# Electric Shock Drowning & Boat Docks



## GaryI (Mar 18, 2015)

Being new to lake house ownership last year, one of the issues that concerned me was ESD (Electric Shock Drowning). Numerous people, particularly children, die tragically due to ESD each year while swimming near boat docks & marinas. Unfortunately, much of the ESD-related content out on the internet is written by people who have little knowledge about the physics of ESD. This leads to advice such as "Don't swim near boat docks", which, while being conservatively safe, isn't a practical solution for many of us. I am providing this content to help those of you who are not aware of ESD come up the learning curve, but I am not an electrician so please consult an expert before making any final decisions.

The best article on the subject is here. The figure below is from this article.

Basically, for ESD to occur at your boat dock, 5 conditions all need to be met (see figure below):
1. AC power is supplied to the boat dock.
2. Stray current escapes from the designed path and tries to find another path back to its source ashore. This could be from a shorted device in your boat, or from an extension cord end fallen into the water.
3. The ground of the AC power is broken so that the cannot easily return to shore through the ground . The stray current then has only one path back to ground â€" through the water.
4. No ground fault protection (GFCIs) is present in the system.
5. A swimmer swims into the path of the stray current. The usual result is a minor shock which causes tingling and possible loss of muscle control (which can lead to drowning). In rare cases of high stray current, swimmers have been killed immediately from electrocution before they drown. Another tragic aspect of ESD is that many times potential rescuers are prevented from saving the victim, and sometimes killed themselves, from the current in the water once they jump in for a rescue.

To try to prevent ESD, I am following these steps for my boat dock:
1. I installed a GFCI in the AC power system as close to the ground source as possible.
2. I checked all of my devices for worn or frayed wires.
3. I permanently mounted, from the rafters, the one extension cord I need out there, so that there is no way it can reach the water when if it hangs freely.
4. I make sure that my devices (cords, battery chargers, etc.) are not powered when swimmers are nearby.

The steps above cost me $20 and took about 2 hours. If you have a boat dock, I highly recommend that you learn about ESD, carefully study your boat dock, and take preventive measure to keep it from happening to your kids or grandkids.

I was very surprised that my boat dock, built 3 years ago, did not have a GFCI installed.

If you have any other thoughts or ideas on the subject, please contribute.

Gary


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## lx22f/c (Jun 19, 2009)

Gary doesn't the stray current only apply to metal docks ? I didn't think that a bad ground on a wooden dock would transfer current to the water. I may be wrong though. Now a ext cord dangling in water is different. Luckily all voltage at Beacon Bay is Gfci 
Thanks for this info.
Robert 


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## GaryI (Mar 18, 2015)

lx22f/c,

My worst grade in college was in Electrical Engineering, so I am not the one to ask. But from reading the ESD pdf which I attached to my original note, the concern is a device in the _boat_ having a short and transmitting stray current from the boat to the water - "If all of these conditions exist, then some or all of the boatâ€™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 short is in a device on a wooden dock, then I believe you are right. It would have to find a conductive path to the water to be a problem.

Gary


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## MrTroutsnot (Dec 6, 2012)

Interesting topic. My story is pre GFI days. My Father and I had built a new pier down at Sargent on the coast. The pier had lights and receptacles at the end. Much of the pier was put together with galvanized through bolts with large washers. Unbeknownst to us the Romex had gotten behind a washer and was pinched to the point of cutting through the insulation. It had been tightened while working from the top on the beck boards. Several weeks later he was in the water going around checking the bolts for tightness. When he got to that particular bolt I saw him lock-up and was unable to speak to tell me what was wrong. I suddenly realized he was being electrocuted and raced up to the house a killed the breaker. Thank God when the power was shut off he was still alive and able to keep his head above water. He lived, with internal burns and story he could tell himself. 

Ya'll be careful on the water. So many ways for it to go wrong VERY quickly.


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## wwind3 (Sep 30, 2009)

Good report. When the lake dropped a few yrs ago I went under my boathouse and saw my ground pipe was rusted out and wire was not attached. Replaced it with new clamps and a new piec of rebar driven into the ground-hope it helps. Definitely need to replace my electrical boxes with GFI


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## Cdi5344 (Jun 6, 2014)

*Dock builders*

Yes there is only one builder on Livingston that uses a licensed electro an and doesn't violate the law. One of the lakes main contractors was killed last week due to a builder wiring a boathouse without a license


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## cwhitney (Sep 9, 2014)

Interesting thread, Gary. I did well in my Electrical Engineering courses (Bachelor's and Master's degrees). The question of whether wood conducts electricity or not came up, so I got out my meter to measure the resistance of dry (been in my garage for a couple of months) and wet (due to the rain) fence boards. With all the recent rains, the fence boards are pretty well soaked. My thinking is that the wood at or below the water line will be saturated all the time. Wood above the water line will probably have more moisture than than the dry fence board that I measured. The meter I used has a maximum scale of 20 Megohms (20,000,000 ohms). The dry board read off the scale, meaning that the resistance is greater than 20 Megohms and will not allow much current to flow. 


Then I measured the rain soaked fence board. The resistance was a lot lower: 0.67 Megohms (670,000 ohms). At 120 volts, this will allow less than 1 milliamp of current to flow. This will not trip most GFCI circuits.



Lake water is generally in the .01 - .1 Megohm (10,000 - 100,000 ohm) range, depending on the mineral / salt content of the water. This means that the lake water will allow more current flow than wet wood. At 120 volts and 10,000 ohms, 12 milliamps of current will flow. This will trip a GFCI circuit.

The wood on my fence was soaked with rain water. I suspect that a deck soaked with lake water would be more conductive. Sounds like I need to take my meter with me on my next fishing trip to test this theory...


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## Whitebassfisher (May 4, 2007)

Anyone that leaves their boats hooked up to battery maintainer/chargers while hanging in lifts using GFCI protection? If so, have you had nuisance trips of the GFCI which left batteries not charged?


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## GaryI (Mar 18, 2015)

Whitebassfisher - I always have my battery charger connected when my boat is in the lift. Never had a problem with the GFCI tripping. The only time it has tripped is when I was cleaning fish and the electric knife cord got wet. At least I know that the GFCI works!


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## Whitey (Dec 16, 2004)

Very good info Gary. Thank you.


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## Dirt Daddy (Sep 11, 2004)

Cdi5344 said:


> Yes there is only one builder on Livingston that uses a licensed electro an and doesn't violate the law. One of the lakes main contractors was killed last week due to a builder wiring a boathouse without a license


I better check mine out, it is new, but I have a feeling it was not wired by a licensed electrician now. :headknock


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## DJ77360 (Jun 10, 2012)

OK, I've got to ask.....who was the boathouse builder killed last week?
Sad to hear.


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## Sac-a-lait Trey (Jun 10, 2015)

Thanks for posting, Gary. All good things to consider. 

Would I assume correctly that similar safety precautions be taken with any permanently installed underwater lights?


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## GaryI (Mar 18, 2015)

Sac-a-lait Trey,

I am sure that you are correct. I think that, in a way, that situation is less of a problem because you are intentionally putting an electrical device under water. So I would think that all involved would take care, use trained professionals and the right equipment. But of course there are exceptions . . . 

Gary


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## Liv'n_the_dream (Jun 11, 2016)

I read this article a few years ago and took your suggestions about extension cords secured where they wonâ€™t fall in etc. A friend of mine recently began renting a slip at the lake to keep his boat. He asked something that reminded me of this article. I sent him a link and suggested he read it. Thanks for the original post, certainly raised awareness on a few people.


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## Dirt Daddy (Sep 11, 2004)

Connie and I installed this dock life alert system after hearing about the worker on Livingston getting electrocuted while fixing a boat cradle. Its a small price to keep our family and friends safe. http://docklifeguard.org/


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## impulse (Mar 17, 2010)

About 9 months ago when one of our green underwater lights went dark, I opened up the control panel on the pier and was appalled at the quality of the components. They used 12V components more suitable for wiring a trailer, and there were plenty of unshielded connections that were corroding away in the salt air because the box was ventilated.

I'm not going to mention the (well known) company name, because they seem to have improved their game. I base that on a replacement we got for another light that went dark. The guy that they sent and the equipment he installed were significantly better than the one I had dissected. 

More than anything, this is a caution to check your equipment, and make sure to test the GFI occasionally. (Or, do what I'm doing and convert your green lights to 12V LED's) 

I've watched half a dozen times over the year I've been in Sea Isle as anglers snag a cable and pull it up to release their hooks. And seen boats running over several neighbors' lights at very low tide. Makes my sphincter tighten each time I see it...


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