Mohammed (1999) stated that in buildings, electrical services is necessary to give power for continuous operation of equipment and appliances and for lighting which provides adequate illumination in and around the building, Chudley and Greeno (2004) made it clear that electricity is usually required at the early stage to provide light and power to the units of accommodation stating that electricity is that part of the building which provides comfortability in addition to the building aesthetics and contributes to the internal ease and safety operations of the building. 231BEG6 (2012) stated that electrical services installation provided in a building comprises of Electrical Supply, Electricity Centre and Main Distribution, Power Distribution Services, Lighting Services, Communication Services, Transport Services and Protective Services. The design of the Electrical Services takes into account the building form, the characteristics of the building, the occupancy trends and orientation of spaces. It also states that buildings should be designed with features to provide better lighting, comfortable space, temperature and air quality, convenient power and communication capability, high quality sanitation and reliable systems for the protection of life and property.
2.2 Electrical Installation and Electrical System
2.2.1 Concept of Electrical Installation
Electrical installation is defined in Building Regulations (2000) as fixed electrical cables or fixed electrical equipment located on the consumer side of the electricity supply meter. It consist of a set of wires and associated fittings, equipment and accessories installed for the conveyance, control, measurement or use of electricity for general power and lighting in a place (Electricity Regulations, 1997).
According to BS 7671 (2001) Electrical installation also consist wiring and concomitant components and fittings, including permanently secured and large stationary equipment, but exclusive of portable equipment and appliances while Davies and Jokiniemi (2008) defined electrical installation as the circuitry, wiring, control gear and fixed appliances for providing and maintaining an electricity supply within a building.
2.2.2 Types of Electrical Installation
Electrical installation according to Electrical Services Handbook (1997) can be divided into two main types:
1. Temporary installation
2. Permanent installation
Temporary installation can be defined as an installation meant for temporary use. This type of installation is usually used in the early stages of building construction to be used in the preliminary work processes (Electrical Services Handbook, 2015)
According to Electrical Services Handbook (2015), temporary installations must also be as safe as permanent ones therefore the principles of design and installation which are used for permanent systems should also be used for the temporal.
Permanent installation: According to Francis and Cooksley (1996), is an installation that is done permanently. This type of installation is to last through out the life span of the building. Permanent installation can be described under the following:
a. Wiring
It has been discovered by Barry (1998) that in most buildings concealed PVC conduit wiring is commonly used putting into contemplations that PVC has a high coefficient of expansion. Conduit wiring can also be made on the surface. PVC conduits are cheaper and readily available compared to galvanized steel conduit pipes. Wiring can be classified into the following types:
1. Conduit installation on walls and ceiling
2. Concealed conduit wiring
3. Sheathed wiring by surface fixing.
Conduit installation on walls and ceiling: it is a usual practice to run cables inside metal or plastic trunking to provide both security and support for the cables where extensive electrical installations and several comparative heavy cables follow similar routes, with standard conduit too small to provide protection. Trunking is fixed and supported horizontally or vertically to wall, floor or ceiling, or above false suspended ceilings and can be either PVC trunking or metal trunking as shown in Figure 2.1. Advantages of trunking is that it gives room for easy maintenance and repair works to be carried out, as many as 15-20 cables can be run inside depending in the size of the trunking and its intended use (Barry, 1998)
Figure 2.1: Different Trunking Types
Source: Barry (1998)
Concealed Conduit Wiring: Barry (1998) showed that Concealed conduit is the most common method of wiring, PVC conduit pipes are laid in slabs before concreting is done not only in slabs or beams also, PVC (polyvinyl chloride) or VIR cables are run through metallic or PVC pipes providing good protection against mechanical injury and fire due to short circuit. They are entrenched inside the walls. The benefit of this method is that it gives good protection against mechanical damage/injuries, lead and return wires can be carried in the same tube, earthing and permanency is assured, waterproof and trouble shooting is easy, durable and maintenance free.
Sheathed Wiring by Surface Fixing: According to Barry (1998), the conductors of the Sheathed Wiring are individually insulated and covered with a common outer lead-aluminum alloy sheath. The sheath guards the cable against dampness, atmospheric extremes and mechanical damages. The sheath is earthed in every junction, and is fixed my means of a metal clip. They are easy to install and are aesthetic in appearance if properly arranged, highly durable, and suitable in adverse climatic condition provided joints are not exposed (Barry 1998).
b. Distribution circuit
In an ordinary building, the supply distribution of electricity from the consumer control unit to other points is divided into the following three separate types of circuits:
i. Lighting circuit of low capacity
ii. Power circuit through ring circuit
iii. Fixed appliance
c. Lighting circuit
Separate circuit is usually provided for the general lighting of the building. One of the following two systems according to Barry (1998) is commonly used for this purpose:
The loop-in system: in this system each loop is rated 6 amps. A live phase cable runs to the live terminals of the first lighting point or lamp holder from a 6 amp fuse from the control board. From here the cable loops out to the next rose and so on till all lighting points are linked together.
Joint- box system: for this system the wires now run to a series of joint (junction) boxes instead of running to the roses with each light switch having a separate junction box. The junction box has a circular in shape.
All installations have to meet the following three key criteria before the installation can be said to have been completed:
i. The secure fixing of systems and components: this applies in particular to switching, cables and conduit, all of which must be adequate and suitable to the environment.
ii. Electrical permanency and maintenance of system integrity: this applies to all protective measures to ensure that the system is safe to use.
iii. Prevention of damage to components and system: obviously, no one wants an installation to be damaged before it is even started!
In order to make sure that the work is carried out satisfactorily and that these conditions are met, the inspection and test procedure must be carefully planned and carried out, and the results correctly documented.
2.2.3 Electrical Service System
Electrical service system can be defined as a network of electric components used to supply, transfer and use electric power. According to Mbamali (1998) electrical service system can be defined by:
a. Supply consumption and accessories: this include low voltage supply 415v three phase supply or 240v single phase and small installations having service cut out box meter.
b. Alternative supply source; standby and backup generator set that is readily available and change over switch.
c. Distribution equipment: this usually includes distribution board or consumer control unit (CCU)
d. Lightening circuit; comprise of:
i. Lamp fittings (more than 12 per circuit)
ii. Wiring (surface or conduit)
iii. 5amp switches
e. Power circuits; this comprises of:
i. Wiring to 13amp socket outlets usually ring circuits by means of 2.5mm2 twin earth sheated cables.
ii. 5amp socket and this are connected in groups of not more than three to each fuseway or MCB by means of 2.5mm2 twin earth sheated cables
iii. Wiring to 15amp sockets. Each socket is connected to individual fuseway or MCB by means of 2.5mm2 twin sheated cable.
f. Power supply to machines and filled appliances;
i. Motors and other appliances
ii. Isolation and connection devices
g. Overload and shut circuit protective devices;
i. Fuses
ii. Earth leakage circuit breakers
iii. Earthing
iv. Lightening protection
2.3 Materials and Devices Used In Electrical Services Installation
1. Cables
According to Varghese (2007), Cables are made up of conductors enclosed by insulation though copper materials are most rather used for conductors. The transportation of electricity is done in metal conductors, which are usually insulated and also have to be protected against mechanical damage. The conductor becomes a cable when it is insulated to make a usable piece of equipment for carrying electricity. In buildings armored cable is used for mains and sub mains. The entry of cables from the outside to the inside of a building sometimes causes difficulty. There must obviously be a hole in the wall which has to be tight round the cable and which has to be sealed to prevent dirt, insects and moisture entering. Whether the cable is an armored type laid directly in the ground or whether it is drawn into a duct, the most practicable way of making the entry into the building is by means of an earthen ware duct built through the wall below ground level (Varghese 2007). The cable is laid below ground level, breaking the surface where it enters sub-stations or transformers and other buildings. Conduit for electrical services is produced in steel (galvanized or painted black) or plastic tube into which isolated cables are drawn. Standard outside diameters are 20, 25, 32 and 40 mm. In the building, conductors (wires) should be preferably of copper. Aluminum conductors are sometimes used to reduce cost but are very inferior to copper cables as uninsulated portions such as connections to switches tend to oxidize and become brittle thus giving trouble in the long run. If possible aluminum cables should not be used for wiring.
Sizes: According to Varghese (2007), currently, the manufacturings of cables are done in metric sizes and are referred by the number and diameter of the conductor. Table 2.1 gives the recommended sizes of wires for different uses.
Table 2.1: Cable sizes for different uses
S/NO. Circuit Fuse Cable Sizes (area) Cable current rating (amp)
1 Lighting 5 amp 1.0 to 1.5mm2 12 to 15
2 Immersion heater 15-20 2.5 mm2 21
3 Ring circuit and spurs 30 2.5 mm2 21
4 Radial circuit 20 2.5 mm2 21
5 Radial circuit 30 4 mm2 27
6 Cooker 45 6 to 10 mm2 35 to 48
Source: Varghese (2007)
2. Fuses
A fuse is a device that opens a circuit by means of a strip of wire, which is designed to melt when an excessive current flows through it (Alan 2003). A fuse major function is to protect appliances and cables from damage by electrical faults. Ideally the rating of fuses should be lower than that of the cables they have to protect (Varghese 2007). Examples of fuse are:
a. Rewirable fuses/semi enclosed fuses
b. Cartridge fuses
Rewirable fuses. These are cheap and usually take twice the current rating of a rewirable fuse to blow it. Thus, a 5A rewirable fuse requires a current of 10A to blow it. One screw of the switch is connected to the live conductor and the other connected to the load side as shown in Figure 2.2. As in the same holder different capacity fuse wire is used, one should take care that the same capacity fuse wire is used during rewiring (Barry, 1998).
Figure 2.2: Rewirable fuse
Cartridge fuses. These are of different ratings, each rating of its own size. It is not possible to fit a 20A cartridge fuse in a 5A fuse holder. A 20A fuse blows at 1.5 times its current rating. Thus a 20A fuse will blow out at 30A (Barry, 1998). The tube of the fuse is made of ceramic and the ends made of brass or copper as shown in figure 2.3
Figure 2.3: Cartridge fuse
3. Circuit breakers
According to Barry (1998), a circuit breaker is a thermal-magnetic, magnetic-hydraulic or assisted bi-metal tripping device designed with intentions to function on overload and break the connected circuit in the case of overload. Electrical installations must be guarded from current overload, otherwise appliances, cables and people using the equipment could be endangered. To avoid damage and threat to safety, protection devices are installed in the system.
2.4 Components of Electrical Fittings
1) Socket outlets
According to Stephen(2010), the name socket outlets or power points are so called because they consist of sockets in a wall fixed front plate into which the terminals of a loose plug top fit to supply electricity to a wide range of moveable, portable and hand held electrical equipment. Connections are usually done to a ring final circuit, which has no limit to the number of sockets connected to each ring circuit and should not serve an area greater than 100m” for domestic installations. The ring circuit is secured with a 30amp fuse at the consumer unit. Stephen (2010) also stated that socket outlets consist of a galvanized steel box to which a front plate is screwed after the terminals of the front plate also it has knockout boxes which are removed to allow cable entry. It is necessary to fit a cartridge fuse to the plug top to provide current overload protection to the flexible cord and appliance connected to the outlet.
According to Barrie (2005) a socket outlet is a female socket linked to the power wiring in the building and has been designed to accept the male plug attached at the end of the flexible cord of an appliance having a front plate which is usually integrated with the outlet. Socket outlets general arrangement is similar to that of switches. The sockets are installed around the room in suitable locations; sockets are valuable in situations where switching of reading lamps is required and a wall switch at the doorway controls the lighting socket circuit. The reading lamps are then all turned on together. Socket outlets maybe single or double outlets, switched or unswitched, surface or flushed and mounted and maybe fitted with indicator lights as shown in Figure 2.4 below.
Figure 2.4: Socket outlets
Source: Barry (2005)
2) Incandescent lamps
According to Barrie (2005), tungsten lamps, or GLS general lighting service as incandescent lamps are also called are the ordinary bulbs still most often times used in homes and they usually consist of a thin filament of tungsten inside a glass bulb. The temperature of this filament rises as a cause of the heat that is produced when a current is passed through the filament and the filament is so designed that it reaches a temperature at which it generates both light energy and heat energy, which means that the filament glows or is incandescent and hence gives it the name incandescent lamp (Stephen 2010). The efficiency of the conversion of electrical energy into light energy is based on the increase in temperature of the filament, that is to say, the higher the temperature of the filament the more efficient the transformation. It should also be noted that if the temperature becomes too high the filament melts and breaks.
Barrie (2005) also states that the colour of the light produced depends on the temperature, becoming whiter as the temperature rises but as no material is known to be operated at a higher temperature than tungsten, lamps of this type cannot be made to give a daylight colour. To prevent the filament from oxidizing, all the air must be evacuated from the bulb, and the early lamps were of the vacuum type. The connections of the filament are brought out to the lamp heads. This is the end of the lamp which fits into the lamp holder when the lamp is put into a luminaires. Lamp heads are shown in Figure 2.5.
Figure 2.5: Incandescent lamps heads
Source: Barrie (2005)
3) Lamp holders and ceiling roses
In housing, the choice of the lampshade or luminaire is usually left to the owner or tenant and is made once the dwelling is occupied (Barrie, 2005). Plain lamp holders are, therefore, provided which will accept ordinary 100W and 150W tungsten bulbs, and which usually have a ring or skirt to which a normal lampshade or similar luminaire can be attached. The top of the lamp holder screws down to grip the flexible cable cord on which it is suspended from the ceiling. Typical lamp holders are shown in Figure 2.6 below. According to Barrie (2005), the flexible cord on which the lamp holder is suspended performs two functions. It carries the electric current to the lamp, and it supports the weight of the holders, lamp and shade. Its physical strength is, therefore, just as important as its current carrying capacity and it has to be selected with this in mind. At the ceiling itself, the wiring in (or on) the ceiling must be connected to the flexible cord (Barry 2005). The connection is made by means of a ceiling rose. It consists of a circular plastic housing with a terminal block inside and a bushed opening on the underside where the flexible cord to the lamp holder can come out of the rose. In installations which have the main wiring inside the ceiling, this wiring enters the rose through the back or top of the rose; when the main wiring runs exposed on the surface of the ceiling, it enters the rose through a cut-out in the side of the rose.
Ceiling roses are made with three line terminals in addition to an earth terminal.
Figure 2.6: lamp holder
Source: Barrie (2005)
4) Switches
According to Barrie (2013), the basic function of a switch is to make or interrupt a circuit. Normally when one talks of switches one has in mind light switches which turn lights on and off. A complete switch consists of three parts. There is the mechanism itself, a box containing it, and a front plate over it. The box is fixed to the wall, and the cables going to the switch are drawn into the box. After this the cables are connected to the mechanism. To carry out this operation the electrician must pull the cables away from the wall sufficiently to give him room to work on the back of the mechanism. The electrician then pushes the mechanism back into the box and the length of cable that he had to pull out from the wall becomes slack inside the box. It is therefore important that the box is large enough to accommodate a certain amount of slack cable at the back of the mechanism.
Barrie (2015) also stated that standard boxes for recessing within a wall are 16, 25, 35 and 47mm deep. Sometimes the wiring is done not in the depth of the structural wall, but within the thickness of the plaster. For use with such wiring, boxes are made 16mm deep (plaster depth boxes). It is often necessary to install wiring and accessories exposed on the surface of wall. For such applications surface boxes are made which are both more robust and neater in appearance than boxes which are to be recessed in walls and made flush with the surface, although they are made to similar depth. There is a maximum current which the contacts of any particular switch can make or break, and a maximum voltage that the contact gap can withstand. A switch must not be put in a circuit which carries a current greater than that which the switch can break. Most manufacturers make switches in standard capacities, the lower being rated at 5, 6, 15, or 20A and the higher rating of 45A for control of instantaneous shower units.
Figure 2.7: Switch mechanism
Figure 2.8: Switches
Source: Barrie (2013)
5) Ceiling Fans
According to Varghese (2007), stipulations of ceiling fans are done based on the diameter of the blades of the fan. The common sizes of fans used 900mm and 1200mm. Fans of sizes 1500mm to 1800mm are also available. Old types of fan regulators are of the resistance type but now the modern regulators are more efficient also the lower speeds of the fans to which they can be regulated are important in their selection.
2.5 Voltage Drop
The length of the conductor regulates the voltage drops in that the longer the conductor, the higher its resistance becomes and thus the greater the voltage drops (Alan 2003). Applying Ohm’s law (using the circuit current and the conductor resistance), it is possible to determine the actual voltage drop. Voltage drop at the supply terminals of the installation and a socket-outlet (or the terminals of the fixed current using equipment) shall not exceed three per cent (3%) of the nominal voltage of the supply for lighting and 5% for other circuits.
2.6 Maintenance of Electrical Services Installation
2.6.1 Concept of Maintenance
BS 3811 (1964) defined maintenance as a combination of any action carried out to return an item or restore it to its satisfactory condition. It is the combination of all technical and associated actions intended to retain an item or restore it to a state in which it can perform its required function (BS 3811, 1984). Maintenance must be regarded in the overall context of the ability of the building asset to support service delivery in terms of physical condition, functionality, capacity, environmental performance and alignment with service demand. Building maintenance is an important program for the sustainability of infrastructural development. It plays an important role among other activities in the building operations ( Zulkarnain et al., 2011).
Odediran et al. (2012) stated that the ability of a building to provide the required environment for a particular activity is a measure of its functionality. Therefore as the components of a building begins to deteriorate, it becomes necessary to take measures to ensure that the desired characteristics of that facility which provides safety and convenience are retained and maintained. Kunya et al. (2007) observed that there is apparent lack of maintenance culture in Nigeria, and that emphasis is placed on the construction of new buildings for public sector and neglecting the aspect of maintenance which commences immediately the builder leaves the site. This is also confirmed by Olagunju (2012) who expressed an opinion that there is lack of maintenance set up in Nigeria that can sustain the current inadequate housing provision in the country. Zubairu (1999) stated that the country does not have a maintenance policy which resulted in the persistent problems of building maintenance. Before any electrical work is untaken the eligibility of the electrician or electrical contractor must be verified first as they will be able to issue the required official certification of the work completed. Also the quality of the electricity to be supplied or that will be supplied has to be verified.
2.6.2 Types of maintenance
i) Planned maintenance: according to BS 3811 (1964), planned maintenance refers to a situation where maintenance work is organized and carried out with forethought, control and records. Planned maintenance can be preventive or corrective.
a) Planned preventive maintenance: this is carried out to prevent failure or break down of a facility within its expected life span to ensure continued function and requirement (BS 3811, 1964).
b) Planned corrective maintenance: this is carried out to restore a facility after a failure has already occurred to return it to its acceptable standard (BS 3811, 1964).
ii) Unplanned maintenance: according to BS 3861 (1964), unplanned maintenance is work carried out to no predetermined plan. Approximately 20% to 30% of maintenance work would fall into this category. It would normally be corrective in nature and include emergency work. Unplanned maintenance may be classified into:
a. Predictable: this is a regular work carried out over a period of time necessary to sustain the performance characteristics of the building as well as change the worn out materials.
b. Unavoidable: this is work carried out to correct failures due to incorrect design, incorrect installation and the use of low quality materials.
2.6.3 Maintenance Operation
According to Mohammed (1999) this is a system of work to correct increasing deterioration and the operation involves patching, servicing, preservation, rectification and placements. Maintenance operation falls into two broad categories and these include minor and major operations.
a. Minor operations: this involves minute repairs and placements, but they are very significant in the total maintenance workload. Therefore they should be taken at predetermined intervals such repairs include electric bulb replacements etc. (Mohammed, 1999).
b. Major operations: this is mostly jobs anticipated in advance and includes patching, replacement, rewiring etc. (Mohammed, 1999).
2.6.4 Maintenance of Electrical System
According to Varghese (2007), maintenance of electrical services can be done in the following ways:
i) Have an ELCB trip switch in the electrical system of all buildings this will show up any leakage.
ii) Anti-ant chemicals for placing in switch boxes should be used and cleaning of switch should be because switches are liable to be clogged by grits especially in the kitchen areas.
iii) Connected plugs of high amperage should not be loose to avoid them getting heated up and burn, they should be plugged in properly of or should be connected through a fuse outlet.
iv) It is suitable to have phase-changing devices in the electric supply system so that if one phase goes, the connections can be made to another available phase.
2.7 Testing and Inspection of Electrical Installations
After electrical installations have been done, testing and proper inspection must be carried out to check that the system will operate efficiently and safely. The tests are extensive, as defined in the Institute of Electrical Engineers Regulations and should be carried out by a qualified electrician or electrical engineer. The following tests are essential part of the proceedings:
i) Earth Continuity test: this is carried out to ensure integrity of the live, neutral and earth conductors without bridging of connectors. Here the resistance between ends of ring circuit are recorded, resistance between closed ends of the circuit and a point midway in the circuit, resistance of test lead and indication of circuit integrity are all taken into account. According to Varghese (2007), the total resistance amount from the earth electrode to any point in the earth continuity conductor in the complete installation should not exceed one ohm. Hall and Greeno (2009) stated that continuity test is done to ensure integrity of the live, neutral and earth conductors.
ii) Insulation resistance test: According to Varghese (2007), this test is made with all links in place, all lamps in position and all switches on. The insulation resistance is measured between the earth and the whole system of conductor or any section thereof. This test is to ensure that there is a high resistance between live and neutral conductors and earth. A low resistance will result in current leakage and energy waste which could deteriorate the insulation and be a potential fire hazard. The test to earth requires all lamps and other equipment to be disconnected all switches and circuit breakers closed and fuses left in. Ohmmeter readings should be at least 1M’.
iii) Resistance between conductor test: According to Varghese (2007), when making this test, all the switches must be on but the lamps and other loads should be removed. The test is made between all the conductors connected to one phase conductor of supply and all the conductors connected to the other neutral phase of supply.
2.8 Problems of Electrical Installation
Problems of electrical installation can be classified as primary causes and sources (George, 1984)
i) Primary causes
a) Faulty design
b) Faulty execution of work usually due to poor workmanship and inadequate supervision
c) Faulty material
d) Faulty systems (refers to a group of components operating together)
e) Inadequate cleaning methods
f) Vandalism (intentional damage and disfigurement)
ii) Primary sources
a) Water
b) Fire
2.9 Conformity of installation to the IEE standards
2.9.1 Safety Requirements
BS 7671 (2001) stated that every electrical installation shall, either during construction, on completion, or both, be inspected and tested to verify, so far as is reasonably practicable, that the requirements of the Regulations have been met. In carrying out such inspection and test procedures, precautions must be taken to ensure no danger is caused to any person or livestock and to avoid damage to property and installed equipment.
BS 7671(2001) wiring regulations recommend good workmanship (qualified employees) in running of cables to avoid damage to insulation an conductors and sound judgment in the selection of materials to prevent danger from shock to persons and the possibility of fires from overheating of conductors due to current overload by short circuit.
1) Earthing the wiring regulation (BS 7671, 2001) include approvals for protection against the dangers of electric shock to persons or livestock, damage to installations and the danger of fire from over-current and earth faults. Earth faults occur when a live conductor makes contact with a conductive part of the installation, or extraneous conductive parts such as metal service pipe and current flows earthing connections.
2) Electric shock to persons it is differentiated as direct and indirect.
a) Direct shock is caused when a person comes into contact with alive electrically charged part which causes current to flow through them to earth (Barry, 1998)
b) Indirect shock occurs when contact is made with an exposed conductive part of an electrical installation, such as the metal casing to an electric fire, which is not normally live but may have become so under earth fault conditions caused by contact of live conductor with a metal casing due to insulation failure (Barry, 1998)
2.9.2 Conformance to Requirement
An electrical installation must be constructed, installed and protected to minimize the risk of fire in building or elsewhere. In normal operation, taking into account the surroundings, it must not create the risk of burns, shocks or other injury to people (BS 7671). It must:
1) Safely accommodate any likely maximum demand
2) Incorporate suitable automatic devices for protection against overcurrent or leakage.
3) Have switches or other means of isolating parts of the installation or equipment connected to it, as are necessary for safe working maintenance.