Suppose the live wire comes into contact with the Earth wire. There would not be a complete circuit for the current to travel across. Therefore, why would there be a short circuit and why would the fuse melt? Can someone guide me through the process of what happens if the live wire touches the Earth wire (and not specifically the metal casing of an appliance)?
[Physics] Why does the fuse melt when a live wire to comes into contact with the Earth wire
electricity
Related Solutions
when you touch the metal casing even if the current leaks, because the current is flowing through the earth wire, down to the Earth.
If there is high resistance in the Earth wire then you can have a voltage on case (in the event of a fault). Generally you try and ensure that the resistance throughof the Earth wire is less than the resistance through you - so no current flows through you.
But then I also heard that a circuit needs to be completed in order for an electric current to flow
Not necessarily. If the place the electric current is flowing to is big enough that its voltage doesn't change then it doesn't need to be connected - electricity can just flow into it.
We sometimes use large tanks of salt or large blocks of metal - insulated from the actual ground to act as local Earths in high voltage experiments
The article already explains that the circuit in the second picture is unsafe due to the possibility of ground faults.
So how does the ground connection protect people from faulty appliances such as when a frayed live wire touches a metal casing.
It seems to me you are actually asking how does a system with a residual-current device (RCD) protect you from getting shocked in such a case. In such a system the picture above would look like this.
The residual current circuit breaker (RCD) forms the sum of all of the currents in the phase line and the neutral line. In a system without a ground fault, the sum is always zero.
If a current now flows back to the power source via an undesired current path, then the sum of all currents in the RCD is no longer zero and the RCD breaks the circuit.
For example in the picture if there is an accidental connection from the phase line to the metal casing of your consumer (red), then a large part of the current will flow through this new path, since the metal casing is connected to the ground. The RCD will break the circuit before a person has a chance to touch the metal casing.
On the other hand, if the person touches the phase line directly (yellow) then the person will still get shocked, but the RCD will limit the time the person is shocked to a few milliseconds, as the RCD will again break the circuit as soon as the missing current is detected. This means it can basically detect if any ground fault occurred somewhere.
Best Answer
The "earth wire" is attached to ground; typically via a cold water pipe, which is in actual contact with damp earth.
If the ground connection is good, it provides a nearly infinite capacity to accept charge, all the time maintaining the same relative voltage level.
Because charge flows according to the difference in voltage, and along low-resistance paths, the combination of the "wire" with the "earth" results in all of the current flowing through this path. As the current exceeds the rated capacity of a fuse it melts/blows, or with a circuit breaker, it pops.
This opens the circuit, and the current flow stops.