Why do we need an Earth wire in our appliances?

[Terocamo]

I was reading about current electricity and some how I came across the idea that a circuit of no earthed point will not cause any electric shock.
I wonder if it is right cause if it is, why do we need an Earth wire in our appliance.
I am also suspicious because if the circuit is not earthed, then there must be a non-zero potential on any point of it, so why is there no electric shock? Given that the person is standing on the ground and has zero potential, a p.d. should arise.

 

[supratim1]

earth wire is provided to pass any accumulated charges on metal parts of electric devices, so that it doesn't get grounded through our body resulting in a shock.

i didnt understand the second part of ur question.

 

[Terocamo]

We cannot define the absolute potential if there is no reference point, earthing a point is one way to define a zero point. Hence, if the circuit is not earthed, then there should be a non-zero potential in practically any point of the circuit. Well I hope this can make my question clearer.

 

[PhanthomJay]

..if the circuit is not earthed, then there must be a non-zero potential on any point of it, so why is there no electric shock? Given that the person is standing on the ground and has zero potential, a p.d. should arise.

There is a potential difference between the energized wire and the person on the ground, but since the insulating properties of air (a dielectric) lies between the two, then there is no earthing to ground (no grounded path for current to flow), although there will be an electric field that could induce currents and shocks, if high enough. If that's what you mean..

 

[Terocamo]

But what if u touch that wire?
It is said that u still will not receive a shock.
I am thinking maybe a circuit that is not grounded does not form a closed circuit with the person touching it, there is no path for the current to flow back to the circuit do the person is not going to receive the shock.