A Systems Approach to Earthing

This application note proposes a systems approach to the design of the earthing system.  It has to perform three functions: conducting lightning and short circuit currents to earth, preventing the dangerous touch and step voltages and providing the low impedance, equipotential environment required for electronic and communication equipment.  These functions are apparently contradictory but can be achieved by careful design. 

The design of ground electrodes is discussed with emphasis on control of the ground voltage gradient during a fault to limit step and touch potentials to safe values.  A meshed electrode design is proposed which provides low resistance and a good voltage profile.

Electronic equipment, especially in computer and communications networks, needs to be connected to earth in order to function properly.  When computers were confined to special room, special precautions could be taken to ensure that the earth was ‘clean’.  Now, with a computer on every desk, that is no longer a solution.  Modern building earthing systems have to have very low impedance over a wide frequency range, so that noise currents and leakage currents can flow to earth without causing noise voltages.

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