Boat Dock Electrical Issue

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JSM8786

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I have a boat dock on a lake in northeast Georgia. The dock is supplied by a 20 amp 110 GFCI protected 12 gauge 3 wire circuit from the house to a power pole near the water where a twist lock disconnect plugs in and leads to the floating dock. The power to the dock is for an air type boat lift, a couple of lights and a couple of 110 outlets. The dock meets all the corp or engineers electrical requirements and all electrical codes and was signed off on by a licensed electrician in March. I test the GFCI at least twice a month.

While swimming one evening, I touched the metal bunks of the boat lift and felt a tingle. I immediately searched and found a local licensed electrician to come out and inspect the dock to determine why I was feeling the tingle. While waiting a few days for the electrician, I did some troubleshooting myself and using the clamp method I read about online, discovered that I had voltage/current leakage on the conduit supplying the power the dock. I isolated the three wires in the conduit. Clamping the black and white together, the reading was 0. When I isolated the green wire and clamped it, the readings on the wire were 30 milivolts and .25 amps or 250 miliamps. i assumed I had a problem in the house with something going to ground so I flipped the main disconnect at the panel and retested. Still had the same readings on the green ground wire with all power to house in the off position. Obviously disconnected everything until the electricians arrival.

A few days later the electrician arrived and immediately said he was very familiar with the problem and it was related to stray voltage from the power company. He incidcated that the way to correct this is to disconnect the ground from the house at the lakeside power pole and drive a ground rod and connect the dock ground to this ground rod. I questioned how it would be safe to disconnect the ground to the panel since rods are really only lightening protection? His response is that by code, homes without ground wires use GFCI protection like I have on the dock and this meets code.

After he left, I continued to read and became more and more uncomfortable with my ground being disconnected to the main panel so I called the power company to ask about stray voltage/current. Guy was very nice and has agreed to dispatch a truck to check power connections to my home. Said it was very unusual to have stray voltage/current problems in my neighborhood due to the underground system but they would check. I am awaiting a response.

So my questions are:
1. Are the voltage/current readings I am getting dangerous to swimmers?
2. Why would I get a higher current reading than volts? The 250 miliamp reading is what worries me.
3. Is disconnecting the ground to panel the correct way to handle this situation?
4. Is there anything else I can try?

I have done basic electrical but realize I am over my head looking for professional advice.
 

Reach4

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I would stick a voltmeter probe into the water or better to a metal boat. Touch the other end to the conduit. What is the voltage?

Also measure the voltage to the ground wire on the outlet. Same?
 

Stuff

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If you are still seeing voltage/current after your main is turned off then it is an issue with the power company or one of your neighbors.
The 250 milliamps is most likely traveling through the dock and to/from the water. When you touched the lift you were part of a parallel path - a lot less than 250 otherwise you would have fried.
Disconnecting the ground is just hiding the problem until someone gets zapped elsewhere.
 

JSM8786

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Thanks for everyone's input. Doesn't seem like a problem with an easy solution. Look slike solar power may be in my future.
 

Reach4

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Thanks for everyone's input. Doesn't seem like a problem with an easy solution. Look slike solar power may be in my future.
An isolation transformer should take care of any ground potential problems.
 

Jadnashua

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If the power is leaking from somewhere else, not sure an isolation transformer would help much assuming you still used a ground. In the real world, ground varies, sometimes considerably, from one place to another.
 

JWelectric

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There is an old belief that current follows the path of least resistance and that current can leak to earth. Both of these are false. Think of a printed circuit board and the number of paths for current to flow in one. Current will flow in every one of those paths of the PC board and the amount of current will be dependent on the resistance of each path.

For current to flow there must be a path from the source to the load and back to the source. Current is the measurement of electron flow. Every electron leaving the source must return to the source.

The codes mandate that any electrical system to be connected to earth. 250.4(A)(1) of the NEC tells us why we make this connection to earth. It outlines four reasons. The utility company connects to earth for the same four reasons.

Under normal circumstances current being used by a single family dwelling will have some amount of current traveling on their grounding electrode system simply because the transformer supplying that dwelling will also be connected to earth and this connection to earth is a parallel path with the secondary of the transformer in parallel with the grounded neutral serving the dwelling.

The primary of this transformer is connected to earth also and this continues through the utility grid and back to the generating plant. When we have a large body of water surrounded by homes that are being supplied by a public utility common sense tells us that the water will also be carrying current through this earth connection.

Lets break away for just a second and talk about the requirements for installing a swimming pool. There are some pretty strict rules concerning bonding everything around a pool including the pool water to create an equal potential. When everything is bonded together creating an equal potential touch difference then no current flows through the human body.

Back to the lake. If we are going to use the lake as a swimming pool then wouldn’t it make perfect sense to bond everything to create an equal potential. Do this and the shock will go away
 
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