Learned something new today - gotta be careful around fresh water docks!

[Bill Douglas]

Phew, scary.

With the explanation and diagram it makes sense too. Sad that it killed the kids mentioned in the article.

[DanielDudley]

No ground, No GFI. How many people have extension cords with the ground tab broken off ?

[billybek]

Wow. Had never heard of this before.
Thanks for posting the link.

[IROC]

Yep, the Cherokee Lake one was right near here. After that incident, people came out of the woodwork reporting how common it is to get shocked.

[billybek]

Found this article by searching for isolation transformer for marine applications.

SAFETY AND ELECTROCUTION PREVENTION

Contrary to popular belief, electricity does not seek ground; instead it will attempt to return to its source. If the source is the utility company (or the transformer at the head of the dock), its power is referenced to earth, which means faults will return to earth in that case, or the water in which a vessel floats. If a fault develops aboard a vessel that is not equipped with a transformer, the current could leave the vessel via a bonded/grounded through-hull fitting, shaft, or rudder, and travel through the water on its way back to its source.

If a person enters that return path, a swimmer, diver, or someone who falls overboard while dockside, they could be electrocuted—it happens every year. Last Independence Day, in three separate incidents, five people were electrocuted on lakes in the United States in this manner. Make no mistake about it, swimming around boats or docks equipped with shorepower is dangerous; it is prohibited in many marinas with good reason. My advice to readers is don’t do it.

Because both isolation and polarization transformers behave very much like a source of power, fault current seeks a path back to them rather than to the shore. This means that onboard faults will not result in current flow through the water. Current will return to the transformer, ideally tripping a circuit breaker and rendering the fault inert in the process, making transformer-equipped vessels inherently safer.

Why wire a transformer in polarization rather than isolation mode, if the former requires the use of a galvanic isolator, whose effectiveness is limited? Essentially, there is a measure of added risk—the level of which is debated by experts within the world of marine electrical systems, in wiring a transformer in the isolation mode, in that the metallic case of the transformer is not referenced to both shore and dockside ground.

Therefore, if the hot, primary, or shoreside input cable of the transformer were too chafe against the case, because the case is connected to the boatside ground, it could become energized without tripping a circuit breaker. (Remember, it can’t be connected to both boat and shore ground without creating a path for corrosion current.) If a person were to then touch the transformer case and a through-hull or rudder stock for instance, they could complete the path, and be electrocuted in the process.

While this is a real concern, if an isolation transformer is properly installed in accordance with the manufacturer’s and ABYC’s guidelines, it will remain safe. Currently, transformers may be wired as isolation or polarization, and remain fully compliant. Among the most common defects in transformer installations are those involving a failure to use manufacturer-specified strain relief connectors for cables entering the transformer’s case.

Under no circumstances should a transformer be wired without the benefit of proprietary strain relief devices, which prevent chafe as well as isolating tension or strain from electrical connections within the transformer.

Finally, shorepower transformers used in marine applications should carry a UL Marine approval decal (many transformers are UL approved, few carry a UL Marine approval) as well as complying with ABYC E-11.17, last revised in 2012. Many older transformers carry an ABYC E-8 approval, which is outdated.

If you have a shorepower transformer, or are considering having one installed, or are purchasing a vessel that is so equipped, make certain it is installed in full compliance with current ABYC guidelines.

[KFC911]

Originally Posted by billybek

Wow. Had never heard of this before.
Thanks for posting the link.

+1....been around sailboat marinas, etc. most of my adult life.

Next I'm gonna learn how to sit, heel, and fetch

[sammyg2]

Shocking!

Captain David Rifkin and James Shafer conducted extensive testing of all aspects of ESD for a Coast Guard study in 2008, including exposing themselves to low-level currents in fresh water. "Anything above 3 milliamps (mA) can be very painful," Rifkin said. "If you had even 6 mA going through your body, you would be in agonizing pain."

Current Level: 5 mA
Probable Effect On Human Body: Slight shock felt; not painful but disturbing. Average individual can let go. However, strong involuntary reactions to shocks in this range may lead to injuries.

[intakexhaust]

^Same here and always around this stuff.

That link is outstanding and very well written.

Since we're discussing lifts / shore stations, another is concerning capacity. And I'm not talking length. Years back had a friend tragically lose his life from a power winch assembly exploding apart. Fragment of metal entered his head. Airlifted to a hospital and later that night he slipped away.

What initiated the accident was not so much the lift but he had a neighbors boat on it and was going to service it. Apparently the hull was filled with enough water and along with the boat weight to exceed limits of the lift. I don't know all the specifics or of that brand design, safety clutch / catch but luck was not on his side.

Careful all.

[island911]

I thought for sure this thread would have a story about a 928. (bump - good info)

[reachme]

WOW. News to me:

some or all of the boat's underwater metals, such as the propeller, stern drive, or through-hull fittings, will be energized, and electricity will radiate out from these fittings into the water. If the boat is in saltwater, the current will dissipate without doing damage unless a diver grabs hold of the energized metal.

I worked my way through college as a scuba diver cleaning barnacles off boat bottoms, replacing zinc anodes, finding lost items that people dropped off the dock. I worked on many strange boats, some poorly maintained that were docked. I often had to grab on to and hold prop shafts etc. since barnacles adhered much better to metal-especially during tidal changes. (try pushing on something in the water without holding on and see what happens). Always wore neoprene gloves so my fingers didn't get cut up but those shredded quickly and fingertips were often exposed-not sure if that would have mattered much.

A lot of harbors have freshwater feeds and at low tide they can act more like freshwater-I could see the densities mixing like oil and water when the saltwater came back in.
Since motors like pumps switch on and off there is really no way to check for this without access into or under the boat so I don't see any safe solutions.

This is a common job for young kids around marinas and nobody I ever worked with, for, or any dive shop had any warnings up about this. It was good money but we all worked alone, quietly under the boat without even telling the marina we were there or they hassle you for not being a member and parking in the lot. This is a risk I never knew about and if this becomes wider known I can see it being banned (in water boat service) by marinas due to risk.

[t-tom]

We have a cabin on Lake of The Ozarks and this is a big deal down there. 4 people in the last year have died from this. The problem is for years and years there has been no inspections or any kind of oversight. Our dock is GFCI'd but hell it could be a dock 1/2 mile away and kill you. It's pretty scary. My family has had a place at the Lake since 1952 and it is scary how reckless people are on and around the water.

[t-tom]

To give you an example of how back woods it it down there, if you are rebuilding a house using an existing foundation you don't need a permit and there are no inspections. It's unreal sometimes.

[peppy]

I live on a lake and have never heard of this. Scares the crap out of me.
I'm sure my wife has, she inspects the marinas.

[flatbutt]

I live on a pond. I'm going to circulate this amongst my neighbors...just in case. Thanks Wayne!

[island911]

I'll add that this type of stuff can work to greatly accelerate corrosion of the metal bits on the boats.

[Scott Douglas]

I had a cousin that was electrocuted while fishing on a private pond. He was in an aluminum boat, barefooted, and reached up and touched a metal bridge that went over the pond. It had lights on it that weren't properly grounded. Needless to say it was very rough on my aunt and uncle and his sisters, to say nothing of the rest of the family.
So even on ponds you have to be careful if there's any kind of power nearby.

[widebody911]

Dumb question: why is this an issue with freshwater and not saltwater?

[Scott Douglas]

The original article explains it very well in the paragraph right after the chart.

[widebody911]

Originally Posted by Scott Douglas

The original article explains it very well in the paragraph right after the chart.

Yup - somehow I missed it

[Drbraunsr]

Silly question, but would a voltmeter be able to pickup the mAmp voltage ?
If not, why not ?