1 of 34© Boardworks Ltd 2007. 2 of 34© Boardworks Ltd 2007

1 of 34 © Boardworks Ltd 2007



How safe is this office?

Can you spot the electrical hazards in this busy office?


Why is electricity dangerous?

Warning signs are used to alert people to the presence of high voltage electricity.

When a current passes through living material, it causes an electric shock.

This interferes with nerve signals from the brain to the body, and can cause a heart attack, muscle spasms and breathing difficulties.

Other dangers are overheated and faulty appliances, which may lead to electrical fires.


Do not stick anything other than a plug in a socket.

Never mix water and electricity.

Do not overload sockets.

What precautions can be taken to make electricity safer?

How can electricity be used safely?

Wire plugs correctly.

Regularly check cables for breaks and lose wires.

Use earth wires, fuses and circuit breakers to prevent accidents, in case faults develop.

Although electricity can be very dangerous, it is also incredibly useful and is essential for modern life.


Electrical safety – true or false?



An electrical cable contains three wires.

copper

insulating plastic

What is inside an electrical cable?

These wires are made of copper because it is a good conductor of electricity. Each wire is made of thin strands of copper to keep the cable flexible.

Each wire is encased in plastic to stop the wires touching and causing a short circuit. Plastic is used as it is a good insulator, as well as being tough and flexible. The whole cable is encased in another layer of plastic.


The three pins in an electrical plugs are connected to the three wires inside a cable.

Why do plugs have three pins?

Two of the wires form the electrical circuit. The third is a safety feature.


How does this colour scheme help avoid confusion?

earth

neutral

live

How are wires identified?

A standard colour scheme is used for the plastic casing to show the function of each type of wire.


What does each wire do?

The neutral wire completes the circuit. It is kept at a zero voltageby the electricity company.

The earth wire is a safety wire that is needed to earth appliances with a metal case. This makes it safer to touch the appliance if it develops a fault.

The live wire carries a current that alternates between a negative and positive voltage.


What does each wire do?



Electrical sockets make mains electricity available for use.

NEVER PUT ANYTHING OTHER THAN A PLUG IN AN ELECTRICAL SOCKET!

Remember, the electricity in a plug socket is at 230 V, which could kill you, if you get a shock.

What is an electrical socket?

They connect the plugs on appliances to the mains electricity system, through the three different types of wire (live, neutral and earth).


An electrical plug is inserted into a socket and the cable that is attached to the plug carries electricity to the appliance.

How do plugs and sockets carry current?

A plug has three pins which fit the three holes on a socket in one way only, so the plug cannot be wrongly connected.

Plugs and sockets are a safe and convenient way of using electricity.

The pins are made of brass, which is a good conductor. It is also hard and so will not bend.


Materials and properties of plug parts


neutral terminal

earth terminal

cable grip

fuse

cable

What are the parts of a plug?

live terminal


Make sure that the wires are connected to the correct terminals:

When wiring a plug, always check the following:

How do you wire a plug?

There are no loose or bare wires.

The grip should firmly hold the cable in place.

A fuse of the correct value is fitted.

blue to neutral/green to earth

brown to live


Can you wire a plug?


Identifying wrongly-wired plugs


Electrical plugs – true or false?



A fuse is a safety device, which breaks the circuit, if the current is too high.

What is a fuse?

This protects the cable from overheating and catching fire.

All UK plugs are fitted with fuses. Fuses are available in a range of amperes to suit different current values.

fuse

Sockets and extensions that are overloaded with appliances are especially at risk of catching fire.


How do fuses work?

A fuse contains a thin wire, which melts if the current is too high.

Fuses act as an early warning system, preventing appliances from being damaged by surges in electricity and warning owners of faults.

thin wire

This breaks the circuit and so electricity is unable to flow through the appliance.

The appliance stops working and any danger has been averted.


What is earthing?

Earthing is a process used to increase the safety of electrical appliances.

Cables contains an earth wire to provide an alternative path for current if appliances develop faults.

An earth wire is essential for an appliance with a metal case.

When an appliance is working correctly, no electricity flows through the earth wire.

If the live wire becomes loose and touches the metal case, a very large current flows to earth and blows the fuse, breaking the circuit.


How does earthing work?


Why do some plugs only have two pins?

Instead of having a pin for the earth connection, the plug has a clip on the side.

This plug and socket system is sometimes referred to as “Continental European”.

Some sockets in Europe have two round slots for the pins. Does this mean that the appliances are not earthed?

This clip corresponds to a contact point in the socket and connects the appliance to earth.


What does ‘double insulated’ mean?

Double insulated appliances have plastic cases, without any wires connected to the case.

symbol on double insulated appliance

This means that the case cannot become live, because plastic does not conduct electricity.

So, if one layer of insulation is damaged the appliance is still safe for the user.

Another way of improving the safety of electrical appliances is to make them double insulated.


Earthing and fuses – true or false?



Glossary (1/2)

double insulated – An appliance that contains internal insulation and a non-conducting case.

earthing – A method to improve the safety of appliances by providing a low resistance path for current to flow to earth.

earth wire – A safety wire that connects the metal case of an appliance to earth. It is covered with a yellow and green insulator.

electric shock – A danger associated with electricity. When current runs through living matter it can cause heart attacks, breathing difficulties and muscle spasms.

fuse – A safety component containing a length of wire,which heats up and melts (‘blows’) if the current is too high.


Glossary (2/2)

live wire – A wire that carries mains electricity to an appliance. It is covered with a brown insulator.

neutral wire – A wire that carries current away from an appliance to complete the circuit. It is covered in a blue insulator.

plug – A device that fits into a socket to connect an appliance to the mains electricity.

socket – A connection point for a plug, which makes mains electricity available for use.


Anagrams


Multiple-choice quiz

Documents

1 of 34© Boardworks Ltd 2007. 2 of 34© Boardworks Ltd 2007