Earthing and types of earthing:

What is Earthing?

Earthing is the first step towards electrical safety. The body of electrical equipments, applinaces etc is to be connected to earth for safe discharge of electric current to the earth, in the event of any leakage , fault etc. The earth is considered to be zero potential. Earthing is done to provide safety to user from electric shock.

  1. It is a set of conductors connected in series or in parallel in order to dissipate the potential difference immediately into the ground.

  2. The wire connected from equipment to earth called earthing wire.

  3. The resistance of earthing wire is low value to provide least resistance path for leakage of fault current.

  4. The area of cross section of conductor is more as resistance is inversely proportional to area of cross section. That is why size of earthing wire is always more.

  5. All metallic part of wiring system must be earthed using one continuous earthing wire in the form of bare copper wire/strip throughout the wiring circuit.

  6. There should be any joints in the earth wire.

There are three methods of earthing widely used,

1.Pipe earthing
  1. Pipe earthing is best form of earthing. It is cheap in system of earthing a GI pipe of 38mm diameter and 2 meters length is embedded vertically in ground to work as earth electrod, but depth depends on soil conditions.
  2. Wire is embedded upto the wet soil.
  3. The earth wire is fastened to the top sction of the pipe with nut and bolts.
  4. The pit area around the pipe is filled with salt and coal mixture for improving soil condition and efficiency of earthing systems.
  5. It can take heavy leakage current for same electrode size in comparison to plate earthing.
  6. The earth wire connection with GI pipes being above the ground level can be checked for carrying out continuity test as and when desired where it is difficult for plate earthing.
  7. In summer season to have effective earthing 3 or 4 buckets of water is put through the funnel for better continuity of earthing.
  8. Galvanised iron pipe of 38mm diameter, 2m length placed to depth of 4.75mtrs. The depth depends on conditions of moisture. The size of pipe depends on the current to be carried and type of soil. The powdered charcoal salt is put 15cm around the pipe. A funnel is connected at the top of pipe and water is poured at regular period of for maintaining resistance as low as possible.

2.Plate earthing:
  1. In this type of earthing plate either copper or G.I is buried into the ground at depth of not less than 3meter from the ground level.
  2. The earth plate is embedded in alternative layer of Coke and salts for minimum thickness of about 15cm.
  3. The earth wire(Copper wire for copper plate earthing and G.I. wire for G.I. plate earthing ) is securely bolted to an earth plate with the help of bolt nut and washer made of copper, in case of copper plate earthing and of G.I. pins in case of G.I. plate earthing.
  4. In this type of earthing the pipe earthing along with additional earth plate is provided at the bottom of the earth rod. If earth plate is made up of iron, size of earth plate is 60cm X60cm X6.3mm. If it is made of copper, size of earth plate is 60cm X60cm X3.15mm. The plate is placed at the depth of 3meter and then alternative layers of charcoal and salt is put below and top of earth plate.

3.Strip earthing:
  1. This type of earthing widely used in transmission.
  2. In this system of earthing, strip electrod of cross section not less than 25mm into 1.6mm of copper or 25mmX4mm of G.I. or steel are buried in horizontal trenches of minimum depth of 0.5m.
  3. If round conuctors are used, their cross section area shall not be smaller than three if copper is used and 6mm2 if G.I. or steel is used.
  4. The length of buried conductor shall be sufficient to give the required earth resistance.(about 0.5ohm to 1.5Ohm)
  5. The electrod shall be widely distributed as possible in single straight or circular trenches radiating from the point.
  6. This type of earthing is used in rocky soil earth bed because at places at such places excavation work for plate earthing is difficult.
  7. In this method, wires made of GI of size 25mmX4mm or wires made of copper of size 25mmX1.6mm are placed below the surface as shown in figure.

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