The document discusses different methods of earthing electrical systems. It defines earthing as providing a direct path for fault current and achieving a common reference potential. It describes designing earthing using rods, strips, infill material or foundations. It also discusses soil resistivity testing to determine the resistivity based on moisture, temperature and depth. It provides formulas to calculate the resistance to earth of rods, strips and infill material based on factors like soil resistivity, length, diameter and material used.

1. EarthingG.V. Nilanka

2. Content………..purpose of earthingEarthing designSoil resistivity testingResistance to earth of a rod or pipe electrodeResistance to earth of a stripResistance to earth of a infill material

3. purpose of earthingWe provide a direct path to fault current.What is fault current?By earthing we can get common reference potential in electrical system.There are several earthing arrangementTo achieve good earthing,a suitable low resistance to earth is desirable.

4. Earthing design Using Rods or pipeUsing Strip Using Infill materialUsing foundation

5. Soil resistivity testingThis varies with some parameters.moisture content

6. temperature

7. Depth Soil resistivity testing

8. Calculate the soil resistivityρ=2πAdρ=soil resistivityA=Apperant resistanceD=distance between adjacent electrode

9. Resistance to earth a rod or pipe electrode R=ρ(ln(8l/D)-1)/2πLL =length of electrodeD=diameterρ = resistivity of soil

10. Cont….l varies with electrode arrangement

11. Three types of copper rods are commonly available. Solid Copper

12. Copper clad steel rod ( copper shrunk onto the core)

13. Copper Bonded steel core (copper is molecularly bonded to nickel plated steel rod) Resistance to earth of a stripL – length of the strip h - the depth buried w - width of the stripP and Q are coefficient for strip or round conductorRn=FR