What is Earthing

  • Earthing in electricity is the process of installing a protective earth wire into the earth surface to limit the chances of an electric shock occurring, in electrical objects with insulation faults.
  • Earthing is the process of creating an alternative path for the flow of fault/excessive currents safely into the ground through the minimal resistance path.

Why We Do Earthing

  • Poor grounding not only contributes to unnecessary downtime, but a lack of good grounding is also dangerous and increase the risk of equipment failure.
  • Without an effective grounding system , we could be exposed to the risk of electric shock.
  • If fault currents have no path to the ground through a properly designed and maintained grounding system , they will find unintended paths that could include people.
  • A good grounding system will improve the reliability of equipment and reduce the likelihood of damage due to lighting & fault currents.
  • In short we require earthing for:

    1. Personal Safety
    2. System Stability

      • Operate over current device during a ground fault.
      • Reduce potential difference b/w non-current carrying part (enclosures) & b/w non-current carrying parts & earth.
      • Protect equipments.
    3. Over voltage protection

      • Lightening dissipation
    4. ESD (Electrostatic Discharge)

      • Reliability of equipment
      • Noise Control

Purpose of Earthing:

The purpose of a ground besides the protection of people, plants and equipments is to provide a safe path for the dissipation of fault currents, lightening strike and other static discharges.

  1. Safety for Human life/ Building/Equipments:

    • 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.
    • 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 equipments 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.
  2. Over voltage protection:

    • Lightning, line surges or unintentional contact with higher voltage lines can cause dangerously high voltages to the electrical distribution system. Earthing provides an alternative path around the electrical system to minimize damages in the System.
  3. Voltage stabilization:

    • There are many sources of electricity. Every transformer can be considered a separate source. If there were not a common reference point for all these voltage sources it would be extremely difficult to calculate their relationships to each other. The earth is the most omnipresent conductive surface, and so it was adopted in the very beginnings of electrical distribution systems as a nearly universal standard for all electric systems.

Why we do Testing of Earth Resistance periodically

  • Over the time, corrosive soils with the high moisture content, high salt content and high temperatures can degrade ground rods and connections.
  • So although the ground system when initially installed, had low earth resistance values. The resistance of the grounding system can increase if the ground rods are eaten away.
  • That's why it is highly recommended that all grounds and ground connections are checked at least annually as a part of normal predictive maintenance plan.


  • Factors affecting on Earth Resistivity

    1. Soil Resistivity:

      • It is the resistance of soil to the passage of electric current. The earth resistance value (ohmic value) of an earth pit depends on soil resistivity. It is the resistance of the soil to the passage of electric current.
      • It varies from soil to soil. It depends on the physical composition of the soil, moisture, dissolved salts, grain size and distribution, seasonal variation, current magnitude etc.
      • In depends on the composition of soil, Moisture content, Dissolved salts, grain size and its distribution, seasonal variation, current magnitude.
    2. Soil Condition:

      • Different soil conditions give different soil resistivity. Most of the soils are very poor conductors of electricity when they are completely dry. Soil resistivity is measured in ohm-meters or ohm-cm.
      • Soil plays a significant role in determining the performance of Electrode.
      • Soil with low resistivity is highly corrosive. If soil is dry then soil resistivity value will be very high.
      • If soil resistivity is high, earth resistance of electrode will also be high.
    3. Moisture:

      • Moisture has a great influence on resistivity value of soil. The resistivity of a soil can be determined by the quantity of water held by the soil and resistivity of the water itself. Conduction of electricity in soil is through water.
      • The resistance drops quickly to a more or less steady minimum value of about 15% moisture. And further increase of moisture level in soil will have little effect on soil resistivity. In many locations water table goes down in dry weather conditions. Therefore, it is essential to pour water in and around the earth pit to maintain moisture in dry weather conditions. Moisture significantly influences soil resistivity.
    4. Dissolved salts:

      • Pure water is poor conductor of electricity.
      • Resistivity of soil depends on resistivity of water which in turn depends on the amount and nature of salts dissolved in it.
      • Small quantity of salts in water reduces soil resistivity by 80%. common salt is most effective in improving conductivity of soil. But it corrodes metal and hence discouraged.
    5. Climate Condition:

      • Increase or decrease of moisture content determines the increase or decrease of soil resistivity.
      • Thus in dry whether resistivity will be very high and in monsoon months the resistivity will be low.
    6. Physical Composition:

      • Different soil composition gives different average resistivity. Based on the type of soil, the resistivity of clay soil may be in the range of 4 – 150 ohm-meter, whereas for rocky or gravel soils, the same may be well above 1000 ohm-meter.
    7. Location of Earth Pit:

      • The location also contributes to resistivity to a great extent. In a sloping landscape, or in a land with made up of soil, or areas which are hilly, rocky or sandy, water runs off and in dry weather conditions water table goes down very fast. In such situation Back fill Compound will not be able to attract moisture, as the soil around the pit would be dry. The earth pits located in such areas must be watered at frequent intervals, particularly during dry weather conditions.
      • Though back fill compound retains moisture under normal conditions, it gives off moisture during dry weather to the dry soil around the electrode, and in the process loses moisture over a period of time. Therefore, choose a site that is naturally not well drained.
    8. Effect of grain size and its distribution:

      • Grain size, its distribution and closeness of packing are also contributory factors, since they control the manner in which the moisture is held in the soil.
      • Effect of seasonal variation on soil resistivity: Increase or decrease of moisture content in soil determines decrease or increase of soil resistivity. Thus in dry weather resistivity will be very high and during rainy season the resistivity will be low.
    9. Effect of current magnitude:

      • Soil resistivity in the vicinity of ground electrode may be affected by current flowing from the electrode into the surrounding soil.
      • The thermal characteristics and the moisture content of the soil will determine if a current of a given magnitude and duration will cause significant drying and thus increase the effect of soil resistivity.
    10. Area Available:

      • Single electrode rod or strip or plate will not achieve the desired resistance alone.
      • If a number of electrodes could be installed and interconnected the desired resistance could be achieved. The distance between the electrodes must be equal to the driven depth to avoid overlapping of area of influence. Each electrode, therefore, must be outside the resistance area of the other.
    11. Obstructions:

      • The soil may look good on the surface but there may be obstructions below a few feet like virgin rock. In that event resistivity will be affected. Obstructions like concrete structure near about the pits will affect resistivity. If the earth pits are close by, the resistance value will be high.
    12. Current Magnitude:

      • A current of significant magnitude and duration will cause significant drying condition in soil and thus increase the soil resistivity.

Differences Between Conventional/Traditional and Chemical/Gel Earthing:

S.No.
Properties
Conventional Earthing
Chemical Earthing
1
Installation
More area of space required.
Less area of space required.
2
Hygroscopic Property
Salt, which are dissolved in water and losses its hygroscopic property.
Eco Friendly chemicals are used as Back Fill Compound which has peculiar capability to absorb water and insoluble in water.
2
Hygroscopic Property
Salt, which are dissolved in water and losses its hygroscopic property.
Eco Friendly chemicals are used as Back Fill Compound which has peculiar capability to absorb water and insoluble in water.
3
Temperature Handling Capability
As soon as the salt dissolved, the Coal burns out due to low burning temperature ~600degree Centigrade.
CCM has high burning temperature~2500 degree Centigrade.
4
High Fault Current Handling
As coal has low burning temp. High fault current burns it and the resistance is increased of the conductor.
The electrode equally distributed the high fault current to the ground due to high burning temperature chemical in it.
5
Current Carrying Capacity
LOW, due to non uniform and small surface area. As current always travel through the surface area of the conductor.
HIGH, upto 60 kilo amperes for 1.00 second due to uniform and large surface area.
6
Corrosion of material
Highly corrosive due to inadequate galvanization.
External: Hot dip galvanized (80-100 microns) zinc/copper coated.
Internal: Anti corrosive chemical mixture used and filled interior cavity of pipe.
7
Maintenance
Need regular maintenance and watering.
No need of water pouring except sandy & hot areas where this need in every six months.
8
Life of Earthing
Average effective life 2-3 years.
Average effective life 12-15 years.
9
Resistance Value
Good values at time of installation. Values vary with time due to fast degradation of earthing system.
Good & consistent values over time.