Reverse Polarity

[Roger Long]

It may not be a problem showing false readings on your boat but they do give false readings in many situations on a boat and this is with shore power, inverters, or generators. My point being that the tests for faults on a boat need to be done with the proper meters and done by someone that has knowledge in doing this properly. Chuck

Good point then. The OP was asking though what he could do as a first step without the knowledge or meters to do it properly and I think the plug tester is probably about the limit of what he could or should do. If it points to the marina, which is most likely, they will fix it. If it points to his boat, he'll need to get someone in.

I never meant to imply that they are a substitute for knowledge and equipment. Have you ever known them to read OK when there was actually a problem?

 

[Witzend]

Proper AC service, is Proper AC service, Gnd, Neutral, Hot... Boat, house or otherwise. Ground and Neutral shall be connected at the service entrance. In a marina installation it should be the same. Unfortunately, many marina owners expand out to sub panels for each pier, some have separate meters for each slip, and other wacko things done by fly-by electricians. One of the more common problems is this common point between Ground and Neutral becomes physically distance from the end user causing a potential difference as loads are introduced.

 

[Chuckbear]

Good point then. The OP was asking though what he could do as a first step without the knowledge or meters to do it properly and I think the plug tester is probably about the limit of what he could or should do. If it points to the marina, which is most likely, they will fix it. If it points to his boat, he'll need to get someone in.

I never meant to imply that they are a substitute for knowledge and equipment. Have you ever known them to read OK when there was actually a problem?

I have not had them read OK when there was a problem but often had them show a fault when none existed. If checking the marina side there is a test plug that will fit the 30 amp twist plug on the dock that would be a much better indicator for that side. We use it all the time to test a dock outlet before we plug the boat in, so they are a handy thing to have. Chuck

 

[TimCup]

Rob, I don't know if you've solved it yet, but-

I'll share my experiences.

I've had boats of all kinds at my house, and often plugged in using a regular extension cord. I kept thinking there was a problem with the boat, or my rewired guest house, because every time I tried to charge, the reverse polarity light would come on. I used the extesion cord for something else, then later tried to charge the boat with a different cord. Everything worked perfectly.

I went back and switched cords again, and sure enough, the light came on.

It was then that I realized this cord had the round ground part of the plug cut off (it was a two prong plug instead of a three prong). I'm sure I did this to make it fit somewhere when I didn't have an adapter.

The point of this is simply that the when the reverse polarity light appears, it's often because all three prongs of the plug aren't making the connection they were designed for. I doubt the "dependable" outlet has a serious issue, it's more likely a connection issue. As always with boats, clean the contacts and try again!

Good luck-


cup

 

[Dan Johnson]

Roger...

I loved your test plug storage idea--will adopt it for the coming season!

Chuckbear, without getting into the complexities of inverter power and generator useage, the plug testers would function the same on a boat as at home for standard shore power wiring. By your reference to the contrary, you may have something else in mind to prompt your remark that I've missed.

 

[Stu Jackson]

Generators & Reverse Polarity

... without getting into the complexities of inverter power and generator useage, the plug testers would function the same on a boat as at home for standard shore power wiring. By your reference to the contrary, you may have something else in mind to prompt your remark that I've missed.

There have been many discussions of Honda generators not showing normal on reverse polarity. I suggest googling it if you need more info, since it's been on a number of different message boards, this one included, so a search would work, too.

 

[Rob McClain]

Reverse Polarity Update w/some test results...

Now that I have had time to look into the polarity problem further, using these posts as guidance (thanks!), I would like to post an update to the original description I had presented. First of all, I checked the polarity of the dockside outlet, as well as the polarity onboard the boat and the polarity at the end of my power cord. ALL checked out ok. I then tried a second power cord that I keep onboard and that made absolutely no difference in the polarity indicator or the problem.

Essentially, as soon as the cord is connected from dockside to the boat the reverse polarity light glows, whether or not the breaker is thrown to the "on" position. When the cord is not plugged into the outlet, the polarity light is dark.

I then tested the AC connection by plugging into a nearby dockside AC outlets that were open in a neighboring slips. I did this 3 times, in 3 different outlets, and checked the polarity onboard with the AC off as well as on. Each time the polarity light onboard remained dark with absolutely no indication of any problem. Of course, this is how it should be...

The results of my puttering lead me to believe the problem is definitely not in my boat but in my specific dockside outlet; thus, it is the marina's problem to fix. Agree or not?? I spoke to the Harbormaster about the results of my tests and he is not yet inclined to act. We agreed that if any my neighbors are onboard their boats this weekend maybe I can do a test and connect another boat to my particular dockside AC outlet to see if it encounters a polarity problem. This is easy enough, if I have any neighbors this rainy/windy weekend.

Any thoughts out there regarding what I have described? Based on the very simple tests I did it seems that the problem must be on the marina side - although it appears limited to only my AC outlet. Before I push the Harbormaster more, am I taking too superficial of an approach on this? I am hopeful that one of my neighbors will visit their boat this weekend since I would like to do that test, but if they don't I would like the marina to engage and troubleshoot the dockside AC box.

Rob

 

[Cayennita]

My Boat was fine until another boat came in and hooked up to the same service on the dock. When I asked him to unplug to check my reverse polarity light, it had gone off. We tried it twice and twice the light went on. How can rhis be possible. I told the owner of the boat next door about it. He found the problem and now we are both OK. Not sure why it did what it did.

 

[MoonSailer]

Through the water??? Most diagrams show the negative going to the engine ground and the shore power ground. Maybe someone's service is shorted to ground and the current is coming through the water. This is from "Boatowner's Illustrated electrical Handbook".
http://bluesea.com/viewresource/84