Earlier this summer a large US Flag passenger / vehicle ferry experienced a catastrophic failure of its main electrical switchboard. Two sections of the switchboard, which housed breakers to various loads, lighting and distribution panels, were effected. Bus bars, circuit breakers, their supporting systems, switchboard framing, bus insulating support members, and cabling were extensively destroyed.
Although the damage was limited to the switchboard, repair estimates exceeded one million dollars while lost revenues due to the vessel's unavailability are anticipated to be significantly higher. Fortunately for the passengers and crew of this vessel the casualty was handled effectively. No one was injured and switchboard damage was localized.The exact cause of the casualty has not been identified. Investigators associated with the case believe the destruction of the bus bars and components may have been caused by a high voltage arcing situation or due to extensive electrical shorting between various buses of the three-phase 440-volt system. Several circumstances may have occurred; a flashover between switchboard components possibly due to the accumulation of contaminates and moisture on insulating surfaces; a failure in the insulation resistance and dielectric strength of insulated assemblies; a conductive object falling on to the bus bars or terminals; a failed connection creating a series arc; any of these circumstances could lead to the development of an arching or shorting condition.
This casualty serves as a reminder for vessel operators to recognize the need for routine switchboard maintenance, inspection and out of service procedures. Dirt, dust, moisture, and foreign objects such as banding or forgotten tools and fasteners all present hazards when permitted to accumulate or remain in switchboard assemblies. Deposits of dirt with or without the presence of moisture on dielectric materials and switchboard components may result in the formation of creepage paths and eventually contribute to flashover.