The Case of the Houseboat Electrocution

Oct 1, 2008 12:00 PM, By Andrew Paris, P.E., Anderson Engineering

Damaged neutral on faulty light fixture and reverse polarity spell disaster for families’ day of water fun at the lake

Soon after a young family purchased a vacation condominium on a local lake, they were anxious to entertain guests. One summer weekend, they invited another couple and their daughters to visit: Tim and his wife Liz, their older daughter Jenny (age 9), and younger daughter Laura (age 2). Toward the end of an eventful day at the lake, both families decided to take a walk along the docks down by the marina, which housed several boat slips.

Photo 1. View of the subject houseboat docked in the marina.

Although the condo owners (Joe, Cindy, and infant son) did not own a boat, they were in the market for one. As they walked along, examining the different models, a large houseboat at the end of the dock immediately attracted their attention (Photo 1). They walked over and started chatting with the boat owner, Dave, and his girlfriend, Kim. While taking a tour of the cabin, Kim asked Jenny if she would be interested in going down the waterslide at the back of the houseboat. Like most girls her age, Jenny jumped at the chance to try out the slide. Unfortunately, the events that transpired would quickly turn a seemingly harmless bit of water fun into pure tragedy.

The accident

Dave turned on the water pump, and with the owners' approval, Jenny climbed up to the roof and slid down the slide. She quickly popped up from the water approximately 10 feet away and grabbed onto a life preserver Dave threw toward her. Holding it to her chest, she began paddling to the rear of the boat. As she got closer to the ladder, however, she began to feel numbness and tingling in her legs. When she was within 4 or 5 feet, she could no longer feel the lower half of her body at all. She screamed out in pain that something was stinging her. Thinking it might be a snake, Joe immediately jumped into the water to help, pushing Jenny toward the rear of the boat.

At the same time, Tim, the girl's father, grabbed onto a metal railing and leaned out over the water to grab Jenny. As he was leaning forward, he slipped into the water but still kept hold of the railing. Quickly, he felt his body painfully tighten and found that he could not release his hands. He was left hanging to the side of the boat in obvious pain. Although Cindy and Liz pleaded with him to let go, Tim told them in slow, contorted speech that he simply could not. Realizing that it might be an electrical problem, Dave ran to the front of the boat and unplugged it from shore power. This immediately allowed Tim to free his grip, and the others helped him back onto the rear deck. Soon thereafter, Jenny also was able to make it to the rear ladder and climb out of the water.

As the chaos subsided, the group's attention soon turned back to Joe, who was nowhere to be found. Dave and another bystander dove into the water and found Joe near the bottom of the lake. They pulled him onto the rear deck and began to perform CPR while another bystander called 911. Unfortunately, Joe never regained full consciousness, and he later died at the hospital. An autopsy concluded that Joe had been electrocuted. In addition, the shock Tim received left him with lasting injuries. Fortunately, Jenny did not suffer any long-term harm.

Investigation and analysis

Based on the circumstances surrounding the accident, the sheriff's department hired a local electrician to assist in the investigation. He initially tested for voltage between the metal dock and the water. Finding none, he plugged the houseboat into shore power and measured the voltage between the water and various locations on the boat. The results were as follows:

Portside stern (location of the ladder): 100.6VAC
Starboard stern: 96.7VAC
Starboard bow cleat: 112.3VAC

Photo 2. Light fixture wiring — neutral wire pinched between cover and grounding plate.

After unplugging the boat from shore power, no voltage potential was found at any of these points. Finally, the electrician performed a continuity test on the hot leg of the 120V shore power. A direct short was found between the hot leg and the hull of the boat. These initial tests showed that the water surrounding the boat was effectively energized to line voltage whenever the boat was plugged into shore power.

Anderson Engineering was hired on behalf of the plaintiff (victim's family) to investigate the accident and determine the particular failure mode that led to the accident. During our preliminary examination, we tracked the shore power connection, finding that 120VAC power originated from a metered disconnect located on the exterior wall of a nearby condo. Underground conductors traveled to a receptacle mounted on shore near the dock. A low-voltage lighting transformer powering several dock lights was plugged into the receptacle.

Rules and regulations

The circuit traveled onto the dock and powered a second duplex receptacle. The run continued on to a 30A female plug-in cord receptacle. A final extension cable traveled from there to a male receptacle on the side of the boat. Closer inspection of the extension cable revealed that the hot and neutral were reversed in the cable-to-cable connection.

Further examination of the houseboat's electrical system and components exposed a faulty interior track lighting fixture. As shown in Photo 2 on page 18, the neutral fixture wire was damaged as it passed out of the covered wiring compartment. Unless the fixture wires were correctly routed during the manufacturing process, the edges of the grounded mounting plate would cut into the conductor insulation when the wiring compartment cover was installed. In this case, the neutral was effectively connected to electrical ground.

The damaged “neutral,” in combination with the reversed polarity, created a dangerous situation. Under normal circumstances on a land-based electrical system, the fault current would have traveled to earth ground. Then, depending on several factors, including the circuit load, the location of the ground fault, and the condition of the ground connection, the rise in current would most likely have tripped the overcurrent protection. However, this did not occur, due to the peculiarities of marine power systems and their interconnection with land-based systems.