwork to comply with the Regulations.

Electrical symbols are used to show the lighting arrangement desired in the home. This

includes all switches, fixtures, and outlets while the electrical plans display all of the circuits

and systems to be used by the electrical contractor during installation.

Electrical installation for new construction occurs in these three phases: Temporary, that this,

the installation of a temporary underground or overhead electrical service nears the

construction site and close to the final meter location, to provides electricity during

construction; Rough-in electrical- also known as simply “rough-in” or pre-wiring, this is

when the electrical boxes and wiring are installed. Rough-in happens after the structure is

framed and covered with roofing. The electrical meter and permanent service can also be

installed at this time; Finish electrical, this is when the light fixtures, outlets and covers, and

appliances are installed prior to occupancy. Finish electrical is one of the last construction

phases.

The building regulations set out overall criteria and requirements to ensure electrical safety in

and around the home. Approved document P (Electrical Safety) from the planning portal

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provides practical guidelines for validating this type of work. It should be bear in mind that

any electrical work carried out within the home, garden, garage, shed and other storage

buildings may need to comply with the requirements of the Building Regulations.

Essentially, electrical works falls into two categories: Non-notifiable and Notifiable. Non-

notifiable electrical work, some work is classed as 'non-notifiable', and this work can be

carried out by a non-certified individual without notification although, obviously, the

individual does need to be competent.

Non-notifiable electrical work covers: Replacement of fittings such as sockets, switches and

light fittings; Replacement of the cable for a single circuit where it has been damaged; Work

that is not in the bathroom or kitchen and consists of: (Adding additional lighting, light

fittings and switches, to an existing circuit; Adding additional sockets and fused spurs to an

existing ring or radial main; Installing additional earth bonding).

All this 'non-notifiable electrical work' is conditional upon the use of suitable cable and

fittings for the application for which they are intended, that the circuit protective measures

are unaffected and suitable for protecting the new circuit, and that all work complies with all

other appropriate regulations.

Notifiable electrical work, these are work which must either be carried out by certified

individuals/companies or notified to the local Building Control before work begins, this

includes: All new or modifications to the electrical wiring within bathrooms or shower

rooms; Installation or modification of electric under-floor or ceiling heating; Garden lighting

or power installation; Other specialist electrical installation, examples being, Photovoltaic

Solar and micro CHP (Combined Heat and Power) power systems.

Electrical installation in general is basically subdivided into Electrical Supply/Power/Light

systems and Communication/Security/Controls systems (Appendix B of Building

Engineering Standard Method of Measurement, BESMM 3). The classification was based on

functions of the installations which could be likened to elements in the case of building. Thus

to measure installation that performs a particular function, requires a combination of trades.

The trades covered in BESMM3 are in Work Group Y and includes among others; Conduit

and Cable trunking (Y60), HV/LV Cables and Wiring (Y61), Earthing and Bonding

components (Y80), switchgear and Distribution boards (Y71), Luminaries and Lamps (Y73)

etc.

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Lawrence listed five main categories of electrical accessories (as cited in Keraminiyage,

Amaratunga, Haigh and Perera, 2009) which are accessories in power circuits, accessories in

lighting circuits, protective devices, accessories in other circuits, cables and other sundry

items. Each of these categories comprise of several key accessories.

Table 1-Electrical Accessories in main groups - Lawrence, (1993)

Group Accessories

Power circuits Accessories Socket outlets, Shaver Sockets, Cooker

Controllers

Lighting circuits Accessories Switches, Light Dimmers, Lamp Holders,

Ceiling Roses, Light fittings

Protective Devices Miniature Circuit Breakers, Residual Current

Circuit Breakers, Earth Terminals

Accessories in other circuits Telephone Sockets, Television Antenna

Sockets, Bell, Switches, Electrical Bell Units,

Ceiling Fans

Cables and other sundry items Wiring Cables, Conduits, Conduit

Accessories, Enclosures, Cable Trunks,

Junction Boxes, Sunk Boxes, Wiring Clips,

Distribution boards

However, the priority of the list of these features varies with the situation and the

characteristics of the person with the need.

Due to the diversification of availability of different types of accessories, a systematic

approach should be adopted in the process of building the model. Several procedures can be

adapted to this effect and the following three steps will be followed in building this particular

cost model:

1. Identification of the Cost Variables

2. Collection and analysis of cost data

3. Representation of analysed data in the model in a way that it reflects the cost

variables of the system, while catering to the need of ease of use of the model

and ability of simulating various combinations

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1.2 STATEMENT OF RESEARCH PROBLEM

Adeniyi, (2004) and Chan, (1999) developed a models for determining building durations in

Nigeria and Hong Kong respectively; also, Temitope, (2001) has also developed a predictive

model for the determination of the final cost of construction project; Onwe (2012), also wrote

a research work that deals with the measurement of electrical services in buildings; but there

is yet not a research work or study carried out to determine the probable cost of electrical

services in residential buildings, nor a model for the costs of final sub-circuits in residential

electrical installations.

Moreover, most architectural drawings for residential buildings such as those of bungalows

and duplexes are not usually accompanied with its corresponding detailed electrical drawings

which have led cost engineers such as quantity surveyors/estimators to find a way of

determining the cost of electrical services through the use of provisional sums which is more

of a guess work.

Also, the non-availability of electrical drawings for residential buildings could lead to

variations and loads of claims by the contractors in situations in which the estimated

allowances for such electrical installations is found to have been underestimated; therefore,

the desire and requirements by the clients to get accurate estimate in order to enable them to

take a right decision regarding the feasibility of proposed building services such as electrical

works in residential buildings becomes unrealisable.

Therefore, a cost model will provide an acceptable solution within this scenario. As identified

by Beeston (1987), “A cost model’s task is to estimate the cost of a whole design or of an

element of it, or to calculate the cost of effect of a design change.” Authors have used this

approach to solve the similar problems.

1.3 RESEARCH QUESTIONS

The following are the research questions.

1. What are the productivity constants of electrical installation technicians?

2. What are the influences of floor area on final sub-circuit costs?

3. What is the predictive power of the cost model?

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1.4 AIM AND OBJECTIVES OF THE STUDY

This study is aimed at developing cost models for predicting the costs of final sub-circuits in

residential electrical installations. The following objectives are proposed in achieving this

aim.

1. To assess the productivity of electrical installation technicians.

2. To assess the influence of floor area on final sub-circuit costs.

3. To assess the predictive power of the cost model.

1.5 JUSTIFICATION OF THE STUDY

Developing an accurate cost estimate is the first step in a successful electrical job. A

contractor who estimates poorly will ultimately fail, no matter how well his technical skills. If

he underestimates his costs, he will find himself either using his own funds to complete a job,

returning to his client to ask for more money or leaving the job incomplete or completed

poorly. Overestimating will put him at a competitive disadvantage and cause him to lose

work to better estimators, Robert (2012)

The study findings will therefore be of use to both clients and contractors alike in the

determination of preliminary cost estimate for electrical installation works thereby helping in

setting budget in client organization.

More so, the determination of a cost model for final sub-circuits in residential buildings will

be of great use and help to cost engineers/quantity surveyors/estimators in getting accurate

estimates of electrical installation works in the absence of electrical drawings for residential

buildings thereby the use of provisional sum which has been found to be inaccurate and

inconsistent as it is considered as a matter of individual intuition.

Also, the study will help the clients and electrical services contractors in the aspect of cost

planning and budgeting for the electrical installation works by ensuring that the cost of

building services does not varies uncontrollably for this aspect of building services work,

through the determination of cost significance and cost distribution of electrical items for

electrical installation works.

The cost model so derived will be of great to the client organizations, consultants and

contractors respectively.

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1.6 SCOPE AND LIMITATION OF THE STUDY

The scope of this research is limited to residential buildings. Such residential buildings to be

considered include bungalows and duplexes. Such residential buildings were categorized on

floor basis.

The study is limited to electrical services installation in residential buildings and covered

only the lighting circuits’ aspect of the final sub-circuits of the residential electrical

installations.

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CHAPTER TWO

LITERATURE REVIEW

2.1 BUILDING SERVICES

Managing building costs is a challenging task for the design team as well as for construction

managers, contractors, and consultants. Owners demand that their design and construction

teams respect the owner’s financial and economic objectives and that they control costs

during project delivery. This expectation is found in both the public and the private sectors in

all client industries, locations, and financial situations.

Owners also have in expectation that a budget prepared early in a project will be accurate and

that the project will be completed to the required scope, quality, and performance within that

budget (in terms of cost and time factors). Owners invariably place a high priority on cost

issues, regardless of the quality or other attributes of the project. They may even judge

success or failure exclusively in terms of cost.

During the past decade, professional organizations, educational institutions, government and

private entities have supported the development of building cost models and provided

seminars and other educational programs on this subject. The success of these efforts has

varied, but one issue has become clear: Achieving high-quality design and implementing

effective cost analysis and management are not contradictory objectives.

Nearly every decision an architect makes during the design stages and construction affects

project costs. Some decisions have direct effect on project costs and as such, straight forward

because they affect building quality or performance. Others are more subtle or have indirect

influence on project costs; affecting ease of construction, complexity of building elements, or

availability of materials. Michael (2013) was of the opinion that some decisions made by the

Architect can profoundly affect other disciplines, such as plenum depths that may confine

mechanical/electrical services or a building module that influences a structural grid. Unless

decisions are managed and expectations kept in check, costs may rise beyond budget limits.

Residential buildings (Wikipedia) are called houses or homes, though buildings containing

large numbers of separate dwelling units are often called apartment buildings or apartment

blocks to differentiate them from 'individual' houses. Houses may also be built in pairs (semi-

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detached), in terraces where all but two of the houses have others either side. Houses which

were built as a single dwelling may later be divided into apartments; they may also be

converted to another use e.g. an office or a shop.

Building types may range from one-room wood-framed, masonry, dwellings to multi-million

naira high-rise buildings able to house thousands of people. Increasing settlement density in

buildings (and smaller distances between buildings) is usually a response to high ground

prices resulting from many people wanting to live close to work or similar attractors. Other

common building materials are brick, concrete or combinations of either of these with stone.

Wikipedia (2013) defines building services engineering as the engineering of the internal

environment and environmental impact of a building. It essentially brings buildings and

structures to life. Building services engineers are responsible for the design, installation,

operations and monitoring of the mechanical, electrical and public health systems required

for the safe, comfortable and environmentally friendly operation of modern buildings.

Building services engineering comprises mechanical engineering, electrical engineering and

plumbing or public health engineering. Building services engineers work closely with other

construction professionals such as architects, structural engineers and quantity surveyors.

They influence the architecture of a building and play a significant role on the sustainability

and energy demand of a building.

As such, a typical building services engineer has a wide-ranging duties and responsibilities:

Design: designing layouts and requirements for building services for residential or

commercial developments.

Construction: supervising the construction of the building services, commissioning

systems and ongoing maintenance and operation of services.

Environmental: developing new energy saving methods for construction, designing

new and improved energy conservation systems for buildings.

Heating, ventilation and air conditioning (HVAC): specialising in the design,

development, construction and operation of HVAC systems.

Electrical technology: specialising in the design and development of electrical

systems required for safe and energy sustaining operation of buildings.

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2.1.1 THE CONSTRUCTION INDUSTRY

The construction industry is one of the UK’s biggest employers, and carries out contracts to

the value of about 10% of the UK’s gross national product. Although a major employer, the

construction industry is also very fragmented. Firms vary widely in size, from the local

builder employing two or three people to the big national companies employing thousands.

Of the total workforce of the construction industry, 92% are employed in small firms of less

than 25 people. The yearly turnover of the construction industry is about £35 billion. Of this

total sum, about 60% is spent on new building projects and the remaining 40% on

maintenance, renovation or restoration of mostly housing. In all these various construction

projects the electro-technical industries play an important role, supplying essential electrical

services to meet the needs of those who will use the completed building, Revor (2006).

Electrical contracting company is as a part of the broader construction industry. The

construction industry carries out all types of building work, from basic residential housing to

hotels, factories, schools, shops, offices and airports while the electrical contracting

companies are concerned with the electrical services installation activities which according to

Simon and Andy (2012) typically account for 20-30% of the total value of a project - and

sometimes a great deal more.

Electrical services works involves the actual physical work of installing, repairing, altering,

removing or adding to an electrical installation/accessories or the supervising of that work.

However, Lawrence (1993) listed five main categories of electrical accessories (as cited in

Keraminiyage, Amaratunga, Haigh and Perera, 2009) which are accessories in power circuits,

accessories in lighting circuits, protective devices, accessories in other circuits, cables and

other sundry items. Each of these categories comprise of several key accessories.

2.1.2 THE NIGERIAN CONSTRUCTION INDUSTRY

The Nigerian construction industry comprises the clients/employers, main contractors, sub-

contractors, nominated suppliers, and key professional actors responsible for design and

supervision of projects. The professionals includes the architects, builders, engineers

(structural and services), and Quantity Surveyors. The services engineers also include the

mechanical and electrical services engineers. There are professional bodies that regulate the

activities of these professionals; these professional bodies include- The Nigerian Institute of

Quantity Surveyors (NIQS), Nigerian Institute of Architects (NIA), Nigerian Institute of

23

Building (NIOB), The Nigerian Institute of Town Planners (NITP), Nigerian Institution of

Estate Surveyors and Valuers (NIESV), Nigerian Institution of Surveyors (NIS), Nigerian

Society of Engineers (NSE).

Contractors’ organizations in Nigeria are comprised of small, medium and large sized firms;

however, small and medium size firms are dominant which seems to in agreement with the

assertion of Revor (2006) as regards the predominant of small sized firms in the UK.

2.2 THE BUILDING TEAM

The construction of a new building is a complex process which requires a team of

professionals working together to produce the desired results.

The Client

The Client is the person or group of people with the actual need for the building and its

services (electrical services inclusive), such as a new house, office or factory. The client is

responsible for financing all the work and, therefore, in effect, employs the entire building

team. The building work starts with them and ends with them, this makes them a very

important part of the building them.

The Architect

This is the client’s agent and is considered to be the leader of the building/design team. The

architect must interpret the client’s requirements and produce working drawings and

sketches. During the building process the architect will issue out instructions as at when due,

approves payment to the contractor, supervise all aspects of the work until the building is

handed over to the client.

The Quantity Surveyors

The quantity surveyor measures the quantities of labour and material necessary to complete

the building services installation from drawings supplied by the architect

Quantity Surveyors are not electricians, and are not trained as such but are trained to

indentify basic faults. They cannot provide specific technical advice in relation to electrical

installations, for example, they cannot advise you how to rewire a property. The role of the

Building Control Surveyor is to provide a visual check during the installation to identify

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obvious signs of incompetence. They are not there to test, but more to ensure that the installer

has tested to ensure the work meets reasonable standards.

This clearly places the responsibility on the person carrying out the work to ensure that

inspection and testing of electrical installations is carried out. The Surveyors will also ensure

that during the course of the electrical installation work, other aspects of the Building

Regulations will have been complied with, for instance, they will consider the effect that the

electrical wiring will have on the structure, fire resistance, accessibility etc.

An inspection should be requested at pre-plaster stage, and once again upon completion.

The following professionals are also involved in electrical services wiring and installation

activities (Building Regulations – Part P 2006);

Specialist engineers advise the architect during the design stage. They will prepare drawings

and calculations on specialist areas of work.

The clerk of works is the architect’s ‘on-site’ representative. He or she will make sure that

the contractors carry out the work in accordance with the drawings and other contract

documents. They also ensure that materials delivered to site for the purpose of incorporation

into the building are of the required quality standard and are only delivered to site when

needed; they can also agree general matters directly with the building contractor as the

architect’s representative.

The local authority ensures that the proposed building and its services components conforms

to the relevant planning and building legislation.

The health and safety inspectors ensure that the government’s legislation concerning health

and safety is fully implemented by the building contractor.

The building contractor enters into a contract with the client to carry out the construction

work in accordance with contract documents. The building contractor is usually the main

contractor and he or she, in turn, may engage sub-contractors to carry out specialist services

such as electrical installation, mechanical services, plastering, plumbing and painting etc.

The electrical team

The electrical contractor is the sub-contractor responsible for the installation of electrical

equipment within the building.

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Electrical installation activities include:

installing electrical equipment and systems into new sites or locations;

installing electrical equipment and systems into buildings that are being refurbished

because of change of use;

installing electrical equipment and systems into buildings that are being extended or

updated;

replacement, repairs and maintenance of existing electrical equipment and systems

The building team

Source: Building Regulations – Part P 2006

The electrical team

An electrical contracting firm is made up of a group of individuals with varying duties and

responsibilities. There is often no clear distinction between the duties of the individuals, and

the responsibilities carried by an employee will vary from one employer to another. If the

firm is to be successful, the individuals must work together to meet the requirements of their

Clerk of works

QuantitySurveyors

SpecialistEngineers

Client

Architect

Local Authority

Building Contractor(main contractor)

Health and SafetyInspector

Suppliers of material,equipment and plant

Electrical, mechanical services,plastering, painting (sub-

contractors

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customers. Good customer relationships are important for the success of the firm and the

continuing employment of the employee.

Source: Revor (2006)

2.3 REQUIREMENTS FOR ELECTRICAL INSTALLATIONS

The Institution of Electrical Engineers Requirements for Electrical Installations (the IEE

Regulations) is non-statutory regulations. They relate principally to the design, selection,

erection, inspection and testing of electrical installations, whether permanent or temporary, in

and about buildings generally and to agricultural and horticultural premises, construction sites

and caravans and their sites. Paragraph 7 of the introduction to the EWR says: ‘the IEE

Wiring Regulations is a code of practice which is widely recognized and accepted in the

United Kingdom and compliance with them is likely to achieve compliance with all relevant

aspects of the EWR’. The IEE Regulations confirm this relationship at Regulation 114 which

states that compliance with the IEE Regulations may be used in a Court of Law to claim

compliance with a statutory requirement such as the EWR. The IEE Wiring Regulations only

apply to installations operating at a voltage up to 1000 V a.c. They do not apply to electrical

installations in mines and quarries, where special regulations apply because of the adverse

conditions experienced there.

ELECTRICALCOMPANY

ELECTRICALCOMPANY

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The current edition of the IEE Wiring Regulations is the 17th edition. The main reason for

incorporating the IEE Wiring Regulations into British Standard BS 7671: 2008 was to create

harmonization with European standards.

Building Regulations – Part P 2006

The Building Regulations lay down the design and build standards for construction work in

buildings in a series of Approved Documents. The scope of each Approved Document is

given below:

Part A structure

Part B fire safety

Part C site preparation and resistance to moisture

Part D toxic substances

Part E resistance to the passage of sound

Part F ventilation

Part G hygiene

Part H drainage and waste disposal

Part J combustion appliances and fuel storage systems

Part K protection from falling, collision and impact

Part L conservation of fuel and power

Part M access and facilities for disabled people

Part N glazing – safety in relation to impact, opening and cleaning

Part P electrical safety

Part P of the Building Regulations was published on 22 July 2004, bringing domestic

electrical installations in England and Wales under building regulations control. This means

that anyone carrying out domestic electrical installation work from 1 January 2005 must

comply with Part P of the Building Regulations. An amended document was published in an

attempt at greater clarity and this came into effect on 6 April 2006.

If the electrical installation meets the requirements of the IEE Regulations BS 7671, then it

will also meet the requirements of Part P of the Building Regulations, which implies that

there is no difference or change, what is going to change under Part P is this new concept of

‘notification’ to carry out electrical work.

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2.3.1 NOTIFIABLE ELECTRICAL WORK

Any work to be undertaken by a firm or individual who is not registered under an ‘approved

competent person scheme’ must be notified to the Local Authority Building Control Body

before work commences. That is, work that involves:

the provision of at least one new circuit,

work carried out in kitchens,

work carried out in bathrooms,

Work carried out in special locations such as swimming pools and hot air saunas.

Upon completion of the work, the Local Authority Building Control Body will test and

inspect the electrical work for compliance with Part P of the Building Regulations.

2.3.2 NON-NOTIFIABLE ELECTRICAL WORK

Work carried out by a person or firm registered under an authorized Competent Persons Self-

Certification Scheme or electrical installation work that does not include the provision of a

new circuit. This includes work such as:

replacing accessories such as socket outlets, control switches and ceiling roses;

replacing a like for like cable for a single circuit which has become damaged by, for

example, impact, fire or rodent;

re-fixing or replacing the enclosure of an existing installation component provided the

circuits protective measures are unaffected;

providing mechanical protection to existing fixed installations;

adding lighting points (light fittings and switches) to an existing circuit, provided that

the work is not in a kitchen, bathroom or special location;

Installing or upgrading the main or supplementary equi-potential bonding provided

that the work is not in a kitchen, bathroom or special location. All replacement work

is non-notifiable even when carried out in kitchens, bathrooms and special locations,

but certain work carried out in kitchens, bathrooms and special locations may be

notifiable, even when carried out by an authorized competent person.

The IEE have published a guide called the Electricians’ Guide to the Building Regulations

which brings clarity to this subject. In specific cases the Local Authority Building Control

Officer or an approved Inspector will be able to confirm whether Building Regulations apply.

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Failure to comply with the Building Regulations is a criminal offence and Local Authorities

have the power to require the removal or alteration of work that does not comply with these

requirements.

2.4 ELECTRICAL ACCESSORIES INSTALLATION

2.4.1 PVC INSULATED AND SHEATHED CABLES

Domestic and commercial installations use this cable, which may be clipped direct to a

surface, sunk in plaster or installed in conduit or trunking. It is the simplest and least

expensive cable. The figure shows a sketch of a twin and earth cable.

The conductors are covered with a colour-coded PVC insulation and then contained singly or

with others in a PVC outer sheath.

Fig 1: A twin and earth PVC insulated and sheathed cable. (Source- Revor 2006)

Installing cables

The final choice of a wiring system must rest with those designing the installation and those

ordering the work, but whatever system is employed, good workmanship by competent

persons and the use of proper materials is essential for compliance with the IEE Regulation

134.1.1. The necessary skills can be acquired by an electrical trainee/worker who has the

correct attitude and dedication to his craft.

PVC insulated and sheathed wiring systems are used extensively for lighting and socket

installations in domestic dwellings. Mechanical damage to the cable caused by impact,

abrasion, penetration, compression or tension must be minimized during installation

(Regulation 522.6.1). The cables are generally fixed using plastic clips incorporating a

masonry nail, which means the cables can be fixed to wood, plaster or brick with almost

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equal ease. Cables should be run horizontally or vertically, not diagonally, down a wall. All

kinks should be removed so that the cable is run straight and neatly between clips fixed at

equal distances providing adequate support for the cable so that it does not become damaged

by its own weight (Regulation 522.8.4 and Table 4A of the On Site Guide). Where cables are

bent, the radius of the bend should not cause the conductors to be damaged (Regulation

522.8.3 and Table 4E of the On Site Guide).

Terminations or joints in the cable may be made in ceiling roses, junction boxes, or behind

sockets or switches, provided that they are enclosed in a non-ignitable material, are properly

insulated and are mechanically and electrically secure (IEE Regulation 526). All joints must

be accessible for inspection testing and maintenance when the installation is completed (IEE

Regulation 526.3). Where PVC insulated and sheathed cables are concealed in walls, floors

or partitions, they must be provided with a box incorporating an earth terminal at each outlet

position. PVC cables do not react chemically with plaster, as do some cables, and

consequently PVC cables may be buried under plaster.

Where cables and wiring systems pass through walls, floors and ceilings the hole should be

made good with incombustible material such as mortar or plaster to prevent the spread of fire

(Regulation 527.2.1). Cables passing through metal boxes should be bushed with a rubber

grommet to prevent abrasion of the cable. Holes drilled in floor joists through which cables

are run should be 50 mm below the top or 50 mm above the bottom of the joist to prevent

damage to the cable by nail penetration (Regulation 522.6.5). PVC cables should not be

installed when the surrounding temperature is below 0°C or when the cable temperature has

been below 0°C for the previous 24 hours because the insulation becomes brittle at low

temperatures and may be damaged during installation (Regulation 522.1.2).

2.4.2 CONDUIT INSTALLATIONS

A conduit is a tube, channel or pipe in which insulated conductors are contained. The conduit,

in effect, replaces the PVC outer sheath of a cable, providing mechanical protection for the

insulated conductors.

A conduit installation can be rewired easily or altered at any time, and this flexibility,

coupled with mechanical protection, makes conduit installations popular for commercial and

industrial applications.

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There are three types of conduit used in electrical installation work: steel, PVC and

flexible (Revor, 2006).

1. Steel conduit

Steel conduits are made to a specification defined by BS 4568 and are either heavy gauge

welded or solid drawn. Heavy gauge is made from a sheet of steel welded along the seam to

form a tube and is used for most electrical installation work. Solid drawn conduit is a

seamless tube which is much more expensive and only used for special gas-tight, explosion-

proof or flame-proof installations.

Conduit is supplied in 3.75 m lengths and typical sizes are 16, 20, 25 and 32 mm. Conduit

tubing and fittings are supplied in a black enamel finish for internal use or hot galvanized

finish for use on external or damp installations. A wide range of fittings is available and the

conduit is fixed using saddles or pipe hooks, as shown in Fig. 2.

Fig 2: Conduit fittings and saddles

Source: Revor (2006).

2. Metal conduits

Metal conduits are threaded with stocks and die and bent using special bending machines.

The metal conduit is also utilized as the CPC and, therefore, all connections must be screwed

up tightly and all burrs removed so that cables will not be damaged as they are drawn into the

conduit. Metal conduits containing a.c. circuits must contain phase and neutral conductors in

the same conduit to prevent eddy currents flowing, which would result in the metal conduit

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becoming hot (Regulations 521.5.2, 522.8.1 and 522.8.11). PVC conduit PVC conduit used

on typical electrical installations is heavy gauge standard impact tube manufactured to BS

4607. The conduit size and range of fittings are the same as those available for metal conduit.

3. PVC conduit

PVC conduits are most often joined by placing the end of the conduit into the appropriate

fitting and fixing with a PVC solvent adhesive. PVC conduit can be bent by hand using a

bending spring of the same diameter as the inside of the conduit. The spring is pushed into

the conduit to the point of the intended bend and the conduit then bent over the knee. The

spring ensures that the conduit keeps its circular shape. In cold weather, a little warmth

applied to the point of the intended bend often helps to achieve a more successful bend.

The advantages of a PVC conduit system are that it may be installed much more quickly than

steel conduit and is non-corrosive, but it does not have the mechanical strength of steel

conduit.

Since PVC conduit is an insulator it cannot be used as the CPC and a separate earth

conductor must be run to every outlet. It is not suitable for installations subjected to

temperatures below 25°C or above 60°C. Where luminaries are suspended from PVC conduit

boxes, precautions must be taken to ensure that the lamp does not raise the box temperature

or that the mass of the luminaries supported by each box does not exceed the maximum

recommended by the manufacturer (IEE Regulations 522.1 and 522.2). PVC conduit also

expands much more than metal conduit and so long runs require an expansion coupling to

allow for conduit movement and help to prevent distortion during temperature changes.

All conduit installations must be erected first before any wiring is installed (IEE Regulation

522.8.2). The radius of all bends in conduit must not cause the cables to suffer damage, and

therefore the minimum radius of bends given in Table 4E of the On Site Guide applies (IEE

Regulation 522.8.3). All conduits should terminate in a box or fitting and meet the boxes or

fit-tings at right angles. Any unused conduit box entries should be blanked off and all boxes

covered with a box lid, fitting or accessory to provide complete enclosure of the conduit

system. Conduit runs should be separate from other services, unless intentionally bonded, to

Cables should be fed into the conduit in a manner which prevents any cable crossing over and

becoming twisted inside the conduit. The cable insulation must not be damaged on the metal

edges of the draw-in box.

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Cables can be pulled in on a draw wire if the run is a long one. The draw wire itself may be

drawn in on a fish tape, which is a thin spring steel or plastic tape. A limit must be placed on

the number of bends between boxes in a conduit run and the number of cables which may be

drawn into a conduit to prevent the cables being strained during wiring.

Other modules

4. Flexible conduit

Flexible conduit is made of interlinked metal spirals often covered with a PVC sleeving. The

tubing must not be relied upon to provide a continuous earth path and, consequently, a

separate CPC must be run either inside or outside the flexible tube (Regulation 543.2.1).

Flexible conduit is used for the final connection to motors so that the vibrations of the motor

are not transmitted throughout the electrical installation and to allow for modifications to be

made to the final motor position and drive belt adjustments.

2.4.3 TRUNKING INSTALLATIONS

A trunking is an enclosure provided for the protection of cables which is normally square or

rectangular in cross-section, having one removable side. Trunking may be thought of as a

more accessible conduit system and for industrial and commercial installations it is replacing

the larger conduit sizes. A trunking system can have great flexibility when used in con-

junction with conduit; the trunking forms the background or framework for the installation,

with conduits running from the trunking to the point controlling the current using apparatus.

When an alteration or extension is required it is easy to drill a hole in the side of the trunking

and run a conduit to the new point. The new wiring can then be drawn through the new

conduit and the existing trunking to the supply point. Trunking is supplied in 3m length. Most

trunking is avail-able in either steel or plastic.

2.5 WIRING

Every lighting system needs a cable from the mains to supply power to all the lighting points

and a switch that can interrupt the supply to each individual point. Here is the outline the two

most common ways to meet that requirement - the loop-in wiring and the radial wiring (also

referred to as 'junction box) installations (Revor, 2006).

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Loop-in wiring

The Figure below shows the basic principle of wiring a loop-in lighting system (the most

modern/common). The power from the mains consumer unit runs into each ceiling rose and

out again, then on to the next ceiling rose. The switch cable and the flex to the lighting fitting

are connected at the ceiling rose.

Fig 3: Loop-in wiring

Radial (or junction box) wiring

The figure below shows a typical radial (or junction box) lighting system, a two-core and

earth cable runs from the consumer unit to a series of junction boxes - one for each lighting

point (ceiling rose). From each junction box a separate cable runs to the light and another

runs to the switch. Whilst this system is rarely used now, it is much less complicated for the

consumer to connect new light fittings.

Fig 4: Radial (or junction box) wiring

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Replacing a light fitting is sometimes a simple task but other times it can be quite tricky.

Under modern Part P Building Regulations, a householder can carry out a 'like for like'

replacement or extend an existing lighting circuit providing that it is not within a kitchen or

special area (defined as a room with a bath, shower basin, pool or sauna). Any addition or

change within a kitchen or special area is notifiable or should be carried out by a suitably

qualified person.

If the client does intend to install the light fitting by himself, before touching the wiring, he

must switch off the lighting circuit at the consumer unit. It would also be wise to let the

people in the building know that he/she is working on the electrics and to hang something on

the consumer unit to remind them that the circuit is switched off for a reason.

Electrical wiring needs to be made of two main materials: a good conductor of electricity,

usually copper, and - to prevent the wires inside a cable from connecting to one another - a

very good insulator, usually PVC (poly-vinyl-chloride) or special rubber.

Cables used for special scientific or military uses may use silver or gold for their wires even

though they are very expensive compared to copper. Aluminium is a cheaper alternative to

copper, silver or gold. Aluminium is a much lighter and cheaper material to use as a

conductor but you must give up some amperage versus a cable that is the same size, but made

from copper, because aluminium is not such a good conductor.

2.6 ELECTRICAL SWITCHES

According Andrew (2013), a switch is an electronic device which stops the circuit and

transmits the current to conducts. It is a binary device which means that it has two states; the

on state or “closed” condition or off state or “open” condition.

The simplest type of switch is one where two electrical conductors are taken into contact with

each other by a current. Other switches are more complex which contain electronic circuits

which turn on or off depending on electric and magnetic field. Type includes electrical

switches, electronic switches and networking switches.

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Fig 5: A Switch

2.6.1 TYPES OF ELECTRICAL SWITCHES

1. Single Pole Switch

The single pole switch is the general purpose pillar of switches. It turns a light and device on

and off from a specific location. A typical single pole switch has two terminals for incoming

wire and the other is for outgoing wire to the device. This type of switch is ideal for

applications that require a lighting fitting to be turn on from a single location.

Fig 6: Single Pole Switch

2. Double Pole Switch

The double pole switch also has also an “on” and “off” markings and the purpose is similar to

a single pole switch. But, because it has four brass terminals instead of two terminals it is

capable of switching two wires which permits to switch a 240 volt circuit.

This type of switch is also very useful for corridors of buildings like schools, or hotels.

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Fig 7: Double Pole Switch

3. Three-Way Electrical Switches

The three way switch comes always in pairs and lets to turn a light or device on and off from

two different location. Three way switches each have three connections and are used

together. Instead of stopping the flow of electricity within them, they passed the electricity to

one connector or the other. So, whether one switch is up or down on one side of the room,

reversing the switch on the other side will turn the light on or off.

For example, a light in a hallway that can be controlled from the first floor and second floor,

or a light in a garage that can be turned on/off from the garage and the kitchen or pantry, etc.

Fig 8: Three-Way Electrical Switch Wiring

4. Four-Way Electrical Switches

The four way switch has four terminals and used relays to connect from three different

locations. It is normally used in combination with three-way switches. Each set of terminals

is one of the changed positions. When the switch is in the up position, the current can flow

through two terminals, when the switch is in the down position, the current flows through the

other two terminals.

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The four way switch appears as the same as a double pole switch but a four-way switch have

no “on” or “off” markings. The four-way switch has four terminals and there is no common

or ground wire like a three-way switch. The four-way switch simply functions as a switching

device for the traveler wires between the three-way switches. Four way switches can be used

in big ballrooms in hotels wherein it needs dozens of entrances and exits lights.

Fig 9: Four-Way Electrical Switch Wiring

2.7 ESSENTIAL TOOLS FOR ELECTRICAL INSTALLATION

Residential electricians work with electrical systems in and around the home. Industrial

electricians work with electrical systems on a larger scale, usually for office buildings, or the

wiring for a whole floor. However, nearly all electricians require the same tools, which may

be hand-held or electrically powered. These tools allow the electrician to complete his work

with ease, precision and security.

Electrical work or installation will require a few tools to accomplish the job. This is a partial

list of needed tools to take care of most electrical jobs. These tools are readily available at

most building material outlet stores or electrical wholesalers.

These tools are listed below with the descriptions which will help in selecting the proper tools

for the type of electrical projects encountered.

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1. Blueprints

Blueprints show the placement of electrical components. The most important tool for every

electrician--and the tool used firs--is the blueprint. Electricians use blueprints as a guide to

where wiring and electrical systems are located or should be located. These diagrams show

circuits, outlets, panel boards, switches and other components. Using this, an electrician will

then connect all the components using wires to create an electrical system.

2. Hand Tools

Screwdrivers are an important hand-held tool. Hand tools include common work tools such as

pliers, screwdrivers and wire strippers. The two most common pliers are the side-cutting

pliers and needle-nose pliers. These are used to grip, hold or bend wires. Screwdrivers are

used to tighten or loosen screws, which fasten components like outlets to the wall. Wire

strippers are used to remove the insulation from the end of a cut wire.

3. Measuring

A tape measure has both imperial and metric units. Measuring devices allow electricians to

measure walls, wire, lengths and widths in order to accurately work. They are made of a thin,

bendable metal with units in feet and inches, and centimetres and millimetres. Laser

measuring devices allow electricians to point at their intended target and then press a key that

gives a distance reading. They are more convenient for measuring very long distances.

4. Power Tools

A power drill has attachments for drill bits and screw bits. Power tools perform just like

hand-held tools, but are faster and more convenient. A power drill can screw and unscrew

without the repetitive hand motions. They can also bore holes into a wooden wall. To bore

through concrete, a heavy-duty power tool is needed.

5. Saws

Powered saws cut faster and easier than hand held saws. There are hand held and powered

saws available to electricians. Hand held saws can be used for quick cutting like a

40

reciprocating saw, but for more intense jobs an electrician might need a portable band saw or

a circular saw.

6. Meters

Electricians can use voltmeters to check their work. In order to make sure electrical

installation complies with electrical regulations, testing equipment is used. Ammeters

measure electrical current in amperes and voltmeters measure the electrical difference of two

points. The ohmmeter measures electrical resistance in ohms

Timothy (2013) also outlined some electrical tools which are essentials for electrical services

installation.

1. Fish Tape

A fish tape is used to pull stranded or solid wire through metal or PVC conduit. Cable lube is

also made use of in pulling the wires through the pipe.

2. Tape Measure

A tape measure is used to measure heights for switches and outlets. You will also need it to

centre lighting fixture boxes.

3. Voltmeter

A voltmeter is used to check voltages and verify that circuits are indeed “live”.

4. Hammer

A hammer is used to secure boxes equipped with nail-on brackets to studs in a home.

5. Channel Lock Pliers

Channel lock pliers are used to take knockouts out of the boxes, tighten down connectors in

the boxes, and adjust expansion-type ceiling-fan boxes.

6. Wire Strippers

Wire strippers are used to cut the insulation off of the wire. They are equipped with different

sized cutting teeth for various sized wires. They also have a cut-off portion in order to cut the

wire.

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7. Non-contact Voltage Detector

A voltage detector is used for a quick safety check to see if there is voltage or current flow

present. Some of these devices are automatic and some must be turned on via a switch.

8. Side Cutter Diagonal Pliers

These cutting pliers, sometimes called side snips, are used to cut wire. They are specially

designed with a cutting edge that goes down to the tip of the pliers. It has the advantage of

being able to trim wires in tight areas. There are some that are equipped with live wire

detection capabilities.

9. Linesman Pliers

These pliers are the do-it-all pliers. They cut, twist wires together, and grip wires for pulling.

They have a squared off end that is great for twisting wires together, a center cutting blade for

cutting wire, and a grip area between the handles to pull wire.

10. Torpedo Level

A level is used to make sure the electrical work is level and plumb. A great installation starts

with straight switch and outlet covers.

11. Flashlight

A light comes in handy in those places where lighting is limited. Never try to reach into a

panel without proper lighting.

12. Allen Wrench Set (Hex Set)

Allen wrenches are used to tighten Allen-headed screws in the electrical panel.

13. Razor Blade Knife (Utility Knife)

This knife is needed to cut the insulation off of wiring. There may be need to open boxes

when doing installation and this tool will come in handy.

14. Screwdriver

A screwdriver has four blades used to install head screws. The tip looks like a plus sign.

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15. Straight-Blade Screwdriver

This screwdriver is used for straight slot screws.

16. Wire Crimpers

This tool strips the wire and also crimps lugs onto the wire.

2.8 PRINCIPLES OF ELECTRICAL INSTALLATION

Fig 10: Electrical distribution

Source: Mohammed (2012)

Distribution Board

This is where distribution of electrical energy to various connected load take place inside the

consumer premises. It also distributes the path for the earthing and neutral wire, and acts as

means of flowing leakage and return current respectively. It is situated inside building and

includes equipment such as circuit breaker and fuse

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Trunking

A rectangular metal made system that either horizontally or vertically fixed to wall. Has a

good mechanical protection. Available size: 50mm x 50mm; 70mm x 100mm; 150mm x

75mm; 150mm x 150mm and equipped with bend, tee, and junction.

2.8.1 Internal Distribution

It may be taken as a general statement that all types of load in a 2-wire installation, lights,

heaters, etc., are connected in parallel at the same voltage. Francis (1996) observes that an

internal distribution system consists in the connection in parallel of a group of loads in a final

circuit and the connection of this final circuit to local distributing busbars in a distribution

board. Each individual load may be separately controlled by a switch in its own circuit. The

separate groups are controlled by fuses or circuit-breakers. Thus, any individual load, or any

group, or the whole is controlled by circuit-breaker, switch, or fuse. The above principle

general system applies to all types of installation, large or small.

2.8.2 Wiring circuits for Lighting

The method for wiring final lighting circuits may be the loop-in, three-plate or the joint-box

methods, Francis (1996).

A) The loop-in method

This enables all joints or terminations to be made at ceiling roses, luminaries, switches or

other accessories. Hence all such joints remain accessible for the purpose of alterations,

additions or for testing. The loop-in method is used with conduit or trunking installations and

although more cable is used, the avoidance of jointed conductors in boxes is seen as a big

advantage.

B) The 3-plate method

This avoids the greater use of cable, as joints are made in the ceiling roses which have

shrouded terminals (to BS 67). The phase conductors are joined here rather than ‘looping in’

at the switch positions. The 3-plate method is widely used on domestic lighting installations

employing wiring systems such as p.v.c sheathed, p.v.c. insulated twin, or 3-core with c.p.c.

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C) Ring final circuits

Each circuit conductor for a ring final circuit commences from a fuseway (30A) at the

distribution board, looping into each socket outlet or fused spur unit and return to the same

fuseway to form a closed ring. This allows for the load current at a particular socket outlet to

be shared between both conductors supplying that socket outlet.

If a separate circuit protective conductor is run, either within a sheathed cable or as a single

insulated (green/yellow) conductor, then this conductor must also commence at the earthing

terminal within the distribution board, looping into all socket outlets and fused spur units

before returning to the same earthing terminal, in exactly the same way as the wire

conductors. The socket outlets used for domestic ring and radial circuits will comply with BS

1363 and are shuttered to prevent accidental contact with live parts.

Two-way intermediate switching: When it is necessary to control a lighting outlet from two

positions, then a 2-way lighting switching circuit may be utilized. When three or more control

positions are necessary then a 2-way intermediate circuit will be required.

2.8.3 Water heating circuits

In a domestic electric water-heating installation, it is normal to install a 3kW immersion

heater, which is screwed into a boss fitted directly into the hot-water cylinder or tank. Such

cylinders or tanks will have a capacity exceeding 15litres. The immersion heater circuit must

be separate from any other circuit. Such a circuit will be protected by a 15A fuse or MCB and

controlled by a 20A double-pole switch having a neon indicator. Final connection to the

heater from the DP switch is normally by 85°C rubber insulated HOFR (heat, oil and flame

retardant) sheathed 3-core flexible cord.

2.8.4 Cooker circuit

There are various types and arrangements for electric cookers in modern kitchens, ranging

from a free-standing cooker to one built into the kitchen units. Latterly, it has become

fashionable to have ‘split level’ cookers whereby a hob unit is built into the worktop, and the

oven/grill unit is housed in the kitchen units. Every fixed or stationary domestic cooking

appliance must be controlled by a double-pole switch separate from the appliance, and has to

be within 2m of the appliance. Such a switch may control both a hub unit and the oven unit

provided that both appliances are not more than 2m from the switch. It is becoming common

45

practice to use a 45A double pole switch incorporating a neon indicator lamp to control

cooking appliances, rather than use cooker control units having a built-in 13A socket outlet.

2.8.5 WIRING SYSTEMS

Francis (1996) defines a wiring system as that which consists of the conductor, its insulation,

its mechanical protection and the various accessories, such as joint boxes etc. the systems are

named mainly in terms of the mechanical protection used. In considering the use of any

particular wiring system, it should be realised that no system can be the ideal one under all

conditions.

Also, Gupta (2009) defines a wiring system as a network of wires connecting various

accessories for distribution of electrical energy from the supplier meter board to the

numerous electrical energy consuming devices such as lamps, fans and other domestic

appliances through controlling and safety devices.

A number of points must be considered e.g. neatness of the finished job; the durability of the

installation; future extensions and alterations; the time required to do the work; damage to the

fabric of the building by cutting away; special conditions to be withstood, such as fumes,

dampness etc.; and the total cost of the job. A surface system will normally necessitate much

less cutting away than a hidden system.

The various systems used for lighting and small power are (Francis, 1996):

1. Bare conductor wiring

2. Steel conduit:

a. Slip-joint conduit with grip fittings

b. Screwed conduit

3. Non-metallic conduit

4. Rubber-sheathed (t.r.s.)

5. P.V.C. sheathed

6. Earthed-concentric

7. Mineral-insulated metal-sheathed

8. Special systems for different conditions

Bare conductors

46

Light insulated or bare conductors may be used for such purposes as earthing connections,

rising mains and busbar systems, collector wires for cranes etc. they should not be used

where flammable or explosive dust, vapour, or gas is present or where explosive materials are

handled or stored. Bare conductors used for rising mains or bus-bars should be installed only

in places inaccessible to unauthorized persons and be supported by insulators so as to be free

to expand and contract with changes of temperature. Conductors passing through walls,

floors, partitions or ceiling shall pass through directly and be protected by incombustible

insulating material, or earthed metal trunking.

Mineral-insulated metal-sheathed system

This type of cable is now extensively used because of its special qualities and advantages.

The cable may be used at much higher temperatures than rubber-insulated or p.v.c. cable, and

is thus suitable for installations in boiler houses, heat treatment shops and the like, Francis

(1996). The cable may also be used successfully under conditions of humidity and moisture.

Steel conduit systems

Annealed mild steel tubing is very widely used for enclosing v.i.r. or p.v.c. - insulated cable

or any other insulated cable. The conduit is specially annealed so that it may readily be bent

or set to any angle without breaking, splitting, or kinking. B.S. specifications govern the

manufacture of the classes of conduit given. Common standard sizes of conduits are 16mm,

20mm, 25mm and 32mm external diameters

Wire and Cable

Gupta (2009) observed that the terms wire and cable are used more or less synonymous in

house wiring. Strictly speaking, single wire may be bare or covered with insulation, is known

as a wire and several wires stranded together is known as a cable. But in practice bare

conductors, single or stranded together are termed as wires and conductors covered with

insulation are referred to as cables.

The necessary requirements of a cable are that it should conduct electricity efficiently,

cheaply and safely. This should neither be so small as to have a large internal voltage drop

nor be too large so as to cost too much. Its insulation should be such as to prevent leakage of

current in unwanted direction and thus to minimize risk of fire and shock.

47

The cable consists of three parts:

1. The conductor or core, that is, the metal wire or strand of wires carrying the current

2. The insulation or dielectric, that is, a covering of insulating material to avoid leakage

of current from the conductors and

3. The protective covering for protection of insulation from mechanical damage.

2.8.6 FIXING THE CONDUITS

Conduits is fixed to bare brick walls by means of crampets, but on finished surfaces such as

plastered walls, enamelled saddles or clips are preferred as making a neater job. The saddles

and clips are screwed to plugs fitted into drilled holes in the wall surfaces. Large wooden

plugs made on the job are unsuitable, as they dry out and become loose later. Conduit fitting

should be screwed together very tightly, as a loose connection involves loss of electrical

continuity. All screwed should be painted after erection, with a good lead or aluminium paint,

which should also be applied to any part of the conduit where the enamel has been damaged.

Conduit fittings: Different kinds of conduit fittings are available, the full range can be found

in the manufacturers’ catalogues. They include screwed elbows, bends and tees, non-

inspection, inspection and split types, junction boxes, circular, oblong, or square. A square

‘adaptable’ box is most useful when a number of conduits running together change direction.

Drawing in the wires: The conduits of each circuit should be erected complete before the

cables are drawn in. One important advantage of drawing in wires after the fixing of the

conduit is the fact that this may be done after all plastering is completed and the walls are

dried out.

2.8.7 WIRING ACCESSORIES

The following are the variety of the wiring accessories available for electrical installation

work (Francis, 1996).

Lampholders: These are designed for quick removal and replacement of the lamp,

and yet they must hold the lamp in firm metallic contact to prevent overheating. There

are three main sizes of Lampholders according to Francis (1996): the Bayonet-cap

(B.C.), the medium Edison screw (E.S.) and the Goliath screw (G.E.S.). There are

other variations such as the three-slot B.C. for the smallest discharge lamps.

Lampholders may be either the insulated type of Bakelite or the brass type with

48

porcelain interior. In wiring lampholders, care must be taken in baring the flexible

wire. The stranded wires must be well twisted together and should not be allowed to

splay, as a loose single strand may touch either the metal frame of the holder or the

opposite terminal.

Plugs and socket-outlets: These are required to enable portable apparatus to be

connected to the final circuits. The socket-outlet is the fixed position connected to the

fixed wiring, and comprises two or three contact tubes and terminals. The plug is the

movable part connected to the apparatus by flexible wire, and comprises two or three

contact pins to fit into the contact tubes. Plugs and socket-outlets are made to British

standard specifications.

Distribution boards: By definition, the distribution board is an assemblage of parts,

including one or more fuses or circuit breakers, arranged for the distribution of

electrical energy to final circuits or to other distribution boards. The regulations

require that the neutral conductors for the different circuits shall be connected in the

same order as the live conductors to the fuses. This is to ensure that no mistakes arise

when disconnecting a circuit. Some distribution board are designed to contain circuit

breakers instead of fuses.

2.8.8 EARTHING SYSTEMS

An earth can be defined as a connection to the general mass of earth. A conductor or other is

‘earthed’ when it is effectually connected to the general mass of the earth by means of a

metal rod or a system of metal water-pipes or other conducting object, and ‘solidly earthed’

when it is earthed without the intervention of a fuse, switch, circuit breaker, resistor, reactor

or solenoid. Obviously, then for safety reasons, any metal liable to become charged should be

earthed, and every part of the earthing circuit should be properly installed (Francis, 1996).

Earthing means connections of the neutral point of a supply system or the non-current

carrying parts of electrical apparatus, such as metallic frame work, metallic covering of

cables, earth terminal of socket outlet, stay wires etc., to the general mass of earth in such a

manner that all times an immediate discharge of electrical energy takes place without danger

(Gupta, 2009).

49

Earthing is provided (Gupta, 2009);

1. To ensure that no current carrying conductor rises to a potential with respect to

general mass of earth than its designed insulation.

2. To avoid electric shock to the human beings, and

3. To avoid risk of fire due to earth leakage current through unwanted path.

2.8.9 CHOICE OF WIRING SYSTEMS

Gupta (2009) observed that the success or failure of a wiring installation depends very largely

on the proper selection of the type of wiring, size and position of light/fan points. Gupta

(2009) also believed that the choice of any wiring system for a particular installation should

be based on technical and economic considerations, both in the context of the wiring system

itself and the installation for which it is proposed. In general, Gupta (2009) outlined the

following factors as it affects the choice of wiring systems;

1. Safety

It is one of the most important factors to be considered. Sometimes poor workmanship may

lead to dangerous results. The first and foremost consideration is safety to the person using

electricity against leakage or shock. For instance, in factory where lot of fumes are produced,

cleat or casing-capping wiring cannot be employed. Where there is possibility of fire hazard,

conduit wiring must be used.

2. Durability

The type of wiring to be selected must be durable and it must be of proper specifications and

also in accordance with accessed life and type of building. For example, cleat wiring suitable

for temporary buildings will definitely be unsuitable for a permanent building. The wiring

should be able to withstand wear and tear due to weather and it must be capable of carrying

the maximum current without overheating.

3. Appearance

The wiring must provide a good look after its installation. In case cleat or casing-capping

wiring is used in a modern beautiful house, it will spoil the outlook of the building. From

aesthetic point of view, concealed conduit wiring system provides beautiful and good

50

appearance but is costly. PVC wiring system also provide good appearance, and is very

popular nowadays.

4. Mechanical Protection

The wiring must be protected from mechanical damage during its use.

5. Permanency: The wiring must not deteriorate unduly by action of weather, fumes,

dampness etc.

6. Accessibility: In a selected wiring system, there should be facilities for extension,

renewal or alterations.

7. Initial Cost: The initial cost of the wiring system to be selected is one of the main

points to be considered. The wiring system selected should be safe as well as economical.

8. Maintenance Cost: The wiring system selected should have, as far as possible, low

maintenance cost.

The other factors, in addition to above, to be kept in view while making the choice of wiring

system are load, voltage to be employed, type of building etc.

2.8.10 CIRCUITS AND SUB-CIRCUITS

Electrical apparatus are connected by cables, to the supply main and to the associated

protecting and controlling devices (usually fuses and switches). This arrangement of cables is

known as a circuit.

A Circuit that feeds apparatus directly is known as sub-circuit; when connected to a

distribution board, this is known as a final sub-circuit. (Gupta, 2009)

1

Table 2.1: Comparison between various systems of wiring

S/N PARTICULARS CLEAT WIRING WOOD CASING

CAPPING

WIRING

TRS WIRING LEAD SHEATHED

WIRING

CONDUIT WIRING

1 Material

required

Cleats, VIR or

PVC cables,

screws, gutties,

blocks, boards etc.

Teak wood casing

and capping, VIR or

PVC cables, wooden

gutties, screws,

blocks, boards etc.

Teak wood batten,

TRS or PVC

cables, wooden

gutties, nails, links

clips, boards etc.

Teak wood batten,

lead sheath cables,

wooden gutties,

screws, clips or joint

clips boards, round

boards etc.

Conduit pipe, VIR or PVC

cables, saddles or pipe

hooks, wooden gutties,

screws, IC boxes, IC bends,

tees etc., with IC socket and

screws.

2 Cost Low Medium Medium Costly Very costly

3 Voltage Low (up to 250 V) Low (up to 250 V) Low (up to 250 V) Low (up to 250 V) Low or medium (up to

660V)

4 Life (durability) Very short Fairly long Long Long Very long

5 Protection

against fire

Poor No Fair Good Very good

6 Mechanical

protection

None Fairly good Good Fairly good Very good

7 Dampness

protection

None Poor Good Good Fairly good

8 Appearance Not good Fair Good Fair Very good

2

9 Safety No Medium Medium Medium High

10 Type of labour

required

Semi-skilled Highly skilled Skilled Skilled Highly skilled

11 General

reliability

Poor Good Good Fairly good Very good

12 Additions or

alterations to the

existing wiring

Very easy Difficult Easy Not very difficult Most difficult

13 Number of

points that can

be wired per day

by a man with a

mate

6 4 5 4 3

14 Fields of

application

For temporary

installations e.g.

for functions,

marriages etc.

For residential,

commercial and

office buildings but

now-a-days being

replaced by PVC

wiring on account of

additional

advantages.

For residential,

commercial and

office buildings but

now-a-days being

replaced by PVC

wiring on account

of inherent

advantages.

Only used for service

mains etc. because of

its high cost and

heavy short circuit in

case of leakage.

Mainly for workshops and

public buildings where

economy is not the prime

factor

Source: Gupta (2009)

1

2.9 MEASUREMENT OF ELECTRICAL SERVICES

The measurement of electrical services poses many of the same problems as the mechanical

services. In fact the two are often grouped together and referred to as ‘m and e services’ as a

collective term. A sound knowledge of electrical technology is required to understand the

specification and to interpret the schematic drawings provided by the consulting engineer.

Also a detailed knowledge of the IEE regulations for the equipment of buildings and

knowledge of circuitry and wiring systems is essential so that trunking, tray and conduit runs

can be plotted and the correct number of cables required measured for the two groups of

services.

Where circuits are to be measured in detail, such as circuits other than lighting and small

power, the route of the conduit and cable must be plotted on the plan or tracing overlay and

the number of cables indicated. This sketch will then form a record of what is taken. When

plotting conduit and cables it is usual to draw runs at right angle to each other rather than

running diagonally. This is usually necessary because of the nature of the structure through

which the conduits and cables are passing, as for example following joists and beams.

Conduits can sometimes be laid diagonally where running in floor, screeds or in pitched roof

spaces.

Once the route has been plotted and the specification fully understood, the measurement is

relatively straightforward comprising basically enumerated items of equipment and final

circuits and linear items of conduit, cable trunking, cable tray and cable, all measured in

accordance with the rules prescribed in BESSM3.

Murray (1997) outlined that cabling involved in final lighting and power circuits is not

normally designed in detail, and the actual routes and locations of cable runs are usually left

to the contractor, who in turn will often leave this to site supervisory staff to decide. This

situation makes detailed measurement of final circuits very difficult for the quantity surveyor,

who would require very intimate knowledge of the installation in order to make an educated

estimate of the linear metres involved from layout drawings. This detailed requirement as

contained in the BESSM3 is often avoided by quantity surveyors in practice by putting the

whole installation of electrical works into the bill as a provisional sum.

2.9.1 INFORMATION REQUIRED FOR EFFECTIVE MEASUREMENT OF

ELECTRICAL INSTALLATIONS

Drawn information is generally required for measurement of electrical installations. At times,

drawn information is supplemented with visual information obtained through site visits with

particular reference to maintenance/refurbishment works. Item 5 under the general rules in

the BESSM3 further subdivided drawn information into location drawings, component

drawings, dimensioned drawings (schematic drawings) and schedules.

A. Location drawings

a) Block Plan: The block plan does not only identify the outlines of a proposed

construction/development, in addition, it shows the geographical location of the

proposed development by identifying a popular street/road along which the

development is to be sited as well as some prominent features within the locality that

will make the very site easily discernible. Block drawing is very vital for Electrical

installation particularly if the source of supply to the building is located within the

area covered by the drawings.

b) Site Plan: As the name implies, the site plan shows intended or planned use of the

land. In other words, it shows the setting out of the various facilities intended for

development on the plot

c) Plans: The earlier plans (block plan and site plan) will not show the details of

internal electrical installations such as lighting and power circuits. It is the plan for

each floor that shows such. Thus the plans show details of the electrical installation in

individual floor in the case of buildings and detailed layout in the case of external

installations. For purpose, in the case of building projects the plans are classified into:

i. Lighting Installation: Plans showing only the lighting points within the plan

of a particular floor.

ii. Power Installation drawings: Plan showing only the power points within a

floor. Power points include all the socket outlets, including water heater

points. In other words, power points are made up of outlet points through

which electrical appliances are connected. In addition, power installation,

include TV outlet points, close circuit television outlets, telephone outlet

points, etc.

B. Component Drawing

Component drawings required for electrical installation include catalogues and

brochures which give specific information on the various components of electrical

installations.

C. Schematic Drawings

The schematic drawings for electrical installations could be likened to dimensioned

drawings for building works. The schematic drawings show the order of arrangement of the

various components that make up the electrical installation including the size and rating of

the components; the sizes, number and type of cables servicing each component and the type

of final circuits. Thus, the schematic drawings give detailed information of the installation,

Abhulimhen (2009).

D. Schedules

The commonest schedule in electrical installation is often classified as legend. The

legend contains the interpretation of the symbols contained in electrical installation drawings.

Work Classification

Electrical installation is basically subdivided into Electrical Supply/Power/Light systems and

Communications/Security/Controls system (Appendix b of BESMM3). The list in each work

classification could be regarded as a checklist; in other words, all the items may not be

applicable to the project on hand at a particular point in time. All that is needed by the

quantity surveyor is to carefully study the project at hand, identify the relevant items and then

generate a checklist for the proposed project; the next stage will be the commencement of

measurement in the order of the checklist so developed. In other words, BESSM3 like the

previous versions before it is basically based on the measurement of trades relating to each

item of work.

2.9.2 ELECTRICAL INSTALLATION ITEMS FOR MEASUREMENT

The trades covered in BESMM3 could be summarized as follows;

a. Conduit and Cable trunking (Y60)

b. Supports components- cables (Y63)

c. HV/LV Cables and Wiring (Y61)

d. Busbar Trunking (Y62)

e. Earthing and Bonding components (Y80)

f. HV Switchgear (Y71)

g. Switchgear and Distribution boards (Y71)

h. Contactors and Starters (Y72)

i. Motor drives- electric (Y92)

j. Luminaires and lamps (Y73)

k. Accessories for electrical services (Y74)

l. Testing and Commissioning of Electrical Services (Y81)

m. Identification (Y82) and

n. Sundry Common Electrical Items (Y89)

Having listed the basic trades covered under electrical installations, the next question that

readily comes to mind bothers on how the various trades are measured. The answer

absolutely resides in BESMM3 hence understanding the application of BESMM3 is

imperative for effective measurement of electrical installations like other sections of

construction works.

2.9.3 CONCISE MEASUREMENT PROCEDURE

Conduits: Conduits (not in final circuits) is measured in metres, distinguishing between

straight and curved, giving the radii, and stating the type, external size, method of fixing and

background as SMM Y60.1.1-2.1.1-5, and particulars of materials as appropriate (SMM

Y60.S1-6). The conduit is measured over all the conduit fittings and branches (SMM

Y60.M2). The conduit is deemed to include bending, cutting, screwing, jointing and such

conduit fittings as tees, elbows, bends, cover plates, bushes, locknuts etc.

Connections of conduit to trunking and to equipment and control gear are enumerated, stating

the type, size and method of jointing (SMM Y60.3-4.1-2.10).

Cable trunking, cable tray, ladders and racks: These are measured similarly to conduit,

but additionally stating the method of jointing and spacing and method of fixing supports

(SMM Y60.5 & 8.1-2.1.1) and both trunking and cable tray are deemed to include

components for earth continuity (SMM Y60.C5 & 7). Fittings for trunking, cable tray,

ladders and racks, which include stop-ends, bends, tees, crosses, offsets and reducers are

enumerated as extra-over the items in which they occur (SMM Y60.6 & 10.1.1.1 and Code of

Procedure).

Final Circuits: Final circuits are basically of two types, namely the final circuit not forming

part of a domestic or similar simple installation from distribution boards and the like and

those that are part of domestic installation or similar simple installation from distribution

boards. While the former include telephone installation, television outlets, CCTV etc. the

latter include lighting and power points. While the former are kept separate and measured in

details in accordance with Sections Y60, Y61, Y63 and Y82, the latter are enumerated as

earlier mentioned. There is always some mix up in the measurement of final circuits from

distribution boards. Most bills of quantities often enumerate the points and not the final

circuits. This is generally regarded as the contractor’s method by=ut not in accordance with

BESMM3.

2.10 COST SIGNIFICANT MODELS

All procurement systems require a contractor to predict the cost of a project, and to determine

a price for the work with a client. The traditional pricing method involves the contractor

pricing the bill of quantities (BoQ) that lists all the items of work in a project, on the premise

that it provides a means of comparing bids from several contractor on a like for like basis

(Munns and Al Haimus, 2000). Munns and Al Haimus (2000) observes that the BoQ as a

method of pricing is not without criticism, one of which is that very large number of small,

insignificant items that requires estimating. This has been described as excessive, creating the

possibility for disputes (Edwards and Edwards, 1995). This method of pricing (use of BoQ)

has been criticised by Horner and Zakieh (1996) because considerable effort is associated

with pricing the large number of small items, distracting the attention of the estimator away

from the important items in the BoQ. The excessive amount of small items has been shown to

possess a wide variety of rates when estimated (Beeston, 1983), perhaps highlighting the

problems associated with trying to predict the price of these items accurately.

Cost significant estimating is one way of predicting the likely cost of a project to a client,

while overcoming the problem of pricing large numbers of small items. From previous

research works by (Barnes and Thompson, 1971; Ashworth, 1981; Seeley, 1981; Ashworth

and Skitmore, 1983; Harmer 1983) have observed and commented upon the fact that 20% of

the measured bill items contribute 80% of the total measured bill value. These findings

conform to the 80/20 rule established by Vilfredo Pareto. The 20% of the items which have

the highest value are generally referred to as the cost significant items.

To develop the model and to test the model and also to test the suitability of the methodology,

a study was completed for 40 housing units- 20 residential bungalows and 20 duplexes

making use of both the architectural and electrical drawings for both set of drawings. The

measurement for the electrical services where done using the Building and Civil Engineering

Standard Method of Measurement (BESMM, 2009) and priced competitively using a single

price bill. A market research/survey was carried out to get the market prices for the electrical

accessories. This method was used to remove the variability of different pricing methods.

This same method was employed by Munns and Al Haimus (2000) in developing a model

while carrying out a research on 41 housing units, 22 of which were of timber framed

construction and 19 were built up of traditional bricks and external walls.

2.10.1 COST ESTIMATION FOR ELECTRICAL SERVICES

A cost estimate establishes the base line of the project cost at different stages of development

of the project. A cost estimate at a given stage of project development represents a prediction

provided by the cost engineer or estimator on the basis of available data. According to the

American Association of Cost Engineers, cost engineering is defined as that area of

engineering practice where engineering judgment and experience are utilized in the

application of scientific principles and techniques to the problem of cost estimation, cost

control and profitability.

Cost estimation of electrical services with high accuracy at the early phase of project

development is crucial for planning and feasibility studies. According to Oberlender and

Trost (2001), conceptual cost estimates are not expected to be precise, but inaccurate

estimates may lead to lost opportunities, and lower than expected returns.

However, a number of difficulties arise when conducting cost estimation during the early

phase. Comparative studies on the building services are rare, mainly because of the lack of

large, reliable, and homogenous database of installation costs. Moreover, most architectural

drawings for residential buildings are not usually accompanied with its corresponding

detailed electrical drawings, thereby making research in this domain difficult. While it is

widely held that a perfect estimate is not possible and even the best possible estimate will

always contain a number of key risks, the goal of the forecaster is a practicable level of

accuracy (Smith 1995). Given its significance, conventional tools such as regression analysis

have been widely employed to tackle the problem.

2.10.2 APPLYING COST-ESTIMATING METHODS

Any cost-estimating method used should be consistent with the level of information available

and the time available to prepare the estimate. Cost estimating methods tend to fall into four

major categories:

Single-unit rate methods (SUR)

Parametric/cost modelling

System/elemental cost analysis

Quantity survey

Application of Estimating Methods during Project Delivery

Source: Michael (2013)

The accompanying figure shows when these estimating methods generally can be applied to

overall delivery of a project.

Single-unit rate methods tend to be appropriate in the planning and programming phases of a

project. Parametric and cost model estimates are generally used during schematic design and

early design development. Systems and elemental estimates are best during design

development and early construction documentation. Estimates based on a quantity survey can

be used almost any time but are generally most appropriate when documents are reasonably

detailed, such as during design development, construction documentation, and bidding and

construction. At any time, these techniques may be used to cross-check overall costs.

1. Single-Unit Rate Estimating Methods

According to Michael (2013), Single-unit rate estimating methods are subdivided into four

major categories:

Accommodation method

Cubic foot method

Square foot method

Functional area method

Accommodation method: For this method, an estimate of overall construction cost is

calculated using the cost of selected units of the facility as a baseline. For example, parking

garages can be measured per parking stall. Apartment buildings might be measured on cost

per apartment. Performing arts facilities and auditoriums can be measured on cost per seat.

Hospitals may be measured on cost per bed. The accommodation method is often used to

provide very preliminary estimates or to provide a quick check and assessment of a current

project estimate.

Cubic foot method: This method of analysis is not generally used in the United States except

for volume-dependent facilities such as warehouses. Although it can be effective, the cubic

foot method tends to be awkward for use in most facility types. Nonetheless, certain

European countries, especially Germany, routinely use cubic measures as a means of

budgeting facilities.

Square foot method: This is the most commonly used initial budgeting mechanism in the

United States. It can be effective, but care must be taken to ensure the programmatic basis of

each is comparable when costs of different facilities are considered. In addition, the method

of measuring must be consistent for project comparisons to be valid. A number of published

sources provide square foot costs. A commonly referenced one is the R. S. Means Company’s

Building Construction Cost Data.

Functional area method: This approach to estimating is based on functional space types. A

functional space type is defined as an area in a building that has a distinct functional purpose,

for example, classrooms, a cafeteria, or a gymnasium in a school. The advantage of

determining cost by functional area rather than pure square footage is that variations in space

types and program can be considered in the basic estimate. The functional area method

allows for sensitivity to program elements.

The functional area method can be applied in two ways, either by pure space type or by core

and shell plus the functional space build-out. The first option assumes equal sharing of the

core and shell costs among space types. The second derives the core and shell costs

separately and then assesses the build out costs of each space type.

2. Parametric/cost modelling method

These cost estimating methods use predetermined models based on statistical analyses used to

predict facility costs. The process is most effective for repetitive facilities that have consistent

programs, such as those with industrial applications. Statistics are gathered from in-place

construction and can be used to predict costs, especially for complicated systems that involve

piping, manufacturing, and processing components. These approaches have less application

in building construction.

Computer Modelling: Cost models can be prepared with computer models that project the

form, shape, and composition of building types. In the last several years, computer based

systems have been developed to help designers model form and shape and determine building

size. These systems can also be used as a front-end device for cost modelling.

3. Systems/Elemental Cost Analysis

This approach to cost estimating provides a bridge between the conceptual estimating

methods described above and estimates based on full, detailed quantity surveys, which are

described below. The concept behind this approach is subdivision of a facility into its

elemental components, generally using UNIFORMAT as a basis. The level of detail included

is a function of the amount of design detail available when the cost estimate is prepared.

UNIFORMAT is a classification system based on physical building elements, originally

developed by the American Institute of Architects (AIA) and the U.S. General Services

Administration (GSA) in the 1970s. The most recent version, UNIFORMAT II, refines

certain aspects of the original system and has been designated ASTM Standard E1557-96.

UNIFORMAT is best applied to conceptual and schematic estimating

When very limited design information is available, a set of assumptions must be made from

which to estimate costs. It is possible to base these estimates on historical information from

similar facilities or historical information about building components and elements. At an

early stage of design, before details have been defined, it may be desirable to develop what

are generally referred to as “assemblies”— composite systems usually drawn from standard

design details. These assemblies can be accurately priced and are especially useful for

comparative purposes. Historical cost is an appropriate basis for estimates when facility types

and programmatic components are similar. Adjustments to the historical cost information can

be made if necessary.

A potentially more accurate estimate is one produced using an elemental format that

represents specific conditions of the developing design. This approach requires a combination

of pricing mechanisms, which could include historical costs, costs of systems and assemblies,

and detail cost analysis for selected items.

4. Quantity Surveys

The quantity survey method of cost estimating is usually employed when detailed design

information is available on the entire project or at least major components thereof. The actual

pricing approach may include only total unit prices or labour, materials, and equipment. The

level of detail in the estimate is intended to reflect individual units of work in the way it will

be carried out.

CHAPTER THREE

RESEARCH METHODOLOGY

3.1 INTRODUCTION

The scope of this study is such that there might not be available data for this class of building;

surrogate cost data will be made use of as opposed historical cost data for the development of

the model. This involves the generation of the priced bill of quantities items from 38

drawings (architectural and electrical), (that is, 20 bungalows and 18 duplexes); current

market prices of electrical items, site-observed productivity constants and relevant interviews

with technicians and electrical engineering constants. This chapter explains the method of

collecting data for the study and subsequently the methods used in analysing the cost data

collected from the generated from the drawings.

Also, the chapter covers aspects such as the research population, sampling frame and size,

data collection instrument, procedure for data collection and method of data analysis.

3.2 RESEARCH DESIGN

Research design is defined as the structuring of investigation aimed at identifying variables

and their relationship to one another. This is used for the purpose of obtaining data to enable

the researcher test hypothesis or answer research questions.

This research is centred on developing a cost model for determining the final sub-circuit cost

of electrical installation in residential building floors.

3.3 STUDY POPULATION

The population for this research involves electrical technicians for the purpose of productivity

constant of electrical technicians and residential buildings owners within the south-western

part of Nigeria for the collection of architectural and electrical drawings of residential

buildings.

3.4 SAMPLING FRAME

The sampling frame for this research was a theoretical list of residential buildings whose

floors are not more than two (bungalows and duplexes).

3.5 SAMPLING SIZE

The sample size for the data is 49 floors of 17 bungalows and 16 duplexes architectural and

electrical drawings.

The unit of analysis is floors with its own distribution boards (self-sufficient residential

floors).

3.6 SAMPLING TECHNIQUES

A convenient sampling techniques was used in carrying out this research, this is because

there is no list of electrical residential floors designs by electrical technicians.

Therefore caution must be exercised in generalizing the result of this research as a result of

the sampling technique used.

3.7 DATA COLLECTION INSTRUMENT

This study made use of architectural and electrical drawings which involved the generation of

the priced bill of quantities from 33 drawings (architectural and electrical), current market

prices and site-observed productivity constants for the development of the cost model for

electrical installation cost for residential buildings.

More so, a table of various headings was used in gathering and collection of surrogate cost

data of current market prices of electrical items, site-observed productivity constants of

electrician technicians.

3.8 DATA COLLECTION PROCEDURE

The estimating technique requires an extensive surrogate cost data base. The architectural and

electrical drawings for both the bungalows and duplexes were collected from

professional/technicians involved in electrical services installation, cost data are then

analysed, with various tabulations called schedules e.g. material schedule, labour schedule

made from the design drawing data to arrive at the grand total estimated cost of electrical

installation of the buildings.

A total of thirty-eight data sets of architectural and electrical drawings were collected, of

which fifty-six (20 bungalows and 18 duplexes floors) were analysed based on the number of

circuits per floor and tabulated to ensure that all costs were considered, to include the

material cost, labour cost etc. None is to be double-counted

3.9 METHOD FOR DATA ANALYSIS

Statistics as noted by Mason, Lind and Marchal (1983) is the body of techniques used to

facilitate the collection, organization, presentation, analysis and interpretation of data for the

purpose of making better decisions.

1. DESCRIPTIVE STATISTICS

a. Tables

A table is used to display numeric, non-numeric, discrete and non-discrete data in an

organized and well- coordinated manner. It is usually arranged in rows and columns each

displaying specific information. This was used in the study to display the productivity

constants of electrical installation technicians.

2. INFERENTIAL STATISTICS

a. Multiple Regression Analysis

Regression Analysis according to Mason et al (1983) is the general process of predicting one

variable based on another variable. It may also be said to be a technique that will find a

formula or mathematical model which best describes data collected. The factor whose value

we wish to estimate (e.g. aggregate scores) is referred to as dependent variable and denoted

by Y. the factor from which these estimates is made is called the independent variable and is

denoted by X.

The multiple regression analysis extends this equation to include multiple dependent

variables following the same principle. Therefore the relationship between the dependent and

independent variables could be defined as;

Y= a + b1x1 + b2x2 + b3x3 + ………………..+ bnxn +eij

Where X1 to Xn = the values of each respective independent variable;

b1 to b3 denotes the coefficients (which is the degree of contribution per unit change

in variable

eij= the equation error

Multiple regression analysis would be used for modelling the costs of final sub-circuits in

residential electrical installations.

Y= c + b1X1 + b2X2 + b3X3.............................................MODEL 1

Y= Total cost of final sub-circuits (lighting circuits)

X1= Number of luminaries

X2= Number of cables

X3= Number of conduits

b. Linear Regressions

In a two variable linear regression, the expression for the straight line is written as;

Y= a + bx

Where a, is the intercept of the line with Y-axis and b is the slope of the line.

Models

1. F = c + b4X4……………………………………….........................MODEL 2

Where;

X4 = Gross floor area

F = Final sub-circuit cost

2. CL= c + b5X5………………………………………………………………..MODEL 3

X5= Number of Lighting points (independent variable)

CL= Length of Cable (dependent variable)

c= regression constant

3. DC= c + b6X6………………………………………………………………..MODEL 4

DC = Length of Conduits (dependent variable)

X6= Length of Cable (independent variable)

c= regression constant

CHAPTER FOUR

DATA PRESENTATION AND ANALYSIS OF RESULTS

4.1 INTRODUCTION

The essence of this chapter is to analyse and discuss the data collected. The data collected are

presented in tabular format. Multiple regression analysis was used to establish the

relationship between the independent variables (length of cables and conduits and number of

luminaries) and the dependent variable (final sub-circuit costs). Also, linear regression

analyses were used to analyse other models as discussed in chapter three.

4.2 DATA ANALYSIS

The individual cost item of the lighting final sub-circuit, including the cost of switches and

the final sub-circuit cost are tabulated and analysed using arithmetic mean and regression

analysis. The results of these findings are presented to form the model needed for this

research work. Also, a Pearson Correlation analysis was carried out to investigate the

relationship between the final sub-circuit costs and the predictor variables.

The results of this study were however established from the result of the analysis and

conclusion drawn to arrive at the basic facts of findings. The statistical breakdowns of data

collected are shown in tables 4.1 and 4.2 and 4.3 below.

TABLE 4.1 BASED ON BUILDING TYPE

BUILDING TYPE FREQUENCY PERCENTAGE

A 17 51.5

B 16 48.5

TOTAL 33 100.0

KEY: A---Bungalow, B---Duplex

TABLE 4.2 BASED ON FLOOR CLASSIFICATION

FLOORS FREQUENCY PERCENTAGE

A 17 34.7

B 32 65.3

TOTAL 49 100.0

KEY: A---Bungalow, B---Duplex

TABLE 4.3 CROSS-TABULATION: Building type to Number of Bedrooms

NUMBER OF BEDROOMS * BUILDING TYPE

BUILDING TYPETOTAL

BUNGALOW DUPLEX

NUMBER OF

BEDROOMS

Two bedroom 4 0 4

Three bedroom 8 1 9

Four bedroom 5 10 15

Five bedroom 0 5 5

TOTAL 17 16 33

4.2.1 IDENTIFICATION OF THE COST SIGNIFICANT ITEMS

Meanwhile, the identification of the cost significant variables used in the formulation of the

developed model follows the technique proposed by Sheref and Pareto that items are

considered as significant when their value is higher than, or equal to, the mean bill value. The

equation goes thus:

Mean (x) =∑

csi ≥ mean value

Where; = 1, 2, 3, 4…… . . ( ℎ / )n = number of items and csi = cost significant items

Work at the University of Dundee also show that BOQ’s analysed using this technique are

successful with the identification of the significant items that constitute 80% of the contract

sum.

Below is the table showing the cost significant items of work for the forty-nine floors of

bungalows and duplexes derived from calculation.

TABLE 4.4: TABLE SHOWING THE COST SIGNIFICANT ITEMS FOR THE

FORTY-NINE FLOORS

NO

BUIL

DIN

GTY

PE

GRO

SSFL

OO

R AR

EA

NO

OF

LUM

INAR

IES

LEN

GTH

OF

CABL

ES

LEN

GTH

OF

CON

DUIT

S

FIN

AL S

UB-

CIRC

UIT

SCO

STS

1 A 114.48 29 233.72 25.20 52422

2 A 64.32 23 145.00 18.00 37636

3 A 213.18 39 299.71 23.40 57277

4 A 166.12 48 287.54 22.50 63143

5 A 168.48 28 243.01 23.40 44691

6 A 195.08 36 279.02 24.30 56806

7 A 125.28 33 231.99 19.80 50397

8 A 102.96 26 200.96 23.40 44092

9 A 249.68 48 384.52 24.30 70966

10 A 165.46 33 277.71 27.00 54292

11 A 164.25 37 287.77 20.70 54769

12 A 190.11 37 300.12 24.30 57130

13 A 78.64 20 151.52 12.60 30031

14 A 170.23 30 254.27 18.00 47474

15 A 110.15 22 190.33 16.20 36573

NO

BUIL

DIN

GTY

PE

GRO

SSFL

OO

R AR

EA

NO

OF

LUM

INAR

IES

LEN

GTH

OF

CABL

ES

LEN

GTH

OF

CON

DUIT

S

FIN

AL S

UB-

CIRC

UIT

SCO

STS

16 A 129.87 33 246.35 25.20 54725

17 A 65.48 22 153.15 11.70 33101

18 DG 332.79 35 308.06 239.30 132986

19 DF 303.57 26 223.14 23.40 43090

20 DG 194.67 33 261.91 202.80 118347

21 DF 182.97 19 176.05 21.60 35498

22 DG 257.74 37 284.55 199.97 123968

23 DF 203.52 22 195.68 18.00 40517

24 DG 232.27 31 262.98 208.69 115518

25 DF 240.91 19 154.74 16.20 29990

26 DG 272.95 40 354.02 281.13 155377

27 DF 288.04 26 239.64 21.60 43668

28 DG 229.71 40 325.28 255.10 139045

29 DF 182.74 25 210.88 18.00 39666

30 DG 178.9 34 265.47 201.46 118542

31 DF 202.55 27 218.15 19.80 43006

32 DG 296.7 30 276.66 215.46 118404

33 DF 255.42 21 207.63 23.40 49066

34 DG 245.74 42 330.29 255.25 148426

35 DF 143.24 10 105.66 8.10 19199

36 DG 229.2 37 346.31 275.48 151802

NO

BUIL

DIN

GTY

PE

GRO

SSFL

OO

R AR

EA

NO

OF

LUM

INAR

IES

LEN

GTH

OF

CABL

ES

LEN

GTH

OF

CON

DUIT

S

FIN

AL S

UB-

CIRC

UIT

SCO

STS

37 DF 289.52 29 284.49 32.40 53691

38 DG 229.2 37 346.31 289.85 156702

39 DF 190.56 23 227.94 27.00 44634

40 DG 245.93 30 315.56 257.99 136776

41 DF 314.29 21 207.57 19.80 39385

42 DG 232.88 31 276.89 219.89 119247

43 DF 232.88 21 177.99 16.20 32562

44 DG 235.07 25 262.71 203.38 108928

45 DF 250.58 15 155.61 13.50 28607

46 DG 140.39 21 212.88 170.27 91942

47 DF 140.39 13 125.08 12.60 22875

48 DG 157.98 33 257.25 197.28 121355

49 DF 137.31 15 141.15 18.00 30143

KEY: A---Bungalow, DG---Duplex ground floor, DF----Duplex first floor

4.2.2 MODEL OF FINAL SUB-CIRCUIT COST AS A FUNCTION OF THE COST

SIGNIFICANT ITEMS.

Given the quantities per project for the predictor variables, the regression model predicted the

total cost in Naira for the electrical installation work, based on three statistically significant

variables as shown in Table 4.5 and 4.6 below, where the p-values for all coefficients

considered in the model are less than or equal to 0.075:

TABLE 4.5 MULTIPLE REGRESSION RESULTS AMONG THE FINAL SUB-

CIRCUIT COSTS & COST SIGNIFICANT ITEMS (for Bungalows and Duplex

First Floors)

REGRESSION STATISTICS VARIABLES COEFF. P-VALUE

No. of observations 33 Number of Luminaries (item) 751.796 0.000

R-square 0.968 Length of Cables (m)Length of Conduits

44.615 0.041

Adjusted R-square 0.965 618.358 0.000

F 292.229

Constant 1407.866 0.400

The multiple regression equation is; Y= c + bX1 + bX2 + bX3..............................MODEL 1a

The Predicted equation is; Y= c + b1X1 + b2X2 + b3X3= 1407.866 + 751.796X1 + 44.615X2 +

618.358X3

Where;

Y= Total cost of final sub-circuits (lighting circuits) (in Naira)

X1= Number of luminaries (m)

X2= Number of cables (m)

X3= Number of conduits (m)

Regression constant = 1407.866

EVALUATION OF THE PREDICTIVE VALIDITY OF THE MODEL

Coefficient of correlation (R) is 0.984; this shows that there is 98.40% relationship

between the dependent and independent variable. That is, the model indicates a very

high level of correlation.

Coefficient of multiple determination (R2) is 0.968; this shows that 96.80% of the

dependent variable is explained is explained by the independent variables. This

indicates that there is a very high degree of fitness of the regression plane to sample

observation and that only 3.20% is explained by other variables not included in the

model

The equation is statistically significant and so the estimated final sub-circuit costs of

electrical installation works using the model will be realistic.

TABLE 4.6 MULTIPLE REGRESSION RESULTS AMONG THE FINAL SUB-

CIRCUIT COSTS & COST SIGNIFICANT ITEMS (Duplex Ground Floors)

REGRESSION STATISTICS VARIABLES COEFF. P-VALUE

No. of observations 16 Number of Luminaries (item) 1020.408 0.005

R-square 0.980 Length of Cables (m)

Length of Conduits

72.364 0.588

Adjusted R-square 0.975 303.168 0.029

F 195.907

Constant 3601.236 0.557

The multiple regression equation is; Y= c + b1X1 + b2X2 + b3X3............................MODEL 1b

The Predicted equation is; Y= c + b1X1 + b2X2 + b3X3 = 3601.236 + 1020.408X1 + 72.364X2

+ 303.168X3

Where;

Y= Total cost of final sub-circuits (lighting circuits) (in Naira)

X1= Number of luminaries (m)

X2= Number of cables (m)

X3= Number of conduits (m)

Regression constant = 3601.236

EVALUATION OF THE PREDICTIVE VALIDITY OF THE MODEL

Coefficient of correlation (R) is 0.990; this shows that there is 99.00% relationship

between the dependent and independent variable. That is, the model indicates a very

high level of correlation.

Coefficient of multiple determination (R2) is 0.980; this shows that 98.00% of the

dependent variable is explained by the independent variables. This indicates that there

is a very high degree of fitness of the regression plane to sample observation and that

only 2.00% is explained by other variables not included in the model

The equation is statistically significant and so the estimated final sub-circuit costs of

electrical installation works using the model will be realistic.

Also, the sample relationship between final sub-circuit cost and the number of luminaries (for

both tables 4.5 and 4.6) is positive, since the coefficient of the number of luminaries (b1

=751.796 and b1=1020.408) is positive for both. This means that the estimated value of the

final sub-circuit cost increases by about 751.8 and 1020.4 respectively for every 1-unit

increase in the number of luminaries, holding all other items of work constant.

Also, the sample relationship between final sub-circuit cost and length of cables is positive,

since the coefficient of earthworks (b2 =44.615 and b2=72.364) is positive for both (tables 4.5

and 4.6) meaning that the estimated value of the final sub-circuit cost increases by about 44.6

and 72.4 respectively for every 1-unit increase in the length of cables, holding all other items

of work constant.

This same positive relationship exists between the final sub-circuit cost and the length of

conduits (b3=618.358 and b3= 303.168 respectively).

The equation above gives the model equation of the analysed data which is subjected to the

research value. The multiple regression models shows that the slope of the partial relationship

between the final sub-circuit cost (Y) and each predictor variable is identical for all

combinations of values with the probability values showing that the equation is statistically

significant.

4.2.3 MULTIPLE CORRELATION AND DETERMINATION

Multiple correlation analysis is used in cases when research design requires that we ascertain

the combined strength of the relationship between a dependent variable and a set of

‘independent’ variables. The coefficient of correlation is denoted by R while the coefficient

of determination is the square of the correlation coefficient denoted by R2.

TABLE 4.7 DETERMINATION COEFFICIENTS AMONG ITEMS OF WORK AND

FINAL SUB-CIRCUIT COST (for Bungalows and Duplex Floor Floors)

Final Sub-

circuit costLuminaries Length of Cables

Length of

Conduits

Final Sub-circuit

cost1.0000

Luminaries 0.944 1.0000

Length of Cables 0.955 0.922 1.0000

Length of

Conduits0.787 0.610 0.748 1.0000

The table shown above is a table of the coefficient of determination (R2) among the cost-

significant items of work and with the final sub-circuit cost, calculated using statistical

package for social science (SPSS) and the result shows that the partial determination

coefficient between the final sub-circuit cost and the number of luminaries is 0.944 which

shows that 94% of the variations in the final sub-circuit cost are determined by the number

of luminaries.

The same principle applies in determining the relationship of final sub-circuit cost with

other items of work in the table; i.e. length of cables is 96%, length of conduits is 79%.

Also, the various coefficients of determination among the various elements of work

included in the table show the relationship within the independent variables (cost

significant items). It is therefore concluded from the table that the individual item identified

as being cost significant determines to a great extent the final sub-circuit cost of the

electrical installation work.

TABLE 4.8 DETERMINATION COEFFICIENTS AMONG ITEMS OF WORK

AND FINAL SUB-CIRCUITS COST (Duplex Ground Floors)

Final Sub-circuit

costLuminaries

Length of

Cables

Length of

Conduits

Final Sub-circuit

cost1.0000

Luminaries 0.837 1.0000

Length of Cables 0.980 0.793 1.0000

Length of Conduits 0.956 0.678 0.973 1.0000

The result shows that the partial determination coefficient between the final sub-circuit cost

and the number of luminaries is 0.837 which shows that 84% of the variations in the final

sub-circuit cost are determined by the number of luminaries.

The same principle applies in determining the relationship of final sub-circuit cost with other

items of work in the table; i.e. length of cables is 98%, length of conduits is 96%. Also, the

various coefficients of determination among the various elements of work included in the

table show the relationship within the independent variables (cost significant items).

4.2.4 MODEL OF FINAL SUB-CIRCUIT COST AS A FUNCTION OF GROSS

FLOOR AREA

A regression model that describes the final sub-circuit cost of residential electrical installation

works as a function of the gross floor area (GFA). The coefficient of determination, R2 for the

developed equation is 0.172. The regression statistics results for the developed model are

shown in Table 4.9

TABLE 4.9 Linear Regression Model F = c + b4X4

REGRESSION STATISTICS VARIABLES COEFF. P-VALUE

No. of observations 49 Gross floor area 270.380 0.003

R-square 0.172

Adjusted R-square 0.155

F 9.786

Constant 17628.68 0.334

The predicted equation is:

F = c + b4X4 = 17628.68 + 270.380 X4.........................MODEL 2

Where;

X4 = Gross floor area (m)

Constant, c = 17628.68

F = Final sub-circuit cost (in Naira)

EVALUATION OF THE PREDICTIVE VALIDITY OF THE MODEL

Coefficient of correlation (R) is 0.415; this shows that there is 41.50% relationship

between the dependent and independent variable. That is, the model indicates a low

level of correlation.

Coefficient of multiple determination (R2) is 0.172; this shows that 17.20% of the

dependent variable is explained is explained by the independent variables. This

indicates that there is a little or no degree of fitness of the regression plane to sample

observation and that a whole lot of 82.80% is explained by other variables not

included in the model

The equation is statistically insignificant and so the estimated final sub-circuit cost of

residential electrical installation work using the model will not be realistic.

4.2.5 MODEL OF THE LENGTH OF CABLES AS A FUNCTION OF THE

NUMBER OF LUMINARIES

A regression model that describes the length of cables of residential electrical installation

works as a function of the number of luminaries. The coefficient of determination, R2 for the

developed equation is 0.823. The regression statistics results for the developed model are

shown in Table 4.10

TABLE 4.10 Linear Regression Model CL = c + b5X5

REGRESSION STATISTICS VARIABLES COEFF. P-VALUE

No. of observations 49 Number of Luminaries 6.850 0.000

R-square 0.823

Adjusted R-square 0.819

F 218.406

Constant 45.565 0.002

The predicted equation is:

CL = c + b5X5 = 45.565 + 6.850X5.........................MODEL 3

Where;

X5 = Number of luminaries (item)

Constant, c = 45.565

CL= Length of Cables (m)

EVALUATION OF THE PREDICTIVE VALIDITY OF THE MODEL

Coefficient of correlation (R) is 0.907; this shows that there is 90.70% relationship

between the dependent and independent variable. That is, the model indicates a very

high level of correlation.

Coefficient of multiple determination (R2) is 0.823; this shows that 82.30% of the

dependent variable is explained is explained by the independent variables. This

indicates that there is a high degree of fitness of the regression plane to sample

observation and that just 17.70% is explained by other variables not included in the

model

The equation is statistically significant and so the estimated length of cables of

residential electrical installation work using the model will be realistic.

4.2.6 MODEL OF THE LENGTH OF CONDUITS AS A FUNCTION OF THE

LENGTH OF CABLES

A) Bungalows and Duplex First Floors

A regression model that describes the length of conduits of residential electrical installation

works as a function of the length of cables. The coefficient of determination, R2 for the

developed equation is 0.559. The regression statistics results for the developed model are

shown in Table 4.11

TABLE 4.11 Linear Regression Model DC= c + b6X6

REGRESSION STATISTICS VARIABLES COEFF. P-VALUE

No. of observations 33 Length of cables 0.063 0.000

R-square 0.559

Adjusted R-square 0.545

F 39.332

Constant 6.523 0.007

The predicted equation is:

DC= c + b6X6= 6.523 + 0.063X6.........................MODEL 4a

Where;

X6 = length of Cables (m)

Constant, c = 6.523

DC= Length of Conduits (m)

EVALUATION OF THE PREDICTIVE VALIDITY OF THE MODEL

Coefficient of correlation (R) is 0.748; this shows that there is 74.80% relationship

between the dependent and independent variable. That is, the model indicates a high

level of correlation.

Coefficient of multiple determination (R2) is 0.559; this shows that 55.90% of the

dependent variable is explained is explained by the independent variables. This

indicates that there is a moderate fitness of the regression plane to sample observation

and that just 44.10% is explained by other variables not included in the model

The equation is statistically significant and so the estimated length of conduits of

residential electrical installation work using the model will be realistic.

B) Duplex Ground Floors

A regression model that describes the length of conduits of residential electrical installation

works as a function of the length of cables. The coefficient of determination, R2 for the

developed equation is 0.947. The regression statistics results for the developed model are

shown in Table 4.12

TABLE 4.12 Linear Regression Model DC= c + b6X6

REGRESSION STATISTICS VARIABLES COEFF. P-VALUE

No. of observations 16 Length of cables 0.858 0.000

R-square 0.947

Adjusted R-square 0.943

F 251.217

Constant -21.739 0.196

The predicted equation is:

DC= c + b6X6= -21.739 + 0.858X6.........................MODEL 4b

Where;

X6 = length of Cables (m) Constant, c = -21.739

DC= Length of Conduits (m)

EVALUATION OF THE PREDICTIVE VALIDITY OF THE MODEL

Coefficient of correlation (R) is 0.973; this shows that there is 97.30% relationship

between the dependent and independent variable. That is, the model indicates a very

high level of correlation.

Coefficient of multiple determination (R2) is 0.947; this shows that 94.70% of the

dependent variable is explained is explained by the independent variables. This

indicates that there is a moderate fitness of the regression plane to sample observation

and that just 5.30% is explained by other variables not included in the model

The equation is statistically significant and so the estimated length of conduits of

residential electrical installation work using the model will be realistic.

4.2.7 PRODUCTIVITY CONSTANT OF ELECTRICAL TECHNICIANS

The table 4.13 below illustrates the site-observed productivity constants of electrical

technicians at three different sites where electrical installation works were on-going.

TABLE 4.13 PRODUCTIVITY CONSTANT OF ELECTRICAL TECHNICIANS

DESCRIPTIONSGANG

SIZE

UNIT

RATE

TIME

RATE

NO/DAY

(8-hrs day)

LABOUR COST

(N)

Draw and fix a roll of Cable

(1.5mm2)2 0.08 5 100 4000

Fixing of Wall brackets 1 0.60 36 14 2500

Fixing of Fluorescent fitting 2 0.53 32 15 3500

Fixing of Luminaries (ceiling

pendant)1 0.64 38 13 2500

Fixing of Luminaries (others) 1 0.44 27 19 2500

Fixing 10A 1,2,3 gang Switches 1 0.63 38 13 2500

Fixing of 10A 2-way, 1 gang

Switches2 0.53 32 15 3500

Fixing of 13A/15A Sockets 1 0.58 35 14 3000

Cutting and fixing Conduits 2 0.61 37 14 4000

See APPENDIX & for the productivity constant of the individual sites A, B and C.

Also see APPENDIX for the Market survey carried out for various electrical items.

KEYS:

UNIT RATE: This is expressed in hour per unit quantity of the respective work items

[hour per unit quantity]

TIME RATE: This is the time taken to performed a unit quantity/an item of work by

respective Electrical Technicians (in minutes)

GANG: This is the number of Electrician technicians involved for a particular item of

work

4.3 VALIDATION OF MODEL

Moreover, model validation is required to test the validity of the various models arrived at

during the course of this research work. This was done using seven (7) floors of 3 bungalows

and 2 duplexes; these sets of drawings are different from those sets of architectural and

electrical drawings used ab-initio in developing the various models for this study. This new

sets of architectural and electrical drawings were analysed separately, with relevant data

derived from them to form the basis of the model validation; to assess whether the various

models (model 1-4) are valid or realistic.

4.3.1 MODEL VALIDATION OF THE FINAL SUB-CIRCUIT COST AS AFUNCTION OF THE COST SIGNIFICANT ITEMS

a) BUNGALOWS AND DUPLEX FIRST FLOORS

Table 4.14 shows the data to be used for this model validation

TABLE 4.14 COST SIGNIFICANT ITEMS TO TEST MODEL VALIDITY (CT)

FLOOR IDNumber ofluminaries

(nr)

Length ofCables

(m)

Length ofConduits

(m)

Final sub-circuit costs

(N)BG1 30 252.90 21.60 50294BG2 28 195.19 23.40 48426BG3 29 218.86 25.20 49032DP2 12 150.37 16.20 28370DP4 18 158.14 19.80 32034

Y= c + bX1 + bX2 + bX3..............................MODEL 1a

The Predicted equation is; Y= c + b1X1 + b2X2 + b3X3= 1407.866 + 751.796X1 + 44.615X2 +

618.358X3

Where;

Y= Total cost of final sub-circuits (lighting circuits) (in Naira)

X1= Number of luminaries (m); X2= Number of cables (m); X3= Number of conduits (m)

Table 4.15 below illustrates the final sub-circuit costs derived from model

TABLE 4.15 FINAL SUB-CIRCUIT COSTS DERIVED FROM MODEL (CM)

FLOOR IDNumber ofluminaries

(nr)

Length ofCables

(m)

Length ofConduits

(m)

Final sub-circuitcosts(N)

BG1 30 252.90 21.60 48601.41

BG2 28 195.19 23.40 45636.13

BG3 29 218.86 25.20 48557.01

DP2 12 150.37 16.20 27155.58

DP4 18 158.14 19.80 34239.10

TABLE 4.16: COMPARISON BETWEEN CT AND CM

FLOOR IDFinal sub-circuit costs

(N) (CT)Final sub-circuit costs

(N) (CM)

BG1 50294 48601.41

BG2 48426 45636.13

BG3 49032 48557.01

DP2 28370 27155.58

DP4 32034 34239.10

b) DUPLEX GROUND FLOORS

Table 4.17 shows the data to be used for this model validation

TABLE 4.17 COST SIGNIFICANT ITEMS TO TEST MODEL VALIDITY (CT)

FLOOR IDNumber ofluminaries

(nr)

Length ofCables

(m)

Length ofConduits

(m)

Final sub-circuitcosts(N)

DP1 34 355.80 284.70 148267

DP3 24 244.03 193.33 105055

Y= c + b1X1 + b2X2 + b3X3............................MODEL 1b

The Predicted equation is; Y= c + b1X1 + b2X2 + b3X3 = 3601.236 + 1020.408X1 + 72.364X2

+ 303.168X3

Table 4.18 below illustrates the final sub-circuit costs derived from model

TABLE 4.18 FINAL SUB-CIRCUIT COSTS DERIVED FROM MODEL (CM)

FLOOR IDNumber ofluminaries

(nr)

Length ofCables

(m)

Length ofConduits

(m)

Final sub-circuitcosts(N)

DP1 34 355.80 284.70 150354.10

DP3 24 244.03 193.33 104361.50

TABLE 4.19 COMPARISON BETWEEN CT AND CM

FLOOR IDFinal sub-circuit costs

(N) (CT)Final sub-circuit costs

(N) (CM)

DP1 148267 150354.10

DP3 105055 104361.50

4.3.2 MODEL VALIDATION OF THE LENGTH OF CABLES AS A FUNCTION

OF THE NUMBER OF LUMINARIES

Table 4.20 shows the data to be used for this model validation

TABLE 4.20 DATA TO TEST MODEL VALIDITY (CT)

FLOOR ID Number of luminaries(nr)

Length of Cables(m)

BG1 30 252.90BG2 28 195.19BG3 29 218.86DP1 34 355.80DP2 12 150.37

DP3 24 244.03DP4 18 158.14

Linear regression; CL = c + b5X5

The predicted equation is:

CL = c + b5X5 = 45.565+ 6.850X5.........................MODEL 3

Where;

X5 = Number of luminaries (nr)

Constant, c = 45.565; CL= Length of Cables (m)

Table 4.21 below illustrates the length of cables derived from model

TABLE 4.21 LENGTHS OF CABLES COSTS DERIVED FROM MODEL (CM)

FLOOR ID Number ofluminaries (nr)

Length ofCables (m)

BG1 205.50 251.07

BG2 191.80 237.37

BG3 198.65 244.22

DP1 232.90 278.47

DP2 82.20 127.77

DP3 164.40 209.97

DP4 123.30 168.87

TABLE 4.22 COMPARISON BETWEEN CT AND CM

FLOOR IDLength of Cables

(m) (CT)Length of Cables

(m) (CM)

BG1 252.90 251.07

BG2 195.19 237.37

BG3 218.86 244.22

DP1 355.80 278.47

DP2 150.37 127.77

DP3 244.03 209.97

DP4 158.14 168.87

4.3.3 MODEL VALIDATION OF THE LENGTH OF CONDUITS AS A FUNCTION

OF THE LENGTH OF CABLES

A) Bungalows and Duplex First Floors

Table 4.23 shows the data to be used for this model validation

TABLE 4.23 DATA TO TEST MODEL VALIDITY (CT)

FLOOR ID Length of Cables(m)

Length of Conduit(m)

BG1 252.90 21.60

BG2 195.19 23.40

BG3 218.86 25.20

DP2 150.37 16.20

DP4 158.14 19.80

Linear regression; DC= c + b6X6

DC= c + b6X6= 6.523 + 0.063X6.........................MODEL 4a

Where;

X6 = length of Cables (m)

Constant, c = 6.523; DC= Length of Conduits (m)

Table 4.24 below illustrates the length of cables derived from model

TABLE 4.24 LENGTHS OF CONDUITS DERIVED FROM MODEL (CM)

FLOOR ID Length of Cables(m)

Length of Conduits(m)

BG1 252.90 22.46BG2 195.19 18.82BG3 218.86 20.31

DP2 150.37 16.00

DP4 158.14 16.49

TABLE 4.25 COMPARISON BETWEEN CT AND CM

FLOOR IDLength of Conduits

(m) (CT)Length of Conduits

(m) (CM)

BG1 21.60 22.46

BG2 23.40 18.82

BG3 25.20 20.31

DP2 16.20 16.00

DP4 19.80 16.49

B) Duplex Ground Floors

Table 4.26 shows the data to be used for this model validation

TABLE 4.26 DATA TO TEST MODEL VALIDITY (CT)

FLOOR ID Length of Cables(m)

Length of Conduit(m)

DP1 355.80 284.70

DP3 244.03 193.33

Linear Regression; DC= c + b6X6

The predicted equation is:

DC= c + b6X6= -21.739 + 0.858X6 .........................MODEL 4b

Table 4.27 below illustrates the final sub-circuit costs derived from model

TABLE 4.27 LENGTHS OF CONDUITS DERIVED FROM MODEL (CM)

FLOOR ID Length of Cables(m)

Length of Conduits(m)

DP1 355.8 283.54

DP3 244.03 187.64

TABLE 4.28: COMPARISON BETWEEN CT AND CM

FLOOR IDLength of Conduits

(m) (CT)Length of Conduits

(m) (CM)

DP1 284.70 283.54

DP3 193.33 187.64

4.4 DISCUSSION OF RESULT

Based on the research questions, research aims and objectives, the following conclusion

could be drawn from the data analyses above.

a. Objective 1

The productivity constants of electrical installation technicians

The productivity constants of electrical installation technicians has to do with the number of

electrician technicians required to performed an item of electrical work at a given time rate.

This is required in order to calculate the labour rate needed in the calculation of unit rate of

work output during the preparation of bill of quantities.

Table 4.13 shows the average productivity constant of electrical technicians of three sites

visited in the course of this research and various on-site data were collated which include as

shown in table 4.13 the descriptions of items of work, the respective gang size, unit rate, time

rate and labour cost. Further breakdown of the productivity constant of each site visited can

be seen in the appendix.

b. Objective 2

The influences of floor area on the final sub-circuits cost. (Cost model 2)

It is a general practice to use the gross floor area to determine the probable cost of a building

construction project, however, based on the SPSS analysis of the linear regression analysis

between the gross floor area (independent variable) and final sub-circuit cost (dependent

variable) as shown in table 4.9 shows that the coefficient of determination R2 is 0.172; this

shows that the equation is statistically insignificant and so therefore the gross floor area

should not be used to estimate the final sub-circuits cost of residential electrical installations

work.

c. Objective 3

The predictive power of the cost model

The objective is to assess the predictive power of the generated cost models. Table 4.4 shows

the data used to derive the cost models generated in this research.

Cost model 1a- Table 4.5 shows a multiple regression result used to generate a cost model

for calculating the final sub-circuit costs of electrical installation from the cost-significant

items of work in residential building for bungalows and duplexes first floors with coefficient

of determination R2 of 0.968; this means the cost model can be used in determining the final

sub-circuit cost. Moreover, a new set of data was gotten from another set of drawings used to

validate the data as shown in Table 4.14; table 4.15 shows the final sub-circuits cost as

derived from the cost model generated in table 4.5. Table 4.16 then compares both table 4.14

and 4.15; this comparison further confirmed the validity of the model earlier generated in

table 4.5 as valid enough to be used as a basis in estimating the final sub-circuit costs of

electrical installation in residential building for bungalows and duplexes first floors.

Cost model 1b- Table 4.6 shows a multiple regression result used to generate a cost model

for calculating the final sub-circuit costs of electrical installation from the cost-significant

items of work in residential building for duplexes ground floors with coefficient of

determination R2 of 0.980; this means the cost model can be used in determining the final

sub-circuit cost. Moreover, a new set of data was gotten from another set of drawings used to

validate the data as shown in Table 4.17; table 4.18 shows the final sub-circuits cost as

derived from the cost model generated in table 4.6. Table 4.19 then compares both table 4.17

and 4.18; this comparison further confirmed the validity of the model earlier generated in

table 4.6 as valid enough to be used as a basis in estimating the final sub-circuit costs of

electrical installation in residential building for duplexes ground floors.

Cost model 3- Table 4.10 shows a linear regression result used to generate a cost model for

estimating the length of cables required in a residential electrical installation from a given

number of luminaries; with coefficient of determination R2 of 0.823; this means the cost

model is very realistic. Table 4.22 shows the comparison of the data generated from new sets

of drawings and that derived from model, this confirmed the validity of the cost model as the

difference between the two values are quite negligible

Cost model 4a- Table 4.11 shows a linear regression result used to generate a cost model for

estimating the length of conduits required in a residential bungalow and duplex first floors

electrical installation from an estimated length of cables; with coefficient of determination R2

of 0.559; this means the cost model is fairly useable. Table 4.25 shows the comparison of the

data generated from new sets of drawings and that derived from model, this confirmed the

validity of the cost model as the difference between the two values are quite negligible

Cost model 4b- Table 4.12 shows a linear regression result used to generate a cost model for

estimating the length of conduits required in a residential duplex ground floors electrical

installation from an estimated length of cables; with coefficient of determination R2 of 0.947;

this means the cost model is very useful. Table 4.28 shows the comparison of the data

generated from new sets of drawings and that derived from model, this confirmed the validity

of the cost model as the difference between the two values are quite negligible

CHAPTER FIVE

CONCLUSION AND RECOMMENDATIONS

5.1 CONCLUSION

This study aims at modeling the costs of final sub-circuits in residential electrical installations

using multiple regression technique. The models were developed based on forty-nine floors

of thirty-three set of data (17 bungalows and 16 duplexes, of architectural and electrical

drawings) collected from professionals working and validated using data of seven (7) floors

consisting of three (3) bungalows and two (2) duplexes.

Such types of models are very useful, especially in its simplicity and ability to be handled by

calculator or a simple computer program. It has a good benefit in estimating electrical

installation cost at early stages of the residential building electrical installation works since

the information needed could be extracted easily from scope definition of such installation.

It must be remembered that an estimated electrical project cost is not an exact number, but it

is opinion of probable cost. The accuracy and reliability of an estimate is totally dependent

upon how well the scope is defined and the time and effort expended in preparation the

estimate.

The aim of this study was achieved by the generation of two multiple regression models both

of whom uses the cost-significant items to determine the final sub-circuits costs; one of the

multiple regression models took care of the bungalows floors and also the duplexes first

floors (as both are quite similar); while the second one took care of the duplexes ground

floors.

The coefficients of determination, R2 for the first developed model (Model 1a) is 0.968

which indicates that the relationship between the independent and dependent variables of the

developed model is good and the predicted values from a forecast model fit with the real-life

data.

The coefficients of determination, R2 for the second developed model (Model 1b) is 0.980

which also indicates that the relationship between the independent and dependent variables of

the second developed model is also good and the predicted values from a forecast model fit

with the real-life data.

Also, in this study, four linear regression models were developed; firstly, a model (Model

2) of the final sub-circuit cost as a function of the gross floor area (GFA) with its coefficient

of determination, R2 been 0.172 which indicates there is little or no relationship between the

independent and dependent variables; therefore the predicted values from this model cannot

fit into the real life data. The second linear regression model (Model 3) is a model of the

length of cables as a function of the number of luminaries; and its coefficient of

determination, R2 is 0.823 which indicates there is a high degree of fitness of the predicted

values from this model into the real life data.

The third linear regression model (Model 4a) is a model of the length of conduits as a

function of the length of cables; and its coefficient of determination, R2 is 0.559 (for

bungalows floors and duplexes first floors) which indicates there is a moderate degree of

fitness of the predicted values from these models into the real life data.

The fourth linear regression model (Model 4b) is also a model of the length of conduits as a

function of the length of cables; and its coefficient of determination, R2 is 0.947 (for duplexes

ground floors) which indicates there is a high degree of fitness of the predicted values from

this model into the real life data.

Therefore, for the determination of the final sub-circuit costs (lighting) of any residential

electrical installation work, it is hereby advisable for such clients, consultants or contractors

as it applies;

1. To first determine the number of luminaries (LM) needed in the building.

2. Then, slot the value of LM in model 3 to determine the length of cables (CL)

3. After the determination of CL, slot the value of CL into model 4a or model 4b as

deem appropriate in order to determine the length of conduits (CD).

4. With the values of LM, CL and CD determined, slot these values to model 1a or

model 1b as deem appropriate in order to determine the cost of the final sub-circuits

of such electrical installation work

Also, during the course of this research, it was established that the gross floor area cannot be

used and should not be used to estimate the probable cost of electrical installation work in

residential buildings types of not more than two floor.

Finally, the productivity constants of electrical technicians was also determined from on-site

visits and interviews, in addition to relevant market survey of the prices of electrical items,

the results was tabulated.

5.2 RECOMMENDATIONS

This paper presents a cost model that outperforms current practice of electrical installation

works estimating techniques, thereby providing a potentially significant benefit. In terms of

the paper’s benefits to researchers, it provides further insight into the relationships between

final sub-circuits costs and the various predictor variables. Based on the models generated for

this research, the following recommendations are made;

The floor area is not a good cost predictor of final sub-circuit cost and should

therefore not be used in estimating for residential electrical installation costing.

The determination of the cost model for the final sub-circuits costs lies heavily on the

accurate determination of the number of luminaries to be used in a residential building

floor which correlates with BESMM3 measurement rule (M7) for Y61- which states

that ” Final circuits are measured on an enumerated points basis where they form

part of a domestic installation- Page 164”.

The cost model is adequate and fit to be used for the forecast of electrical (lighting)

installation works in the early stages of the residential building design and in

situations where no or less detailed electrical plans are available.

5.3 AREA OF FURTHER RESEARCH

1. I would suggest that another researcher to develop a cost model for the final sub-circuits

(power sub-circuits) in residential electrical installations.

2. I would suggest that another research be conducted to assess the determinants of electrical

installation costs in residential/commercial buildings.

3. I would suggest that another research be carried out to develop a cost model for the final

sub-circuits (lighting and power sub-circuits) in commercial electrical installations.

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APPENDIX

DATA STATISTICS AND FREQUENCIESBUILDING TYPE

Frequency Percent

ValidPercent

CumulativePercent

Valid BUNGALOW

17 34.0 51.5 51.5

DUPLEX 16 32.0 48.5 100.0

Total 33 66.0 100.0

NUMBER OF BEDROOMS

Frequency Percent Valid PercentCumulative

Percent

Valid Two bedroom 4 8.0 12.1 12.1

Three bedroom 9 18.0 27.3 39.4

Four bedroom 15 30.0 45.5 84.8

Five bedroom 5 10.0 15.2 100.0

Total 33 66.0 100.0

NUMBER OF FLOORS

Frequency Percent Valid PercentCumulative

Percent

Valid DUPLEX 32 64.0 65.3 65.3

BUNGALOWS 17 34.0 34.7 100.0

Total 49 98.0 100.0

NUMBER OF BEDROOMS * BUILDING TYPE CrosstabulationCount

BUILDING TYPE

TotalBUNGALOW DUPLEX

NUMBER OFBEDROOMS

Two bedroom 4 0 4

Three bedroom 8 1 9

Four bedroom 5 10 15

Five bedroom 0 5 5Total 17 16 33

NUMBER OF FLOORS * BUILDING TYPE CrosstabulationCount

BUILDING TYPE

TotalBUNGALOW DUPLEX

NUMBER OF FLOORS DUPLEX 0 32 32

BUNGALOWS 17 0 17Total 17 32 49

ELECTRICAL TECHNICIANS PRODUCTIVITY

SITE A- 3-BEDROOM FLAT at Ado-Ekiti, Ekiti State, Nigeria

DESCRIPTIONS GANG UNITRATE

TIMERATE

NO/DAY(8-hrs day)

LABOUR COST(N)

Draw and fix a Roll of Cable(1.5mm2) 2 0.08 5 100 4000

Fixing of Wall Brackets 1 0.80 48 10 2500

Fixing of Fluorescent fitting 2 0.50 30 16 4000

Fixing of Luminaries (ceilingpendant) 1 0.67 40 12 2500

Fixing of Luminaries (others) 1 0.50 30 16 2500

Fixing 10A 1,2,3 gangSwitches 1 0.80 48 10 2500

Fixing of 10A 2-way, 1 gangSwitches 2 0.58 35 14 4000

Fixing of 13A/15A Sockets 1 0.67 40 12 2500

Cutting and fixingConduits 2 0.50 30 16 4000

SITE B- 3-BEDROOM FLAT at Ado-Ekiti, Ekiti State, Nigeria

DESCRIPTIONS GANG UNITRATE

TIMERATE

NO/DAY(8-hrs day)

LABOUR COST(N)

Draw and fix a Roll of Cable(1.5mm2) 2 0.10 6 80 4000

Fixing of Wall Brackets 1 0.50 30 16 2500

Fixing of Fluorescent fitting 1 0.58 35 14 2500

Fixing of Luminaries (ceilingpendant) 1 0.58 35 14 2500

Fixing of Luminaries (others) 1 0.50 30 16 2500

Fixing 10A 1,2,3 gang Switches 1 0.50 30 16 2500

Fixing of 10A 2-way, 1 gangSwitches 1 0.50 30 16 2500

Fixing of 13A/15A Sockets 1 0.58 35 14 2500

Cutting and fixingConduits 2 0.83 50 10 4000

SITE C- 4-BEDROOM FLAT at Ado-Ekiti, Ekiti State, Nigeria

DESCRIPTIONS GANG UNITRATE

TIMERATE

NO/DAY(8-hrs day)

LABOUR COST(N)

Draw and fix a Roll of Cable(1.5mm2) 2 0.07 4 120 4000

Fixing of Wall Brackets 1 0.50 30 16 2500

Fixing of Fluorescent fitting 2 0.50 30 16 4000

Fixing of Luminaries (ceilingpendant) 1 0.67 40 12 2500

Fixing of Luminaries (others) 1 0.33 20 24 2500

Fixing 10A 1,2,3 gang Switches 1 0.58 35 14 2500

Fixing of 10A 2-way, 1 gangSwitches 2 0.50 30 16 4000

Fixing of 13A/15A Sockets 2 0.50 30 16 4000

Cutting and fixingConduits 2 0.50 30 16 4000

MARKET SURVEY as at 15th August 2013

ITEMS PRICE LIST(N) REMARKS

LuminariesSecurity Light 850CeilingPendants 1500

Wall Brackets 650Fluorescents 900Lampholders 150Recessedlighting 600

Switches1 gang 802 way 1602gang 1003gang 150Sockets13A 12015A 150Wiring1.5mm2 2500 per roll2.5mm2 3500 per roll4mm2 5000 per roll6mm2 7500 per rollConduits20mm pipe 2600 per bundle (25pcs)25mm pipe 3300 per bundle (25pcs)

REGRESSION MODEL FOR THE FINAL SUB-CIRCUIT COST AS A FUNCTION

OF THE COST SIGNIFICANT ITEMS (DUPLEX FIRST FLOORS & BUNGALOWS

FLOORS)

Variables Entered/Removed

Model Variables Entered Variables Removed Method

1 Length of Conduits(CCD), Number ofLuminaries (LM), Lengthof Cables (CLT)a

. Enter

a. All requested variables entered.

Model Summary

Model R R Square Adjusted R SquareStd. Error of the

Estimate

1 .984a .968 .965 2238.292a. Predictors: (Constant), Length of Conduits (CCD), Number of Luminaries (LM),Length of Cables (CLT)

ANOVAb

ModelSum ofSquares df

MeanSquare F Sig.

1 Regression 4.392E9 3 1.464E9 292.229 .000a

Residual 1.453E8 29 5009951.965

Total 4.537E9 32a. Predictors: (Constant), Length of Conduits (CCD), Number ofLuminaries (LM), Length of Cables (CLT)b. Dependent Variable: FINAL SUB-CIRCUIT COST (LC)

Coefficientsa

Model

UnstandardizedCoefficients

StandardizedCoefficients

t Sig.B Std. Error Beta

1 (Constant) 1407.866 1649.649 .853 .400

Number of Luminaries(LM)

751.796 119.115 .569 6.312 .000

Length of Cables(CLT)

44.615 20.879 .230 2.137 .041

Length of Conduits(CCD)

618.358 121.318 .268 5.097 .000

a. Dependent Variable: FINAL SUB-CIRCUIT COST (LC)

REGRESSION MODEL FOR THE FINAL SUB-CIRCUIT COST AS A FUNCTION

OF THE COST SIGNIFICANT ITEMS (DUPLEX GROUND FLOORS)

Variables Entered/Removed

Model Variables Entered Variables Removed Method

1 Length of Conduits(CCD), Number ofLuminaries (LM), Lengthof Cables (CLT)a

. Enter

a. All requested variables entered.

Model Summary

Model R R Square Adjusted R SquareStd. Error of the

Estimate

1 .990a .980 .975 2889.418a. Predictors: (Constant), Length of Conduits (CCD), Number of Luminaries(LM), Length of Cables (CLT)

ANOVAb

ModelSum ofSquares df Mean Square F Sig.

1 Regression 4.907E9 3 1.636E9 195.907 .000a

Residual 1.002E8 12 8348736.126

Total 5.007E9 15a. Predictors: (Constant), Length of Conduits (CCD), Number of Luminaries(LM), Length of Cables (CLT)b. Dependent Variable: FINAL SUB-CIRCUIT COST (LC)

Coefficientsa

Model

UnstandardizedCoefficients

Standardized

Coefficients

t Sig.B Std. Error Beta

1 (Constant) 3601.236 5959.638 .604 .557

Number of Luminaries(LM)

1020.408 295.221 .310 3.456 .005

Length of Cables(CLT)

72.364 129.903 .160 .557 .588

Length of Conduits(CCD)

303.168 122.280 .590 2.479 .029

a. Dependent Variable: FINAL SUB-CIRCUIT COST (LC)

REGRESSION MODEL FOR THE FINAL SUB-CIRCUIT COST AS A FUNCTION

OF GROSS FLOOR AREA

Variables Entered/Removedb

Model Variables Entered Variables Removed Method

1 Gross Floor Areaa . Enter

a. All requested variables entered.b. Dependent Variable: Final Sub-circuit Cost

Model Summary

Model R R Square Adjusted R SquareStd. Error of the

Estimate

1 .415a .172 .155 39196.064a. Predictors: (Constant), Gross Floor Area

ANOVAb

ModelSum ofSquares df Mean Square F Sig.

1 Regression 1.503E10 1 1.503E10 9.786 .003a

Residual 7.221E10 47 1.536E9

Total 8.724E10 48a. Predictors: (Constant), Gross Floor Areab. Dependent Variable: Final Sub-circuit Cost

Coefficientsa

Model

UnstandardizedCoefficients

StandardizedCoefficients

t Sig.B Std. Error Beta

1 (Constant) 17628.680 18077.467 .975 .334

Gross FloorArea

270.380 86.433 .415 3.128 .003

a. Dependent Variable: Final Sub-circuit Cost

REGRESSION MODEL FOR THE LENGTH OF CABLES AS A FUNCTION OF

THE NUMBER OF LUMINARIES

Model Summary

Model R R Square Adjusted R SquareStd. Error of the

Estimate

1 .907a .823 .819 27.74006

a. Predictors: (Constant), Number of Lighting points (LM)

ANOVAb

ModelSum ofSquares df Mean Square F Sig.

1 Regression 168065.651 1 168065.651 218.406 .000a

Residual 36167.013 47 769.511

Total 204232.664 48a. Predictors: (Constant), Number of Lighting points (LM)b. Dependent Variable: Length of Cable (LC)

Coefficientsa

Model

UnstandardizedCoefficients

Standardized

Coefficients

t Sig.B Std. Error Beta

1 (Constant) 45.565 13.933 3.270 .002

Number of Lightingpoints (LM)

6.850 .464 .907 14.779 .000

a. Dependent Variable: Length of Cable (LC)

REGRESSION MODEL FOR THE LENGTH OF CONDUITS AS A FUNCTION OF

THE LENGTH OF CABLES (DUPLEX FIRST FLOORS & BUNGALOWS FLOORS)

Model Summary

Model R R Square Adjusted R SquareStd. Error of the

Estimate

1 .748a .559 .545 3.4844

a. Predictors: (Constant), Length of Cables (CLT)

ANOVAb

ModelSum ofSquares df Mean Square F Sig.

1 Regression 477.520 1 477.520 39.332 .000a

Residual 376.367 31 12.141

Total 853.887 32a. Predictors: (Constant), Length of Cables (CLT)b. Dependent Variable: Length of Conduits (CCD)

ANOVAb

ModelSum ofSquares df Mean Square F Sig.

1 Regression 477.520 1 477.520 39.332 .000a

Residual 376.367 31 12.141

Total 853.887 32a. Predictors: (Constant), Length of Cables (CLT)b. Dependent Variable: Length of Conduits (CCD)

REGRESSION MODEL FOR THE LENGTH OF CONDUITS AS A FUNCTION OF

THE LENGTH OF CABLES (DUPLEX GROUND FLOORS)

Variables Entered/Removedb

Model Variables Entered Variables Removed Method

1 Length of Cables (CLT)a . Enter

a. All requested variables entered.b. Dependent Variable: Length of Conduits (CCD)

Model Summary

Model R R Square Adjusted R SquareStd. Error of the

Estimate

1 .973a .947 .943 8.45737

a. Predictors: (Constant), Length of Cables (CLT)

ANOVAb

ModelSum ofSquares df Mean Square F Sig.

1 Regression 17968.855 1 17968.855 251.217 .000a

Residual 1001.380 14 71.527

Total 18970.235 15a. Predictors: (Constant), Length of Cables (CLT)b. Dependent Variable: Length of Conduits (CCD)

Coefficientsa

Model

UnstandardizedCoefficients

Standardized

Coefficients

t Sig.B Std. Error Beta

1 (Constant) -21.739 15.997 -1.359 .196

Length of Cables(CLT)

.858 .054 .973 15.850 .000

a. Dependent Variable: Length of Conduits (CCD)