EGC of boat docks

[jwelectric]

Below are two separate posts from two different web sites. As you can see in both instances the equipment grounding conductor was cut.

I know the dangers of doing this but was wondering if some of you would comment on this, please. Notice that in both cases the poster said that it was an engineer with the utility who gave them this advice.

I talked to a home owner that works for the power co.HE said that they took the ground loose to stop the shock. Generators from the dam puts power in to the water from the generators on the grounds and all the land around this is rock very little dirt ,very loose dirt.When they build New houses they dig down about 2 foot and lay the ground rod down flat and #6 bare wire in the ditch. about 40 foot to ground. anybody ever heard of any thing like this? This is not just one house, this lake is 500 and something miles around this lake with a number of docks this way.

I live on a lake and most of the floating docks here are wired for electric lights, air pumps for floating boat lifts, and usually a provision for battery chargers. Also, many docks will have well pumps to use the lake water for washing down boats. Generally a boat dock will have 2 to 6 outlets and a couple of 8 ft florescent light fixtures and maybe some kind of light out over the water. The distance to the main switch box in a lake house is typically 200 ft from the dock.

Generally the docks are wired with 12/2 WG in conduit. Also, if the ground comes from the switch box rather than a ground rod at the walkway to the dock you can get a 6 to 8 volt "tickle" when you climb upon a metal boat dock... So, I've installed several ground rods at the walk way and cut the safety ground from the switch box to stop this "tickle" voltage which is a result of voltage drop from the long distance of wiring to the dock. A typical walkway to the dock is 65 ft.
I do definitely appreciate your reply tho' it is a bit over my head with all the theory. I do know for a fact that the way I've done the ground rod does stop the tickle and insures a safety ground. I found out how to do this from an Alabama Power company engineer.

 

[charlie b]

I never really understood the current flow paths that arise in marina applications. But I am fairly confident that the second poster's "statement of fact" that ground rods will "insure a safety ground" is total, and dangerous, nonsense.

 

[zbang]

I'd say that these utility engineers shouldn't be giving advice. Like charlie, I'm not up on marina's and the like, but I do know that fault current needs a good path in order to trip the OCPD and 50' of earth usually doesn't cut it.

 

[jwelectric]

Thank you for taking the time to reply and I am in total agreement but don't know what to tell them to remove the current at the dock

 

[don_resqcapt19]

Given that the most common source of the voltage between the metal parts that are connected to the electrical grounding system and the water is the voltage drop on the utility primary grounded conductor, the cutting of the EGC is a way that will eliminate this voltage. The problem is that it creates a very serious shock hazard if any of the electrical equipment on the dock would have a ground fault. There would be no fault clearing path and the metal parts would have 120 volts as measured to the water.

There are very few code compliant methods that can be used to eliminate the voltage to the water and still keep the EGC connected.

The only one that I can think of is to use an 240 to 240/120 volt transformer that is installed so it meets Exception #2 to 250.110. This will let you eliminate any connection to the utility grounded conductor. The secondary side would have its own grounding electrode system and a system bonding jumper. There would be no voltage from the EGC to the water and you would still have a fault clearing path.