Shore power

When it comes to electrical systems aboard boats, Arild Jensen knows his stuff. Here's where to ask the simplest or most complex questions about marine electrics.

Shore power

Postby Vincent P. Chianese » Mon Mar 01, 2010 7:16 pm

Several weeks ago I was adding a electrical outlet to my boat. I decided that the easiest source for power was the Ground Fault outlet in my head. Also it would not hurt for this to be on a GF circuit. So I throw the fuse breaker and to my surprise I got a few sparks when I was disconnecting the wires from the GF plug. So I throw the main in the boat and still some sparks. I go out to the dock and throw the main on the 50 Amp. Still sparks. I disconnect the shore power cable and the sparks go away.

So I reconnect the shore power and with a volt meter determined that the White (common) is carrying about 12-15 volts unless the shore power is totally disconnected. I mentioned it to the Dock Master and he said he knew about it and at times it is up to 20-24 volts and they weren't going to do anything about it..

Now my question is: Isn't that dangerous and couldn't that cause problems on the boats?


Vincent P. Chianese
Posts: 7
Joined: Wed May 27, 2009 11:22 pm

Re: Shore power

Postby elnav » Thu Mar 04, 2010 9:24 pm

The white wire should be grounded and at zero potential at all times. Such a high voltage on the white wire suggests the neutral to ground connection is NOT secure and should be fixed. Its probably due to corrosion of a connector. At some point it could rise to a lethal level and electrocute somebody.
To make sure it isn't you that gets electrocuted; either move to another marina or install an isolation transformer and be quite vocal about why you did this in order that other people also become aware of the hazard.
Quite apart from the possible shock hazard. If the neutral to ground connection in the marina wiring is deterioating; it could mean you no longer have a solid ground path for fault current. If that happens, any fault current would seek the next best path back to ground by way of who knows what. The collateral damage, personal injury, and what have you is not predictable, but if something happened, the marina operator who knew about it and did nothing would certainly be held liable in a court.
The other explanation could be the voltage rise is due to unbalanced neutral current which is an equally bad situation. Such a rise of voltage suggest a badly unbalanced circuit. My guess is the Dock master knows its going to be an expensive fix and he is hoping people will not notice and that an accident will not happen. One fatality or one damaged boat from fire or whatever would cetainly result in a lawsuit far greater than the repair bill amounted to .
Personally I would not want to plug into a dock with such a wiring problem. I would move to another dock.
Why not do a bit of checking of other docks in your vicinity. Its easy enough to make up a temporary test plug.
Arild Jensen
Custom electrical design for cruising boats
Telephone: 250 998 4474
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Re: Shore power

Postby Vincent P. Chianese » Tue Mar 09, 2010 10:39 am

Thank you.
Vincent P. Chianese
Posts: 7
Joined: Wed May 27, 2009 11:22 pm

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