Household equipments power cord usually has 3 terminals Neutral, Line and Ground. For a 3 phase circuit, circuit below shows Line and neutral.
3 Phase supply is used for a long distance transmission. Houses usually get single phase and a limited number of 2 phase outlets for high demanding Electrical loads.
Voltage across the two phases(two coils) will be double the voltage across the single phase(Single coil).
The main purpose of the Neutral cable is to send the current difference back to the source, “The Difference”- because two loads are connected at the same time.
As Kirchhoff Current Law (KCL) says the net current flowing into the Node is equal to the total current coming out of the Node.
When both loads are equal, same current will be drawn i1=i2. In that case we do not require a Neutral wire to send back the difference current back to the source. This condition is called “Balanced Circuit”. This balanced condition doesn’t apply to a household with multiple different loads. The Unbalanced Condition occurs with an unequal loads are present.
The above circuit is already complete with Line and Neutral.
What does ground do here?
Well, the ground protects from any short or dangers caused when a Line connection is exposed. The current chooses a lower resistance path to travel and ground is made with very low resistance material.
Where is it connected?
the ground connection is connected to the chassis of the load or any other susceptible spots closer to the “Line”. Because when a bad Line wire touches the chassis, the current chooses ground path and saves from danger.
As shown in the circuit above. When the neutral connection is connected to Ground, it reduces the risk of the Line wire touching the Neutral. When Neutral touches Line, the current chooses lower resistant Ground wire and eliminates the risk of shorting Line and Neutral.