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DOCK BONDING.

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billydrowne

Member
Location
Massachusetts
Occupation
electrician
Company I work for recently installed a power pedestal on a floating dock. 100ma GFI protection for the whole circuit out of a specifically made marine disconnect, submersion rated marine cable, individual GFI protection at all receptacles and equipment at the pedestal. Supposedly a diver was re connecting a set of chains to mooring blocks underwater to keep the docks in place and got shocked WHILE submerged. Everything is on a lake that feeds other ponds, canals, etc, we really have no way to bond the water around everything being that its so large and not man made. Took voltage readings at the pedestal to the water, 120v from each phase to the water, neutral and ground was showing 4v to the water. Another section of dock has an aluminum ladder in the water, go from ladder to water and get 1-3vdc. Our best guess is that one of their boats, or a neighboring boat or dock may be leaking current into the water and our system is not picking anything up. Called our local inspector and he re assured us our equipment would have picked anything up if it was a problem on our install. our solution is to install some from of an equipotential plane to all metallic parts much like a swimming pool. Any thoughts on this one would be highly appreciated.
 
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billydrowne

Member
Location
Massachusetts
Occupation
electrician
jim dungar said:
Did you turn your power off, its source, then take the same measurements?
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yes. we turned power off, re made the connections on the neutral at the service drop, properly bonded main panel, which has been un bonded for god knows how long, and then we had zeros all across the board when reading the pedestal. still have the DC voltage at that ladder though.
 
Buck Parrish

Buck Parrish

Senior Member
Location
NC & IN
Sounds like you guys may have fixed it when you bonded the main panel. Sounds like you did a good job, and done every thing you were supposed to. That main neutral connection should be checked any time you're doing something like a pool or boat dock.


My thoughts are what Mike Holt said when it comes to equipotential " If the NEC does not require it then do not do it" He said that in one of his videos about equipotential and swimming pools. I watched them all numerous times. At least one of them have been taken down.


I don't think any of us can be positive about what you have described doing as positvely fixing the problem, esspecially because the water can not be included in the equipotential. So you would not be able to say , okay folks it safe now. Let your kids go swimming.

How much DC current are you getting on your meter now ?
I might tell the owners in writing to get an electrical engineer to look into the matter.
 
mtnelect

mtnelect

HVAC & Electrical Contractor
Location
Southern California
Occupation
Contractor, C10 & C20 - Semi Retired
When we had our 40-foot sloop moored in Marina Del Rey, more and more people were living aboard. This was a wood hull with brash screws securing the planks of the boat. In order to protect the brass screws and the keel, you had to install a zinc plate to neutralize the electrolysis action. We usually replaced it once a year, but we had to do it twice a year, as more electricity use increased.

Electrocutions will always be a problem where electricity is present. There should be a requirement around water and electricity, post a sign "Swimming Not Allowed".
 
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