Page 112 - Physics 10_Float

CURRENT ELECTRICITY

(ii) Fuses should be connected in the livewire so that the
appliance will not operate after the fuse has blown.
(iii) Switch OFF the main before changing any fuse.

Circuit Breaker

The circuit breaker (Fig. 14.19) acts as a safety device in the
same way as a fuse. It disconnects the supply automatically if
current exceeds the normal value. When the normal current
Fig. 14.19: Circuit Breaker
passes through the livewire the electromagnet is not strong
enough to separate the contacts. If something goes wrong
with the appliance and large current flows through the
livewire, the electromagnet will attract the iron strip to
separate the contacts and break the circuit (Fig. 14.20). The Contacts
spring then keeps the contacts apart. After the fault is
repaired, the contacts can then be pushed back together by
Pivot
pressing a button on the outside of the circuit breaker box.
Livewire
Earthwire Spring

Sometimes, even the fuse cannot capture the high currents Fig. 14.20: Working principle
coming from the livewire into the household appliance. of circuit breaker
Earthing further protects the user from electric shock by
connecting the metal casing of the appliance to Earth (a wired
connection to the bare ground). Many electrical appliances
have metal cases, including cookers, washing machines and
refrigerators. The Earthwire provides a safe route for the
current to flow through, if the livewire touches the casing
(Fig.14.21). We will get an electric shock if the livewire inside an
appliance comes loose and touches the metal casing.

Switch Fuse Insulated cable Livewire

Neutral wire

Earthwire
Fig. 14.21

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