Earthing is the connection between the home appliances or machines through a conducting material to the ground.
In this particular diagram we have supply system which will connect the home appliances through the phase wire and neutral wire. The body of the appliance will be shorted through the conducting material to the ground. The conducting material will offer low resistance to the flow of abnormal current this process is known as Earthing. Usually in interviews or exams it is generally asked that why the earth wire is thick as compare to the other wires. So the reason is that as we know that:
The above equation states that if we want to decrease the amount of the resistance we will increase the cross section area of the conductor. Whenever there is fault in appliance or electrical system earth discharge the electrical energy through earth wire by providing low resistance path. The Earthing provides safety to the human. The current will only from Earthing whenever there is fault or abnormal condition. In normal condition no current will flow from the earth wire.
How to do Earthing?
To make Earthing a 2 to 3 meter hole is dug with the ground near the house. A thick copper plate roughly 1/2 meter by 1/2 meter is placed in the hole. This plate is welded to a thick copper rod and the plate is covered with a mixture of charcoal and salt to make good connection with earth.
The copper rod is protected by a hollow insulating pipe to save the life of the rod in soil and accidental touching by humans. The plate and rod are then buried in the ground. The copper rod is connected to the house and is called the earth. Electrical power from substation is supplied to house through a live wire and a neutral wire. This is a schematic of an electrical circuit with an appliance in the house here there is no Earthing the line fire carries current from the source example the battery to the appliance and the neutral wire carries it back to the battery but in a faulty appliance if the circuit comes in contact with a metal body it causes an electric shock to the person touching it to prevent it the metal casing is connected to the earth flyer.
Now if there is a fault in the appliance the electric current flows from the metallic body into the ground or earth this prevents electric shock in an electric plug we have a lie a neutral and an earth connection these made connection to the appliance .
How Earthing system provide safety:
Now we will discuss that how Earthing provide safety to the human. Let us consider an example in which we have electrical equipment to which we have not provided the electrical Earthing. The load resistance of the equipment is 100 ohm.
In normal condition some current will flow from it. As we know that from Ohm law:
Consider that the voltage is 230 V then the current will be:
I= 2.3 A
It means that in normal condition 2.3 A current will flow. But whenever there is abnormal condition means that a fault will occur due to failure of insulation and live wire touches the body of the appliance. Then the leakage current will start from the body of the appliance. So if we touch the body of the appliance. We will feel shock means that current will be from both appliance and the human body. We know that the normal resistance of the human body is about 1000 ohm. So whenever a human will touch the appliance then the current will be:
I= 0.23 A
This amount of current can damage our body part or it may cause a death. So therefore Earthing is necessary.
Now if we have Earthing and we have fault in an appliance and in this case if human touch the body of the appliance then no current will flow from the body of the human. Because in the earth we have no resistance or very less about 4 to 5 ohm while in the human body we have about 1000 ohm resistance. The current has tendency that it choose the low resistance path and from ohm law we know that:
I= 57.5 A
So if this large amount of current flow then our MCB will trap and the circuit will open. If the current is less then it will flow through the earth wire and the MCB will not trip and in this case we will use ELCB. ELCB open up the circuit if small amount of current will flow from it.
Why we do not use Earthing in mobile charger or TV plug?
The outer body of the TV is made up of plastic and if a fault occurs and a human touch the TV we will not feel shock because current cannot flow through plastic. Similar condition is for the mobile charger whose body is made up of plastic and in which we do not need Earthing.
We need phase and neutral wire to run any load. In fridge we use three pin plug in which one pin phase, one is neutral and one is ground. We can also run it through two pin plug means we can use only phase and neutral but if there is abnormal condition and we touch its body then there is chance of shock. Because the body of the fridge is made up of metal and current can easily flow through it.
Need of Earthing:
Now let us consider that we have a three pin socket in which we have three pin socket which has neutral and phase wire which is connected with the electrical machine. The electrical machine will receive the power from supply through the socket. The machine or home appliance consists of insulation. This insulation will offers infinite resistance. if in any case there is leakage of current there or we touch the machine or appliance then in case of touch the internal resistance of the body of the machine and your body will have some insulation resistance. if the insulation of the machine break and we have no Earthing then the entire current or leakage current will flow through your body and you will get a shock.
Now when we do Earthing and if touch the appliance then their will two different paths for the current to flow. The first path is through the body and another through the earth wire. In this case the earth wire will have low resistance and the entire current will flow through the earth wire and you will become safe. Earth is necessary requirement to safe the shock of your body.
How much earth Resistance Permissible?
Normally the earth resistance is to be 0 ohm but practically it is not possible. In power plant the earth resistance is maintain about 0.5 ohm, in substation the earth resistance is about 2 ohm, in light poles the earth resistance is 5 ohm, in H.T tower the earth resistance is about 10 ohm. In our homes the earth resistance should be less then 8 ohm.
How to reduce earth resistance:
Maintain moistuMre of earth:
In first method to reduce the resistance, we have To maintain the moisture of earth we used water at electrode of earth.
Increase the contact area of electrode:
In the second method to reduce the resistance If we increase the diameter of the wire of the Earthing the resistance will be decrease.
Use of salt and coal in Earthing:
In the third method if make mixture of the salt and charcoal with water it will maintain the moisture and due to which the resistance will be decrease.
Increase the depth of the electrode:
In the fourth method if we increase the depth of the electrode then the earth resistance will be decrease.
Use extra Earthing:
If the resistance does not decrease then we can also use 2 electrode to reduce the resistance.
Grounding in the home:
Now we will discuss that how the ground is connected in the home. The AC source that consists of line, neutral and ground connection and we have circuit breaker which is connected at the line circuit breaker through cable with the socket. Here we have typical washing machine inside the washing machine we have live and neutral connected to the switch and the ground terminal is connected to the metal case of the washing machine.
When we closed the circuit breaker to turn on the washing machine. When the system is operating correctly current flows through the live wires, through the load and back through the neutral. No current will flow through the ground wire.
What happens if the live conductor becomes disconnected and touches the metal case of the washing machine?
The current will then flow from the live wire through the case of the washing machine about to the ground connection. This will be detected by the circuit breaker which then open automatically disconnecting the fault and removing the danger. This is the main reason of grounding the electrical system.
Let now see what happens if for some reason the ground system is not connected. This time when a fault occurs fault current will not flow as there is no defined fault path for the current the circuit breaker will therefore not open. Then the metal case of the washing machine is now live so anyone touching it will be in danger.
Methods of Earthing:
Strip or wire Earthing:
This type of Earthing is used in place where we have mostly stones where duging hole is difficult. This is mostly used for the transmission line.
This type of Earthing is used places where we have less moisture in the earth and we have to dug a deep hole.
The pipe Earthing is mostly used technique of Earthing. In which use pipe which is about 5 to 10 feet in length and we dug it in the earth.
Plate Earthing is also good technique of Earthing and is normally used in substation and power station. It usually use in such place where we have huge load like industries.
In this type of Earthing we use coil and it is mostly used in railways. It is used for Earthing of railway bridges.