2011X45 Switchboard Casualty - Lesson Learned

Switchboard Casualty - Lesson Learned

USCG Official Report

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 localised.
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 recognise 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. Moisture, and in some cases high humidity, can cause losses in insulation resistance. Vibrations developed by engineering equipment, propulsion and auxiliary engines can also contribute to the loosening of fasteners effecting various components of the switchboard, its breakers, monitoring and control equipment.

Loose or dirty connections resulting in high resistance paths on electrical conductors are capable of developing tremendous amounts of heat which could lead to fire or the breakdown of nearby insulating material, associated losses of insulation resistance and the melting of joints and resultant series arching. Sparks and contamination created by series arching or by conductive objects falling on conductors can develop into cross conductor, phase to phase arcing with current values exceeding ten thousand amperes, producing temperatures between three and six thousand degrees Celsius. This type of arching is capable of causing extensive damage in a matter of seconds.

Vessel owner and operators are encouraged to examine their switchboard systems, related maintenance and vessel lay up routines in accordance with their safety management system procedures. Any work performed on switchboards and other electrical distribution systems should follow manufacturer's recommendations or other well established documented and approved procedures. Operators should examine their lay up procedures to ensure that these activities include methods that prevent the formation of condensation within switchboards, distribution panels, motor controllers, and other electrical equipment. It is also recommended that operators consider utilising or employing thermographic imaging services to identify potential trouble spots as a preventative measure or when the securing of electrical power and isolation of switchboards impedes routine vessel service.

General Guidelines for Switchboard Maintenance

Any substantial switchboard maintenance should take place towards the ends of shipyard and maintenance periods to minimise the reintroduction of dirt dust and debris. All electrical power should be de-energised, tagged and locked out in accordance with established procedures. Access covers and enclosures should be removed and all assemblies should be hand cleaned with a dry lint free cloth and non-metallic brushes. Special attention should be given to insulating surfaces. High-powered vacuums should be used to remove all loose debris. Compressed air should be avoided to prevent forcing dust and contaminates into other components. Further cleaning may be achieved by using approved solvents. Contacts in circuit breakers, contactors, relays, rheostats and other switching equipment should be cleaned of all dirt and inspected. Generally all the components of the switchboard should be examined for cracks, defective plating, frayed wires, burned insulation, and general overall condition. Cable, connections and components should be touched and handled, mechanical and electric connections shaken to ensure tightness and that mechanical parts are free to function. Loose connections and damaged insulation should be repaired or replaced.

Other Inspection Items

bus-work supports and fasteners, to ensure tightness;
frame grounding cable, for tight connections;
insulating materials / creepage surfaces, clean, intact / retape taped bars as needed, repaint Glyptal coated surfaces as needed.
ventilation fins of rheostats and resistors, clean;
fuses and clips, right size and tight;
switches, levers, knobs, present and all in good condition;
breakers, open and close at least four times, ensure shafts linkages and other mechanical parts operate freely;
lubricate appropriate components, do not over lubricate;
cables and bundles; secure, no abrasive contacts;
grab rods and rails; in position and secure;
insulating matting; always in place;
device labelling, as correct;
structural integrity of enclosures, drip proof covers and shields in place, latches and locks operating;
This material is provided for informational purposes only. It is not intended to replace any existing shipboard operational practice or procedure. Work performed on electrical equipment presents serious hazard to life and limb and should not occur unless all safety precautions have been taken. Vessel personnel are advised to contact their shoreside engineering and operational staff for technical support prior to performing any work on switchboard equipment.

Questions or comments pertaining to this information may be directed to Mr. Ken Olsen of the USCG Headquarters, Office of Investigations and Analysis, at 202.267.1417 or kolsen@comdt.uscg.mil.