Content……….. purpose of earthing Earthing design Soil resistivity testing Resistance to earth of a rod or pipe electrode Resistance to earth of a strip Resistance to earth of a infill material
purpose of earthing We 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 arrangement To achieve good earthing,a suitable low resistance to earth is desirable.
Earthing design Using Rods or pipe Using Strip Using Infill material Using foundation
Soil resistivity testing This varies with some parameters.
Three types of copper rods are commonly available.
Copper clad steel rod ( copper shrunk onto the core)
Copper Bonded steel core (copper is molecularly bonded to nickel plated steel rod)
Resistance to earth of a strip L – length of the strip h - the depth buried w - width of the strip P and Q are coefficient for strip or round conductor Rn=FR
Resistance to earth of a infill material Where ρ = resistivity of soil in Ω-m ρc = resistivity of infill material Ω-m d = Diameter of the electrode – m D = Diameter of infill – m L = Driven Length – m