IS 3043 (1987): Code of practice for earthing

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2 ! $ ' + - Satyanarayan Gangaram Pitroda Invent a New India Using Knowledge 0 1 ' 5 Jawaharlal Nehru Step Out From the Old to the New 1 + , 1 + Mazdoor Kisan Shakti Sangathan The Right to Information, The Right to Live ! > 0 B Bhart hari N ti atakam Knowledge is such a treasure which cannot be stolen Invent a New India Using Knowledge is 3043 ( 1987 ): Code of practice for earthing [ETD 20:Electrical Installation]IS : 3043 - 1987 (Reaffirmed 2006) Indian Standard CODE OF practice FOR earthing (First Revision) Fourth Reprint JUNE 2007 (Including Amendment No.)

3 1) UDC : Copyright 1988 BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG NEW DELHI 110002 Price Rs September 1988 AMENDMENT NO. 1 JANUARY 2006 TO is 3043 : 1987 CODE OF practice FOR earthing (First Revision) (Page 19, clause ) Substitute the following for the existing formula: (ET 20) AMENDMENT NO. 2 JANUARY 2010 TO is 3043 : 1987 CODE OF practice FOR earthing (First Revision) (Page 17, clause ) Add the following new sub-clause after : Corrosion Allowance On an average, steel corrodes about six times as fast as copper when placed in soil.

4 The extent of corrosion depends upon the properties of soil. The generally accepted correlation between the electrical resistivity of soil and its corrosivity is as indicated in the table below: Soil Resistivity and Corrosion Range of Soil Resistivity (ohm-metres) Less than 25 25-50 50-100 Above 100 (Class of Soil) Severely corrosive Moderately corrosive Mildly corrosive Very mildly corrosive This following methods can be adopted to safeguard Conductor against excessive corrosion: a) Use of cathodic protection, and b) Use current conducting, corrosion resistant coating on steel (for example, zinc coating).

5 The zinc coating on the tubes shall be in accordance with IS 4736 : 1986 'Hot dip zinc coatings on mild steel tubes (first revision) with coating thickness 150 microns, Min. a) Use steel conductor with large cross-section having allowance for corrosion. Based on the results of the field studies on rates of corrosion, the following allowances in cross-sectional area of the earthing conductor are recommended to take the effect of corrosion into account.

6 Allowances in Cross-Sectional Area of the earthing Conductor to Take the Effect of Corrosion into Account Type of Laying of the Earth Conductor a) b) c) Conductors laid to soils having resistivity greater then 100 ohm-meters Conductors laid in soils having resistivity from 25 to 100 ohm-meters Conductor laid in soils having resistivity lower than 25 ohm-meters or where treatment of soil around electrode is carried out Allowances to be Considered in Sizing 0 (No allowance)

7 15 percent 30 percent For the purpose of determining the allowance to be made for corrosion, the minimum resistivity of the soil encountered at the location of grounding electrodes to be considered The. resistivity will be the minimum in wet weather. Thus, for very mildly corrosive soils, steel conductors meeting the stability and mechanical requirement are adequate. However, the steel conductors in the soil of other types should be at least 6 mm thick if it is steel flat and have a diameter of at least 16 mm if it is in the form of steel rod.

8 1 Price Group 3 Amend No. 1 to is 3043 : 1987 (Page 19, clause , para 1) Substitute the following for the existing formula. (Page 20, clause , para 1) Substitute the following for the existing formula: (Page 20, clause , para 4) Substitute the following for the existing 'Pipes may be of cast iron of not less than 100 mm diameter, to 3 m long and 13 mm thick. Such pipes cannot be driven satisfactorily and may, therefore, be more expensive to install than plates for the same effective area.

9 Alternatively, mild steel water-pipes of 38 to 50 mm diameter are sometimes employed. These can be driven but are less durable than copper rods. Alternatively, 40 mm diameter G1 pipe in treated earth pit or 40 mm diameter MS rod can be directly driven in virgin soil. The earth rod shall be placed at m below ground.' (Page 21, clause , para 1) Substitute the following for the existing formula alongwith its terms: where = resistivity of soil (.)

10 M) (assumed uniform): l = length of the strip in cm; and t = width (strip) or twice the diameter (conductors) in cm (Page 24, Fig. 14) Substitute the figure given on page 3 of this Amendment for the existing: (Page 25, Fig. 15) Substitute the figures given on pages 4 and 5 of this Amendment for the existing: (Page 49, clause , first para, last sentence) Substitute the following for the existing: 'It is recommended that the duration of earth fault current should be taken as one second for 66 kV and above voltage level substations; and 3 seconds while designing earth grids for all other voltage levels below 66 kV.