Power = voltage x currentCurrent = power / voltagevoltage = power / current1. A 60 W lamp is connected to a 240V

supply.What current does it take?

Power= 60 WVoltage = 240VCurrent = ?2. A kettle has a power rating of 2kW on

the 230 mains.What fuse should be fitted in the plug?

Lesson Objectives

To understand ‘earthing’

To know the differences between a fuse and a miniature circuit breaker

To know the function of an RCD

Earthing appliances

Appliances used in the U.K. are either metal on the outside or they are plastic.

Metal ones are earthed. The earth wire is screwed on to the metal

body of the appliance. The other end is connected down into the

ground through a long brass rod. Earthing

Your Task

Complete Sheet 1 - Earthing

Fuses and miniature circuit breakers (mcb)

Circuit breakers act in the same way as fuses however they;

respond quicker than fuses.

are more sensitive.

Unlike fuses which only operate once and need to be replaced a circuit-breaker can be reset.

A miniature circuit breaker

The circuit breaker acts as a safety device in the same way as a fuse.It disconnects the supply if too large a current flows

Miniature Circuit Breaker An mcb does the same job as a ____, but in

a different way.

A switch is held in position by a spring. When the current becomes too _______ the circuit _______.

The mcb acts much _____ than a fuse

•If a fault occurs in the appliance some of the current will flow through the _____ wire. •The amount of current flowing through the neutral wire decreases and now there is a difference between the _______ in the live and neutral wire.•This difference is called the ______ current.

An electromagnetic switch responds to the difference in ______ and ______ the circuit.

Past paper Practise

Jan 2009 Higher Tier Qu.doc