What does the reverse polarity light mean? - SailNet Community
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What does the reverse polarity light mean?

After sailing yesterday, we returned to the marina and plugged in shore power. For the first time the polarity light on the switch panel was on. I double checked the shore power connection and it was installed correctly. I then unplugged the pedistal end of the shore power and reconnected it. The polarity light went out.
How does that work? I assume the light came on because one or the legs had a bad connection. Is there anything further that I need to do?

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Re: What does the reverse polarity light mean?

Reverse polarity means that the hot and neutral legs have been reversed. This can be due to faulty wiring in the boat or the pedestal. Marine shore power connectors canít typically be physically plugged in backwards, which is why one prong has a tang. You said you double checked. Is yours somehow reversible?

Intermittent makes no sense. If itís intermittent, I have to wonder if a ground leak/short is somehow involved.


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Re: What does the reverse polarity light mean?

Was the light bright and strong, or just dim? Dim means that there is a slight voltage delta between neutral and ground. These are common and can be caused by a bit of poor contact on one or the other. Unplugging and replugging may just have made better contact.

If it was bright and strong, then I don't have a suggestion. Perhaps you have a faulty plug and moving it a bit was enough to re-establish contact/

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Re: What does the reverse polarity light mean?

See above post...

I have a small invwrter that uses a cig plug connection. It will sometimes show rev polarity. Fiddle with the connection a bit and finally get the green light...
When it bothers me enough...maybe ill install new spare ourlet...
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Re: What does the reverse polarity light mean?

It could be an intermittent fault in the dockside power and or pedestal.

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Re: What does the reverse polarity light mean?

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Originally Posted by boatpoker View Post
There is no current in the ground unless something has shorted. I think you mean a delta between hot and neutral.
No, that isn't what I meant. A reverse polarity light is connected between the neutral and safety ground through a resistor. If there is a voltage difference between these two legs, the light will activate.

If the load and neutral have been switched (a true reverse polarity), then there will be a voltage difference between safety ground and the other leg of the LED circuit (now the load instead of the neutral), and the light will activate.

If everything is wired fine, and there is a large load on the system, this can cause a small voltage differential between the neutral and safety ground because there will be a voltage drop on the neutral from the high load. This can cause the reverse polarity light to dimly glow, but is of no concern.

Similarly, if there is a bit of poor connection on the neutral or safety ground, a small voltage drop can occur and the light will glow dimly without a heavy load. Not really a concern, but one should look for these potentially unclean connections.

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Re: What does the reverse polarity light mean?

When the light was on, we had no power on the boat. Both ends were installed correctly, so this leads me to believe there was no contact between either the neutral or ground at the pedistal end. Does the RP light measure a difference in continuity? It would have to be that, there should never be voltage at the ground.....
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Re: What does the reverse polarity light mean?

It does sound like a contact problem. The RP light only measures a difference in voltage between the neutral wire and the safety ground. Ideally, there should be no voltage on either of those two since they are bonded together on the power producing end.

It is possible you just didn't get the plug in all the way, or there is an intermittent on the shore side receptacle. However, if you didn't have power at all, then it would be the load wire that wasn't connected, and this wouldn't light the RP light.

And I think all of us are assuming you are using a typical Hubbel type connector that cannot be plugged in different orientations - so if it fits in the receptacle, then the wires are matched correctly between receptacle and plug.

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Re: What does the reverse polarity light mean?

Quote:
Originally Posted by RichF28 View Post
When the light was on, we had no power on the boat. Both ends were installed correctly, so this leads me to believe there was no contact between either the neutral or ground at the pedistal end. Does the RP light measure a difference in continuity? It would have to be that, there should never be voltage at the ground.....
No the light is simply connected between what should be your neutral wire (white) and shoreside earth (green) via a 250K resistor, if there is AC current on it then the light will light, which should never happen in a perfect world. Googling Reverse Polarity light how to install, or how it works will give you a plethora of info to peruse, also Blue Sea has info on their website.

But as it is only a light it does not "measure" as it only indicates the presence of current on the neutral wire, it is a simple Go( light not lit)/NoGo (light lit) indicator.
Found a diagram on this blog, Nice read...https://themarineinstallersrant.blog...c-leaking.html


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Last edited by CVAT; 4 Weeks Ago at 10:49 AM.
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