What is Electrical Earthing?Definition,Types of Earthing & its Importance

The method of passing the fault current directly to the earth through low resistance path is  known as electrical earthing. Electrical earthing is  done through connecting the non-current carrying part of the equipment  to the earth.

Mostly, the galvanized iron strips  are used for the earthing. The earthing provides the low resistance path to the leakage current. The fault current of the equipment flows to the earth which has zero potential. The fault current actuates the earth fault relay and thus equipment remain protected from damage.

Types of Electrical Earthing

The electrical equipment mainly have two points which is at zero potential. The neutral point of the equipment is at the zero potential when there is no fault. The metallic frame of the equipment remains at zero potential and it attains the potential if the live wire touch to the frame of the equipment. The earthing can be classified into two category. These are as below.

Neutral Earthing or system earthing or Grounding

Equipment Earthing.

Neutral Earthing or Grounding

In 3 phase 4 wire system, the neutral potential is zero if all three phases are balanced. During fault the phase voltage does not remain constant and as a result the neutral voltage rise. To protect the equipment the neutral point is connected to earth through a low resistance GI wire. A earth fault relay senses the neutral current and trips the breaker. In distribution transformer and generator neutral earthing is used. 

Equipment  Earthing

The equipment metallic enclosure remains at zero potential. However, if live conductor touches to the enclosure body or if the insulation system of the panel fails, the enclosure body attains full potential. If the metallic body is not earthed, the person touching the enclosure get electric shock. 

To safeguard the person and equipment, the enclosure body is connected to the earth so that the current flows to the ground and consequently the protection system operates and the faulty section gets electrically isolated.

Importance of Earthing

Importance of electrical earthing in electrical installation is as follows.

• The fault current flows through the least resistance earthing path and  the protection relay isolate the faulty section. Thus, the   machine and the person safety is ensured.

• The earthing protects electrical network from the voltage  surges, spikes and lightening discharge. Thus, the reliability of electrical network gets enhanced.

•  The earthing reduces the risk of fire.

• The earthing dissipates the static charge set up in the conductor.

How earthing protects person?

If equipment metallic body is not connected to earthing, the person who comes in the contact of metallic body having potential provides the circuit path and the current starts flowing through the body. The current above 30mA flowing through the human body can cause electrocution. The main purpose of earthing is to protect the human being from electric shock or electrocution. 

Now if the equipment is connected to the earth, the fault current will flow through the least resistance path and no current will flow through the human body. The current will flow from the enclosure to earth. Thus, the person remains protected.

Thus, the earthing is essentially for human safety.

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