ID S205_04_Electrical System.pdf
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ID-S205_04 BUILDING SCIENCE Electrical System ELECTRICAL SERVICES POWER SUPPLY SYSTEM L ELECRICAL DRAWING AND SINGLE LINE DIAGRAM E WIRING SYSTEM AND ELECTRICAL INSTALLATIONS C T U R E SINGAPORE POWER LTD & SUBSIDIARIES SP Services Ltd (SPSL), SP Powe...
ID-S205_04 BUILDING SCIENCE Electrical System ELECTRICAL SERVICES POWER SUPPLY SYSTEM L ELECRICAL DRAWING AND SINGLE LINE DIAGRAM E WIRING SYSTEM AND ELECTRICAL INSTALLATIONS C T U R E SINGAPORE POWER LTD & SUBSIDIARIES SP Services Ltd (SPSL), SP PowerAssets Ltd (SPPA) and SP PowerGrid Ltd (SPPG) are subsidiaries of Singapore Power Ltd. L SPSL provides support services: E offers terms and conditions of service connection; arranges for service connection C for the electricity market, It receives requests for electricity service connection; T Energisation/turn-on; and collects transmission charges, security deposits and U charges for other services on behalf of SPPA. SPSL also bills customers R for consumption SPPA is the Transmission Licensee and owner of the transmission and E distribution network. SPPG, the managing agent for and on behalf of SPPA, develops, operates and maintains the transmission and distribution facilities. L E C Power Supply System T U R E Power Supply System MODE OF POWER SUPPLY The mode of power supply depends on: Capacity of building load Location of building relative to supply network L Based on the above consideration, the voltage level at which the power is supplied to various buildings is presented below E SUPPLY VOLTAGES AND CONNECTED LOADS C 230V, 50 Hz, single-phase, up to a maximum of 23kVA, 100A 400V, 50 Hz, 3-phase, 4-wire up to 2000 kVA T 22kV, 50 Hz, 3-phase, 3-wire for a Contracted Capacity of: U between 1,700 kW and 12,750kW for 2 HT 22kV services between 12,751kW and 25,500kW for 4 HT 22kV services. R 66kV, 50 Hz, 3-phase, 3-wire for connection with minimum Contracted Capacity E of 25,500 kW. 230kV, 50 Hz, 3-phase, 3-wire for connection with minimum Contracted Capacity of 85,000 kW Voltage variation or fluctuation at the supply point is maintained as far as possible within ± 6% of the nominal voltage. Power Supply System INTRODUCTION TO POWER SYSTEM High Voltage : > 1000 V alternated current (AC) and >1500 V direct current Low Voltage: 50-1000 V alternated current (AC) and 120-1500 V direct current Extra Low Voltage: < 50 V alternated current and < 120 V direct current L SELV/PELV (Separated ELV) : 0 – 12 V alternated current and 0 – 30 V direct current E SELV (For dry area) : 0 – 25 V alternated current and 0 – 60 V direct current C Low-Voltage System T A low-voltage (LV) system refer to distribution voltages below 1000V. Typical nominal voltages in this range are 240,380,400,415,480,550 and 600 V. In Singapore, a LV U system refers to the three-phase four-wire system of 400 V between line-to-line, and 230 R V between each line to neutral. LV is not only supply voltage, it is also the utilisation E voltage if most of the electrical appliances. Consumer whose incoming supply is 22KV or 6.6KV will have to design and install their own HT and LV systems. For consumer taking LV supply from the utility, the LV system prior to incoming supply will be managed by the utility and these consumers have to design and install only their own inter LV network. Power Supply System CONSUMERS TAKING HIGH VOLTAGE SUPPLY L E C T U R All the equipment such as high voltage switchgears, transformers, low E voltage switchgears and associated cabling must be supplied installed and maintained by the consumer Power Supply System Consumers Taking Low Voltage Supply Consumer load < 23 kVA at 230 V or 400 V L E C Consumer load > 23 kVA T and < 280 kVA at 400 V U R E Consumer load > 280 kVA at 400 V Power Supply System Power Supply System Electricity is generated in power stations, usually located far from the consumers. After generation, the electricity is being transmitted to sub-stations near the load centres and then distributed to consumers. L E C T U R E Power Supply System Generation One form of electricity generation is by thermal power station. These power stations employ steam turbines to run the alternators. L The steam is obtained from high-pressure boilers. The fuel burnt in the boilers can be solid, liquid or gaseous. The liquid fuels used are fuel oil, crude oil, E petrol or paraffin oil. Generally fuel oil is used for firing the boilers. The other C types of fuels are better quality and are used in internal combustion engine. T The scheme of thermal generation can be divided into two phases: U Formation of steam in the boiler house Generation of electrical power in the generation (Turbine) room R E Power Supply System Generation Figure shows below a power flow diagram for a thermal power station. In the boiler house the fuel is burnt and the water is converted into high-pressure steam [converts chemical energy to thermal energy], which is further heated in a superheater. The superheated steam passes the turbine rotating the turbine L blades. Thermal energy is converted into mechanical energy. E The pressure of the steam decreases and its volume increases, after imparting energy to the turbine rotor it passes out of the turbine blades into the condenser C (vacuum). In the condenser the cold water is circulated with the help of pump that condenses the low-pressure wet steam. This condensed water is then heated T again and converted into high-pressure steam to rotate the turbine blades. U The turbine in the generation room acts as a prime mover [converts mechanical R energy to electrical energy] of the alternator, which generates electrical energy generally at a voltage of 11–16kV. This energy is then fed through the generator E switchboards and circuit breakers to transformers. The transformer step-up the voltage of the generator to a higher values at 400kV or 230kV for transmission. The overall efficiency of the Thermal Power Station varies from 20% to 26% depending on the plant capacity. Power Supply System Thermal Power Station L E C T U R E Power Supply System Transmission The ideal arrangement for supply of electricity is to have a power station located right at the load centre and generate power at the utilisation voltage. Then transmission system can be eliminated. However, it is obviously not feasible to L have a power station right in the city centre and also it is not technically feasible to generate power in a large scale at the utilisation voltage. An electrical system E operated at 400V can only supply up to a maximum demand of 3 to 4MW. At a higher voltage of 22kV, the maximum demand can be increased to 200MW. C Transmission of electrical energy by high voltage circuit is required in order to T bring bulk energy from a remote source to a load centre and at the same time to interconnect power stations. The interconnection would increase the reliability of U supply and provide the spooling of generating plants so that the standby capacity can be reduced. R The reason for the transformation from a lower voltage to one considerably high E for transmission is that it is much more economical to transmit bulk supplies of electrical energy by using the highest voltage possible. In this way, the overhead lines or underground cables need have only comparatively small conductors, with the minimum electrical losses (I2R). Power Supply System Transmission To illustrate this aspect of electricity transmission, a conductor of 18mm diameter is sufficient to transmit 50000kW at 132000V. To transmit the same L amount of power at 250V, the conductor diameter would have to be something like 400mm. E C In Singapore the transmission network consists of three levels, 400kV, T 230kV and 66kV. The transmission system in Singapore is totally using the UNDERGROUND CABLE NETWORK. U R E Power Supply System Distribution L E C T U R E Figure: Electricity Transmission and Distribution System Power Supply System Distribution The main function of a distribution system is to receive electric power from large, bulk power sources and to distribute electric power to consumers at various voltage levels with acceptable degrees of reliability. The most commonly used nominal voltages are 3.3kV, 6.6kV, 11kV, 22kV and 33kV. L Depending on the load density and the annual growth rate in a service area, the E tendency is toward higher distribution voltage especially for urban areas that have an increasing consumption of electrical energy. C By selecting a higher distribution voltage, appreciable savings in overall cost can T be achieved if the load density within the service area is high. U A simple transmission and distribution system is shown in Figure. In Singapore, R the primary distribution voltages adopted are 22kV and 6.6kV, and the secondary distribution voltage at utilisation level is 400V. E Connecting to one phase and neutral of a three-phase 400V supply gives 230V single-phase supply suitable for domestic consumers. Power Supply System Distribution In the city centre or industrial estate, where the load density is high, it is distributed at 22kV and stepped down directly to the utilisation voltage through 22kV/400V transformer. In areas where the load density is low, it is distributed at 6.6kV and stepped down through 6.6kV/400V transformers. L E The voltage variation or fluctuation at the supply point is maintained, as far as it is practical, to within ±6% of the normal voltage. The supply frequency is 50Hz and C the variation is maintained at ±1%. T All distribution networks in Singapore are by underground cables from substations placed near to the load centre and supplied at 22kV or 6.6kV. U Transformers in these local substations reduce the voltage to 400V, three-phase and neutral distributor cables connect this supply to consumers. R E Power Supply System Electricity Transmission and Distribution System L E C T U R E A typical 400V/230V distribution system Power Supply System Three-Phase Four-Wire AC System The voltage between any phase conductor and the neutral will be 230V, known as single-phase. Colours Red, Yellow and Blue identify the three phases. The neutral is always black. Supplies to premises are always connected to different phases to balance the loads. L A three-phase, four wire AC system is illustrated in Figure. There are three ‘live’ conductors called ‘phases’ or ‘lines’. The voltage between any of these three E phases is usually 400V. The star point is earthed to an earth electrode sunk into the ground below the substation, and from this point is taken the fourth conductor, C the ‘neutral’. If the consumer is a small one, a house for instance, the supply cable contains T two cables, a live and neutral. The colour of the live will depend on the phase from which it has been taken. U A three-phase 400V supply is used for supplying small industrial and commercial loads such as factory, schools, blocks of flat, commercial building, etc. The higher R voltage (400V) is used generally for motors. The lighting loads are connected across the other phases and the neutral such that when the whole installation is E operating, the loads across the three phases are reasonably balanced so that each phase conductor carries approximately the same current. A single-phase 230V supply is usually provided for individual domestic consumers like our home. Power Supply System Three-Phase Four-Wire AC System L E C T U R E Three-phase four-wire distribution system Power Supply System 6.6 kV Substation Plan L E C T U R E Power Supply System 6.6 kV Substation Section L E C T U R E Power Supply System 6.6 kV Substation Elevation L E C T U R E Power Supply System TYPE OF TRANSFORMERS Two types of liquid filled transformers Mineral oil filled transformers Silicon oil filled transformers L Cast resin dry type transformers E C T U R E Power Supply System CABLES A cable essentially consists of one or more conductors covered with suitable insulation and surrounded by a protective covering. Although several types of cables are available, the type of cable to be used L depends on working voltage and service requirements. E C T U R E Figure above shows the general constructional features of a paper insulated underground cable The basic components are conductor, insulation and serving. Other components such as lead sheath, bedding and armouring varies from cable to cable Power Supply System CABLES L E C SINGLE-CORE PVC 3 OR 4 CORE PVC/SWA/PVC VOLTAGES UP TO 1000 V T Available in standard sizes from 1.5 Used as main incoming cable U mm2 to 300 mm2 to MSB or in urban low voltage Rated current from 13 A to 540 A power distribution R (Depends on method of installation) Used for wiring to socket outlets, E wiring to equipment & appliance and for submain cabling Used in conduits, trunking or on cable trays Power Supply System CABLES 3 & 4 core – 16 mm2 to 400 mm2 (100 A to 740 A) L E XLPE CABLES – 600/1000V (ARMOURED) C T Single core – 50 mm2 to U 1000 mm2 (275 A to 1775 A) R 3 & 4 core – 16 mm2 to 400 mm2 (100 A to 740 A) E XLPE CABLES – 600/1000V (NON-ARMOURED) L E Electrical Drawings and Single-Line C Diagram T U R E Electrical Drawings and Single-Line Diagram Electrical Drawings There are 3 types of electrical drawings: 1) block diagram 2) schematic diagram 3) single-line diagram L 1) Block Diagram E A block diagram is used primarily to present a general description of a system C and its functions. This type of diagram is generally used in conjunction with text material. A block diagram shows the major components of a system and T the interconnections of these components. All components are shown in block form, and each block islabelled for identification purposes. U R E Example of block diagram of car electrical supply Electrical Drawings and Single-Line Diagram 2) Schematic Diagram The schematic diagram shows, by means of graphic symbols, the electrical connections and functions of specific circuit arrangement. The schematic diagram is used to trace the circuit and its functions without regard to the actual physical size, shape, or location of the component devices or parts. The schematic diagram L is the most useful of all the diagrams in knowing the overall system operation. E C T U R E Example of motor DOL Example of schematic schematic diagram diagram of lighting circuit Electrical Drawings and Single-Line Diagram SINGLE-LINE DIAGRAM It is relatively easy and simple to design and draw a schematic diagram of a lighting circuit or the schematic diagram of a motor starting circuit. However, if all the electrical connections in a building were to be represented by L schematic diagrams, there would not be enough space in the drawing plan. E A way, therefore, has to be found to show how the electrical system in an electrical installation is connected. The diagram should show the electrical C connection from the mainsupply cable to all of the installation distribution panels and electrical loads. A single-line diagram is used. T U A single or one-line diagram of a distribution system is a simple and easy-to- read diagram showing power supplies, loads, and major components in the R distribution system. E Electrical Drawings and Single-Line Diagram SINGLE-LINE DIAGRAM A single-line diagram uses symbols rather than label blocks to represent components and shows all components in a single line. There are standard symbols in the Singapore Standards SS202:1999, which L are closely followed for electrical single- line diagrams in Singapore. However, not all components are represented in the SS202. It is therefore acceptable to E see components represented in symbols, which can be interpreted from the legend of the drawing. Descriptions in words are usually added along the C line or components togive an accurate description of the item T U R E Electrical Drawings and Single-Line Diagram SINGLE-LINE DIAGRAM In the above example of the single-line diagram of the lighting circuit, the load is described in words (2 nos. 40W filament lamps). The solid line after the symbol of the 6A SPN MCB is used to represent the live, neutral and cpc cable. To avoid ambiguity, the cable sizes are described in words alongside L the line. Notice the difference between the single line diagram and the schematic diagram for the same lighting circuit. In the schematic diagram the E functional connections are shown, whereas the single-line diagram shows the type of equipment that is being connected, no function connection. C A good single-line diagram will show: T a) the mains (supply) cables size and the method of installation, U b) the main distribution board and type of protective devices used c) the sub-circuits connecting sub-distribution boards or final circuit R connecting electrical loads and equipment. E Electrical Drawings and Single-Line Diagram SINGLE-LINE DIAGRAM L E C T U R E Example of complete single-line diagram of an electrical installation taking supply at 400V Electrical Drawings and Single-Line Diagram SINGLE-LINE DIAGRAM Explanation of terms kVA – kilovolt Ampere L 60A TPN MCB 15kA – 60Amperes Triple Pole and Neutral Miniature Circuit Breaker with short circuit breaking rating of up to 15 kiloAmperes E KWH – Kilowatt Hour meter C 63A 4P ELCB 30mA – 63Amperes 4 Poles Earth Leakage Circuit breaker with T 30milliAmperes tripping current U 10A SPN MCB 10kA – 10Amperes Single Pole and Neutral Miniature Circuit Breaker with short circuit capacity of up to 10kiloAmperes R 4x25mm2 PVC + 16mm2 CPC in trunking – 4 numbers of 25mm2 PVC E insulated copper cable + 16mm2 Circuit Protective Conductor installed in trunking Electrical Drawings and Single-Line Diagram SINGLE-LINE DIAGRAM In order to better identify circuits branching off from the main distribution board and the supply cable, different names are used for L the different cables. The supply cable is called the mains. The circuits branching off the main distribution board are called sub-mains or sub- E circuits. However circuits from feeding any equipment (such as C machine or, motor), lighting or switched socket outlets or isolators are T called final circuits. It is quite common to find final circuits and sub- circuits originating from the same distribution board. U R E Electrical Drawings and Single-Line Diagram SINGLE-LINE DIAGRAM L E C T U R E In the above example, the mains, sub-circuit and final circuits are marked below for easy identification. Electrical Drawings and Single-Line Diagram SINGLE-LINE DIAGRAM Explanation of terms Mains – the Mains are the incoming cable providing supply (electricity) to the installation also called the incoming cable,. L Main Distribution Boards – where the incoming supply cable is connected, E consists of busbars, circuit breakers, etc. This is where all other distribution boards in the installation are connected to. C Submains – the submains are outgoing cables from the Distribution Board T providing supply to another distribution board. U Final circuit – the final circuit is an outgoing cable from the Distribution Board providing supply to electrical equipment such as motor, lighting, switched socket R outlets, etc. E Electrical Drawings and Single-Line Diagram LIGHTING LAYOUT PLAN L E C T U R E Electrical Drawings and Single-Line Diagram POWER LAYOUT PLAN L E C T U R E Electrical Drawings and Single-Line Diagram SINGLE-LINE DIAGRAM L E C T U R E Electrical Drawings and Single-Line Diagram Lighting and Power Load density Lighting Equipment Types of use (W/m²) (W/m²) Shop 25 80 L Main Lobby 30 - F&B Area/Restaurant 35 80 E Mall/ meeting/ 30 20 C Conference Room Pre Function/ 30 50 T Ballrooms Office 15 20 U Office Foyer 30 - R Circulation/ Corridor 15 - Special Retail 30 50 E Electrical Drawings and Single-Line Diagram Lighting Power Load density SS530:2006 L E C T U R E Electrical Drawings and Single-Line Diagram Electrical Load Calculation Electrical Power Supply Unit Loading Demand Tenant's S/N Descriptions Floor Area (W/m2) Factor Tenant's Demand Tenant's Demand (kW) Demand (A) (kVA) L 1 M&E Room 166 30 0.8 3.98 4.69 6.77 E 2 Operation Office 77.7 65 0.8 4.04 4.75 6.86 3 Changing Room 121.57 15 0.8 1.46 1.72 2.48 C 4 Canteen 250 40 0.8 8.00 9.41 13.58 5 Linen Office 176.6 20 0.8 2.83 3.32 4.80 T 6 Restaurant 369.7 65 0.8 58.93 69.33 100.07 8 Convenenice Store 228.5 40 0.8 24.74 29.11 42.02 Toilet U 9 22 20 0.8 0.35 0.41 0.60 10 Store 24 11 0.8 0.21 0.25 0.36 11 Café 270 30 0.8 36.13 42.50 61.35 R 12 Café Service Area 87 30 0.8 2.09 2.46 3.55 13 Staff Access 27.5 30 0.8 0.66 0.78 1.12 E 14 Lobby 211.46 20 0.8 3.38 3.98 5.75 15 Luggage Room 20 30 0.8 0.48 0.56 0.82 16 Staircase 58 11 0.8 0.51 0.60 0.87 17 F.F.L 16.16 20 0.8 0.26 0.30 0.44 Sub Total 2126.19 148.05 174.18 251.41 L E C Wiring System and Electrical T Installation U R E Wiring System and Electrical Installation WIRING SYSTEM A wiring system is an assemblage of parts used in forming an electric circuit, or electric circuits. It consists of the conductor together with its insulation, mechanical protection and certain accessories for fixing, joining and terminating. L Conduit Installations A conduit is a tube, channel or pipe in which insulated conductors are E contained. The conduit, in effect, replaces the PVC outer sheath of a cable, providing mechanical protection for the insulated conductors. A conduit C installation can be rewired easily or altered at any time, and this flexibility, coupled with mechanical protection, makes conduit installations popular for T commercial and industrial applications. There are three types of conduit used in electrical installation work: steel, PVC and flexible. U Steel Conduit R Steel conduit systems are probably the most widely used in electrical installation, due to their strength and durability, as well as ease of handling. E Most are used for enclosing PVC-insulated cable or any other insulated cable. Heavy gauge is made from a sheet of steel welded along the seam to form a tube and is used for most installation work. Wiring System and Electrical Installation Steel Conduit Solid drawn conduit is a seamless tube which is much more expensive and only used for special gas-tight, explosion-proof or flameproof installations. Conduit is supplied in 3.75m lengths. The typical sizes are 16mm[5/8”], L 20mm[3/4”], 25mm[1”] and 32mm[1¼”]. Conduit tubing and fittings are supplied in black enamel finish for internal use or hot galvanized finish for use E in external or damp installations. There is a wide range of fittings and the conduits are fixed usingsaddles or pipe hooks, as shown in Figure. C T U R E Figure 1 Conduit fittings and saddles Wiring System and Electrical Installation Metal conduits Metal conduits are threaded with stocks and dies. The metal conduits also function as the circuit protective conductor and therefore, all connections must be screwed tightly. All the burrs must be removed so that cables will not be damaged when they are drawn into the conduit. L Metal conduits used in AC circuits must contain phase and neutral conductors E in the same conduit to prevent eddy currents from flowing. Eddy current causes the metal conduit to become hot. C Bending conduits T It is often necessary to set or bend the conduit to enable it to pass over an obstruction or to turn a corner. A good electrician is able to make very neat sets, U either by means of a bending machine or by using a simple bending block. The sets are made cold except in the larger sizes of conduit, when the tubing needs R to be heated. E Figure 2 Passing obstruction Wiring System and Electrical Installation Conduit bending machines Bending machines are commonly used, especially for the larger conduit sizes. It is portable and requires no fixing or bolting down. It has serrated jaw pipe vice for cutting and screwing purposes. They are fitted with a safety pin to secure the bending lever in an upright position when removing the bend from L machine. It is fitted with bosses to retain lever in position when changing formers and with positive and adjustable degree of bend quadrant to facilitate E repetitive bending. These benders are supplied as standard with formers only to bend screwing size conduit. C T U R E Figure 3 Conduit bending machine Wiring System and Electrical Installation Conduit bending machines U-shaped bends and places where condensed moisture may collect should be avoided. Where this is not possible, drainage holes should be drilled at appropriate positions in the conduits. L E Threading conduit C The cutting of the screw thread is achieved by using stocks and dies of the T appropriate size. The length of screw thread should be sufficiently long to fit halfway into the couplings and fully into the fittings. After screwing, the end of U the tube must be properly reamered to clean off any sharp edges that will R damage the cable insulation, and the oil used to lubricate the dies must be E wiped and cleaned off. Wiring System and Electrical Installation Fixing the conduit Conduit is fixed to bare brick walls by means of crampets but on finished surfaces such as plastered walls, enamelled saddles or clips are preferred in making a neater job. L The saddles and clips are screwed to plug fitted into drilled holes in the wall E surfaces. Large wooden plugs made on the job are not suitable, as they will dry out and become loose later. C Saddles are often used to hold the conduit away from the wall and to facilitate T wall decoration. Where running along or across steel girders, girder clips are used. Conduit fittings should be screwed together very tightly, as a loose U connection involves loss of electrical continuity. R All screwed joints should be painted, after erection, with a good lead or aluminium paint, which should also be applied to any part of the conduit where E the enamel has been damaged. A conduit run should terminate in a screwed brass bush if a terminal box is not used. Wiring System and Electrical Installation Running coupler Sometimes it is impossible to screw the various parts of the conduit run together consecutively, and a running coupler is used to connect together two pieces of screwed conduit. See Figure 4. L One conduit A is normally threaded half the length of an ordinary coupler whilst the other conduit B is screwed sufficiently to accommodate the coupler C and a E locknut D. C The tubes are butted together, and the coupler C is screwed tightly onto tube A, so that both tubes are held together. The locknut D is then screwed and tightened T to butt against the coupler C to preventmovement. U R E Figure 4 Running Coupler Wiring System and Electrical Installation Conduit fittings Many different kinds of conduit fittings are available. They include screwed elbows, bends and tees, non- inspection, inspection, and split types, junction boxes,circular, oblong, or square. L A square ‘adaptable’ box is most useful when a number of conduits running together change direction. Figure 5 below shows such a box. When conduits E run into such a box or into a distribution fuse board, proper mechanical and electrical continuity must be maintained. C T U R E Figure 5 Mechanical and electrical continuity at conduit box The conduit is screwed of sufficient length to accommodate a coupler, a brass bush, and the thickness of the box wall. After the bush has been screwed tightly at the end of the conduit, the coupler, or alternatively a locknut, is screwed to butt nicely against the wall of the box. Wiring System and Electrical Installation Drawing in the wires The conduits of each circuit shall be erected complete before the cables are drawn in. The advantage of drawing in wires after fixing the conduit is the fact that this may be done after all plastering is completed and the walls are dried out. L Before starting to pull in the cables, it is advisable to ensure that the conduit system is free from obstruction and moisture. Where the draw wire is required, E it should be inserted during the erection of the conduit. C The ends of the wires to be drawn are bared and twisted together to form a firm loop (see Figure 6). The draw wire is firmly attached to the loop. The cable can T only be drawn in one short section of the conduit at a time, generally from one connection box to another. U While one wireman is pulling the draw wire gently, another must guide the R cables into the tube. The cables must not twist round each other and must be parallel throughout the run. Once the cables are twisted, it would be difficult to E them pull in. It would also be impossible to withdraw them if necessary, at a later date. Wiring System and Electrical Installation Drawing in the wires L E C T U R E Figure 6 Drawing wires into the conduit Wiring System and Electrical Installation PVC Conduit PVC conduit used on typical electrical installations is heavy gauge standard impact tube manufactured to BS4607. The conduit size and range of fittings are the same as those available for metal conduit. PVC conduit is often joined by placing the end of the conduitinto the appropriate fitting and fixing with a PVC L solventadhesive. E 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 C the point of the intended bend and the conduit is then bent over the knee. The spring ensures that the conduit maintains its circular shape. T PVC conduit is not suitable for installations subjected to temperatures below U -5°C or above 60°C. Where luminaires are suspended from PVC conduit boxes, precautions must be taken to ensure that the lamp does not raise the R box temperature or that the mass of the luminaire supported by each box does not exceed the maximum recommended by the manufacturer. E PVC conduit also expands much more than metal conduit. So for a long run, an expansion coupling is required for conduit movement in order to prevent distortion during temperature change. Wiring System and Electrical Installation PVC Conduit Installing a PVC conduit is much faster as compared to installing a steel conduit. PVC conduit is also non- corrosive but it does not have the mechanical strength of a steel conduit. Since PVC conduit is an insulator, it cannot be used as the circuit protective conductor (CPC) and a separate L earth conductor must be run to every outlet. E All conduits should be terminated in a box or fitting and meet the boxes or fittings at right angles, as shown in Figure 3-7. Any unused conduit box C entries should be blanked off and all boxes covered with a box lid, fitting or accessory to provide complete enclosure of the conduit system. T Conduit runs should be separated (unless intentionally bonded) from other U services to prevent arcing from occurring due to a faulty circuit within the conduit, which might punctured the pipe of another service. R E Wiring System and Electrical Installation PVC Conduit L E C T U R E Figure 7 Terminating conduits Wiring System and Electrical Installation 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. A separate CPC must be run either inside or outside the flexible tube (CP5 Clause 543-02-01). L Flexible conduits are used so that excessive tensile and torsional stresses to the E conductors and connections are avoided. C Flexible conduits are used for the final connection to motors so that the vibrations of the motor are not transmitted throughout the electrical installation T and to allow for modifications to be made to the final motor position and for drive belt adjustments. U Trunking Installations R A trunking is an enclosure provided for the protection of cables that is normally square or rectangular in cross-section, having one removable side. E Trunking may be thought of as a more accessible conduit system. In industrial and commercial installations, it replaces the larger conduit sizes. Wiring System and Electrical Installation Trunking Installations A trunking system can have great flexibility when used in conjunction with conduit; the trunking forms the background or framework for the installation, with conduits running from the trunking to the apparatus. L When an alteration or extension is required, it is easy to drill a new hole at the side of the trunking and run a conduit to the new point. The new wiring can then E be drawn through the new conduit and the existing trunking to the supply point. C Trunking is supplied in 3m length and various cross- sections measured in millimetres from 50x50 up to 300x150. Generally, trunkings are available in either T steel or plastic. ADVANTAGES U It is much lighter then conduit of the same capacity. R Wiring is easier and faster as the cables are ‘laid in’ instead of being drawn in. E Trunking bends itself more easily and is more adaptable than conduit. Conduit can be easily connected to trunking when required for situations where the larger capacity of trunking is not necessary. Multi-compartment trunking can be used where segregation of services is necessary. Wiring System and Electrical Installation Metallic trunking Metallic trunking is formed from mild steel sheet, coated with grey or silver enamel paint for internal use or a hot-dipped galvanized coating where damp conditions might be encountered. A wide range of accessories is available, such as 45° bends, 90° bends, tee and four-way junctions for on- site L assembly. Alternatively, fabricated bends can be made (see Figure 3-8). This may be necessary or more convenient if the bend is non-standard. E When making fabricated bends, the trunking should be supported with C wooden blocks for sawing and filing, to prevent the sheet steel from vibrating or becoming deformed. Fishplates must be riveted or bolted to the trunking to T form a solid and secured bend. U If standard bends are used, the continuity of the earth path must be ensured at the joints. This is achieved by tightening the fixing screw connections or by R fitting a separate copper strip between the trunking and the standard bend. E Wiring System and Electrical Installation Metallic trunking L E C T U R Figure 8 Standard and Fabricated trunking bends E If an earth continuity test on the trunking is found to be unsatisfactory, an insulated circuit protective conductor (CPC) must be installed inside the trunking Wiring System and Electrical Installation Non-Metallic trunking Trunking and trunking accessories are also available in high- impact PVC. The accessories are usually secured to the length of trunking with a PVC solvent adhesive. PVC trunking is easy to install and non-corrosive. A separate CPC is needed and non-metallic trunking will require more frequent fixings because it is L less rigid than metallic trunking. Min-trunking E Mini-trunking is a very small PVC trunking, ideal for surface wiring in domestic C and commercial installations such as offices. The trunking has a cross-section of 16mmx16mm, 25mmx16mm, 38mmx16mm or 3mmx25mm and is ideal for switch T drops or for housing auxiliary circuits such as telephone or audio equipment wiring (see Figure 9). U Skirting trunking R Skirting trunking is manufactured from PVC or steel in the shape of a skirting board. It is frequently used in commercial buildings such as hospitals, E laboratories and offices. The trunking is fitted around the walls of a room and contains the wiring for socket outlets and telephone points that are mounted on the lid, as shown in Figure 9. Wiring System and Electrical Installation Trunking L E Figure 9 C Cable Tray Installations T U R E Figure 10 Cable tray with bends The whole tray should provide a firm support for the cables and therefore the tray fixings must be capable of supporting the weight of both the tray and cables. Wiring System and Electrical Installation Cable Tray Installations Cable tray is a sheet-steel channel with multiple holes. The most common finish is hot-dipped galvanized but PVC-coated tray is also available. It is used extensively in large industrial and commercial installations for supporting MI and SWA cables that are laid on the cable tray and secured with cable ties through L the tray holes. E Cable tray should be adequately supported during installation by brackets that are appropriate for a particular installation. The tray should be bolted to the C brackets with round-headed bolts and nuts, with the round head inside the tray so that cables drawn along the tray are not damaged. T The tray is supplied in standard widths from 50mm to 900mm, and a wide range U of bends, tees and reducers are available. R Figure 3-10 shows a factory-made 90° bend at B. The tray can also be bent using a cable tray-bending machine to create bends such as that shown at A in E Figure 3-10. The installed tray should be securely bolted with round- headed bolts where lengths or accessories are attached, so that there is a continuous earth path that may be bonded to an electrical earth. Wiring System and Electrical Installation Lighting Circuits Most lighting circuits comprise several switching arrangements, such as one- way, two-way and intermediate. A typical domestic circuit is derived from a 5A or 6A way in a consumer unit. In larger installations, the rating of the circuit protective device can be either 15A or 16A. Domestic lighting is largely based L on the use of fluorescent lamp and filament lamps. Commercial installations are based on mainly fluorescent lamps. E The simplest lighting circuit is a one-way, comprising one lamp or two lamps C controlled by a one-way switch, as shown in Figure 3-11 and Figure 3-12. The one-way switch must always be connected to the live side of the supply. T During installation, the switches must be positioned so that the circuit is energised when the rocker is in the ‘down’ position. U R Supply Voltage E N L Figure 11 Two lamps in parallel controlled by a one-way switch Wiring System and Electrical Installation Lighting Circuits Supply Voltage N L L E C Figure 12 Two lamps, each controlled by a one-way switch T U R E Figure 11 Two lamps in parallel controlled by a one-way switch Wiring System and Electrical Installation Lighting Circuits The two-way switching arrangement (Figure 13) is used when a room has two entry points and the lamp can be switch ON/OFF from any two positions. The two- way switch has no OFF position. The lamps are switched ON and OFF by L the operation of one or the other switch. Similarly, these switches must also be connected to the live side of the supply. E It is recommended that all domestic installations have at least two lighting C circuits. The reason for having two lighting circuits is to ensure that part of the house will still have some light should one circuit fails. T Lighting circuits are usually wired in 1.0mm2 or 1.5mm2 cross sectional area U (CSA) cable, using either loop-in or joint-box method of installation. R The loop-in method is universally employed. The only joints are at the switches or lighting points. The live conductors are looped from switch to switch and the E neutrals from one lighting point to another. Wiring System and Electrical Installation Lighting Circuits L E C Figure 13 Two-way control of a lamp T Power Circuits U Two types of circuits are used to feed socket-outlet units and fused connection R units: radial and ring. Ring or radial circuits may be used for domestic or other premises where the maximum demand of the current using equipment does not E exceed the rating of the protective devices for the chosen circuit. Socket- outlets (except for shaver units) are not permitted in bathrooms. In industrial or commercial premises, adjacent socket-outlets must be connected to the same phase of the supply. Wiring System and Electrical Installation Radial Circuit In a radial circuit, each socket outlet is fed from the previous one. Live is connected to live, neutral to neutral and earth to earth at each socket outlet. L E The radial circuit is derived from a 20A way in a distribution board or consumer unit and is intended to serve a floor area not exceeding 20m2. If C the floor area to be served is not more than 50m2, the rating of the protective T device is 30A or 32A. Kitchens in domestic premises (where a large number U of socket- outlets are often needed for electrical appliances) are often fed by radial circuits. R E Wiring System and Electrical Installation Radial Circuit L E C T U R E Figure 14 Radial final sub-circuit installation supplying three 13A switch socket outlets Wiring System and Electrical Installation Ring Circuit Ring circuits are very similar to radial circuits in that each socket outlet is fed from the previous one, but in ring circuits, the last socket is wired back to the supply source. Each ring final circuit conductor must be looped into every socket outlet or joint box that forms the ring and must be electrically L continuousthroughout its length. E The ring circuit is derived from a 30A or 32A way and has its conductors terminated at its point of origin in the distribution board or consumer unit. C An unlimited number of socket-outlets may be connected to the circuit T provided that the floor area served does not exceed 100m2 in domestic installations. As most modern domestic premises have a floor area in excess U of this figure, two ring circuits are usually provided (or one ring and one radial circuit for the kitchen). When more than one ring circuit is installed in the R same premises, the socket-outlets should be reasonably shared between the circuits to balance the loading. E Wiring System and Electrical Installation Ring Circuit L E C T U R E Figure 15 Ring final sub-circuit installation supplying four 13A switch socket outlets Wiring System and Electrical Installation Sample electrical electrical switch board connection L E C T U R E Wiring System and Electrical Installation New Color Code for Electrical Wiring L E C T U R E Wiring System and Electrical Installation One Gang One Way Switch L E C T U R E Wiring System and Electrical Installation Switch – Socket outlet (SSO) L E C T U R E ID-S205_04 BUILDING SCIENCE Electrical System_Assessments (1) Draw or indicate the lighting point for the restaurant as per given by below layout plan. Cad drawing will be provided for it. L E C T U R E ID-S205_04 BUILDING SCIENCE Electrical System_Assessments (2) Draw or indicate the single line and wiring diagram for meeting room as per given by below layout plan. Cad drawing will be provided for it. L E C T U R E THANK YOU
