9 c] Why earthing is need in a building service. With neat diagram explain the pipe earthing.
Solution :
Necessity of Earthing
- To protect the human beings from danger of shock in case they come in contact with the charged frame due to defective insulation.
- It guarantees the safety of electrical appliances and devices from the excessive amount of electric current.
- It protects the appliances from high voltage surges and lightning discharge.
- It provides an alternative path for leakage of current hence protects the equipment.
- It keeps the voltage constant in the healthy phase
- It protects the Electric system and buildings from lightning.
- It avoids the risk of fire in the electrical installation system.
- To maintain the line voltage constant under unbalanced load condition.
Pipe Earthing :
In this method a Galvanized iron pipe of 38 mm diameter and length of 2 meters with 12 mm holes is placed vertically into the ground at a depth of 4.75m.This pipe acts as an earth electrode. The depth depends upon the condition of the soil
The pit area around the pipe is filled with the alternate layers of salt and coal for improving the condition of the soil and earthing efficiency. The earth wires are connected to the top section of the pipe above the ground level with nut and bolts. The funnel is provided to pour the salt water. The schematic arrangement is as shown below.
The contact surface of GI pipe with the soil is more as compare to the plate. Hence it can handle large leakage current for the same electrode size. The earth wires connected to the GI pipe above the ground level can be physically inspected time to time.
The only disadvantage of pipe earthing is that, the pipe length has to be increased sufficiently in case of soil of high specific resistivity. This increases excavation work and hence increased in cost.
