Boat lift shock

[Rlytle]

my name is Ron, I have been a licensed electrical contractor in NC since 1998. I currently wire a lot of piers and boatlifts with no problems, However, some time around 2003 to 2005 we wired a pier with a boat lift, this is the job I have a question about. A #6 feeder was used to feed a sub panel at the pier. All circuits on the pier are ground fault protected with breakers at the subpanel. The customer complained of being shocked when swimming and touching the boat lift. While investigating the matter I found that even with the sub feeder breaker turned off the shock was still there. The only way to stop it is disconnect the feeder ground wire from the sub panel. I contacted the power company and there engineer said that the lake was a better ground than the power company had and they would do nothing about it. I watched the video about grounding at agriculture buildings and I feel that this is a similar problem as discussed in that video. My question, is there any thing I can do to correct this problem. Like a copper grounding ring on the bottom of the lake.

Thank you for your time, I look forward to a reply

 

[don_resqcapt19]

What happens when the service itself and not just the sub-feeder is shut off?

 

[cowboyjwc]

What happens when the service itself and not just the sub-feeder is shut off?

Great question.

 

[domnic]

boat dock

boat dock

Great question.

Turing off the main panel will not help. as long as the EGC is connected to the poco neutral it will not change.

 

[GoldDigger]

Turing off the main panel will not help. as long as the EGC is connected to the poco neutral it will not change.

This is correct as long as none of the current flowing trough the GEC is originating from the customer side of the POCO transformer. It is still worth conducting the experiment.

Look up Neutral Isolator on Google.
Among other things you will find an explanation of what they do and why: http://www.bassengineering.com/sv_utility_.htm
and a history of the use of neutral isolators: http://mrec.org/files/2011/03/tachick-Dairyland-Isolators.pdf

Any utility that declines to install a neutral isolator under the conditions you describe is asking for a lawsuit, and a short letter on your behalf from an attorney might change their mind about what they can and cannot do.

 

[don_resqcapt19]

Turing off the main panel will not help. as long as the EGC is connected to the poco neutral it will not change.

That is correct if the source of the voltage is from the power company. The purpose of turning off the main is to find that out.

 

[domnic]

boat lift

boat lift

I would turn off the main also and check. but I can not think of anything in the main panel that could cause this.

 

[luckylerado]

Are there neighboring docks? It could be that the water is energized from somewhere else and disconnecting the ground just makes the dock poorly grounded so the shock would go away even while still floating in energized water. This happens often.

The hazard could also be coming from a boat with power on it.

 

[GeorgeB]

I can not think of anything in the main panel that could cause this.

Unbalanced (difference in 2 "phases") currents will flow through the POCO neutral, elevating it above earth. Eliminating that current will eliminate the main's contribution. Other loads (houses, etc) on the transformer would (could) still elevate ground with their unbalanced currents.

 

[don_resqcapt19]

I would turn off the main also and check. but I can not think of anything in the main panel that could cause this.

The biggest thing would be a high impedance service neutral conductor, but other faults can elevate the EGC to a voltage that is higher than "remote earth".

 

[readydave8]

might this help?

 

[don_resqcapt19]

might this help?

Very unlikely that would help. Additional grounding almost never solves the problem, but it may mask it in some cases.

You need to find the source of the voltage and solve that problem.

 

[mtfallsmikey]

Sounds like the same problem we found in a house many years ago, shock would occur when someone got in a bathtub and touched the faucet, neutral from the POCO was messed up, we checked everything under the sun from the meter back.