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Old 10-02-2015, 22:14   #1
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Reverse Polarity

I just got into another marina and my boat is registering "reverse polarity" on my panel. My connectors have been fine all the way up and down the Melacca Straits.
I took apart the connector plug and reversed the wires--positive went to negative and the negative wire to the positive position and still I get the same reading.
I put my volt tester into the plug and got 240 volts when I touched the positive and negative wires. I got 240 volts when I touched the positive and ground wires. I got nothing when I tried the ground wire to the negative plug. Not sure if this is correct as to the power in the lines. I've checked all my connections and they appear to be fine. The marina's position is that it has to be me since everyone else is fine. The electrician they sent down tried numerous power posts in the marina and all came back the same as mine but he thinks there is a problem with the ground and positive wires showing volts.
Any thoughts as to what to try next? I'm going to be here for a couple of weeks and I'm sure my neighbors won't like hearing my generator ever other day.
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Old 11-02-2015, 00:44   #2
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Re: Reverse Polarity

are those measurements at the dock or at your panel? they sound fine for 230v euro.


or are you talking about 240v north American. then you'd have have 4 wires and not 240 from hot to ground.
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Old 11-02-2015, 03:16   #3
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Re: Reverse Polarity

Those are at the power post as well as at the outlet where I plug my cord into my stepdown transformer that then goes into the boat through a Marinco adapter and over past a Blue Seas Reverse Polarity box and down to my panel.
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Old 11-02-2015, 08:26   #4
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Re: Reverse Polarity

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Originally Posted by mestrezat View Post
I just got into another marina and my boat is registering "reverse polarity" on my panel. My connectors have been fine all the way up and down the Melacca Straits.
I took apart the connector plug and reversed the wires--positive went to negative and the negative wire to the positive position and still I get the same reading. ..................
Think about what you just wrote.

If your electrical connections have been fine at several other marinas, why would you think you need to reverse the wires on your plug for this marina?

Nothing changed on your boat traveling from the last marina to this one so why would you think the problem is on your boat or your shorepower cord?

What to try next? If the marina's electrician can't figure it out, your best bet might be to move on to another marina. But first, put all the wires back exactly how you found them.
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Old 11-02-2015, 10:46   #5
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Re: Reverse Polarity

Why does polarity actually matter? This is alternating current after all...


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Old 11-02-2015, 12:01   #6
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Re: Reverse Polarity

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Why does polarity actually matter? This is alternating current after all...


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I believe it's because when you turn a switch off, you want that to be on the "hot" side of the device.

My understanding is that things will still work, but if you inadvertently have or create a short, it could be deadly, and the switch (and maybe fuses) won't help you.
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Old 11-02-2015, 12:09   #7
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Re: Reverse Polarity

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I believe it's because when you turn a switch off, you want that to be on the "hot" side of the device.

My understanding is that things will still work, but if you inadvertently have or create a short, it could be deadly, and the switch (and maybe fuses) won't help you.
Danger is the issue.
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Old 11-02-2015, 12:14   #8
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Re: Reverse Polarity

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Danger is the issue.
In AC circuits, polarity doesn’t matter until it does.

Polarity matters in AC wiring - Licensed Electrician Robert Monk Licensed Electrician Robert Monk
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Old 11-02-2015, 12:20   #9
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Re: Reverse Polarity

Ron's right. That made NO sense. It's the dock end that's wonky, not YOU.

Although there is a danger associated with it, read Monk's material and then decide what equipment you may have running that would cause an issue. For a week or so, I'd forget about it, after telling the marina their power is wrong.

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Originally Posted by rwidman View Post
Think about what you just wrote.

If your electrical connections have been fine at several other marinas, why would you think you need to reverse the wires on your plug for this marina?

Nothing changed on your boat traveling from the last marina to this one so why would you think the problem is on your boat or your shorepower cord?

What to try next? If the marina's electrician can't figure it out, your best bet might be to move on to another marina. But first, put all the wires back exactly how you found them.
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Old 11-02-2015, 12:38   #10
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Re: Reverse Polarity

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Originally Posted by rwidman View Post
Think about what you just wrote.

If your electrical connections have been fine at several other marinas, why would you think you need to reverse the wires on your plug for this marina?

Nothing changed on your boat traveling from the last marina to this one so why would you think the problem is on your boat or your shorepower cord?

What to try next? If the marina's electrician can't figure it out, your best bet might be to move on to another marina. But first, put all the wires back exactly how you found them.
I have to agree with above-But,you mentioned you use a stepdown transformer-which should totally isolate your boat from the shore hot & neutral.
https://www.bluesea.com/support/arti...ity_Indicators

The only way? your Blue Seas rev pol. light can light,is if it sees voltage from boat neutral to boat earth(the water).
Is the third wire(green earth ground) in your shore power cord connected to the boat earth ground?

I'm not familiar with shore power set-ups.Perhaps someone can offer a lesson. Tks/ Leonard
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Old 11-02-2015, 12:53   #11
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Re: Reverse Polarity

"my boat is registering "reverse polarity" on my panel."
You mention this is on YOUR panel, and that you have a genset on board.


There have been some long discussions, here and elsewhere, about gensets and properly "grounding" them in different ways for different purposes. Sometimes the neutral and ground have to be tied differently and this will cause the reverse polarity indication, which isn't really reverse polarity.


There was a great article on the web from some cinematographer's group explaining the same thing, same problems and choices, for Honda gensets when used as portable sets without a real ground being available (or used.)


I'd look into that, and expect the wiring of your genset is the real problem. If you totally disconnect it, on all three leads, and the reverse indicator goes away? That's proof right there.
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Old 11-02-2015, 18:30   #12
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Re: Reverse Polarity

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Why does polarity actually matter? This is alternating current after all...


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Please! Get yourself a book on electricity and marine electricity in particular. You need a basic understanding of electricity if you're going to do any more than plug things in and operate switches.

Reversing the polarity exposes one to possible electrocution.
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Old 11-02-2015, 18:48   #13
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Re: Reverse Polarity

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........... I'd look into that, and expect the wiring of your genset is the real problem. If you totally disconnect it, on all three leads, and the reverse indicator goes away? That's proof right there.
Most of my career was troubleshooting and correcting problems with electrical and electronic systems. One key thing to understand about troubleshooting is that wires cannot disconnect themselves and reconnect in a different configuration.

So: If the boat's wiring and the genset's wiring was not changed by someone and the boat was fine before being connected at this marina, and now it is not, it's a waste of time and can just cause further problems to mess with the boat's or genset's wiring.

It is possible that a connection came undone or a wire broke so this should be checked.

I would expect an isolation transformer to isolate the boat from shorepower so it's odd that a problem such as this would occur. It's also odd that an electrician could not figure out the problem but this might not be a "real" electrician.

Speaking only of the US system of three wire 120 volt AC, the "hot" wire (black) would measure 120 volts AC to both the neutral (white) and the ground (green). No voltage should exist between the neutral (white) and ground (green).

"Reverse polarity" exists when the 120 volts AC exists between the white wire and the green wire and no voltage exists between the black wire and the green wire. Simply put, reversing the black and white wires causes reverse polarity.

You can go to any home center and buy a plug in tester for under $15 that will indicate wiring problems at a glance.




Klein Tools GCFI Receptacle Tester-RT200 - The Home Depot
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Old 11-02-2015, 23:12   #14
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Re: Reverse Polarity

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Please! Get yourself a book on electricity and marine electricity in particular. You need a basic understanding of electricity if you're going to do any more than plug things in and operate switches.

Reversing the polarity exposes one to possible electrocution.

ANY boat wired for 230 vac show be done so to be perfectly safe if the polarity is reversed. There should be no additional risks. This is in my view a failing os US 110 practice.

In the ops case all you may have is a slightly elevated ( or fully floating ) AC line. Your system should remain safe

Polarity reversal lights are uncommon on European boats, because the electrical system should still remain safe.

And Kvb is right the polarity shouldn't be an issue. It's poor US practice , on transferring domestic wiring standards to boats that's the cause of it.

In the med for example , I carried a pre made up reverse pigtail shore lead , because I needed it from time to time., when I got floating neutrals ( sone what misnamed ) I just lived with it.

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Old 12-02-2015, 00:58   #15
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Re: Reverse Polarity

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Please! Get yourself a book on electricity and marine electricity in particular. You need a basic understanding of electricity if you're going to do any more than plug things in and operate switches.



Reversing the polarity exposes one to possible electrocution.

No it doesn't.

Not if the boat is properly wired. Appliance makers have stopped making assumptions about which wire is live and which is neutral decades ago. You should do likewise.
Just install a double pole main breaker and RCD and you do t have to worry about reverse polarity. That is what my book about marine electricity tells me anyway...




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