The basic purpose of grounding is to protect the electrical system and equipment from super-imposed voltages caused by high frequency transits, lightning, and accidental contact with higher voltage system. Earthing is also required to prevent the build-up of static charges on the equipment and materials An Additional purpose of earthing is to establish a “Zero Voltage”reference point for the system. A Zero Voltage reference point is necessary to insure proper equipment performance. In contrast to earthing (grounding), the purpose of equipment grounding is to assure that all exposed non-current carrying conductive surfaces, such as equipment enclosures, conduits, raceways, etc. are effectively inter-connected and tie to Earth. It minimizes, to the greater extent possible, the appearance of any voltages on the equipment enclosures. This will provide protection from serious shock and/or electrocution to personnel in contact with the enclosure Equipment Equipment grounding must maintain “Zero Voltage” on the equipment enclosure during normal operation. grounding also must provide an intentional path of ample current carrying capacity.
Design Consideration - Earthing of Distributed Control System / Programmable logic Controllers
Any grounding system (safety, lightning, MRG, etc.) for a site is designed by Measuring the soil resistivity, Determining the best electrode configuration for the soil, and Installing and interconnecting the electrodes
The only way to get electrical information about the soil at a given site is to drive electrodes down to the water table and measure resistance by James Biddle Tester. A single 3-meter (10-foot) electrode might have a contact resistance of, typically, 5 ohms to earth.