I recently completed a service to a 4 slip dock and a month later, received a call from the builder of said dock who told me the owner reported to him feeling a tingle when he and his sons approached the metal ladder while swimming. The power distribution is as follows: The meter and house are at the top of the hill with 4-#2 Al conductors about 750 feet to a panel on the cliff above the dock. Fron this panel I ran 110' of 6-4 SOOW through the water to the dock.

With one lead of my meter attached to some bare wire in the water, the metal of the dock shows 2.75 Volts. The system ground wire is carrying 1.8 Amps and if I pull the ground wire off the bar I get 8 Volts to the dock metal. With the mains to the house, garage and dock off I still have the same current flow, yet neither the new copper ground rod at the meter, nor the poco ground, nor their guy wire show any current flow. I have of course started communication with the engineer at the 'lectric co, but he hasn't been out yet. Any ideas as to what's happening here? Am I correct in wanting to disconnect my ground wire until the power company figures out what's happening? Obviously this is the thing that the $ 200 an hour professionals (called attorneys) pay for their own places on the lake with, so I want to solve this situation before it worsens.

Is the house connected by a metallic path to any other systems such as cable TV, city water, city gas, sewer lines, etc? Perhaps some other house is using your ground wire as a ground path.

Check if some of the current is flowing across the water main bond. Also check if current is flowing thru the bonding wires for the telephone system and cable system.

Here is a relevant thread over at Mike Holt:
http://forums.mikeholt.com/showthread.php?t=78799

In addition to checking for current flow from other systems as suggested above, also look for current flow between grounding electrodes.

-Jon

This might just be regular ground shift. You may never figure out where it comes from but the utility is certainly a suspect. Bear in mind the dirt is always a parallel current path in a grounded system. Have you tried establishing a local ground electrode system at the dock, connected to your equipment grounding conductor?

Hello,
I would check the service at the house first. Check the ground and the neutral/messenger at the house. It could be bad and all current running to the water. I put in ser and and 150amp diconnect/meter in my parents place a couple of years back. I cut free the service drop with gloves. When I reconnected the bare messenger first I got spark. When I finished my work, I looked at the neigbors house. Her messenger was broke and all the current was traveling through her water main and back through mine, out my messenger. Current loves the lowest resistance path home and just because the main is off in the house you are fed by, doesnt mean current can not come from a neighbors service. This is just some personal experience.

I'm not saying that this is a code requirement anywhere BUT: The only system that I would let anyone I loved around would include a transformer at the boat slip. Naturally, the secondary Neutral would be bonded to a locally established ground. That's the same thing I would have done where they were shocking all the dairy cows in the remotely fed barn.
Joe

Thank you all for your input and comments.

Cable is from a dish on the house. Water is from a well on the premises, haven't checked the ground current on that possibility. This home is quite a distance from other structures, the closest house is 1/4 mile away and on its own xfmr. A local ground would have to be bare wire into the lake as the shoreline is at best a few feet of gravel over bedrock. The dock is moored to an almost vertical cliff face. I have current flow through the steel cables extending down to the downriggers that space the dock from the shore.

I assume there are NO boats connected to this system when you show the current. A miss-wired boat or shore cord will sure cause this problem. Robert

Are there any boats in the water connected to this power?
Ob

Wow,
I am curious about this problem. The only thing I can think of is the dc battery system on the boat or the electrical on the boat itself. Maybe disconnect the negative on the dc battery system and turn shore power off and see if you have the same readings. Maybe a problem on the boat itself. Anyway, very interesting. Keep us posted when you figure it out.

Brian

Joe,

How would that change anything? The EGC of the primary and the secondary must both be connected to the case of the transformer. That means you are still directly tied to the service grounded conductor.
Don

The last thing I would want is to be a connecting link for a ground loop over 700' apart at the ends, especially with one end being a body of water. It would really be a total waste to bypass the transformer's excellent isolating properties and the fact that it is now a separately derived source. I would want to maintain the feeder side ground clear into the transformer enclosure. You would definitely want a L-L or L-G fault to clear and need to get back to the source for that. The only thing I would tie that ground to might be some primary surge protection for the transformer. My goal for the secondary grounding would obviously be to be at a zero potential difference with the water. One would also think that this would be closer to the ideal ground than 2 rods in clay up on some cliff. Now, can you buy a grounding electrode boat anchor???
Joe

Joe,

While the code calls it an SDS, it is not electrically isolated and can't be if it is installed per code.

Again, I ask how can that be done and remain in compliance with the code? The primary EGC must be connected to the transformer. The secondary of the transformer is required to be a grounded system. The secondary EGC will also be connected to the transformer case completing the path back to the service grounded conductor.
Don

I'm not saying that this is a code requirement anywhere BUT: The only system that I would let anyone I loved around would include a transformer at the boat slip.

Don,
If we go back to my original statement, I wouldn't worry climbing onto that slip my way and wouldn't go near it the code compliant way you mentioned. I would like a specific code reference if you wouldn't mind because I'm more of a theory guy than a code guru. My only hope is that anyone going up or down that ladder now, as built, is in compliance with J3:16. Our poster has already measured a more than lethal current and our code experiment, future victim, has already felt the warning tingle. Alot of folks don't get that many chances or warnings.
Joe

Why would we treat this any different than a swimming pool or a agricultural building. If you create an equipotential ground reference at the dock with the land or the water I think the problem goes away.
If you just want a quick experiment. put a ground rod clamp on a 10' stick of EMT or rigid and drop it in the water, connect that to the EGC. Test it.
If that makes the trouble go away you should look for a more compliant grounding electrode near the dock.

It is really not that unusual to see a couple volts ground shift between systems 100' apart. The worst I ever saw was more like 35 volts.

Joe,
As far as code references, you start with 250.20(B) which will require the secondary of your transformer to be a grounded system, at least for any of the commonly used voltages. Then to 250.30(A)(1) that will require a system bonding conductor to bond the secondary grounded conductor to the equipment grounding conductors. 250.110 will require the exposed metal parts to be connected to the EGC. This results in the primary and secondary EGCs both connected to the transformer case. Under the NEC it is really impossible to have a electrically isolated system with some rare exceptions.
In addition the voltage in this case most likely has nothing to do with the power service to the dock. It is most likely stray voltage from utility primary grounded conductor current flowing in the earth/water.
Don

Almost,

Did you remove the main bonding jumper for this test? The utility primary and secondary grounded conductors are connected together. In many cases like this the source of the voltage is the voltage drop on the utility primary neutral.
Don

Just found this thread... here's how others have handled the problem and their logic concerning panel grounds to docks.
http://www.lakesonline.com/Forum/sh...CB1831E2F&tid=40878&SiteID=AL008 The thread is a good read. If anyone can tell me what's wrong with this method (other than it may not be described in the NEC) please let me know.

Refer to Gfretwells post above # 167497. The link IMHO is primarily DIY and homeowners looking for 'help'.

My opinion is to seek professional help from a licensed electrical contractor. In the event you may be located in an area that does not license electricians, seek a reference for a qualified electrical contractor or electrician.

I would say that the link describes the same as Gfretwells post by establishing an equipotential ground between the dock, land, and water. This appears to be different from a ground wire back to the panel. Apparently not all electrical contractors know the solution to this problem and the solution may not be in agreement with NEC

All electrodes are still required to be bonded together so you will be running a wire back to the panel.