Difference between grounding and earthing

1. What is the Difference between Earthing & Grounding?
1. Grounding means connecting the live part (it means the part which carries current under normal condition) to the earth for example neutral of power transformer.
2. Earthing means connecting the dead part (it means the part which does not carries current under normal condition) to the earth for example electrical iron etc.
3. One of the most misunderstood concepts is earthing and grounding. We all understand that it is necessary, we need to understand that there are really two separate things we are doing that we call grounding.
The first, is to reference our electrical source to earth (usually via connection to some kind of rod driven into the earth or some other metal that has direct contact with the earth). In the system, this is typically accomplished via a 120/240-3 wire system where neutral has a connection to earth at the source (for residences). Industrial power that has an earth reference has other means of referencing to earth, but generally all have some direct connection to earth. The exception of course is 440V delta which often has no earth connection.
The second thing we often call grounding is really bonding. That is when we take and connect all the metal parts in our systems that might become energized (such as if a conductor came loose). This is done with equipment grounding conductors or sometimes with conduit or raceway systems. The key is to get all the metal pieces electrically connected together. All these metal parts are then connected to the electrical reference point (neutral in the case of residences). That way if a hot conductor comes in contact with a piece of metal a current path exists back to the neutral point that causes the branch circuit protector to open up because there is a short circuit.
In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth.
Electrical circuits may be connected to ground (earth) for several reasons. In mains powered equipment, exposed metal parts are connected to ground to prevent contact with a dangerous voltage if electrical insulation fails. Connections to ground limit the build-up of static electricity when handling flammable products or when repairing electronic devices. In some telegraph and power transmission circuits, the earth itself can be used as one conductor of the circuit, saving the cost of installing a separate return conductor.
For measurement purposes, the Earth serves as a (reasonably) constant potential reference against which other potentials can be measured. An electrical ground system should have an appropriate current-carrying capability in order to serve as an adequate zero-voltage reference level. In electronic circuit theory, a "ground" is usually idealized as an infinite source or sink for charge, which can absorb an unlimited amount of current without changing its potential. Where a real ground connection has a significant resistance, the approximation of zero potential is no longer valid. Stray voltages or earth potential rise effects will occur, which may create noise in signals or if large enough will produce an electric shock hazard.
The use of the term ground (or earth) is so common in electrical and electronics applications that circuits in portable electronic devices such as cell phones and media players as well as circuits in vehicles such as ships, aircraft, and spacecraft may be spoken of as having a "ground" connection without any actual connection to the Earth. This is usually a large conductor attached to one side of the power supply (such as the "ground plane" on a printed circuit board) which serves as the common return path for current from many different components in the circuit.

2. Whether earth can be used as neutral? If yes then why neutral required?
Earth
1. It is used for safety purpose. i.e whenever leakage current pass through electric machine body, earth will conduct directly to earth. So it is prevent electric shock to human body.
2. In 3 phase star connection its act as a neutral & same point connected to ground.

Neutral
3. It is one of the wires in AC circuit.
4. It is used for return path of the circuit in single phase & three phase.
Since the neutral point of an electrical supply system is often connected to earth ground, ground and neutral are closely related. Under certain conditions, a conductor used to connect to a system neutral is also used for grounding (earthing) of equipment and structures. Current carried on a grounding conductor can result in objectionable or dangerous voltages appearing on equipment enclosures, so the installation of grounding conductors and neutral conductors is carefully defined in electrical regulations. Where a neutral conductor is used also to connect equipment enclosures to earth, care must be taken that the neutral conductor never rises to a high voltage with respect to local ground.
Ground or earth in a mains (AC power) electrical wiring system is a conductor that provides a low impedance path to the earth to prevent hazardous voltages from appearing on equipment (the terms "ground" and "earth" are used synonymously here). Normally a grounding conductor does not carry current.
Neutral is a circuit conductor (that carries current in normal operation), which is connected to earth (or ground) generally at the service panel with the main disconnecting switch or breaker.
In a polyphase or three-wire (single-phase) AC system, the neutral conductor is intended to have similar voltages to each of the other circuit conductors. By this definition, a circuit must have at least three wires for one to serve as a neutral.
In the electrical trade, the conductor of a 2-wire circuit that is connected to the supply neutral point and earth ground is also referred to as the "neutral". This is formally described electrical codes as the "identified" circuit conductor.
All neutral wires of the same electrical system should have the same electrical potential, because they are all connected together through the system ground.


Earth can use as neutral but neutral can't use as earth.
1) For closing the complete circuit neutral is mandatory.
2) Once the circuit is closed then only current will flow through any Electrical & Electronic circuit so without neutral any AC Electrical & Electronic circuits won't work.

3. Why we should provide link instead of fuse in neutral line?
1. In AC power system we should not use fuse in neutral. (neutral is using at distribution level for getting single phase or 3 phase 3wire 4wire system to supply the power to the some loads), if we provide fuse in neutral, during the fault condition the fuse in neutral will be blown and the faulty current will not be grounded, this may leads to damage the whole circuit, if we provide link in the neutral the faulty current will be grounded and the circuit will be protected against the fault.
This is the purpose of providing link in neutral.