By Jim Shafer,
Everyone was relaxing and enjoying the atmosphere at a party to welcome a new houseboat to the marina when the scene was suddenly shattered by the piercing screams of a young girl! The owner had given the girl permission to try out the new swim slide. She was in serious trouble from the moment she hit the water. One of the guests immediately jumped in to help-now there were two people in the water in great distress. The rescuer managed to push the girl to safety, and then disappeared below the surface - leaving a wife and two children.
Subsequent investigation disclosed that an AC "hot" lead in the lighting circuit developed a fault (insulation failure) to the metal hull, at a current level below the circuit protection trip point, and something had happened to the green safety grounding wire. Thus, because this occurred in fresh water, the hull potential (voltage) went to some lethal level. It could have been as little as 25 VAC.
During the two years that I have been looking into low level AC ground fault incidents the term "Hot Marina" has taken on a whole new meaning. While this term is often used as a catch all description of any unusual electrical problem in the marina environment it will be referred to here specifically as a symptom of a low level AC ground fault. This is a condition where the insulation on a current carrying conductor in the electrical system has developed a fault to ground (short circuit) at a current level too low to trip a circuit breaker. Poor workmanship, chafe, water intrusion, vibration, and insulation ageing can cause this. In both fresh and salt water this condition creates a fire hazard, and in fresh water lethal conditions may be established near the boat with the fault. I have catalogued thirty-five ground fault related fatalities, including two dogs and six ducks. Even more disturbing, "electric shock drowning" is not disclosed by a post mortem. The cause of death is always determined to be drowning. Because of this we may not be aware of all the incidents of electric shock induced drowning.
At a leakage current through the body of only 0.005A (5mA) a person will be in considerable distress, at 10 mA a child cannot release his grip, and at 20 ma an adult is also "stuck". It is in this current range that muscle control is lost, rendering a person helpless. Beginning at 50 mA heart failure may occur.
Fresh water and salt water are separated here because of the wide difference in electrical conductivity between the two. Fresh water is a very poor conductor so when a fault occurs on a boat with a damaged safety ground wire the fault current meets a very high resistance as it attempts to enter the water, which results in a rise in potential (voltage) on underwater metals. A swimmer represents a very low resistance by comparison and provides a path for the fault current. A hair dryer falling into a bathtub has caused many a fatality!
Salt water is a very good conductor on the other hand, so the hull potential will not rise because of a fault, and, because of the protection afforded by the skin, little or no current will attempt to enter the body. Tests have shown that salt water actually is just about as good a conductor as the safety ground, so even with the safety ground missing there is much less danger.
While not part of this discussion any AC fault is a fire hazard and there is some feeling that the mysterious, late night, fire on a yacht may result from this cause in some cases.
We will separate the possible solutions for dealing with troublesome ground faults into two steps a marina operator may take. Posting a "No Swimming" sign is not a solution.
Since the hull potential cannot rise to lethal levels if the green safety grounding wire is functioning merely complying with SEC 3.21.1 of NFPA303 - 2000 will at least assure the marina personnel that their ground system is OK. In presentations I have made to marina groups I find almost no awareness of this document, much less any attempt to comply. Step one, get the publication and see what it suggests. There are several methods to assure ground integrity and probably could be the subject of another article. Assuring a good dock ground does not solve the problem of faulty wiring on a boat, however, which is the primary cause of some fires and most fatalities.
Now we come to step two, "Ground Fault Monitoring". Without going into a complicated technical discussion, please accept the statement that fault currents take all paths back to the source. If a boat is wired to ABYC (American Boat and Yacht Council) recommended practices the AC green safety wire is joined on board to the bonding system and the DC negative circuit. This places anything metal in the water at an assured ground potential relative to the AC circuits - and precludes an electric shock fatality. The problem is that this ideal condition of the ground system cannot be assured 24 hours a day, and further, a fire hazard may still exist because of the fault.
With the technology
widely used in other applications it is possible for the marina to monitor very
low-level AC ground faults (the Hot Marina Syndrome) from a central location.
Even with a good ground system some portion of any fault will enter the water,
and can be detected. The Marina Guard, incorporating existing technology, has
been developed to detect these low-level water currents. Marina Guard systems
are being evaluated in actual marina operation on both the East and West coasts,
and the results are very interesting, to say the least. A well-known supplier
of marina power substations may be including monitoring as an option.
Perhaps the time
is right to "clean up" electrical systems both in the marina and aboard
the yacht to cool off the hot marina. The methods and technology are available,
and at relatively nominal costs. As with smoke detectors, CO monitors, bilge fume
detectors, and GFCI's, we have another tool to warn of an impending lethal trap.
James D. Shafer,
This material to be published in Marina Dock Age, December 2003.
Copyright © 2002 Mike Holt Enterprises,Inc.