Safety Features in mains Safety Features in mains circuitscircuits

Household wiringHousehold wiring

Use p268 to answer the following Use p268 to answer the following questionsquestions

1.1. Where is your electricity generated Where is your electricity generated and how does it get to your house?and how does it get to your house?

2.2. What do the letters L, N, and E stand What do the letters L, N, and E stand for in wiring?for in wiring?

3.3. What is the function of the L, N, and E What is the function of the L, N, and E wires?wires?

4.4. What does a.c. mean?What does a.c. mean?

Learning ObjectivesLearning Objectives

To know how electricity enters our To know how electricity enters our homeshomes

To know the functions of the wires in To know the functions of the wires in the UK mains electricity systemthe UK mains electricity system

Mains ElectricityMains Electricity

There are a large number of appliances There are a large number of appliances which use mains electricity.which use mains electricity.

An appliance is a useful arrangement of An appliance is a useful arrangement of electrical components.electrical components.

These include cookers, heaters, lighting, These include cookers, heaters, lighting, TV, radio, hi-fi and computers.TV, radio, hi-fi and computers.

UK mains electricity SupplyUK mains electricity Supply

The UK mains electricity supply has The UK mains electricity supply has three wires.three wires.They are called They are called LiveLive, , NeutralNeutral and and EEaarrtthhand each wire has its own colour.and each wire has its own colour.

Live is BrownLive is Brown, , Neutral is BlueNeutral is Blue, , Earth Earth is Green and Yellow stripes.is Green and Yellow stripes.

The live wireThe live wire

The Live wire is connected directly to The Live wire is connected directly to the generators of the electricity the generators of the electricity supply company.supply company.

NEVER touch this wire, it can kill you!NEVER touch this wire, it can kill you!

The Neutral WireThe Neutral Wire

The Neutral wire returns the The Neutral wire returns the electricity to the generator after it electricity to the generator after it has passed through the appliance, to has passed through the appliance, to complete the circuit.complete the circuit.NEVER touch this wire!!NEVER touch this wire!!

In a complete circuit, it carries the In a complete circuit, it carries the same electricity as the Live wire.same electricity as the Live wire.

The Earth WireThe Earth Wire The Earth wire usually carries no The Earth wire usually carries no

electricity, it is there as a safety electricity, it is there as a safety device.device.

If something in the appliance goes If something in the appliance goes wrong, or it is wired incorrectly, then wrong, or it is wired incorrectly, then the Earth wire carries the same the Earth wire carries the same electricity as the Live wire.electricity as the Live wire.

To be completely safe, NEVER touch To be completely safe, NEVER touch this wire eitherthis wire either

The Three Pin PlugThe Three Pin Plug

How to RememberHow to Remember

bLue goes LEFTbLue goes LEFT

bRown goes RIGHTbRown goes RIGHT

sTriped goes to the TOPsTriped goes to the TOP

A Mains PlugA Mains Plug

Complete your diagram and write down the function of each part of the plug

What is a fuse?What is a fuse?

A fuse is a safety device which A fuse is a safety device which switches off an appliance if too large switches off an appliance if too large a current flows through the Live wire.a current flows through the Live wire.

The fuse is connected between the Live pin and the Live wire of a plug.

How does a fuse work?How does a fuse work? The fuse has a rating printed on the outside The fuse has a rating printed on the outside

in amps.in amps.

If the current going through the fuse rises If the current going through the fuse rises above its rated value, then the fuse "blows" above its rated value, then the fuse "blows" (it melts) which turns off the appliance.(it melts) which turns off the appliance.

For example, if the fuse says 5 amps,For example, if the fuse says 5 amps,then a current greater than 5 amps will then a current greater than 5 amps will blow the fuse. blow the fuse.

FusesFuses The fuse breaks the circuit if a fault in an The fuse breaks the circuit if a fault in an

appliance causes too much appliance causes too much ____________ flow. flow.

If the current going through the fuse is If the current going through the fuse is ______ than it’s rating then the wire heats ______ than it’s rating then the wire heats up until it melts and ______ the circuit. up until it melts and ______ the circuit.

The fuse used should be rated at a current The fuse used should be rated at a current slightly _____ than the appliance normally slightly _____ than the appliance normally usesuses

Power = Current x VoltagePower = Current x Voltage

• A vacuum cleaner has a rating of 460W A vacuum cleaner has a rating of 460W on the 230 mains.on the 230 mains.

What fuse should be fitted in the plug?What fuse should be fitted in the plug?

Your taskYour task

Complete the ‘calculating which fuse Complete the ‘calculating which fuse to use’ sheetto use’ sheet

PlenaryPlenary

Write down any keys skills we have Write down any keys skills we have used during today’s lessonsused during today’s lessons