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Double-Insulated Appliance – Air purifier in the classroom

Double-insulated appliances are common around us. The air purifiers in our classroom are one good example.

In these appliances, only two wires are needed, namely Live and Neutral wires. Earth wire is not required as the casing is made of insulator like plastic for this case.

The classic air purifier in our classroom
The “double squares” symbol means that this appliance is double-insulated.
As you see, the earth wire is not required.

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Why do we need earth wire and fuse?

Simply put, electric appliance can be very simple with just a live wire bring in the current and a neutral wire to bring the current out. The appliance can just work like this forever (without the hassle of having earth wire, fuse etc), provided there is no electric fault developed.

Both the earth wire and the fuse are safety features to protect the user and the appliance respectively. Take a look at the video below to understand the rationale.

Recall these notes given:

Function of earth wire.JPG


Function of fuse.JPG

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