Lesson.5: Lesson.5: Fuses and Safe PlugsFuses and Safe Plugs

ObjectivesObjectives

State the colour, function and position of State the colour, function and position of the three wires in a domestic plug.the three wires in a domestic plug.

Describe the function, operation and safety Describe the function, operation and safety purposes of fuses, circuit breakers and purposes of fuses, circuit breakers and

earth wires.earth wires.

Explain the meaning of the term, double Explain the meaning of the term, double insulated and why such an appliance does insulated and why such an appliance does not not require an earth wire.require an earth wire.

Plug Questions

Wiring a Plug PracticalWiring a Plug Practical

Complete

Higher‘Charge in Circuits’ page 137and ‘Fuses and Safe Plugs’ page 138and ‘Resistance’ page 139.

FoundationCharge in Circuits’ page 126and ‘Resistance’ page 128.

Foundation MARK SCHEME

Learning ObjectivesLearning Objectives

State the colour coding for live, neutral and earth wires:State the colour coding for live, neutral and earth wires:live – brown;live – brown;neutral – blue;neutral – blue;earth – green/yellow.earth – green/yellow.

Describe and explain the functions of the live, neutral and earth wires:Describe and explain the functions of the live, neutral and earth wires:live – carries the high voltage;live – carries the high voltage;neutral – the second wire to complete the circuit;neutral – the second wire to complete the circuit;earth – a safety wire to stop the appliance becoming live.earth – a safety wire to stop the appliance becoming live.

State that an earthed conductor cannot become live.State that an earthed conductor cannot become live.

Describe that an earthed conductor cannot become live.Describe that an earthed conductor cannot become live.

Describe reasons for the use of fuses/circuit breakers (as re-settable Describe reasons for the use of fuses/circuit breakers (as re-settable fuses).fuses).

Explain the reasons for the use of fuses/circuit breakers as re-settable Explain the reasons for the use of fuses/circuit breakers as re-settable fuses (structure and mode of operation not required).fuses (structure and mode of operation not required).

Describe how a wire fuse works:Describe how a wire fuse works:if the current becomes too large;if the current becomes too large;wire fuse melts, breaking the circuit.wire fuse melts, breaking the circuit.

Explain how a wire fuse reduces the risk of fire:Explain how a wire fuse reduces the risk of fire:If the appliance develops a fault:If the appliance develops a fault:too large a current causes the fuse melt;too large a current causes the fuse melt;preventing flow of current;preventing flow of current;prevents flex overheating and causing fire;prevents flex overheating and causing fire;prevents further damage to appliance.prevents further damage to appliance.

Describe and recognise that “double insulated” appliances do not need Describe and recognise that “double insulated” appliances do not need earthingearthing

Explain why “double insulated” appliances do not need earthing:Explain why “double insulated” appliances do not need earthing:case of appliance is a non conductor and cannot become case of appliance is a non conductor and cannot become

live.live.

Explain how a wire fuse and earthing protects people.Explain how a wire fuse and earthing protects people.