Dock on the lake with ground current

G

gaspower

Member
Location
United States
Aluminum floating dock. 20amp 120v service. GFCI on shore and on the dock.

Dock structure is bonded to ground wire from house load panel.

When swimming to aluminum ladder a strong tingle (uncomfortable) can be felt as you approach the ladder. Local EMC admitted it seemed odd but couldn’t figure it out. Almost all our neighbors had same issue, everyone had a ground rod installed on shore by a local electrician and issue went away (I measured a couple amps of current to ground rod on mine).

A few years later the tingle is back. Disconnecting the hot and neutral to the dock does not remove the tingle, but disconnecting the ground wire does.

Should I lean on EMC or call electrician back?
 
Fred B

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
ptonsparky said:
Find an electrician that works with this type of problem. A different one than before. He did nothing but mask the problem. Call the POCO.
NOW. Both should have been done yesterday!
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Particularly someone very familiar with 680 and 682 of NEC.
ptonsparky said:
NO SWIMMING !!
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Many people have DIED as a result of "a little tingle" at a dock or marina. That "little tingle" can quickly escalate and diminish without warning to the point of a fatal incidence. Many time cause is caused not by a fault but as a function of the POCO multi-grounded system working correctly, other times it can be a result of as mentioned someone's poor neutral connection and on a lake or body of water can be miles from source. Thus Required signage of "NO SWIMMING".
 
G

gaspower

Member
Location
United States
Blue Ridge EMC, small rural coop.

Our house is on a peninsula with 22 other houses and the peninsula next to us has about 12. Both peninsulas are served by typical aerial lines with a single transition to underground distribution to all the homes.
 
kwired

kwired

Electron manager
Location
NE Nebraska
I'm surprised a ground rod solved the problem. Normally it would just equalize the voltage in a pretty small area in the immediate vicinity of the rod and would need to be really close to what you are trying to protect with it.

The problem here is a rise in voltage on the service neutral.

When current flows on a conductor there is voltage drop across that conductor, maybe not very much but always is some voltage drop.
Your service neutral is an extension of everything connected to it not only in your premises wiring but on the utility grid as well. POCO's primary neutral is nothing more than a large network of interconnected grounded conductors with possible rise in voltage from multiple circuits that happen to connect to it.

It very likely is a problem from ahead of your service disconnect. If you shut your main breaker off and it still persists it is coming from the supply side. If you disconnect your service neutral while you have the main off - it likely goes away. Other than if POCO has some bad connection somewhere the most they can do is try to balance loading on their primary distribution better, but you can expect there may almost always be at least some voltage present here.

With art 680 and swimming pools we fix this issue with equipotential bonding. That just is not practical thing to do with natural bodies of water though. GFCI will not detect it as it has nothing to do with the protected conductors.

Only thing that you can do if you can't eliminate what is causing this rise that I am aware of is use something like Ronk blocker.
 
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
The source of current might be the utility primary network, or in might be a fault on the low voltage side of the shared transformer. The problem could even be elsewhere, some source of current finding it was to your local grounded conductors.

I would get an electrician out to measure the voltages in the water. I would also try to get all of your neighbors to shut off their electricity at the same time to see if the problem goes away.

The best approach might be to remove electricity and grounding from the dock.

I agree with the NO SWIMMING instruction. This problem could evolve from an annoying tingle to a drowning hazard.
 
W@ttson

W@ttson

Senior Member
Location
USA
gaspower said:
A few years later the tingle is back. Disconnecting the hot and neutral to the dock does not remove the tingle, but disconnecting the ground wire does.
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This is the key point. If the nearby power is off and you still have a tingle. That means that current is flowing. How can you have current flow if the power is shut off? You can have current flow because its not coming from the homes or docks power source. It is likely coming from the utilities Neutral circuit path. This shows itself as Neutral to Earth voltage. You have have the main breaker off at the house or dock but if you measure a bonded (which ultimately is bonded to the service neutral through a main bonding jumper) metal entity you will have a potential difference between the bonded entity and remote earth/dirt.

If you disconnect the bonding, now there is no path for the utilities primary current to catch a free ride back.

They address this for swimming pools by requiring massive ground grids (massive meaning minimum 5' away from pool edge) around inground swimming pools. This way you are actually bringing the surrounding environment to the Neutral potential so that there is no potential difference.
 
G

gaspower

Member
Location
United States
Thank you all for the insights. I’m trying to determine whether electrician or POCO is the route.

Doing some testing this morning (Klein autoranging multimeter)

Ladder out voltage dock structure to water - 6-7v (slight tingle felt as your hand gets within a couple inches of ladder swimming to it)
Ladder in voltage - 4 volts

Disconnect neutral and hot on shore, no change.
Disconnect ground on shore, leave hot and neutral connected - ladder in <1v, ladder out 1.4v

Dock ground bonded to ground rod, disconnected from house ground
Ladder out 1.2v
Ladder in <1v

I have a neighbor on one side, he has a similar ground rod at shore. I checked his dock
Ladder out - 1.4v
Ladder in <1v


1) I’m inclined to call electrician since neighbor has similar setup and less of an issue
2) bonding dock ground to only shore ground rod removes the symptoms, is this less safe than also bonding to house ground?
3) given that this issue has been variable over the years with know changes in our dock/ house electrical I am inclined to have a continuous monitor installed, any thoughts on these? https://www.docklifeguard.com/?gad_...40FveXXERxye7C3xTWmTK-NVmhCEg3thoCXXkQAvD_BwE
 
tortuga

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
gaspower said:
Thank you all for the insights. I’m trying to determine whether electrician or POCO is the route.
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Its POCO all the way, quit testing the water and put up caution tape around the shoreline, document when you lost the full use of your property. The utility electrical system is 'leaking' into the lake. What you have here is basically electricity trespass, there is established case law on the issue. If the local sewage system or a marina gas pump was leaking into the lake I bet it would be dealt with promptly. Since your dock is unusable you might even have what they call 'inverse condemnation'.
Time to lawyer up with your neighbors.
I'd retain a EE with medium voltage experience as a expert witness.
 
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
gaspower said:
100% I would like to talk with him.
I would appreciate contact info. I have a feeling the right kind of “lawyer letter” informed by someone like your friend might get the POCO in gear
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Let me get in touch with him first and make sure it's okay and he's interested.

Plus, he keeps vampire hours on weekends. I'll let you know as soon as I can.
 
G

gaspower

Member
Location
United States
LarryFine said:
Where are you, what body of water, and what power co?
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Blue Ridge Georgia
Lake Blue Ridge
TVA owns and operates the power generating dam (13MW) on the lake.
Distribution is Blue Ridge Mountain EMC. Small rural mountain service area.

Incidentally my sister lives in Richmond VA and is on her way here today.

I am a mechanical engineer by education and worked on the prime mover and thermal parts of power plants for the first 8 years of my career so I picked up just enough to be dangerous, at this point would appreciate talking with an expert in the space to determine the best next steps.
 
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