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.
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?
Re: Ground wire leakage on boat dock
#167425 08/12/0711:06 AM08/12/0711:06 AM
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
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.
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.