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Reverse Polarity Indicator

RoyS

.
Jun 3, 2012
1,160
Hunter 33 Steamboat Wharf, Hull, MA
Cruising in Maine recently. Decided to indulge myself and took a slip for a few nights in a very expensive marina. Attempted to connect shore power cord to nearby pedestal and discovered that the pedestal outlet rain cover prevented my standard Marinco 30 Amp cord from engaging. Explained problem to the dock hand who said, "Oh yeah those don't fit here, let me get you a 50 Amp adaptor." He handed me a 50A splitter cord adaptor with two 30A ends. I examined that and found that the terminals were all pitted and burned. Connected it anyway and for the first time in all my years of sailing my reverse polarity light came on. Removed the marina's adaptor and fetched my own. Connected that and still reverse polarity indicated. Marina staff had gone home for the night so did without shore power for that night. Next day explained problem to new dock staff. Guy said, "Oh that pedestal. Thought they fixed that. Plug into other side, that should work." That side did work. This marina, BTW, charges $30 extra for each night for a 30A electric hook-up. The moral of this story is be cautious with marina electric wiring. My only consolation, at least I now know that my reverse polarity indicator actually works.
 
Feb 14, 2014
5,623
Hunter 430 Waveland, MS
There is a second moral to your story.

"Use your own trusted adapter."

My 50 to 2-30 pigtail has indicator lights on the 3 points of connection.

Jim...
 
Jan 4, 2010
972
Farr 30 San Francisco
I think the error was in the pedestal not the cord.

Which brings to mind an idea, you could make your own cord and intentionally swap H and N to rectify this situation. So a de-reverser adapter as it were.
 
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Likes: captcoho
Oct 22, 2014
15,807
CAL 35 Cruiser moored EVERETT WA
Maybe the marina is using that Canadian electricity that is being sent south through the Maine wilderness to Massachusetts.
 

RoyS

.
Jun 3, 2012
1,160
Hunter 33 Steamboat Wharf, Hull, MA
Your boat would probably not detect a ground and neutral switch. Maine Sail?

It would appear that to arrive at this polarity reverse situation that the dock electrician used the eenie meenie method of determining the connections at the pedestal outlet. I could have told him from personal experience that the eenie meenie hasn't worked since 2019 and maybe earlier.
 
Jan 21, 2014
18
hunter 356 malta
Ah reverse polarity. A question that has puzzled me for some time is if the live and neutral are swapped why does it matter because its alternating current?
Anyway back to the problem. My hunter gets very cross with reverse polarity and marinas everywhere have pedestals that don't work or are wired incorrectly. This simple domestic tester plus adapter is one of my tools in the battle and an answer to the marinero "it must be your boat" standard response.
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May 17, 2004
3,423
Beneteau Oceanis 37 LE Havre de Grace
A question that has puzzled me for some time is if the live and neutral are swapped why does it matter because its alternating current?
In a properly wired setup alternating current means that the hot wire alternates, going above and below the potential of the neutral and ground wires. Reverse polarity means that the neutral wire is going above and below the potential of the hot and ground wires.

In both cases the hot and neutral wires are at alternating potential, so you’re right that it makes no difference there. What it does effect is the voltage of the wires relative to the ground wire, and the rest of earth ground. If everything on the boat is wired properly that’s not too big of a deal, but if there are other faults on the boat it can be dangerous. For example on some boats the neutral wire is incorrectly tied to ground on board. With reverse polarity this could lead to a situation where the boat’s ground becomes hot, putting voltage into the water that could electrocute swimmers. Also if there are any circuits that are protected by single pole breakers, switching what should be the hot wire, those circuits will still be hot even when the breaker is off.
 

RoyS

.
Jun 3, 2012
1,160
Hunter 33 Steamboat Wharf, Hull, MA
If you want to test your reverse polarity light, I can give you directions to a very expensive marina that has defective wiring on one side of one particular pedestal.
 
  • Ha
Likes: jssailem
Jan 21, 2014
18
hunter 356 malta
In a properly wired setup alternating current means that the hot wire alternates, going above and below the potential of the neutral and ground wires. Reverse polarity means that the neutral wire is going above and below the potential of the hot and ground wires.

In both cases the hot and neutral wires are at alternating potential, so you’re right that it makes no difference there. What it does effect is the voltage of the wires relative to the ground wire, and the rest of earth ground. If everything on the boat is wired properly that’s not too big of a deal, but if there are other faults on the boat it can be dangerous. For example on some boats the neutral wire is incorrectly tied to ground on board. With reverse polarity this could lead to a situation where the boat’s ground becomes hot, putting voltage into the water that could electrocute swimmers. Also if there are any circuits that are protected by single pole breakers, switching what should be the hot wire, those circuits will still be hot even when the breaker is off.
Brilliant response! However I remain none the wiser!