Service Entrance Disconnect Near Miss

A case study detailing the prevention of a potentially harmful equipment failure at the service entrance disconnect in a manufacturing plant. Annual thermal analysis being performed on the enclosure and through an infrared (IR) window on February 1, 2017 found a 3,000 amp, 480 volt ungrounded delta main electrical service with an enclosure surface temperature of 155° F and disconnect components inside with temperatures approaching 500 °F. The main electrical service disconnect in the enclosure was non-operable. The only upstream equipment from the service entrance is local utility equipment outside the building. The plant was immediately shut down after an on-the-spot risk assessment. Replacement parts were searched for while the local utility arrived to disconnect the power from the building. Subsequent investigation of the overheated disconnect switch found that it had not fully closed during the last maintenance performed on it four months earlier. As a result of the near miss, several maintenance program and prevention actions were taken.