Number of Earthing Electrode and Earthing Resistance depends on the resistivity of soil and time for fault current to pass through (1 sec or 3 sec). If we divide the area for earthing required by the area of one earth plate gives the number of earth pits required.
There is no general rule to calculate the exact number of earth pits and size of earthing strip, but discharging of leakage currentis certainly dependent on the cross section area of the material so for any equipment the earth strip size is calculated on the current to be carried by that strip.
First the leakage current to be carried is calculated and then size of the strip is determined.
For most of the electrical equipment like transformer, diesel generator set etc., the general concept is to have 4 number of earth pits. 2 no’s for body earthing with 2 separate strips with the pits shorted and 2 nos for Neutral with 2 separate strips with ….Read Full Article
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