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Watt's Up Blog

For the staff and management of Bethesda Dilworth Assisted Living facility, an incident on the morning of Friday, October 18, 2019 was sudden, highly dramatic and anything but routine.  Sometime around 10:30am there was a violent explosion in their electrical switching system located immediately behind the building and appeared as a fiery jet-like stream of lightning pouring from the substantial bus-duct tying the building’s switching system to Ameren’s utility feed.  The steel casing that surrounded and protected the heavy copper bus bars had, over time, corroded sufficiently causing it to finally and catastrophically give way, allowing a phase to phase short which generated a violent and continuous arc-flash.  In a matter seconds a substantial length of the duct itself had melted oozing molten copper onto the pavement, and cutting all power to the Bethesda facility.

Only one of a number of the system’s 1200amp fuses had blown, but it was on the 480 volt side of the transformer connected directly to the utility cutouts on the pole immediately adjacent.  This had the effect of keeping the fire going and assuring that bus duct was thoroughly melted and utterly destroyed. 

Within minutes, the facility Director, Mark Jeffries made a call to Guarantee Electrical Company’s CEO, Rick Oertli.  Rick immediately contacted John Bennett, Guarantee’s Director of Production and Quality.  John utilized Guarantee’s GPS dispatch system to assign two technicians who were on the road before 10:55 – less than 30 minutes after the emergency was discovered.  The quick response service team began taking stock of the emergency within minutes. 

By this time, Ameren had been contacted and were able to disconnect the feeders connecting the facility, putting a stop to the arc-flash thereby ending the fire. Whereupon Guarantee’s service team assessed the situation while they waited for the equipment to cool sufficiently for them to more closely inspect the equipment and begin framing out a plan to bring power back to the building and then to address a more permanent solution for restoration of the equipment involved.

As the facilities backup generator brought limited service back to the facility, the team considered their options.  By isolating the switch that controlled the 3000amp bus, the service team was able to restore many of the critical services to the building while the repairs were being made. Long lead times meant that replacing custom manufactured bus duct was not practical, so there had to be an alternative that could effectively deliver a complete restoration of service.  Since cable was the only realistic way to replace the solid copper bridge connection provided by the duct, given the tight spaces involved, it had to be ultra-high capacity and highly flexible so as to be able to accommodate the space while easily transmitting the loads involved.

Upon restoring the building to full power, the Guarantee team investigated the root cause of the incident.  Water had infiltrated the joint of the bus duct, which was installed by others.  The dampness in the bus duct commenced a cascading arc flash event.  Guarantee has ordered new bus duct to replace the damaged equipment and will assure it is properly protected against water infiltration.

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