The Case Of The Floating Dock

By John Cavallaro

This covered dock on Lake Waccamaw stretches 200 feet out on the lake.

Covered dock

A grandfather and grandson went swimming in the area where a boat would have been located. The grandfather lifted the metal rails of the boat lift about two feet out of the water to clear an area for swimming. The boatlift was powered by a 1-horsepower motor. Normally, the rails sit in the water. Several neighbor children joined in swimming in the shaded area.  

The grandfather noticed a child hanging and swinging from the metal rails. He told the child to get off. Another child said he felt a tingle on his legs. The grandfather touched the metal rails and immediately felt a large electrical shock. He yelled, “Get out of the water, NOW!”

After everyone scrambled out, the grandfather noticed a child face down in the water, unconscious. He administered CPR, while his wife dialed 911. The emergency medical staff couldn’t revive the child.

I was part of a team that investigated this freakish accident.

The electricity to the dock was fed by an underground (UG) 12-2 rated cable routed from a junction box in the house’s crawl space. A bare ground wire in the junction box had been severed then reconnected after the accident.  

Whoever did the wiring hadn’t obtained an electrical permit. The electrical inspector said he found a small plastic junction box under the dock. The internal wires served the boat lift motor. When he removed the cover, water had poured out of the box. The ground (green) wire and the phase (black) wire had clearly been under water.

The house circuit breaker did not have a ground fault circuit interrupter (GFCI) as per code. The boatlift motor had two GFCI devices connected in series, in between the boat lift and the plastic junction box.

An internal short in the motor’s casing would energize everything back to the metal railings. Or the two wires in the junction box could have been the source of the short. Either the motor had an internal short to its casing, or the plastic junction box had filled with enough water to allow a conductive path between the black (hot) wire and the “floating” green (ground) wire.

The motor measured zero volts on a digital meter, so it wasn’t the source of the leaked voltage. The only other path was through the water-filled plastic junction box. To make that connection, a person would have to make direct contact between any metal and the water. When the boy hung from the rails with his feet in the water, he provided a direct path for current to flow.

Neither the severed ground wire nor the water buildup alone would have caused this fatality. But together, a dangerous and fatal electrical condition was waiting for someone to provide the grounding connection.

John Cavallaro is a P.E. at Forensic Engineering, Inc. in Raleigh, N.C. He holds a B. A. Physics, a M.S Electrical Engineering, and is a Certified Fire and Explosion Investigator (CFEI). He has been involved in electrical accident investigations, fire cause and origin investigations, and electrical equipment failure analysis.