Electrical Supply To Our Homes Electricity supply to our ... · voltage it carries can kill!! ... Relationship Between Power, Voltage & Current! • Info given on the label means

8.4 : Electrical Supply & Wiring System at Home

Electrical Supply To Our Homes

•  Electricity supply to our homes comes from the local substation

•  Current is brought in by the live wire – high voltage it carries can kill!

•  Current is then returned to the substation by the neutral wire which is earthed

Prepared by Ms Sue Soh Ya Lee


Electrical Supply To Our Homes

•  Wiring system at home also has an earth wire

•  Earth wire connects the metal part of an electrical appliance eg electric kettle to the earth

•  Any current leaked while in use is transmitted to the Earth by the Earth wire Prepared by Ms Sue Soh Ya Lee

8.4 : Electrical Supply & Wiring System at Home Electrical Supply To Our Homes

•  Current supplied is an alternating current at a votage of 220 V – 240 V

•  This main voltage is used by many countries so that electrical appliances can be used internationally

•  All lamps & electrical appliances in the house are connected in parallel Prepared by Ms Sue Soh Ya Lee


Wiring System at Home •  2 main types of circuit :

–  For lighting - For power •  Have a

–  live wire to bring current from a local substation –  Neutral wire to carry current back to substation which is

earthed at the local substation –  Earth wire to carry any leaked current to the Earth



Wiring System at Home •  Domestic electric

supply passes through several safety devices eg main fuse box & main switch

•  Main fuse box : –  Contains main fuse

connected on the live wire

–  Excess current flowing into the house will cause it melt & break the circuit

•  Electric meter : –  Records the amount of

electrical energy used –  Unit used : kilowatt-

hour (kWh) Prepared by Ms Sue Soh Ya Lee


Wiring System at Home •  Main switch :

–  On the live wire –  Controls the current

flowing into house –  Turning it off prevents

the current from entering house

•  Automatic circuit breaker –  Found in consumer unit –  Trips automatically &

breaks the house circuit when excess current flows through it

•  Fuses –  If 1 fuse from 1 circuit

breaks, others not affected



Wiring System at Home •  A house which

consumes normal amount of current may use single-phase wiring

•  A house which consumes a large amount of current at 1 time must use three-phase wiring –  Cable in this

wiring system can take in high current



The Use of 3-pin Plugs •  Has 3 pins : –  1 pin for live wire

(L) with brown insulation

–  1 pin for neutral wire (N) with blue insulation

–  1 pin for earth wire (E) which has strips of green and yellow

•  Has a fuse which is connected to the live wire –  The fuse is usually

of 13 A Prepared by Ms Sue Soh Ya Lee


The Use of 3-pin Plugs •  Path of current flows in an electric kettle :

•  Fuse will melt & break the circuit if excess current flows through – prevents electrical appliances from being damaged/burnt

•  No current flows through earth wire unless there is a leakage of current into the body of the electrical appliance

Current from the mains Live pin Fuse Live wire Hea5ng element of iron Neutral wire Neutral pin The mains



The Use of 3-pin Plugs in Electric Kettle


8.5 : Cost of Using Electrical Energy

Relationship Between Power, Voltage & Current

•  Info given on the label means that the electric iron has a power of 1400W when supplied with 220V

•  SI Unit for power : watt (W)

Relationship between Power, Voltage & Current

Power = Voltage x Current Wa?s = Volts x Amperes



Relationship Between Power, Energy & Time •  SI Unit for power : watt

•  SI Unit for energy : Joule

•  SI Unit for time : second

1000 wa?s (W) = 1 kilowa? (kW)

1000 joules (J) = 1 kilojoule (kJ)

1 hour = 60 minutes 1 minute = 60 seconds

Power (W) = Energy (J) Time (s)

From the equa5on, we can define power as the rate of using

energy. 1 wa? is the

power of using 1 Joule of energy per second



Relationship Between Power, Voltage & Current

•  Picture beside shows a reading on an electric meter

•  1 kWh : Amount of electrical energy by an appliance of 1 kW power for 1 hour

1 kWh = 1kW x 1hr = 1000W x (60x60)s = 3 600 000 joules = 3 600 kJ



Cost for Using Electrical Energy

1.  An electric iron of 1 500 W is used for 2 hours. (a) How many kWh of energy are used? (b) If 1 kWh of energy costs 30 cents, how much has to be paid for the energy used?

2. A house has two 500 W lamps and five 100 W lamps. All the lamps are switched on everyday from 8:00 pm until midnight. The cost of energy is as follows : First 100 units (kWh) = 20 cents per unit Next 100 units = 30 cents per units (a) How much electrical energy is used in a month of 30 days? (b) What is the cost of using that amount of electrical energy?


8.6 : Functions of a Fuse and Earth Wire

Fuse and Its Function •  Fuse prevents excess

current from flowing through an electrical appliance

•  Each fuse is rated to carry certain current

•  Any excess current melts the fuse & break the circuit – prevents electrical appliance

•  Usually made from tin/lead or an alloy of tin & lead

•  Has high resistance but have low melting points

•  Always connected to Live Wire Prepared by Ms Sue Soh Ya Lee


Fuse and Its Function •  Fuses are rated in ampere eg 0.25A, 2A, 5A, 10A, 13A,

15A and 400A •  Fuse required for an aplliance/circuit is calculated as

below:

Example : A television set is rated at 200W. What current will pass through if it is connected to a supply of 240V?

Ampere = Wa?s Volts



Earth Wire and Its Function •  Earth wire = Safety device •  Connects the metal casing of

an electrical appliance to the earth through a 3-pin plug & a wall socket

•  Any current leaked from the metal casing will be directed into the earth by the earth wire

•  Anyone touching the casing will not be electrocuted because the current will flow through the earth wire rather than the body

•  Earth wire : has very low resistance than the body


Documents

Electrical Supply To Our Homes Electricity supply to our ... · voltage it carries can kill!! ... Relationship Between Power, Voltage & Current! • Info given on the label means