4 - System earthing

Abstract

This chapter covers the various methods of grounding that are adopted in electrical systems. The grounding methods are also applicable in the case of generators whose windings are also invariably star-connected. The earthing method is called effectively earthed when it is directly connected to the earth (solidly earthed) without any passive component in between. Non-effective earthing refers to the method of earthing through a resistance, reactance, and transformer. The chapter compares the various methods of earthing. The main reason for adopting solid earthing is that the resistance earthing cannot be used for single-phase loads, whereas most of the LV distributions (mainly for households) comprise single-phase loads. The chapter explains the effect of electric shock on human beings. There are four major factors that determine the seriousness of an electric shock—path taken by the electric current through the body, the amount of current, the time duration for which the current is flowing, and the body's electrical resistance. Earthing does not ensure that humans will be protected when coming in contact with a live conductor. Though there may be relays, which are set to sense the earth leakages, invariably their settings are high. Hence earth leakage circuit breakers (ELCB) or residual current circuit breakers (RCCB) are adopted where the possibility of human interaction to a live conductor is high.