Getting shocked from dock

[normel]

At a floating dock (private), the customer claims he is getting a mild shock when in the water and touching the support cables connected to a driven stake and the dock. This occurs even when power to the dock is disconnected.
I know there have previous posts relating similar problems, but no-one had posted back about how the problem was resolved.
Looking for some ideas to help with the troubleshooting.

 

[bphgravity]

Re: Getting shocked from dock

It sounds like a problem with stray voltage. The possible casues are numerous and in reality could be extremely difficult to locate.

Considering the problem remains after the power to the dock is deenergized, my guess would be a neighboring dock or boat. Corrosion and/or miswiring could be putting current to the water. This current is finding a return path through your neighbor and his dock. Not good.

We had a case similar to this a while back. A worker inadvertainly drove a rebar spike into the feeder serving a boat lift. Unfortunately, two young boys died while getting out of the water while climbing onto the dock.

 

[jimwalker]

Re: Getting shocked from dock

When you say the supply is de energized is the ground wire still hooked up ? Consider the possibility of an open neutral on the house service.

 

[rickg]

Re: Getting shocked from dock

Can you turn off the main power to the nearby buildings, one at a time while monitoring the voltage at the dock? Maybe you could narrow down the problem this way.
Rick

 

[charlie b]

Re: Getting shocked from dock

How close is the nearest other dock? Stray current can originate from a boat with incorrect onboard wiring, or with an incorrect shore power feed, even if it is not close to your boat.

[ September 16, 2004, 11:01 PM: Message edited by: charlie b ]

 

[andrew]

Re: Getting shocked from dock

stray voltage can be found by using a cheap trick. Using your digital stick a screw driver in the ground and put one probe on the screw driver the other on the equip. ground at the dock. You should probably read a voltage. If you were to extend the test leads(whatever method you want, I.E. alligator clips and a 10ft piece of wire)and did let's say a semi circle at a greater distance from the dock (and equip ground, remember one lead on the equip ground) you will probably see a rise in voltage somewhere in that testing pattern. Obviously the higher voltage will point you in the direction of the problem. I hope I explained it correctly. This method has worked for me and I did not have to buy an expensive tracer.

Good Luck,
Tom

Of course no voltage from equip ground to earth itself will make a strong case for Jimwalkers' theory.

 

[photon]

Re: Getting shocked from dock

I agree with Bryan. I've had numerous problems with "stray voltage" originating from neighboring docks. I've been successful with tracing it back by using a digital voltmeter with 20ft leads; Drop the leads in the water and follow the increase in voltage as you move in one direction or the other. When you find the offender, call the Corps of Engineers (if you don't have a backside full of buck shot!)

 

[hornetd]

Re: Getting shocked from dock

OK, I'll bite. What would the Army Corps of Engineers have to do with anything. Do they have some authority over privately owned docks that I was heretofore unaware of?
--
Tom H

 

[haskindm]

Re: Getting shocked from dock

Is the floating dock plastic?
If so the problem may be static electricity. We had a military installation in our are that installed floating plastic docks in their marina. Static electricity was such a problem that they had posted signs prohibiting boat owners from carrying portable gas cans on the dock!

 

[charlie b]

Re: Getting shocked from dock

Originally posted by hornetd: OK, I'll bite. What would the Army Corps of Engineers have to do with anything?

They have jurisdictional authority over all inland navigable waters within the Unites States.