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IS 3043:1987

Code of Practice For Earthing

The code includes guidelines on earth fault protection and choosing the proper sixe of the various components of the earthing system particularly earth electrodes

Guidelines:-

  • 1) All medium voltage equipment shall be earthed by two separate distinct connection with earth. In case of high voltage neutral points be earth by two separate & distinct connection having own electrode.
  • 2) Earth electrode shall be provided at generating stations substations and consumer promises in accordance with the requirement of the code.
  • 3) As far as possible all earth connections should be visible for inspection.
  • 4) All connections should be carefully done.
  • 5) Earth system shall be so devised that testing of individual earth electrode is possible.
  • 6) It is recommended that a drawing showing the main earth connection & earth electrode be prepared for each installation.
  • 7) All material fitting etc used in earthing shall confirm to Indian standard specification.
Marking of earthing/protection conductor.
Earthing Identification By Colour)
  Alphanumeric Graphical system  
  Bare Colour
Earth E I  
Protective conductor PB   strip yellow/green
Resistance:- Earthing resistance of an electrode consist of:-
  • 1.Resistance of metal.
  • 2. Contact resistance of metal and soil.
  • 3 .Resistance of soil

The first two factors are very small fractions of an ohm. The major factor is soil resistivity.

A site should be choosen based on the following priorities.

  • a) Wet Marshy ground.
  • b) Clay, loamy, soil. Clay soil.
  • c) Clay & loam mixed with varying property of sand, ground and stone.
  • d) Damp and wet sand

Note:-Dry sand, ground chalk limestone, ground and very stony ground should be avoided.

Artificial Treatment of soil:- To reduce the resistivity of the soil are used material which is Highly conductive in its wet solution. The most commonly used substance sodium chloride, sodium carbonate, calcium chloride, copper sulphate, salt, soft coke salt and charcoal.

Shape of Electrode:-
  • 1)Plate Size=> 60cmX60cm
  • 2) CI Plate=> 12mm at least
  • 3) GI or Steel Plate=> 6.3mm
  • 4) CU Plate=> 3.15mm

Plate electrode shall be buried such that its top edge is at a depth 15m.

Pipes:-
  • CI Pipe- 100mm dia, Length- 2.5 to 3m long, thickness- 13mm
  • Ms- 38 to 50mm dia
  • Gs- 13/16 or 19mm dia, Length- 1220 to 2440mm
  • Strips:- there have special advantages where high resistivity soil.
Metal of Electrode:-
  • Copper (tinned or untinned)=> 0.2% per year
  • Cast Iron, MI or mild steel => 2.2% per year
  • Mild steel by galvanized => 0.5% per year Choosing of material depends on metal resistivity=> material used for connection
Coating:-

Zinc or galvanized iron is used.

  • Zinc or galvanised iron atleast 150mm micron.
  • The earth rod should be placed at 1.250m below ground for Installation.
  • Bitumen greasing [ especially GI Plate earthing] [solution free compound]
  • It is valid only for land installation not for shipping and aircrafts.
Installation:-

In order to order to lower down the resistance the earthing may be connected in parallel.

10meter

Atleast 2 meter distance

Power Station:-
  • All neutral points need to be earth specially.
  • All panels with earthing should be framed.
  • Generator & Transformer neutral & body separate earthing.
Maintenance:-

[ Testing must for earthing]

  • 1) Soil moisture
  • 2) Checking connection of electrode at various points.
  • 3) Watering.