ABSTRACT
The electro-mechanical properties of copper cables produced in Nigeria for electric power distribution were assessed in this study as a precursor to frequent electrical induced fire outbreaks in our residence and work places. The four brands of the cable mostly used for home and work place wiring in southern Nigeria were sampled from industrial markets at Aba, Lagos and Portharcourt and compared with NIS and IEEE specifications. The cable brands include Wesco, Cutix, Scan and Coleman with cross sectional area of 1mm2 to 16mm2 while resistivity, elongation, flame retardant and core diameter/tensile strength constitute the evaluation parameters. The IEEE recommended minimum copper diameter for 1 mm2, 1.5mm2, 2.5mm2, 4mm2, 6mm2, 10mm2 and 16mm2 are 1.15mm, 1.45mm, 1.82mm, 2.2mm, 2.9mm, 3.6mm and 4.6mm respectively. 1mm2 wire gauge of Scan and Wesco cable fall short of set standard for core diameter. In addition, 2.5mm2 wire gauge of the sampled cables did not meet the core diameter specification except Cutix cable. The 1.5mm2, 6mm2, 10mm2, and 16mm2 wire gauge of the four cable brands sampled complied with NIS and IEEE specification. Analysis of the experimental results indicated that all the cable brands met the recommended standard for resistivity and flame retardant. Wesco, Cutix and Coleman cables exhibit low smoke and fume while scan revealed low smoke and halogen free cable burning features. Coleman cable exhibited a linear relationship in the elongation curve while Wesco, Cutix and Scan tend to follow the plasticity profile. Thus, proper care must be taken during installation of Coleman cables to avoid damage to the cable surface. Although, the tensile strength of all the sampled cable brands falls within the recommended range of 12.5N/mm2 – 25N/mm2 with Cutix cable as the top performer. Cutix cable is the most expensive for all gauges and this can be attributed to the high copper content of their cables as evidenced by the thickness of their conductor material compared to other sampled brands. Hence, the overheating of the cables during service and its consequential high rate of fire outbreak in this country can be attributed to the reduction in the core diameters of some electrical cables used in our house wiring. It is therefore recommended that Nigeria regulatory agencies and cable producers should step up fight against piracy in this sector to save the nation from this fire inducing scourge.
TABLE OF CONTENTS
Title Page i
Declaration ii
Dedication iii
Certification iv
Acknowledgements v
Table of Contents vi
List of Tables viii
List of Figures ix
List of Plates x
Abstract xi
CHAPTER 1: INTRODUCTION
1.1 Background to the Study 1
1.2 Statement of the Problem 6
1.3 Aim and Objectives of Study 7
1.4 Scope of Study 7
1.5 Justification for the Study 8
CHAPTER 2: LITERATURE REVIEW
2.1 Nigerian Electric Cable Industry 9
2.2 Electrical Cable Conductor Materials 11
2.2.1 Copper 11
2.2.2 Aluminium 12
2.3 Electrical Cable Sizing 13
2.4 Electrical Cable Coatings 15
2.5 Improving the Electro-Mechanical Properties of Electrical Cables 18
2.5.1 Alloying 18
2.5.2 Stranding 19
2.5.3 Shielding 21
2.6 Factors Influencing Choice of Wiring System 23
CHAPTER 3: MATERIALS AND METHODS
3.1 Materials 26
3.2 Methods 26
3.2.1 Core diameter test 26
3.2.2 Tensile test procedure 27
3.2.3 Conductor material resistance test procedure 28
3.2.4 Insulation material elongation test procedure 29
3.2.5 Flammability test procedure 31
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Core Diameter Test Results 32
4.2 Tensile Test Results 35
4.3 Resistivity Test Results 38
4.4 PVC Elongation Test Results 45
4.5 Flammability Test Results 47
4.6 Cost Evaluation 54
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion 55
5.1.1 Contributions to knowledge 56
5.2 Recommendations 57
REFERENCES 58
APPENDICES 62
LIST OF TABLES
2.1 Wire gauges and uses 15
2.2 Maximum operating temperature for cable insulating materials 16
2.3 Cable insulating materials 17
2.4 Guide for shield design 23
4.1 Analysis of copper diameter of 1mm2 32
4.2 Analysis of copper diameter of 1.5mm2 32
4.3 Analysis of copper diameter of 2.5mm2 33
4.4 Analysis of copper diameter of 4mm2 33
4.5 Analysis of copper diameter of 6mm2 34
4.6 Analysis of copper diameter of 10mm2 34
4.7 Analysis of copper diameter of 16mm2 34
4.8 Tensile test result of 1mm2 cables 36
4.9 Tensile test result of 1.5mm2 cables 36
4.10 Tensile test result of 2.5mm2 cables 36
4.11 Tensile test result of 4mm2 cables 36
4.12 Tensile test result of 6mm2 cables 37
4.13 Tensile test result of 10mm2 cables 37
4.14 Tensile test result of 16mm2 cables 38
4.15 Cost comparison of sampled cables valued at 10meters length each. 54
LIST OF FIGURES
1.1 Main parts of an electrical cable 4
3.1 Flammability test set up (CSA 2018) 31
4.1 Resistivity of 1mm2 brands 39
4.2 Resistivity of 1.5mm2 brands 40
4.3 Resistivity of 2.5mm2 brands 41
4.4 Resistivity of 4mm2 brands 41
4.5 Resistivity of 6mm2 brands 42
4.6 Resistivity of 10mm2 brands 43
4.7 Resistivity of 16mm2 brands 44
4.8 Load vs elongation graph for wesco insulation material 45
4.9 Load vs elongation graph for cutix insulation material 46
4.10 Load vs elongation graph for scan insulation material 46
4.11 Load vs elongation graph for coleman insulation material 47
4.12 Flame propagation of 1mm 2 brands 48
4.13 Flame propagation of 1.5mm 2 brands 49
4.14 Flame propagation of 2.5mm 2 brands 50
4.15 Flame propagation of 4.0mm 2 brands 50
4.16 Flame propagation of 6.0mm 2 brands 51
4.17 Flame propagation of 10.0mm 2 brands 52
4.18 Flame propagation of 16.0mm 2 brands 53
LIST OF PLATES
3.1 XHET 2000 microcomputer tensile testing machine 27
3.2 ZDCY intelligent resistance tester/ SC 7032 general conductor
resistance fixture 29
3.3 XHET 2000 PVC elongation testing machine 30
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF STUDY
The pathetic death toll due to electrocution in the country, increasing incidence of cable overheating, electrical disruptions, short life of electrical appliances and fire outbreak calls to question the quality of electrical cables sold in the Nigerian markets and used in homes and work places. Electrical cables refer to electrical conductors of thin cylindrical cross section drawn in form of a slender rod insulated and grouped together in an overall covering (Stauart et al., 2000). In every home, office or a building in general, there are electrical cables that distribute electricity for daily consumption. These electrical cables connect electrically powered appliances to the main electricity source.
It is essential that these electrical cables conduct electricity efficiently, cheaply, safely and meet the required standards, quality and specifications recommended by the standardization body – standard organization of Nigeria (SON) for convenient and effective installation, free from electrical hazards (Osaru, 2017) but in what looks like an annual sacrifice that must be offered to please the gods, the lives of many promising Nigerians have been wasted on the altars of faulty live electricity cables over the years. The invidious development has remorselessly brought indelible sorrows and devastation to many homes, as it has callously been responsible for death of many citizens (Duru, 2015). Though uncommon, but nevertheless a significant cause of multisystem injury is electrical burns due to faulty electrical cables (Oludiran and Innih, 2011). They reported that electrical burns associated with faulty electrical cables cause significant morbidity, mortality and often associated with amputation from tissue necrosis.
The frequent cause of fire outbreak at homes and offices have also been linked to the use of inferior quality or substandard electrical cables for electricity distribution and wiring applications (Chikezie, 2014). Substandard cables are not test approved to meet the requirements in safety standards. Jonathan (2017) reported that some of the features of substandard cables are reduced diameter of conductor material, using copper clad aluminium or other metals instead of copper conductor, reduced insulation thickness, shorter length per coil and the use of metal content which does not meet recommended Nigerian Industrial standard (NIS) specification in addition to fake labels and packaging.
The influx of substandard cables in the Nigerian market is mainly due to the activities of scrupulous manufacturers who skimp on quality and safety to produce cheaper cables (Berhard, 2017). These scrupulous activities of skimpy manufacturers and some importers also contribute to the influx of substandard electrical cables in the Nigerian markets. The import of inferior quality electrical cables from Europe and Asia which are non-conforming to the Nigerian electricity demand and electrical cable standards not only cause untold havoc in the society but also impart on the nation’s economy negatively. Also, some of the malicious importers have been reported to clone the inferior cables with named Nigerian brands tarnishing the image and destroying the reputation of the local industry (Thisday, 2017).
It has also been reported that unscrupulous importers ask for reduction in the specified diameter of copper content of electrical cables imported into country (Chikezie, 2014). The smaller diameter of a substandard electricity distribution cable applied either in surface or conduit wiring reduces its ability to conduct electricity effectively thereby causing the cable to overheat (Berhard, 2017). Cable overheating causes the cable to burn or melt which leads to electrical disruptions. Also, the reduced conductance an electrical cable might causes the cable to lose insulating properties which ultimately will lead to circuit malfunction, electrocution and/or fire outbreak created from the electrical sparks. Such electrical havoc deteriorates an electrical system reliability, destroys sensitive electrical industrial appliances and loss of revenue and/or life. While it is gratifying that the electrical cable companies in Nigeria are making significant strides in the quality of electrical cables produced in Nigeria, the incidence of death by electrocution which has become so rampant in the country is still a marvel.
Although Nigerian cables are claimed to be among the best in terms of quality and durability (Alabashop, 2011), yet the industry still contend with cheap and substandard cables from Asian countries exacerbated by the weak regulation and compliance (Chikezie , 2014). It was also reported that the influx of substandard electrical cables in Nigerian market is due to weak regulatory institutions, poor legal framework and poor policy implementations (Yusuf, 2014). This also calls to question the capacity of the Standards Organisation of Nigeria (SON) to stem the tide/ influx of fake and sub-standard cables into the country (Muda Yusuf, 2019).
Most often, these issues associated with the use of substandard electrical cables are found in the distribution line. A distribution cable is an assembly of electrical conductors in an overall sheath (Fig. 1.1). Generally, electrical cables consist of the conductor material, insulation material (Warne, 2016), mechanical protection (jacketing) and an optional filler material (Haddad, 2000; Adetoro, 2014). The assembly is used for transmission of electrical power. Electric power distribution cables can be used as permanent wiring within buildings, run overhead, buried in the ground, or exposed. Distribution lines are for short distances, their voltage is lower, and they transport electricity locally (Lener, 2018).
Fig. 1.1: Main Parts of an electrical cable
The voltage of distribution lines varies between 4KV and 69KV while the conductor materials are mainly copper and aluminum. The choice of copper and aluminium as the major conductor materials in power and lighting cables is influenced by the high ductility of copper which makes it easy to be drawn into wires than silver which is the best metallic conductor of electricity. Aluminium however has profound application in overhead electric cable because it is light and possess good conducting property. The low resistivity of copper as compared to aluminium means that it takes up less space and permits better passage of electricity than aluminium and hence most suitable for outdoor and indoor wiring also, copper is resistant to corrosion and can withstand load surge better than aluminium.
Copper wire is a strong electrical conductor and quite stable overtime (Steiner, 2016). It would not need to be replace often and thus has a long service life unlike aluminum and therefore it can be used in commercial or industrial buildings. Copper is less dense than aluminum, and is most economical of all conductors as well. Copper doesn’t creep - a deformation of metal conductor that result from subjection to stress or pulling forces- and it is the preferred conductor material by electricians because it strips and can bend easily without breaking nor nicking (Steiner, 2016). Unlike copper, aluminum conductor materials are for wiring overhead transmission lines and they have become more popular for use in commercial facilities such as high rise buildings, commercial buildings, wastewater treatment plants, stadiums, shopping malls and manufacturing facilities. Copper cable is approved by electrical codes nationwide while Aluminum wiring is popular within the construction industry and provides many advantages such as low cost, lightweight and easy to use.
The key mechanical, thermal and electrical parameter used to classify and compare electrical distribution cables include conductor tensile strength, resistance to flame propagation, heat shock resistance, cold bend strength, insulation thickness, conductivity of the conductor material, insulation resistance and insulation dielectric strength. According to Institute of Electrical and Electronics Engineers (IEEE), tensile testing of electrical cables determines their tensile strength because cables are often subjected to pull from one end during layering, installing and manufacturing (Insulated Conductors Committee, 2005; D.F.Jingle Jabha, 2016), hence it should exhibit high tensile strength to withstand the pulling force without breaking. Also, the resistivity test on the conductor material determines how easily the conductor allow the flow of electric current through it and it depends on the material of the conductor, operating temperature and size (Steve et al., 2000).
The rate at which metals conduct electric current is a function of its resistance to the flow of current. The higher its resistance, the lower its conductivity and vice versa. Hence, electrical conductivity is a measure of the materials’ ease to the passage of current when a potential difference is applied at a specific temperature (Steve et al., 2000). Insulation property test determines the sheath and thickness of insulation material. Adequate insulation thickness is required to meet the mechanical stresses and voltage stresses that the electrical cable is subjected during service. A breach of the set standards for any of the key parameters constitutes a substandard electrical cable product, this work will empirically analyse copper cables of five brands of 1mm2 to 16mm2 sizing sold in the Nigerian market.
1.2 STATEMENT OF PROBLEM
There exist a wide range of electrical cable brands available in the Nigerian market and the choice of cables to be used for either power transmission, distribution, indoor and outdoor electrical wiring is influenced by the purpose and area to which it is applied but often, many Nigerians pay little attention to the quality and kind of electrical cables used in wiring their homes or work place.
Niger State government stated in a press conference that electrical faults accounted for 60% of fire related disasters across the state between January to December 2012 (Duru, 2015), similarly, In May 2014 at Mushin, Lagos State, a family lost all their personal belongings in an electrical fire which was said to originate in one of the wall outlets (Adebayo et al., 2019). Also, in October 2013, a fault in the electric distribution system was determined to be the cause of an apartment complex fire resulting in injury of the occupants (Nimlyat et al., 2017). In December 2015, Nigerian Telecomm. building situated at Lagos was gutted by fire, damaging properties worth millions of Naira and the fire was reportedly caused by electrical sparks (Triumph, 2015). Similarly, there was fire outbreak in a federal civil service secretariat, Abuja, and the fire incidence was reportedly caused by electrical sparks (lauryn, 2017).
Recent development in assessing the quality of electrical cable in the Nigerian market carried out by Adetoro (2012) confirmed that five cable brands in the Nigerian market conform to the Nigerian Industrial Standard (NIS) for single core 1.5mm2, twin core 2.5mm2 and three core 2.5mm2 electrical cables at 95% confidence interval for the mechanical and electrical properties but the study failed to consider the imported cables in the market neither did the study exhaust the available cable brands produced in Nigeria. Also, the study limited its research to 1.5mm2, 2.5mm2 twin core and three core electrical cables while other cable sizing have found profound application in the electricity distribution network, lighting points and sockets of work places and residential buildings.
The insulation resistance, insulation property test, resistance to flame propagation, aging test which are key parameters to classify or quantify the quality of an electrical cable are among other tests not reported in the study. Hence, this study is the empirical analysis of copper cables for electric power distribution in Nigeria.
1.3 AIM AND OBJECTIVES OF STUDY
The aim of this work is to make an empirical analysis of copper cables for electric power distribution in Nigeria. The specific objectives are to:
i. evaluate experimentally the electrical, mechanical and thermal properties of electrical cables sampled from Nigerian markets and
ii. make comparative analysis of cost and conformance levels of different brands of electrical cables in Nigerian markets with the Institute of Electrical and Electronics Engineer and Nigerian Industrial Standard specifications.
1.4 SCOPE OF STUDY
This work involves empirical assessment of five brands of 1mm2 to 16mm2 copper electric cables sampled from industrial markets in Abia, Lagos and Rivers States of Nigeria for compliance with set standards. The parameters assessed include conductor material test – tensile test, aging test, resistivity test and core diameter test, and insulating material test – elongation test and flammability test as well as the cost of the cable sampled.
1.5 JUSTIFICATION FOR THE STUDY
Evaluation of the electrical cables and wires is very vital as it seeks to assess the quality and properties of cables used in electricity distribution that will serve safely and efficiently, the lighting appliance and equipment needs of various households and industries. Evaluation of the electrical cable brands in Nigerian markets will either validate their conformance for various wiring applications or disprove their acceptance in the cable industry. This will help reduce the risks of electrocution, fire hazards and cable overheating associated with the use of inferior cable brands as well as alert relevant authorities to take decisive actions against erring cable companies or importers.
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