ELECTRICAL ENGINEERING – PART – 23 – EARTHING & GROUNDING

EARTHING means connecting the dead part to the earth.

It means, the part which does not carries current under normal condition to the earth.

Example - electrical equipment’s frames, enclosures, supports etc.

The purpose of earthing is to minimize risk of receiving an electric shock if touching metal parts when a fault is present.

GROUNDING means connecting the live part to the earth.

It means, the part which carries current under normal condition.

Example – grounding of neutral point of a star connected transformer.

The purpose of grounding is the protections of power system equipment and to provide an effective return path from the machine to the power source.

A true earth ground, as defined by the National Electrical Code, physically consists of a conductive pipe or rod driven into the earth to a minimum depth of 8 feet.

The earth was an electrically neutral body, i.e. an equal number of negative and positive charges are distributed throughout the earth at any given time.

Earth is considered to be zero potential and establishes a convenient reference frame for voltage measurement.

Voltmeters read only the difference in potential between two points, absolute measurements can be made by using earth as reference.

The voltage at one point is in a circuit is always measured relative to another point in the circuit, hence, voltage is relative.

The reference point in a circuit is called as ground point. The ground point is used as reference point in the circuit for specifying voltages.

The ground is represented as (i) Earth ground (ii) common ground and (iii) Chassis ground.

CHASSIS – The electronic and electrical components are mounted on a metal base called chassis. Chassis is a good conductor, it provides is conducting return path.

The earth symbol is often used in place of chassis or common ground.