"Potential" problem with boat lifts

[fisherelectric]

My brother called me last year to tell me his kids were getting shocked while swimming up to the boat lifts at his lake house. I drove down to take a look. He has two lifts, each has steel guard rail for lifting pontoon boats. Both lifts are plugged into GFIs, which I replaced , and then bonded all the metal parts together. I didn't get shocked when I put one hand in the water while in contact with the lifts but my brother said he had gotten a good jolt while attempting to climb out of the water onto the lift. I dropped one probe of an amprobe into the water and checked between water and the lifts, got a reading of 1.5 volts (not sure wether that means anything or not) with or without power to the entire dock (there's a sub-panel in the yard that feeds various loads on the dock- lights, well pump, refrigerator, some receptacles). I told my brother to keep everyone away from the lifts while swimming and to call the local power co. A power company rep came out and said they have this problem all around the lake, esp when the transformer is at the end of a run. He also said that the potential is still there even when the neighboring transformers are shut down, and that it has been like that for years and no one has gotten seriously hurt. Smith Mountain Lake, Virginia. Any ideas on how this happens or how to reduce this current and make it a little safer other than telling people to not climb out of the water on the lifts?
Edit to say 1.5 volts

 

[iwire]

I think the best thing to do is remove all branch circuits supplying the dock.

Change the boat lifts to the hand cranked type.

This may seem radical but unless the power company changes something your brothers EGC from his panel will always be at an elevated potential from the lake.

The EGC is using the lake water as a path for unbalanced neutral current to get back to the electrical source.

It would not take more than one shock while I was swimming before I would do something about it.

 

[fisherelectric]

Iwire you just jolted my memory..When I disconnected the EGC at the subpanel the amprobe reading between the water and the lift went to zero. I found it hard to believe I was getting an accurate reading with one lead dangling in the water. How is unbalanced neutral current getting onto the EGC?
By the way my brothers dock is a beautiful two story deck with a bar, refrigerator, LV lighting, spot lights, stereo, and a well pump for lake water at the dock and yard sprinkler system. The swimming area is a good 30 feet from the boat lifts. He ain't gonna like the idea of disconnecting all the electric to his dock. I don't think you could hand cranck his boats. But I would have to agree none of that is worth losing someone, especially to a condition you know exists.

 

[iwire]

Your brothers EGC is connected to every neutral in the entire area.

As far as what to do I am just guessing not having seen it, but maybe if the boat lifts are the only bonded metal within reach of swimmers some sort of wood guards could be installed to keep swimmers from touching the metal?

I just don't see many options.

If you have line voltage power on the dock it must include a grounding conductor.

The grounding conductor is the problem, or at least it is where the problem of voltage drop or broken neutrals is showing itself.

 

[bob]

Iwire you just jolted my memory..When I disconnected the EGC at the subpanel the amprobe reading between the water and the lift went to zero. I found it hard to believe I was getting an accurate reading with one lead dangling in the water. How is unbalanced neutral current getting onto the EGC?

This condition is everywhere. You can take you amprobe and stick the leads into the ground and read a voltage. This returning current is from everyone in the area. The utility drives ground rods into the ground at various intervals along the distribution line. There is one at the pole that services your brothers house. The pole ground is connected to the neutral at the pole. At the main the EGC is connected to the neutral and GEC. The circuit to the boat house has a EGC installed. When you connect it to the winch motor, the motor is now at the same potential as the utility ground rod. When the metal
guard rails are lowered into the water there is a voltage difference and a current flow.

By the way my brothers dock is a beautiful two story deck with a bar, refrigerator, LV lighting, spot lights, stereo, and a well pump for lake water at the dock and yard sprinkler system. The swimming area is a good 30 feet from the boat lifts. He ain't gonna like the idea of disconnecting all the electric to his dock. I don't think you could hand crank his boats. But I would have to agree none of that is worth losing someone, especially to a condition you know exists.

Your brother may not want disconnect or not but have him read this article before he decides.

http://www.mikeholt.com/documents/mojofiles/DrowningsAtMarina.pdf

One way it might be corrected is to install a dry type transformer at the boat
house and establish a new ground by driving a rod into the water. However, over time the rod would corrode. The other problem is that you would have to connect the origional system EGC to the transformer frame and we may be back to the beginning.
Another solution is to use a 12 volt winch with a battery.

 

[iwire]

Another thought is to really check out your brothers part of the service from service point to main bonding jumper. Make sure that the neutral is in good shape at each termination.

If your brothers home has a poor neutral path back to the utility it will add to the problem at the dock.

 

[fisherelectric]

I have suggested wood guards around the lifts and we slid PVC over the cables and chains that lift the guard rails, but it sure would be better to eliminate the voltage altogether.
I'm aware that the EGC is grounded back at the service (about 150 feet away) so what you're saying is that the whole equipment grounding system is at a slightly higher voltage than the lake. I checked the service neutral and it seemed fine. I guess what I don't understand is how the lake water is at a lower potential than the ground at the service. I also don't get why the power co seems so nonchalant about the whole thing..saying that the problem is present all around the lake and there's nothing they can do about it. The lake is a hydroelectric reservoir.
I even thought about sinking an old anchor connected by steel cable to the 2 lifts but wasn't sure if that would help the problem, make it worse, or have no effect at all. Thanks for the input.

 

[bob]

I have suggested wood guards around the lifts and we slid PVC over the cables and chains that lift the guard rails, but it sure would be better to eliminate the voltage altogether..

Did you read the article. A child's life is in danger. This is nothing to play around with. A jerry rig is not sufficient.

I'm aware that the EGC is grounded back at the service (about 150 feet away) so what you're saying is that the whole equipment grounding system is at a slightly higher voltage than the lake.
I checked the service neutral and it seemed fine. I guess what I don't understand is how the lake water is at a lower potential than the ground at the service.

What we are saying is there is a difference in potential when you measure voltage anywhere on earth. There is a voltage gradient (different voltage level in the earth)in the ground even at you house.

. I also don't get why the power co seems so nonchalant about the whole thing..saying that the problem is present all around the lake and there's nothing they can do about it. Thanks for the input.

All utilities have this problem. Up in Wisconsin the cows are getting shocked.

 

[fisherelectric]

Thanks for the link, Bob, I will send that to him. Very scary stuff. I'm thinking he really needs to get rid of those guard rails and use wood runners to lift those boats, at the very least.

 

[fisherelectric]

I guess in this case running #6 or #4 equip. gr cond back to the main service has the potential of actually making the problem worse. There really is no solution other than eliminating all metal parts of this boat lift system from being reached from the water. Period. Although I do like the idea of the 12 volt winches.

 

[ghostbuster]

Try opening the main panel disconnect feeding this entire complex.

Then measure the current on the neutral in this main panel connected back to this utility street transformer.

This will get you started in determining this current source .

Good Luck

 

[dbuckley]

You could try putting in some supplemental grounding rods very close by and bonding them to the local ground; that would attempt to provide a preferable path for the stray currents, so reducing the voltage...

The safest (but non-compliant) approach is an isolating transformer supplying the lift, with a local ground rod, and an RCD, but no bond back to the supply ground wire.

 

[bob]

Thanks for the link, Bob, I will send that to him. Very scary stuff. I'm thinking he really needs to get rid of those guard rails and use wood runners to lift those boats, at the very least.

You would still have to isolate the steel cables that lift the frame. If they get into the water you still have the same problem. You might be able to find fiberglass rods to attach to the lift frame and cables to prevent the complete electrical circuit.

 

[fisherelectric]

At one point I thought of using a 3pole disc to switch H,N, and G off to the lifts so there was no connection at all except when he was actually standing there using them, but that's still an accident waiting to happen, and not legal either. I believe that the 12volt winch idea is the best idea so far, but then he's got to deal with chargers which have their own set of problems. I also told him to check with the local homeowners association and the local fire and rescue, and code enforcement to find out how other people are dealing with this problem. There must be others with this problem all around down there. This county didn't even have code enforcement til '92.
My brother says "I got a tingle but I could still climb out of the water". I told him he's just been really lucky no one's been hurt or worse. He's had this place for 7 years and never had this problem til last fall. His daughter first noticed it and brought it to his attention. I told him he's lucky she was able to bring it to his attention. Thanks for the input all.

 

[benaround]

Fisherelec,

I just did a 'Google' search for boat lifts, one company has a remote controlled

hydrollic driven unit, I thought it might interest you.