buildinggroupppt-130512115915-phpapp02.pptx
- 2. ◾ Most domestic premises receive a single- phase supply of electricity from an area electricity board at a rating of 230 volts and frequency of 50 hertz. ◾ The area electricity board's cable, from which the domestic supply is taken, consists of four lines, three lines each carrying a 230 volt supply and the fourth is the common return line or neutral. 25-Apr-13 2
- 3. 25-Apr-13 3 ◾ Neutral is connected to earth at the transformer or substation as a safety precaution should a fault occur on the electrical appliance. ◾ Each line or phase is tapped in turn together with the neutral to provide the single-phase 240V supply
- 4. ◾ The supply or intake cable may enter building in two ways I. Underground duct II. Overhead supply. ◾ An underground supply is preferred since all of the electrical service is hidden. 25-Apr-13 4
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- 9. 25-Apr-13 9 ◾ From the service cable, the supply passes through the meter, which records the electricity consumed in units of kilowatthours. ◾ Then the supply passes through the fuse which protects the distribution board when excessive currents flow in the system. ◾ From the fuse, the supply is passed to the distribution board. ◾ The distribution board has a main switch to control (Switch off and switch on) the circuit breakers (MCBs and ELCBs). ◾ These fuses are a protection against excess current or overload, the fuse or circuit breaker will isolate the circuit from the source of the problem.
- 10. Electric Meter Electric meters use either digital displays or dials. The difference between one month's reading and the next is the amount of energy in kWh that have been used for that billing period.
- 11. Electricity meters operate by continuously measuring the instantaneous voltage (volts) and current (amperes) to give energy used (in joules, kilowatt-hours etc.). Meters for smaller services (such as small residential customers) can be connected directly in-line between source and customer. For larger loads, more than about 200 ampere of load, current transformers are used, so that the meter can be located somewhere other than in line with the service conductors. The meters fall into two basic categories, electromechanical and electronic.
- 12. Electromechanical On a single-phase AC supply, the electromechanical induction meter operates through electromagnetic induction . This is done by counting the revolutions of a non-magnetic, but electrically conductive, metal disc which is made to rotate at a speed proportional to the power passing through the meter. The number of revolutions is thus proportional to the energy usage. Electronic meters Display the energy used on an LCD or LED display, and some can also transmit readings to remote places. In addition to measuring energy used, electronic meters can also record other parameters of the load and supply such as instantaneous and maximum rate of usage demands, voltages, power factor and reactive power used etc. They can also support time-of-day billing, for example, recording the amount of energy used during on-peak and off-peak hours. The meter has a power supply, a metering engine, a processing and communication engine (i.e. a microcontroller), and other add-on modules such as a real time clock (RTC), a liquid crystal display, infra red communication ports/modules and so on.
- 13. MAIN SWITCH: 1. The main switch is connected in the live and the neutral wires. 2. It is used to cut the connections from the live wire and the neutral wire simultaneously from the main supply. 3. The main switch is installed in the distribution board, from where the supply is divided into sub-circuit through ELCBs and MCBs. 4. The main switch can be cut off by a human or a computerized system to control the flow of power in the building.
- 14. 25-Apr-13 14 ◾ The consumer unit should be fitted close to the point of service entry and from here the service is divided into a number of sub- circuits. ◾ It is normal in a domestic installation to separate power circuits and lighting circuits so that if a fault occurs then not all socket outlets or lights are isolated.
- 15. RECEPTION AND DISTRIBUTION OF MAIN SUPPLY There should be a circuit breaker or a linked switch on live conductor of the supply mains at the point of entry The wiring throughout the installation should be such that there is no break in the neutral wire in the form of a switch or fuse unit. All main switches should be either metal clad enclosed pattern or of any insulated enclosed pattern and should be fixed at close proximity to the point of entry of supply.
- 16. SINGLE PHASE SUPPLY All loads in a single phase installation are connected in parallel and supplied at the same voltage. Figure shows a simple diagram of a single phase installation.
- 17. The consumer’s main switch-fuse is connected after the meter and feeds a distribution board. A switch fuse is a composite unit, comprising a switch with the fuse not being carried by the moving member of the switch. A distribution fuse board consists of one or more fuses or circuit breakers mounted on a distribution to and protection of one or more sub-mains or final sub-circuits.
- 18. Panel Board: A distribution board (also known as panelboard, breaker panel, electric panel, DB board or DB box) is a component of an electricity supply system . divides an electrical power feed into subsidiary circuits while providing a protective fuse or circuit breaker for each circuit in a common enclosure. Normally, a main switch, and in recent boards, one or more residual-current devices (RCDs) or residual current breakers with overcurrent protection (RCBOs) are also incorporated.
- 19. ◾ Protection against electric shock is provided by insulating and placing live parts out of reach in suitable enclosures, earthing and bonding metal work and providing fuses or circuit breakers. ◾ A fuse or miniature circuit breaker (MCB) will disconnect the supply automatically before the overload current can cause a rise in temperature which would damage the installation. 25-Apr-13 19
- 20. 25-Apr-13 20 ◾ An isolator is a mechanical device, which is opened manually and is provided so that the whole of the installation, one circuit or one piece of equipment may be cut off from the live supply. ◾ In addition, a means of switching off for maintenance or emergency switching must also be provided. ◾ In practice it is the aim to bring the Electrical supply to the appliance with as small a loss of voltage through the conductor as possible. ◾ This means that the wiring must have the smallest resistance that is economical
- 21. ◾ The electrical distribution system in high rise flats and office buildings uses a busbar system. ◾ A busbar is a solid copper bar that carries the electrical current. ◾ The busbars run vertically inside trunking and are supported by insulated bars across the trunking chamber. ◾ The electrical supply to each floor is connected to the rising main by means of tap-off units. 25-Apr-13 21
- 22. 25-Apr-13 22 ◾ To balance electrical distribution across the phases, connections at each floor should be spread between the phase bars. ◾ To prevent the spread of fire and smoke, fire barriers are incorporated with the busbar chamber at each compartment floor level. ◾ The chamber must also be fire stopped to the full depth of the floor.
- 23. ◾ The types of light fitting that we use in modern buildings can be divided into five sections. 1. Decorative lighting 2. Commercial lighting 3. Industrial lighting 4. Outdoor lighting 5. Emergency lighting 25-Apr-13 23
- 24. Quantity of light ◾ The amount of light emitted from a light fitting is given in lumens (lm). ◾ A lumen is the unit of luminous flux. ◾ The amount of light falling on a surface is measured in lux. ◾ One lux is equal to 1 lumen per square metre …….. 1 lux = 1 lm/m2. 25-Apr-13 24
- 25. 25-Apr-13 25 Illuminance (lux) Activity Area 100 Casual seeing Corridors, changing rooms, stores 150 Some perception of detail Loading bays, switch rooms, plant rooms 200 Continuously occupied Foyers, entrance halls, dining rooms 300 Visual tasks moderately easy Libraries, sports halls, lecture theatres. 500 Visual tasks moderately difficult General offices, kitchens, laboratories, retail shops. 750 Visual tasks difficult Drawing offices, meat inspection, chain stores. 1000 Visual tasks very difficult General inspection, electronic assembly, paintwork, supermarkets. 1500 Visual tasks extremely difficult Fine work and inspection, precision assembly. 2000 Visual tasks exceptionally difficult Assembly of minute items, finished fabric inspection.