|Hot Marina Lethal AC Ground Faults
|By Jim Shafer, AMS
Harbor Marine Consultants, Inc.
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 i
s always determined to be drowning. Because of this we may
not be aware of all the incidents of electric shock induced drowning.
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
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
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
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.
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.
fault monitoring will detect faults anywhere in the shore power system,
including faults on connected yachts, down stream of the monitoring point, and
send a signal to the dock office.
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.
electrical systems that depend on marina supplied power are very reliable and
unbelievably tolerant of abuse, but the potential for harm should always be
considered and dealt with by the most up-to-date methods available.
D. Shafer, AMS
Harbor Marine Consultants, Inc.
This material to be published in Marina Dock Age,
Copyright © 2002 Mike Holt Enterprises,Inc.