High resistance grounding of low voltage systems: a standard for the petroleum and chemical industry

A debate has existed in the petroleum and chemical industry for years concerning the grounding of LV (480-600 V) power systems. Since reliability and continuity of service are important in the petrochemical industry, some engineers in the past preferred using an ungrounded system. The practicality of such ungrounded systems becomes questionable as the size and extent of coverage increases. This paper begins with a brief history of low voltage grounding which includes ungrounded, solidly grounded and resistance grounded systems. As part this discussion, benefits and limitations of each system are covered. Reliability, continuity of service and personnel safety are important issues and are discussed. It is shown that the use of high resistance grounded LV power systems makes good sense in the petrochemical industry. Design, construction, operation and maintenance factors for high resistance grounded power systems are discussed and analyzed. The use of a high resistance grounded power system when three-phase, four-wire loads are present is discussed, Finally, operational problems and solutions are discussed where significant variable speed drive loads are utilized. The use of a high-resistance grounded power system provides so many benefits that it should become a standard of the industry, and the solidly grounded power system should be used only in applications where the high resistance grounded system becomes impractical.