What is difference between neutral and earth ,what would happen if in a three conductor system(single phase) we interchange neutral and earth?

Earth point is the point connected locally to ground, while Neutral point is a point that is connected to ground (earthed) as well but faraway at some point of the power equipment .

IF INTERCHANGE NOTHING WILL BE CHANGED 

Neutral is provided to complete electrical circuits in the case of single phase requirements. Earth is being provided for safety and to permit flow of fault currents in the case of earth faults. If earth is not provided, current based earth fault protections will not work. During normal operation, neutral conductor is the part of main electrical circuit whereas earth conductor remains isolated.

1)While neutral requires to be effectively connected to Earth, it is nothing but a common point of all three phases which is nearly to earth potential.

2)Earthing or Ground is required to protect  the equipment & its user from electric shock.The body of every equipment should be connected to earth either by a strip or a conductive wire.

The similarity between these two is that both should be well connected deeply into the earth with salts and chemicals for providing least resistive path for current.

If physically we interchange the two,i.e,earth & neutral, the effect would be nothing.

Neutral is a path to complete the circuit for Flow of current , Where as Earth is a Point to discharge any leakage current to ground. If we make earth as neutral the circuit will not work cause all the current will be grounded

Neutral is the reverse current path while earth is used for grounding unbalance current.............

In balance condition no current flow in earth......................................neutral provide a complete path.............

load current flows through neutral, but in normal operation, no load current will ever flow through earth.

From generation point earth and neutral has a common point.

One can use the same conductor as neutral and earth but not at the same connection. Neutral can be grounded but earth itself is a ground path to flow the abnormal current in the circuit.

1-A Ground represents an electrical path, normally designed to carry fault current when a insulation breakdown occurs within electrical equipment

2-A Neutral represents a reference point within an electrical distribution system.

3-A Earthing means connecting the dead part (it means the part which does not carries current under normal condition) to the earth. For example electrical equipment’s frames, enclosures, supports etc

The wire which is used as a return path i.e to form a close path is known as neutral whereas, the wire or conductor which is used for grounding or earthing the system is known as earth or ground wire.

Interchanging of neutral and earth will lead to complications and therefore it must be avoided at all times.