AC on Ground Wire Dock to Boat

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AC on Ground Wire Dock to Boat

Post by saileagleswings »

My boat is docked behind my house. Using a clamp meter, I see 150 ma AC on the ground wire from the dock receptacle to the boat AC plug if 1) the AC ground wire is connected from the ground of the dock receptacle to the ground of the boat receptacle with A/C white & black either connected or not from dock to boat, with A/C main breaker off at the boat or not and 2) main A/C breaker for house On with all other breakers including breaker for dock power either off or on. If I turn off the main house breaker I get 0 ma AC. Turning off the all the A/C breakers on the boat's electrical panel makes no difference. I also disconnected the power from the solar panels to the controller.

If I connect the ground wire from the dock receptacle to a zinc fish in the water or a copper pipe in the water I see 0 ma AC.

So how am I getting 150 ma of AC current on the ground wire with only when the main breaker at the house is ON and with the ground from the dock receptacle is connected to the boat ground but not when the ground wire is connected to the water via a zinc fish or a copper pipe? The connections to the pipe or zinc are good (zero ohms).
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Location: League City, Texas

Re: AC on Ground Wire Dock to Boat

Post by wolfe10 »

OK, quite a few have looked at this but not jumped in. Suspect I am one of those who is not quite clear in what is happening.

BUT, would be interested in reading with boat shore power cord disconnected between ground terminal on pier outlet and metal stake driven into (wet) ground.

Any reading would make me suspect a problem with the hot coming from house breaker box to pier outlet assuming you have already checked the pier outlet for corrosion, mud dubbers nest between hot and ground, etc.

Brett Wolfe
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League City, TX
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Re: AC on Ground Wire Dock to Boat

Post by AynB »

Before I weigh in...
This months issue of the BoatU.S. "Seaworthy" flyer has an article on in-water electrocution. This is the event that I addressed a bit ago when talking about galvanic isolators and 'leaky' ground. I think that this article is a must read for any boater. I will ask BoatUS if I can repost the entirety both here and through the regular mailman list.

Weighing in: First test : Disconnect the boat from the shore power cord and plug any 110 VAC appliance ( Drop Light, Lamp, TV, etc. ) into a 30Amp Male to 110 VAC Female pigtail, and turn the appliance on. Then test the ground clamp. If you now have 0 mAmps, the problem is at the boat. If you have 150 mAmps, then the problem lies in the run of power coming from the circuit breaker panel at the house to the shore box.

If the latter, then you'll have to break the run into smaller pieces and check again at each step.
If the former, then there is a leak to ground in one of the energized circuits on the boat.
If you have, as you say, the same 150 mA when the Master AC breaker is off, and you have a solar controller, I'd next physically disconnect the controller from the entire system and retest.

150mA is a bit too much to explain away with parasitic induced current - a fancy way of saying that 'some other working wire is inducing a small current in this circuit', but it is enough juice to shock someone in the water.

Honestly, I'd probably be on the phone to an electrician familiar with marine wiring.

Hope this helps.
Halona #17
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