Unit 7- Practical Electricity II [Compatibility Mode]

8/14/2019 Unit 7- Practical Electricity II [Compatibility Mode]

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Unit 7

Practical Electricity II

2009 Mr Chung T W David, Coral SecondarySchool


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state some electrical hazards and precautionary

measures to ensure the safe use of electricity inthe home.



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Attention! This lesson may save your life!

Electricity can be very dangerous! Do not take itfor granted!



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Living and Physics

Demonstration: Deadly Spark

Observation: See what happens to the wire

http://www.youtube.com/watch?v=pNsUDmlG6js



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Living and Physics

Demonstration: Deadly Spark

Questions: What was that spark?

a cause e spar o occur



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Living and Physics

Common Household Wiring

Live or Hot wire (Brown orRed)

This is a wire at highvoltage.

between countries

In Singapore, this voltage is

240V.

Neutral (Blue or Black)


This is a wire at 0V.

It is kept at zero by earthing.


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Living and Physics

Common Household Wiring

Earth wire (Yellow & Green) This is a wire at 0V.

under normal operation

It is connected to the ground



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A short circuit is an accidental low-resistance

connection between two nodes of an electricalcircuit that are meant to be at different voltages

n examp e s e acc en a connec on o eLive and Neutral wires for Household Wiring



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Grouping: In pairs

Duration: 5min Questions:

What was that spark?

What caused the spark to occur?



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ec ca aza s Electric Shocks and Electrocution

Electrical Fires

oss e auses:1. Damaged Insulation

2. Overheating of Cables3. Damp Conditions



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Occurs: When a person is injured or killed bylar e current flowin throu h the bod .

Example: touching exposed live wire.

Electric Shocks and Electrocution Occurs: A short circuit occurs causing the wire to

be overheated and a fire starts.

xamp e: onnec ng oo many e ec r caappliances to same output socket, causing a fireto break.



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1. Damaged Insulation

The wires of electrical appliances are insulated withinsulating materials such as rubber

,damaged and the wires exposed

If a person comes into contact with the exposedwire



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2. Overheating of Cables

Refers to the unusuallylarge amount of heat

-sized

current flowing through

Overloading of a poweroint can enerate a

huge amount of heat too



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3. Damp Conditions et con t ons o t e

skin greatly reduce theelectrical resistance of

.

Dry skin has a typical

resistance of 100 k or. ,drop below 1k whenwet

,a deadly current of0.23A can flow throughthe bod



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ec ca a e y Never overload a socket

Never use instruments to poke into an electricalsocket

Do not wet electrical appliances, plugs or

sockets Never use electrical gadgets in wet places

Disconnect the appliance when cleaning it

Call the electrician



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Safety Precautions in Using Electricity (I)

Earthing

Why is there an earth wire?

When a fault occurs, the earth wire will carry the.

This prevents the person who is in contact with the

ground and touching the live appliance to beelectrocuted. Appliances with metalsurface are usually

.



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Safety Precautions in Using Electricity (II)

Switches

Used to cut off electric current when we are notoperating the electrical appliance

lamp

neutralelectriccontact

live

fuse springymetal


two-wayswitches


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Safety Precautions in Using Electricity (III)

Consist of a thin piece of copper wire, the fuse is given acurrent rating (i.e the maximum current it can carryw ou me ng

When a fault occurs and the size of the current flowexceeds the rated value of the fuse, the fuse will blow(the fuse wire will melt, cutting off current flow)

Must be fitted to the live wire

Normal

Lperat on

N



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Safety Precautions in Using Electricity (III)

Consist of a thin piece of copper wire, the fuse is given acurrent rating (i.e the maximum current it can carryw ou me ng

When a fault occurs and the size of the current flowexceeds the rated value of the fuse, the fuse will blow(the fuse wire will melt, cutting off current flow)

Must be fitted to the live wire

Abnormal

Lperat on

Fuse

NNo current flow



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Safety Precautions in Using Electricity

Switch and Fuse must always be wired into the live wire!

live

neutral

neutral

(off) ve(on)



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Safety Precautions in Using Electricity (IV)

Circuit Breakers A special type of switch that automatically cuts off electricity

su l in a circuit if the flow of current becomes too lar e

The circuit breaker can only be reset after the fault has beencorrected

instead of blowing

Earth Leakage Circuit Breakers (ELCB) detect small leakages in



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esso u a y Household Wiring and Short Circuits

Hazards of Electricity Electrical Safety Rules

Safety Precautions in Using Electricity


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Unit 7- Practical Electricity II [Compatibility Mode]