Case of the Month: A yacht electrical fire

Apr 1, 2014 by

An electrical fire damaged a 1989 34 foot Luhrs 342 Tournament Sportfisherman. GEI was assigned to inspect the yacht and the shore power connections to determine the predominant cause and origin of the fire.

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The owner and his wife were on board the night of the fire. Sometime around 5:30am, the helm instrument panel caught on fire, causing a short blast of the yacht horn. The owner was awakened by the horn sound and discovered a fire in the helm. He quickly began to extinguish it with the onboard fire extinguishers. A local jogger also noticed the fire and called 911. The fire department arrived a few minutes later. By the time the firemen reached the yacht, the owner had already extinguished the fire.

The horn was controlled by a push button on the top left side of the helm instrument panel. Here is an image of an exemplar 1989 Luhrs 342 Tournament Sportfisherman Yacht without fire damage to its helm or instrument panel.

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In the early stages of the fire, some of the insulation on the wires behind the helm instrument panel melted. When this happened, the lack of insulation allowed the wires to short circuit. One of the shorts was in the horn relay circuit. A short in this circuit is the same as pushing the horn button. The horn then sounded a short burst of sound and then stopped.

Other shorted wires for the horn switch then caused the horn electrical fuse to blow, which then stopped the horn. A short time later, the heat was sufficient to cause most of the wires behind the instrument panel to short, blowing the fuses in the fuse panel (seven of the eight fuses were blown). The heat was so intense that it melted the fuse panel and burned insulation off many of the wires.

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There were no signs of electrical arcing between the wires or on any of the helm instruments. It was not possible to determine which specific instrument or switch started by fire. None of the wiring leaving the helm showed any signs of overheating which would indicate that the failure was confined to the back of the helm instrument panel.

 

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There were no visible signs of major heat damage to the helm structure. The fire on the yacht was caused by the overheated wires behind the helm, which resulted from a high resistance load. The short was not sufficient to trip the 30-ampere circuit breaker in the shore power dock panel and it showed no signs of heat damage. There were signs of corrosion, which is common for electrical and other equipment in the dock area. The connector on the yacht did show signs of heat damage, but it was not sufficient to melt the cable insulation.

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The helm wiring showed excessive heat damage that was hot enough to melt the insulation of many of the interconnecting cables and many had been on fire. There were no signs of electrical arching between the wires even though the insulation was either melted or was burned off. The blown fuses connected to each sub circuit prevented arching. Only the fuse, which was located below the tachometer, was not blown. This fuse had a cracked glass enclosure. It had probably been cracked by heat from the fire. There were no apparent National Electrical Code (NEC) violations.

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Major damage to the yacht was prevented by the quick action of the owner when he extinguished the fire. It was good that the relay that failed was connected to the horn to provide a morning wake up call, and not to something quieter.

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