Electrical Works Earthing and its types

[archdevil]

Earthing is the process of connecting an earth conductor to the earth electrode. It helps to prevent electric shocks by providing a low impedance, low resistance, return path for any fault current to get back to the distribution panel. This high return fault current will cause the circuit's breaker to trip and disconnect the fault.

Earthing means any connection given to the earth mass by means of a conductor connected to the earth electrode buried in soil.

The qualities of a good earthing system are :
Must be of low electrical resistance (ideally zero but practically between 1 to 1.5 ohm)
Must be of good corrosion resistance
Must be able to dissipate high fault current repeatedly

Need of Good Earthing

• To save human life from danger of electrical shock or death by blowing a fuse i.e. To provide an alternative path for the fault current to flow so that it will not endanger the user
• To protect buildings, machinery & appliances under fault conditions ie. To ensure that all exposed conductive parts do not reach a dangerous potential.
• To provide safe path to dissipate lightning and short circuit currents.
• To provide stable platform for operation of sensitive electronic equipment's i.e. To maintain the voltage at any part of an electrical system at a known value so as to prevent over current or excessive voltage on the appliances or equipment.
• To provide protection against static electricity from friction.

Types of Earthing
There are various ways of doing Earthing.
Conventional EARTHING
Pipe Earthing,
GI Plat Earthing,
Cast Iron plat Earthing,
Copper plat Earthing
Maintenance Free EARTHING

Conventional EARTHING
The Conventional system of Earthing calls for digging of a large pit into which a GI pipe or a copper plate is positioned amidst layers of charcoal and salt.
The Conventional system of GI pipe Earthing or copper plate Earthing requires maintenance and pouring of water at regular interval.

Maintenance Free EARTHING

• It is a new type of earthing system which is readymade, standardized, scientifically developed. Its Benefits are
• Maintenance Free: No need to pour water at regular interval- except in sandy soil.
• Consistency: Maintain stable and consistent earth resistance around the year.
• More Surface Area: The conductive compound creates a conductive zone, which provides the increased surface area for peak current dissipation. And also get stable reference point.
• Low earth resistance. Highly conductive. Carries high peak current repeatedly.
• No corrosion. Eco Friendly.
• Long Life.
• Easy Installation.

Technical details of Maintenance Free EARTHING
Two ‘B’ class mild steel pipes, one inside the other, are subjected to Hot dip Galvanization .
Back Fill Compound (B.F.C)"Ashlok" earthing system comes with a compound named Back Fill Compound (B.F.C) when has all the qualities of the ideal backfill material for an earthing system.
It is easily compacted and when water is added to it, it will absorb up to thirteen times its dry volume.
This consistently holds its own shape and adheres to any surface it touches.
These capabilities resolve the issues of compatibility and soil / rod contact that are crucial to an earthing system.
BFC absorbs whatever moisture is present and maintains within itself, in contrary to surface appearances.

Benefits of Back Fill Compound (B.F.C)

• Maintains moisture within the sphere of influence of electrode. The B.F.C. will cause the low soil resistivity around the electrode., which results in a significantly lower earth resistance, that could not otherwise be obtained using a conventional earth electrode installation.
• Provides cathodic protection for the electrode
• Enhances the surrounding soil conductivity thereby making it more effective for high fault, noise, ripples, harmonics, neutral to earth balance and lightning current dissipation.
• he enhancement backfill material has special application with non-toxic enhancers to further improve its durability and performance.

Measurement of Earth Resistance:
Earth resistance is measured using Earth Tester. This meter consists of 4 terminals E, P1, P2, and P3.
E & P1 will be shorted & connected to grid or electrode & P2, P3 are the reference electrode that will be kept on the Earth surface at two different locations for taking ref resistance of the earth.
The meter shows the value of Earth resistance than is less than 1 ohm.

Factors affecting earth resistance are
Shape & material of the earth electrode.
Depth of the electrode at which they are buried in soil.
Specific resistance of the soil surrounding the electrode

Methods of Earth Ground Testing
There are four types of earth ground testing

1. Soil Resistivity (using stakes)
2. Fall of potential (using stakes)
3. Selective (using 1 clamp and stakes)
4. Stakeless (using 2 clamps only)

Soil Resistivity measurement
Why determine the soil resistivity ?

• Soil resistivity is most necessary when determining the design of the grounding system for new installation (green field application ) to meet ground resistance requirement.
• The soil composition , moisture content, and temperature all impact the soil resistivity .
• Soil is rarely homogenous and the resistivity of the soil will vary geographically and at different soil depths.
• Since soil and water are generally more stable at deeper strata , it is recommended that the ground rods to be placed as deep as possible into the earth.
• Ground rods should be installed where there is stable temperature.
• For grounding system to be effective, it should be designed to withstand the worst possible conditions.

How to calculate soil resistivity?
Formula is as follows
ρ = 2ΠAR
ρ = average soil resistivity to the depth A in ohm-cm.
Π = 3.1416
A = distance between the electrodes in cm
R = measured resistance value in ohms from the test instrument.

Note: Divide ohm-centimeters by 100 to convert to ohm-meters.