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Phantom" Earth Grounds on Some UPS Installations

Charles Burns

Maintenance personnel have become accustomed to working around battery terminals that are floating with respect to the earth grounded racks and switchgear. When a battery terminal connection or path to ground cannot be found by visibly tracing the cables from the battery to the switchgear and is not indicated on any diagram, a technician can become complacent during maintenance and testing. This paper will show that a path to ground through a UPS can result in extremely hazardous voltages being present between the battery terminals and the earth grounded racks and switchgear enclosures. This condition can result in electrical shocks to experienced battery technicians as well as possible hardware damage and improper indications from grounded battery test equipment that is connected to the battery terminals.

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