UNIT V–ELECTRICAL SAFETY, WIRING &INTRODUCTION TO POWER SYSTEM Safety measures in electrical system- types of wiring- wiring accessories staircase, fluorescent lamps & corridor wiring- Basic principles of earthing-Types of earthing- Simple layout of generation, transmission & distribution of power.

Safety Precautions When Working With Electricity 1. Avoid water at all times when working with electricity. Never touch or try repairing any electrical equipment or circuits with wet hands. It increases the conductivity of electric current. 2. Never use equipment with damaged insulation or broken plugs. 3. If you are working on any electrical socket at your home then always turn off the mains. It is also a good idea to put up a sign on the service panel so that nobody turns the main switch ON by accident. 4. Always use insulated tools while working. 5. Electrical hazards include exposed energized parts and unguarded electrical equipment which may become energized unexpectedly. Such equipment always carries warning signs like “Shock Risk”. Always be observant of such signs and follow the safety rules established by the electrical code followed by the country you’re in. 6. Always use appropriate insulated rubber gloves and goggles while working on any branch circuit or any other electrical circuit.

7. Never try repairing energized equipment 7. Never try repairing energized equipment. Always check that it is de-energized first by using a tester. When an electric tester touches a live or hot wire, the bulb inside the tester lights up showing that an electrical current is flowing through the respective wire. Check all the wires, the outer metallic covering of the service panel and any other hanging wires with an electrical tester before proceeding with your work. 8. Never use an aluminium or steel ladder if you are working on any receptacle at height in your home. An electrical surge will ground you and the whole electric current will pass through your body. Use a bamboo, wooden or a fibreglass ladder instead. 9. Know the wire code of your country. 10. Always use a circuit breaker or fuse with the appropriate current rating. Circuit breakers and fuses are protection devices that automatically disconnect the live wire when a condition of short circuit or over current occurs. The selection of the appropriate fuse or circuit breaker is essential. Normally for protection against short circuits a fuse rated of 150% of the normal circuit current is selected. In the case of a circuit with 10 amperes of current, a 15 ampere fuse will protect against direct short circuits whereas a 9.5 amperes fuse will blow out.

House Wiring Single phase 230 V Power supply. Three phase 440 V Power supply. Total load divided to three single phase. Earth has connected to the all heavy load (Heater, electric iron, air conditioner, etc.,)

Wiring materials Switches: Lamp Holders: Ceiling Roses: Fuses: Switches allow the user to control a load (on/off) Flush type, pull cord and door bell types. Single way and double way switches. Lamp Holders: Bayonet cap type (up to 250 W) Screwed Lamp holder (up to 1000 W) Fluorescent lamp holder. Ceiling Roses: Tapping point for supply to load Two plate type and three plate type. Fuses: Its melt when abnormal current flow across it; copper, tin or lead. Plug & Socket: Wires & Cables:

Accessories. Screw driver Cutting pliers. Wire stripper Knife Hammer Drilling machines Test lamp Wood saw Hacksaw.

Types of Wiring

STAIRCASE WIRING

CORRIDOR WIRING

Fluorescent lamp wiring

Fluorescent tube: Starter: Ballast: Filled with organ gas and a drop of mercury; Filaments are used as electrode at two ends. Tube coated with phosphors powder (Electron emitting material) – convert the ultraviolet radiation to visible light. Due to the initial high voltage for the use of ballast; electron will flow within two filments. Starter: Capacitor is used for improve the power factor. Ballast: Give a transient high voltage to initiate the electron movement; it is an iron cored coil with high inductance.

Basic Principle of Earthing. Earthing provides discharge of electric current due to leakage and fault to ground. All metallic parts of electrical appliances shall be connected by earth wire made of very good conductor and finally the earth wire is connected to the ground. Its done by G,I plate or G.I pipe; grounded point surrounded by charcoal and common salt to provide good conductivity; ensure the earth resistance is very low.

Objectives of the earthing Provide an alternative path for the fault current to flow so that it will not endanger the user Ensure that all exposed conductive parts do not reach a dangerous potential Maintain the voltage at any part of an electrical system at a known value so as to prevent over current or excessive voltage on the appliances or equipment.

Good Earthing Low resistance to flow of high current. Earth resistance. Copper wire – 1 ohm . Galavanized iron (G.I) – 3 ohm. Step for reduced the earth resistance, Pouring water. Increase in plate area. Increase in depth. Electrodes in parallel.

Types of Earthing Plate Earthing Pipe Earthing

Pipe Earthing

G.I pipe used for earth electrode; size of the pipe depends on the current and soil nature. Ordinary soil – 2m long & 38 mm dia or 1.37 m long & 51mm dia. Dry and rocky soil – length 2.75m or 1.85m. Pipe placed vertically not less than 2m; it is near to the moisture place (0.6m away from water tap). 80mm charcoal with 30mm salt around it for the purpose of reduced earth resistance.

Plate Earthing

GI plate area .3mX.3mX6.35mm; deeper with 3m in ground. Copper plate (galvanized iron plat) not affected in soil moisture;

INTRODUCTION TO POWER SYSTEM

HVDC Transmission system

Distribution System